A current collector

Abstract

The application provides a current collector, comprising a copper foil and a modified coating, the modified coating is arranged on the surface of the copper foil, and the modified coating comprises a Cu-Si composite material which is composed of elemental Cu and elemental Si. Since Cu and Si are both highly conductive substances, the current collector provided by the application adopts the Cu-Si composite material as the modified coating of the foil material, so that the current collector has more excellent contact performance with active substances on the basis of ensuring the conductive performance, is not easy to fall off in the cycle process, and the Cu-Si composite material has excellent electron transport performance, so that the internal resistance of the battery can be reduced, and the rate performance and cycle performance of the battery can be improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically, it relates to a current collector. Background Technology

[0002] Lithium-ion batteries possess advantages such as high specific energy, high stability, low self-discharge rate, and no pollution. In lithium-ion batteries, the current collector generally refers to the base metal foil used to attach the active material at the positive and negative electrodes. It contacts the active material, thereby converging and outputting current. The current collector serves both to adsorb and support the active material and to act as a conductor to converge the generated current, ensuring charging and discharging efficiency. In lithium-ion batteries, a slurry of active material is uniformly coated on the surface of the current collector. The current collector, through contact with the active material, converges and conducts electrons generated by the electrochemical reaction to the external circuit, thus realizing the conversion of chemical energy into electrical energy. Therefore, the contact condition between the current collector and the active material profoundly affects battery performance.

[0003] Currently, lithium-ion batteries use metal foil as the current collector. However, the physical properties of the foil often result in poor contact and adhesion between the foil and the active material, leading to high interfacial resistance and excessive internal resistance. Furthermore, during battery cycling, changes in electrode volume can easily cause active particles to detach, reducing battery capacity and cycle performance. Simultaneously, due to the high reactivity of metal foil, it readily reacts with oxygen in the air, necessitating passivation of the foil surface. However, copper foil passivation often results in defects, leading to decreased adhesion and exposed foil spots, severely impacting battery capacity, internal resistance, cycle life, and even directly causing electrode failure. Therefore, improving the contact performance between the current collector and the active material, thereby enhancing the cycle performance and electrochemical performance of lithium-ion batteries, is a pressing technical problem that those skilled in the art must address in their research. Summary of the Invention

[0004] The purpose of this invention is to provide a current collector that uses Cu-Si composite material as a modified coating of copper foil, which can ensure its conductivity while having better contact performance with active materials, and ensure that it is not easily detached during the cycle.

[0005] According to one aspect of the present invention, a current collector is provided, comprising a copper foil and a modified coating. The modified coating is disposed on the surface of the copper foil and comprises a Cu-Si composite material, which is composed of elemental Cu and elemental Si. Since both Cu and Si are highly conductive materials, the current collector provided by the present invention, using a Cu-Si composite material as a modified coating for the copper foil, can maintain its conductivity while exhibiting superior contact performance with the active material, ensuring it is less prone to detachment during cycling. Furthermore, the Cu-Si composite material possesses excellent electron transport properties, thereby reducing the internal resistance of the battery and improving its rate performance and cycle performance. In addition, the current collector exhibits superior mechanical strength.

[0006] Preferably, the Cu-Si composite material has a core-shell structure, in which the core is composed of elemental Cu and the outer shell is composed of elemental Si. The Cu-Si composite material with the stable core-shell structure described above can prevent the agglomeration of nano-Cu particles, improve the utilization rate of nano-Cu particles, and thus reduce the interfacial resistance between the current collector and the active material provided by this invention, thereby improving the conductivity and contact performance of the current collector.

[0007] Preferably, the core of the above-mentioned core-shell structure contains a number of nano-Cu particles with a particle size of 15-20 nm. For example, the particle size of nano-Cu is 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, or 20 nm.

[0008] Preferably, the particle size of the Cu-Si composite material is ≤75μm. For example, the particle size of the Cu-Si composite material is 50μm, 55μm, 60μm, 65μm, 70μm or 75μm.

[0009] Preferably, the molar ratio of elemental Cu to elemental Si is 1–5:16–24. For example, the molar ratios of elemental Cu to elemental Si are 1:16, 1:20, 1:24, 2:16, 2:20, 2:24, 3:16, 3:20, 3:24, 4:16, 4:20, 4:24, 5:16, 5:20, or 5:24, etc. In the Cu-Si composite material with the above ratios, nano-Cu particles are uniformly dispersed in Si, forming a stable multi-core-shell structure, thereby giving the negative electrode current collector provided by this invention excellent conductivity and contact performance.

[0010] Preferably, the synthesis method of Cu-Si composite material includes the following steps:

[0011] S1. Mix elemental Si, a reducing agent, and a cuprous compound to form a premix;

[0012] S2. The premix is ​​melted, during which the cuprous compound produces elemental Cu through a redox reaction with a reducing agent;

[0013] S3. The melt obtained after S2 is subjected to stress-relief annealing to obtain an intermediate;

[0014] S4. The intermediate is subjected to high-temperature solid-state treatment to obtain the Cu-Si composite material. This method first uses a high-temperature melting method to utilize the strong reducing properties of the reducing agent to remove Cu from the cuprous compound. + Elemental Cu was reduced to Si and melted into it. Then, stress-relief annealing and high-temperature solid-phase melting were performed at different temperatures. Stress-relief annealing eliminated internal stress, facilitating the subsequent precipitation of nano-Cu particles. High-temperature solid-phase melting allowed the nano-Cu particles to crystallize in Si, ultimately forming a Cu-Si composite material with nano-Cu uniformly dispersed in Si. The method provided by this invention uses a high-temperature solid-phase melting method to synthesize nano-Cu particles using a reducing agent and cuprous compounds. This method can effectively control the crystal structure and phase purity of the Cu-Si composite material, thereby synthesizing a Cu-Si composite material with nano-Cu particles uniformly dispersed in Si. This results in the current collector provided by this invention having excellent contact performance, thus enabling the battery to have superior cycle performance and electrochemical performance. Furthermore, the synthesis method provided by this invention is simple to operate and suitable for industrial production.

[0015] Preferably, the reducing agent includes at least one of silicon carbide and silicon nitride.

[0016] Preferably, the cuprous compound includes at least one of CuI, CuCl, and CuBr.

[0017] Preferably, the cuprous compound is CuI, and the reducing agent is Si3N4. Compared with other cuprous compounds, CuI is a structurally stable compound, while Si3N4 has better reducing properties and a lower melting temperature, which is beneficial for reducing the monovalent copper ions of the cuprous compound to elemental copper during high-temperature melting.

[0018] Preferably, in the raw materials used to prepare Cu-Si composite materials, the molar ratio of Si:reducing agent:cuprous compound is 60-80:20-40:5-20. For example, in the raw materials used to prepare Cu-Si composite materials, the molar ratio of Si:reducing agent:cuprous compound is 60:20:5, 60:20:10, 60:20:20, 70:20:5, 70:20:10, 70:20:20, 70:25:5, 70:25:10, 70:25:20, 80:20:5, 80:20:10, or 80:20:20, etc.

[0019] Preferably, the reducing agent is Si3N4, and the molar ratio of Si:Si3N4:cuprous compound in the raw materials used to prepare Cu-Si composite materials is 70:25:5.

[0020] Preferably, the reducing agent is SiC, and the molar ratio of Si:SiC:cuprous compound in the raw materials used to prepare Cu-Si composite materials is 70:20:10.

[0021] Preferably, in step S2, the melting temperature is 1000–1500°C, and the time is 15–45 minutes. For example, in step S2, the melting temperature is 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, or 1500°C, and the time is 15 minutes, 25 minutes, 35 minutes, or 45 minutes, etc. By controlling the melting temperature and time, on the one hand, excess impurities can be removed, improving the purity of the product; on the other hand, high-temperature melting within the above temperature range allows the reducing agent and cuprous compound to react fully, obtaining a molten Cu in Si, which is beneficial for the subsequent precipitation of nano-Cu particles, thereby obtaining a Cu-Si composite material with good dispersibility and stable crystal structure.

[0022] Preferably, the melting treatment temperature is 1200°C and the time is 15 minutes.

[0023] Preferably, in S2, the heating rate of the melting treatment is 5 to 25°C / min. For example, in S2, the heating rate of the melting treatment is 5°C / min, 10°C / min, 15°C / min, 20°C / min, or 25°C / min.

[0024] Preferably, the heating rate of the melting process is 10°C / min.

[0025] Preferably, in step S3, the stress-relief annealing temperature is 300–400°C, and the time is 1–3 hours. For example, in step S3, the stress-relief annealing temperature is 300°C, 350°C, or 400°C, and the time is 1 hour, 2 hours, or 3 hours. Performing stress-relief annealing within the above temperature range can, on the one hand, avoid the problem of excessive internal stress during melt solidification due to excessive temperature difference, and on the other hand, prevent the inability to precipitate nano-Cu particles during subsequent phase formation. Moreover, the annealing time is relatively short within the above temperature range, which can save synthesis time.

[0026] Preferably, the stress-relief annealing temperature is 350°C and the time is 3 hours.

[0027] Preferably, in S3, the stress-relief annealing is carried out in a vacuum atmosphere or an inert gas atmosphere, wherein the inert gas includes one of nitrogen, helium, and argon.

[0028] Preferably, the inert gas is argon.

[0029] Preferably, in step S4, the high-temperature solid-state treatment temperature is 500–600°C, and the time is 1–3 hours. For example, in step S4, the high-temperature solid-state treatment temperature is 500°C, 550°C, or 600°C, and the time is 1 hour, 2 hours, or 3 hours. These temperatures are beneficial for the formation of nano-Cu grains during the high-temperature solid-state process, and also help control the particle size of the nano-Cu, preventing grain enlargement from adversely affecting the performance of the Cu-Si composite material.

[0030] Preferably, the high-temperature solid-phase treatment is carried out at a temperature of 550°C for 3 hours.

[0031] According to another aspect of the present invention, a negative electrode sheet is provided, comprising a negative electrode current collector and a negative electrode active coating, wherein the negative electrode current collector is the aforementioned current collector, and the negative electrode active coating is composite with a modified coating of the current collector. Attached Figure Description

[0032] Figure 1 , 2 This is a TEM image of the Cu-Si composite material obtained in Example 1 of the present invention. Detailed Implementation

[0033] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0034] Example 1

[0035] Processing Group 1

[0036] This processing group provides a current collector, the preparation method of which includes the following steps:

[0037] S1. Place the raw materials used to prepare Cu-Si composite materials into an agate mortar and grind them thoroughly to form a premix. The raw materials used to prepare Cu-Si composite materials consist of Si powder, reducing agent powder SiC, and cuprous compound powder CuI. Among them, the molar percentage of Si in the raw materials used to prepare Cu-Si composite materials is 70%, the molar percentage of SiC is 25%, and the molar percentage of CuI is 5%.

[0038] S2. Pour the premix into a 20ml platinum crucible, then place the crucible in a vacuum furnace and melt it at 1200℃ for 15 minutes to obtain the melt.

[0039] S3. Pour the melt obtained after S2 onto a stainless steel plate that has been wiped and cleaned with medical alcohol. Then place the stainless steel plate in a vacuum muffle furnace at 350°C and keep it at that temperature for 3 hours to perform stress-relief annealing treatment to obtain an intermediate.

[0040] S4. Then, the temperature is raised to 550℃ and held for 3 hours for high-temperature solid-phase treatment. After the holding period, the muffle furnace is turned off and the Cu-Si block is cooled with the furnace. Subsequently, the Cu-Si block is placed in an agate mortar and ground thoroughly, and then passed through a 200-mesh sieve to obtain the Cu-Si composite material.

[0041] S5. The above Cu-Si composite material is coated onto the surface of copper foil to obtain the current collector. In the current collector prepared in this treatment group, the molar ratio of elemental Cu to elemental Si in the Cu-Si composite material is 1:19.

[0042] TEM images of the Cu-Si composite materials obtained in this treatment group are as follows: Figure 1 , 2 As shown, by Figure 1 , 2 It can be seen that the nano-Cu particles are uniformly dispersed in Si, exhibiting a core-shell structure. The nano-Cu particles have a size of 15 nm, and the distance between the nano-Cu particles dispersed in Si is 50–200 nm. This indicates that the Cu-Si composite material has been successfully synthesized.

[0043] Processing Group 2

[0044] This processing group provides a current collector prepared by melting and smelting. The preparation steps are as follows: elemental Cu and elemental Si are repeatedly melted four times in a vacuum non-consumable arc furnace under argon protection, followed by vacuum annealing at 800℃, thereby obtaining a Cu-Si composite material. In the current collector prepared by this processing group, the Cu-Si composite material is a Cu-Si alloy, in which elemental Cu and elemental Si are mixed together.

[0045] Processing Group 3

[0046] This treatment group prepares the current collector according to treatment group 1 in this embodiment. The difference between this treatment group and treatment group 1 in this embodiment is that the temperature of the high-temperature solid phase in step S4 of treatment group 1 is replaced with 450°C instead of 550°C. Apart from the above difference, the materials and process operations used in this treatment group are strictly consistent with those of treatment group 1 in this embodiment. In the current collector prepared by this treatment group, the Cu-Si composite material is a copper-silicon mixture.

[0047] Comparison group 1

[0048] This comparative treatment group provides a current collector, which is a common planar copper foil.

[0049] Comparison group 2

[0050] This comparative treatment group provides a current collector, the preparation method of which includes the following steps: coating an equal amount of Si powder onto the surface of a copper foil using treatment group 1 in this embodiment and drying it, thereby obtaining the current collector. The current collector obtained by this comparative treatment group is a silicon-coated copper foil.

[0051] Example 2

[0052] Processing Group 1

[0053] The current collector in this treatment group was prepared according to treatment group 1 in Example 1. The materials and process operations used in this treatment group were strictly consistent with those in treatment group 1 in Example 1.

[0054] Processing Group 2

[0055] This treatment group prepares the current collector according to treatment group 1 of this embodiment. The difference between this treatment group and treatment group 1 of this embodiment is that step S3 (stress-relief annealing) is omitted. Apart from the above differences, the materials and process operations used in this treatment group are strictly consistent with those of treatment group 1 of this embodiment. In the current collector prepared by this treatment group, the size of Cu particles in the Cu-Si composite material is 100-200 μm.

[0056] Processing Group 3

[0057] This treatment group prepares the current collector according to treatment group 1 in this embodiment. The difference between this treatment group and treatment group 1 in this embodiment is that the stress-relief annealing temperature in step S3 of treatment group 1 is replaced with 250°C instead of 350°C. Apart from the above difference, the materials and process operations used in this treatment group are strictly consistent with those in treatment group 1 in this embodiment. In the current collector prepared by this treatment group, the size of the Cu particles in the Cu-Si composite material is 150–300 nm.

[0058] Processing Group 4

[0059] This treatment group prepares the current collector according to treatment group 1 in this embodiment. The difference between this treatment group and treatment group 1 in this embodiment is that the stress-relief annealing temperature in step S3 of treatment group 1 is replaced with 450°C instead of 350°C. Apart from the above difference, the materials and process operations used in this treatment group are strictly consistent with those in treatment group 1 in this embodiment. In the current collector prepared by this treatment group, the size of the Cu particles in the Cu-Si composite material is 70–120 nm.

[0060] Processing Group 5

[0061] This treatment group prepares the current collector according to treatment group 1 in this embodiment. The difference between this treatment group and treatment group 1 in this embodiment is that the temperature of the high-temperature solid phase in step S4 of treatment group 1 is replaced with 650°C instead of 550°C. Apart from the above difference, the materials and process operations used in this treatment group are strictly consistent with those of treatment group 1 in this embodiment. In the current collector prepared by this treatment group, the size of Cu particles in the Cu-Si composite material is 100-300 nm.

[0062] Processing Group 6

[0063] This treatment group prepares the current collector according to treatment group 1 in this embodiment. The difference between this treatment group and treatment group 1 in this embodiment is that the temperature of the high-temperature solid phase in step S4 of treatment group 1 is replaced with 600°C instead of 550°C. Apart from the above difference, the materials and process operations used in this treatment group are strictly consistent with those of treatment group 1 in this embodiment. In the current collector prepared by this treatment group, the size of Cu particles in the Cu-Si composite material is 18 nm.

[0064] Processing Group 7

[0065] This treatment group prepares the current collector according to treatment group 1 in this embodiment. The difference between this treatment group and treatment group 1 in this embodiment is that the temperature of the high-temperature solid phase in step S4 of treatment group 1 is replaced with 500°C instead of 550°C. Apart from the above difference, the materials and process operations used in this treatment group are strictly consistent with those of treatment group 1 in this embodiment. In the current collector prepared by this treatment group, the size of Cu particles in the Cu-Si composite material is 20 nm.

[0066] Example 3

[0067] Processing Group 1

[0068] The current collector in this treatment group was prepared according to treatment group 1 in Example 1. The materials and process operations used in this treatment group were strictly consistent with those in treatment group 1 in Example 1.

[0069] Processing Group 2

[0070] This treatment group prepares the current collector according to treatment group 1 in this embodiment. The difference between this treatment group and treatment group 1 in this embodiment is that the raw materials used in this treatment group to prepare the Cu-Si composite material are composed of Si, SiC, and CuI. Specifically, the molar ratio of Si:SiC:CuI in the raw materials used to prepare the Cu-Si composite material is 70:20:3. Apart from the above difference, the materials and process operations used in this treatment group are strictly consistent with those in treatment group 1 in this embodiment. In the current collector prepared by this treatment group, the molar ratio of elemental Cu to elemental Si in the Cu-Si composite material is 1:30.

[0071] Processing Group 3

[0072] This treatment group prepares the current collector according to treatment group 1 in this embodiment. The difference between this treatment group and treatment group 1 in this embodiment is that the raw materials used in this treatment group to prepare the Cu-Si composite material are composed of Si, SiC, and CuI. Specifically, the molar ratio of Si:SiC:CuI in the raw materials used to prepare the Cu-Si composite material is 80:10:10. Apart from the above difference, the materials and process operations used in this treatment group are strictly consistent with those in treatment group 1 in this embodiment. In the current collector prepared by this treatment group, the molar ratio of elemental Cu to elemental Si in the Cu-Si composite material is 1:9.

[0073] Processing Group 4

[0074] This treatment group prepares the current collector according to treatment group 1 in this embodiment. The difference between this treatment group and treatment group 1 in this embodiment is that the raw materials used in this treatment group to prepare the Cu-Si composite material are composed of Si, SiC, and CuI. Specifically, the molar ratio of Si:SiC:CuI in the raw materials used to prepare the Cu-Si composite material is 70:15:15. Apart from the above difference, the materials and process operations used in this treatment group are strictly consistent with those in treatment group 1 in this embodiment. In the current collector prepared by this treatment group, the molar ratio of elemental Cu to elemental Si in the Cu-Si composite material is 3:17.

[0075] Processing Group 5

[0076] This treatment group prepares the current collector according to treatment group 1 in this embodiment. The difference between this treatment group and treatment group 1 in this embodiment is that the raw materials used in this treatment group to prepare the Cu-Si composite material are composed of Si, SiC, and CuI, wherein the ratio of Si:SiC:CuI in the raw materials used to prepare the Cu-Si composite material is 45:15:30. Apart from the above difference, the materials and process operations used in this treatment group are strictly consistent with those in treatment group 1 in this embodiment. In the current collector prepared by this treatment group, the molar ratio of elemental Cu to elemental Si in the Cu-Si composite material is 1:2.

[0077] Test Example 1

[0078] 1. Test subject:

[0079] Batteries were prepared using the current collectors obtained in Examples 1-3 and tested. The preparation method of the batteries is as follows: (1) Lithium iron phosphate, the positive electrode active material, and graphite, the negative electrode active material, were prepared into positive and negative electrode slurries, respectively; (2) The positive and negative electrode slurries were uniformly coated on the above-mentioned negative electrode current collector and aluminum foil; (3) The coated positive and negative electrodes were baked; (4) Then, they were slit and the tabs were laser-cut; (5) The cut positive and negative electrode sheets and the separator were stacked in the form of positive electrode-separator-negative electrode to form a core pack; (6) The tabs were ultrasonically welded while the core pack was wrapped with an inner protective film; (7) After the core pack was put into the shell, the positive and negative electrode tab covers were laser-welded; (8) Electrolyte was injected for formation; (9) After replenishing the electrolyte, the sealing nails were welded; (10) The capacity OCV test was performed; (11) The battery was obtained.

[0080] 2. Test items:

[0081] (1) Tensile strength of negative electrode: First measure the size of the electrode, then place the electrode on the testing machine and stretch it according to different strain rates. Measure the force generated by the electrode during the stretching process. The testing machine will automatically output the tensile strength value.

[0082] (2) Battery capacity retention rate after 2000 cycles: The battery is subjected to normal cycling at 25℃ at 1C / 1C, and the battery capacity is tested after 2000 cycles. The capacity retention rate after 2000 cycles is calculated by dividing the capacity of the 2000th cycle by the capacity of the 1st cycle.

[0083] (3) Battery discharge at 25℃ with 2C rate: The battery is discharged at 25℃ with 2C current. Compared with the discharge at 25℃ with 1 / 3C current, the discharge capacity of the battery at 25℃ with 2C current is divided by the discharge capacity of 1 / 3C current to calculate the battery discharge at 25℃ with 2C rate.

[0084] (4) Battery internal resistance: The battery resistance is tested using a lithium battery voltage internal resistance tester.

[0085] 3. Test Results:

[0086] Table 1 Performance test results of the battery in Example 1

[0087]

[0088]

[0089] Table 2 Performance test results of the battery in Example 2

[0090]

[0091] Table 3 Performance test results of the battery in Example 3

[0092]

[0093]

[0094] The test results are shown in Tables 1-3. The performance test results of treatment group 1 in Example 1 were compared with those of control treatment groups 1 and 2. Table 1 shows that, under the same conditions of other materials and operations in battery preparation, control treatment group 1 used ordinary copper foil as the negative electrode current collector. This current collector had poor contact with the negative electrode active material, was prone to detachment during cycling, and had a large interfacial resistance. Therefore, the electrochemical performance, conductivity, and mechanical strength of the resulting battery were significantly lower than those of the battery prepared in treatment group 1. Table 1 also shows that, under the same conditions of other materials and operations in battery preparation, control treatment group 2 used silicon-coated copper foil as the negative electrode current collector. This current collector had poor contact with the negative electrode active material and had a large interfacial resistance. Therefore, the electrochemical performance, conductivity, and mechanical strength of the resulting battery were significantly lower than those of the battery prepared in treatment group 1. This demonstrates that, compared to comparative treatment groups 1 and 2, the current collector provided by the present invention uses a Cu-Si composite material composed of elemental Cu and elemental Si as a modified coating of copper foil, giving the current collector provided by the present invention excellent contact performance and mechanical strength, making it less prone to detachment during cycling. The current collector also has excellent electrical conductivity, thereby reducing the internal resistance of the battery and improving the electrochemical performance and cycle performance of the battery.

[0095] The performance test results of treatment group 1 in Example 1 were compared with those of treatment groups 2 and 3. Table 1 shows that, under the same conditions of other materials and operations in battery preparation, the melting of raw materials composed of elemental Si and elemental Cu in treatment group 2 failed to form a core-shell Cu-Si composite material. Therefore, the electrochemical performance, conductivity, and mechanical strength of the resulting battery were lower than those of the battery prepared in treatment group 1. Similarly, under the same conditions of other materials and operations in battery preparation, the temperature during the high-temperature solid-state treatment process in treatment group 3 was below 500°C, preventing the formation of a core-shell Cu-Si composite material. Consequently, the electrochemical performance, conductivity, and mechanical strength of the resulting battery were also lower than those of the battery prepared in treatment group 1. This indicates that, compared to treatment groups 2 and 3, the current collector provided by treatment group 1 uses a core-shell Cu-Si composite material as a modified coating on the copper foil, giving the current collector excellent contact performance with the active material, thereby resulting in a battery with excellent electrochemical and cycle performance.

[0096] The performance test results of treatment group 1 in Example 2 were compared with those of treatment groups 2 to 7. As shown in Table 2, under the same conditions of other materials and operations in battery preparation, treatment group 2 omitted the stress-relief annealing operation. The Cu particles in the synthesized Cu-Si composite material could not reach the nanoscale size, and the Cu particles were unevenly dispersed and prone to agglomeration. As a result, the electrochemical performance, cycle performance, and mechanical strength of the battery prepared by this method were lower than those prepared by treatment group 1, and the internal resistance of the battery prepared by treatment group 2 was higher than that prepared by treatment group 1. The stress-relief annealing temperature of treatment groups 3 and 4 was not set in the range of 300-400℃. The Cu particles in the synthesized Cu-Si composite material had a particle size >20nm. Compared with the battery prepared by treatment group 1, the batteries prepared by treatment groups 3 and 4 had higher internal resistance and poorer rate performance, cycle performance, and mechanical strength. The high-temperature solid phase temperature of treatment group 5 was above 500℃. The Cu particles in the synthesized Cu-Si composite material had a particle size >20nm. Compared with the batteries prepared by treatment groups 1, 6, and 7, the battery prepared by treatment group 5 had higher internal resistance and poorer rate performance, cycle performance, and mechanical strength. This demonstrates that, compared to treatment groups 2-5, treatment groups 1, 6, and 7, by adjusting the stress-relief annealing temperature and the high-temperature solid phase temperature, control the size of Cu particles in the Cu-Si composite material within the range of 15-20 nm. This is beneficial for synthesizing a uniformly dispersed, non-agglomerated, and structurally stable Cu-Si composite material, resulting in the current collector provided by this invention having superior contact performance. Consequently, it reduces the internal resistance of the battery thus produced and improves the battery's electrochemical and cycle performance.

[0097] The performance test results of treatment group 1 and treatment groups 2-5 in Example 3 were compared. Table 3 shows that, under the same conditions of other materials and operations in battery preparation, the molar ratio of elemental Cu to elemental Si in the Cu-Si composite materials prepared by treatment groups 2 and 5 was not set within the range of 1-5:16-24. Compared with the battery prepared by treatment group 1, the batteries prepared by treatment groups 2 and 5 had higher internal resistance and poorer rate performance and cycle performance. Under the same conditions of other materials and operations in battery preparation, the molar ratio of elemental Cu to elemental Si in the Cu-Si composite materials prepared by treatment groups 3 and 4 was not set to 1:19. Compared with the battery prepared by treatment group 1, the batteries prepared by treatment groups 2 and 5 had slightly higher internal resistance and slightly worse rate performance and cycle performance. This demonstrates that, compared to treatment groups 2 to 5, treatment group 1, by rationally setting the molar ratio of elemental Cu and elemental Si in the Cu-Si composite material, is beneficial for synthesizing Cu-Si composite materials with high purity, small particle size, uniform dispersion, and stable structure. This results in the current collector provided by the present invention having superior conductivity and contact performance, thereby enabling the battery to have excellent electrochemical performance and cycle performance.

[0098] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention, but such modifications or substitutions are all within the scope of protection of the present invention.

Claims

1. A current collector, characterized in that, The invention includes a copper foil and a modified coating, wherein the modified coating is disposed on the surface of the copper foil, and the modified coating includes a Cu-Si composite material, wherein the Cu-Si composite material is composed of elemental Cu and elemental Si. The synthesis method of the Cu-Si composite material includes the following steps: S1. Mix elemental Si, a reducing agent, and a cuprous compound to form a premix; S2. The premix is ​​melted, during which the cuprous compound produces elemental Cu through a redox reaction with the reducing agent; S3. The melt obtained after step S2 is subjected to stress-relief annealing to obtain an intermediate; S4. The intermediate is subjected to high-temperature solid-state treatment to obtain the Cu-Si composite material.

2. The current collector as described in claim 1, characterized in that, The Cu-Si composite material has a core-shell structure, in which the core is composed of elemental Cu and the outer shell is composed of elemental Si.

3. The current collector as described in claim 2, characterized in that, The core contains several nano-Cu particles with a particle size of 15–20 nm.

4. The current collector as described in claim 1, characterized in that, The particle size of the Cu-Si composite material is ≤75μm.

5. The current collector as described in claim 1, characterized in that, In the Cu-Si composite material, the molar ratio of elemental Cu to elemental Si is 1-5:16-24.

6. The current collector as described in claim 5, characterized in that, In step S2, the melting treatment temperature is 1000–1500°C, and the time is 15–45 minutes.

7. The current collector as described in claim 5, characterized in that, In step S3, the stress-relief annealing temperature is 300–400°C, and the time is 1–3 hours.

8. The current collector as described in claim 5, characterized in that, In step S4, the temperature of the high-temperature solid phase treatment is 500–600°C, and the time is 1–3 hours.

9. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and a negative electrode active coating, wherein the negative electrode current collector is the current collector as described in any one of claims 1 to 8, and the negative electrode active coating is composite with the modified coating of the current collector.

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