WO2023024404A1 - 一种锂离子电池预锂化方法及锂离子电池 - Google Patents

一种锂离子电池预锂化方法及锂离子电池 Download PDF

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WO2023024404A1
WO2023024404A1 PCT/CN2022/070955 CN2022070955W WO2023024404A1 WO 2023024404 A1 WO2023024404 A1 WO 2023024404A1 CN 2022070955 W CN2022070955 W CN 2022070955W WO 2023024404 A1 WO2023024404 A1 WO 2023024404A1
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lithium
ion battery
composite sheet
source composite
lithium source
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English (en)
French (fr)
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徐兴无
林少雄
刘超辉
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Hefei Gotion High Tech Power Energy Co Ltd
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Hefei Gotion High Tech Power Energy Co Ltd
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Priority to US17/927,753 priority Critical patent/US20240234794A1/en
Priority to KR1020227042141A priority patent/KR102853478B1/ko
Priority to EP22808567.6A priority patent/EP4164023B1/en
Priority to JP2022574413A priority patent/JP7668823B2/ja
Publication of WO2023024404A1 publication Critical patent/WO2023024404A1/zh
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Definitions

  • the invention relates to a lithium ion battery pre-lithiation method and the lithium ion battery, belonging to the technical field of lithium ion battery production.
  • the electrification of automobiles has become an irreversible trend in the world. Therefore, the requirements for lithium-ion batteries, the core components of electric vehicles, are getting higher and higher.
  • the focus is on the ever-increasing energy density and cycle life.
  • the weight energy density of ternary semi-solid batteries is required to be more than 350-400Wh/Kg
  • the weight energy density of lithium iron phosphate single batteries is required to be more than 230Wh/Kg.
  • the cycle life is required to be more than 15,000 times, and so on.
  • portable electronic products such as mobile phones, etc.
  • the silicon negative electrode usually refers to metal silicon (Si) or silicon oxide (SiO).
  • Si can form Li 15 Si 4 alloy with Li at room temperature, and the theoretical gram capacity is 3579mAh/g, which is 10 times that of graphite negative electrode.
  • the volume expansion rate of silicon is about 300-400%.
  • this causes the expansion of the negative electrode and the entire battery core. new surface, thereby consuming a large amount of lithium ions.
  • the graphite negative electrode consumes about 6% of the irreversible lithium ions due to the SEI film formed on the negative electrode during the formation process, while the silicon-containing negative electrode consumes about 10-20% of the lithium ions. This is the main reason for the low efficiency of the silicon-containing negative electrode formation for the first time.
  • pre-lithiation technology or lithium supplementation technology. 10 No. 3 reviewed the technology. To sum up, the current main pre-lithiation technologies are divided into metal lithium powder pre-lithiation, metal lithium foil calendering pre-lithium, metal lithium evaporation pre-lithium, positive electrode additive pre-lithium, electrochemical pre-lithium, etc.
  • Chinese patent applications with publication numbers CN112310336A and CN112397682A disclose devices and methods for calendering lithium metal foil.
  • the device is very complex, the process control requirements are very high, the environmental control requirements are harsh and there are great safety hazards. Simultaneously, because this method uses the lubricant of special requirement, release agent and bearing material etc., manufacturing cost is very high.
  • the Chinese patent application with publication number CN111430659A discloses a pre-lithiation method of vacuum evaporation. This method has the advantages of thin and uniform metal lithium evaporation layer, but the outstanding disadvantage is that the vacuum evaporation equipment is expensive and it is difficult to obtain industrial application.
  • the positive electrode lithium supplement additives there are mainly Li 2 O, Li 2 S, Li 3 N, Li 4 FeO 5 , Li 6 CoO 4 , Li 2 NiO 2 , Li 4 DHBN and so on.
  • the residual substance after pre-lithium in this method affects the energy density and performance of the battery, and also has many side effects (such as gas production, etc.), and there is still no additive that can meet the requirements of industrial applications.
  • the patent whose authorized announcement number is CN105845894B provides an electrochemical wet pre-lithiation method. During the implementation of this method, it was found that the method of reassembling the battery with the negative electrode monolithic pre-lithium is still relatively complicated and needs further improvement.
  • the patent application with publication number CN110224182A discloses an improved scheme of electrochemical "wet pre-lithium", but this method has a step of taking out the bare cell after the pre-lithium is completed, which is still not the simplest process.
  • the patent application whose publication number is CN110061299A discloses a method for electrochemical pre-lithium.
  • This method needs to open a round hole on the cover plate of the battery cell, put the metal electrode and metal lithium into the inside of the battery cell to electrochemically pre-lithium, and then take it out. Since it is difficult to seal the opening after liquid injection, and there is a risk of liquid leakage, this method is difficult to carry out industrial application. At the same time, this method also has the risk of metal lithium dissolution and local lithium precipitation on the pole piece.
  • the patent application with publication number CN111969266A discloses a method for automatic pre-lithiation of cylindrical lithium ion batteries. This method is limited to cylindrical batteries, and metal lithium is placed in the central hole of the cylindrical battery and is in contact with the negative electrode casing to complete automatic pre-lithiation.
  • the local concentrated placement of lithium metal in this method will lead to local lithium deposition in the battery cell, and its industrialization still has great limitations.
  • the biggest problem of the electrochemical pre-lithium method is that it requires a particularly long pre-lithium time, the amount of pre-lithium is small, and it is easy to dissolve metal lithium particles.
  • the purpose of the present invention is to provide a pre-lithiation method for lithium-ion batteries.
  • the lithium source composite sheet connected to the negative electrode is arranged inside, which can realize the pre-lithiation process of the negative electrode, so that the battery has a higher energy density and a longer life.
  • the present invention provides a kind of pre-lithiation method of lithium ion battery, and this method is a kind of electrochemical pre-lithiation method that is easy to industrialization, low cost, and it comprises:
  • more than one lithium source composite sheet is arranged in the core body (such as winding core or stacked core, the same below), and at least one of the lithium source composite sheets Connect with the negative tab of the lithium-ion battery;
  • the lithium source composite sheet is a metal composite lithium sheet formed by combining lithium foil and metal foil (such as a composite structure of one layer of lithium foil and one layer of metal foil, or two layers of lithium foil “sandwich” structure respectively arranged on both sides of a layer of metal foil), wherein the metal foil can be a metal foil usually used as a current collector, including copper foil, nickel foil or platinum foil, etc.; or, the lithium The source composite sheet is made of a lithium-containing material whose electrochemical properties are similar to metallic lithium.
  • the shape of the lithium source composite sheet can be set according to needs, preferably in the shape of a sheet, strip or strip, and can have tabs.
  • the surface of the lithium source composite sheet close to the core is provided with a blocking member capable of blocking the passage of lithium ions.
  • a blocking member capable of blocking the passage of lithium ions.
  • the blocking member may preferably be metal foil or insulating tape.
  • the lithium content of the lithium source sheet should be moderate, neither excessive to cause lithium precipitation, nor insufficient to meet the pre-required lithium content, and also to consider the demand for lithium supplementation during the cycle. Or it can also be said that the thickness of the lithium source sheet should be moderate, which can be placed in the space where it is placed, and it should not fall off during the pre-lithiation process, and at the same time, the lithium can be completely consumed after the pre-lithiation is completed. Any thickness under this principle is within the protection scope of this patent. Specifically, according to the embodiment of the present invention, preferably, the thickness of the lithium source composite sheet does not exceed the thickness of the core body.
  • the thickness of the lithium source composite sheet can be 5-500 ⁇ m, preferably 20-300 ⁇ m, more preferably 30-280 ⁇ m, further preferably 50-250 ⁇ m, for example: 50 ⁇ m, 80 ⁇ m, 150 ⁇ m, 200 ⁇ m, 220 ⁇ m, etc. specific values are available.
  • the lithium source composite sheet is provided with an insulating porous elastic material on the surface close to the lithium ion battery case.
  • an insulating porous elastic material By setting the insulating porous elastic material, on the one hand, it can avoid the dissolution and shedding of metallic lithium, and can elastically constrain the core (stacked core or winding core), improving the structural stability of the lithium-ion battery. On the other hand, it can ensure the pre-lithium process. There is enough electrolyte in it.
  • the lithium source composite sheet can be wrapped with an elastic liquid-absorbing material, more preferably, the elastic liquid-absorbing material is a diaphragm material. By using elastic material for wrapping, during the pre-lithiation process, along with the consumption of the lithium source composite sheet, the elastic material is deformed, which can fill the space left after consumption and improve the structural stability.
  • the lithium source composite sheet is directly connected to the negative electrode tab (for example, welded together), or the lithium source composite sheet is connected to the positive electrode or the negative electrode through an external circuit through the third electrode. That is, in the technical solution of the present invention, the lithium source composite sheet and the negative electrode can be connected in two ways:
  • the first type the lithium source composite sheet is directly connected to the negative electrode tab, for example, through metal wires, metal sheet connections or direct welding.
  • the negative electrode starts to be pre-lithiated immediately without additional load; this method is suitable for the case where the pre-lithium amount is small, for example, the pre-lithium amount is below 10% SOC, for example, the pre-lithium amount is 5% SOC.
  • the second type the lithium source composite sheet is connected to the third electrode, and the third electrode is connected to the negative electrode tab of the lithium-ion battery by an external circuit to perform pre-lithiation of the negative electrode; Connect to the positive tab of the lithium-ion electrode for positive pre-lithiation.
  • the process of pre-lithiation can be controlled by an external circuit, and the speed of pre-lithiation can be increased, which is suitable for the situation where the amount of pre-lithium is large.
  • Complementary pre-lithiation can be performed via the third electrode. This method is suitable for the case where the amount of pre-lithium is relatively large, for example, the amount of pre-lithium is above 10% SOC.
  • the pre-lithiation method of the above-mentioned lithium ion battery comprises:
  • more than one lithium source composite sheet and a third electrode are arranged in the lithium ion battery, and the lithium source composite sheet is connected to the third electrode;
  • the lithium source composite sheet is connected to the tab of the negative electrode by an external circuit, and the negative electrode is pre-lithiated.
  • the lithium source composite sheet is connected to the tab of the positive electrode through the third electrode through an external circuit, and the positive electrode is pre-lithiated. That is, the pre-lithiation method of the lithium ion battery of the present invention may also include:
  • more than one lithium source composite sheet and the third electrode are arranged in the lithium ion battery, and the lithium source composite sheet is connected to the third electrode;
  • the lithium source composite sheet is connected to the positive electrode tab through the third electrode and an external circuit, and the positive electrode is pre-lithiated.
  • the connection between the lithium source composite sheet and the negative electrode tab is located inside the casing of the lithium ion battery.
  • the connection between the lithium source composite sheet and the tab can be realized by metal wire, metal sheet connection or welding, for example: the lithium source composite sheet is connected to the negative electrode tab by ultrasonic welding; , the lithium source composite sheet can be added and the metal foil (such as copper foil) of the lithium source composite sheet and the copper foil of the negative electrode can be welded on the same tab (Tab sheet) at the same time, which is easy to industrialize into production.
  • the metal wires, metal sheets or welding positions used to realize the connection are all located inside the shell.
  • the connection is located inside the shell to improve safety and avoid extreme Problems such as liquid leakage caused by ears extending out of the shell, and the production process is greatly simplified.
  • connection between the lithium source composite sheet and the negative electrode is located inside the housing, without the need to set the tabs for the lithium source composite sheet and extend it to the outside of the housing (of course, for the convenience of connection, the lithium source composite sheet can also be provided with tabs, but The tab is located inside the shell and will not extend to the outside of the shell), after pre-lithiation, the lithium in the lithium source composite sheet will be completely consumed, this method will not change the structure of the existing lithium-ion battery, and can be applied It is suitable for more types of lithium-ion batteries, and the lithium-ion battery pre-lithiation method of the present invention has good production convenience, less adjustment to the existing production line, and lower overall cost.
  • the third electrode, etc. can also be located inside the casing, or extend out of the casing of the lithium-ion battery through a certain position .
  • the lithium-ion battery is provided with a liquid injection port
  • the third electrode communicates with the positive electrode tab or the negative electrode tab through the liquid injection port through the liquid injection port
  • the charging and discharging device of the external circuit is in the discharge state , the battery undergoes a pre-lithium reaction.
  • the lithium source composite sheet, the negative electrode tab, and the positive electrode tab can be connected to the charging and discharging device through the liquid injection port to allow the electrolyte to flow inside the cell, thereby Realize the pre-lithiation operation of negative electrode or positive electrode.
  • the arrangement position of the liquid injection port there is no special requirement for the arrangement position of the liquid injection port, and it can be understood that it is a conventional arrangement in the prior art.
  • the third electrode is mainly used when the demand for pre-lithium is large.
  • the third electrode can be arranged on the battery case, or a temporary pre-lithium tab through the liquid injection port can be adopted. The way.
  • the battery pre-lithium amount when the battery pre-lithium amount is lower than 5% SOC, no measures are taken to keep the electrolyte inside the battery dynamic; when the battery pre-lithium amount is greater than 10% SOC, measures are taken to keep the battery inside
  • the electrolyte remains dynamic. That is, in the pre-lithiation process of the negative electrode and the positive electrode, certain measures are taken to make the electrolyte flow inside the lithium-ion battery cell, so that the locally dissolved lithium ions can be embedded in the negative electrode or the positive electrode sheet through the flowing electrolyte.
  • the above "measures to keep the electrolyte dynamic” include but are not limited to vibration, rotation, inert gas agitation, electromagnetic agitation, etc., for example, by rotating the lithium ion battery, vibrating the lithium ion battery, and injecting Inert gas, or electromagnetic agitation of the electrolyte is used to realize the flow of the electrolyte inside the cell of the lithium-ion battery. Any manner capable of realizing the flow of the electrolyte may be adopted, and is not limited to the manners listed above.
  • the lithium ion battery in addition to the lithium source composite sheet, can also include some other conventional components, such as a core and a casing, wherein the core is composed of a positive electrode sheet, a negative electrode sheet, and a diaphragm, and the lithium ion battery At least one lithium source composite sheet is respectively arranged on the surface of the battery core and/or in other spaces where it can be placed.
  • the positive electrode sheet and the negative electrode sheet are respectively provided with positive electrode tabs and negative electrode tabs.
  • the material, size, and arrangement of the diaphragm can refer to the conventional methods in the field of lithium-ion batteries.
  • the lithium-ion battery may include a core assembly composed of several cores connected in series or parallel, and the surface and/or other surface of each core in the core assembly At least one lithium source composite sheet is respectively arranged in the space where it can be placed.
  • the lithium-ion battery targeted by the pre-lithiation method of the present invention can be a conventional stacked core battery, a rolled core battery, and a JTM (Jellyroll To Module) battery.
  • At least one lithium source composite sheet is respectively arranged on the surface of the core body of the lithium-ion battery and/or other space where it can be placed; or, the lithium-ion battery is composed of several A core assembly composed of cores connected in series or in parallel, each stacked core in the core assembly is respectively provided with at least one lithium source composite sheet on the surface and/or in other spaces where it can be placed.
  • the core body of the lithium-ion battery is a stacked core
  • at least one side surface of the stacked core is provided with at least one lithium source composite sheet
  • at least one lithium source composite sheet is respectively provided, or lithium source composite sheets are placed on the side and other spaces where they can be placed.
  • the core body of the lithium ion battery is a winding core, and at least one lithium source composite sheet is provided on the side or top surface of the winding core; preferably, the lithium source composite sheet Coated on the side of the winding core, during the pre-lithiation process, the lithium source composite sheet coated on the side of the winding core can be evenly diffused to evenly replenish lithium for the negative electrode.
  • the lithium-ion battery comprises a core assembly (such as a JTM battery) composed of several cores connected in series or in parallel, and each stack in the core assembly At least one lithium source composite sheet is provided on at least one side surface of the core.
  • the core body may be a laminated core or a rolled core composed of positive and negative plates.
  • the negative electrode of the core body of the lithium ion battery is one or a combination of two or more of negative electrodes such as silicon negative electrodes, graphite negative electrodes, lithium titanate negative electrodes, and tin negative electrodes; more preferably Specifically, the anode is a silicon-containing anode, and the lithium source composite sheet is located in the expansion space reserved for the anode in the casing of the lithium-ion battery.
  • the lithium source composite sheet is located in the expansion space reserved for the anode in the casing of the lithium-ion battery.
  • the lithium source composite sheet (for example, 1 or 2 lithium source composite sheets) can be placed in this space. In this way, the lithium source composite sheet can be placed without affecting the battery structure.
  • the lithium source composite sheet is set in the battery case. After the pre-lithiation is completed, the lithium source composite sheet is completely consumed, and the reserved expansion space is vacated again, which will not affect the normal use of the lithium-ion battery.
  • the electrolyte used in the present invention may also be an electrolyte commonly used in the field of lithium-ion batteries, wherein the amount of injected electrolyte should ensure that the lithium source composite sheet can be immersed therein.
  • the current and the current system need to be controlled when the negative electrode or the positive electrode is pre-lithiated through the third electrode.
  • the speed of pre-lithium can be accelerated, and at the same time, the uniformity of pre-lithium can be controlled and local lithium precipitation can be avoided.
  • a certain amount of lithium is intercalated from the positive electrode to the negative electrode, preferably, the lithium intercalation amount is 10% to 80% SOC, and then the pre-lithium of the positive electrode is carried out. change.
  • the voltage is preferably 2.5V-3.5V, more preferably 3.0V-3.4V , such as 2.5V, 2.6V, 2.7V, 2.8V, 2.9V, 3.0V, 3.1V, 3.2V, 3.3V, 3.4V, 3.5V, or two of these specific voltage values as the upper and lower limits respectively range of composition.
  • the current for pre-lithiation of the positive electrode is 0.00001C-1C; more preferably 0.0001C-0.5C.
  • the pre-lithiation of the positive electrode is performed in a batch manner.
  • the time of current intermittent can be controlled as 1-3600 seconds, preferably 300-1800 seconds, more preferably 60-600 seconds, for example: 60 seconds, 100 seconds, 200 seconds, 300 seconds, 400 seconds, 500 seconds, 600 seconds, Or a range consisting of two of these specific time values as upper and lower bounds, respectively.
  • the voltage is preferably 0.1V-0.3V, more preferably 0.2V.
  • the pre-lithiation current of the negative electrode is 0.00001C-1C; more preferably 0.0001C-0.5C, further preferably 0.01C-0.2C.
  • the pre-lithiation of the negative electrode is performed in a batch manner.
  • the current intermittent time can be controlled to be 1-3600 seconds, preferably 300-1800 seconds, preferably 60-600 seconds, for example: 60 seconds, 100 seconds, 200 seconds, 300 seconds, 400 seconds, 500 seconds, 600 seconds, or A range consisting of two of these specific time values as upper and lower bounds.
  • the pre-lithiation time is 8h to 200h, such as 10h, 20h, 30h, 40h, 50h, 60h, 70h, 80h, 90h, 100h, 110h, 120h, 130h, 140h, 150h, 160h, 170h, 180h, 190h, 200h, or a range consisting of two of these specific time values as upper and lower limits, respectively.
  • the lithium content of the lithium source composite sheet is calculated according to the required pre-lithium amount, and the utilization rate is properly considered.
  • the thickness of the lithium source composite sheet is controlled according to the needs, and it is necessary to meet the requirements that it can be placed in the corresponding space and ensure that it will not fall off during the pre-lithiation process.
  • the lithium source composite sheet Lithium should be completely consumed.
  • the calculation formula of the theoretical pre-lithium amount Y required per Ah is:
  • n is the measured number of Li
  • F is Faraday's constant
  • A is the atomic weight of lithium
  • the required number of Ah is equal to the loss of the first effect multiplied by the design capacity of the cell.
  • the present invention also provides a lithium-ion battery with high energy density and long life, which is prepared by the above-mentioned pre-lithiation method.
  • the lithium source composite sheet is directly connected to the negative electrode tab, and the pre-lithiation reaction occurs after the electrolyte is injected, and then the lithium source can be discharged (for example, through an external circuit connected to the positive electrode and the negative electrode, constant voltage discharge) , so that lithium ions enter the positive electrode) to achieve pre-lithiation of the positive electrode, and finally to achieve pre-lithiation of the battery.
  • the pre-lithiation method provided by the present invention does not require an external load during the pre-lithiation of the negative electrode, and the pre-lithiation can be completed in the process of core infiltration, formation, and volume separation.
  • the lithium source composite sheet is directly connected to the negative electrode and the connection is controlled within the casing of the lithium-ion battery, which can also avoid the safety problems that are easily caused by separately setting the pre-lithiated tabs and extending them outside the battery casing. .
  • the existing electrochemical pre-lithiation methods all adopt the pre-lithium method of the pole piece, and the battery is assembled after the pre-lithiation is completed, which leads to problems such as difficult battery cell assembly, high environmental requirements, and high production costs.
  • the method provided by the present invention is carried out after the battery assembly is completed, avoiding the impact of pre-lithiation on battery assembly, and can solve the problems of long electrochemical pre-lithiation time, low amount of pre-lithium, uneven pre-lithium, and dissolution of metal lithium particles.
  • the problem is that the requirements for the environment are low, which makes the pre-lithiation simple and easy to industrialize, and the cost is low.
  • Adopting the pre-lithiation method provided by the present invention can completely consume the lithium in the lithium source composite sheet during the pre-lithiation process, and will not remain inside the battery, avoiding the long-term existence of the lithium source composite sheet in the prior art. Potential safety hazards caused by the inside of the battery.
  • pre-lithiation can be achieved through a simple method by adopting the pre-lithiation method provided by the present invention.
  • This method basically does not change the original process of the lithium-ion battery, but only partially changes the equipment, such as setting a lithium source composite sheet such as pre-lithiation electrolysis on the surface of the core body and adding tooling to make the electrolyte flow when pre-lithium is added. These changes are all easy to realize and easy to industrialized production.
  • the beneficial effects brought by the present invention include: the pre-lithiation method provided by the present invention can realize the industrial application of the pre-lithiation technology with little modification of the existing lithium-ion battery technology and equipment, and the cost low.
  • the capacity of the lithium ion battery manufactured by the pre-lithiation method of the present invention can be increased by more than 5%, and the energy density is high (for example, the ternary battery can achieve more than 370Wh/kg, and the lithium iron phosphate battery can achieve more than 230Wh/kg, etc.) , long cycle life (such as lithium iron phosphate battery can achieve more than 15,000 cycles, etc.), low cost (increasing power while reducing cost), is a very promising revolutionary lithium-ion battery process method.
  • Fig. 1 is a schematic structural diagram of a lithium source composite sheet.
  • FIG. 2 is a schematic structural diagram of the prismatic battery provided in Example 1.
  • FIG. 3 is a schematic structural diagram of the pouch battery provided in Example 2.
  • FIG. 4 is a schematic structural diagram of the pouch battery provided in Example 3.
  • FIG. 4 is a schematic structural diagram of the pouch battery provided in Example 3.
  • Example 5 is a graph showing the cycle life results of the prismatic battery of Example 1 and the prismatic battery of Comparative Example 1.
  • the structure of the lithium source composite sheet used in the present invention can be shown in Figure 1, which is formed by compounding lithium foil 15 on one or both sides of the metal foil 14, and the outside of the lithium foil 15 is wrapped with an elastic absorbent Liquid material layer 16.
  • the lithium source composite sheet can be compounded to the side of the stacked core 11 (or any other space with electrolyte, for example: when a winding core is used, the lithium source composite sheet can be compounded to the top of the winding core or coated on the side of the winding core ), and the insulation tape 13 is used to insulate the two, and the lithium source composite sheet is connected to the negative electrode tab 12 through the metal foil 14.
  • the preparation process of the lithium source composite sheet and the composite process with the core can be carried out in the following manner:
  • the lithium foil 15 is composited on the metal foil 14 by calendering, the thickness of the metal foil 14 can be controlled between 4-100 ⁇ m, the thickness of the lithium foil 15 can be controlled between 0.01-10 mm, and the lithium foil 15 can be on one side Can also be on both sides;
  • Paste a layer of insulating tape 13 resistant to electrolyte corrosion on the bonding surface of the stacked core 11 and the lithium source composite sheet;
  • the tab 12 of the stacked core 11 is connected to the metal foil 14 , and the upper end of the metal foil 14 may be provided with a corresponding tab.
  • This embodiment provides a method for pre-lithiation of a square battery.
  • the structure of the square battery is shown in FIG. 2 .
  • the prismatic battery includes:
  • the core body 22 is made of a positive electrode sheet, a negative electrode sheet, and a diaphragm through winding or lamination processes, wherein the positive electrode sheet is made of lithium iron phosphate material, and the negative electrode sheet is made of graphite material, and the two are respectively provided with positive electrodes.
  • housing 21 the housing 21 is used to accommodate the core 22, and the upper part of the housing 21 is provided with a positive connection part 27 and a negative connection part 25.
  • This pre-lithiation method comprises the following steps:
  • a lithium source composite sheet 23 which is a lithium-copper composite strip with a structure as shown in Figure 1, that is, a composite of one layer of copper foil and one layer of lithium foil, the lithium foil
  • the thickness of the copper foil is 0.1 mm, and the thickness of the copper foil is 4.5 ⁇ m.
  • the lithium source composite sheet 23 is connected to the negative electrode tab 24; before the electrolyte is injected, the lithium-copper composite strip is located at a position that can be immersed in the electrolyte;
  • the pre-lithium time is controlled according to the requirements of the pre-lithium amount.
  • the pre-lithium amount in this embodiment is 5% SOC, and the pre-lithium time is controlled at 48 hours; the pre-lithiation time is within the acceptable range of the lithium-ion battery manufacturing process;
  • Capacitance charge with a constant current of 0.33C, the cut-off voltage is 3.65V, then charge with a constant voltage of 3.65V, the cut-off current is 0.05C; after completion, put it aside for 10 minutes, and then discharge with a current of 0.33C, the cut-off voltage is 2.0V , to complete the partition.
  • This comparative example provides a conventional manufacturing method of a prismatic battery, which is different from Example 1 in that no lithium source sheet is placed and no pre-lithiation is performed, and the others are the same.
  • the lithium ion battery cell obtained by the pre-lithiation method of Example 1 can have a capacity about 5% higher than that of Comparative Example 1, and can reach about 2000 cycles without attenuation and tend to 15000 cycles cycle life, while the sample of Comparative Example 1 has a cycle life of less than 6000 cycles (as shown in Figure 5).
  • This embodiment provides a pre-lithiation method for a pouch battery, wherein the structure of the pouch battery is shown in FIG. 3 , and its length is 360 mm.
  • the pouch battery includes:
  • the core body 32, the core body 32 is made of the positive electrode sheet, the negative electrode sheet, and the diaphragm through a lamination process, wherein the positive electrode sheet is a ternary material NCM, and the negative electrode sheet is a silicon 600 negative electrode, and the two are respectively provided with a positive electrode tab 35,
  • the negative electrode tab 34 is arranged on the same side of the core body 32;
  • the casing 31 which is an aluminum-plastic film, is used to house the core 32 .
  • This pre-lithiation method comprises the following steps:
  • Lithium source composite sheet 33 is set on one side of core body 32, and the position of this lithium source composite sheet 33 should guarantee that it can be immersed in electrolyte;
  • This lithium source composite sheet 33 is the lithium copper composite strip of structure as shown in Figure 1, That is, a composite of a layer of copper foil and a layer of lithium foil.
  • the thickness of the lithium foil is 0.1-0.2mm, and the thickness of the copper foil is 4.5 ⁇ m. shape;
  • the lithium source composite sheet 33 is provided with a third electrode 36, and is drawn out through the liquid injection port; the negative electrode, the positive electrode and the lithium source composite sheet 33 can be connected to carry out pre-lithium to the negative electrode and the positive electrode, as shown in Figure 3;
  • the lithium source composite sheet 33 is connected to the negative electrode tab 34 through the third electrode 36 by using an external circuit, and the negative electrode is pre-lithiated.
  • the third electrode 36 is connected to the positive electrode tab 35, and the positive electrode is pre-lithiated.
  • the current of the pre-lithiated is controlled at 0.01C, which can be carried out by constant voltage and intermittent discharge.
  • the voltage is 3.0V and the intermittent time is 60. Second;
  • the electrolyte inside the core body 32 is flowed by rotating and vibrating the pouch battery, so as to speed up the pre-lithiation speed and make the pre-lithiation proceed evenly.
  • the rotation can be forward rotation 180° and reverse 180° alternately, the rotation speed is 5 revolutions per minute, and the vibration motor speed is 1000 revolutions per minute; the specific rotation is carried out in an intermittent manner by turning 180 degrees for 60 seconds and then turning 180 degrees.
  • the pre-lithium time is controlled according to the requirement of the pre-lithium amount.
  • the pre-lithium amount is 12% SOC, and the pre-lithiation time is 96 hours.
  • the conventional aging and capacity separation process is carried out on the battery cell, as follows:
  • This comparative example provides a conventional manufacturing method of a pouch battery, which is different from Example 2 in that no lithium source sheet is placed and no pre-lithiation is performed, and the others are the same.
  • the lithium-ion battery manufactured by the method of Example 2 has a higher first-time charge and discharge efficiency, and a higher capacity performance, and the specific energy of the battery cell can reach 370Wh/kg, while the comparative example The specific energy of the sample of 2 is only 320Wh/kg.
  • This embodiment provides a method for pre-lithiation of a pouch battery, wherein the structure of the pouch battery is shown in Figure 4, and its length is 357 mm. Its structure is similar to that of the pouch battery in Example 2, the only difference being
  • the pouch battery in this embodiment is a pouch battery with tabs at both ends.
  • the pouch battery includes:
  • Core body 42 the core body 42 is made of positive electrode sheet, negative electrode sheet, and diaphragm through lamination process, wherein, the positive electrode is lithium iron phosphate material, the negative electrode is silicon 600 negative electrode material, and the two are respectively provided with positive electrode tabs 45, Negative pole tabs 44 are respectively arranged at the upper and lower ends of the core 42;
  • the casing 41 , the casing 41 is an aluminum-plastic film, used to house the core 42 .
  • the lithium source composite sheet, the pre-lithiation process and the aging and volume separation process are the same as in Example 2.
  • This comparative example provides a conventional manufacturing method for a pouch battery, which is different from Example 3 in that no lithium source sheet is placed and no pre-lithiation is performed, and the others are the same.
  • the lithium-ion battery manufactured by the method of Example 3 has a higher first-time efficiency of charging and discharging (the first-time efficiency has increased by 19%, which is a major breakthrough), and higher capacity is brought into play,
  • the specific energy of the cell can reach 230.3Wh/kg, while the specific energy of the sample in Comparative Example 3 is only 199.6Wh/kg.

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Abstract

本发明涉及一种锂离子电池预锂化方法及锂离子电池。该方法包括：在注入电解液之前，在芯体中设置一个以上的锂源复合片，并且，至少一个所述锂源复合片与锂离子电池的负极极耳连接；注入电解液，使电解液浸没所述锂源复合片，对负极进行预锂化。本发明的预锂化方法得到的锂离子电池具有较高的容量，电池的容量同比可以提升10％以上，循环寿命可以提升100％以上，软包磷酸铁锂电芯的比能量可以做到230Wh/Kg以上，而且易于产业化，综合成本非常低。

Description

一种锂离子电池预锂化方法及锂离子电池 技术领域
本发明涉及一种锂离子电池预锂化方法及锂离子电池，属于锂离子电池生产技术领域。
背景技术
目前，汽车电动化已成为全世界不可逆转的潮流，因此，对电动汽车核心零部件—锂离子电池的要求越来越高。重点体现在不断提升的能量密度以及循环寿命上，例如三元半固态电池，重量能量密度要求做到350～400Wh/Kg以上，磷酸铁锂单体电池的重量能量密度要求做到230Wh/Kg以上，循环寿命要求做到15000次以上，等等。这时候就需要使用含硅负极材料，预锂化技术的真正工业化应用也变得越来越迫切了。同时，便携式电子产品(如手机等)对高容量(如更长的待机时间)和长寿命也有同样的需求。
硅负极通常是指金属硅(Si)或氧化亚硅(SiO)。Si在常温下可以和Li形成Li 15Si 4合金，理论克容量为3579mAh/g，是石墨负极的10倍。但是，在形成合金的过程中，硅的体积膨胀率约300～400％，这一方面造成负极及整个电芯的膨胀，同时过大的膨胀导致了含硅颗粒材料的碎裂，重新生成大量的新表面，从而消耗大量的锂离子。一般来说，石墨负极由于在化成过程中负极形成SEI膜而消耗的不可逆锂离子约为6％，而含硅负极消耗的锂离子约为10～20％。这是含硅负极化成时首次效率低的主要原因。
为了解决这个问题，学术界及工业界对预锂化技术(或补锂技术)进行了大量的研究，文献《锂离子电池补锂技术》(《储能科学与技术》2021年5月，第10卷第3期)对该技术进行了综述。概括起来，目前主要的预锂化技术分为金属锂粉体预锂化、金属锂箔压延预锂、金属锂蒸镀预锂、正极添加剂预锂、电化学预锂等。
FMC公司在中国申请的专利(公告号CN1290209C)给出了一种金属锂粉预锂化的方法。但该方法对工艺要求极高，原料及过程的成本也非常高，故至今仍未得到产业化应用。
公布号为CN112310336A和CN112397682A的中国专利申请公开了金属锂箔压延预锂的装置和方法。该装置非常复杂，过程控制要求很高，环境控制要求苛刻且具有较大的安全隐患。同时，由于该方法使用特殊要求的润滑剂、脱模剂以及承载材料等，制造成本很高。
公布号为CN111430659A的中国专利申请公开了一种真空蒸镀的预锂化方法。该方法有金属锂蒸镀层薄而均匀的优点，但突出的缺点是真空蒸镀设备昂贵，很难得到产业 化应用。
关于正极补锂添加剂，目前主要有Li 2O、Li 2S、Li 3N、Li 4FeO 5、Li 6CoO 4、Li 2NiO 2、Li 4DHBN等等。但该方法预锂后残留的物质影响电池的能量密度及性能，同时也有许多副作用(如产气等)，至今仍未有一种添加剂能满足产业化应用的要求。
授权公告号为CN105845894B的专利给出了一种电化学湿法预锂化方法。该方法在实施过程中发现，对负极单片预锂再组装电池的方法仍然较复杂，需要进一步改进。公布号为CN110224182A的专利申请公开了一种电化学“湿法预锂”的改进方案，但该方法在预锂完成后有取出裸电芯的步骤，仍然不是最简单的工艺。公布号为CN110061299A的专利申请公开了一种电化学预锂的方法。该方法需要在电芯盖板上开一圆孔，把金属电极及金属锂放入电芯内部进行电化学预锂，然后取出。由于注液后开孔很难再进行密封，并有漏液的风险，所以该方法是很难进行产业化应用的。同时，该方法也有金属锂溶出及极片局部析锂的风险。公布号为CN111969266A的专利申请公开了一种圆柱型锂离子电池的自动预锂化方法。该方法仅限于圆柱型电池，把金属锂放入圆柱型电池的中心孔内并和负极壳体接触，完成自动预锂化。该方法在局部集中放置锂金属会导致电芯局部析锂，其产业化是仍有很大的局限性。同时，电化学预锂方法最大的问题在于其所需预锂时间特别长、预锂量较小、易于溶出金属锂颗粒等。
综上所述，目前的各种预锂化方法仍有这样或那样的缺点而未实现真正的产业化。因此，非常有必要寻找一种简单易行、成本低廉的预锂化方法，以便得到产业化应用。
发明内容
为解决电化学预锂化的时间长、预锂量低、预锂不均匀、金属锂颗粒溶出等技术问题，本发明的目的在于提供一种锂离子电池的预锂化方法，通过在电芯内部设置与负极连接的锂源复合片，能够实现负极的预锂化过程，使得电池具有较高的能量密度和较长的寿命。
为达到上述目的，本发明提供了一种锂离子电池的预锂化方法，该方法是一种易于产业化的、低成本的电化学预锂化方法，其包括：
在常规的锂离子电池制造过程中，在注入电解液之前，在芯体(例如卷芯或叠芯，以下同)中设置一个以上的锂源复合片，并且，至少一个所述锂源复合片与锂离子电池的负极极耳连接；
注入电解液，使电解液浸没所述锂源复合片，对负极进行预锂化。
根据本发明的具体实施方案，优选地，所述锂源复合片为锂箔和金属箔复合形成的 金属复合锂片(例如一层锂箔和一层金属箔的复合结构，或者两层锂箔分别设置在一层金属箔的两侧表面的“夹心”结构)，其中，所述金属箔可以是通常作为集流体的金属箔，包括铜箔、镍箔或铂箔等；或者，所述锂源复合片由电化学性质和金属锂相近的含锂物质制成。
根据本发明的具体实施方案，优选地，锂源复合片的形状可以根据需要进行设置，优选为片状、条状或带状，并可以带有极耳。
根据本发明的具体实施方案，优选地，所述锂源复合片贴近芯体的面(例如面向正极片或负极片的面)设有能阻挡锂离子通过的阻挡部件。通过设置阻挡部件，能够阻挡锂的局部析出。所述阻挡部件优选可以为金属箔或者绝缘胶带。当采用具有一层锂箔和一层金属箔的复合结构的锂源复合片时，可以将未设置锂箔的金属箔表面面向正极片或负极片，以实现阻挡。
所述锂源片的含锂量要适中，既不能过盈造成析锂，又不能不足而导致满足不了预锂量要求，同时也要考虑循环过程中的补锂需求。或者也可以说，所述锂源片的厚度要适中，既能放进放置的空间内，又要考虑预锂过程中不能脱落，同时在预锂化结束锂又能被完全消耗掉。在此原则下的任何厚度都在本专利保护范围之内。具体的，根据本发明的实施方案，优选所述锂源复合片的厚度不超过芯体的厚度。所述锂源复合片的厚度可以为5-500μm，优选为20-300μm，更优选为30-280μm，进一步优选为50-250μm，例如：50μm、80μm、150μm、200μm、220μm等所述范围内容的具体数值均可。
根据本发明的具体实施方案，优选地，所述锂源复合片贴近锂离子电池壳体的面设有绝缘多孔弹性材料。通过设置绝缘多孔弹性材料，一方面可以避免金属锂溶出及脱落，可以对芯体(叠芯或卷芯)进行弹性约束，提高锂离子电池内部的结构稳定性，另一方面可以保证预锂过程中有足够的电解液。所述锂源复合片可以采用弹性吸液材料进行包裹，更优选地，所述弹性吸液材料为隔膜材料。通过采用弹性材料进行包裹，在预锂化过程中，伴随着锂源复合片的消耗，弹性材料发生形变，能够填充消耗之后留下空间，提高结构稳定性。
根据本发明的具体方案，优选地，所述锂源复合片与负极极耳直接连接(例如焊接在一起)，或者，所述锂源复合片通过第三电极利用外接电路与正极或负极连接。即在本发明的技术方案中，锂源复合片与负极可以有两种连接方式：
第一种：锂源复合片与负极极耳直接连接，例如通过金属导线、金属片连接或直接焊接等方式实现。采用这种方式，注入电解液之后，负极立刻开始预锂化，无需外加负 载；该方式适合于预锂量较小的情况，例如预锂量为10％SOC以下的情况，例如预锂量为5％SOC。
第二种：锂源复合片连接第三电极，该第三电极利用外接电路与锂离子电池的负极极耳连接，以进行负极预锂化；在锂离子电池化成后，第三电极利用外接电路与锂离子电极的正极极耳连接以进行正极预锂化。通过这种方式可以通过外接电路来控制预锂化的进程，可以提高预锂化的速度，适合于预锂量较大的情况，而且，在锂离子电池的使用过程中，在有需要时，可以通过第三电极进行补充的预锂化。该方式适合于预锂量较大的情况，例如预锂量为10％SOC以上的情况。
根据本发明的具体实施方案，优选地，上述锂离子电池的预锂化方法包括：
在注入电解液之前，在锂离子电池中设置一个以上的锂源复合片和第三电极，并且，所述锂源复合片与所述第三电极连接；
注入电解液，使电解液浸没所述锂源复合片；
通过第三电极，利用外接电路将所述锂源复合片与负极极耳连接，对负极进行预锂化。
根据本发明的具体实施方案，优选地，电芯经过正常化成后，通过第三电极，利用外接电路将锂源复合片与正极极耳连接，对正极进行预锂化。即本发明的锂离子电池的预锂化方法还可以包括：
在注入电解液之前，在锂离子电池中设置一个以上的锂源复合片和第三电极，并且，锂源复合片与第三电极连接；
注入电解液，使电解液浸没锂源复合片；
电芯经过正常化成后，通过第三电极，利用外接电路将锂源复合片与正极极耳连接，对正极进行预锂化。
根据本发明的具体实施方案，优选地，当锂源复合片与负极极耳直接连接时，所述锂源复合片与所述负极极耳的连接位于锂离子电池的壳体内部。该锂源复合片与极耳之间的连接可以通过金属导线、金属片连接或焊接等方式实现，例如：通过超声焊接方式使锂源复合片与负极极耳连接；在电芯叠片过程中，可以将锂源复合片加入并同时将锂源复合片的金属箔(例如铜箔)与负极的铜箔焊接在同一极耳(Tab片)上，这样易于工业化成生产。当锂源复合片与负极极耳直接连接时，用于实现连接的金属导线、金属片或焊接位置等均位于壳体内部，这种情况下，连接位于壳体内部能够提高安全性，避免极耳延伸出壳体而导致的漏液等问题，同时生产工艺也大大简化。将锂源复合片与负 极的连接设于壳体内部，无需为锂源复合片设置极耳并使其延伸至壳体外部(当然为了便于连接，也可以为锂源复合片设置极耳，但是该极耳位于壳体内部，不会延伸至壳体外部)，在预锂化之后，锂源复合片中的锂会完全消耗，这种方式不会改变现有锂离子电池的结构，能够适用于更多类型的锂离子电池，而且本发明的这种锂离子电池预锂化方法具有良好的生产便利性，对现有生产线的调整较小，综合成本较低。当通过锂源复合片通过第三电极并利用外接电路与负极极耳或正极极耳连接时，第三电极等也可以位于壳体的内部，或者通过一定的位置延伸出锂离子电池的壳体。
根据本发明的具体实施方案，优选地，锂离子电池设有注液口，第三电极通过注液口利用外接电路与正极极耳或负极极耳连通，外接电路的充放电设备在放电状态下，电池发生预锂反应。在需要对负极、正极进行预锂化时，可以通过注液口将锂源复合片和负极极耳、正极极耳连接到充放电设备的放电状态下，使电解液在电芯内部流动，从而实现负极或正极的预锂化操作。其中注液口的布置位置无特殊要求，可以理解是现有技术中的常规布置方式。
根据本发明的具体实施方案，第三电极主要在预锂量需求较大时使用，优选地，第三电极可以设置在电芯壳体上，也可以采取通过注液口的临时预锂极耳的方式。
根据本发明的具体实施方案，优选地，当电池预锂量低于5％SOC时，不采取措施让电池内部的电解液保持动态；电池预锂量大于10％SOC时，采取措施让电池内部的电解液保持动态。即在负极和正极的预锂化过程中，采取一定的措施使电解液在锂离子电池的电芯内部流动，这样能够使局部溶出的锂离子通过流动的电解液而嵌入负极或正极极片中(即带动锂源复合片表面的锂离子流动而嵌入负极或正极极片内部)，这样既可以加大预锂速度和预锂量，又可以提高嵌锂的均匀性。这是本发明的关键点之一。上述“使电解液保持动态的措施”包括但不限于振动、转动、惰性气体搅动、电磁搅动等等，例如，通过转动锂离子电池、振动锂离子电池、向锂离子电池的电芯内部通入惰性气体、或者利用电磁对电解液进行搅动等方式实现电解液在锂离子电池的电芯内部流动。任何能够实现电解液的流动的方式均可以采用，并不限于上述列举的方式。
根据本发明的具体实施方案，除了锂源复合片之外，锂离子电池还可以包括其它一些常规部件，例如芯体和壳体，其中，芯体由正极片、负极片、隔膜组成，锂离子电池的芯体表面和/或其它可以放置的空间内分别设置有至少一个锂源复合片。正极片、负极片分别设有正极极耳、负极极耳，隔膜的材质、尺寸、设置方式可以参考锂离子电池领域的常规方式。
根据本发明的具体实施方案，所述锂离子电池可以包含由若干个相互串联或并联的芯体组成的芯体集合体，所述芯体集合体中的每个芯体的表面和/或其它可以放置的空间内分别设置有至少一个锂源复合片。
根据本发明的具体实施方案，本发明的预锂化方法所针对的锂离子电池可以是常规的叠芯电池、卷芯电池以及JTM(Jellyroll To Module)电池等。
根据本发明的具体实施方案，优选地，所述锂离子电池的芯体表面和/或其它可以放置的空间内分别设置有至少一个锂源复合片；或者，所述锂离子电池包含由若干个相互串联或并联的芯体组成的芯体集合体，所述芯体集合体中的每个叠芯的表面和/或其它可以放置的空间内分别设置有至少一个锂源复合片。
根据本发明的具体实施方案，优选地，所述锂离子电池的芯体为叠芯，所述叠芯的至少一侧表面设有至少一个锂源复合片，或者所述叠芯的两侧表面分别设有至少一个锂源复合片，或者在侧面以及其它可以放置的空间内放置锂源复合片。
根据本发明的具体实施方案，优选地，所述锂离子电池的芯体为卷芯，所述卷芯的侧面或顶面设有至少一个锂源复合片；优选地，所述锂源复合片包覆于所述卷芯的侧面，在预锂化过程中，包覆于卷芯侧面的锂源复合片能够均匀地扩散，均匀地为负极进行补锂。
根据本发明的具体实施方案，优选地，所述锂离子电池包含由若干个相互串联或并联的芯体组成的芯体集合体(例如JTM电池)，所述芯体集合体中的每个叠芯的至少一侧表面设有至少一个锂源复合片。在上述锂离子电池中，芯体可以为正极片、负极片组成的叠芯或卷芯。
根据本发明的具体实施方案，优选地，所述锂离子电池的芯体的负极为硅负极、石墨负极、钛酸锂负极、锡负极等负极中的一种或两种以上的组合；更优选地，所述负极为含硅负极，所述锂源复合片位于所述锂离子电池的壳体内为负极预留的膨胀空间之中。对于采用含硅负极的电池，考虑到含硅负极的芯体的膨胀，在外壳的大面和芯体之间需留一定的膨胀空间。本发明在进行锂离子电池的预锂化时，可以借助此空间放置锂源复合片(例如1片或2片锂源复合片)，通过这种方式，可以在不影响电池结构的情况下将锂源复合片设置于电池壳体之中，完成预锂化之后，锂源复合片完全消耗，预留的膨胀空间重新腾空，不会影响锂离子电池的正常使用。
根据本发明的具体实施方案，本发明所采用的电解液也可以是锂离子电池领域常用的电解液，其中，注入的电解液的量应确保能够使锂源复合片浸没于其中。
根据本发明的具体实施方案，优选地，通过第三电极对负极或正极预锂时需控制电流和电流制式。这样做一方面能够加快预锂速度，同时还能够控制预锂的均匀性以及避免局部析锂。
根据本发明的具体实施方案，优选地，在电芯化成过程中，由正极向负极嵌入一定量的锂，优选地，所述嵌锂量为10％～80％SOC，然后进行正极的预锂化。
根据本发明的具体实施方案，优选地，在通过第三电极实现正极的预锂化过程中，采用恒压放电的方式进行，电压优选为2.5V～3.5V，更优选为3.0V～3.4V，例如2.5V、2.6V、2.7V、2.8V、2.9V、3.0V、3.1V、3.2V、3.3V、3.4V、3.5V，或者由这些具体电压值中的两个分别作为上、下限组成的范围。
根据本发明的具体实施方案，优选地，正极的预锂化的电流为0.00001C～1C；更优选为0.0001C～0.5C。
根据本发明的具体实施方案，优选地，采用间歇的方式进行正极的预锂化。电流间歇的时间可以控制为1～3600秒，优选为300～1800秒，更优选为60～600秒，例如：60秒、100秒、200秒、300秒、400秒、500秒、600秒，或者由这些具体时间值中的两个分别作为上、下限组成的范围。
根据本发明的具体实施方案，优选地，在通过第三电极实现负极的预锂化过程中，采用恒压放电的方式进行，电压优选为0.1V～0.3V，更优选为0.2V。
根据本发明的具体实施方案，优选地，负极的预锂化的电流为0.00001C～1C；更优选为0.0001C～0.5C，进一步优选为0.01C～0.2C。
根据本发明的具体实施方案，优选地，采用间歇的方式进行负极的预锂化。电流间歇的时间可以控制为1～3600秒，优选为300-1800秒，优选为60～600秒，例如：60秒、100秒、200秒、300秒、400秒、500秒、600秒，或者由这些具体时间值中的两个分别作为上、下限组成的范围。
根据本发明的具体实施方案，优选地，所述预锂化的时间为8h～200h，例如10h、20h、30h、40h、50h、60h、70h、80h、90h、100h、110h、120h、130h、140h、150h、160h、170h、180h、190h、200h，或者由这些具体时间值中的两个分别作为上、下限组成的范围。
根据本发明的具体实施方案，锂源复合片的含锂量按照所需要的预锂量进行计算，适当考虑利用率。锂源复合片的厚度根据需要进行控制，要满足既能放进相应的空间内，又能够保证在预锂化过程中不会脱落的要求，同时在预锂化结束，锂源复合片中的锂应 能被完全消耗掉。
根据本发明的具体实施方案，优选地，每Ah所需要的理论预锂量Y的计算公式为：
Y＝1000nF/3.6A；
其中，n为Li计量个数，F为法拉第常数，A为锂的原子量，所需的Ah数等于损失的首效乘电芯的设计容量。
本发明还提供了一种高能量密度及长寿命的锂离子电池，其是由上述预锂化方法制备的。
本发明所提供的预锂化方法将锂源复合片与负极极耳直接连接，在注入电解液之后即发生预锂化反应，然后可以通过放电(例如通过外接电路连通正极、负极，恒压放电，使锂离子进入正极)实现正极预锂化，最终实现电池预锂化。采用本发明所提供的预锂化方法在进行负极的预锂化时可以不需要外加负载，在芯体浸润、化成、分容的过程中就可以完成预锂化。同时，锂源复合片与负极直接连接并且将该连接控制在锂离子电池的壳体之内还能够避免单独设置预锂化极耳并使其延伸至电池壳体之外而容易导致的安全问题。
现有的电化学预锂化方法都是采用极片预锂的方式，在完成预锂化之后再组装电池，由此导致电芯组装难度大、环境要求高、生产成本高等问题。本发明所提供的方法在完成电池组装之后进行，避免了预锂化对于电池组装的影响，能够解决电化学预锂化的时间长、预锂量低、预锂不均匀、金属锂颗粒溶出等问题，对于环境的要求较低，使得预锂化简单并易于产业化，且成本低廉。
采用本发明所提供的预锂化方法能够使锂源复合片中的锂在预锂化过程中完全消耗，不会残留于电池内部，避免了现有技术中锂源复合片长期存在于锂离子电池内部而带来的安全隐患。
采用本发明所提供的预锂化方法能够通过简单的方法达到预锂的目的。该方法基本不改变锂离子电池原有的工艺，只是在局部进行设备的改动，例如在芯体表面设置预锂化电解等锂源复合片以及增加预锂时使电解液流动的工装等。这些改动均很容易实现，易于工业化生产。
本发明所能够带来的有益效果包括：在现有锂离子电池工艺及设备改动不大的情况下，本发明所提供的预锂化方法就可以实现预锂化技术的产业化应用，且成本低廉。用本发明的预锂化方法制造的锂离子电池的容量可以提升5％以上，能量密度高(如三元电池可以做到370Wh/kg以上，磷酸铁锂电池可以做到230Wh/kg以上等)，循环寿命 长(如磷酸铁锂电池可以做到15000周以上等)，成本低(提高电量的同时降低了成本)，是一种非常有前途的革命性的锂离子电池工艺方法。
附图说明
图1为锂源复合片的结构示意图。
图2为实施例1提供的方形电池的结构示意图。
图3为实施例2提供的软包电池的结构示意图。
图4为实施例3提供的软包电池的结构示意图。
图5为实施例1的方形电池和对比例1的方形电池的循环寿命结果图。
具体实施方式
为了对本发明的技术特征、目的和有益效果有更加清楚的理解，现对本发明的技术方案进行以下详细说明，但不能理解为对本发明的可实施范围的限定。
本发明所采用的锂源复合片的结构可以如图1所示，其是由锂箔15复合在金属箔14的一侧或两侧表面形成的，并且，锂箔15的外部包裹有弹性吸液材料层16。
该锂源复合片可以复合到叠芯11的侧面(或其它任何有电解液的空间，例如：当采用卷芯时，锂源复合片可以复合到卷芯的顶部或者包覆在卷芯的侧面)，并且二者之间通过绝缘胶带13进行绝缘，并且，该锂源复合片通过金属箔14与负极极耳12连接。
该锂源复合片的制备过程以及与芯体的复合过程可以按照以下方式进行：
采用压延的方法把锂箔15复合到金属箔14上，金属箔14的厚度可以控制在4-100μm之间，锂箔15的厚度可以控制在0.01-10mm之间，锂箔15可以在单面也可以在双面；
采用弹性吸液材料对锂箔15进行包裹形成弹性吸液材料层16；
在叠芯11和锂源复合片的结合面上贴一层耐电解液腐蚀的绝缘胶带13；
然后通过叠芯11的极耳12与金属箔14连接，金属箔14的上端可以设有相应的极耳。
实施例1
本实施例提供了一种方形电池的预锂化方法，该方形电池的结构如图2所示。该方形电池包括：
芯体22，所述芯体22由正极片、负极片、隔膜通过卷绕或叠片工艺制成，其中，正极片为磷酸铁锂材料，负极片为石墨材料，二者分别设有正极极耳26、负极极耳24；
壳体21，该壳体21用于容装芯体22，壳体21上部设有正极连接部27和负极连接 部25。
该预锂化方法包括以下步骤：
在芯体22的一侧设置锂源复合片23，该锂源复合片23为如图1所示的结构的锂铜复合带，即一层铜箔和一层锂箔的复合体，锂箔的厚度为0.1mm，铜箔的厚度为4.5μm，该锂源复合片23与负极极耳24连接；在注入电解液前，所述锂铜复合带位于能够浸没于电解液的位置；
将设有锂源复合片的叠芯放入壳体21之内，在完成组装之后，向方形电池内部注入电解液，使其浸没锂源复合片，即开始预锂化；
预锂时间根据预锂量的要求进行控制，本实施例的预锂量为5％SOC，预锂时间控制在48小时；该预锂化时间在锂离子电池制造工艺的可接受范围之内；
预锂完成后即进行常规的化成、搁置、分容工艺，具体如下：
1、化成：以0.02C的电流充电4h，搁置10min，再以0.1C的电流充电2h；
2、老化：完成化成之后，静置老化12h；
3、分容：以0.33C的恒流充电，截至电压3.65V，然后以3.65V的恒压充电，截止电流0.05C；完成之后，搁置10min，再以0.33C的电流放电，截止电压2.0V，完成分容。
对比例1
本对比例提供了一种方形电池的常规制作方法，其与实施例1的区别在于不放置锂源片以及不进行预锂化，其他均相同。
对实施例1和对比例1制备的方形电池的相关性能进行检测，结果如表1所示。
表1
Figure PCTCN2022070955-appb-000001
根据表1的内容可以看出：采用实施例1的预锂化方法得到的锂离子电芯能够比对比例1高出约5％的容量，并且能够达到约2000周无衰减并趋于15000周的循环寿命，而对比例1的样品只有不到6000周的循环寿命(如图5所示)。
实施例2
本实施例提供了一种软包电池的预锂化方法，其中，该软包电池的结构如图3所示，其长度为360mm。该软包电池包括：
芯体32，该芯体32由正极片、负极片、隔膜通过叠片工艺制成，其中，正极片为三元材料NCM，负极片为硅600负极，二者分别设有正极极耳35、负极极耳34，设置在芯体32的同一侧；
壳体31，该壳体31为铝塑膜，用于容装芯体32。
该预锂化方法包括以下步骤：
在芯体32的一侧设置锂源复合片33，该锂源复合片33的位置应该保证其能够浸没于电解液；该锂源复合片33为如图1所示结构的锂铜复合带，即一层铜箔和一层锂箔的复合体，锂箔的厚度为0.1-0.2mm，铜箔的厚度为4.5μm，该锂铜复合带可以做成矩形、带状、U形等各种形状；
该锂源复合片33设有第三电极36，并通过注液口引出；将负极、正极和锂源复合片33连接即可进行对负极、正极的预锂，如图3所示；
将设有锂源复合片的芯体放入壳体内，在完成组装之后，向软包电池中注入电解液，使其浸没锂源复合片；
利用外接电路通过第三电极36将锂源复合片33与负极极耳34连接，对负极进行预锂化。
完成负极预锂化之后，即进行常规的化成工艺，具体如下：
以0.02C的电流充电2h，搁置10min，再以0.05C的电流充电2h，搁置10min，然后以0.1C的电流充电1h；
然后将第三电极36与正极极耳35连接，对正极进行预锂化，预锂化的电流控制在0.01C，可采取恒压、间歇放电的方式进行，电压为3.0V，间歇时间为60秒；
在预锂化过程中，采取对软包电池进行转动加振动的方式使芯体32内部的电解液流动，以加快预锂速度，并使得预锂化均匀地进行，其中，转动可采取正转180°和反转180°交替的方式进行，转动速度为5转/分钟，振动电机转速为1000转/分钟；具体转动采取转动180°停留60秒再转动180°的间歇方式进行。
预锂时间根据预锂量的要求进行控制，本实施例的预锂量为12％SOC，预锂化时间为96小时。
预锂完成后，对电芯进行常规的老化、分容工艺，具体如下：
1、老化：完成化成之后，静置老化24h；
2、分容：以0.33C的恒流充电，截至电压4.25V，然后以4.25V的恒压充电，截止电流0.05C；完成之后，搁置10min，再以0.33C的电流放电，截止电压2.0V，完成分 容。
对比例2
本对比例提供了一种软包电池的常规制作方法，其与实施例2的区别在于不放置锂源片以及不进行预锂化，其他均相同。
对实施例2和对比例2制备的方形电池的相关性能进行检测，结果如表2所示。
表2
Figure PCTCN2022070955-appb-000002
由表2的内容可以看出：采用实施例2的方法制造的锂离子电池有着较高的充放电首次效率，以及较高的容量发挥，电芯的比能量可达370Wh/kg，而对比例2的样品的比能量只有320Wh/kg。
实施例3
本实施例提供了一种软包电池的预锂化方法，其中，该软包电池的结构如图4所示，其长度为357mm，其结构与实施例2的软包电池类似，区别仅在于本实施例的软包电池是两端出极耳的软包电池。该软包电池包括：
芯体42，所述芯体42由正极片、负极片、隔膜通过叠片工艺制成，其中，正极为磷酸铁锂材料，负极为硅600负极材料，二者分别设有正极极耳45、负极极耳44，分别设置在芯体42的上下两端；
壳体41，所述壳体41为铝塑膜，用于容装芯体42。
锂源复合片、预锂化过程及老化、分容工艺同实施例2。
对比例3
本对比例提供了一种软包电池的常规制作方法，其与实施例3的区别在于不放置锂源片以及不进行预锂化，其他均相同。
对实施例3和对比例3制备的方形电池的相关性能进行检测，结果如表3所示。
表3
Figure PCTCN2022070955-appb-000003
由表3的内容可以看出：采用实施例3的方法制造的锂离子电池有着较高的充放电 首次效率(首次效率提高了19％，这是一个重大突破)，以及较高的容量发挥，电芯的比能量可达230.3Wh/kg，而对比例3的样品的比能量只有199.6Wh/kg。

Claims (21)

  1. 一种锂离子电池的预锂化方法，其特征在于：该方法包括：
    在常规的锂离子电池制造过程中，在注入电解液之前，在芯体中设置一个以上的锂源复合片，并且，至少一个所述锂源复合片与锂离子电池的负极极耳连接；
    注入电解液，使电解液浸没所述锂源复合片，对负极进行预锂化。
  2. 根据权利要求1所述的方法，其特征在于：所述锂源复合片为锂箔和金属箔复合形成的金属复合锂片。
  3. 根据权利要求2所述的方法，其特征在于：所述金属箔为铜箔、镍箔或铂箔。
  4. 根据权利要求2所述的方法，其特征在于：所述锂源复合片贴近芯体的面设有能阻挡锂离子通过的阻挡部件，所述锂源复合片贴近锂离子电池壳体的面设有绝缘多孔弹性材料。
  5. 根据权利要求4所述的方法，其特征在于：所述阻挡部件为金属箔或者绝缘胶带。
  6. 根据权利要求4所述的方法，其特征在于：所述锂源复合片的厚度不超过芯体的厚度。
  7. 根据权利要求6所述的方法，其特征在于，所述锂源复合片的厚度为5-500μm。
  8. 根据权利要求1-7任一项所述的方法，其特征在于：所述锂源复合片与负极极耳直接连接对负极进行预锂化，或者，
    所述锂源复合片连接第三电极，第三电极利用外接电路与锂离子电池的负极极耳连接以进行负极预锂化；锂离子电池化成后，第三电极利用外接电路与锂离子电池的正极极耳连接以进行正极预锂化。
  9. 根据权利要求8所述的方法，其特征在于：所述锂源复合片与负极极耳直接连接时，所述锂源复合片与所述负极极耳的连接位于锂离子电池的壳体内部。
  10. 根据权利要求9所述的方法，其特征在于：锂离子电池设有注液口，第三电极通过注液口利用外接电路与正极极耳或负极极耳连通，外接电路的充放电设备在放电状态下，电池发生预锂反应。
  11. 根据权利要求10所述的方法，其特征在于：电池预锂量低于5％SOC时，不采取措施让电池内部的电解液保持动态；电池预锂量大于10％SOC时，采取措施让电池内部的电解液保持动态。
  12. 根据权利要求11所述的方法，其特征在于：电解液保持动态的措施包括：转动锂离子电池，或者振动锂离子电池，或者向锂离子电池的电芯内部通入惰性气体，或者 利用电磁对电解液进行搅动。
  13. 根据权利要求8所述的方法，其特征在于：所述芯体由正极片、负极片、隔膜组成，锂离子电池的芯体表面和/或其它可以放置的空间内分别设置有至少一个锂源复合片；
    或者，所述锂离子电池包含由若干个相互串联或并联的芯体组成的芯体集合体，所述芯体集合体中的每个芯体的表面和/或其它可以放置的空间内分别设置有至少一个锂源复合片。
  14. 根据权利要求8所述的方法，其特征在于：所述芯体由正极片、负极片、隔膜组成；
    所述锂离子电池的芯体为叠芯，所述叠芯的至少一侧表面设有至少一个锂源复合片，或者所述叠芯的两侧表面分别设有至少一个锂源复合片，或者在侧面以及其它能够放置的空间内放置锂源复合片；
    或者，所述锂离子电池的芯体为卷芯，所述卷芯的侧面或顶面设有至少一个锂源复合片；优选地，所述锂源复合片包覆于所述卷芯的侧面；
    或者，所述锂离子电池包含由若干个相互串联或并联的芯体组成的芯体集合体，所述芯体集合体中的每个芯体的至少一侧表面设有至少一个锂源复合片。
  15. 根据权利要求8所述的方法，其特征在于：所述锂离子电池的芯体的负极为硅负极、石墨负极、钛酸锂负极、锡负极中的一种或两种以上的组合；优选地，所述负极为含硅负极，所述锂源复合片位于所述锂离子电池的壳体内为负极预留的膨胀空间之中。
  16. 根据权利要求11所述的方法，其特征在于：正极预锂化的电流为0.00001C～1C；优选为0.0001C～0.5C。
  17. 根据权利要求11所述的方法，其特征在于：正极预锂化过程中，采用恒压放电的方式进行，电压优选为2.5V～3.5V，更优选为3.0V～3.4V。
  18. 根据权利要求11所述的方法，其特征在于：采用间歇的方式进行正极预锂化，间歇的时间间隔为1～3600秒，优选为60～600秒。
  19. 根据权利要求11所述的方法，其特征在于：每Ah所需要的理论预锂量Y的计算公式为：
    Y＝1000nF/3.6A；
    其中，n为Li计量个数，F为法拉第常数，A为锂的原子量，所需的Ah数等于损 失的首效乘电芯的设计容量。
  20. 根据权利要求11所述的方法，其特征在于：所述预锂化的时间为8h～200h。
  21. 一种锂离子电池，其是采用权利要求1-20任一项所述的方法制备。
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