CN115360323A

CN115360323A - Lithium ion battery

Info

Publication number: CN115360323A
Application number: CN202211138862.1A
Authority: CN
Inventors: 潘驭一; 刘荣江; 黄彬彬
Original assignee: Eve Energy Co Ltd
Current assignee: Eve Energy Co Ltd
Priority date: 2022-09-19
Filing date: 2022-09-19
Publication date: 2022-11-18

Abstract

The invention provides a lithium ion battery, which comprises a positive pole piece and a negative pole piece, wherein the positive pole piece comprises a positive current collector, a positive active material layer and a safety coating arranged between the positive current collector and the positive active material layer; the cathode pre-lithiation material can supplement active lithium ions consumed by an SEI film and a CEI film generated by the anode and the cathode while lithiating the phosphate material in the anode safety coating, and improve the energy density of the battery.

Description

Lithium ion battery

Technical Field

The invention belongs to the technical field of lithium ion batteries, and relates to a lithium ion battery.

Background

Lithium ion batteries have been widely used in everyday portable electronic products, power batteries and energy storage systems because of their high energy density, high operating voltage and no memory effect. And the lithium ion battery can cause safety accidents due to thermal runaway and other reasons. At present, the safety performance of the lithium ion battery is improved by adopting a mode of coating a flame-retardant electrolyte, a flame-retardant diaphragm, a solid electrolyte, an active material with a flame-retardant substance, a mode of coating a pole piece with a safety coating and the like, but the safety performance is required to be ensured at present, and meanwhile, the safety problem of the lithium ion battery is solved by a method of not influencing the electrochemical performance of the lithium ion battery.

The safety coating is arranged between the current collector and the electrochemical active substance layer, the electrolyte is difficult to infiltrate, the active material in the safety coating is low in proportion, and active substance particles are tightly wrapped by the binder and the conductive agent. These factors make it difficult for lithium ions in the active material in the coating to be intercalated and deintercalated, while lithium ions that cannot be intercalated and deintercalated cannot provide capacity while having a certain quality, and the main cost of the active material in the safety coating comes from the lithium ions, resulting in waste of lithium resources.

CN109755465A discloses an electrode piece, an electrochemical device and a safety coating. The electrode plate comprises a current collector, an electrode active material layer and a safety coating arranged between the current collector and the electrode active material layer, wherein the An Quantu layer comprises a polyvinylidene fluoride and/or polyvinylidene chloride polymer matrix, a conductive material and an inorganic filler. The active material lithium ions in the coating are difficult to be inserted and extracted, the lithium ions which cannot be inserted and extracted cannot provide capacity and have certain quality, and the main cost of the active material in the safety coating comes from the lithium ions, so that the waste of lithium resources is caused.

CN103059613A discloses a lithium ion battery safety coating, the material used in the lithium ion battery safety coating is one or a mixture of several of alkali metal hydroxide, alkali metal carbonate and alkali metal bicarbonate, the disclosed lithium ion battery safety coating has the functions of heat decomposition and heat absorption, crystal structure change or pulverization and water or carbon dioxide release, the battery temperature can be reduced in the state that the battery is overheated, but the lithium ion battery safety coating can increase the impedance of the battery at normal temperature, and the rate capability is poor.

Disclosure of Invention

The invention aims to provide a lithium ion battery, wherein a safety coating is arranged in a positive pole piece, a pre-lithiation material is arranged in a negative pole piece, the safety coating is phosphate without lithium and is lithiated by the pre-lithiation material of the negative pole in the formation and circulation processes, and under the condition of reasonable system proportion, the safety of the battery can be improved, and the design can also reduce the cost of the battery and improve the energy density; the cathode pre-lithiation material can supplement active lithium ions consumed by an SEI film and a CEI film generated by the anode and the cathode while lithiating the phosphate material in the anode safety coating, and improve the energy density of the battery.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present invention provides a lithium ion battery, which includes a positive electrode plate and a negative electrode plate, wherein the positive electrode plate includes a positive current collector, a positive active material layer, and a safety coating disposed between the positive current collector and the positive active material layer, and the negative electrode plate includes a negative current collector, a negative active material layer disposed on the surface of the negative current collector, and a pre-lithiation material.

In the lithium ion battery, the safety coating comprises phosphate, and lithium ions released in the discharging process of the pre-lithiation material at the negative electrode end can lithiate the phosphate capable of exerting capacity in the safety coating into LiFe _1-x-y Mn _x M _y PO ₄ An electrochemically active substance. Active materials of sites which cannot exert capacity cannot be lithiated, lithium ions released by the lithium supplementing material are just matched with the lithiated active materials of the safety coating through system optimization, the quality of the safety coating can be reduced, and the quality of the battery is further reduced. Since the phosphate that cannot exert capacity is not lithiated, and the decomposition rate of the prelithiation material at the negative electrode end is high, lithium element is the most expensive substance in the lithium ion battery. The system is optimized to ensure that the lithium ions released by the lithium supplement material are just matched with the active material of the safe coating layer which can be lithiated, can reduce the size of the novelCost of battery construction

Preferably, the prelithiation material is disposed inside the anode active material layer, between the anode active material layer and the anode current collector, or on a surface of a side away from the anode current collector.

Preferably, the positive electrode active material layer, the safety coating layer, the negative electrode active material layer, and the pre-lithiation material each include a binder and a conductive agent.

Preferably, the binder comprises any one of polyvinylidene fluoride, modified polyvinylidene fluoride, polyvinylidene chloride, modified polyvinylidene chloride, polyvinylidene fluoride copolymer, polyvinylidene chloride copolymer, polymethyl methacrylate or styrene butadiene rubber or a combination of at least two of them.

Preferably, the conductive agent includes any one of conductive carbon black, acetylene black, graphite, graphene, carbon nanotubes, or carbon nanofibers, or a combination of at least two thereof.

Preferably, the positive electrode active material layer includes a positive electrode active material.

Preferably, the positive electrode active material includes any one of lithium cobaltate, lithium manganate, lithium nickelate, lithium nickel manganate, lithium nickel manganese cobaltate, lithium nickel manganese aluminate, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, or lithium manganese silicate, or a combination of at least two thereof.

Preferably, the security coating comprises an inorganic filler.

Preferably, the inorganic filler comprises a phosphate material.

Preferably, the phosphate material has the chemical formula of Fe _1-x-y Mn _x M _y PO ₄ Wherein x is more than or equal to 0 and less than or equal to 1,0 and less than or equal to 0.1,0 and less than or equal to x + y and less than or equal to 1,M comprises any one or combination of at least two of Sn, cr, mg, ti, al, zn, W, nb or Zr.

Preferably, the anode active material layer includes an anode active material.

Preferably, the negative active material includes any one of a graphite-based material, a silicon carbon material, or a lithium titanate, or a combination of at least two thereof.

Preferably, the graphite-based material includes any one of or a combination of at least two of artificial graphite, natural graphite, hard carbon, soft carbon, or mesocarbon microbeads.

Preferably, the prelithiation material includes an inert lithium powder and/or a lithium foil.

Note that, when the prelithiation material described in the present application is added to the negative electrode active material layer in a mixed manner, the prelithiation material does not include a binder and a conductive agent, and only when the prelithiation material is provided as a prelithiation material layer on a surface of the negative electrode active material layer on a side away from the current collector or between the negative electrode active material layer and the current collector, the prelithiation material includes a binder and a conductive agent.

The thickness of the security coating is 0.05 to 30 μm, for example: 1 μm, 2 μm, 5 μm, 10 μm, 20 μm or the like, preferably 1 to 6 μm.

Preferably, the inorganic filler is present in a mass ratio of 20 to 95% based on 100% by mass of the security coating, for example: 20%, 25%, 50%, 80%, 95%, etc., preferably 60 to 85%.

Preferably, the mass ratio of the binder is 5-65%, such as: 5%, 10%, 20%, 30%, 65%, etc.

Preferably, the conductive agent is 5 to 25% by mass, for example: 5%, 10%, 15%, 20%, 25%, etc.

Preferably, the inorganic filler has a particle size of 0.02 to 100 μm, for example: 0.02 μm, 0.1 μm, 0.5 μm, 1 μm, 10 μm, 100 μm or the like, preferably 0.1 to 1 μm.

Preferably, the capacity C of the prelithiated material ₁ Volume C of inorganic filler in Security coating ₂ Capacity C of active material in Positive electrode active Material layer ₃ Positive pole first effect-negative pole first effect = eta, and satisfies the relation C ₁ ＝λ*C ₂ +C ₃ * Eta, wherein lambda is more than or equal to 0.5 and less than or equal to 1, and eta is 0 when less than 0.

Compared with the prior art, the invention has the following beneficial effects:

(1) According to the invention, the safe coating is arranged in the positive pole piece, the pre-lithiation material is arranged in the negative pole piece, the safe coating is phosphate without lithium, and is lithiated by the pre-lithiation material of the negative pole in the formation and circulation processes, so that under the condition of reasonable system proportion, the safety of the battery can be improved, the design can also reduce the cost of the battery and improve the energy density; the cathode pre-lithiation material can supplement active lithium ions consumed by an SEI film and a CEI film generated by the anode and the cathode while lithiating the phosphate material in the anode safety coating, and improve the energy density of the battery.

(2) The lithium ion battery can pass 100% of needling and extrusion tests, the cycle life can reach 534 circles, and the capacity can reach 4890mAh.

Drawings

Fig. 1 is a side view of a single-sided positive plate of the lithium ion battery described in example 1, 1-positive current collector, 2-safety coating, 3-positive active material layer.

Fig. 2 is a side view of a single-sided negative plate of the lithium ion battery described in example 1, 4-negative current collector, 5-negative active material layer, 6-prelithiation material.

Fig. 3 is a side view of a single-sided negative plate of the lithium ion battery described in example 2, 4-the negative current collector, 5-the negative active material layer, 7-the prelithiation material added to the negative active material layer in a batch fashion.

Detailed Description

The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.

In the examples and comparative examples of the present invention, lithium ion batteries were prepared by the following methods:

1.1 preparation of safety coating

Dispersing a binder material, a conductive agent material and an inorganic filler in a certain ratio in N-methyl-2-pyrrolidone (NMP), uniformly stirring, coating on a positive current collector, and drying to obtain the safe coating.

1.2 preparation of Positive plate with safety coating

Positive pole piece: 95 percent of lithium cobaltate, 2 percent of PVDF, 3 percent of SP and NMP are used as solvents, the mixture is evenly stirred and coated on the safety coating on the surface of the aluminum foil of the positive current collector prepared by the method in 1.1, the mixture is baked at 85 ℃, rolled and stripped, and then baked at 85 ℃ for 4 hours to weld tabs and paste to obtain the positive plate.

1.3 preparation of negative plate with prelithiation material

Inert lithium powder + graphite negative electrode sheet: mixing inert lithium powder, active material graphite, a conductive agent, a binder and a thickening agent according to a certain proportion, wherein the mass ratio of the active material graphite to the conductive agent to the binder to the thickening agent is (C) 1.5 ₁ ＝λ*C ₂ +C ₃ * Eta calculation) is added into NMP and evenly mixed, the obtained slurry is coated on a copper foil of a negative current collector, the copper foil is baked at 87 ℃, rolled and stripped, and then the copper foil is baked at 80 ℃ for 12 hours, and a negative plate is obtained by welding electrode lugs.

Lithium foil + graphite: mixing active material graphite, a conductive agent, a binder and a thickening agent according to a mass ratio of 96.5 ₁ ＝λ*C ₂ +C ₃ * Eta calculation), applying a certain pressure on the lithium foil for a period of time, completing pre-lithiation, and finally welding and gluing the tab to obtain the negative plate.

1.4 preparation of lithium ion batteries

The isolation film, the negative plate, the isolation film and the positive plate are sequentially stacked, so that the isolation film is positioned between the positive plate and the negative plate to play an isolation role, and then the isolation film is wound into a bare cell. Then the preparation of the lithium ion battery is finished through the processes of shell filling, liquid injection, formation and packaging

Example 1

The embodiment provides a lithium ion battery, and the parameters of the lithium ion battery are as follows:

the lithium ion battery comprises a positive pole piece, a negative pole piece, a diaphragm and electrolyte, wherein the positive pole piece comprises an aluminum foil with the thickness of 9 mu m and a safety coating with the thickness of 3 mu m which are sequentially stacked, and the safety coating is free of aluminum foilThe iron phosphate with the median particle size of 0.2 mu m is selected as the organic filler, the mass ratio of the iron phosphate to the polyvinylidene fluoride to the conductive carbon black in the safety coating is 80 ² The length of the coating film on the surface A is 1118mm, the length of the surface B is 996mm, and the width of the pole piece is 76mm. The single-side view of the positive pole piece is shown in fig. 1, wherein 1 is a positive current collector, 2 is a safety coating, and 3 is a positive active material layer;

the negative pole piece comprises copper foils which are sequentially stacked and have the thickness of 8 mu m, and the single-side density of 99.8g/m ² The length of the A surface coating film is 1130mm, the length of the B surface coating film is 1017mm, the width of a pole piece is 77.5mm, the mass ratio of the artificial graphite, the polyvinylidene fluoride and the conductive carbon black in the negative active material layer is 96;

in the lithium ion battery, the first positive effect is 97%, the first negative effect is 92%, η =5%, λ =0.7, and the side view of the negative electrode plate is shown in fig. 2, where 4 is a negative electrode current collector, 5 is a negative electrode active material layer, and 6 is a pre-lithiation material;

the diaphragm is a 9 mu m polyethylene-based film double-sided adhesive 1 mu m diaphragm, and the electrolyte is 1mol/L LiPF ₆ a/EC + DMC + EMC electrolyte (EC is ethylene carbonate, EMC is ethyl methyl carbonate, DMC is dimethyl carbonate, the volume ratio of EC, DMC and EMC is 1.

Example 2

This example differs from example 1 only in that the security coating has a thickness of 0.5 μm, the other conditions and parameters being exactly the same as in example 1.

Example 3

This example differs from example 1 only in that the security coating has a thickness of 10 μm, and the other conditions and parameters are exactly the same as in example 1.

Example 4

This example differs from example 1 only in that the theoretical capacity ratio of the prelithiated material to the inorganic filler in the security coating is 0.4 (i.e. λ = 0.4) 1, with the other conditions and parameters being exactly the same as in example 1.

Example 5

This example differs from example 1 only in that the theoretical capacity ratio of the prelithiated material to the inorganic filler in the security coating is 1.2 (i.e.. Lambda. = 1.2), and the other conditions and parameters are exactly the same as in example 1.

Example 6

This example differs from example 1 only in that the particle size of the inorganic filler in the security coating is 0.05 μm, and the other conditions and parameters are exactly the same as in example 1.

Example 7

This example differs from example 1 only in that the particle size of the inorganic filler in the security coating is 2 μm, and the other conditions and parameters are exactly the same as in example 1.

Example 8

This example differs from example 1 only in that the negative prelithiation material is a lithium foil, and the other conditions and parameters are exactly the same as example 1.

Comparative example 1

The comparative example adopts a conventional lithium ion battery, namely, the positive electrode is not added with a safety coating, the negative electrode is not added with a lithium supplement agent, and other conditions and parameters are completely the same as those of the example 1.

Comparative example 2

The comparative example is different from example 1 only in that the inorganic filler of the safety coating in the positive electrode plate is lithium iron phosphate with the same mole number as that of the ferric phosphate in example 1, and the negative electrode is not provided with a pre-lithiation material, wherein the mole amount of the lithium iron phosphate is the same as that of the ferric phosphate in example 1, and other conditions and parameters are completely the same as those in example 1.

Comparative example 3

This comparative example differs from example 1 only in that the negative electrode is not provided with a prelithiation material, and the other conditions and parameters are exactly the same as example 1.

And (3) performance testing:

1. and (3) needle punching test:

fully charging the secondary battery to the charge cut-off voltage with the current of 1C, then charging the secondary battery at constant voltage until the current is reduced to 0.05C, and stopping charging. By using

The high temperature resistant steel needle (the conical angle of the needle tip is 45 degrees) penetrates through the battery from the direction vertical to the polar plate of the battery at the speed of 25mm/s, the penetrating position is preferably close to the geometric center of the punctured surface, the steel needle stays in the battery, and whether the battery has combustion and explosion phenomena within 1h or not is observed.

2. And (3) extrusion testing:

fully charging the secondary battery to the charge cut-off voltage with the current of 1C, then charging the secondary battery at constant voltage until the current is reduced to 0.05C, and stopping charging. The battery is placed in two planes and extruded in the direction perpendicular to the polar plates, and the extrusion force of 13.0kN +/-0.78 kN is applied between the two plates. The squeeze test was stopped once the pressure reached a maximum value and the cell could not be externally short circuited during the test.

3. Cycle performance test

The cycle number test conditions were: and (3) carrying out 1C/1C cycle test on the secondary battery at 25 ℃, determining the charging and discharging voltage range according to a battery system, and stopping the test when the capacity is attenuated to 80% of the first discharging specific capacity.

4. And (3) capacity testing:

at 25 ℃, charging the battery to cut off the upper limit voltage at a constant current of 0.2 ℃, and then cutting off the current at a constant voltage charging value of 0.02C; standing for 10min; and discharging at constant current of 0.2C to cut-off lower limit voltage, and recording the discharge capacity at cut-off current of 0.02C, namely the cell capacity.

To reduce systematic errors, 50 cells were made and tested for each example and comparative example, with the life and capacity averaged and integers.

The test results are shown in table 1:

TABLE 1

	Needle stick test	Squeeze test	Cycle life/cycle	capacity/mAh
					Example 1	100% pass through	100% pass through	534	4891
Example 2	92％NG	86％NG	528	4905
					Example 3	100% pass through	100% pass through	423	4776
Example 4	100% pass through	100% pass through	522	4735
					Example 5	62％NG	48％NG	320	4884
Example 6	100% pass through	100% pass through	541	4792
					Example 7	100% pass through	100% pass through	447	4815
Example 8	100% pass through	100% pass through	546	4889
					Comparative example 1	100％NG	100％NG	524	4885
Comparative example 2	100% pass through	100% pass through	531	4821
					Comparative example 3	100% pass through	100% pass through	537	4703

As can be seen from table 1, by comparing example 1 with examples 2 to 3, the thickness of the safety coating in the lithium ion battery of the present invention affects the performance thereof, and the thickness of the safety coating is controlled to be 1 to 6 μm, so that the performance of the lithium ion battery is good, and if the thickness of the safety coating is too large, the cycle life and the capacity thereof, and the thickness of the battery is affected, thereby affecting the volumetric energy density; if the thickness of the safety coating is too small, the function of the safety coating cannot be exerted.

As can be seen from the comparison of example 1 with examples 4-5, the amount of prelithiation material added to the lithium ion battery of the present invention, the capacity C of which affects the battery performance ₁ Volume C of inorganic filler in Security coating ₂ Active material capacity C in the positive electrode active material layer ₃ Positive electrode first effect-negative electrode first effect = η. C ₁ ＝λ*C ₂ +C ₃ * η, where λ = 0.5-1, the performance of the lithium ion battery is good, and if λ is too large, the cycle life is attenuated too fast and the safety test passing rate is seriously affected, because too much active lithium causes formation of lithium dendrite in the formation and cycle process, which leads to capacity attenuation and internal short circuit; if λ is too small, the battery capacity is affected.

Compared with the examples 6 to 7, the lithium ion battery of the present invention has the advantages that the particle size of the inorganic filler in the safety coating affects the battery performance, and if the particle size is too large, the lithium iron is easily crushed in the rolling process, the electric contact is lost, and the battery performance is affected; if the particle diameter is too small, the binder may wrap the active material, and the capacity may not be exhibited.

By comparing the embodiment 1 and the embodiment 8, the selection of the inert lithium powder or the lithium foil as the prelithiation material can supplement active lithium ions consumed by an SEI film and a CEI film generated by a positive electrode and a negative electrode while lithiating the phosphate material in the positive electrode safety coating, thereby improving the energy density of the battery. .

Compared with the comparative examples 1 and 1-2, the invention has the advantages that the safe coating is arranged in the positive pole piece, the pre-lithiation material is arranged in the negative pole piece, the safe coating is phosphate without lithium, and is lithiated by the pre-lithiation material of the negative pole in the formation and circulation processes, under the condition of reasonable system proportion, the safety of the battery can be improved, and the design can also reduce the cost of the battery and improve the energy density; the cathode pre-lithiation material can supplement active lithium ions consumed by an SEI film and a CEI film generated by the anode and the cathode while lithiating the phosphate material in the anode safety coating, and improve the energy density of the battery.

As can be seen from a comparison of example 1 with comparative examples 2 and 3, the battery system of the present invention has a significantly lower energy density than the system with the prelithiation material without the prelithiation material, since the prelithiation material can replenish the active lithium consumed by the SEI film and lithiate the iron phosphate.

The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention disclosed herein fall within the scope and disclosure of the present invention.

Claims

1. The utility model provides a lithium ion battery, its characterized in that, lithium ion battery includes positive pole piece and negative pole piece, positive pole piece include the anodal mass flow body, anodal active material layer and set up in the safety coating between the anodal mass flow body and the anodal active material layer, negative pole piece include the negative pole mass flow body, set up in negative active material layer and the prelithiation material on negative current flow body surface.

2. The lithium ion battery of claim 1, wherein the prelithiation material is disposed within the negative electrode active material layer, between the negative electrode active material layer and the negative electrode current collector, or on a surface of a side away from the negative electrode current collector.

3. The lithium ion battery of claim 1 or 2, wherein the positive electrode active material layer, the safety coating layer, the negative electrode active material layer, and the pre-lithiation material each comprise a binder and a conductive agent;

preferably, the binder comprises any one or a combination of at least two of polyvinylidene fluoride, modified polyvinylidene fluoride, polyvinylidene chloride, modified polyvinylidene chloride, polyvinylidene fluoride copolymer, polyvinylidene chloride copolymer, polymethyl methacrylate or styrene butadiene rubber;

4. The lithium ion battery according to any one of claims 1 to 3, wherein the positive electrode active material layer comprises a positive electrode active material;

5. The lithium ion battery of any of claims 1-4, wherein the safety coating comprises an inorganic filler;

preferably, the inorganic filler comprises a phosphate material;

6. The lithium ion battery according to any one of claims 1 to 5, wherein the negative electrode active material layer comprises a negative electrode active material.

Preferably, the negative active material comprises any one or a combination of at least two of a graphite-based material, a silicon-carbon material or lithium titanate;

7. The lithium ion battery of any of claims 1-6, wherein the prelithiation material comprises an inert lithium powder and/or a lithium foil.

8. The lithium-ion battery according to any of claims 1 to 7, characterized in that the thickness of the safety coating is 0.05 to 30 μm, preferably 1 to 6 μm.

9. The lithium-ion battery according to any of claims 1 to 8, characterized in that the mass proportion of the inorganic filler is 20 to 95%, preferably 60 to 85%, based on 100% by mass of the safety coating;

preferably, the mass ratio of the binder is 5-65%;

preferably, the conductive agent is 5 to 25 percent by mass;

preferably, the particle size of the inorganic filler is 0.02 to 100 μm, preferably 0.1 to 1 μm.

10. The lithium-ion battery of any of claims 1-9, wherein the pre-lithiated material has a capacity C ₁ Volume C of inorganic filler in Security coating ₂ Capacity of active material in Positive electrode active Material layer C ₃ Positive pole first effect-negative pole first effect = eta, and satisfies the relation C ₁ ＝λ*C ₂ +C ₃ * Eta, wherein lambda is more than or equal to 0.5 and less than or equal to 1, and eta is 0 when less than 0.