Preparation and application of battery pole piece

Abstract

The invention belongs to a lithium ion battery, and particularly relates to a high-power lithium ion battery pole piece and a preparation process and application thereof.The pole piece comprises a current collector and coatings attached to the surfaces of the two sides of the current collector, the current collector is made of aluminum foil or copper foil, and the coatings are of a double-layer structure sequentially attached to the surfaces of the current collector; the current collector comprises a first coating and a second coating, the first coating contains active substances and is attached to the surface of the current collector on the lower layer, and the second coating is a functional coating and is attached to the surface of the first coating on the upper layer. And the rate capability, namely the power performance, of the lithium ion battery can be improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a high-power lithium-ion battery positive electrode sheet, its preparation process, and a lithium-ion battery. Background Technology

[0002] High-power lithium-ion batteries are energy storage devices of great significance in fields such as electric vehicles, drones, and portable electronic devices. Compared to traditional lithium-ion batteries, high-power lithium-ion batteries can provide a greater current output in a short time, thus having an irreplaceable advantage in applications requiring instantaneous high current output. However, achieving high power performance in lithium-ion batteries is affected by many factors. Poor battery power performance can often be explained from the perspective of electrode structure. The electrode structure of a battery directly affects the charge transport rate and the battery's internal resistance, thereby affecting power performance. In some cases, the electrode structure may have the following problems: First, uneven particle size of the electrode material may lead to inconsistent surface areas of the electrodes, thus affecting the uniformity of charge transport. This can cause local overheating or overload under high power demand, reducing the battery's power output capability. Second, poor bonding or poor interface contact between electrode layers may lead to increased internal resistance of the battery. In this case, charge transport is hindered, and the battery will experience a significant voltage drop during high-power discharge, resulting in insufficient power output capability. In addition, the design of the electrode material may not have fully considered the charge transport rate and ion diffusion efficiency, leading to local charge accumulation or ion entanglement within the electrode. This limits the battery's response speed under high power demands, reducing the battery's power performance. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides an electrode design and its fabrication process, which can improve the rate performance, i.e., power performance, of lithium-ion batteries.

[0004] To improve battery power performance, this invention is achieved primarily through the following methods.

[0005] This invention prepares an electrode with a special structure, which includes a current collector and a coating. The current collector is made of aluminum foil or copper foil, and the coating has a double-layer structure, including a first coating and a second coating. The first coating is a coating containing active substances and is located in the lower layer, while the second coating is a functional coating and is located in the upper layer.

[0006] For the positive electrode plate:

[0007] The coating consists of two parts: a main material and an auxiliary material. The main material is the positive electrode active material, and the auxiliary materials are a conductive agent and a binder. The positive electrode active material can be one or more of commonly used positive electrode materials such as lithium nickel cobalt manganese oxide (NCM), lithium cobalt oxide (LCO), lithium iron phosphate (LFP), lithium manganese oxide (LMO), lithium manganese iron phosphate, and lithium vanadium phosphate. The binder is preferably polytetrafluoroethylene (PVDF), and the conductive agent is preferably one or more of conductive carbon black (SP) and carbon nanotubes.

[0008] The second coating comprises three parts: main material, auxiliary material, and functional material. The main material is one or more of the commonly used cathode materials such as lithium nickel manganese cobalt oxide (NCM), lithium cobalt oxide (LCO), lithium iron phosphate (LFP), lithium manganese oxide (LMO), lithium manganese iron phosphate, and lithium vanadium phosphate. The auxiliary material includes a conductive agent and a binder. The functional material is activated carbon material, and the proportion of activated carbon in the solid matter of the second coating ranges from 0.2% to 10%, preferably 1% to 3%. The binder is preferably PVDF, and the conductive agent is preferably one or more of conductive carbon black (SP) and carbon nanotubes.

[0009] For the negative electrode plate:

[0010] The coating consists of two parts: a main material and an auxiliary material. The main material is the negative electrode active material, and the auxiliary material is a conductive agent and a binder. The active material can be one or more of commonly used negative electrode materials such as graphite, silicon carbide, hard carbon, and mesophase carbon microspheres. The binder is preferably sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR), and the conductive agent is preferably one or more of conductive carbon black (SP) and carbon nanotubes.

[0011] The second coating comprises three parts: main material, auxiliary material, and functional material. The main material is one or more commonly used negative electrode materials such as graphite, silicon carbide, hard carbon, and mesophase carbon microspheres. The auxiliary material includes a conductive agent and a binder. The functional material is an active material. The proportion of activated carbon in the solid matter of the second coating is in the range of 0.2%-10%, preferably 1%-3%. The binder is preferably PVDF. The conductive agent is preferably one or more of conductive carbon black (SP) and carbon nanotubes.

[0012] The specific implementation process of the above-mentioned high-power positive electrode is as follows:

[0013] Coating slurry preparation: The positive electrode active material, conductive agent, and binder are stirred and mixed until homogeneous. A solvent is then added, and stirring continues until the slurry is evenly dispersed. The solvent is preferably N-methylpyrrolidone. The viscosity of the slurry is adjusted to a suitable viscosity for coating by adjusting the amount of solvent added.

[0014] Preparation of the second coating slurry: The positive electrode active material, activated carbon, conductive agent, and binder are stirred and mixed evenly. After uniform mixing, a solvent is added, and stirring is continued until the slurry is evenly dispersed. The solvent is preferably N-methylpyrrolidone. The viscosity of the slurry is adjusted to a suitable viscosity for coating by adjusting the amount of solvent added.

[0015] Double-layer electrode coating: Two slurries are coated onto a 12μm thick aluminum foil using a double-layer coating machine. The first coating accounts for 10%-90% of the total weight of the coating, preferably 50%-70%, and the second coating accounts for 10%-90% of the total weight of the coating, preferably 30%-50%. After coating, the coatings are dried in an oven to obtain a positive electrode with a double-layer coating structure.

[0016] The specific implementation process of the above-mentioned high-power negative electrode is as follows:

[0017] Coating slurry preparation: The negative electrode active material, conductive agent, and binder are stirred and mixed until homogeneous. A solvent is then added, and stirring continues until the slurry is evenly dispersed. Deionized water is preferred as the solvent. The viscosity of the slurry is adjusted to a suitable viscosity for coating by adjusting the amount of solvent added.

[0018] Preparation of the second coating slurry: The negative electrode active material, activated carbon, conductive agent, and binder are stirred and mixed evenly. After uniform mixing, a solvent is added, and stirring is continued until the slurry is evenly dispersed. The solvent is preferably deionized water. The viscosity of the slurry is adjusted to a suitable viscosity for coating by adjusting the amount of solvent added.

[0019] Double-layer electrode coating: Two slurries are coated onto a 6μm thick copper foil using a double-layer coating machine. The first coating accounts for 10%-90% of the total weight of the coating, preferably 50%-70%, and the second coating accounts for 10%-90% of the total weight of the coating, preferably 30%-50%. After coating, the coatings are dried in an oven to obtain a negative electrode with a double-layer coating structure.

[0020] Beneficial Effects: Lithium-ion batteries are rocking chair batteries. During charging, lithium ions are deintercalated at the positive electrode and then intercalated into the negative electrode material after passing through the electrolyte and separator. The discharge process is the reverse, with lithium ions deintercalating from the negative electrode material and then intercalating into the positive electrode material. This invention organically combines an active material coating (coating one) with a functional material coating (coating two) using a double-layer coating process, improving the rate of lithium ion intercalation and deintercalation during charging and discharging, thus improving battery power performance. The presence of activated carbon functional material in the upper layer of the positive and negative electrode sheets allows for rapid adsorption and desorption of lithium ions during their shuttle movement between the positive and negative electrodes. Furthermore, the activated carbon coating in this invention must be located on the upper layer of the two coatings. This ensures that lithium ions preferentially undergo adsorption and desorption on the surface of the upper activated carbon during transfer between the positive and negative electrodes, while reducing the proportion of activated carbon in the battery and avoiding a significant impact on the battery's energy density.

[0021] In the second coating, activated carbon plays two crucial roles during battery charging and discharging. First, it rapidly adsorbs and desorbs lithium ions, improving the overall pulse power performance and giving the lithium-ion battery a function similar to a supercapacitor. Second, compared to other active materials, activated carbon has a smaller particle size and larger specific surface area, allowing it to retain more electrolyte within the electrodes. Since the electrolyte is the carrier for lithium ions between the positive and negative electrodes, increasing the electrolyte retention reduces the internal resistance of the lithium-ion battery and increases its cycle life.

[0022] In this invention, activated carbon material cannot be used alone as the active material of coating two. It must be used in combination with positive and negative electrode active materials. This is because the interaction between activated carbon material and lithium ions is an adsorption and desorption process. When lithium ions are adsorbed on the activated carbon of coating two, the lithium ions need to be transferred inside the activated carbon layer. They cannot be quickly and timely transferred to coating one to complete the entire charge and discharge process, which will affect the overall power performance of the battery. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] This invention protects a double-layer coating process for battery electrodes. Conventional lithium-ion battery electrodes are coated with a single layer. This invention adds a second coating layer to the single-layer coating. The second coating layer contains activated carbon material, which improves the adsorption rate of lithium ions during charging and discharging, and at the same time increases the amount of electrolyte adsorbed, thereby improving the battery power performance.

[0025] The following are specific examples.

[0026] The specific implementation process of the positive electrode is as follows:

[0027] 1) Coating slurry preparation: The positive electrode active material, conductive agent and binder are stirred and mixed. After the mixture is uniform, a solvent is added and the mixture is stirred and mixed until the slurry is uniformly dispersed. The solvent is preferably N-methylpyrrolidone. The viscosity of the slurry is adjusted to 6000mPa·s-8000mPa·s by adjusting the amount of solvent added.

[0028] Preparation of coating slurry: The positive electrode active material, activated carbon, conductive agent and binder are stirred and mixed. After the mixture is uniform, a solvent is added and the mixture is stirred and mixed until the slurry is uniformly dispersed. The solvent is preferably N-methylpyrrolidone. The viscosity of the slurry is adjusted to 6000mPa·s-8000mPa·s by adjusting the amount of solvent added.

[0029] 2) Double-layer electrode coating: Two slurries are coated on both sides of an aluminum foil with a thickness of 12μm or 13μm using a double-layer coating machine. The weight ratio of coating one to the total coating (coating one + coating two) is 10%-90%, preferably 50%-70%, and the weight ratio of coating two to the total coating is 10%-90%, preferably 30%-50%. After coating, the coating is dried to obtain a positive electrode with a double-layer coating structure.

[0030] The specific implementation process of the negative electrode is as follows:

[0031] 1) Coating slurry preparation: The negative electrode active material, conductive agent and binder are stirred and mixed. After the mixture is uniform, a solvent is added and the mixture is stirred and mixed until the slurry is uniformly dispersed. The solvent is preferably deionized water. The viscosity of the slurry is adjusted to 6000mPa·s-8000mPa·s by adjusting the amount of solvent added.

[0032] Preparation of coating slurry: The negative electrode active material, activated carbon, conductive agent and binder are stirred and mixed. After the mixture is uniform, a solvent is added and the mixture is stirred and mixed until the slurry is uniformly dispersed. The solvent is preferably deionized water. The viscosity of the slurry is adjusted to 6000mPa·s-8000mPa·s by adjusting the amount of solvent added.

[0033] 2) Double-layer electrode coating: Two slurries are coated on both sides of a 6μm thick copper foil using a double-layer coating machine. The first coating accounts for 10%-90% of the total weight of the coating, preferably 50%-70%, and the second coating accounts for 10%-90% of the total weight of the coating, preferably 30%-50%. After coating, the coating is dried to obtain a negative electrode with a double-layer coating structure.

[0034] Example 1

[0035] This embodiment designs a total of 7 positive electrode formulations (by mass), numbered 0 to 6. Formulation 0 is 95% activated carbon + 2% PVDF + 3% SP; formulation 1 is 95% LCO + 2% PVDF + 3% SP; formulation 2 is 94.8% LCO + 0.2% activated carbon + 2% PVDF + 3% SP; formulation 3 is 94% LCO + 1% activated carbon + 2% PVDF + 3% SP; formulation 4 is 92% LCO + 3% activated carbon + 2% PVDF + 3% SP; formulation 5 is 85% LCO + 10% activated carbon + 2% PVDF + 3% SP; and formulation 6 is 94.9% LCO + 0.1% activated carbon + 2% PVDF + 3% SP.

[0036] In addition, this embodiment also designs seven negative electrode formulations (by mass) numbered 7 to 13. Formulation 7 is 95% graphite + 1% CMC + 2% SBR + 2% SP; formulation 8 is 94.8% graphite + 0.2% activated carbon + 1% CMC + 2% SBR + 2% SP; formulation 9 is 94% graphite + 1% activated carbon + 1% CMC + 2% SBR + 2% SP; formulation 10 is 92% graphite + 3% activated carbon + 1% CMC + 2% SBR + 2% SP; formulation 11 is 85% graphite + 10% activated carbon + 1% CMC + 2% SBR + 2% SP; formulation 12 is 94.9% graphite + 0.1% activated carbon + 1% CMC + 2% SBR + 2% SP; and formulation 13 is 95% activated carbon + 1% CMC + 2% SBR + 2% SP.

[0037] The positive electrode sheets for the battery were prepared according to the above positive electrode formula. Six sets of positive electrode sheets were prepared, namely A, B, C, D, E, and F. A positive electrode sheet A is a single-layer coating with formula No. 1. The upper layer (coating two, the same below) of B positive electrode sheet is formula No. 2, and the lower layer (coating one, the same below) is formula No. 1, with each layer accounting for 50% (by mass). The upper layer of C positive electrode sheet is formula No. 3, and the lower layer is formula No. 1, with each layer accounting for 50%. The upper layer of D positive electrode sheet is formula No. 4, and the lower layer is formula No. 1, with each layer accounting for 50%. The upper layer of E positive electrode sheet is formula No. 5, and the lower layer is formula No. 1, with each layer accounting for 50%. F consists of a top layer of formula 6 and a bottom layer of formula 1, with each layer comprising 50% of the total weight. G consists of a top layer of formula 0 and a bottom layer of formula 1, with each layer comprising 50% of the total weight. N-methylpyrrolidone was used as a solvent to stir the above formulas. After thorough stirring, the slurry viscosity was adjusted to 6500 mPa·s, and then coated onto a 13 μm thick aluminum foil using a double-layer coating machine. The total coating surface density on the aluminum foil side was 12 mg / cm³. 2The weight of the first layer (the lower layer) is 50% of the total weight of the coating, and the weight of the second layer (the upper layer) is 50% of the total weight of the coating.

[0038] The negative electrode sheets for the battery were prepared according to the above negative electrode formula. Six sets of negative electrode sheets were prepared, namely A negative, B negative, C negative, D negative, E negative, and F negative. A negative electrode is a single-layer coating with formula No. 7. B negative electrode has an upper layer (coating two, the same below) with formula No. 8 and a lower layer (coating one, the same below) with formula No. 7. The upper and lower layers each account for 50% (by mass, the same below). C negative electrode has an upper layer with formula No. 9 and a lower layer with formula No. 7. The upper and lower layers each account for 50%. D negative electrode has an upper layer with formula No. 10 and a lower layer with formula No. 7. The upper and lower layers each account for 50%. E negative electrode has an upper layer with formula No. 11 and a lower layer with formula No. 7. The upper and lower layers each account for 50%. F negative electrode has an upper layer with formula No. 12 and a lower layer with formula No. 7. The upper and lower layers each account for 50%. The upper layer (G-type) uses formulation #13, and the lower layer uses formulation #7, with each layer comprising 50% of the total weight. Deionized water was used as the solvent to stir the formulations. After thorough stirring, the slurry viscosity was adjusted to 6500 mPa·s, and then coated onto a 6 μm thick copper foil using a double-layer coating machine. The total coating area density on the copper foil side of the substrate was 7.63 mg / cm³. 2 The weight of the first layer (the lower layer) is 50% of the total weight of the coating, and the weight of the second layer (the upper layer) is 50% of the total weight of the coating.

[0039] A 2Ah soft-pack battery was assembled using the above-mentioned positive and negative electrode sheets. The battery used a 12-micron polyethylene (PE) separator, and the electrolyte used ethylene carbonate (EC) and ethyl methyl carbonate (EMC) as solvents, with EC accounting for 30% by weight and EMC accounting for 70% by weight. The lithium salt was 1 mol / L lithium hexafluorophosphate, and the additives included 2% by weight of vinylene carbonate (VC) and 2% by weight of fluoroethylene carbonate (FEC). The batteries were divided into 12 groups (Group ①- Group 1: Electrode type A (positive) and A (negative); Group 2: Electrode type A (positive) and B (negative); Group 3: Electrode type A (positive) and C (negative); Group 4: Electrode type A (positive) and D (negative); Group 5: Electrode type A (positive) and E (negative); Group 6: Electrode type A (positive) and F (negative); Group 7: Electrode type A (negative) and B (positive); Group 8: Electrode type A (negative) and C (positive); Group 9: Electrode type A (negative) and D (positive); Group 10: Electrode type A (negative) and E (positive). The electrodes used in this group are A (negative) and F (positive). The electrodes used in the group were D-negative and D-positive. The 30C rate discharge performance of 12 groups of batteries was tested, and the 30C discharge capacity retention rate of different groups was compared. The electrode combinations of the assembled batteries and the battery test results are shown in Table 1.

[0040] Table 1 Battery Assembly Groups and 30C Discharge Capacity Retention Rate

[0041]

[0042]

[0043]

[0044] Comparing the 30C discharge capacity retention rates of groups ①-⑥, the 30C discharge capacity retention rates of groups ⑤ and ④ are not significantly different. This means that when the activated carbon addition exceeds 3%, the high-rate discharge capacity retention rates of the batteries are roughly the same. Furthermore, adding excessive activated carbon reduces the proportion of active material in the battery electrodes, increases the amount of liquid absorbed, and leads to a decrease in battery energy density. In addition, increasing the proportion of activated carbon in the electrodes requires increasing the overall weight of the electrodes to ensure sufficient effective active material, resulting in increased electrode thickness, which is detrimental to the rapid transport of lithium ions. Therefore, 3% activated carbon is the upper limit of the optimal addition amount. In groups ②-④, the 30C discharge capacity retention rate gradually increases with the increase of activated carbon addition. Group ① has the lowest capacity retention rate compared to groups ②-⑤. This indicates that the double-layer coating process for the negative electrode, with the addition of activated carbon in the upper coating layer, can achieve rapid adsorption and desorption of lithium ions during charging and discharging, which has a positive effect on improving the rate performance of lithium-ion batteries. Although activated carbon was added to the upper coating of group ⑥, the amount was too small to effectively adsorb lithium ions. Similarly, compared to group ⑦... The same conclusion can be drawn from the 30C discharge capacity retention rate: the positive electrode can improve the rate performance of lithium-ion batteries by using a double-layer coating process and adding activated carbon to the upper coating. Both the positive and negative electrodes of this group adopt a double-layer coating process. The proportion of activated carbon in the upper coating is 3%. This group has the highest capacity retention rate at 30C discharge. The negative electrode is coated with a double layer, with the upper layer consisting of a 95% activated carbon coating as the main material. The positive electrode is coated with a double layer, with the upper layer being a 95% activated carbon coating as the main material. Groups and The group with the worst rate performance compared to the other groups is mainly because the interaction between activated carbon material and lithium ions is mainly an adsorption and desorption process. When lithium ions are adsorbed on the activated carbon of the second coating, the lithium ions need to be transferred inside the activated carbon layer and cannot be quickly and timely transferred to the first coating to complete the entire charge and discharge process, thus affecting the overall power performance of the battery.

[0045] Example 2

[0046] This embodiment designs two positive electrode formulations (by mass): No. 1 and No. 4. Formulation No. 1 is 95% LCO + 2% PVDF + 3% SP, and formulation No. 4 is 92% LCO + 3% activated carbon + 2% PVDF + 3% SP. In addition, this embodiment also designs two negative electrode formulations (by mass): No. 7 is 95% graphite + 1% CMC + 2% SBR + 2% SP, and formulation No. 10 is 92% graphite + 3% activated carbon + 1% CMC + 2% SBR + 2% SP.

[0047] The positive electrode sheets for the battery were prepared according to the above positive electrode formula. Six sets of positive electrode sheets were prepared, namely A-positive, D-positive, D-positive-1, D-positive-2, D-positive-3, and D-positive-4. A-positive is a single-layer coating with formula No. 1. The upper layer (coating two, the same below) of D-positive is formula No. 4, and the lower layer (coating one, the same below) is formula No. 1, with each layer accounting for 50% (by mass, the same below). The upper layer of D-positive-1 is formula No. 4, and the lower layer is formula No. 1, with each layer accounting for 10% and 90%. The upper layer of D-positive-2 is formula No. 4, and the lower layer is formula No. 1, with each layer accounting for 70% and 30%. The upper layer of D-positive-3 is formula No. 4, and the lower layer is formula No. 1, with each layer accounting for 90% and 10%. D-4 has an upper layer of formula 4 and a lower layer of formula 1, with each layer comprising 5% and 95% of the total. D-5 has an upper and lower layer of formula 4, with each layer comprising 50%. N-methylpyrrolidone was used as a solvent to stir the above formulas. After thorough stirring, the slurry viscosity was adjusted to 6500 mPa·s. The slurry was then coated onto a 13 μm thick aluminum foil using a double-layer coating machine. The total coating surface density of the positive electrode coating was set to 12 mg / cm³. 2 D-positive, D-positive-1, D-positive-2, D-positive-3, and D-positive-4 are coated according to the proportions of the upper and lower layers mentioned above.

[0048] The negative electrode sheets for the battery were prepared according to the above negative electrode formula. Six sets of negative electrode sheets were prepared, namely A-negative, D-negative, D-negative-1, D-negative-2, D-negative-3, and D-negative-4. A-negative was a single-layer coating with formula No. 7. The upper layer (coating two, the same below) of D-negative was formula No. 10, and the lower layer (coating one, the same below) was formula No. 7, with each layer accounting for 50% (by mass, the same below). The upper layer of D-negative-1 was formula No. 10, and the lower layer was formula No. 7, with each layer accounting for 10% and 90%. The upper layer of D-negative-2 was formula No. 10, and the lower layer was formula No. 7, with each layer accounting for 70% and 30%. The upper layer of D-negative-3 was formula No. 10, and the lower layer was formula No. 7, with each layer accounting for 90% and 10%. D-4 has an upper layer of formula 10 and a lower layer of formula 7, with each layer comprising 5% and 95% of the total. D-5 has an upper and lower layer of formula 10, with each layer comprising 50%. Deionized water was used as the solvent to stir the above formulas. After thorough stirring, the slurry viscosity was adjusted to 6500 mPa·s, and then coated onto a 6 μm thick copper foil using a double-layer coating machine. The total coating surface density was set to 7.63 mg / cm³. 2 D-negative, D-negative-1, D-negative-2, D-negative-3, and D-negative-4 are coated according to the proportions of the upper and lower layers mentioned above.

[0049] A 2Ah soft-pack battery is assembled using the above-mentioned positive and negative electrode sheets. The battery uses a 12-micron polyethylene (PE) separator, and ethylene carbonate (EC) and ethyl methyl carbonate (EMC) as solvents. EC accounts for 30% by weight, EMC accounts for 70% by weight, the lithium salt is 1 mol / L lithium hexafluorophosphate, and the additives include 2% by weight of vinylene carbonate (VC) and 2% by weight of fluoroethylene carbonate (FEC). The battery is divided into 13 groups: Group ① uses A positive and A negative electrodes, Group ④ uses A positive and D negative electrodes, Group ④-1 uses A positive and D negative-1 electrodes, Group ④-2 uses A positive and D negative-2 electrodes, Group ④-3 uses A positive and D negative-3 electrodes, and Group ④-4 uses A positive and D negative-4 electrodes. Group ⑧ used electrodes with A negative and D positive; Group ⑧-1 used electrodes with A negative and D positive -1; Group ⑧-2 used electrodes with A negative and D positive -2; Group ⑧-3 used electrodes with A negative and D positive -3; Group ⑧-4 used electrodes with A negative and D positive -4; Group ⑧-5 used electrodes with D positive and D negative; and Group ⑧-6 used electrodes with D positive -5 and D negative -5. The 30C rate discharge performance of the 13 groups of batteries was tested, and the 30C discharge capacity retention rate and battery energy density of different groups were compared. The assembled battery electrode combinations and battery test results are shown in Table 2.

[0050] Table 2 Battery Assembly Groups and 30C Discharge Capacity Retention Rate

[0051]

[0052]

[0053] Comparing the 30C discharge capacity retention rates of the above battery groups, the proportion of activated carbon in the double-coated electrodes is 3% in all groups. Among groups ④, ④-1, ④-2, and ④-3, group ④ has the highest capacity retention rate. When the weight proportion of the upper layer increases to 90%, the battery capacity retention rate decreases by 3%, but it is still higher than group ①. When the weight proportion of the upper layer is 5%, it cannot effectively adsorb lithium ions, resulting in a lower battery capacity retention rate. Similarly, comparing groups ⑧, ⑧-1, ⑧-2, and ⑧-3, group ⑧ has the highest capacity retention rate. When the weight proportion of the upper layer increases to 90%, the battery capacity retention rate decreases by 3%, but it is still higher than group ①. Group ⑧-5 uses double-coated electrodes for both positive and negative electrodes, with the activated carbon content in the upper layer being 3%, and the upper layer accounting for 50% of the entire coating. This group has the highest capacity retention rate. Group ⑧-6 contains 3% activated carbon in both the positive and negative electrodes, and the activated carbon content in both the upper and lower layers of the positive and negative electrodes is 3%. Compared with Group ①, although this group improves the capacity retention rate during 30C discharge, the energy density of the battery is affected because the activated carbon is distributed in both the upper and lower layers, which is not conducive to the overall performance of the battery.

[0054] The above embodiments illustrate that a double-coated electrode design with activated carbon in the upper coating can improve the rate performance of the battery. The highest rate performance is achieved when the upper coating accounts for 50%-70% of the total coating weight. When the proportion of the upper coating is too high (over 70%), the activated carbon content in the electrode becomes too high, leading to a decrease in the proportion of battery performance materials. To ensure the amount of effective active material in the electrode, the electrode coating density needs to be increased, resulting in an increase in the overall weight of the electrode, i.e., an increase in electrode thickness. This is not conducive to the rapid transport of lithium ions within the electrode, leading to a decrease in battery rate performance. The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the invention. Therefore, equivalent variations made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A battery pole piece, characterized in that: the pole piece comprises a current collector and two parts of a coating attached to the two side surfaces of the current collector, the current collector is made of aluminum foil or copper foil, the coating is a double-layer structure attached to the surface of the current collector in turn, comprising two parts of coating one and coating two, coating one is an active material coating, coating one is attached to the surface of the current collector in the lower layer, coating two is a functional coating, coating two is attached to the surface of coating one in the upper layer; the pole piece is divided into a positive pole piece and a negative pole piece; for the positive pole piece: coating one comprises two parts of a main material and an auxiliary material, the main material is a positive active material, the auxiliary material is a conductive agent and a binder, the positive active material can be one or more than two of commonly used positive materials such as lithium nickel cobalt manganese oxide ternary material (NCM), lithium cobalt oxide (LCO), lithium iron phosphate (LFP), lithium manganese oxide (LMO), lithium manganese iron phosphate, lithium vanadium phosphate, etc., the binder is preferably polytetrafluoroethylene (PVDF), and the conductive agent is preferably one or both of conductive carbon black (SP) and carbon nanotubes; coating two comprises three parts of a main material, an auxiliary material and a functional material; the main material is one or more than two of commonly used positive materials such as lithium nickel cobalt manganese oxide ternary material (NCM), lithium cobalt oxide (LCO), lithium iron phosphate (LFP), lithium manganese oxide (LMO), lithium manganese iron phosphate, lithium vanadium phosphate, etc.; the functional material is an activated carbon material, the mass ratio of the activated carbon to the solid matter of coating two is in the range of 0.2% to 10%, preferably 1% to 3%; the auxiliary material comprises a conductive agent and a binder, the binder is preferably PVDF, and the conductive agent is preferably one or both of conductive carbon black (SP) and carbon nanotubes; for the negative pole piece: coating one comprises two parts of a main material and an auxiliary material, the main material is a negative active material, the auxiliary material is a conductive agent and a binder, the active material can be one or more than two of commonly used negative materials such as graphite, silicon carbon, hard carbon, mesocarbon microbeads, etc.; the binder is preferably one or both of sodium hydroxymethyl cellulose (CMC) and styrene butadiene rubber (SBR), and the conductive agent is preferably one or both of conductive carbon black (SP) and carbon nanotubes; coating two comprises three parts of a main material, an auxiliary material and a functional material; the main material is one or more than two of commonly used negative materials such as graphite, silicon carbon, hard carbon, mesocarbon microbeads, etc.; the functional material is an active material, the mass ratio of the activated carbon to the solid matter of coating two is in the range of 0.2% to 10%, preferably 1% to 3%; the auxiliary material comprises a conductive agent and a binder, the binder is preferably PVDF, and the conductive agent is preferably one or both of conductive carbon black (SP) and carbon nanotubes. 2.A preparation method of the battery pole piece of claim 1, characterized in that: the specific implementation process of the positive pole piece is as follows: 1) coating one slurry preparation: mix the positive active material, the conductive agent and the binder by stirring, add a solvent after uniform mixing, continue to stir and mix until the slurry is uniformly dispersed, the solvent is preferably N-methyl pyrrolidone, and the viscosity of the slurry is adjusted to a suitable viscosity for coating by adjusting the amount of solvent added. Coating two slurry preparation: the positive active material, activated carbon, conductive agent and binder are mixed by stirring, after mixing evenly, adding solvent, continue to stir and mix until the slurry is uniformly dispersed, the solvent is preferably N-methyl pyrrolidone, the slurry viscosity is adjusted to a suitable coating viscosity by adjusting the amount of solvent added; 2) Double layer electrode coating: using double layer coating machine to coat two kinds of slurry on both sides of 10-15 μm thick aluminum foil, coating one accounts for 10%-90% of the weight of the entire coating (coating one+coating two), preferably the ratio is 50%-70%, the corresponding coating two accounts for 10%-90% of the weight of the entire coating, preferably the ratio is 30%-50%; after coating, the coating is dried to obtain a positive electrode sheet with a double layer coating structure; The negative electrode sheet is specifically implemented as follows: 1) Coating one slurry preparation: the negative active material, conductive agent and binder are mixed by stirring, after mixing evenly, adding solvent, continue to stir and mix until the slurry is uniformly dispersed, the solvent is preferably deionized water, the slurry viscosity is adjusted to a suitable coating viscosity by adjusting the amount of solvent added; Coating two slurry preparation: the negative active material, activated carbon, conductive agent and binder are mixed by stirring, after mixing evenly, adding solvent, continue to stir and mix until the slurry is uniformly dispersed, the solvent is preferably deionized water, the slurry viscosity is adjusted to a suitable coating viscosity by adjusting the amount of solvent added; 2) Double layer electrode coating: using double layer coating machine to coat two kinds of slurry on one side or both sides of 4.5-8 μm thick copper foil, coating one accounts for 10%-90% of the weight of the entire coating, preferably the ratio is 50%-70%, the corresponding coating two accounts for 10%-90% of the weight of the entire coating, preferably the ratio is 30%-50%; After coating, the coating is dried to obtain a negative electrode sheet with a double layer coating structure.

3. Use of the battery electrode of claim 1, characterized in that: The positive electrode sheet and the negative electrode sheet are used as lithium ion battery positive electrode sheet and negative electrode sheet respectively in lithium ion battery. The positive electrode sheet and the negative electrode sheet are used as lithium ion battery positive electrode sheet and negative electrode sheet respectively in lithium ion battery.

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