WO2023070770A1 - 一种正极极片及包含其的锂离子二次电池 - Google Patents

一种正极极片及包含其的锂离子二次电池 Download PDF

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WO2023070770A1
WO2023070770A1 PCT/CN2021/131365 CN2021131365W WO2023070770A1 WO 2023070770 A1 WO2023070770 A1 WO 2023070770A1 CN 2021131365 W CN2021131365 W CN 2021131365W WO 2023070770 A1 WO2023070770 A1 WO 2023070770A1
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positive electrode
lithium
active material
positive
electrode active
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French (fr)
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周墨林
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Ningde Amperex Technology Ltd
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Ningde Amperex Technology Ltd
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Priority to JP2024524757A priority Critical patent/JP7852042B2/ja
Priority to CN202180010680.3A priority patent/CN115136357B/zh
Priority to EP21962114.1A priority patent/EP4425596A4/en
Publication of WO2023070770A1 publication Critical patent/WO2023070770A1/zh
Priority to US18/644,652 priority patent/US12444739B2/en
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
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    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
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    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H01M4/1315—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx containing halogen atoms, e.g. LiCoOxFy
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    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
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    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the application belongs to the field of battery technology, and relates to a positive electrode sheet and a lithium ion secondary battery containing the same.
  • a solid electrolyte interface (SEI) will be formed on the surface of the negative electrode, causing irreversible capacity loss and reducing the energy density of lithium-ion energy storage devices.
  • SEI solid electrolyte interface
  • the first cycle will consume about 10% of the active lithium source; when using high specific capacity negative electrode materials, such as alloys (silicon, tin, etc.), oxides (silicon oxide, tin oxide),
  • high specific capacity negative electrode materials such as alloys (silicon, tin, etc.), oxides (silicon oxide, tin oxide)
  • the negative electrode is made of materials such as amorphous carbon, the consumption of active lithium source will be further aggravated. Therefore, a suitable lithium supplementation method is of great significance for further improving the energy density of lithium-ion secondary batteries.
  • Patent CN1427490A proposes a method for replenishing lithium in the negative electrode, specifically mixing metal lithium powder, negative electrode material and non-aqueous liquid to form a slurry, and coating the slurry on the current collector.
  • This method can increase the energy density of the battery.
  • the control of moisture is extremely strict, which increases the difficulty of the process.
  • the FMC company in the United States has carried out certain improvements on lithium powder, and the stabilized lithium metal powder SLMP (stabledlithium metal powder) produced has better stability, but it can only exist stably in dry air for a few hours, which is safe. There are great hidden dangers. If wet operation is adopted, there will also be problems in the selection of non-aqueous solvents and the control of moisture.
  • Patent CN104037418A discloses a positive electrode lithium supplement material based on lithium oxygen compound, lithium source and alkyllithium, but the decomposition potential of the lithium-containing compound is high, and oxygen and other by-products are generated during the decomposition process, which affects the battery life.
  • Patent CN101877417A discloses Li 2 NiO 2 lithium-supplementing materials. The free lithium content on the surface of this type of material is extremely high, and it is easy to cause the slurry to form gel during the slurry mixing process, which seriously affects the processing performance, causes continuous growth of impedance, and affects circulation. performance.
  • the purpose of this application is to overcome the deficiencies of the prior art and provide a positive pole piece and a lithium-ion secondary battery containing it, aiming at making the positive pole piece stable and simple in processing, and making the lithium-ion secondary battery It has high energy density, rate performance and cycle life.
  • the present application provides a positive electrode sheet, which includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, and the positive electrode active material layer includes The first positive electrode active material and the second positive electrode lithium supplement material; the positive electrode sheet satisfies 1.5 ⁇ R ⁇ P/Q ⁇ 30, wherein, R is the resistance of the positive electrode sheet, and the unit is ⁇ ; P is the positive electrode The compacted density of the pole piece, the unit is g/cm 3 ; Q is the single surface density of the positive pole piece, the unit is g/1540.25mm 2 .
  • the first positive electrode active material is Li 1+x Mny M 2-y O 4-t At , wherein -0.1 ⁇ x ⁇ 0.2, 1 ⁇ y ⁇ 2, 0 ⁇ t ⁇ 0.5, M is at least one of Ni, Fe, Zn, Mg, Al, Ti, and Zr, and A is at least one of S, N, F, Cl, and Br.
  • the second positive electrode lithium-supplementing material is Li 1+r Mn 1-p N p O 2-s B s , where -0.1 ⁇ r ⁇ 0.2, 0 ⁇ p ⁇ 0.2, 0 ⁇ s ⁇ 0.2, N is at least one of Fe, Co, Ni, Ti, Zn, Mg, Al, V, Cr, and Zr, and B is at least one of S, N, F, Cl, and Br.
  • the positive pole piece satisfies at least one of the following characteristics:
  • the weight content of the first positive electrode active material in the positive electrode active material is 80%-98%. More preferably, the weight content of the first positive electrode active material in the positive electrode active material is 85%-98%.
  • the present application provides a lithium ion secondary battery, which includes the positive pole piece, the negative pole piece, a separator and an electrolyte.
  • the electrolyte solution contains the following components in weight percentage: 0.001% to 5% of vinylene carbonate, and/or 0.001% to 5% of 1,3-propane sultone.
  • the beneficial effects of the present application are: the free lithium content on the surface of the second positive electrode lithium-replenishing material in the positive electrode sheet of the present application is very low, the slurry has good stability, and the processability is excellent. Moreover, under the synergistic effect of the first positive electrode active material and the second positive electrode lithium-replenishing material, the positive electrode plate is limited to satisfy 1.5 ⁇ R ⁇ P/Q ⁇ 30, so that the obtained lithium-ion secondary battery has higher energy density and rate performance and cycle life.
  • Fig. 1 is the XRD pattern of the second positive electrode lithium-replenishing material in Example 1 before and after the first cycle of charging, where Fig. b is a partial enlarged view of Fig. a.
  • FIG. 2 is the first-cycle charge-discharge curve of the second positive electrode lithium-supplementing material in Example 1.
  • the positive electrode sheet of the present application includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector.
  • the positive electrode current collector includes two opposite surfaces in its thickness direction, and the positive electrode active material layer is disposed on any one or both of these two surfaces.
  • the positive electrode active material layer includes the first positive electrode active material and the second positive electrode lithium supplement material; the positive electrode sheet satisfies 1.5 ⁇ R ⁇ P/Q ⁇ 30, where R is the resistance of the positive electrode sheet, in units of is ⁇ ; P is the compacted density of the positive pole piece, the unit is g/cm 3 ; Q is the single surface density of the positive pole piece, the unit is g/1540.25mm 2 .
  • the first positive electrode active material is Li 1+x Mny M 2-y O 4-t At , wherein -0.1 ⁇ x ⁇ 0.2, 1 ⁇ y ⁇ 2, 0 ⁇ t ⁇ 0.5, M is Ni, Fe, At least one of Zn, Mg, Al, Ti, Zr, A is at least one of S, N, F, Cl, Br.
  • the second positive electrode lithium supplement material is Li 1+r Mn 1-p N p O 2-s B s , where -0.1 ⁇ r ⁇ 0.2, 0 ⁇ p ⁇ 0.2, 0 ⁇ s ⁇ 0.2, N is Fe, Co , Ni, Ti, Zn, Mg, Al, V, Cr, Zr at least one, B is at least one of S, N, F, Cl, Br.
  • the positive electrode sheet of this application adopts the first positive electrode active material and the second positive electrode lithium replenishing material with a specific composition, wherein the first positive electrode active material has a stable structure, good cycle stability and high first-time Coulombic efficiency; the second positive electrode The free lithium content on the surface of the lithium supplement material is low, and the processing performance is excellent.
  • the second positive electrode lithium supplement material has a higher initial charge specific capacity and a lower initial discharge specific capacity, that is, the first Coulombic efficiency is low, When charging for the first time, the second positive electrode lithium supplement material can release a large amount of lithium ions to make up for the loss of active lithium caused by the formation of SEI.
  • the combination of the first positive electrode active material and the second positive electrode lithium supplement material used in this application can more significantly Improve the energy density, rate performance and cycle life of lithium-ion secondary batteries.
  • this application specifically designs the resistance R, compaction density P, and single-sided surface density Q of the positive electrode sheet, which can further improve the energy density, rate performance, and cycle life of lithium-ion secondary batteries to achieve high energy density. , the organic unity of good rate performance and long cycle life.
  • the second positive electrode lithium replenishing material in this application must satisfy 1-p>0.8 (that is, 0 ⁇ p ⁇ 0.2).
  • the second positive electrode lithium replenishing material in this application has two The phase structures belong to the Pmmn and C2/m space groups respectively.
  • the Pmmn space group corresponds to the characteristic diffraction peak A appearing at 15° to 16° in the ray diffraction spectrum
  • the C2/m space group corresponds to the 18° to 16° in the ray diffraction spectrum.
  • the positive pole piece should satisfy 1.5 ⁇ R ⁇ P/Q ⁇ 30, so as to ensure that the lithium-ion secondary battery has high energy density, rate performance and cycle life.
  • R ⁇ P/Q is a value among 1.5, 3, 6, 9, 12, 15, 18, 21, 24, 27, 30 and the like.
  • R P/Q satisfies 3.0 ⁇ R P/Q ⁇ 15, so that the resulting lithium-ion secondary battery has longer cycle life and rate performance, such as R P/Q is One of 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, etc.
  • the calculation of R ⁇ P/Q only involves the calculation of numerical values.
  • the resistance R of the positive pole piece is 1.0 ⁇
  • the compacted density P is 3.0g/cm 3
  • the single surface density of the positive pole piece is Q is 0.35g/1540.25mm 2
  • R ⁇ P/Q 8.57.
  • the resistance R of the positive pole piece is the resistance value measured by the DC two-probe method, wherein the contact area between the probes and the positive pole piece is 49 ⁇ mm 2 .
  • the resistance R of the positive pole piece was tested by using the Rizhi BT23562 internal resistance tester. The specific operation is: clamp the upper and lower sides of the positive pole piece between the two conductive terminals of the tester, and apply The pressure is fixed, the diameter of the conductive segment is 14mm, and the applied pressure is 15MPa-27MPa, that is, the resistance R of the positive pole piece is measured.
  • the sheet resistance R, compaction density P, and single-sided surface density Q of the positive electrode sheet are key parameters in the design and manufacture of lithium-ion secondary batteries. If the sheet resistance R of the positive electrode sheet is too large, the cycle performance and rate performance of the lithium-ion secondary battery will be deteriorated. If the compacted density P is too large or too small, the cycle performance and rate performance of the lithium-ion secondary battery will deteriorate.
  • the cycle life of the lithium-ion secondary battery will be reduced, and it will also affect the penetration of the electrolyte, thereby affecting the rate performance of the battery, especially reducing the discharge capacity of the battery at high rates; and
  • the single surface density Q of the positive electrode sheet is too small, which means that under the same battery capacity, the length of the current collector and separator increases, which increases the ohmic internal resistance of the battery. This requires that these parameters can be comprehensively designed in the production of the battery to ensure that the positive electrode sheet reaches the expected design value, so that the electrochemical performance of the lithium-ion secondary battery can achieve the expected result.
  • the sheet resistance R of the positive pole piece is preferably R ⁇ 5 ⁇ , so as to improve the cycle performance and rate performance of the lithium-ion secondary battery.
  • the sheet resistance R of the positive pole piece is more preferably R ⁇ 2 ⁇ , so as to further improve the cycle performance and rate performance of the lithium-ion secondary battery.
  • the compacted density P of the positive electrode sheet is preferably 2.5g/cm 3 ⁇ P ⁇ 3.2g/cm 3 , which is conducive to the migration of electrons and ions in the positive electrode sheet, thereby improving the cycle performance of the lithium-ion secondary battery.
  • the single surface density Q of the positive electrode sheet is preferably 0.3g/1540.25mm 2 ⁇ Q ⁇ 0.55g/1540.25mm 2 , which can improve the cycle performance and rate performance of the lithium-ion secondary battery on the premise of ensuring the charge and discharge capacity.
  • the weight ratio of the first positive electrode active material to the second positive electrode lithium-replenishing material is preferably 5:1 to 99:1. Most of this positive electrode sheet is the first positive electrode active material, which has higher structural stability and can be used Reduce the capacity loss and impedance increase caused by the structural damage of the positive electrode active material, and maintain cycle stability and kinetic performance.
  • the weight ratio of the first positive electrode active material to the second positive electrode lithium-supplementing material is more preferably 9:1 ⁇ 99:1, so as to further improve cycle stability and kinetic performance.
  • the weight content of the first positive electrode active material in the positive electrode active material is 80%-98%, more preferably 85%-98%.
  • the positive electrode active material layer may further include a conductive agent and a binder.
  • the present application does not specifically limit the types of the conductive agent and the binder, which can be selected according to actual needs.
  • the conductive agent can be at least one of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, carbon nanofibers, etc.
  • the binder can be styrene-butadiene Rubber (SBR), water-based acrylic resin (waterbased acrylic resin), carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), At least one of ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA), and the like.
  • SBR styrene-butadiene Rubber
  • water-based acrylic resin waterbased acrylic resin
  • CMC carboxymethyl cellulose
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PVB polyvinyl butyral
  • EVA ethylene-vinyl a
  • the weight percentage of the conductive agent in the positive electrode active material layer is greater than or equal to 0.5%, so as to obtain a lower positive electrode sheet resistance.
  • the weight percentage of the binder in the positive electrode active material layer is ⁇ 2.0%, so as to obtain a lower positive electrode sheet resistance.
  • the positive current collector can be a metal foil or a porous metal plate, such as aluminum, copper, nickel, titanium, silver and other metals or their alloys, such as aluminum foil.
  • the thickness of the positive electrode current collector is preferably 5 ⁇ m to 20 ⁇ m, more preferably 6 ⁇ m to 18 ⁇ m, and more preferably 8 ⁇ m to 16 ⁇ m.
  • Lithium-ion secondary battery Lithium-ion secondary battery
  • the positive electrode sheet of the present application can be used as the positive electrode of a lithium ion secondary battery.
  • the lithium-ion secondary battery includes a positive pole piece, a negative pole piece, a separator and an electrolyte, wherein the positive pole piece adopts the positive pole piece of this application. Due to the use of the positive electrode sheet of the present application, the lithium ion secondary battery of the present application has high energy density, cycle performance and rate performance at the same time.
  • the negative electrode sheet may be a metal lithium sheet, or may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector.
  • the negative active material layer generally includes a negative active material, a conductive agent, a binder, and a thickener.
  • the negative electrode active material can be natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy , Sn, SnO, SnO 2 , lithium titanate Li 4 Ti 5 O 12 with spinel structure, Li-Al alloy, lithium metal, etc.
  • the conductive agent can be graphite, superconducting carbon, acetylene black, At least one of carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, carbon nanofibers, etc.
  • the binder can be styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene At least one of vinyl fluoride (PTFE), polyvinyl butyral (P
  • the negative electrode current collector can use materials such as metal foil or porous metal plate, such as foil or porous plate formed of metals such as copper, nickel, titanium, iron or their alloys, such as copper foil.
  • the negative electrode sheet can be prepared according to conventional methods in the art. Usually negative electrode active material and optional conductive agent, binding agent and thickener are dispersed in solvent to form uniform negative electrode slurry, solvent can be N-methylpyrrolidone (NMP) or deionized water, negative electrode slurry Coated on the negative electrode current collector, after drying, cold pressing and other processes to obtain the negative electrode sheet.
  • solvent can be N-methylpyrrolidone (NMP) or deionized water
  • any known porous structure separator with electrochemical stability and chemical stability can be selected, such as glass fiber, non-woven fabric, polyethylene (PE), polypropylene (PP), polylidene Monolayer or multilayer films of at least one of vinyl fluoride (PVDF).
  • the above electrolytic solution includes an organic solvent, an electrolyte lithium salt and additives. This application does not specifically limit the types of organic solvents and electrolyte lithium salts, which can be selected according to actual needs.
  • the above electrolyte lithium salt can be LiPF 6 (lithium hexafluorophosphate), LiBF 4 (lithium tetrafluoroborate), LiClO 4 (lithium perchlorate), LiAsF 6 (lithium hexafluoroarsenate), LiFSI (lithium difluorosulfonimide) , LiTFSI (lithium bistrifluoromethanesulfonyl imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium difluorooxalate borate), LiPO 2 F 2 (lithium difluorophosphate ), LiDFOP (lithium difluorooxalate phosphate), LiTFOP (lithium tetrafluorooxalate phosphate), and the like.
  • LiPF 6 lithium hexafluorophosphate
  • LiBF 4 lithium tetrafluoroborate
  • the above electrolyte additive includes vinylene carbonate (VC), based on the total weight of the electrolyte, the weight content of the vinylene carbonate is 0-5% and not 0.
  • VC vinylene carbonate
  • the above electrolyte additive includes 1,3-propane sultone (PS), based on the total weight of the electrolyte, the weight content of the 1,3-propane sultone is 0-5% and not 0.
  • PS 1,3-propane sultone
  • the electrolyte solution may also optionally include other additives, which may be any additives that can be used as lithium-ion secondary batteries.
  • additives may also include ethylene carbonate (VEC), succinonitrile (SN), adiponitrile (AND), 1,3-propene sultone (PST), sulfonate cyclic quaternary ammonium At least one of salt, tris(trimethylsilane) phosphate (TMSP), and tris(trimethylsilane) borate (TMSB).
  • the above-mentioned electrolyte solution can be prepared according to conventional methods in the art.
  • the electrolyte solution can be obtained by uniformly mixing organic solvent, electrolyte lithium salt, vinylene carbonate, 1,3-propane sultone and other optional additives, and the order of adding each material is not particularly limited.
  • electrolyte lithium salt, vinylene carbonate, 1,3-propane sultone and other optional additives are added into an organic solvent and mixed evenly to obtain an electrolyte solution.
  • the electrolyte lithium salt can be added into the organic solvent first, and then the vinylene carbonate, 1,3-propane sultone and other optional additives can be added into the organic solvent separately or simultaneously.
  • Charge-discharge curve test At 45°C, charge the lithium-ion secondary battery at a constant current rate of 0.1C to 4.3V, then charge it at a constant voltage until the current is less than or equal to 0.025C, and then discharge it at a constant current rate of 0.1C to 3.0V. Record the charge and discharge curve of the lithium-ion secondary battery.
  • High-temperature cycle performance test At 45°C, charge the lithium-ion secondary battery with a constant current rate of 1.5C to 4.3V, then charge it with a constant voltage until the current is less than or equal to 0.05C, and then discharge it with a constant current rate of 1C to 3.0V.
  • a charge-discharge cycle record the discharge capacity of the lithium-ion secondary battery for the first cycle.
  • the lithium ion secondary battery is charged and discharged according to the above method, and the discharge capacity of each cycle is recorded until the discharge capacity of the lithium ion secondary battery decays to 80% of the discharge capacity of the first cycle, and the number of charge and discharge cycles is recorded.
  • Preparation of positive electrode sheet mix the first positive electrode active material LiMn 2 O 4 , the second positive electrode lithium supplement material LiMnO 2 , binder PVDF and conductive carbon black, wherein LiMn 2 O 4 , LiMnO 2 , PVDF and conductive carbon
  • the weight ratio of black is 92.5:4.0:1.5:2.0
  • the solvent NMP is added according to the material-to-liquid ratio of 7:3, and stirred under vacuum stirring until a uniform transparent system is obtained to obtain the positive electrode slurry; the positive electrode slurry is evenly coated on On the aluminum foil of the positive electrode current collector, transfer it to an oven for drying, the drying temperature is 120°C, and then cold press and cut to obtain the positive electrode sheet.
  • the weight percentage of the first positive electrode active material LiMn 2 O 4 in the positive electrode active material layer The content is 92.5%, and the weight percent content of the second positive electrode lithium-supplementing material LiMnO 2 in the positive electrode active material layer is 4.0%.
  • the negative active material artificial graphite, thickener sodium carboxymethylcellulose (CMC), binder (SBR) and conductive carbon black are mixed according to the mass ratio of 95.7:1.0:1.8:1.5, according to The ratio of solid to liquid is 4:6, add solvent deionized water, and obtain the negative electrode slurry under the action of vacuum mixer; evenly coat the negative electrode slurry on the copper foil of the negative electrode current collector; then transfer to the oven for drying, and the drying temperature is 120°C , and then cold-pressed and cut to obtain the negative electrode sheet.
  • electrolyte Preparation of electrolyte: mix ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) according to the volume ratio of 1:1:1 to obtain an organic solvent; dissolve LiPF 6 in the above In an organic solvent, so that the concentration of LiPF 6 is 1mol/L; based on the total mass of the electrolyte, 3% by weight of vinylene carbonate and 3% by weight of 1,3-propane sultone are added, and mixed uniformly to obtain electrolyte.
  • EC ethylene carbonate
  • EMC ethyl methyl carbonate
  • DEC diethyl carbonate
  • the positive electrode sheet, the separator and the negative electrode sheet are laminated once, and the separator adopts a polypropylene (PP) film (provided by Celgard Company) with a thickness of 14 ⁇ m, which is placed between the positive electrode sheet and the negative electrode sheet.
  • PP polypropylene
  • the sheets play an isolation role, and then wound into an electrode assembly, welded the tabs, put the electrode assembly into the casing, injected electrolyte and sealed, and then passed through the processes of standing, forming, and shaping to obtain a lithium-ion secondary battery .
  • Example 1 The difference from Example 1 is that the material components in the positive electrode and the relevant parameters in the preparation steps are adjusted, see Table 1 for details (in this table, the weight percentage of the first positive electrode active material refers to the first positive electrode active material in the positive electrode active material. - the weight percentage of the positive electrode active material, the weight percentage of the second positive electrode lithium supplement material refers to the weight percentage of the second positive electrode lithium supplement material in the positive electrode active material).
  • Example 1 The difference from Example 1 is that the weight ratios of the first positive electrode active material and the second positive electrode lithium-supplementing material in the positive electrode are different.
  • Example 1 The difference from Example 1 is that the sheet resistance, compaction density and density of one side of the positive electrode sheet are different.
  • Example 2 The difference from Example 1 is that the weight percentages of vinylene carbonate and 1,3-propane sultone in the electrolyte are different.
  • Example 26 The difference from Example 26 is that only vinylene carbonate or 1,3-propane sultone is contained in the electrolyte.
  • the content of conductive carbon black and binder PVDF in the positive electrode active material in Example 18 is respectively 0.5wt%
  • the content of conductive carbon black in the positive electrode active material in other embodiments and comparative examples is 2.0wt%.
  • the binder PVDF content is 1.5wt%.
  • Example 26 7.2 673 97.8
  • Example 27 7.2 681 97.7
  • the joint use of the first positive electrode active material and the second positive electrode lithium supplementing material in the present application produces a synergistic effect.
  • the free lithium content on the surface of the second positive electrode lithium supplement material used in this application is small, and when it is added to the positive electrode, the resulting slurry has good stability and excellent processability; in the second aspect, the second positive electrode lithium supplement material used in this application is the first
  • the high charging specific capacity and low initial Coulombic efficiency can better compensate for the loss of active lithium caused by the formation of SEI. During discharge, more lithium ions are back-intercalated into the lattice of the first positive electrode active material, effectively improving the lithium ion secondary.
  • the lithium supplement strategy of the vinylene carbonate added in the electrolyte and the first positive electrode active material and the second lithium supplement active material can play a synergistic effect. Lithium intercalation into the negative electrode leads to a further decrease in the real potential of the negative electrode, resulting in continuous reduction of the solvent in the electrolyte and affecting cycle performance.
  • the vinylene carbonate additive within the scope of this application can induce the formation of a denser and thinner SEI layer, preventing the The continuous consumption of the electrolyte, in addition, the 1,3-propane sultone additive is added to the electrolyte, which can form an interface protective layer on the surface of the positive electrode active material, further improving the cycle performance.

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Abstract

本申请公开了一种正极极片及包含其的锂离子二次电池。本申请正极极片包括正极集流体以及设置于该正极集流体的至少一个表面上的正极活性材料层，正极活性材料层包括第一正极活性材料Li 1+xMn yM 2-yO 4-tA t和第二正极补锂材料Li 1+rMn 1-pN pO 2-sB s，正极极片满足1.5≤R·P/Q≤30，其中，R是所述正极极片的电阻，单位为Ω；P是所述正极极片的压实密度，单位为g/cm 3；Q是所述正极极片的单面面密度，单位为g/1540.25mm 2。本申请正极极片中第二正极补锂材料的表面游离锂含量非常低，加工性能优良。由本申请的正极极片所制作的锂离子二次电池具有较高的能量密度、倍率性能和循环寿命。

Description

一种正极极片及包含其的锂离子二次电池 技术领域
本申请属于电池技术领域，涉及一种正极极片及包含其的锂离子二次电池。
背景技术
锂离子二次电池在首次充放电过程中，负极表面会形成固态电解质界面(SEI)，造成不可逆容量损失，降低锂离子储能器件的能量密度。在使用石墨负极的器件中，首次循环会消耗大约10％的活性锂源；当采用高比容量的负极材料，如合金类(硅、锡等)、氧化物类(氧化硅、氧化锡)、无定形碳等材料的负极时，活性锂源的消耗将进一步加剧。因此，合适的补锂方法对进一步提升锂离子二次电池的能量密度具有重要的意义。
专利CN1427490A提出了一种负极补锂的方法，具体为将金属锂粉、负极材料和非水液体混合形成浆料，将浆料涂布到集流体上，这种方法能提高电池的能量密度，在生产过程中对水分的控制极为严苛，增大了工艺难度。美国的FMC公司对锂粉进行了一定的改进处理，生产的稳定化金属锂粉SLMP(stabledlithium metal powder)具有更好的稳定性，但其在干燥空气中也仅能稳定存在几个小时，安全隐患很大，若采用湿法操作，同样存在非水溶剂的选择和对水分的控制问题。
鉴于负极补锂策略面临着巨大的挑战，相对更加安全和便于操作的正极补锂方法得到了产业界越来越多的关注。专利CN104037418A公开了一种基于锂氧化合物、锂源和烷基锂的正极补锂材料，但其中含锂化合物的分解电位较高，且分解过程中产生氧气和其它副产物，影响电池寿命。专利CN101877417A公开了Li 2NiO 2类补锂材料，这类材料的表面游离锂含量极高，在调浆过程极易造成浆料形成凝胶，严重影响加工性能，造成阻抗的持续增长，影响循环性能。
发明内容
本申请的目的在于克服现有技术的不足之处而提供一种正极极片及包含其的锂离子二次电池，旨在使正极极片稳定，加工方法简单的同时，使锂离子二次电池具有较高的能量密度、倍率性能和循环寿命。
为实现上述目的，第一方面，本申请提供了一种正极极片，其包括正极集流体以及设置于所述正极集流体的至少一个表面上的正极活性材料层，所述正极活性材料层包括第一正极活性材料和第二正极补锂材料；所述正极极片满足1.5≤R·P/Q≤30，其中，R是所述正极极片的电阻，单位为Ω；P是所述正极极片的压实密度，单位为g/cm 3；Q是所述正极极片的单面面密度，单位为g/1540.25mm 2。
优选地，所述第一正极活性材料为Li 1+xMn yM 2-yO 4-tA t，其中，-0.1<x<0.2，1<y≤2，0≤t<0.5，M为Ni、Fe、Zn、Mg、Al、Ti、Zr中的至少一种，A是S、N、F、Cl、Br中的至少一种。
优选地，所述第二正极补锂材料为Li 1+rMn 1-pN pO 2-sB s，其中，-0.1<r<0.2，0≤p<0.2，0≤s<0.2，N是Fe、Co、Ni、Ti、Zn、Mg、Al、V、Cr、Zr中的至少一种，B是S、N、F、Cl、Br中的至少一种。
优选地，所述正极极片满足如下特征中的至少一种：
(a)所述正极极片满足3.0≤R·P/Q≤15；
(b)所述R≤5Ω，优选所述R≤2Ω；
(c)所述P满足2.5g/cm 3<P<3.2g/cm 3；
(d)所述Q满足0.3g/1540.25mm 2<Q<0.55g/1540.25mm 2。
优选地，所述第一正极活性材料和所述第二正极补锂材料的重量比为第一正极活性材料：第二正极补锂材料＝5:1～99:1。更优选地，所述第一正极活性材料和所述第二正极补锂材料的重量比为第一正极活性材料：第二正极补锂材料＝9:1～99:1。
优选地，所述正极活性材料中所述第一正极活性材料的重量含量为80％～98％。更优选地，所述正极活性材料中所述第一正极活性材料的重量含量为85％～98％。
第二方面，本申请提供了一种锂离子二次电池，其包括所述正极极片、负极极片、隔离膜和电解液。
优选地，所述电解液包含以下重量百分含量的组分：碳酸亚乙烯酯0.001％至5％，和/或1,3-丙烷磺酸内酯0.001％至5％。
与现有技术相比，本申请的有益效果为：本申请正极极片中第二正极补锂材料的表面游离锂含量非常低，浆料稳定性好，加工性能优良。而且在第一正极活性材料和第二正极补锂材料协同作用下，并限定正极极片满足1.5≤R·P/Q≤30，使所得锂离子二次电池具有较高的能量密度、倍率性能和循环寿命。
附图说明
图1为实施例1中的第二正极补锂材料在首圈充电前后的XRD图谱，其中图b为图a的局部放大图。
图2为实施例1中的第二正极补锂材料的首圈充放电曲线。
具体实施方式
为更好地说明本申请的目的、技术方案和优点，下面将结合具体实施例对本申请进一步说明。本领域技术人员应当理解，此处所描述的具体实施例仅用以解释本申请，并不用于限定本申请。
实施例中，所使用的实验方法如无特殊说明，均为常规方法，所用的材料、试剂等，如无特殊说明，均可从商业途径得到。
正极极片：
本申请正极极片包括正极集流体以及设置于该正极集流体的至少一个表面上的正极活性材料层。作为一个示例，正极集流体在自身厚度方向上包括相对的两个表面，正极活性材料层设置于这两个表面中的任意一者或两者上。
本申请正极极片中，正极活性材料层包括第一正极活性材料和第二正极补锂材料；正极极片满足1.5≤R·P/Q≤30，其中，R是正极极片的电阻，单位为Ω； P是正极极片的压实密度，单位为g/cm 3；Q是正极极片的单面面密度，单位为g/1540.25mm 2。
第一正极活性材料为Li 1+xMn yM 2-yO 4-tA t，其中，-0.1<x<0.2，1<y≤2，0≤t<0.5，M为Ni、Fe、Zn、Mg、Al、Ti、Zr中的至少一种，A是S、N、F、Cl、Br中的至少一种。
第二正极补锂材料为Li 1+rMn 1-pN pO 2-sB s，其中，-0.1<r<0.2，0≤p<0.2，0≤s<0.2，N是Fe、Co、Ni、Ti、Zn、Mg、Al、V、Cr、Zr中的至少一种，B是S、N、F、Cl、Br中的至少一种。
本申请正极极片采用特定组成的第一正极活性材料和第二正极补锂材料，其中，第一正极活性材料结构稳定，具有较好的循环稳定性和较高的首次库仑效率；第二正极补锂材料表面游离锂含量低，加工性能优良，相比第一正极活性材料，第二正极补锂材料具有较高的首次充电比容量和较低的首次放电比容量，即首次库仑效率低，首次充电时第二正极补锂材料可脱出大量的锂离子以弥补生成SEI造成的活性锂损失，首次放电时有足够的锂离子回嵌至第一正极活性材料中以提升电池的能量密度，在第一正极活性材料和第二正极补锂材料的协同作用下，锂离子二次电池的能量密度、倍率性能和循环寿命得到有效提升。相比我们之前申请的专利CN110265627A中的第一正极活性物质和第二正极活性物质的组合而言，本申请所采用的第一正极活性材料和第二正极补锂材料的组合，能更加显著地提升锂离子二次电池的能量密度、倍率性能和循环寿命。同时，本申请对正极极片的电阻R、压实密度P和单面面密度Q进行特定的设计，能够更进一步提升锂离子二次电池的能量密度、倍率性能和循环寿命，实现高能量密度、良好的倍率性能和长循环寿命的有机统一。
为实现补锂的功能，本申请中的第二正极补锂材料要满足1-p>0.8(即0≤p<0.2)，具体来说，本申请中的第二正极补锂材料具有两种相结构，分别归属于Pmmn和C2/m空间群，Pmmn空间群对应其射线衍射谱中15°至16°处出现的特征衍射峰A，C2/m空间群对应其射线衍射谱中18°至19°处出现的特征衍射峰B，特征衍射峰A的强度I A和特征衍射峰B的强度I B的比值I A/I B满足0<I A/I B≤0.2。在首圈充电后，特征衍射峰A和特征衍射峰B均向低角度方向偏 移，偏移幅度均<0.5°。
本申请中，正极极片要满足1.5≤R·P/Q≤30，以确保锂离子二次电池具有较高的能量密度、倍率性能和循环寿命。在本申请某些实施方案中，R·P/Q为1.5、3、6、9、12、15、18、21、24、27、30等中的一种数值。在本申请一些优选实施方案中，R·P/Q满足3.0≤R·P/Q≤15，以使所得锂离子二次电池具有更长的循环寿命和倍率性能，如R·P/Q为3、4、5、6、7、8、9、10、11、12、13、14、15等中的一种数值。
在本文中，R·P/Q的计算仅涉及数值的计算，举例来说，正极极片的电阻R为1.0Ω，压实密度P为3.0g/cm 3，正极极片的单面面密度Q为0.35g/1540.25mm 2，则R·P/Q＝8.57。
正极极片的电阻R为采用直流两探针法所测得的电阻值，其中探针与正极极片的接触面积为49πmm 2。本申请在研究过程中，采用日置BT23562型内阻测试仪测试正极极片的电阻R，具体操作为：将正极极片的上下侧夹持于该测试仪的两个导电端子之间，并施加压力以固定，导电段子的直径为14mm，施加压力为15MPa～27MPa，即测得正极极片的电阻R。
正极极片的压实密度P可以通过公式P＝m/v计算得出，式中m是正极活性材料层的重量，单位为g；v是正极活性材料层的体积，单位为cm 3。其中正极活性材料层的体积v可以是正极活性材料层的面积A r与正极活性材料层的厚度之积。
正极极片的单面面密度Q可以通过公式Q＝1540.25m/A r计算得出，式中m是正极活性材料层的重量，单位为g；A r是正极活性材料层的面积，单位为mm 2。
需要指出的是，正极极片的膜片电阻R、压实密度P和单面面密度Q是锂离子二次电池设计和制作中的关键参数。正极极片的膜片电阻R过大，会恶化锂离子二次电池的循环性能和倍率性能。压实密度P过大或过小，都会使锂离子二次电池的循环性能和倍率性能变差。正极极片的单面面密度Q过大，锂离子二次电池的循环寿命降低，还会影响电解液的渗透，进而影响电池的倍率性能，特别是使得电池高倍率下的放电容量降低；而正极极片的单面面密度Q过 小，意味着相同电池容量下，集流体和隔膜的长度增加，增大了电池的欧姆内阻。这就要求在电池的制作中对这些参数能够进行综合设计，保证正极极片达到预期的设计值，以使锂离子二次电池的电化学性能达到预期的结果。
正极极片的膜片电阻R优选为R≤5Ω，以利于提升锂离子二次电池的循环性能和倍率性能。正极极片的膜片电阻R更优选为R≤2Ω，以进一步提升锂离子二次电池的循环性能和倍率性能。
正极极片的压实密度P优选为2.5g/cm 3<P<3.2g/cm 3，有利于正极极片中电子和离子的迁移，从而提高锂离子二次电池的循环性能。
正极极片的单面面密度Q优选为0.3g/1540.25mm 2<Q<0.55g/1540.25mm 2，能够在保证充放电容量的前提下，提高锂离子二次电池的循环性能和倍率性能。
第一正极活性材料和第二正极补锂材料的重量比优选为5:1～99:1，这种正极极片中绝大部分是第一正极活性材料，具有更高的结构稳定性，可减少正极活性材料结构破坏所造成的容量损失和阻抗增加，保持循环稳定性和动力学性能。第一正极活性材料和第二正极补锂材料的重量比更优选为9:1～99:1，以进一步提高循环稳定性和动力学性能。
正极活性材料中第一正极活性材料的重量含量为80％～98％，更优选为85％～98％。
本申请实施例的正极极片，正极活性材料层中还可以包括导电剂和粘结剂。本申请对导电剂及粘结剂的种类不做具体限制，可以根据实际需求进行选择。
作为示例，导电剂可以是石墨、超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯、碳纳米纤维等中的至少一种；粘结剂可以是丁苯橡胶(SBR)、水性丙烯酸树脂(waterbased acrylic resin)、羧甲基纤维素(CMC)、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、聚乙烯醇缩丁醛(PVB)、乙烯-醋酸乙烯酯共聚物(EVA)、聚乙烯醇(PVA)等中的至少一种。
在一些可选的实施方式中，导电剂在正极活性材料层中的重量百分含量≥0.5％，以利于获得较低的正极膜片电阻。
在一些可选的实施方式中，粘结剂在正极活性材料层中的重量百分含量≤2.0％，以利于获得较低的正极膜片电阻。
正极集流体可以采用金属箔材或多孔金属板，例如使用铝、铜、镍、钛、银等金属或它们的合金形成的箔材或多孔板，如铝箔。
正极集流体的厚度优选为5μm～20μm，进一步优选为6μm～18μm，更优选为8μm～16μm。
锂离子二次电池：
本申请正极极片能用作锂离子二次电池的正极。锂离子二次电池包括正极极片、负极极片、隔离膜和电解液，其中正极极片采用本申请正极极片。由于使用了本申请正极极片，使得本申请锂离子二次电池同时具有较高的能量密度、循环性能和倍率性能。
负极极片可以是金属锂片，也可以是包括负极集流体及设置于负极集流体至少一个表面上的负极活性材料层。
负极活性材料层通常包括负极活性材料、导电剂、粘结剂和增稠剂。作为示例，负极活性材料可以是天然石墨、人造石墨、中间相微碳球(MCMB)、硬碳、软碳、硅、硅-碳复合物、SiO、Li-Sn合金、Li-Sn-O合金、Sn、SnO、SnO 2、尖晶石结构的钛酸锂Li 4Ti 5O 12、Li-Al合金、金属锂等中的至少一种；导电剂可以是石墨、超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯、碳纳米纤维等中的至少一种；粘结剂可以是丁苯橡胶(SBR)、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、聚乙烯醇缩丁醛(PVB)、水性丙烯酸树脂(water-basedacrylic resin)、羧甲基纤维素(CMC)等中的至少一种；增稠剂可以是羧甲基纤维素(CMC)等。但本申请并不限定于这些材料，本申请还可以使用可被用作锂离子二次电池负极活性材料、导电剂、粘结剂和增稠剂的其它材料。
负极集流体可以使用金属箔材或多孔金属板等材料，例如使用铜、镍、钛、铁等金属或它们的合金形成的箔材或多孔板，如铜箔。
负极极片可以按照本领域常规方法制备。通常将负极活性材料及可选的导 电剂、粘结剂和增稠剂分散于溶剂中形成均匀的负极浆料，溶剂可以是N-甲基吡咯烷酮(NMP)或去离子水，将负极浆料涂覆在负极集流体上，经烘干、冷压等工序得到负极极片。
对上述隔离膜没有限制，可以选用任意公知的具有电化学稳定性和化学稳定性的多孔结构隔离膜，例如玻璃纤维、无纺布、聚乙烯(PE)、聚丙烯(PP)、聚偏二氟乙烯(PVDF)中至少一种的单层或多层薄膜。
上述电解液包括有机溶剂、电解质锂盐和添加剂。本申请对有机溶剂和电解质锂盐的种类不做具体限制，可以根据实际需求进行选择。
作为示例，上述有机溶剂可以为碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸丁烯酯(BC)、氟代碳酸乙烯酯(FEC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1、4-丁内酯(GBL)、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)、二乙砜(ESE)等中的至少一种，优选为两种以上。
上述电解质锂盐可以为LiPF 6(六氟磷酸锂)、LiBF 4(四氟硼酸锂)、LiClO 4(高氯酸锂)、LiAsF 6(六氟砷酸锂)、LiFSI(双氟磺酰亚胺锂)、LiTFSI(双三氟甲磺酰亚胺锂)、LiTFS(三氟甲磺酸锂)、LiDFOB(二氟草酸硼酸锂)、LiBOB(二草酸硼酸锂)、LiPO 2F 2(二氟磷酸锂)、LiDFOP(二氟二草酸磷酸锂)、LiTFOP(四氟草酸磷酸锂)等中的至少一种。
上述电解液添加剂包含碳酸亚乙烯酯(VC)，基于电解液的总重量，所述碳酸亚乙烯酯的重量含量为0-5％且不为0。通过在电解液中添加碳酸亚乙烯酯添加剂，使得负极形成了更加均匀致密的SEI膜，抑制了活性锂的持续损失。
上述电解液添加剂包含1,3-丙烷磺酸内酯(PS)，基于电解液的总重量，所述1,3-丙烷磺酸内酯的重量含量为0-5％且不为0。通过在电解液中添加1,3-丙烷磺酸内酯，在正极侧形成了一层界面保护层，可更进一步提升锂离子二次电池的循环寿命。
上述电解液中还可选地包括其它添加剂，其可以是任意可被用作锂离子二次电池的添加剂，本申请不做具体限制、可以根据实际需求进行选择。作为示例，添加剂还可以包括碳酸乙烯亚乙酯(VEC)、丁二腈(SN)、己二腈(AND)、1、3-丙烯磺酸内酯(PST)、磺酸酯环状季铵盐、三(三甲基硅烷)磷酸酯(TMSP)、三(三甲基硅烷)硼酸酯(TMSB)中的至少一种。
上述电解液可以按照本领域常规的方法制备。可以是将有机溶剂、电解质锂盐、碳酸亚乙烯酯，1,3-丙烷磺酸内酯及其它可选的添加剂混合均匀，得到电解液，其中各物料的添加顺序并没有特别的限制。例如，将电解质锂盐、碳酸亚乙烯酯、1,3-丙烷磺酸内酯及其它可选的添加剂加入到有机溶剂中混合均匀，得到电解液。其中可以是先将电解质锂盐加入有机溶剂中，然后再将碳酸亚乙烯酯、1,3-丙烷磺酸内酯和其它可选的添加剂分别或同时加入有机溶剂中。
将上述正极极片、隔离膜及负极极片按顺序堆叠好，使隔离膜处于正极极片与负极极片之间起到隔离的作用，得到电芯，也可以是经卷绕后得到电芯；将电芯置于包装外壳中，注入电解液并封口，得到锂离子二次电池。
本申请在研究过程中，采用以下方法测试锂离子二次电池的充放电曲线，高温循环性能和倍率性能：
充放电曲线测试：在45℃下，将锂离子二次电池以0.1C倍率恒流充电至4.3V，再恒压充电至电流小于等于0.025C，再以0.1C倍率恒流放电至3.0V，记录锂离子二次电池的充放电曲线。
高温循环性能测试：在45℃下，将锂离子二次电池以1.5C倍率恒流充电至4.3V，再恒压充电至电流小于等于0.05C，再以1C倍率恒流放电至3.0V，此为一个充放电循环，记录锂离子二次电池第一次循环的放电容量。将锂离子二次电池按照上述方法进行充放电循环，记录每一次循环的放电容量，直至锂离子二次电池的放电容量衰减至第一次循环的放电容量的80％，记录充放电循环次数。
倍率性能测试：在25℃下，将锂离子二次电池以0.2C倍率恒流充电至4.3V，再恒压充电至电流小于等于0.05C，再以0.2C倍率恒流放电至3.0V，记录0.2C倍率的放电容量；在25℃下，将锂离子二次电池以0.2C倍率恒流充电至4.3V， 再恒压充电至电流小于等于0.05C，再以2C倍率恒流放电至3.0V，记录2C倍率的放电容量。锂离子二次电池2C倍率放电容量保持率(％)＝2C倍率放电容量/0.2C倍率放电容量×100％。
实施例1
正极极片的制备：将第一正极活性材料LiMn 2O 4、第二正极补锂材料LiMnO 2、粘结剂PVDF及导电炭黑进行混合，其中LiMn 2O 4、LiMnO 2、PVDF及导电炭黑的重量比为92.5：4.0：1.5：2.0，按料液比为7：3加入溶剂NMP，在真空搅拌作用下搅拌至均一透明状体系，获得正极浆料；将正极浆料均匀涂覆在正极集流体铝箔上，之后转移至烘箱干燥，烘干温度为120℃，再经过冷压，分切，得到正极极片，正极活性材料层中第一正极活性材料LiMn 2O 4的重量百分含量为92.5％，正极活性材料层中的第二正极补锂材料LiMnO 2的重量百分含量为4.0％。
负极极片的制备：将负极活性材料人造石墨、增稠剂羧甲基纤维素钠(CMC)、粘结剂(SBR)及导电炭黑按照质量比95.7：1.0：1.8：1.5进行混合，按料液比为4：6加入溶剂去离子水，在真空搅拌机作用下获得负极浆料；将负极浆料均匀涂覆在负极集流体铜箔上；之后转移至烘箱干燥，烘干温度为120℃，再经过冷压，分切，得到负极极片。
电解液的制备：将碳酸乙烯酯(EC)、碳酸甲乙酯(EMC)及碳酸二乙酯(DEC)按照体积比为1:1:1混合均匀，得到有机溶剂；将LiPF 6溶解于上述有机溶剂中，以使LiPF 6浓度为1mol/L；基于电解液的总质量，再加入3重量％的碳酸亚乙烯酯和3％重量的1,3-丙烷磺酸内酯，混合均匀，得到电解液。
锂离子二次电池的制备：将正极极片、隔离膜和负极极片一次层叠设置，隔离膜采用厚度为14μm的聚丙烯(PP)薄膜(Celgard公司提供)，其处于正极极片和负极极片之间起到隔离作用，然后卷绕成电极组件，焊接极耳，将电极组件装入外壳中，注入电解液并封口，之后经过静置、化成、整形等工序，得到锂离子二次电池。
实施例2～27
与实施例1不同的是，调整正极中的材料组分和制备步骤中的相关参数，详见表1(该表中，第一正极活性材料的重量百分含量是指正极活性材料中的第一正极活性材料的重量百分含量，第二正极补锂材料的重量百分含量是指正极活性材料中的第二正极补锂材料的重量百分含量)。
对比例1
与实施例1不同的是，正极中仅含有LiMn 2O 4。
对比例2
与实施例1不同的是，正极中仅含有LiMnO 2。
对比例3～4
与实施例1不同的是，正极中的第一正极活性材料和第二正极补锂材料的重量比不同。
对比例5～6
与实施例1不同的是，正极极片的膜片电阻、压实密度和单面面密度有所不同。
对比例7～8
与实施例1不同的是，电解液中的碳酸亚乙烯酯和1,3-丙烷磺酸内酯的重量百分含量有所不同。
对比例9～10
与实施例26不同的是，电解液中仅含碳酸亚乙烯酯或1,3-丙烷磺酸内酯。
各实施例和对比例中，除实施例18中正极活性材料中导电炭黑和粘结剂PVDF含量分别为0.5wt％外，其他实施例和对比例中正极活性材料中导电炭黑含量为2.0wt％，粘结剂PVDF含量为1.5wt％。
依照前述方法，测试各实施例和对比例所得锂离子二次电池的高温循环性 能和倍率性能，结果见表2。
表1
Figure PCTCN2021131365-appb-000001
Figure PCTCN2021131365-appb-000002
表2
类别 R·P/Q 高温循环次数 倍率性能(％)
对比例1 7.2 620 98.3
对比例2 8.74 1 81.2
对比例3 7.2 647 98.1
对比例4 7.2 611 85.5
对比例5 32.0 556 94.6
对比例6 1.82 501 91.8
对比例7 7.2 382 97.1
对比例8 7.2 681 97.0
对比例9 7.2 514 97.4
对比例10 7.2 538 97.2
实施例1 7.2 753 97.6
实施例2 7.2 728 97.5
实施例3 7.2 751 97.2
实施例4 7.2 719 97.0
实施例5 7.2 745 97.4
实施例6 7.2 701 96.9
实施例7 7.2 712 97.1
实施例8 7.2 725 97.3
实施例9 7.2 709 97.2
实施例10 7.2 718 97.1
实施例11 7.2 720 97.4
实施例12 7.2 645 90.1
实施例13 7.2 691 94.7
实施例14 7.2 703 95.3
实施例15 7.2 798 96.8
实施例16 7.2 681 98.0
实施例17 7.2 661 97.9
实施例18 7.2 666 97.8
实施例19 3.33 772 97.9
实施例20 14.53 729 97.6
实施例21 11.44 668 96.8
实施例22 30 652 96.1
实施例23 1.5 706 97.5
实施例24 7.2 691 97.9
实施例25 7.2 782 97.5
实施例26 7.2 673 97.8
实施例27 7.2 681 97.7
通过上述实施例和对比例可知，(1)本申请中第一正极活性材料和第二正极补锂材料共同使用产生了协同效应。第一方面，本申请所用第二正极补锂材料的表面游离锂含量少，将其加入正极，所得浆料稳定性好，加工性能优良；第二方面，本申请所用第二正极补锂材料首次充电比容量高、首次库伦效率低，可更好的弥补因生成SEI造成的活性锂损失，放电时有更多的锂离子回嵌至第一正极活性材料晶格中，有效提升了锂离子二次电池的能量密度；第三方面，第一正极活性材料的结构稳定，循环稳定性较好，并通过控制正极极片的膜片电阻R、压实密度P和单面面密度Q在本申请范围内，能够使锂离子二次电池具有良好的循环性能和倍率性能。(2)电解液中添加的碳酸亚乙烯酯和第一正极活性材料及第二补锂活性材料的补锂策略能发挥协同作用，在首次充电时，由于第二正极补锂材料脱出的大量活性锂嵌入负极，导致负极的真实电位进一步降低，造成电解液中溶剂的持续还原，影响循环性能，采用本申请范围内的碳酸亚乙烯酯添加剂，可以诱导生成更加致密和轻薄的SEI层，阻止了电解液的持续消耗，此外，电解液中还添加了1,3-丙烷磺酸内酯添加剂，可以在正极活性材料表面形成一层界面保护层，进一步提升了循环性能。
最后所应当说明的是，以上实施例仅用以说明本申请的技术方案而非对本申请保护范围的限制，尽管参照较佳实施例对本申请作了详细说明，本领域的普通技术人员应当理解，可以对本申请的技术方案进行修改或者等同替换，而不脱离本申请技术方案的实质和范围。

Claims (10)

  1. 一种正极极片，其特征在于，包括正极集流体以及设置于所述正极集流体的至少一个表面上的正极活性材料层，所述正极活性材料层包括第一正极活性材料和第二正极补锂材料；所述正极极片满足1.5≤R·P/Q≤30，其中，R是所述正极极片的电阻，单位为Ω；P是所述正极极片的压实密度，单位为g/cm 3；Q是所述正极极片的单面面密度，单位为g/1540.25mm 2。
  2. 如权利要求1所述的正极极片，其特征在于，所述第一正极活性材料为Li 1+xMn yM 2-yO 4-tA t，其中，-0.1<x<0.2，1<y≤2，0≤t<0.5，M为Ni、Fe、Zn、Mg、Al、Ti、Zr中的至少一种，A是S、N、F、Cl、Br中的至少一种。
  3. 如权利要求1所述的正极极片，其特征在于，所述第二正极补锂材料为Li 1+rMn 1-pN pO 2-sB s，其中，-0.1<r<0.2，0≤p<0.2，0≤s<0.2，N是Fe、Co、Ni、Ti、Zn、Mg、Al、V、Cr、Zr中的至少一种，B是S、N、F、Cl、Br中的至少一种。
  4. 如权利要求1所述的正极极片，其特征在于，满足如下特征中的至少一种：
    (a)所述正极极片满足3.0≤R·P/Q≤15；
    (b)所述R≤5Ω，优选所述R≤2Ω；
    (c)所述P满足2.5g/cm 3<P<3.2g/cm 3；
    (d)所述Q满足0.3g/1540.25mm 2<Q<0.55g/1540.25mm 2。
  5. 如权利要求1所述的正极极片，其特征在于，所述第一正极活性材料和所述第二正极补锂材料的重量比为5:1～99:1。
  6. 如权利要求5所述的正极极片，其特征在于，所述第一正极活性材料和所述第二正极补锂材料的重量比为9:1～99:1。
  7. 如权利要求1所述的正极极片，其特征在于，所述正极活性材料中所述第一正极活性材料的重量含量为80％～98％。
  8. 如权利要求7所述的正极极片，其特征在于，所述正极活性材料中所述第一正极活性材料的重量含量为85％～98％。
  9. 一种锂离子二次电池，其特征在于，包括正极极片、负极极片、隔离膜和电解液，所述正极极片为如权利要求1-8中任一项所述的正极极片。
  10. 如权利要求9所述的锂离子二次电池，其特征在于，所述电解液包含以下重量百分含量的组分：碳酸亚乙烯酯0.001％至5％，和/或1,3-丙烷磺酸内酯0.001％至5％。
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