Calculation method for using amount of lithium ion battery positive electrode conductive agent and application of calculation method in lithium ion battery production

Abstract

The invention provides a method for calculating the dosage of a lithium ion battery positive electrode conductive agent and application of the method in lithium ion battery production, and relates to the technical field of batteries. The invention provides a method for calculating the dosage of a positive electrode conductive agent of a lithium ion battery. The calculation formula of the dosage of the positive electrode conductive agent is mCB positive = K * mAM * phi / D2 / psi, wherein mCB positive is the weight of the positive conductive agent; k is the conductivity coefficient of the positive electrode, and the value of K is 0.02-0.07; mAM is the weight of the positive active material; phi is the specific surface area of the positive active material; d is the diameter of the positive conductive agent; and psi represents the number of particles of the conductive agent (particles / g). According to the calculation method, unnecessary excessive addition can be avoided by accurately calculating the content of the conductive agent, so that the cost is saved; meanwhile, the problems that the battery electrical property is reduced due to too few conductive agents and the capacity is reduced due to too many conductive agents are solved.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, in particular to a method for calculating the amount of a positive electrode conductive agent used in a lithium ion battery and an application of the method in lithium ion battery production. Background Art

[0002] During the charge and discharge process of lithium-ion batteries, both lithium ions and electrons need to migrate within the electrodes. Therefore, the electrodes must be mixed conductors of ions and electrons. However, the positive electrode active materials of lithium-ion batteries are usually transition metal oxides or transition metal phosphates, which are semiconductors or insulators with poor electrical conductivity.

[0003] In order to ensure that the electrode has good electrical conductivity, conductive agents are added when producing positive electrode sheets. These conductive agents are usually carbon-based materials, such as superconducting carbon black, carbon nanotubes, graphene, and other carbon-based materials with good electrical conductivity. These materials collect microcurrents between active materials and between active materials and current collectors, reduce contact resistance, increase the migration rate of lithium ions in electrode materials, and effectively increase the movement rate of electrons, thereby improving the overall electrical conductivity of the electrode.

[0004] The content of conductive agent also has a significant impact on the performance of the battery. Too much conductive agent means less active ingredient and low capacity; too little conductive agent means poor conductivity and the battery is prone to polarization. Therefore, adding an appropriate amount of conductive agent is crucial.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The first object of the present invention is to provide a method for calculating the amount of positive electrode conductive agent used in a lithium ion battery to solve the above technical problems.

[0007] The second object of the present invention is to provide application of the above calculation method in lithium ion battery production.

[0008] In order to achieve the above objectives, the following technical solutions are adopted:

[0009] In a first aspect, the present invention provides a method for calculating the amount of a positive electrode conductive agent for a lithium ion battery, wherein the positive electrode sheet of the lithium ion battery comprises a current collector and a positive electrode slurry layer coated on the current collector;

[0010] The positive electrode slurry comprises a positive electrode active material, a positive electrode conductive agent and a binder;

[0011] In the positive electrode slurry, the calculation formula for the amount of positive electrode conductive agent is as follows:

[0012] m CB正 =K*m AM *Φ / D 2 / Ψ;

[0013] Among them, m CB正 is the weight of the positive electrode conductive agent; K is the positive electrode conductivity coefficient; m AM is the weight of the positive electrode active material; Φ is the specific surface area of ​​the positive electrode active material; D is the diameter of the positive electrode conductive agent; Ψ is the number of particles of the conductive agent (particles / g);

[0014] The K=0.02-0.07.

[0015] As a further technical solution, the calculation formula for the specific surface area of ​​the positive electrode active material is as follows:

[0016] Φ=(Φ1*βAM1+Φ2*βAM2+…+Φ n *βAM n );

[0017] Among them, βAM1+βAM2+…+βAM n =1; βAM n is the weight proportion of the nth positive electrode active material; Φ n is the specific surface area of ​​the nth positive electrode active material; n is a positive integer.

[0018] As a further technical solution, the positive electrode conductive agent includes: acetylene black.

[0019] As a further technical solution, the positive electrode active material includes: lithium iron phosphate.

[0020] As a further technical solution, the binder includes PVDF.

[0021] As a further technical solution, the mass proportion of the binder in the positive electrode slurry layer is 1.5%-3%.

[0022] As a further technical solution, the current collector includes aluminum foil.

[0023] In a second aspect, the present invention provides application of the above calculation method in lithium ion battery production.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The method for calculating the amount of a positive electrode conductive agent for a lithium ion battery provided by the present invention can avoid unnecessary excessive addition by accurately calculating the content of the conductive agent, thereby saving costs; at the same time, it can avoid problems such as a decrease in battery electrical performance due to too little conductive agent and a decrease in capacity due to too much conductive agent. DETAILED DESCRIPTION

[0026] The embodiments of the present invention will be described in detail below in conjunction with the embodiments and examples, but it will be appreciated by those skilled in the art that the following embodiments and examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified, proceed according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0027] In a first aspect, the present invention provides a method for calculating the amount of a positive electrode conductive agent for a lithium ion battery, wherein the positive electrode sheet of the lithium ion battery comprises a current collector and a positive electrode slurry layer coated on the current collector;

[0028] The positive electrode slurry comprises a positive electrode active material, a positive electrode conductive agent and a binder;

[0029] In the positive electrode slurry, the calculation formula for the amount of positive electrode conductive agent is as follows:

[0030] m CB正 =K*m AM *Φ / D 2 / Ψ;

[0031] Among them, m CB正 is the weight of the positive electrode conductive agent; K is the positive electrode conductivity coefficient; m AM is the weight of the positive electrode active material; Φ is the specific surface area of ​​the positive electrode active material; D is the diameter of the positive electrode conductive agent; Ψ is the number of conductive agent particles (particles / g);

[0032] The K=0.02-0.07.

[0033] The principles of this solution are as follows:

[0034] In an ideal state, the surface of the positive electrode active material is uniformly coated with a layer of conductive agent (the ratio of the diameter of the positive electrode active material to the diameter of the conductive agent is, for example, in the range of 200-625). Assuming that the mass of the active material is m AM , the specific surface area of ​​the active material is Φ(m 2 / g), the diameter of the positive electrode conductive agent is D, the number of particles of the conductive agent is Ψ (particles / g), then the area of ​​the conductive agent is m AM *Φ, the number of conductive agents is m AM *Φ / D 2 , the mass of the conductive agent in the ideal state is calculated to be m AM *Φ / D 2 / Ψ, considering the actual application, the conductivity coefficient K is designed according to actual experience, so the dosage formula of the conductive agent is m CB正 =K*m AM *Φ / D2 / Ψ.

[0035] The method for calculating the amount of a positive electrode conductive agent for a lithium ion battery provided by the present invention can avoid unnecessary excessive addition by accurately calculating the content of the conductive agent, thereby saving costs; at the same time, it can avoid problems such as a decrease in battery electrical performance due to too little conductive agent and a decrease in capacity due to too much conductive agent.

[0036] In some optional embodiments, the calculation formula of the specific surface area of ​​the positive electrode active material is as follows:

[0037] Φ=(Φ1*βAM1+Φ2*βAM2+…+Φ n *βAM n );

[0038] Among them, βAM1+βAM2+…+βAM n =1; βAM n is the weight proportion of the nth positive electrode active material; Φ n is the specific surface area of ​​the nth positive electrode active material; n is a positive integer.

[0039] In some optional embodiments, the Φ may be, for example, 10-14 m 2 / g; D can be, for example, 40-50 nm.

[0040] In some optional embodiments, the positive electrode conductive agent is: acetylene black.

[0041] In some optional embodiments, the positive electrode active material includes: lithium iron phosphate.

[0042] In some optional embodiments, the binder includes but is not limited to PVDF, or other binders well known to those skilled in the art.

[0043] In some optional embodiments, the mass proportion of the binder in the positive electrode slurry layer is 1.5%-3%.

[0044] In some optional embodiments, the current collector comprises aluminum foil.

[0045] In a second aspect, the present invention provides application of the above calculation method in lithium ion battery production.

[0046] The content of the positive electrode conductive agent calculated by the calculation method of the present invention can avoid unnecessary excessive addition, thereby saving costs; at the same time, it can avoid problems such as a decrease in battery electrical performance due to too little conductive agent and a decrease in capacity due to too much conductive agent.

[0047] The present invention is further described below by means of specific examples. However, it should be understood that these examples are only used for more detailed description and should not be construed as limiting the present invention in any form.

[0048] Example 1

[0049] A method for calculating the amount of positive electrode conductive agent used in a lithium ion battery, the calculation formula for the amount of positive electrode conductive agent used is as follows:

[0050] m CB正 =K*m AM *Φ / D 2 / Ψ;

[0051] Among them, m CB正 is the weight of the positive electrode conductive agent; K is the positive electrode conductivity coefficient; m AM is the weight of the positive electrode active material; Φ is the specific surface area of ​​the positive electrode active material; D is the diameter of the positive electrode conductive agent; Ψ is the number of particles of the conductive agent (particles / g);

[0052] K = 0.02. The calculation formula of the specific surface area of ​​the positive electrode active material is as follows:

[0053] Example 2

[0054] A method for calculating the amount of positive electrode conductive agent used in a lithium ion battery, the calculation formula for the amount of positive electrode conductive agent used is as follows:

[0055] m CB正 =K*m AM *Φ / D 2 / Ψ;

[0056] Among them, m CB正 is the weight of the positive electrode conductive agent; K is the positive electrode conductivity coefficient; m AM is the weight of the positive electrode active material; Φ is the specific surface area of ​​the positive electrode active material; D is the diameter of the positive electrode conductive agent; Ψ is the number of particles of the conductive agent (particles / g);

[0057] The K=0.05.

[0058] Example 3

[0059] A method for calculating the amount of positive electrode conductive agent used in a lithium ion battery, the calculation formula for the amount of positive electrode conductive agent used is as follows:

[0060] m CB正 =K*m AM *Φ / D 2 / Ψ;

[0061] Among them, m CB正 is the weight of the positive electrode conductive agent; K is the positive electrode conductivity coefficient; m AMis the weight of the positive electrode active material; Φ is the specific surface area of ​​the positive electrode active material; D is the diameter of the positive electrode conductive agent; Ψ is the number of particles of the conductive agent (particles / g);

[0062] The K=0.07.

[0063] Comparative Example 1

[0064] A method for calculating the amount of positive electrode conductive agent used in a lithium-ion battery, the calculation formula for the amount of positive electrode conductive agent used is as follows:

[0065] m CB正 =K*m AM *Φ / D 2 / Ψ;

[0066] Among them, m CB正 is the weight of the positive electrode conductive agent; K is the positive electrode conductivity coefficient; m AM is the weight of the positive electrode active material; Φ is the specific surface area of ​​the positive electrode active material; D is the diameter of the positive electrode conductive agent; Ψ is the number of particles of the conductive agent (particles / g);

[0067] Said K=0.001.

[0068] Comparative Example 2

[0069] A method for calculating the amount of positive electrode conductive agent used in a lithium ion battery, the calculation formula for the amount of positive electrode conductive agent used is as follows:

[0070] m CB正 =K*m AM *Φ / D 2 / Ψ;

[0071] Among them, m CB正 is the weight of the positive electrode conductive agent; K is the positive electrode conductivity coefficient; m AM is the weight of the positive electrode active material; Φ is the specific surface area of ​​the positive electrode active material; D is the diameter of the positive electrode conductive agent; Ψ is the number of particles of the conductive agent (particles / g);

[0072] Said K=0.3.

[0073] Test Example 1

[0074] With lithium iron phosphate as the positive electrode active material, conductive carbon black as the conductive agent, and PVDF as the binder, the amount of the conductive agent is calculated using the calculation method of Example 1-3 and Comparative Example 1-2:

[0075] Positive electrode active material: m AM =0.29197kg,Φ=10m 2 / g, positive electrode active material diameter d = 12 μm;

[0076] Conductive agent: D = 50nm; Ψ = 17*10^15 particles / g.

[0077] By calculation, m in Example 1 CB =0.02*0.29197*1000*10 / ((50*10^-9)^2) / (17*10^15) / 1000=

[0078] 0.00137kg;

[0079] Example 2 m CB＝ 0.05*0.29197*1000*10 / ((50*10^-9)^2) / (17*10^15) / 1000=

[0080] 0.0034kg;

[0081] Example 3 m CB正 =0.07*0.29197*1000*10 / ((50*10^-9)^2) / (17*10^15) / 1000=

[0082] 0.0048kg;

[0083] m of Comparative Example 1 CB正 =0.001*0.29197*1000*10 / ((50*10^-9)^2) / (17*10^15) / 1000=6.86988E-05kg;

[0084] m of Comparative Example 2 CB正 =0.3*0.29197*1000*10 / ((50*10^-9)^2) / (17*10^15) / 1000=

[0085] 0.0206kg;

[0086] Then, the conductive agent obtained by the above calculation is mixed with the positive electrode active material and the binder and coated on the aluminum foil to obtain the positive electrode sheet, wherein the amount of the binder in the slurry layer of the positive electrode sheet (mass of the binder / mass of the active material) is 2%.

[0087] Negative electrode sheet: The current collector is copper foil; the slurry layer is composed of active material graphite, conductive agent SP and binder (CMC+SBR, the mass ratio of CMC and SBR is 1:1), among which the active material, conductive agent and binder account for 94.%:3.3%:2.7%.

[0088] Diaphragm: PP diaphragm.

[0089] Electrolyte: The electrolyte is lithium hexafluorophosphate (1 mol / L), and the solvent is ethylene carbonate and dimethyl carbonate, the ratio of the two is 1:1, and the electrolyte contains 2% by weight of vinylene carbonate.

[0090] The positive electrode sheets prepared in Examples 1-3 and Comparative Examples 1-2 were respectively combined with the above-mentioned negative electrode sheets, separators and electrolytes to prepare lithium-ion batteries, and then the performance of the batteries was tested. The results are as follows:

[0091]

[0092]

[0093] Note: First efficiency: Coulombic efficiency of the battery in the first charge and discharge cycle; Cycle: Discharge capacity retention rate after 1000 charge and discharge cycles at 0.5C at 25 degrees; Rate: Capacity retention rate when the initial capacity is charged at 0.2C and discharged at 0.2C at 25 degrees, and charged at 0.2C and discharged at 1C; Storage: Capacity retention rate after 30D (30 days) of storage at 100% SOC at 25 degrees.

[0094] It can be seen from the experimental results that if the content of the conductive agent is too little, the cycle performance and rate performance of the battery will be reduced, and if the content of the conductive agent is too much, the first coulombic efficiency of the battery will be reduced.

[0095] Test Example 2

[0096] With lithium iron phosphate as the positive electrode active material, acetylene black as the conductive agent, and PVDF as the binder, the amount of the conductive agent is calculated using the calculation method of Example 1-3 and Comparative Example 1-2:

[0097] Positive electrode active material: m AM =0.29197kg,Φ=14m 2 / g, positive electrode active material diameter d = 20 μm;

[0098] Conductive agent: D = 40nm; Ψ = 17*10^15 particles / g.

[0099] By calculation, m in Example 1 CB =0.02*0.29197*1000*14 / ((40*10^-9)^2) / (17*10^15) / 1000=0.003kg;

[0100] Example 2 m CB =0.05*0.29197*1000*14 / ((40*10^-9)^2) / (17*10^15) / 1000=0.0075kg;

[0101] Example 3 m CB正 =0.07*0.29197*1000*14 / ((40*10^-9)^2) / (17*10^15) / 1000=0.0105kg;

[0102] m of Comparative Example 1 CB正 =0.001*0.29197*1000*14 / ((40*10^-9)^2) / (17*10^15) / 1000=0.00015kg;

[0103] m of Comparative Example 2 CB正 =0.3*0.29197*1000*14 / ((40*10^-9)^2) / (17*10^15) / 1000=0.045kg;

[0104] Then, the conductive agent obtained by the above calculation is mixed with the positive electrode active material and the binder and coated on the aluminum foil to obtain the positive electrode sheet, wherein the amount of the binder in the slurry layer of the positive electrode sheet (mass of the binder / mass of the active material) is 2%.

[0105] Negative electrode sheet: The current collector is copper foil; the slurry layer is composed of active material graphite, conductive agent SP and binder (CMC+SBR, the mass ratio of CMC and SBR is 1:1), among which the active material, conductive agent and binder account for 94.%:3.3%:2.7%.

[0106] Diaphragm: PP diaphragm.

[0107] Electrolyte: The electrolyte is lithium hexafluorophosphate (1 mol / L), and the solvent is ethylene carbonate and dimethyl carbonate, the ratio of the two is 1:1, and the electrolyte contains 2% by weight of vinylene carbonate.

[0108] The positive electrode sheets prepared in Examples 1-3 and Comparative Examples 1-2 were respectively combined with the above-mentioned negative electrode sheets, separators and electrolytes to prepare lithium-ion batteries, and then the performance of the batteries was tested. The results are as follows:

[0109] Test Example 1 First effect cycle Ratio (0.2C / 1C) Storage (30D) Example 1 90.56％ 1000cls@85.60% 94.74％ 97.50％ Example 2 91.26％ 1000cls@85.39% 95.13％ 98.09％ Example 3 91.84％ 1000cls@85.34% 96.56％ 98.05％ Comparative Example 1 90.26％ 1000cls@71.33% 89.36％ 93.12％ Comparative Example 2 88.65％ 1000cls@85.37% 96.87％ 97.18％

[0110] Test Example 3

[0111] With lithium iron phosphate as the positive electrode active material, acetylene black as the conductive agent, and PVDF as the binder, the amount of the conductive agent is calculated using the calculation method of Example 1-3 and Comparative Example 1-2:

[0112] Positive electrode active material: m AM =0.29197kg, Φ=(Φ1*βAM1+Φ2*βAM2+Φ3*βAM3)=12m 2 / g, Φ1=1 / 3, Φ2=1 / 3, Φ3=1 / 3, βAM1=1 / 3*10, βAM2=1 / 3*12, βAM3=1 / 3*14, positive electrode active material diameter d1=22μm, d2=18μm, d3=10μm;

[0113] Conductive agent: D = 45nm; Ψ = 17*10^15 particles / g.

[0114] By calculation, m in Example 1 CB =0.02*0.29197*1000*12 / ((45*10^-9)^2) / (17*10^15) / 1000=0.002kg;

[0115] Example 2 m CB =0.05*0.29197*1000*12 / ((45*10^-9)^2) / (17*10^15) / 1000=0.005kg;

[0116] Example 3 m CB正 =0.07*0.29197*1000*12 / ((45*10^-9)^2) / (17*10^15) / 1000=0.007kg;

[0117] m of Comparative Example 1 CB正 =0.001*0.29197*1000*12 / ((45*10^-9)^2) / (17*10^15) / 1000=0.00015kg;

[0118] m of Comparative Example 2 CB正 =0.3*0.29197*1000*12 / ((45*10^-9)^2) / (17*10^15) / 1000=0.0305kg;

[0119] Then, the conductive agent obtained by the above calculation is mixed with the positive electrode active material and the binder and coated on the aluminum foil to obtain the positive electrode sheet, wherein the amount of the binder in the slurry layer of the positive electrode sheet (mass of the binder / mass of the active material) is 2%.

[0120] Negative electrode sheet: The current collector is copper foil; the slurry layer is composed of active material graphite, conductive agent SP and binder (CMC+SBR, the mass ratio of CMC and SBR is 1:1), among which the active material, conductive agent and binder account for 94.%:3.3%:2.7%.

[0121] Diaphragm: PP diaphragm.

[0122] Electrolyte: The electrolyte is lithium hexafluorophosphate (1 mol / L), and the solvent is ethylene carbonate and dimethyl carbonate, the ratio of the two is 1:1, and the electrolyte contains 2% by weight of vinylene carbonate.

[0123] The positive electrode sheets prepared in Examples 1-3 and Comparative Examples 1-2 were respectively combined with the negative electrode sheets, separators and electrolytes to prepare lithium-ion batteries, and then the performance of the batteries was tested. The results are as follows:

[0124] Test Example 1 First effect cycle Ratio (0.2C / 1C) Storage (30D) Example 1 89.56％ 1000cls@86.60% 94.23％ 97.60％ Example 2 90.26％ 1000cls@86.30% 95.60％ 98.94％ Example 3 90.84％ 1000cls@85.69% 96.10％ 98.93％ Comparative Example 1 89.26％ 1000cls@70.36% 90.21％ 95.39％ Comparative Example 2 88.21％ 1000cls@85.32% 96.90％ 97.28％

[0125] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although detailed descriptions have been made with reference to the aforementioned inventions, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for calculating the amount of positive electrode conductive agent for lithium ion batteries, characterized in that: The positive electrode sheet of the lithium-ion battery comprises a current collector and a positive electrode slurry layer coated on the current collector; The positive electrode slurry comprises a positive electrode active material, a positive electrode conductive agent and a binder; In the positive electrode slurry, the calculation formula for the amount of positive electrode conductive agent is as follows: m CB正 =K*m AM *F / D 2 / Ψ; Among them, m CB正 is the weight of the positive electrode conductive agent; K is the positive electrode conductivity coefficient; m AM is the weight of the positive electrode active material; Φ is the specific surface area of ​​the positive electrode active material; D is the diameter of the positive electrode conductive agent; Ψ is the number of particles of the conductive agent (particles / g); The K=0.02-0.

07.

2. The calculation method according to claim 1, characterized in that: The calculation formula of the specific surface area of ​​the positive electrode active material is as follows: Φ=(Φ1*βAM1+Φ2*βAM2+…+Φ n *βAM n ); Among them, βAM1+βAM2+…+βAM n =1; βAM n is the weight proportion of the nth positive electrode active material; Φ n is the specific surface area of ​​the nth positive electrode active material; n is a positive integer.

3. The calculation method according to claim 1, characterized in that: The positive electrode conductive agent includes: acetylene black.

4. The calculation method according to claim 1, characterized in that: The positive electrode active material includes lithium iron phosphate.

5. The calculation method according to claim 1, characterized in that: The binder includes PVDF.

6. The calculation method according to claim 1, characterized in that: The mass proportion of the binder in the positive electrode slurry layer is 1.5%-3%.

7. The calculation method according to claim 1, characterized in that: The current collector includes aluminum foil.

8. Application of the calculation method according to any one of claims 1 to 7 in the production of lithium-ion batteries.

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