CN113300051A - Method for compounding pole piece and diaphragm of lithium ion battery and lithium ion battery - Google Patents
Method for compounding pole piece and diaphragm of lithium ion battery and lithium ion battery Download PDFInfo
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- CN113300051A CN113300051A CN202110240658.XA CN202110240658A CN113300051A CN 113300051 A CN113300051 A CN 113300051A CN 202110240658 A CN202110240658 A CN 202110240658A CN 113300051 A CN113300051 A CN 113300051A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/058—Construction or manufacture
- H01M10/0583—Construction or manufacture of accumulators with folded construction elements except wound ones, i.e. folded positive or negative electrodes or separators, e.g. with "Z"-shaped electrodes or separators
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/058—Construction or manufacture
- H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract
The invention provides a method for compounding a pole piece and a diaphragm tightly and supplementing lithium safely and thoroughly, aiming at solving the problems of untight compounding of the pole piece and the diaphragm of a battery cell and safety or inexhaustibility in a lithium supplementing process in the prior art, and the method comprises the steps of uniformly mixing lithium powder and a solvent to obtain a lithium powder mixture; coating the lithium powder mixture on the surface of the negative plate in a solvent molten state; coating a solvent which does not contain lithium powder in a molten state on at least one of the surface of the separator or the surface of the negative plate coated with the lithium powder mixture; sequentially laminating at least one negative plate coated with the ethylene carbonate, the diaphragm and the positive plate, and winding or laminating to form a battery cell; and carrying out hot pressing on the battery cell, and then cooling to obtain the battery cell compounded by the pole piece and the diaphragm. The invention not only solves the problem of loose battery core after winding and lamination, but also combines the pole piece diaphragm compounding and the negative pole lithium supplement together, and simplifies the assembly process.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a method for compounding a pole piece and a diaphragm of a lithium ion battery.
Background
Lithium ion batteries are currently the most widely used commercial battery technology due to their advantages of higher voltage, long cycle life, lower self-discharge rate, high energy density, and the like.
At present, the manufacturing process of the lithium ion battery mainly comprises winding and lamination. The winding process is high in production efficiency and simple in assembly process, but the tension in the winding process is not easy to control and is influenced by the tension of the pole piece diaphragm, the battery core made by winding is loose, the battery core needs to be compacted when the space utilization rate needs to be improved, but the stress at the bent part is too large due to the larger pressure, the material is easily dropped, the capacity of the battery is reduced, and the diaphragm can be punctured to cause the short circuit of the battery. The lamination process has the advantages that the pole pieces and the diaphragms are alternately arranged, so that the space utilization rate is improved, the consistency of the pole pieces is better, the stacking positions of the pole pieces are not easy to control in the lamination process, the pole pieces are easy to misplace, the stacking process is long in time consumption, the uniformity detection difficulty is high, and the pole pieces are easy to misplace in the assembly process of the laminated battery cell, so that the short circuit of the battery cell is caused.
In order to solve the above problems, a mainstream solution at present is to coat a certain amount of polymer material (mainly PVDF, PMMA, etc.) with a binding function in a specific manner on a diaphragm substrate (or a ceramic surface of a ceramic-coated diaphragm). The current common coating method is to use acetone as a solvent to dissolve PVDF to dip-coat the diaphragm, and then to heat and evaporate the solvent to coat the adhesive on the surface of the diaphragm. However, the coating mode easily causes uneven coating, so that the consistency of the diaphragm is poor, and the later cycle performance is poor; more serious, PVDF molecules may be locally aggregated too much to cause hole blocking, so that lithium is separated out in the process of charging and discharging of the battery, and huge potential safety hazards exist.
In addition, in the conventional lithium ion battery cell, due to the formation of the SEI film, a part of lithium ions are consumed in the first charge process, so that the consumed part of lithium ions cannot become active lithium capable of providing effective capacity for the battery cell.
At present, two different lithium supplementing modes exist in the industry, one mode is that lithium powder and a negative active material are stirred together, the lithium powder is added into a negative electrode, but the lithium powder can form a cavity inside a pole piece after being absorbed and dissolved by the negative active material, or the surface of the pole piece is uneven, the thickness is not uniform, and the safety problem is easily caused. The other is a lithium foil method, which is relatively safe, but is prone to the problem of incomplete reaction of lithium foil.
Disclosure of Invention
The invention provides a method for tightly compounding a pole piece and a diaphragm and safely and thoroughly supplementing lithium, aiming at solving the problems of untight compounding of the pole piece and the diaphragm and safety or halfway deficiency in a lithium supplementing process in the prior art.
In order to solve the technical problem, the invention provides a method for compounding a lithium ion battery pole piece and a diaphragm, which comprises the steps of providing a negative pole piece, a diaphragm, a positive pole piece, lithium powder and a solvent; uniformly mixing the lithium powder in the solvent to obtain a lithium powder mixture; coating the lithium powder mixture on the surface of the negative plate in a molten state of the solvent; coating a solvent which does not contain lithium powder in a molten state on at least one of the surface of the separator or the surface of the negative plate coated with the lithium powder mixture; sequentially laminating at least one of the negative electrode sheet, the diaphragm and the positive electrode sheet coated with the lithium powder-free solvent, and winding or laminating to form a battery cell; and carrying out hot pressing on the battery cell, and then cooling to obtain the battery cell compounded by the pole piece and the diaphragm.
Optionally, the solvent is an organic solvent or an inorganic solvent or a mixed system which does not react with the lithium powder, and more preferably an organic solvent with a melting point higher than 25 ℃.
Optionally, the solvent is at least one selected from ethylene carbonate, 1, 3-propane sultone and vinylene carbonate.
Optionally, in the lithium powder mixture, the mass ratio of the lithium powder to the solvent is 5:95-95: 5.
Optionally, the thickness of the coating of the lithium powder mixture coated on the surface of the negative electrode plate is 1-50 microns.
Optionally, the hot-pressing temperature of the battery core is higher than the melting point of the solvent, so that the solvent solidified on the surfaces of the positive plate, the negative plate and/or the diaphragm is melted, and the hot-pressing temperature of the battery core is preferably higher than 35 ℃ and lower than 100 ℃.
Optionally, the coating mode of the lithium powder mixture on the surface of the negative electrode sheet comprises spraying, roll coating or leaching the negative electrode sheet in the lithium powder mixture.
Optionally, the coating step of the lithium powder-free solvent on the surface of the positive plate or the negative plate is performed before rolling the positive plate and the negative plate after rolling, or after rolling the positive plate and the negative plate by a winding machine or a laminating machine.
Optionally, the coating mode of the solvent without lithium powder comprises a full coating mode, a line coating mode or a point coating mode.
Optionally, after the step of coating the lithium powder-free solvent on at least one of the surface of the positive electrode sheet, the surface of the separator or the surface of the negative electrode sheet coated with the lithium powder mixture, a step of cooling and solidifying the lithium powder-free solvent is further included.
Optionally, the cooling is performed by a cold air device or natural cooling, and the cooling temperature is below the melting point temperature of the solvent and the ethylene carbonate.
In order to solve the technical problems, in some embodiments, the invention further provides a lithium ion battery prepared by the method for compounding the lithium ion battery pole piece and the diaphragm.
The embodiment provided by the invention has the beneficial effects that: (1) the lithium ion battery pole piece and the diaphragm only adopt the solvent without adding the binder in the compounding process, are hot-pressed in the melting state of the solvent, and realize the close compounding between the pole piece and the diaphragm in the cooling and solidifying state of the solvent, thereby not only solving the problem of loose battery core after winding or lamination, but also simplifying the assembly process; (2) the lithium ion battery pole piece and the diaphragm only adopt the solvent in the compounding process, so that the problems of poor consistency, poor later cycle performance, thermal shrinkage of the diaphragm in the heating process caused by uneven coating caused by coating a binder such as PVDF on the surface of the pole piece or the diaphragm in the prior art, and more serious hole blocking caused by local excessive aggregation of the binder such as PVDF molecules, lithium precipitation of the battery in the charging and discharging process, huge potential safety hazard and the like can be avoided; (3) the lithium ion battery pole piece and the diaphragm of the invention introduce the negative pole lithium supplement in the compounding process, and the compounding of the pole piece diaphragm and the negative pole lithium supplement are combined together, thereby simplifying the process; (4) after the pole piece and the diaphragm are compounded, metal dust can be prevented from falling in the assembling process, and the short circuit rate of the battery in the assembling process is reduced.
Drawings
FIG. 1 is a schematic diagram of a composite of a pole piece and a separator according to an embodiment of the present invention;
FIG. 2 is a schematic view of a composite of a pole piece and a separator according to another embodiment of the present invention;
FIG. 3 is a schematic view of a composite of a pole piece and a separator according to another embodiment of the present invention;
FIG. 4 is a schematic diagram of a full coating of the surface of a pole piece according to another embodiment of the present invention;
FIG. 5 is a schematic illustration of a wire coating of the surface of a pole piece according to another embodiment of the present invention;
FIG. 6 is a schematic view of a spot coating of the surface of a pole piece according to another embodiment of the present invention;
the reference numerals in the specification are as follows:
1. a negative plate; 2. a positive plate; 3. a diaphragm; 4. a lithium powder mixture; 5. solvent without lithium powder.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
As shown in fig. 1 to 3, in one embodiment, the present invention provides a method for compounding a lithium ion battery electrode sheet and a separator, comprising providing a negative electrode sheet 1, a separator 3 and a positive electrode sheet 2, and lithium powder and a solvent; uniformly mixing the lithium powder in the solvent to obtain a lithium powder mixture; heating the lithium powder mixture to melt the solvent, and then coating the lithium powder mixture 4 on the surface of the negative electrode sheet 1; additionally adding a solvent without lithium powder and melting the solvent, and coating the solvent 5 without lithium powder on at least one of the surface of the positive plate 2, the surface of the diaphragm 3 or the surface of the negative plate 1 coated with the lithium powder mixture 4; sequentially laminating at least one of the negative electrode sheet 1, the diaphragm 3 and the positive electrode sheet 2 coated with the solvent 5 without containing lithium powder, and winding or laminating to form a battery cell; and carrying out hot pressing on the battery cell, and then cooling to obtain the battery cell compounded by the pole piece and the diaphragm.
As shown in fig. 2, in some embodiments, the molten solvent 5 not containing lithium powder is coated on both upper and lower surfaces of the positive electrode sheet 2; as shown in fig. 3, in some embodiments, the molten solvent 5 containing no lithium powder is coated on both upper and lower surfaces of the separator 3; in other embodiments, as shown in fig. 4, the molten solvent 5 containing no lithium powder is coated on both upper and lower surfaces of the positive electrode sheet 2 and the separator 3, respectively.
The negative electrode sheet, the separator and the positive electrode sheet are not particularly limited, and may be prepared by a method known in the art. In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material coated on the negative electrode current collector, and the negative electrode current collector may employ a current collector conventional in the art, such as a copper foil. The at least one negative active material may be any active material known in the art. The negative active material may include, for example, an intercalation material (e.g., carbon, graphite, and/or graphene), an alloying/dealloying material (e.g., silicon oxide, tin, and/or tin oxide), a metal alloy or compound (e.g., Si-Al and/or Si-Sn), and/or a conversion material (e.g., manganese oxide, molybdenum oxide, nickel oxide, and/or copper oxide). The negative active materials may be used alone or mixed together to form a multi-phase material (such as Si-C, Sn-C, SiOx-C, SnOx-C, Si-Sn, Si-SiOx, Sn-SnOx, Si-SiOx-C, Sn-SnOx-C, Si-Sn-C, SiOx-SnOx-C, Si-SiOx-Sn, or Sn-SiOx-SnOx). In some embodiments, the at least one active material of the negative electrode may comprise synthetic graphite, natural graphite, hard carbon, soft carbon, graphene, mesoporous carbon, silicon oxide, tin oxide, germanium, lithium titanate, mixtures or composites thereof.
In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material coated on the positive electrode current collector, and the positive electrode current collector may employ a current collector conventional in the art, such as an aluminum foil. At least one positive electrode active material may beThe positive active material may include, for example, a metal oxide, a metal sulfide, or a lithium metal oxide, as any active material known in the art. The lithium metal oxide may be, for example, lithium nickel manganese cobalt oxide (NMC), Lithium Manganese Oxide (LMO), lithium iron phosphate (LFP), Lithium Cobalt Oxide (LCO), Lithium Titanate (LTO), and/or lithium nickel cobalt aluminum oxide (NCA). In some embodiments, the positive electrode active material may include, for example, a layered transition metal oxide (e.g., LiCoO)2(LCO)、Li(NiMnCo)O2(NMC) and/or LiNi0.8Co0.15Al0.05O2(NCA)), spinel manganese oxide (e.g. LiMn)2O4(LMO) and/or LiMn1.5Ni0.5O 4(LMNO)) or olivine (e.g. LiFePO)4). The cathode active material may comprise sulfur or a sulfur-containing material, such as lithium sulfide (Li)2S) or other sulfur-based material, or mixtures thereof.
The separator functions to electrically isolate two electrodes (e.g., a positive electrode tab and a negative electrode tab) adjacent to opposite sides of the separator while allowing ionic communication between the two adjacent electrodes. In some embodiments, the septum may comprise a polymeric material. For example, the separator may comprise a cellulosic material (e.g., paper), a Polyethylene (PE) material, a polypropylene (PP) material, and/or a composite of polyethylene and polypropylene.
In the invention, the solvent has the functions of hot pressing in the melting state of the solvent and realizing the tight compounding between the pole piece and the diaphragm in the cooling and solidifying state of the solvent, so as to solve the problem of loose battery cell after winding or lamination; the solvent is mixed with lithium powder to form a lithium powder mixture, and the lithium powder mixture is coated on the surface of the negative plate to supplement a lithium source. In some embodiments, the solvent is an organic solvent or an inorganic solvent or a mixed system that does not react with the lithium powder. More preferably, the organic solvent has a melting point higher than 25 ℃, so that the battery core assembly and other works can be completed in a room temperature environment without changing the ambient temperature in the battery assembly process. In some embodiments, the solvent is selected from at least one of ethylene carbonate, 1, 3-propane sultone, vinylene carbonate. The solvent is more preferably ethylene carbonate, and may be commercially available or prepared by conventional methods. In some embodiments, the ethylene carbonate is an electrolyte solvent applied to the current commercial lithium ion battery, has high electrochemical stability, has a melting point of 35-38 ℃, a boiling point of 238 ℃, is solid at normal temperature, can be hot-melted when heated to above 35 ℃, and has a viscosity of 1.9 mpa.s.
In some embodiments, the ambient temperature of the formulation is lower than the melting point of the solvent, so that the lithium powder mixture is heated to melt the solvent before the lithium powder mixture is coated on the surface of the negative electrode sheet, and the solvent without lithium powder is heated to melt the solvent before the solvent without lithium powder is coated on the surface of the positive electrode sheet, so as to facilitate coating. In some embodiments, the ambient temperature of the batch is above the melting point of the solvent, so that the solvent in the molten state can be directly edible without heating for mixing with the lithium powder, and subsequent coating.
The lithium powder is not particularly limited, and in some embodiments, the lithium powder may be metal lithium powder or metal lithium particles, wherein the metal lithium powder and the metal lithium particles are commercially available, and the particle size thereof is not particularly limited and may be appropriately adjusted according to actual needs. The lithium powder serves as a supplementary lithium source for supplementing lithium ions consumed during the formation of the SEI film.
In some embodiments, the coating of the lithium powder mixture on the surface of the negative electrode sheet includes spraying, roll coating, or leaching the negative electrode sheet in the lithium powder mixture. The solvent may be applied to the surface of the positive electrode sheet in any of the above-described manners.
In some embodiments, the coating step of the lithium powder-free solvent on the surface of the positive or negative electrode sheet is performed before the positive or negative electrode sheet is rolled, or after the positive or negative electrode sheet is unwound by a winder or a laminator. As shown in fig. 4 to 6, in some embodiments, the hot-melt lithium powder-free solvent coating manner includes any one of a full coating manner, a line coating manner, or a dot coating manner, which may be selected according to actual needs, wherein the full coating (as shown in fig. 2) is performed by coating a large area of the lithium powder-free solvent 5 on the surface of the positive electrode sheet 2, the separator 3, or the negative electrode sheet coated with the lithium powder mixture 4; the line coating (as shown in fig. 3) is to intermittently coat a solvent 5 without lithium powder on the surface of the positive electrode sheet 2, the separator 3 or the negative electrode sheet coated with the lithium powder mixture 4, and the coating pattern shape includes, but is not limited to, straight stripes, curved stripes, mesh-shaped stripes, and the like; the spot coating (as shown in fig. 4) is to perform discrete spot coating of a solvent 5 containing no lithium powder on the surface of the positive electrode sheet 2, the separator 3, or the negative electrode sheet coated with the lithium powder mixture 4.
The hot-pressing temperature of the battery core is higher than 35 ℃, so that the positive plate, the diaphragm and/or the ethylene carbonate solidified on the surface of the negative plate are melted, the hot-pressing compounding of the plate and the diaphragm is facilitated, and the compound strength and the bonding force after cooling and solidification are improved. In some embodiments, the hot-pressing temperature of the battery cell is lower than 100 ℃, so that damage to the battery cell caused by overhigh hot-pressing temperature is prevented.
In some embodiments, after the step of coating the melted ethylene carbonate on at least one of the surface of the positive electrode sheet, the surface of the separator, or the surface of the negative electrode sheet coated with the lithium powder mixture, the step of cooling and solidifying the ethylene carbonate is further included.
In some embodiments, the cooling is performed by a cold air device or natural cooling, the temperature of the cooling is below the melting point temperature of the solvent and the ethylene carbonate, and the solvent on the pole piece is rapidly solidified by air cooling, or the tape-moving time of the pole piece is prolonged, so that the pole piece is naturally cooled and solidified.
After the battery core compounded by the pole pieces and the diaphragm is prepared by the embodiment, the battery is assembled. The invention has no special limitation on the assembly of the battery, and can adopt the conventional assembly mode in the field, such as providing a battery shell, arranging the battery core into the battery shell, completing the subsequent conventional assembly steps of liquid injection, formation, sealing, capacity grading and the like, and finally preparing the lithium ion battery.
The present invention will be described in further detail with reference to examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1
Preparation of positive plate
LiNi, a positive electrode active material, was mixed in a mass ratio of 93:4:30.7Co0.1Mn0.2O2Conductive carbon black Super-P, and a binder polyvinylidene fluoride (PVDF), which are then dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. And uniformly coating the slurry on two sides of the aluminum foil, and drying, rolling and vacuum drying to obtain the positive plate. Then, ethylene carbonate in a molten state was coated on the surface of the positive electrode sheet at a temperature of 60 ℃ to a coating thickness of 5 μm, followed by cooling to room temperature.
Preparation of negative plate
Mixing a negative electrode active material, conductive carbon black Super-P, Styrene Butadiene Rubber (SBR) and carboxymethyl cellulose (CMC) as binders according to a mass ratio of 94:1:2.5:2.5, and then dispersing the materials in deionized water to obtain negative electrode slurry. And coating the slurry on two sides of the copper foil, and drying, rolling and vacuum drying to obtain the negative plate.
According to the weight ratio of 30: and 70, uniformly mixing the lithium powder and the ethylene carbonate according to the mass ratio to obtain a lithium powder mixture. Then, the lithium powder mixture in a molten state was coated on the surface of the negative electrode sheet at a temperature of 60 ℃ to a coating thickness of 20 μm, and then cooled to room temperature.
Then, ethylene carbonate in a molten state was coated on the surface of the positive electrode sheet at a temperature of 60 ℃ to a coating thickness of 5 μm, followed by cooling to room temperature.
Preparation of the separator
Then, ethylene carbonate in a molten state was coated on the surface of the separator at a temperature of 60 c to a coating thickness of 3 μm, and then cooled to room temperature.
Preparation of cell
At the room temperature of 25 ℃, a diaphragm is placed between a positive plate and a negative plate, then a sandwich structure consisting of the positive plate, the negative plate and the diaphragm is wound to form an electric core, then the electric core is subjected to hot pressing at 60 ℃ so that the positive plate, the negative plate and the diaphragm in the electric core are bonded together under the action of the hot pressing, then air cooling is carried out to the room temperature, then the electric core is placed into an aluminum-plastic composite membrane shell, vacuum baking is carried out for 48 hours at the temperature of 75 ℃, liquid injection formation is carried out, and a finished product battery is obtained.
Example 2
Preparation of positive plate
LiNi, a positive electrode active material, was mixed in a mass ratio of 93:4:30.7Co0.1Mn0.2O2Conductive carbon black Super-P, and a binder polyvinylidene fluoride (PVDF), which are then dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. And uniformly coating the slurry on two sides of the aluminum foil, and drying, rolling and vacuum drying to obtain the positive plate.
Preparation of negative plate
Mixing a negative electrode active material, conductive carbon black Super-P, Styrene Butadiene Rubber (SBR) and carboxymethyl cellulose (CMC) as binders according to a mass ratio of 94:1:2.5:2.5, and then dispersing the materials in deionized water to obtain negative electrode slurry. And coating the slurry on two sides of the copper foil, and drying, rolling and vacuum drying to obtain the negative plate.
According to the weight ratio of 30: and 70, uniformly mixing the lithium powder and the vinylene carbonate according to the mass ratio to obtain a lithium powder mixture. Then, the lithium powder mixture in a molten state was coated on the surface of the negative electrode sheet at a temperature of 60 ℃ to a coating thickness of 20 μm, and then cooled to room temperature.
Preparation of the separator
Then, 1, 3-propane sultone in a molten state was coated on the surface of the separator at a temperature of 60 ℃ to a coating thickness of 3 μm, and then cooled to room temperature.
Preparation of cell
At the room temperature of 25 ℃, a diaphragm is placed between a positive plate and a negative plate, then a sandwich structure consisting of the positive plate, the negative plate and the diaphragm is wound to form an electric core, then the electric core is subjected to hot pressing at 60 ℃ so that the positive plate, the negative plate and the diaphragm in the electric core are bonded together under the action of the hot pressing, then air cooling is carried out to the room temperature, then the electric core is placed into an aluminum-plastic composite membrane shell, vacuum baking is carried out for 48 hours at the temperature of 75 ℃, liquid injection formation is carried out, and a finished product battery is obtained.
Example 3
Preparation of positive plate
Mixing the materials according to the mass ratio of 93:4:3LiNi, a polar active material0.7Co0.1Mn0.2O2Conductive carbon black Super-P, and a binder polyvinylidene fluoride (PVDF), which are then dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. And uniformly coating the slurry on two sides of the aluminum foil, and drying, rolling and vacuum drying to obtain the positive plate. Then, vinylene carbonate in a molten state was coated on the surface of the positive electrode sheet at a temperature of 40 ℃ to a coating thickness of 5 μm, and then cooled to room temperature.
Preparation of negative plate
Mixing a negative electrode active material, conductive carbon black Super-P, Styrene Butadiene Rubber (SBR) and carboxymethyl cellulose (CMC) as binders according to a mass ratio of 94:1:2.5:2.5, and then dispersing the materials in deionized water to obtain negative electrode slurry. And coating the slurry on two sides of the copper foil, and drying, rolling and vacuum drying to obtain the negative plate.
According to the weight ratio of 30: 70, uniformly mixing the lithium powder and the 1, 3-propane sultone to obtain a lithium powder mixture. Then, the lithium powder mixture in a molten state was coated on the surface of the negative electrode sheet at a temperature of 40 ℃ to a coating thickness of 20 μm, and then cooled to 15 ℃.
Then, vinylene carbonate in a molten state was coated on the surface of the negative electrode sheet at a temperature of 40 ℃ to a coating thickness of 5 μm, and then cooled to room temperature.
Preparation of cell
Placing a three-layer isolating membrane with the thickness of 15 mu m between a positive plate and a negative plate at the room temperature of 15 ℃, then winding a sandwich structure consisting of the positive plate, the negative plate and a diaphragm to form an electric core, then carrying out hot pressing at 40 ℃ on the electric core to bond the positive plate, the negative plate and the diaphragm in the electric core together under the action of the hot pressing, then cooling to 15 ℃, then placing the electric core into an aluminum-plastic composite membrane shell, carrying out vacuum baking at 75 ℃ for 48 hours, injecting liquid and forming to obtain the finished battery.
Comparative example 1
Preparation of positive plate
LiNi, a positive electrode active material, was mixed in a mass ratio of 93:4:30.7Co0.1Mn0.2O2Conductive carbon blackSuper-P and a binder polyvinylidene fluoride (PVDF), which are then dispersed in N-methyl-2-pyrrolidone (NMP), to obtain a positive electrode slurry. And uniformly coating the slurry on two sides of the aluminum foil, and drying, rolling and vacuum drying to obtain the positive plate.
Preparation of negative plate
Mixing a negative electrode active material, conductive carbon black Super-P, Styrene Butadiene Rubber (SBR) and carboxymethyl cellulose (CMC) as binders according to a mass ratio of 94:1:2.5:2.5, and then dispersing the materials in deionized water to obtain negative electrode slurry. And coating the slurry on two sides of the copper foil, and drying, rolling and vacuum drying to obtain the negative plate.
Preparation of the separator
PVDF was dissolved in an acetone solvent at a mass ratio of 90:10, a three-layer separator 15 μm thick was dip-coated, and then the solvent was evaporated by heating to coat the binder on the surface of the separator.
Preparation of cell
And placing a diaphragm between the positive plate and the negative plate at the room temperature of 25 ℃, then winding a sandwich structure consisting of the positive plate, the negative plate and the diaphragm to form a battery core, then placing the battery core into an aluminum-plastic composite membrane shell, baking the battery shell in vacuum at 75 ℃ for 48 hours, injecting liquid and forming to obtain the finished battery.
[ test of cycle Performance ]
And (3) charging the prepared lithium ion battery to 4.2V by using a current of 1C at a constant current, then charging the lithium ion battery at a constant current and a constant voltage until the current is reduced to 0.05C, then discharging the lithium ion battery to 3.0V by using a current of 1C at a constant current, circulating the lithium ion battery, recording the 1 st discharge capacity and the last discharge capacity, and measuring the initial battery volume of the battery and the volume of the battery after 1000 cycles.
The capacity retention for the high temperature cycle was calculated as follows:
capacity retention rate is the last discharge capacity/1 st discharge capacity × 100%.
The test results are shown in Table 1
TABLE 1
As shown in table 1 test data:
in embodiments 1 to 3, the lithium ion battery pole piece and the diaphragm of the invention only adopt a solvent and are not added with a binder in the compounding process, the hot pressing is carried out in the molten state of the solvent, and the close compounding between the pole piece and the diaphragm is realized in the cooling and solidifying state of the solvent, so that the problems of poor later cycle performance caused by uneven coating caused by coating the binder PVDF on the surface of the diaphragm in comparative example 1, or lithium precipitation of the battery in the charging and discharging process due to hole blocking caused by the fact that PVDF molecules may be locally aggregated too much, and huge potential safety hazards and the like are avoided; in addition, compared with comparative example 1, the lithium ion battery pole piece and the diaphragm of the embodiments 1-3 of the invention introduce negative electrode lithium supplement in the compounding process, and the capacity retention rate of the battery is further improved by combining the pole piece diaphragm compounding and the negative electrode lithium supplement together.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (13)
1. A method for compounding a lithium ion battery pole piece and a diaphragm is characterized by comprising the following steps:
providing a negative plate, a diaphragm, a positive plate, lithium powder and a solvent;
uniformly mixing the lithium powder in the solvent to obtain a lithium powder mixture;
coating the lithium powder mixture on the surface of the negative plate in a molten state of the solvent;
coating a solvent which does not contain lithium powder in a molten state on at least one of the surface of the separator or the surface of the negative plate coated with the lithium powder mixture;
sequentially laminating at least one of the negative electrode sheet, the diaphragm and the positive electrode sheet coated with the lithium powder-free solvent, and winding or laminating to form a battery cell;
and carrying out hot pressing on the battery cell, and then cooling to obtain the battery cell compounded by the pole piece and the diaphragm.
2. The method for compounding the lithium ion battery pole piece and the separator according to claim 1, wherein the solvent is an organic solvent or an inorganic solvent or a mixed system which does not react with lithium powder.
3. The method for compounding the lithium ion battery pole piece and the separator according to claim 2, wherein the solvent is an organic solvent having a melting point higher than 25 ℃.
4. The method for compounding the pole piece and the separator of the lithium ion battery according to claim 1, wherein the solvent is at least one selected from ethylene carbonate, 1, 3-propane sultone and vinylene carbonate.
5. The method for compounding the lithium ion battery pole piece and the diaphragm of claim 1, wherein the mass ratio of the lithium powder to the solvent in the lithium powder mixture is 5:95-95: 5.
6. The method for compounding the lithium ion battery pole piece and the separator according to claim 1, wherein the coating thickness of the lithium powder mixture coated on the surface of the negative pole piece is 1-50 micrometers.
7. The method of claim 1, wherein the hot-pressing temperature of the battery core is higher than the melting point of the solvent, so that the solvent solidified on the surface of the positive plate, the negative plate and/or the separator is melted.
8. The method of claim 1, wherein the cell is hot pressed at a temperature of less than 100 ℃.
9. The method of claim 1, wherein the coating of the lithium powder mixture on the surface of the negative electrode sheet comprises spraying, roll coating, or leaching the negative electrode sheet in the lithium powder mixture.
10. The method for compounding the lithium ion battery pole piece and the diaphragm of claim 1, wherein the step of coating the lithium powder-free solvent on the surface of the negative pole piece comprises the steps of coating the negative pole piece with the lithium powder-free solvent before rolling the negative pole piece after rolling, or after unreeling the negative pole piece by a winder or a laminator; the coating mode comprises a full coating mode, a line coating mode or a point coating mode.
11. The method for compounding the lithium ion battery pole piece and the separator according to claim 1, further comprising a step of cooling and solidifying the lithium powder-free solvent after the step of coating the lithium powder-free solvent on at least one of the surface of the separator or the surface of the negative pole piece coated with the lithium powder mixture.
12. The method for compounding the lithium ion battery pole piece and the diaphragm according to claim 1, wherein the cooling is performed by a cold air device or natural cooling, and the temperature of the cooling is below the melting point temperature of the solvent.
13. A lithium ion battery, characterized in that, the lithium ion battery is prepared by the method for compounding the lithium ion battery pole piece and the diaphragm of any one of claims 1 to 12.
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