WO2019165795A1 - 锂离子二次电池及其制备方法 - Google Patents

锂离子二次电池及其制备方法 Download PDF

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WO2019165795A1
WO2019165795A1 PCT/CN2018/112959 CN2018112959W WO2019165795A1 WO 2019165795 A1 WO2019165795 A1 WO 2019165795A1 CN 2018112959 W CN2018112959 W CN 2018112959W WO 2019165795 A1 WO2019165795 A1 WO 2019165795A1
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lithium
negative electrode
unit area
per unit
ion secondary
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English (en)
French (fr)
Inventor
王国宝
刘江
刘晓梅
谢斌
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Contemporary Amperex Technology Co Ltd
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Contemporary Amperex Technology Co Ltd
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Priority to PL18907863T priority Critical patent/PL3761436T3/pl
Priority to US16/976,633 priority patent/US20210050617A1/en
Priority to KR1020207026062A priority patent/KR102463995B1/ko
Priority to JP2020545286A priority patent/JP7104163B2/ja
Priority to EP18907863.7A priority patent/EP3761436B1/en
Publication of WO2019165795A1 publication Critical patent/WO2019165795A1/zh
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    • H01M4/044—Activating, forming or electrochemical attack of the supporting material
    • H01M4/0445—Forming after manufacture of the electrode, e.g. first charge, cycling
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    • H01M4/139—Processes of manufacture
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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Definitions

  • the invention relates to the field of batteries, and in particular to a lithium ion secondary battery and a preparation method thereof.
  • lithium ion secondary batteries have a higher energy density advantage than other types of secondary batteries, making them dominant in the market.
  • lithium ion secondary batteries with lithium iron phosphate as a positive electrode active material are widely used in electric bus power systems due to their high safety, low cost and long life, and have broad application prospects in large-scale energy storage.
  • lithium iron phosphate has high structural stability, the dissolution-repair balance of the solid-electrolyte interface film (SEI film) occurs on the surface of the graphite negative electrode, resulting in a decrease in active lithium ions that can be used for shuttle between the positive and negative electrodes. Therefore, capacity loss inevitably occurs.
  • SEI film solid-electrolyte interface film
  • a lithium ion secondary battery using lithium titanate as a negative electrode active material and lithium iron phosphate as a positive electrode active material can avoid a capacity loss caused by a negative electrode side reaction caused by a dissolution-repair balance of the SEI film because no SEI film is formed.
  • the higher voltage platform of lithium titanate leads to lower discharge voltage platform of lithium ion secondary battery, lower energy density, and the expensive unit price of lithium titanate leads to excessive cost of unit Wh. Therefore, effective technology is needed to solve lithium ion II. The long life of the secondary battery.
  • the main means to improve the life of lithium ion secondary batteries are: selection of lithium iron phosphate type and graphite type with good cycle performance and storage performance, optimization of electrolyte formulation (changing organic solvents, additives), optimization of positive and negative membrane formulations Optimize the film forming conditions of the SEI film. These methods all have a limited effect on the reduction of active lithium ions by suppressing the negative side reaction caused by the dissolution-repair balance of the SEI film, and the lithium ion secondary battery has the highest cycle life. It can be achieved from 5,000 to 6,000 times, and there is still a big gap between the long-life electric bus and the large-scale energy storage system with a cycle life of more than 10,000 cycles.
  • an object of the present invention is to provide a lithium ion secondary battery having a good cycle performance and storage performance, and a method of producing the same.
  • the present invention provides a lithium ion secondary battery comprising: an electric cell; an electrolyte, an impregnated cell; and a package.
  • the battery cell includes a negative electrode sheet including a negative electrode current collector, and a negative electrode film disposed on a surface of the negative electrode current collector and containing a negative electrode active material, the positive electrode plate including a positive electrode current collector and being disposed on the positive electrode A positive electrode membrane having a surface of the current collector and containing a positive electrode active material, the separator being spaced between the adjacent negative electrode sheets and the positive electrode sheets.
  • the negative electrode sheet is a lithium plated negative electrode piece
  • the negative electrode active material is a carbon-based negative electrode material
  • capacity per unit area of negative electrode active material / capacity per unit area of positive electrode active material 1.2 to 2.1
  • the amount of active lithium that can be deintercalated is ⁇ 1.10.
  • the present invention provides a method for producing a lithium ion secondary battery for preparing a lithium ion secondary battery according to an aspect of the present invention, comprising the steps of: coating a positive electrode slurry on a surface of a positive electrode current collector After drying, a positive electrode sheet is obtained; a negative electrode slurry is coated on the surface of the negative electrode current collector, and after drying, a metal lithium layer is disposed on the surface of the negative electrode film, and then assembled into a battery core with the separator and the positive electrode sheet; The core is placed in the package shell, and the electrolyte is injected and encapsulated.
  • the metal lithium layer is lithiated by the electrolyte and the carbon-based anode material in the anode active material is lithiated into a pre-lithium compound LiC x , and then pre-charged to obtain a finished product.
  • Lithium ion secondary battery Lithium ion secondary battery.
  • the present invention at least includes the following beneficial effects:
  • the negative electrode active material may have sufficient vacancies to receive all lithium ions from the positive active material, and store excess lithium ions in the negative electrode after being fully discharged, thereby enabling The lithium ion secondary battery is effectively reduced in capacity loss, and the lithium ion secondary battery has better cycle performance and storage performance.
  • Example 1 is a graph showing the normal temperature cycle performance curves of Example 1 and Comparative Example 1.
  • a lithium ion secondary battery includes: an electric cell; an electrolyte, an impregnated cell; and a package.
  • the battery cell includes a negative electrode sheet including a negative electrode current collector, and a negative electrode film disposed on a surface of the negative electrode current collector and containing a negative electrode active material, the positive electrode plate including a positive electrode current collector and being disposed on the positive electrode A positive electrode membrane having a surface of the current collector and containing a positive electrode active material, the separator being spaced between the adjacent negative electrode sheets and the positive electrode sheets.
  • the negative electrode sheet is a lithium plated negative electrode piece
  • the negative electrode active material is a carbon-based negative electrode material
  • the capacity per unit area of the negative electrode active material / the capacity of the positive electrode active material per unit area 1.2 to 2.1, the unit The area of the negative electrode active material capacity / (the positive electrode active material capacity per unit area + the amount of active lithium per unit lithium-releasable LiC x deintercalated in the negative electrode film per unit area) ⁇ 1.10.
  • the capacity of the negative electrode active material per unit area is based on the reversible capacity of the negative electrode active material (ie, the carbon-based negative electrode material) which has not been lithiated (or has not been intercalated with lithium), and the positive electrode active material capacity per unit area is calculated as the reversible gram capacity of the positive electrode active material.
  • the lithium ion secondary battery can be completely discharged and then disassembled to obtain a positive electrode sheet and a negative electrode sheet, and a positive electrode sheet per unit area and a negative electrode sheet per unit area are respectively cut out to perform the following tests:
  • the positive electrode piece per unit area and the lithium metal piece per unit area are combined into a button type half-cell, and fully charged at a rate of not more than 0.1 C, and the charging capacity is obtained, that is, the amount of active lithium which can be deintercalated per unit area of the positive electrode film;
  • the half-cell is allowed to stand for a period of time (preferably not less than 5 min, more preferably 5 to 30 min), and then fully discharged at a rate of not more than 0.1 C (preferably the same as the charging magnification) to obtain a discharge capacity, that is, a positive electrode membrane per unit area
  • the amount of active lithium embedded is not less than 5 min, more preferably 5 to 30 min
  • the negative electrode piece per unit area and the lithium metal piece per unit area are combined into a button type half-cell, and fully charged at a rate of not more than 0.1 C, and the charging capacity is obtained, that is, the amount of active lithium that can be deintercalated per unit area of the negative electrode film.
  • the cutting position of the positive electrode sheet and the negative electrode sheet is not particularly limited as long as the positive electrode film and the negative electrode film are completely covered.
  • the charge and discharge voltage interval is determined according to the specific type of the positive electrode active material and the negative electrode active material, that is, according to the recommended voltage of the commercially available positive and negative active material manufacturers, the charge and discharge voltages of the different positive and negative active materials are slightly different. difference.
  • the composition of the electrolyte and the type of the separator in the assembled button half-cell are not particularly limited in selection, and it is preferable to carry out the test under the same conditions as the lithium ion secondary battery, and the specific The type change has negligible effect on the calculated amount of active lithium of the pre-calium compound LiC x deintercalable in the negative electrode film per unit area.
  • the calculation method and test method for the amount of active lithium deintercalated by the lithium compound LiC x in the negative electrode film per unit area described above are applicable to the newly prepared lithium ion secondary battery, and also to the lithium ion which has been circulated several times.
  • a secondary battery especially a lithium ion secondary battery having a small capacity attenuation in the early stage, for example, a capacity retention rate of ⁇ 98% after the first 100 cycles).
  • the capacity per unit area of the negative electrode active material/the capacity of the positive electrode active material per unit area 1.2 to 2.1, the capacity of the negative electrode active material per unit area / (the capacity per unit area of the positive electrode active material + the negative electrode per unit area)
  • the amount of active lithium in which the lithium compound LiC x can be deintercalated in the film is ⁇ 1.10, so that when the lithium ion secondary battery is fully charged during use, the negative electrode active material can have sufficient vacancies to receive all the positive electrode active material.
  • Lithium ion and excessive lithium ions are stored in the negative electrode after being fully discharged, thereby effectively reducing the capacity loss of the lithium ion secondary battery and improving the cycle performance and storage performance of the lithium ion secondary battery.
  • the capacity per unit area of the negative electrode active material / the capacity of the positive electrode active material per unit area 1.3 to 2.1.
  • the degree of pre-intercalation of lithium is high, and lithium metal residue is liable to occur on the surface of the negative electrode, thereby causing a safety hazard;
  • x 12 to 50 in the lithium intercalation compound LiC x .
  • the anode film may be disposed on one surface of the anode current collector or may be disposed on both surfaces of the anode current collector.
  • the carbon-based negative electrode material is one or more selected from the group consisting of natural graphite, artificial graphite, soft carbon, hard carbon, mesocarbon microbeads, nanocarbon, and carbon fiber.
  • the carbon-based anode material is selected from natural graphite, artificial graphite or a mixture of the two.
  • the negative electrode film further includes a binder and a conductive agent.
  • the types of the binder and the conductive agent are not particularly limited and can be selected according to actual needs.
  • the binder may be selected from one or more of styrene-butadiene rubber emulsion (SBR), sodium carboxymethyl cellulose (CMC).
  • the conductive agent may be selected from one or more of conductive carbon black, superconducting carbon black, conductive graphite, acetylene black, ketjen black, graphene, and carbon nanotubes.
  • the positive electrode film may be disposed on one surface of the positive electrode current collector or may be disposed on both surfaces of the positive electrode current collector.
  • the positive electrode active material may be selected from materials capable of accepting and extracting lithium ions.
  • the positive active material may be selected from one or more of a lithium transition metal oxide, a lithium transition metal oxide, another transition metal or a non-transition metal or a non-metal derived compound.
  • the positive active material may be selected from the group consisting of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and olivine structure.
  • lithium-containing phosphates One or more of lithium-containing phosphates.
  • the positive electrode active material is a lithium-containing phosphate having an olivine structure. This is because the lithium-containing phosphate of the olivine structure itself has high structural stability, and does not cause structural loss like structural changes of other positive active materials in the lithium ion secondary battery cycle, so the olivine structure is used.
  • the capacity decay of a lithium ion secondary battery containing lithium phosphate is mainly derived from the active lithium ion loss between the positive and negative electrodes (for example, participation in forming a negative SEI film), whereby the positive active material is olivine
  • the structure contains lithium phosphate, the capacity loss of the lithium ion secondary battery can be effectively reduced, and the cycle performance and storage performance of the lithium ion secondary battery are greatly improved.
  • the lithium-containing phosphate of the olivine structure has the formula of LiFe 1-xy Mn x M' y PO 4 , 0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 0.1, 0 ⁇ x+y ⁇ 1, M'
  • One or more of other transition metal elements or non-transition metal elements other than Fe, Mn, M' is preferably selected from one or more of Cr, Mg, Ti, Al, Zn, W, Nb, Zr .
  • the lithium-containing phosphate of the olivine structure is selected from one or more of lithium iron phosphate, lithium manganese phosphate, and lithium iron manganese phosphate.
  • the positive electrode film further includes a conductive agent and a binder.
  • the type of the binder and the conductive agent are not particularly limited and can be selected according to actual needs.
  • the binder may be selected from the group consisting of polyvinylidene fluoride (PVDF), polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene One or more of a meta-copolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.
  • the conductive agent may be selected from one or more of conductive carbon black, superconducting carbon black, conductive graphite, acetylene black, ketjen black, graphene, and carbon nanotubes.
  • the electrolytic solution includes a lithium salt, an organic solvent, and an optional additive.
  • the lithium salt may be an organic lithium salt or an inorganic lithium salt.
  • the lithium salt may contain at least one of a fluorine element, a boron element, and a phosphorus element.
  • the lithium salt may be selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium tetrafluorooxalate phosphate, LiN(SO 2 R F ) 2 , LiN(SO 2 F) ( One or more of SO 2 R F ), bistrifluoromethanesulfonimide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalate)borate, and lithium difluorooxalate borate, preferably LiPF 6 , LiN ( One or more of SO 2 R F ) 2 wherein the substituent R F is represented by C n F 2n+1 and n is an integer of from 1 to 10.
  • the organic solvent may include: dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl propionate, butyric acid. One or more of ethyl ester, ethyl propionate, and propyl butyrate; and ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, vinyl sulfite, propylene sulfite, ⁇ One or more of butyrolactone and tetrahydrofuran. Further, the organic solvent may further include different classes of ionic liquids and the like. In addition, the organic solvent used in the present application may be used alone or in combination of two or more kinds in any combination and in any ratio depending on the application.
  • the kind of the separator is not particularly limited, and may be any separator material used in the existing lithium ion secondary battery, such as polyethylene, polypropylene, poly Vinylidene fluoride and their multilayer composite films are not limited to these.
  • a method for preparing a lithium ion secondary battery according to a second aspect of the present invention for preparing the lithium ion secondary battery of the first aspect of the present invention includes the steps of: coating a positive electrode slurry on the surface of the positive electrode current collector, and drying A positive electrode sheet is obtained; a negative electrode slurry is coated on the surface of the negative electrode current collector, and after drying, a layer of metallic lithium is disposed on the surface of the negative electrode film, and then assembled with the separator and the positive electrode sheet into a battery core; In the package shell, the electrolyte is injected and encapsulated, and the lithium metal is converted into a pre-lithium compound LiC x by the lithiation of the carbon-based anode material in the anode active material under the action of the electrolyte, and then pre-charged to obtain the finished lithium ion twice. battery.
  • the metal lithium has a weight of 0.5% to 5% based on the total weight of the negative electrode film.
  • the content of lithium metal is too high, which tends to cause lithium precipitation in the negative electrode.
  • the metal lithium may be disposed on the surface of the negative electrode membrane by roll pressing, using a molecule of a lithium metal and an anode active material such as graphite.
  • the intervening force will stably fix the metallic lithium on the surface of the negative electrode diaphragm.
  • the form of metallic lithium may be selected from one or more of lithium powder, lithium ingot, and lithium sheet.
  • the lithium ion secondary batteries of Examples 1 to 11 and Comparative Examples 1 to 7 were each prepared according to the following procedure:
  • the positive electrode active material lithium iron phosphate (reversible gram capacity is 139 mAh/g), the conductive agent acetylene black, and the binder PVDF are mixed at a weight ratio of 94:4:2, and the solvent N-methylpyrrolidone is added thereto, and the mixture is uniformly stirred and uniformly obtained.
  • the positive electrode slurry was then coated on both surfaces of a positive electrode current collector aluminum foil, and then dried and cold pressed to obtain a positive electrode sheet.
  • the negative electrode active material artificial graphite (reversible gram capacity is 340 mAh/g), the conductive agent acetylene black, and the binder SBR+CMC are mixed at a weight ratio of 95:1.5:3.1:0.4, and the solvent deionized water is added, and the mixture is thoroughly stirred and uniformly mixed.
  • the negative electrode slurry is obtained, and then coated on both surfaces of the negative electrode current collector copper foil, and after drying and cold pressing, an anode film is obtained, and then the lithium piece (the theoretical gram capacity is 3861.3 mAh/g) is rolled.
  • the film was laminated to the surface of the negative electrode film to obtain a negative electrode sheet.
  • EC:PC:DMC 3:3:3
  • a polyethylene porous film having a thickness of 20 ⁇ m was used as a separator.
  • the positive electrode sheet, the separator film and the negative electrode sheet are stacked in this order, so that the separator is in the middle of the positive and negative electrodes to function as an isolation, and is wound up to obtain a battery core.
  • the battery cell is placed in a package, and the prepared electrolyte is injected and packaged, and then pre-filled to obtain a finished lithium ion secondary battery.
  • the lithium ion secondary battery S1 was prepared by the above method, wherein the coating weight of the negative electrode slurry was 0.120 g / 1540.25 mm 2 (based on the weight excluding the solvent), and the coating weight of the positive electrode slurry was 0.198 g / 1540.25 mm. 2 (based on the weight excluding the solvent), the weight of the lithium sheet was 3.05 mg / 1540.25 mm 2 .
  • the lithium ion secondary battery S2 was prepared by the above method, wherein the coating weight of the negative electrode slurry was 0.136 g / 1540.25 mm 2 , the coating weight of the positive electrode slurry was 0.198 g / 1540.25 mm 2 , and the lithium film on the surface of the negative electrode film was used.
  • the weight is 3.05mg / 1540.25mm 2 .
  • the lithium ion secondary battery S3 was prepared by the above method, wherein the coating weight of the negative electrode slurry was 0.104 g / 1540.25 mm 2 , the coating weight of the positive electrode slurry was 0.198 g / 1540.25 mm 2 , and the lithium film on the surface of the negative electrode film was used.
  • the weight is 1.52mg / 1540.25mm 2 .
  • the lithium ion secondary battery S6 is prepared by the above method, wherein the coating weight of the negative electrode slurry is 0.136 g / 1540.25 mm 2 , the coating weight of the positive electrode slurry is 0.177 g / 1540.25 mm 2 , and the weight of the lithium piece on the surface of the negative electrode film. It is 3.45 mg / 1540.25 mm 2 .
  • the lithium ion secondary battery S7 was prepared by the above method, wherein the coating weight of the negative electrode slurry was 0.136 g / 1540.25 mm 2 , the coating weight of the positive electrode slurry was 0.259 g / 1540.25 mm 2 , and the lithium film on the surface of the negative electrode film was used. The weight is 1.99mg / 1540.25mm 2 .
  • the lithium ion secondary battery S8 was prepared by the above method, wherein the coating weight of the negative electrode slurry was 0.136 g / 1540.25 mm 2 , the coating weight of the positive electrode slurry was 0.177 g / 1540.25 mm 2 , and the surface of the negative electrode film was lithium. The weight is 5.44 mg / 1540.25 mm 2 .
  • the lithium ion secondary battery S9 is prepared by the above method, wherein the coating weight of the negative electrode slurry is 0.136 g / 1540.25 mm 2 , the coating weight of the positive electrode slurry is 0.160 g / 1540.25 mm 2 , and the surface of the negative electrode film is lithium. The weight is 6.16 mg / 1540.25 mm 2 .
  • the lithium ion secondary battery S10 was prepared by the above method, wherein the coating weight of the negative electrode slurry was 0.136 g / 1540.25 mm 2 , the coating weight of the positive electrode slurry was 0.280 g / 1540.25 mm 2 , and the lithium film on the surface of the negative electrode film was used. The weight is 1.10 mg / 1540.25 mm 2 .
  • the lithium ion secondary battery S11 was prepared by the above method, wherein the coating weight of the negative electrode slurry was 0.136 g / 1540.25 mm 2 , the coating weight of the positive electrode slurry was 0.280 g / 1540.25 mm 2 , and the lithium film on the surface of the negative electrode film was used. The weight is 0.68mg / 1540.25mm 2 .
  • the lithium ion secondary battery DS1 is prepared by the above method, wherein the surface of the negative electrode film is not provided with a lithium sheet, the coating weight of the negative electrode slurry is 0.120 g/1540.25 mm 2 , and the coating weight of the positive electrode slurry is 0.198 g/1540.25. Mm 2 .
  • the lithium ion secondary battery DS2 was prepared by the above method, wherein the surface of the negative electrode film was not provided with a lithium sheet, the coating weight of the negative electrode slurry was 0.094 g/1540.25 mm 2 , and the coating weight of the positive electrode slurry was 0.198 g/1540.25. Mm 2 .
  • the lithium ion secondary battery DS3 is prepared by the above method, wherein the surface of the negative electrode film is not provided with a lithium sheet, the coating weight of the negative electrode slurry is 0.136 g / 1540.25 mm 2 , and the coating weight of the positive electrode slurry is 0.224 g / 1540.25. Mm 2 .
  • the lithium ion secondary battery DS4 was prepared by the above method, wherein the surface of the negative electrode film was not provided with a lithium sheet, the coating weight of the negative electrode slurry was 0.136 g / 1540.25 mm 2 , and the coating weight of the positive electrode slurry was 0.287 g / 1540.25. Mm 2 .
  • the lithium ion secondary battery DS5 was prepared by the above method, wherein the coating weight of the negative electrode slurry was 0.136 g / 1540.25 mm 2 , the coating weight of the positive electrode slurry was 0.280 g / 1540.25 mm 2 , and the lithium film on the surface of the negative electrode film was used. The weight is 1.99mg / 1540.25mm 2 .
  • the lithium ion secondary battery DS6 was prepared by the above method, wherein the coating weight of the negative electrode slurry was 0.104 g / 1540.25 mm 2 , the coating weight of the positive electrode slurry was 0.198 g / 1540.25 mm 2 , and the lithium film on the surface of the negative electrode film was used. The weight is 3.05mg / 1540.25mm 2 .
  • the lithium ion secondary battery DS7 was prepared by the above method, wherein the coating weight of the negative electrode slurry was 0.136 g / 1540.25 mm 2 , the coating weight of the positive electrode slurry was 0.287 g / 1540.25 mm 2 , and the surface of the negative electrode film was lithium. The weight is 3.45 mg / 1540.25 mm 2 .
  • the finished lithium ion secondary batteries pre-filled with Examples 1-11 and Comparative Examples 1-7 were fully disassembled at a nominal magnification of 1 C (that is, the current value of the theoretical capacity was completely discharged within 1 h), and then the positive electrode sheets were obtained.
  • the negative electrode sheets were cut out, and the positive electrode sheets per unit area and the negative electrode sheets per unit area were respectively cut and tested.
  • the positive electrode sheets of the cut unit area were the same as the electrolytic solution (the same as Examples 1-11 and Comparative Examples 1-7), the separator (the same as Examples 1-11 and Comparative Examples 1-7), and the unit area.
  • the lithium metal sheet is composed of a button type half-cell, and is fully charged to 3.75V at a rate of 0.1 C to obtain a charging capacity, that is, an amount of active lithium that can be deintercalated per unit area of the positive electrode diaphragm. After that, the button half-cell was allowed to stand for 30 min, and then discharged to 2.0 V at a rate of 0.1 C to obtain a discharge capacity, that is, the amount of active lithium that can be embedded in the positive electrode membrane per unit area.
  • the cut negative electrode sheet per unit area was the same as the electrolytic solution (the same as Examples 1 to 11 and Comparative Examples 1 to 7), the separator (the same as Examples 1 to 11 and Comparative Examples 1 to 7), and the unit area.
  • the lithium metal sheet is composed of a button type half-cell, and is fully charged to 1.0V at a rate of 0.1 C to obtain a charging capacity, that is, an amount of active lithium that can be deintercalated per unit area of the negative electrode diaphragm.
  • the sum of the amount of active lithium that can be deintercalated per unit area of the positive electrode diaphragm and the amount of active lithium that can be deintercalated per unit area of the negative electrode film minus the amount of active lithium that can be embedded in the positive electrode film per unit area is pre-embedded in the negative electrode film per unit area.
  • the amount of active lithium that the lithium compound LiC x can deintercalate.
  • the finished lithium ion secondary battery in which Example 1 and Comparative Example 1 were pre-filled at 25 ° C was first tested at a nominal magnification of 1 C.
  • the test process is as follows: the lithium ion secondary battery is charged at a constant current of 1 C to a voltage of 3.65 V, and then charged at a constant voltage of 3.65 V until the current is 0.05 C. After standing for 5 min, the lithium ion secondary battery is discharged at a constant current of 1 C. The voltage is 2.5V, which is a charge and discharge cycle. The discharge capacity of this time is the discharge capacity of the first cycle.
  • the lithium ion secondary battery was subjected to a plurality of cycles of charge and discharge tests as described above until the discharge capacity of the lithium ion secondary battery was attenuated to 80%, and the number of cycles of the lithium ion secondary battery was recorded.
  • the finished lithium ion secondary batteries pre-filled with Examples 1-11 and Comparative Examples 1-7 at 60 ° C were first tested at a nominal full rate of 1 C.
  • the test process is as follows: the lithium ion secondary battery is charged at a constant current of 1 C to a voltage of 3.65 V, and then charged at a constant voltage of 3.65 V until the current is 0.05 C. After standing for 5 min, the lithium ion secondary battery is discharged at a constant current of 1 C.
  • the voltage is 2.5V, which is a charge and discharge cycle.
  • the discharge capacity of this time is the discharge capacity of the first cycle.
  • the lithium ion secondary battery was subjected to a plurality of cycles of charge and discharge tests as described above, and the discharge capacity at the 500th cycle was detected.
  • the capacity retention ratio of the lithium ion secondary battery after 500 cycles at 60 ° C (discharge capacity at the 500th cycle / discharge capacity at the first cycle) ⁇ 100%.
  • the finished lithium ion secondary batteries which were pre-charged in Examples 1 to 11 and Comparative Examples 1 to 7 were filled at a nominal magnification of 1 C at 25 ° C, and then tested.
  • the test process is as follows: the lithium ion secondary battery is charged at a constant current of 0.5 C to a voltage of 3.65 V, and then charged at a constant voltage of 3.65 V until the current is 0.05 C. After standing for 5 min, the lithium ion secondary battery is kept at 0.5 C constant.
  • the discharge discharge voltage is 2.5V, and the discharge capacity of this time is the discharge capacity before storage; then the lithium ion secondary battery is fully charged with a charging current of 0.5C, and is allowed to stand at 60 ° C for 90 days, after which the juxtaposition is taken out.
  • the capacity retention ratio of the lithium ion secondary battery after storage at 60 ° C for 90 days (discharge capacity after 90 days of storage / discharge capacity before storage) ⁇ 100%.
  • Formula 1 capacity per unit area of negative electrode active material / capacity of positive electrode active material per unit area.
  • Formula 2 capacity per unit area of the negative electrode active material / (the capacity of the positive electrode active material per unit area + the amount of active lithium of the pre-calium compound LiC x deintercalable in the negative electrode film per unit area).
  • Example 1 is a graph showing the normal temperature cycle performance curves of Example 1 and Comparative Example 1.
  • the lithium ion secondary battery of Comparative Example 1 is expected to be cycled up to about 6000 times when the capacity is attenuated to 80% in a normal temperature environment, and the lithium ion secondary battery of Example 1 is further recycled after 6000 cycles.
  • 90% reversible discharge capacity, and expected to cycle about 16,000 times when the capacity is attenuated to 80% it can meet the needs of long-life electric buses and large-scale energy storage systems.
  • Button to change the following half-cell electrolyte and an isolation film composition, their influence on the amount of active lithium LiC x Example 1 may deintercalation embodiment.
  • the sufficiently dried lithium salt LiN(SO 2 CF 3 ) 2 was dissolved in the above mixed organic solvent, and after stirring uniformly, an electrolytic solution was obtained in which the concentration of LiN(SO 2 CF 3 ) 2 was 1 mol/L.
  • the separator was made of a polypropylene porous film having a thickness of 20 ⁇ m as a separator.
  • the sufficiently dried lithium salt LiPF 6 was dissolved in the above mixed organic solvent, and after stirring uniformly, an electrolytic solution was obtained in which the concentration of LiPF 6 was 1 mol/L.
  • the separator was made of a polypropylene porous film having a thickness of 20 ⁇ m as a separator.
  • the sufficiently dried lithium salt LiPF 6 was dissolved in the above mixed organic solvent, and after stirring uniformly, an electrolytic solution was obtained in which the concentration of LiPF 6 was 1 mol/L.
  • the separator was made of a polypropylene porous film having a thickness of 20 ⁇ m as a separator.
  • the sufficiently dried lithium salt LiPF 6 was dissolved in the above mixed organic solvent, and after stirring uniformly, an electrolytic solution was obtained in which the concentration of LiPF 6 was 0.8 mol/L.
  • the separator was made of a polyethylene porous film having a thickness of 20 ⁇ m as a separator.
  • the sufficiently dried lithium salt LiPF 6 was dissolved in the above mixed organic solvent, and after stirring uniformly, an electrolytic solution was obtained in which the concentration of LiPF 6 was 1.2 mol/L.
  • the separator was made of a polyethylene porous film having a thickness of 20 ⁇ m as a separator.
  • the composition of the electrolyte and the type of the separator change the amount of active lithium that can be deintercalated per unit area of the positive electrode membrane, the amount of active lithium that can be deintercalated per unit area of the negative membrane, and the positive diaphragm per unit area.
  • the amount of active lithium that can be embedded and the amount of active lithium that can be deintercalated by the pre-calium compound LiC x per unit area of the negative electrode film are negligible.
  • the composition of the electrolyte and the separator is the same as that of the whole battery.

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Abstract

本发明提供一种锂离子二次电池及其制备方法。所述锂离子二次电池的负极片为预嵌锂的负极片，负极活性物质为碳基负极材料，且所述碳基负极材料与负极片中预嵌入的锂金属锂化形成预嵌锂化合物LiC x，x＝12～150；单位面积负极活性物质容量/单位面积正极活性物质容量＝1.2～2.1，单位面积负极活性物质容量/(单位面积正极活性物质容量+单位面积负极膜片中预嵌锂化合物LiC x可脱嵌的活性锂量)≥1.10。本发明的锂离子二次电池在使用过程中满充后，负极活性物质可有足够的空位接收来自正极活性物质脱出的所有锂离子，并在满放后于负极储存过量的锂离子，因此能有效降低锂离子二次电池的容量损失，使锂离子二次电池具有较好的循环性能和存储性能。

Description

锂离子二次电池及其制备方法 技术领域
本发明涉及电池领域，尤其涉及一种锂离子二次电池及其制备方法。
背景技术
在二次电池中，锂离子二次电池相对于其它种类的二次电池来说，其较高的能量密度优势使其在市场上占据主流地位。其中，以磷酸铁锂为正极活性物质的锂离子二次电池以其高安全性、低成本、长寿命的特点广泛应用于电动大巴动力系统，并在大规模储能领域拥有广泛的应用前景。
近年来，基于度电成本考虑，对锂离子二次电池寿命的要求越来越高。虽然磷酸铁锂具有较高的结构稳定性，但是在石墨负极表面会发生固体-电解质液界面膜(SEI膜)的溶解-修复平衡，导致可用于正负极之间穿梭的活性锂离子不断减少，从而不可避免地发生容量损失。以钛酸锂为负极活性物质、以磷酸铁锂为正极活性物质的锂离子二次电池由于不生成SEI膜，可以避免由SEI膜的溶解-修复平衡引起的负极副反应导致的容量损失，但是钛酸锂较高的电压平台导致锂离子二次电池的放电电压平台较低，能量密度过低，且钛酸锂昂贵的单价导致单位Wh成本过高，因此，需要有效的技术解决锂离子二次电池的长寿命问题。
目前改善锂离子二次电池寿命的主要手段有：选择循环性能和存储性能好的磷酸铁锂种类和石墨种类、优化电解液配方(改变有机溶剂、添加剂)、优化正极膜片和负极膜片配方、优化SEI膜成膜条件等。这些手段均从抑制由SEI膜的溶解-修复平衡引起的负极副反应角度考虑，通过节流的方式延缓活性锂离子的减少，因此能起到的作用有限，锂离子二次电池的循环寿命最高可以做到5000～6000次左右，与长寿命电动大巴和大规模储能系统10000次以上循环寿命的目标尚有较大差距。
发明内容
鉴于背景技术中存在的问题，本发明的目的在于提供一种锂离子二次电池及其制备方法，所述锂离子二次电池具有较好的循环性能和存储性能。
为了达到上述目的，在本发明的一方面，本发明提供了一种锂离子二次电池，其包括：电芯；电解液，浸渍电芯；以及包装壳。电芯包括负极片、正极片以及隔离膜，所述负极片包括负极集流体以及设置在负极集流体的表面且含有负极活性物质的负极膜片，所述正极片包括正极集流体以及设置在正极集流体的表面且含有正极活性物质的正极膜片，所述隔离膜间隔于相邻负极片和正极片之间。其中，所述负极片为预嵌锂的负极片，负极活性物质为碳基负极材料，且所述碳基负极材料与负极片中预嵌入的锂金属锂化形成预嵌锂化合物LiC x，x＝12～150；单位面积负极活性物质容量/单位面积正极活性物质容量＝1.2～2.1，单位面积负极活性物质容量/(单位面积正极活性物质容量+单位面积负极膜片中预嵌锂化合物LiC x可脱嵌的活性锂量)≥1.10。
在本发明的另一方面，本发明提供了一种锂离子二次电池的制备方法，用于制备本发明一方面的锂离子二次电池，包括步骤：在正极集流体的表面涂覆正极浆料，干燥后，得到正极片；在负极集流体的表面涂覆负极浆料，干燥后，再在负极膜片的表面设置金属锂层，之后与隔离膜、正极片组装成电芯；将电芯置于包装壳中，注入电解液并封装，金属锂层在电解液作用下与负极活性物质中的碳基负极材料锂化转变为预嵌锂化合物LiC x，之后经过预充化成，得到成品锂离子二次电池。
相对于现有技术，本发明至少包括如下有益效果：
本发明的锂离子二次电池在使用过程中满充后，负极活性物质可有足够的空位接收来自正极活性物质脱出的所有锂离子，并在满放后于负极储存过量的锂离子，因此能有效降低锂离子二次电池的容量损失，使锂离子二次电池具有较好的循环性能和存储性能。
附图说明
图1为实施例1和对比例1的常温循环性能曲线图。
具体实施方式
下面详细说明根据本发明的锂离子二次电池及其制备方法。
首先说明根据本发明第一方面的锂离子二次电池。
根据本发明第一方面的锂离子二次电池包括：电芯；电解液，浸渍电芯；以及包装壳。电芯包括负极片、正极片以及隔离膜，所述负极片包括负极集流体以及设置在负极集流体的表面且含有负极活性物质的负极膜片，所述正极片包括正极集流体以及设置在正极集流体的表面且含有正极活性物质的正极膜片，所述隔离膜间隔于相邻负极片和正极片之间。其中，所述负极片为预嵌锂的负极片，负极活性物质为碳基负极材料，且所述碳基负极材料与负极片中预嵌入的锂金属锂化形成预嵌锂化合物LiC x，x＝12～150，即负极膜片中包含的碳基负极材料以预嵌锂化合物LiC x形式存在于负极膜片中；单位面积负极活性物质容量/单位面积正极活性物质容量＝1.2～2.1，单位面积负极活性物质容量/(单位面积正极活性物质容量+单位面积负极膜片中预嵌锂化合物LiC x可脱嵌的活性锂量)≥1.10。
这里单位面积负极活性物质容量以尚未被锂化(或尚未嵌锂)的负极活性物质(即碳基负极材料)的可逆容量计，单位面积正极活性物质容量以正极活性物质的可逆克容量计。
单位面积负极膜片中预嵌锂化合物LiC x可脱嵌的活性锂量可通过下述公式得到：单位面积负极膜片中预嵌锂化合物LiC x可脱嵌的活性锂量＝单位面积正极膜片可脱嵌的活性锂量+单位面积负极膜片可脱嵌的活性锂量-单位面积正极膜片可嵌入的活性锂量。
具体地，可将锂离子二次电池完全放电后拆解得到正极片、负极片，并分别裁切出单位面积的正极片和单位面积的负极片进行下述测试：
将单位面积的正极片与单位面积的锂金属片组成扣式半电池，以不大于0.1C倍率满充，得到充电容量，即为单位面积正极膜片可脱嵌的活性锂量；之后将扣式半电池静置一段时间(优选不小于5min，更优选为5～30min)，再以不大于0.1C倍率(优选与充电倍率相同)满放，得到放电容量，即为单位面积正极膜片可嵌入的活性锂量；
将单位面积的负极片与单位面积的锂金属片组成扣式半电池，以不大于0.1C倍率满充，得到充电容量，即为单位面积负极膜片可脱嵌的活性锂量。
需要说明的是，正极片和负极片的裁切位置不受具体的限制，只要保证 正极膜片和负极膜片全覆盖即可。
在上述测试中，充放电电压区间根据正极活性物质和负极活性物质的具体种类确定，即根据商购正负极活性物质厂家建议电压确定，不同的正负极活性物质对应的充放电电压略有差异。
在上述测试中，组装的扣式半电池中电解液的组成以及隔离膜的种类在选择时并不受到具体的限制，优选在与锂离子二次电池相同的条件下进行测试即可，其具体种类的改变对计算得到的单位面积负极膜片中预嵌锂化合物LiC x可脱嵌的活性锂量的影响可以忽略。
上述单位面积负极膜片中预嵌锂化合物LiC x可脱嵌的活性锂量的计算方法以及测试方法既适用于新制备好的锂离子二次电池，也适用于已经循环了若干圈的锂离子二次电池(尤其是前期循环容量衰减较小，例如前100循环后的容量保持率≥98％的锂离子二次电池)。
在本发明第一方面的锂离子二次电池中，单位面积负极活性物质容量/单位面积正极活性物质容量＝1.2～2.1，单位面积负极活性物质容量/(单位面积正极活性物质容量+单位面积负极膜片中预嵌锂化合物LiC x可脱嵌的活性锂量)≥1.10，这样当锂离子二次电池使用过程中满充后，负极活性物质可有足够的空位接收来自正极活性物质脱出的所有锂离子，并在满放后于负极储存过量的锂离子，因此能有效降低锂离子二次电池的容量损失，提高锂离子二次电池的循环性能和存储性能。优选地，单位面积负极活性物质容量/单位面积正极活性物质容量＝1.3～2.1。
在本发明第一方面的锂离子二次电池中，在预嵌锂化合物LiC x中，当x＜12时，预嵌锂程度较高，在负极表面易发生锂金属残留，造成安全隐患；当x＞150时，预嵌锂程度较低，对锂离子二次电池的循环寿命的改善效果不显著。优选地，预嵌锂化合物LiC x中x＝12～50。
在本发明第一方面的锂离子二次电池中，负极膜片可设置在负极集流体的其中一个表面上，也可以设置在负极集流体的两个表面上。
在本发明第一方面的锂离子二次电池中，所述碳基负极材料选自天然石墨、人造石墨、软碳、硬碳、中间相碳微球、纳米碳、碳纤维中的一种或几种。优选地，所述碳基负极材料选自天然石墨、人造石墨或二者的混合物。
在本发明第一方面的锂离子二次电池中，所述负极膜片还包括粘结剂以 及导电剂。粘结剂以及导电剂的种类均不受到具体的限制，可根据实际需求进行选择。优选地，所述粘接剂可选自丁苯橡胶乳液(SBR)、羧甲基纤维素钠(CMC)中的一种或几种。优选地，所述导电剂可选自导电炭黑、超导炭黑、导电石墨、乙炔黑、科琴黑、石墨烯、碳纳米管中的一种或几种。
在本发明第一方面的锂离子二次电池中，正极膜片可设置在正极集流体的其中一个表面上，也可以设置在正极集流体的两个表面上。
在本发明第一方面的锂离子二次电池中，所述正极活性物质可选自能接受、脱出锂离子的材料。优选地，所述正极活性物质可选自锂过渡金属氧化物、锂过渡金属氧化物添加其它过渡金属或非过渡金属或非金属得到的化合物中的一种或几种。具体地，所述正极活性物质可选自锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物、橄榄石结构的含锂磷酸盐中的一种或几种。
在本发明第一方面的锂离子二次电池中，优选地，所述正极活性物质为橄榄石结构的含锂磷酸盐。这是由于橄榄石结构的含锂磷酸盐本身具有较高的结构稳定性，不会像其它正极活性物质在锂离子二次电池循环过程中出现结构变化而导致容量损失，因此使用橄榄石结构的含锂磷酸盐的锂离子二次电池的容量衰减主要源自电池内部可穿梭于正负极之间的活性锂离子损失(例如参与形成负极SEI膜)，由此，当正极活性物质为橄榄石结构的含锂磷酸盐时，可以有效降低锂离子二次电池的容量损失，大幅提高锂离子二次电池的循环性能和存储性能。优选地，橄榄石结构的含锂磷酸盐的通式为LiFe 1-x-yMn xM’ yPO 4，0≤x≤1，0≤y≤0.1，0≤x+y≤1，M’选自除Fe、Mn外的其它过渡金属元素或非过渡金属元素中的一种或几种，M’优选选自Cr、Mg、Ti、Al、Zn、W、Nb、Zr中一种或几种。进一步优选地，所述橄榄石结构的含锂磷酸盐选自磷酸铁锂、磷酸锰锂、磷酸锰铁锂中的一种或几种。
在本发明第一方面的锂离子二次电池中，所述正极膜片还包括导电剂以及粘结剂。粘结剂以及导电剂的种类并不受到具体的限制，可根据实际需求进行选择。优选地，所述粘接剂可选自聚偏氟乙烯(PVDF)、聚四氟乙烯、偏氟乙烯-四氟乙烯-丙烯三元共聚物、偏氟乙烯-六氟丙烯-四氟乙烯三元共聚物、四氟乙烯-六氟丙烯共聚物、含氟丙烯酸酯树脂中的一种或几种。优选地，所述导电剂可选自导电炭黑、超导炭黑、导电石墨、乙炔黑、科琴黑、石墨 烯、碳纳米管中的一种或几种。
在本发明第一方面的锂离子二次电池中，所述电解液包括锂盐、有机溶剂以及可选的添加剂。所述锂盐可为有机锂盐，也可为无机锂盐，具体而言，所述锂盐中可含有氟元素、硼元素、磷元素中的至少一种。具体地，所述锂盐可选自六氟磷酸锂、四氟硼酸锂、高氯酸锂、六氟砷酸锂、四氟草酸磷酸锂、LiN(SO 2R F) 2、LiN(SO 2F)(SO 2R F)、双三氟甲烷磺酰亚胺、双(氟磺酰)亚胺锂、双草酸硼酸锂、二氟草酸硼酸锂中的一种或几种，优选为LiPF 6、LiN(SO 2R F) 2中的一种或几种，其中，取代基R F表示为C nF 2n+1，n为1～10的整数。所述有机溶剂可包括：碳酸二甲酯、碳酸二乙酯、碳酸甲乙酯、碳酸甲丙酯、甲酸甲酯、甲酸乙酯、乙酸甲酯、乙酸乙酯、丙酸丙酯、丁酸乙酯、丙酸乙酯、丁酸丙酯中的一种或几种；以及碳酸乙烯酯、碳酸丙烯酯、碳酸丁烯酯、碳酸亚乙烯酯、亚硫酸乙烯酯、亚硫酸丙烯酯、γ-丁内酯、四氢呋喃中的一种或几种。此外，所述有机溶剂还可包括不同类别的离子液体等。另外，对于本申请中使用的有机溶剂，可以单独使用一种，还可以根据用途以任意的组合、比率混合使用两种以上。
在本发明第一方面的锂离子二次电池中，隔离膜的种类并不受到具体的限制，可以是现有锂离子二次电池中使用的任何隔离膜材料，例如聚乙烯、聚丙烯、聚偏氟乙烯以及它们的多层复合膜，但不仅限于这些。
其次说明根据本发明第二方面的锂离子二次电池的制备方法，用于制备本发明第一方面的锂离子二次电池，包括步骤：在正极集流体的表面涂覆正极浆料，干燥后，得到正极片；在负极集流体的表面涂覆负极浆料，干燥后，再在负极膜片的表面设置一层金属锂，之后与隔离膜、正极片组装成电芯；将电芯置于包装壳中，注入电解液并封装，金属锂在电解液作用下与负极活性物质中的碳基负极材料锂化转变为预嵌锂化合物LiC x，之后经过预充化成，得到成品锂离子二次电池。
在本发明第二方面的锂离子二次电池的制备方法中，金属锂的重量为负极膜片的总重量的0.5％～5％。金属锂的含量过高，容易导致负极析锂。
在本发明第二方面的锂离子二次电池的制备方法中，所述金属锂可采用辊压的方式设置于所述负极膜片的表面，利用锂金属与负极活性物质(诸如 石墨)的分子间作用力将使金属锂稳定地固定设置在负极膜片的表面。其中，金属锂的形式可选自锂粉、锂锭、锂片中的一种或几种。
下面结合实施例，进一步阐述本申请。应理解，这些实施例仅用于说明本申请而不用于限制本申请的范围。
实施例1-11和对比例1-7的锂离子二次电池均按照下述流程制备：
(1)正极片的制备
将正极活性物质磷酸铁锂(可逆克容量为139mAh/g)、导电剂乙炔黑、粘结剂PVDF按重量比94:4:2进行混合，加入溶剂N-甲基吡咯烷酮，充分搅拌混合均匀得到正极浆料，然后涂覆于正极集流体铝箔的两个表面上，然后烘干、冷压，得到正极片。
(2)负极片的制备
将负极活性物质人造石墨(可逆克容量为340mAh/g)、导电剂乙炔黑、粘结剂SBR+CMC按照重量比95:1.5:3.1:0.4进行混合，加入溶剂去离子水，充分搅拌混合均匀得到负极浆料，然后涂覆于负极集流体铜箔的两个表面上，经烘干、冷压后得到负极膜片，然后将锂片(理论克容量为3861.3mAh/g)采用辊压的方式复合到负极膜片的表面，得到负极片。
(3)电解液制备
在含水量<10ppm的氩气气氛手套箱中，将碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、碳酸二甲酯(DMC)按照重量比为EC:PC:DMC＝3:3:3进行混合后，得到混合有机溶剂，再将充分干燥的锂盐LiPF 6溶解于上述混合有机溶剂中，搅拌均匀后，获得电解液，其中LiPF 6的浓度为1mol/L。
(4)隔离膜的制备
以厚度20μm聚乙烯多孔膜作为隔离膜。
(5)锂离子二次电池的制备
将正极片、隔离膜、负极片按顺序叠好，使隔离膜处于正负极中间起到隔离的作用，并卷绕得到电芯。将电芯置于包装壳中，注入配好的电解液并封装，之后经过预充化成，获得成品锂离子二次电池。
实施例1
采用上述方法制备锂离子二次电池S1，其中，负极浆料的涂布重量为0.120g/1540.25mm 2(以不包含溶剂的重量计)，正极浆料的涂布重量为0.198g/1540.25mm 2(以不包含溶剂的重量计)，锂片的重量为3.05mg/1540.25mm 2。
单位面积(以面积为1540.25mm 2计，以下实施例类似)负极活性物质容量＝单位面积的负极涂布重量×负极活性物质重量比×负极活性物质的可逆克容量＝0.120g×95％×340mAh/g＝38.76mAh。
单位面积(以面积为1540.25mm 2计，以下实施例类似)正极活性物质容量＝单位面积的正极涂布重量×正极活性物质重量比×正极活性物质的可逆克容量＝0.198g×94％×139mAh/g＝25.87mAh。
实施例2
采用上述方法制备锂离子二次电池S2，其中，负极浆料的涂布重量为0.136g/1540.25mm 2，正极浆料的涂布重量为0.198g/1540.25mm 2，负极膜片表面的锂片的重量为3.05mg/1540.25mm 2。
单位面积负极活性物质容量＝0.136g×95％×340mAh/g＝43.93mAh。
单位面积正极活性物质容量＝0.198g×94％×139mAh/g＝25.87mAh。
实施例3
采用上述方法制备锂离子二次电池S3，其中，负极浆料的涂布重量为0.104g/1540.25mm 2，正极浆料的涂布重量为0.198g/1540.25mm 2，负极膜片表面的锂片的重量为1.52mg/1540.25mm 2。
单位面积负极活性物质容量＝0.104g×95％×340mAh/g＝33.59mAh。
单位面积正极活性物质容量＝0.198g×94％×139mAh/g＝25.87mAh。
实施例4
采用上述方法制备锂离子二次电池S4，其中，负极浆料的涂布重量0.136g/1540.25mm 2，正极浆料的涂布重量0.224g/1540.25mm 2，负极膜片表面的锂片的重量为3.45mg/1540.25mm 2。
单位面积负极活性物质容量＝0.136g×95％×340mAh/g＝43.93mAh。
单位面积正极活性物质容量＝0.224g×94％×139mAh/g＝29.27mAh。
实施例5
采用上述方法制备锂离子二次电池S5，其中，负极浆料的涂布重量0.136g/1540.25mm 2，正极浆料的涂布重量0.198g/1540.25mm 2，负极膜片表面的锂片的重量为3.45mg/1540.25mm 2。
单位面积负极活性物质容量＝0.136g×95％×340mAh/g＝43.93mAh。
单位面积正极活性物质容量＝0.198g×94％×139mAh/g＝25.87mAh。
实施例6
采用上述方法制备锂离子二次电池S6，其中，负极浆料的涂布重量0.136g/1540.25mm 2，正极浆料的涂布重量0.177g/1540.25mm 2，负极膜片表面的锂片的重量为3.45mg/1540.25mm 2。
单位面积负极活性物质容量＝0.136g×95％×340mAh/g＝43.93mAh。
单位面积正极活性物质容量＝0.177×94％×139mAh/g＝23.13mAh。
实施例7
采用上述方法制备锂离子二次电池S7，其中，负极浆料的涂布重量为0.136g/1540.25mm 2，正极浆料的涂布重量为0.259g/1540.25mm 2，负极膜片表面的锂片的重量为1.99mg/1540.25mm 2。
单位面积负极活性物质容量＝0.136g×95％×340mAh/g＝43.93mAh。
单位面积正极活性物质容量＝0.259g×94％×139mAh/g＝33.84mAh。
实施例8
采用上述方法制备锂离子二次电池S8，其中，负极浆料的涂布重量0.136g/1540.25mm 2，正极浆料的涂布重量为0.177g/1540.25mm 2，负极膜片表面的锂片的重量为5.44mg/1540.25mm 2。
单位面积负极活性物质容量＝0.136g×95％×340mAh/g＝43.93mAh。
单位面积正极活性物质容量＝0.177×94％×139mAh/g＝23.13mAh。
实施例9
采用上述方法制备锂离子二次电池S9，其中，负极浆料的涂布重量0.136g/1540.25mm 2，正极浆料的涂布重量为0.160g/1540.25mm 2，负极膜片表面的锂片的重量为6.16mg/1540.25mm 2。
单位面积负极活性物质容量＝0.136g×95％×340mAh/g＝43.93mAh。
单位面积正极活性物质容量＝0.160g×94％×139mAh/g＝20.91mAh。
实施例10
采用上述方法制备锂离子二次电池S10，其中，负极浆料的涂布重量为0.136g/1540.25mm 2，正极浆料的涂布重量为0.280g/1540.25mm 2，负极膜片表面的锂片的重量为1.10mg/1540.25mm 2。
单位面积负极活性物质容量＝0.136g×95％×340mAh/g＝43.93mAh。
单位面积正极活性物质容量＝0.280g×94％×139mAh/g＝36.58mAh。
实施例11
采用上述方法制备锂离子二次电池S11，其中，负极浆料的涂布重量为0.136g/1540.25mm 2，正极浆料的涂布重量为0.280g/1540.25mm 2，负极膜片表面的锂片的重量为0.68mg/1540.25mm 2。
单位面积负极活性物质容量＝0.136g×95％×340mAh/g＝43.93mAh。
单位面积正极活性物质容量＝0.280g×94％×139mAh/g＝36.58mAh。
对比例1
采用上述方法制备锂离子二次电池DS1，其中，负极膜片的表面不设置锂片，负极浆料的涂布重量为0.120g/1540.25mm 2，正极浆料的涂布重量为0.198g/1540.25mm 2。
单位面积负极活性物质容量＝0.120g×95％×340mAh/g＝38.76mAh。
单位面积正极活性物质容量＝0.198g×94％×139mAh/g＝25.87mAh。
对比例2
采用上述方法制备锂离子二次电池DS2，其中，负极膜片的表面不设置锂片，负极浆料的涂布重量为0.094g/1540.25mm 2，正极浆料的涂布重量为0.198g/1540.25mm 2。
单位面积负极活性物质容量＝0.094g×95％×340mAh/g＝30.36mAh。
单位面积正极活性物质容量＝0.198g×94％×139mAh/g＝25.87mAh。
对比例3
采用上述方法制备锂离子二次电池DS3，其中，负极膜片的表面不设置锂片，负极浆料的涂布重量为0.136g/1540.25mm 2，正极浆料的涂布重量为0.224g/1540.25mm 2。
单位面积负极活性物质容量＝0.136g×95％×340mAh/g＝43.93mAh。
单位面积正极活性物质容量＝0.224g×94％×139mAh/g＝29.27mAh。
对比例4
采用上述方法制备锂离子二次电池DS4，其中，负极膜片的表面不设置锂片，负极浆料的涂布重量为0.136g/1540.25mm 2，正极浆料的涂布重量为0.287g/1540.25mm 2。
单位面积负极活性物质容量＝0.136g×95％×340mAh/g＝43.93mAh。
单位面积正极活性物质容量＝0.287g×94％×139mAh/g＝37.50mAh。
对比例5
采用上述方法制备锂离子二次电池DS5，其中，负极浆料的涂布重量为0.136g/1540.25mm 2，正极浆料的涂布重量为0.280g/1540.25mm 2，负极膜片表面的锂片的重量为1.99mg/1540.25mm 2。
单位面积负极活性物质容量＝0.136g×95％×340mAh/g＝43.93mAh。
单位面积正极活性物质容量＝0.280g×94％×139mAh/g＝36.58mAh。
对比例6
采用上述方法制备锂离子二次电池DS6，其中，负极浆料的涂布重量为0.104g/1540.25mm 2，正极浆料的涂布重量为0.198g/1540.25mm 2，负极膜片 表面的锂片的重量为3.05mg/1540.25mm 2。
单位面积负极活性物质容量＝0.104g×95％×340mAh/g＝33.59mAh。
单位面积正极活性物质容量＝0.198g×94％×139mAh/g＝25.87mAh。
对比例7
采用上述方法制备锂离子二次电池DS7，其中，负极浆料的涂布重量0.136g/1540.25mm 2，正极浆料的涂布重量为0.287g/1540.25mm 2，负极膜片表面的锂片的重量为3.45mg/1540.25mm 2。
单位面积负极活性物质容量＝0.136g×95％×340mAh/g＝43.93mAh。
单位面积正极活性物质容量＝0.287g×94％×139mAh/g＝37.50mAh。
接下来说明锂离子二次电池的测试过程。
(1)单位面积负极膜片中预嵌锂化合物LiC x可脱嵌的活性锂量的测试
将实施例1-11和对比例1-7预充化成后的成品锂离子二次电池以标称倍率1C(即1h内完全放掉理论容量的电流值)满放后拆解得到正极片、负极片，并分别裁切出单位面积的正极片和单位面积的负极片进行测试。
将裁切好的单位面积的正极片与电解液(与实施例1-11和对比例1-7相同)、隔离膜(与实施例1-11和对比例1-7相同)和单位面积的锂金属片组成扣式半电池，以0.1C倍率满充至3.75V，得到充电容量，即为单位面积正极膜片可脱嵌的活性锂量。之后将扣式半电池静置30min，再以0.1C倍率满放电至2.0V，得到放电容量，即为单位面积正极膜片可嵌入的活性锂量。
将裁切好的单位面积的负极片与电解液(与实施例1-11和对比例1-7相同)、隔离膜(与实施例1-11和对比例1-7相同)和单位面积的锂金属片组成扣式半电池，以0.1C倍率满充至1.0V，得到充电容量，即为单位面积负极膜片可脱嵌的活性锂量。
单位面积正极膜片可脱嵌的活性锂量与单位面积负极膜片可脱嵌的活性锂量之和减去单位面积正极膜片可嵌入的活性锂量即为单位面积负极膜片中预嵌锂化合物LiC x可脱嵌的活性锂量。
(2)LiC x中x的计算方法
x＝(单位面积负极活性物质容量/石墨的可逆克容量/石墨摩尔质量)/(单位面积负极膜片中LiC x可脱嵌的活性锂量/锂金属的理论克容量/锂金属摩尔质量)。
(3)锂离子二次电池的常温循环性能测试
在25℃下，将实施例1和对比例1预充化成后的成品锂离子二次电池先以标称倍率1C满放后进行测试。测试过程为：将锂离子二次电池以1C恒流充电至电压为3.65V，然后以3.65V恒压充电至电流为0.05C，静置5min之后，将锂离子二次电池以1C恒流放电至电压为2.5V，此为一个充放电循环过程，此次的放电容量为首次循环的放电容量。将锂离子二次电池按上述方法进行多次循环充放电测试，直至锂离子二次电池的放电容量衰减至80％，记录锂离子二次电池的循环次数。
(4)锂离子二次电池的高温循环性能测试
在60℃下，将实施例1-11和对比例1-7预充化成后的成品锂离子二次电池先以标称倍率1C满放后进行测试。测试过程为：将锂离子二次电池以1C恒流充电至电压为3.65V，然后以3.65V恒压充电至电流为0.05C，静置5min之后，将锂离子二次电池以1C恒流放电至电压为2.5V，此为一个充放电循环过程，此次的放电容量为首次循环的放电容量。将锂离子二次电池按上述方法进行多次循环充放电测试，检测得到第500次循环的放电容量。
锂离子二次电池60℃循环500次后的容量保持率＝(第500次循环的放电容量/首次循环的放电容量)×100％。
(5)锂离子二次电池的存储性能测试
首先，在25℃下，将实施例1-11和对比例1-7预充化成后的成品锂离子二次电池以标称倍率1C满放后进行测试。测试过程为：将锂离子二次电池以0.5C恒流充电至电压为3.65V，然后以3.65V恒压充电至电流为0.05C，静置5min之后，将锂离子二次电池以0.5C恒流放电至电压为2.5V，此次的放电容量为存储前的放电容量；而后以0.5C的充电电流将锂离子二次电池满充，并于60℃下静置90天，之后取出并置于25℃下静置2小时，再以0.5C恒流放电至电压为2.5V，静置5min之后，以0.5C恒流充电至电压为3.65V，然后以3.65V恒压充电至电流为0.05C，静置5min之后，将锂离子二次电池以0.5C恒流放电至电压为2.5V，此时的放电容量为存储90天后的放电容量。
锂离子二次电池60℃存储90天后的容量保持率＝(存储90天后的放电容量/存储前的放电容量)×100％。
表1实施例1-11以及对比例1-7的参数
Figure PCTCN2018112959-appb-000001
注：
公式1＝单位面积负极活性物质容量/单位面积正极活性物质容量。
公式2＝单位面积负极活性物质容量/(单位面积正极活性物质容量+单位面积负极膜片中预嵌锂化合物LiC x可脱嵌的活性锂量)。
表2实施例1-11以及对比例1-7的性能测试结果
  60℃循环500次后的容量保持率 60℃存储90天后的容量保持率
对比例1 86.9％ 84.8％
对比例2 84.6％ 85.1％
对比例3 85.6％ 84.7％
对比例4 85.5％ 85.7％
对比例5 N/A(跳水) N/A(跳水)
对比例6 N/A(跳水) N/A(跳水)
对比例7 N/A(跳水) N/A(跳水)
实施例1 98.3％ 97.7％
实施例2 98.0％ 98.1％
实施例3 91.0％ 92.3％
实施例4 98.0％ 97.3％
实施例5 97.4％ 97.8％
实施例6 97.1％ 98.1％
实施例7 90.1％ 91.2％
实施例8 101.0％ 102.2％
实施例9 101.1％ 102.4％
实施例10 88.4％ 88.7％
实施例11 87.2％ 86.2％
图1为实施例1和对比例1的常温循环性能曲线图。从图1可以得知，对比例1的锂离子二次电池在常温环境下容量衰减至80％时预期最多可以循环约6000次，而实施例1的锂离子二次电池在循环6000次以后还有90％的可逆放电容量，且容量衰减至80％时预期可以循环约16000次，因此可以满足长寿命电动大巴和大规模储能系统的使用需求。
从对比例1-2的比较可以得知，在正极活性物质容量一定的条件下，增加负极涂布重量进而增加负极活性物质容量后，对锂离子二次电池循环寿命和存储寿命影响不大，仍旧难以满足使用需求。从实施例1-2的比较可以得知，在负极膜片表面设置金属锂层后，显著提高了锂离子二次电池的循环寿命和存储寿命。
从对比例3-4的比较可以得知，在负极活性物质容量一定的条件下，减 少正极涂布重量进而减小正极活性物质容量后，对锂离子二次电池的循环寿命和存储寿命影响不大。从实施例4-6的比较可以得知，在负极膜片表面设置金属锂层后，显著提高了锂离子二次电池的循环寿命和存储寿命。
在对比例5-7中，若公式2的比值过低，锂离子二次电池的循环性能和存储性能均较差，这是由于该比值过低，正负极活性物质容量与预嵌锂化合物LiC x可脱嵌的活性锂量不匹配，满充后负极活性物质没有足够的空位接收来自正极活性物质脱出的所有锂离子，造成负极析锂，从而导致锂离子二次电池胀气漏液，使锂离子二次电池的循环性能及存储性能变差。
下面改变扣式半电池的电解液以及隔离膜组成，观察其对实施例1的LiC x可脱嵌的活性锂量的影响。
在测试1中：
电解液制备过程为：在含水量<10ppm的氩气气氛手套箱中，将EC、PC、DMC按照重量比为EC:PC:DMC＝2:2:4进行混合后，得到混合有机溶剂，再将充分干燥的锂盐LiN(SO 2CF 3) 2溶解于上述混合有机溶剂中，搅拌均匀后，获得电解液，其中LiN(SO 2CF 3) 2的浓度为1mol/L。
隔离膜采用以厚度20μm聚丙烯多孔膜作为隔离膜。
在测试2中：
电解液制备过程为：在含水量<10ppm的氩气气氛手套箱中，将EC、PC、DMC按照重量比为EC:PC:DMC＝4:2:2进行混合后，得到混合有机溶剂，再将充分干燥的锂盐LiPF 6溶解于上述混合有机溶剂中，搅拌均匀后，获得电解液，其中LiPF 6的浓度为1mol/L。
隔离膜采用以厚度20μm聚丙烯多孔膜作为隔离膜。
在测试3中：
电解液制备过程为：在含水量<10ppm的氩气气氛手套箱中，将EC、PC、DMC按照重量比为EC:PC:DEC＝3:3:3进行混合后，得到混合有机溶剂，再将充分干燥的锂盐LiPF 6溶解于上述混合有机溶剂中，搅拌均匀后，获得电 解液，其中LiPF 6的浓度为1mol/L。
隔离膜采用以厚度20μm聚丙烯多孔膜作为隔离膜。
在测试4中：
电解液制备过程为：在含水量<10ppm的氩气气氛手套箱中，将EC、PC、DMC按照重量比为EC:PC:EMC＝3:3:3进行混合后，得到混合有机溶剂，再将充分干燥的锂盐LiPF 6溶解于上述混合有机溶剂中，搅拌均匀后，获得电解液，其中LiPF 6的浓度为0.8mol/L。
隔离膜采用以厚度20μm聚乙烯多孔膜作为隔离膜。
在测试5中：
电解液制备过程为：在含水量<10ppm的氩气气氛手套箱中，将EC、PC、DMC按照重量比为EC:PC:EMC＝2:2:4进行混合后，得到混合有机溶剂，再将充分干燥的锂盐LiPF 6溶解于上述混合有机溶剂中，搅拌均匀后，获得电解液，其中LiPF 6的浓度为1.2mol/L。
隔离膜采用以厚度20μm聚乙烯多孔膜作为隔离膜。
表3不同电解液组成对LiC x可脱嵌的活性锂量的影响
Figure PCTCN2018112959-appb-000002
从表3可以看出：电解液的组成以及隔离膜的种类的改变对单位面积正极膜片可脱嵌的活性锂量、单位面积负极膜片可脱嵌的活性锂量、单位面积 正极膜片可嵌入的活性锂量以及单位面积负极膜片中预嵌锂化合物LiC x可脱嵌的活性锂量的影响可以忽略。在本申请的测试中，组装扣式半电池时，电解液以及隔离膜的组成与全电池相同。

Claims (10)

  1. 一种锂离子二次电池，包括：电芯；电解液，浸渍电芯；以及包装壳；
    其中，电芯包括：
    负极片，包括负极集流体以及设置在负极集流体的表面且含有负极活性物质的负极膜片；
    正极片，包括正极集流体以及设置在正极集流体的表面且含有正极活性物质的正极膜片；以及
    隔离膜，间隔于相邻负极片和正极片之间；
    其特征在于，
    所述负极片为预嵌锂的负极片，负极活性物质为碳基负极材料，且所述碳基负极材料与负极片中预嵌入的锂金属锂化形成预嵌锂化合物LiC x，x＝12～150；
    单位面积负极活性物质容量/单位面积正极活性物质容量＝1.2～2.1；
    单位面积负极活性物质容量/(单位面积正极活性物质容量+单位面积负极膜片中预嵌锂化合物LiC x可脱嵌的活性锂量)≥1.10。
  2. 根据权利要求1所述的锂离子二次电池，其特征在于，单位面积负极膜片中预嵌锂化合物LiC x可脱嵌的活性锂量＝单位面积正极膜片可脱嵌的活性锂量+单位面积负极膜片可脱嵌的活性锂量-单位面积正极膜片可嵌入的活性锂量。
  3. 根据权利要求2所述的锂离子二次电池，其特征在于，
    将锂离子二次电池完全放电后拆解得到正极片、负极片，并分别裁切出单位面积的正极片和单位面积的负极片进行下述测试：
    将单位面积的正极片与单位面积的锂金属片组成扣式半电池，以不大于0.1C倍率满充，得到充电容量，即为单位面积正极膜片可脱嵌的活性锂量；之后将扣式半电池静置一段时间，再以不大于0.1C倍率满放，得到放电容量，即为单位面积正极膜片可嵌入的活性锂量；
    将单位面积的负极片与单位面积的锂金属片组成扣式半电池，以不大于 0.1C倍率满充，得到充电容量，即为单位面积负极膜片可脱嵌的活性锂量。
  4. 根据权利要求1所述的锂离子二次电池，其特征在于，所述碳基负极材料选自天然石墨、人造石墨、软碳、硬碳、中间相碳微球、纳米碳、碳纤维中的一种或几种，优选地，所述碳基负极材料选自天然石墨、人造石墨或二者的混合物。
  5. 根据权利要求1所述的锂离子二次电池，其特征在于，所述正极活性物质选自锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物、橄榄石结构的含锂磷酸盐中的一种或几种，优选地，所述正极活性物质为橄榄石结构的含锂磷酸盐。
  6. 根据权利要求1所述的锂离子二次电池，其特征在于，预嵌锂化合物LiC x中x＝12～50。
  7. 根据权利要求1所述的锂离子二次电池，其特征在于，单位面积负极活性物质容量/单位面积正极活性物质容量＝1.3～2.1。
  8. 一种锂离子二次电池的制备方法，用于制备权利要求1-7中任一项所述的锂离子二次电池，其特征在于，包括步骤：
    在正极集流体的表面涂覆正极浆料，干燥后，得到正极片；
    在负极集流体的表面涂覆负极浆料，干燥后，再在负极膜片的表面设置一层金属锂，之后与隔离膜、正极片组装成电芯；
    将电芯置于包装壳中，注入电解液并封装，金属锂在电解液作用下与负极活性物质中的碳基负极材料锂化转变为预嵌锂化合物LiC x，之后再经过预充化成，得到成品锂离子二次电池。
  9. 根据权利要求8所述的锂离子二次电池的制备方法，其特征在于，所述金属锂的重量为所述负极膜片的总重量的0.5％～5％。
  10. 根据权利要求8所述的锂离子二次电池的制备方法，其特征在于，金属锂的形式选自锂粉、锂锭、锂片中的一种或几种。
PCT/CN2018/112959 2018-02-28 2018-10-31 锂离子二次电池及其制备方法 Ceased WO2019165795A1 (zh)

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