CN112271271B - Negative plate, preparation method, lithium ion battery core, lithium ion battery pack and application of lithium ion battery pack - Google Patents
Negative plate, preparation method, lithium ion battery core, lithium ion battery pack and application of lithium ion battery pack Download PDFInfo
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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- 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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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/04—Processes of manufacture in general
- H01M4/0402—Methods of deposition of the material
- H01M4/0404—Methods of deposition of the material by coating on electrode collectors
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/139—Processes of manufacture
- H01M4/1393—Processes of manufacture of electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/621—Binders
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- H—ELECTRICITY
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
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- H—ELECTRICITY
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention discloses a negative plate and a preparation method thereof, a lithium ion cell, a lithium ion battery pack and application thereof. The structure of the negative plate can improve the bonding strength of the negative electrode and the negative current collector and reduce the increase of contact resistance in the charging and discharging process; the lithium ion battery has the advantages that the lithium precipitation on the surface of the negative electrode under the condition of large-current charging is relieved, and the side reaction of the negative electrode and the electrolyte is relieved, so that the cycle life and the rate characteristic of the lithium ion battery cell are improved; effectively improving the phenomenon that the negative pole is stuck to the roller in the rolling process.
Description
Technical Field
The invention relates to the field of energy storage devices, in particular to a negative plate, a preparation method of the negative plate, a lithium ion battery cell, a lithium ion battery pack and application of the lithium ion battery pack.
Background
At present, the commercial lithium ion battery cathode material mainly adopts graphite cathode materials, but the theoretical specific capacity is only 372mAh/g, and the requirements of future development of lithium ion batteries with higher specific energy and high power density cannot be met. Therefore, it is an important development direction to find a high specific capacity negative electrode material to replace carbon. The silicon material has the highest lithium storage capacity (the theoretical specific capacity is 4200mAh/g) and abundant resources, so that the silicon material is considered to have the most potential and is expected to become the next generation lithium ion battery negative electrode material. However, structural destruction of the silicon material and pulverization of the material due to a large volume change during lithium intercalation/deintercalation may result in structural destruction of the electrode and exfoliation of the active layer from the current collector, resulting in loss of electrical contact of the silicon active component. In addition, the continuous generation of SEI film can be caused by the pulverization and huge volume change of the material, so that the electrochemical cycle stability of the battery is poor, and the large-scale application of the silicon material as the lithium ion battery cathode material is hindered.
In order to solve the problems of silicon cathode materials in application, researchers mainly use a means of combining nano-crystallization and compounding of silicon and a method of constructing a multi-element multi-layer composite material to solve various problems of silicon in practical application. However, the silicon-based composite negative electrode material still has large volume expansion in the practical application process, so that large internal stress exists in the pole piece, and the pole piece is easy to pulverize and fall off from a current collector in the circulation process, thereby losing electrical contact and losing activity. Meanwhile, in order to pursue higher volume energy density, the cathode needs to reach higher compaction density, which inevitably affects the rate performance of the battery, if the cathode cannot bear large-current charging, ions can be directly reduced and separated out on the surface of the cathode instead of being embedded into the cathode active material when the battery is rapidly charged, and meanwhile, a large amount of byproducts can be generated on the surface of the cathode when the battery is rapidly charged, thereby affecting the cycle life and the safety of the battery. Therefore, the key for improving the quick charging performance of the battery lies in the design of the negative active material and the negative pole piece.
Patent document CN 109950470 a discloses a negative electrode sheet, which includes a negative electrode current collector and a negative electrode membrane containing a negative electrode active material, which is disposed on at least one surface of the negative electrode current collector, wherein a porous inorganic dielectric layer is disposed on a surface of the at least one negative electrode membrane on a side away from the current collector; the thickness of the porous inorganic dielectric layer is 20 nm-2000 nm, and the porous inorganic dielectric layer does not contain a binder. The negative pole piece can relieve lithium precipitation on the surface of the negative pole under the condition of high-current charging, stabilize a negative pole interface and reduce the side reaction of the negative pole and electrolyte, thereby prolonging the cycle life of the battery cell, reducing the short circuit risk in the battery cell and prolonging the high-temperature service life of the battery cell. However, this solution has the following drawbacks: 1) the porous inorganic dielectric layer is prepared by adopting gas phase methods such as an atomic layer deposition method, a chemical vapor deposition method, a physical vapor deposition method, a thermal evaporation method and the like, the cost is higher, and continuous large-scale production is difficult to realize; 2) the porous dielectric layer is metal oxide and the like, and can generate side reaction with lithium ions, so that the coulomb efficiency of the first circumference of the battery cell is influenced, and the capacity loss of the battery cell is caused; 3) the porous dielectric layer is not suitable for estimating a negative electrode system with larger expansion such as silicon base, and due to no adhesive, the porous dielectric layer is cracked and falls off due to repeated expansion and contraction of the active layer in the charging and discharging processes, so that the effect of the porous dielectric layer is influenced, and even potential safety hazards are caused.
In summary, the following problems exist in the practical application process of the current silicon-based negative electrode material: (1) the volume expansion is large, so that the active layer and the current collector are peeled off, the contact resistance is increased, and the polarization is increased; (2) in order to achieve a higher energy density, the high compaction density of the negative electrode is often higher, and lithium precipitation is likely to occur on the surface of the negative electrode close to the side of the diaphragm in a high-current charging state, so that the safety is deteriorated and the cycle stability is reduced; (3) the silicon-containing negative electrode binder has strong hydrophilicity, the binder is easy to float upwards in the coating and drying process, the stripping force of a pole piece is reduced, the phenomenon of roller adhesion is easy to occur during rolling, and the quality and the production yield of the negative electrode piece are reduced.
Therefore, it is necessary to provide a new silicon-containing negative electrode plate to meet the requirements of the new generation of high specific energy lithium ion battery on high energy density, fast charge characteristic, cycle life and safety, to solve the problems of negative electrode lithium precipitation, active layer and current collector peeling and the like under the condition of high current charge and discharge of the high specific energy battery, and to greatly improve the cycle life and safety characteristics.
Disclosure of Invention
The invention aims to provide a negative plate, a preparation method, a lithium ion battery cell, a lithium ion battery pack and application thereof, wherein the structure of the negative plate can improve the bonding strength between a negative electrode and a negative current collector and reduce the increase of contact resistance in the charging and discharging process; the lithium ion battery has the advantages that the lithium precipitation on the surface of the negative electrode under the condition of large-current charging is relieved, and the side reaction of the negative electrode and the electrolyte is relieved, so that the cycle life and the rate characteristic of the lithium ion battery cell are improved; effectively improving the phenomenon that the negative pole is stuck to the roller in the rolling process.
In order to achieve the above purpose, the present invention provides a negative plate, which includes a negative current collector, a high conductivity active buffer layer coated on the surface of the negative current collector, a silicon-containing active layer coated on the surface of the high conductivity active buffer layer, and a fast ion conduction active layer coated on the surface of the silicon-containing active layer.
Further, the high-conductivity active buffer layer comprises 85-98% of a carbon-based active material, 1-5% of a conductive agent and 1-10% of a binder in percentage by weight.
Further, the carbon-based active material is one or more of artificial graphite, natural graphite and mesocarbon microbeads.
Further, the silicon-containing active layer comprises 85-98% of silicon-based active material, 1-5% of conductive agent and 1-10% of adhesive by weight percentage; preferably, the silicon-based active material accounts for 90-95%, the conductive agent accounts for 2-4%, and the binder accounts for 3-6%.
Further, the fast ion conduction active layer comprises 90-98% of fast ion conduction active material, 1-5% of conductive agent and 1-5% of binder by weight percentage; preferably, the fast ion conduction active material is 93-97%, the conductive agent is 3-4%, and the binder is 2-4%.
Further, the fast ion conduction active material is one or more of carbon-coated secondary granulation artificial graphite, carbon-coated primary particle artificial graphite, hard carbon, soft carbon, mesocarbon microbeads and lithium titanate.
Further, the conductive agent is one or more of carbon black, carbon nanotubes, graphene, carbon fibers and conductive graphite.
Further, the binder is one or more of polyvinylidene fluoride, sodium carboxymethylcellulose (CMC), Styrene Butadiene Rubber (SBR), polyacrylic acid and modified polymers thereof, polyimide, polyamide, polyacrylonitrile and modified polymers thereof, sodium alginate, carboxymethyl chitosan, polyvinyl alcohol and conductive polymers.
The invention also provides a preparation method of the negative plate, which comprises the following steps: according to the weight percentage, 85% -98% of carbon-based active material, 1% -5% of conductive agent and 1% -10% of binder are mixed, and after a solvent is added, the mixture is stirred and mixed uniformly under the vacuum condition to prepare first slurry; uniformly coating the first slurry on a negative current collector, and drying to form a high-conductivity active buffer layer coated on the surface of the negative current collector; mixing 85% -98% of silicon-based active material, 1% -5% of conductive agent and 1% -10% of binder, adding solvent, stirring and mixing uniformly under vacuum condition to prepare second slurry; mixing 90-98% of fast ion conduction active material, 1-5% of conductive agent and 1-5% of binder, adding solvent, stirring and mixing uniformly under vacuum condition to prepare third slurry; and simultaneously coating the second slurry and the third slurry on the surface of the high-conductivity active buffer layer by adopting an extrusion coating machine with a double-cavity die head, wherein the second slurry is positioned at the lower layer of the third slurry, and drying to form a silicon-containing active layer coated on the surface of the high-conductivity active buffer layer and a fast ion conduction active layer coated on the surface of the silicon-containing active layer. And then rolling, slitting and slicing are sequentially carried out to obtain the negative plate.
The negative electrode current collector may be selected from metal foils, and preferably, the negative electrode current collector is selected from copper foils. The thickness of the negative electrode current collector is not particularly limited, and preferably, the thickness of the negative electrode current collector is 0.006mm to 0.020 mm. The thickness of the negative electrode slurry layer is not particularly limited, and preferably, the thickness of the negative electrode slurry layer is 0.03mm to 0.15 mm.
Further, the pole piece peeling strength of the negative pole piece is 24-26N/m.
The invention also provides a lithium ion battery cell, which comprises the negative pole piece, the positive pole piece, the isolating film and the packaging bag, wherein the isolating film is arranged between the negative pole piece and the positive pole piece, the packaging bag is made of an aluminum-plastic film composite material, and a bare battery cell made of the negative pole piece, the positive pole piece and the isolating film is arranged in the packaging bag.
The lithium ion cell further comprises a positive plate, and the positive plate comprises a positive current collector and a positive slurry layer positioned on the positive current collector. The positive current collector is aluminum foil.
Further, the lithium ion battery core further comprises electrolyte, the electrolyte is liquid electrolyte, the electrolyte comprises lithium salt and organic solvent, and the lithium salt is selected from LiPF6、LiBF4、LiN(SO2F)2、LiN(CF3SO2)2、LiClO4、LiAsF6、LiB(C2O4)2、LiBF2C2O4And LiPF2O2One or more of the above; preferably, the organic solvent is a non-aqueous organic solvent, which may include a carbonate ester, a halogenated compound of the carbonate ester, or a carboxylic acid ester, and the carbonate ester may include a cyclic carbonate ester or a chain carbonate ester. Specifically, the organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, butylene carbonate, pentylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylethyl carbonate, methyl formate, ethyl propionate, propyl propionate and tetrahydrofuran.
The invention also provides a lithium ion battery pack which comprises the lithium ion battery cell.
The lithium ion battery pack is also applied to products such as automobiles, motorcycles, bicycles, consumer battery products and the like.
Compared with the prior art, the invention provides a negative plate and a preparation method thereof, wherein the negative plate comprises a negative current collector, a high-conductivity active buffer layer coated on the surface of the negative current collector, a silicon-containing active layer coated on the surface of the high-conductivity active buffer layer, and a fast ion conduction active layer coated on the surface of the silicon-containing active layer. The beneficial effects at least comprise: (1) the high-conductivity active buffer layer coated on the surface of the negative current collector adopts a carbon-based active material which has small volume expansion, good conductivity and relatively high lithium intercalation capacity in the charging and discharging processes, can buffer the volume expansion of the silicon-containing active layer in the charging and discharging processes, slows down the stripping with the negative current collector, reduces the increase of contact resistance in the circulating process and improves the circulating life; (2) for a high specific energy battery, because the coating weight and the compaction density are larger, the multiplying power performance of the silicon-based active material is poor, and the lithium precipitation phenomenon is easy to occur on the side of the negative electrode close to the isolating membrane; (3) the high adhesive content is designed on the silicon-containing active layer, the low adhesive content is designed on the fast ion conduction active layer, on one hand, the adhesive force of the silicon-containing active layer is improved, the circulation is improved, on the other hand, even if the adhesive floats upwards in the coating and drying process, the enrichment of the surface adhesive can not occur, the roller sticking phenomenon in the rolling process is slowed down, and the preparation yield and the battery cell performance are improved; (4) the whole capacity and the first effect of the battery cell are not influenced, the mass production is easy to realize, the cost is low, and the improvement effect is good.
Detailed Description
The "ranges" disclosed herein are in the form of lower and upper limits. There may be one or more lower limits, and one or more upper limits, respectively. The given range is defined by the selection of a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges that can be defined in this manner are inclusive and combinable, i.e., any lower limit can be combined with any upper limit to form a range. For example, ranges of 60-120 and 80-110 are listed for particular parameters, with the understanding that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present invention, all embodiments and preferred embodiments mentioned herein may be combined with each other to form a new technical solution, if not specifically stated.
In the present invention, all the technical features mentioned herein and preferred features may be combined with each other to form a new technical solution, if not specifically stated.
In the present invention, all the steps mentioned herein may be performed sequentially or randomly, if not specifically stated, but preferably sequentially.
The invention provides a lithium ion battery pack, which comprises a battery module, a circuit board, a shell and the like, wherein the battery module, the circuit board and the like are assembled in the shell to form the lithium ion battery pack, the lithium ion battery pack has various specifications, can be adjusted and designed according to needs, and is not limited in the process, and the assembly mode of the lithium ion battery pack in the prior art can be applied to the invention.
The battery module is composed of a plurality of lithium ion battery cells connected in series and in parallel, and similarly, the battery module has various specifications and can be adjusted and designed according to needs.
The lithium ion battery pack can be applied to products such as automobiles, motorcycles, bicycles, consumer battery products and the like so as to provide energy for the products such as the automobiles, the motorcycles, the bicycles, the consumer battery products and the like.
Various embodiments of the negative electrode sheet, the preparation method thereof and the lithium ion battery cell of the present invention are described below.
Example 1
(1) Preparation of the electrolyte
In a glove box or a drying room, Ethylene Carbonate (EC), Propylene Carbonate (PC) and diethyl carbonate (DEC) which are subjected to rectification dehydration treatment are mixed according to the mass ratio of EC: PC: DEC ═ 2: 3: 5 mixing and then slowly adding LiPF6And (3) adding fluoroethylene carbonate (FEC) accounting for 10% of the total mass of the electrolyte to 1mol/L, and uniformly stirring and mixing to obtain the final electrolyte.
(2) Preparation of positive plate
Uniformly mixing a positive active material lithium nickel cobalt manganese LiNi0.8Co0.1Mn0.1O2, a conductive agent super-P, CNT and a binding agent PVDF according to the mass ratio of 96.8:1.5:0.5:1.2, adding N-methylpyrrolidone (NMP), and uniformly stirring and mixing through a vacuum stirrer to obtain positive active material slurry. And (3) uniformly coating the slurry on two surfaces of a current collector of an aluminum foil (with the thickness of 13 mu m), and drying, cold-pressing and slitting to obtain the positive plate.
(3) Preparation of negative plate
Mixing the negative active material artificial graphite (with a median particle size of 8 μm), conductive carbon black (super-P), sodium carboxymethylcellulose (CMC) and Styrene Butadiene Rubber (SBR) in a mass ratio of 96: 1.6: 1.3: 2.1, adding solvent deionized water, and stirring and mixing uniformly under a vacuum condition to prepare first slurry. And uniformly coating the first slurry on a copper foil of a negative current collector, and drying at 80-95 ℃ to obtain the negative electrode I coated with the high-conductivity active buffer layer.
Mixing a negative electrode material with reversible specific capacity of 700mAh/g of silica and artificial graphite, a single-walled carbon nanotube, conductive carbon black (super-P), sodium carboxymethylcellulose (CMC) and Styrene Butadiene Rubber (SBR) according to a mass ratio of 94: 0.06: 1.94: 1.3: 2.7, adding solvent deionized water, and stirring and mixing uniformly under a vacuum condition to prepare second slurry; coating an amorphous secondary granulation artificial graphite active material (with the median particle size of 10 mu m), conductive carbon black (super-P), sodium carboxymethylcellulose (CMC), Styrene Butadiene Rubber (SBR) on the surface, wherein the mass ratio of the amorphous secondary granulation artificial graphite active material to the surface is 97: 1.0: 1.3: 1.7, adding solvent deionized water, and stirring and mixing uniformly under a vacuum condition to prepare third slurry; and simultaneously coating the second slurry and the third slurry on the surface of the negative electrode I by using an extrusion coating machine with a double-cavity die head, wherein the second slurry is positioned at the lower layer of the third slurry, and drying at 80-95 ℃ to obtain a negative electrode II. The compacted density of the obtained product is 1.70g/cm after rolling3The thickness of the high-conductivity active buffer layer is 10 +/-2 mu m, the thickness of the silicon-containing active layer is 40 +/-2 mu m, the thickness of the fast ion-conducting active layer is 15 +/-2 mu m, and the N/P ratio is ensured to be 1.16.
(4) Preparation of lithium ion cell
The isolation film is arranged between the negative plate and the positive plate, the square bare cell is prepared in a winding mode, the packaging bag is made of an aluminum-plastic film composite material, the bare cell is placed in the packaging bag for packaging to obtain a dry cell, and the dry cell is subjected to the procedures of baking, dewatering, liquid injection, sealing, standing, formation, degassing packaging, capacity grading and the like to obtain the lithium ion cell.
It should be noted that, in this embodiment, the square bare cell is prepared by winding, of course, in other embodiments, the bare cell may also be prepared by lamination, or the bare cell may also be prepared into other shapes, such as a cylinder or an ellipse, that is, the conventional preparation method of the lithium ion cell may be applied to the present invention, and is not limited herein.
Example 2
The only difference between the positive plate and the lithium ion cell prepared by the method described in example 1 is the preparation of the negative plate.
Preparing negative active material artificial graphite (with a median particle size of 8 mu m), conductive carbon black (super-P), sodium carboxymethylcellulose (CMC), Styrene Butadiene Rubber (SBR) according to a mass ratio of 96: 1.6: 1.3: 2.1, adding solvent deionized water, and stirring and mixing uniformly under a vacuum condition to prepare first slurry. And uniformly coating the first slurry on a copper foil of a negative current collector, and drying at 80-95 ℃ to obtain the negative electrode I coated with the high-conductivity active buffer layer.
Mixing a negative electrode material with reversible specific capacity of 700mAh/g of silica and artificial graphite, a single-walled carbon nanotube, conductive carbon black (super-P), sodium carboxymethylcellulose (CMC) and Styrene Butadiene Rubber (SBR) according to a mass ratio of 94: 0.06: 1.94: 1.3: 2.7, adding solvent deionized water, and stirring and mixing uniformly under a vacuum condition to prepare second slurry; mixing a surface carbon-coated primary particle artificial graphite active material (with a median particle size of 6 microns), hard carbon (with a median particle size of 8 microns), conductive carbon black (super-P), sodium carboxymethylcellulose (CMC) and Styrene Butadiene Rubber (SBR) in a mass ratio of 87: 10: 1.0: 1.3: 1.7, adding solvent deionized water, and stirring and mixing uniformly under a vacuum condition to prepare third slurry; and simultaneously coating the second slurry and the third slurry on the surface of the negative electrode I by using an extrusion coating machine with a double-cavity die head, wherein the second slurry is positioned at the lower layer of the third slurry, and drying at 80-95 ℃ to obtain a negative electrode II. The compacted density of the obtained product is 1.70g/cm after rolling3The thickness of the high-conductivity active buffer layer is 10 +/-2 mu m, the thickness of the silicon-containing active layer (second slurry layer) is 40 +/-2 mu m, the thickness of the fast ion conduction active layer is 15 +/-2 mu m, and the N/P ratio is ensured to be 1.16.
Example 3
The only difference between the positive plate and the lithium ion cell prepared by the method described in example 1 is the preparation of the negative plate.
Preparing negative active material artificial graphite (with a median particle size of 8 m), conductive carbon black (super-P), sodium carboxymethylcellulose (CMC), Styrene Butadiene Rubber (SBR) according to a mass ratio of 96: 1.6: 1.3: 2.1, adding solvent deionized water, and stirring and mixing uniformly under a vacuum condition to prepare first slurry. And uniformly coating the first slurry on a copper foil of a negative current collector, and drying at 80-95 ℃ to obtain the negative electrode I coated with the high-conductivity active buffer layer.
Mixing a negative electrode material with reversible specific capacity of 700mAh/g of silica and artificial graphite, a single-walled carbon nanotube, conductive carbon black (super-P), sodium carboxymethylcellulose (CMC) and Styrene Butadiene Rubber (SBR) according to a mass ratio of 94: 0.06: 1.94: 1.3: 2.7, adding solvent deionized water, and stirring and mixing uniformly under a vacuum condition to prepare second slurry; mixing a hard carbon material (with a median particle size of 5 mu m), conductive carbon black (super-P), sodium carboxymethylcellulose (CMC) and Styrene Butadiene Rubber (SBR) in a mass ratio of 97: 1.0: 1.3: 1.7, adding solvent deionized water, and stirring and mixing uniformly under a vacuum condition to prepare third slurry; and simultaneously coating the second slurry and the third slurry on the surface of the negative electrode I by using an extrusion coating machine with a double-cavity die head, wherein the second slurry is positioned at the lower layer of the third slurry, and drying at 80-95 ℃ to obtain a negative electrode II. And rolling to obtain the negative electrode III with the compaction density of 1.70g/cm3, wherein the thickness of the high-conductivity active buffer layer is 10 +/-2 mu m, the thickness of the silicon-containing active layer (second slurry layer) is 40 +/-2 mu m, the thickness of the fast ion conduction active layer is 15 +/-2 mu m, and the N/P ratio is ensured to be 1.16.
Comparative example 1
A lithium ion cell was fabricated as in example 1, except that negative electrode iii included no fast ion active conductive layer, the highly conductive active buffer layer was 10 ± 2 μm thick, and the silicon-containing active layer (second slurry layer) was 47 ± 2 μm thick.
Comparative example 2
A lithium ion cell was fabricated as in example 1, except that the negative electrode iii did not include a highly conductive active buffer layer, the silicon-containing active layer (second slurry layer) was 45 ± 2 μm thick, and the fast ion-conducting active layer was 15 ± 2 μm thick.
Comparative example 3
A lithium ion cell was fabricated as in example 1, except that the negative electrode iii did not include a highly conductive active buffer layer and a fast ion active conductive layer, and the silicon-containing active layer (second paste layer) was 52 ± 2 μm thick.
And (3) testing the performance of the lithium ion battery cell:
(1) charging to 4.2V at constant current with 1C multiplying power, then charging at constant voltage to 0.05C, standing for 30min, discharging to 2.5V at 1C multiplying power, standing for 30min, and circularly charging and discharging for 500 times according to the charging and discharging system, thus obtaining the capacity retention rate after 500 weeks of 1C circulation.
(2) And charging to 4.2V at a constant current of 2C multiplying power, standing for 30min, and then discharging to 2.5V at a multiplying power of 0.33C to obtain the reversible capacity retention rate of 2C charging.
The performance test data of the negative electrode sheets and the lithium ion cells of the examples 1 to 3 and the comparative examples 1 to 3 are shown in the table 1.
Table 1 data of performance test of negative electrode sheet and lithium ion cell in each example and comparative example
From comparative example 1 and examples 1 to 3, it can be seen that coating a fast ion-conducting active layer on the surface of a silicon-containing active layer can improve the cycle life of a cell; the pole piece peeling strength of the embodiments 1 to 3 is improved, the adhesive force of the silicon-containing active layer can be improved, the circulation is improved, the roller sticking phenomenon in the rolling process is reduced, and the preparation yield and the battery cell performance are improved.
As can be seen from comparative example 2 and examples 1 to 3, the pole piece peel strength of comparative example 2, which does not include the highly conductive active buffer layer, is significantly reduced, and the highly conductive active buffer layer coated on the surface of the negative current collector adopts a carbon-based active material with small volume expansion in the charge-discharge process, good conductivity and relatively high lithium intercalation capacity, so that the volume expansion of the silicon-containing active layer in the charge-discharge process can be buffered, the peeling from the negative current collector is slowed, the increase of contact resistance in the cycle process is reduced, and the cycle life is improved.
As can be seen from comparative example 3 and examples 1 to 3, comparative example 3 is the existing silicon-based negative electrode material, the pole piece peeling strength is low, the roll sticking is serious, the cycle performance is poor, and the cycle stability is reduced in a large-current charging state. The negative electrode sheet of embodiments 1 to 3 includes a negative electrode current collector, a high-conductivity active buffer layer coated on a surface of the negative electrode current collector, a silicon-containing active layer coated on a surface of the high-conductivity active buffer layer, and a fast ion-conducting active layer coated on a surface of the silicon-containing active layer. The beneficial effects at least comprise: (1) the high-conductivity active buffer layer coated on the surface of the negative current collector adopts a carbon-based active material which has small volume expansion, good conductivity and relatively high lithium intercalation capacity in the charging and discharging processes, can buffer the volume expansion of the silicon-containing active layer in the charging and discharging processes, slows down the stripping with the negative current collector, reduces the increase of contact resistance in the circulating process and improves the circulating life; (2) for a high specific energy battery, because the coating weight and the compaction density are larger, the multiplying power performance of the silicon-based active material is poor, and the lithium precipitation phenomenon is easy to occur on the side of the negative electrode close to the isolating membrane; (3) the high adhesive content is designed on the silicon-containing active layer, the low adhesive content is designed on the fast ion conduction active layer, on one hand, the adhesive force of the silicon-containing active layer is improved, the circulation is improved, on the other hand, even if the adhesive floats upwards in the coating and drying process, the enrichment of the surface adhesive can not occur, the roller sticking phenomenon in the rolling process is slowed down, and the preparation yield and the battery cell performance are improved; (4) the whole capacity and the first effect of the battery cell are not influenced, the mass production is easy to realize, the cost is low, and the improvement effect is good.
The above disclosure is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the scope of the present invention, therefore, the present invention is not limited by the appended claims.
Claims (15)
1. A negative electrode sheet, comprising:
a negative current collector;
a high-conductivity active buffer layer coated on the surface of the negative current collector;
a silicon-containing active layer coated on the surface of the high-conductivity active buffer layer; and
the fast ion conduction active layer is coated on the surface of the silicon-containing active layer and comprises a fast ion conduction active material, the fast ion conduction active material is one or more of carbon-coated secondary granulation artificial graphite, carbon-coated primary particle artificial graphite and mesocarbon microbeads, and the content of the binder in the silicon-containing active layer is higher than that in the fast ion conduction active layer.
2. The negative electrode sheet according to claim 1, wherein the high-conductivity active buffer layer comprises, by weight, 85% to 98% of a carbon-based active material, 1% to 5% of a conductive agent, and 1% to 10% of a binder.
3. The negative electrode sheet of claim 2, wherein the carbon-based active material is one or more of artificial graphite, natural graphite, mesocarbon microbeads.
4. The negative plate of claim 1, wherein the silicon-containing active layer comprises, by weight, 85% to 98% of a silicon-based active material, 1% to 5% of a conductive agent, and 1% to 10% of a binder.
5. The negative electrode sheet of claim 4, wherein the silicon-based active material is 90% to 95%, the conductive agent is 2% to 4%, and the binder is 3% to 6%, by weight.
6. The negative electrode sheet according to claim 1, wherein the fast ion-conducting active layer comprises 90% to 98% by weight of the fast ion-conducting active material, 1% to 5% by weight of the conductive agent, and 1% to 5% by weight of the binder.
7. The negative electrode sheet according to claim 6, wherein the fast ion conductive active material comprises 93% to 97%, the conductive agent comprises 3% to 4%, and the binder comprises 2% to 4% by weight.
8. The negative electrode sheet according to claim 2, 4 or 6, wherein the conductive agent is one or more of carbon black, carbon nanotubes, graphene, carbon fibers and conductive graphite.
9. The negative electrode sheet according to claim 2, 4 or 6, wherein the binder is one or more of polyvinylidene fluoride, sodium carboxymethylcellulose (CMC), Styrene Butadiene Rubber (SBR), polyacrylic acid and modified polymers thereof, polyimide, polyamide, polyacrylonitrile and modified polymers thereof, sodium alginate, carboxymethyl chitosan, polyvinyl alcohol, and conductive polymers.
10. A preparation method of the negative electrode sheet, wherein the negative electrode sheet prepared by the preparation method is as defined in any one of claims 1 to 9, and the preparation method comprises the following steps:
according to the weight percentage, 85% -98% of carbon-based active material, 1% -5% of conductive agent and 1% -10% of binder are mixed, solvent is added, and then the mixture is stirred and mixed uniformly under the vacuum condition to prepare first slurry; uniformly coating the first slurry on a negative current collector, and drying to form a high-conductivity active buffer layer coated on the surface of the negative current collector;
mixing 85% -98% of a silicon-based active material, 1% -5% of a conductive agent and 1% -10% of a binder, adding a solvent, and uniformly stirring and mixing under a vacuum condition to prepare a second slurry; mixing 90-98% of fast ion conduction active material, 1-5% of conductive agent and 1-5% of binder, adding solvent, and stirring and mixing uniformly under a vacuum condition to prepare third slurry; and simultaneously coating the second slurry and the third slurry on the surface of the high-conductivity active buffer layer by adopting an extrusion coating machine with a double-cavity die head, wherein the second slurry is positioned at the lower layer of the third slurry, and drying to form a silicon-containing active layer coated on the surface of the high-conductivity active buffer layer and a fast ion conduction active layer coated on the surface of the silicon-containing active layer.
11. The preparation method according to claim 10, wherein the negative electrode sheet has a sheet peel strength of 24 to 26N/m.
12. A lithium ion battery cell, comprising:
the negative electrode sheet according to any one of claims 1 to 9;
a positive plate;
the isolating film is arranged between the negative plate and the positive plate; and
the packaging bag is made of an aluminum-plastic film composite material, and the negative pole piece, the positive pole piece and the bare cell made of the isolating film are arranged in the packaging bag.
13. The lithium ion battery cell of claim 12, further comprising an electrolyte comprising a lithium salt selected from LiPF and an organic solvent6、LiBF4、LiN(SO2F)2、LiN(CF3SO2)2、LiClO4、LiAsF6、LiB(C2O4)2、LiBF2C2O4And LiPF2O2The organic solvent is one or more selected from ethylene carbonate, propylene carbonate, butylene carbonate, pentylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylethyl carbonate, methyl formate, ethyl propionate, propyl propionate and tetrahydrofuran.
14. A lithium ion battery pack, characterized in that the lithium ion battery pack comprises the lithium ion battery cell according to any one of claims 12 to 13.
15. Applying the lithium ion battery pack of claim 14 to an automobile, motorcycle, or bicycle.
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| CN114927642B (en) * | 2021-01-28 | 2024-01-30 | 广汽埃安新能源汽车有限公司 | Negative plate, preparation method and lithium ion battery |
| CN113013379A (en) * | 2021-03-08 | 2021-06-22 | 昆山宝创新能源科技有限公司 | Negative pole piece, preparation method thereof and lithium ion battery |
| CN112952031B (en) * | 2021-03-24 | 2022-03-29 | 蜂巢能源科技(无锡)有限公司 | Negative electrode and preparation method and application thereof |
| CN113013394A (en) * | 2021-03-26 | 2021-06-22 | 蜂巢能源科技有限公司 | Negative electrode material and preparation method and application thereof |
| CN113078291A (en) * | 2021-03-26 | 2021-07-06 | 珠海冠宇电池股份有限公司 | Negative plate, preparation method thereof and battery |
| CN113421999B (en) * | 2021-06-21 | 2022-10-21 | 宁德新能源科技有限公司 | Electrochemical device and electronic device |
| CN113644231A (en) * | 2021-07-15 | 2021-11-12 | 恒大新能源技术(深圳)有限公司 | Composite negative plate, preparation method thereof and secondary battery |
| CN113851609B (en) * | 2021-08-26 | 2023-07-14 | 蜂巢能源科技有限公司 | Silicon-based negative electrode plate, preparation method thereof and all-solid-state lithium ion battery |
| CN114927688A (en) * | 2022-04-20 | 2022-08-19 | 重庆市紫建新能源有限公司 | Negative pole piece containing composite binder and preparation method thereof |
| CN116598422B (en) * | 2023-07-19 | 2024-01-19 | 广汽埃安新能源汽车股份有限公司 | Negative plate, electrode assembly, lithium ion battery and electric equipment |
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Effective date of registration: 20220105 Address after: 511400 No.36 Longying Road, Shilou Town, Panyu District, Guangzhou City, Guangdong Province Patentee after: GAC AIAN New Energy Vehicle Co.,Ltd. Address before: 510030 23 building, Cheng Yue mansion 448-458, Dongfeng Middle Road, Yuexiu District, Guangzhou, Guangdong. Patentee before: GUANGZHOU AUTOMOBILE GROUP Co.,Ltd. |