Current collector, negative electrode sheet, and lithium ion battery

Abstract

This application relates to the field of batteries, specifically to a current collector, a negative electrode, and a lithium-ion battery. The current collector includes a current collector substrate and a lithium replenishing agent. Along the thickness direction of the current collector substrate, it is divided into a first region, a second region, and a third region from one side surface to the other. The pore size in the first region is smaller than that in the second region, and the pore size in the third region is smaller than that in the second region. The lithium replenishing agent fills the pores in the first, second, and third regions. The current collector substrate provided by this application has a gradient pore structure, reducing lithium replenishing agent shedding and the volume expansion of the silicon negative electrode material, thus reducing stress concentration. Simultaneously, it can reduce the weight of the metal foil on the battery, lower the cost of metal foil raw materials, and provide higher energy density.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a current collector, a negative electrode, and a lithium-ion battery. Background Technology

[0002] Silicon anode materials have become a research hotspot in lithium-ion battery anode materials due to their high capacity, abundant reserves, and good cycle performance. However, during charging and discharging, silicon anode materials undergo volume expansion due to lithium-ion insertion and extraction. This volume change leads to structural damage to the silicon anode material, causing capacity decay and loss of cycle performance. In addition, during the first charge, the electrolyte on the surface of the silicon anode in lithium-ion batteries undergoes reduction and decomposition, forming an SEI film that permanently consumes a large amount of lithium from the positive electrode, reducing the capacity and energy density of the lithium-ion battery.

[0003] The current collector, which needs to be coated on the negative electrode material, is also an important component of lithium batteries. Traditional electrolytic copper foil and composite copper foil have good conductivity, which collects the current generated by the battery's active materials to form a larger current output. At the same time, the thinner the copper foil, the lighter the battery will be, the lower the internal resistance will be, and the better the battery's performance will be. Therefore, reducing the weight of the copper foil on the battery, lowering the cost of copper foil raw materials, and providing higher energy density have become key to the use of copper foil in lithium batteries.

[0004] The problems caused by the volume expansion effect and initial capacity loss of silicon materials include: 1) Particle pulverization, which worsens the electrical contact between silicon particles and the conductive agent; 2) The generation of large amounts of shear and compressive stress, causing silicon particles to crack, increasing internal resistance, and affecting the direct transport of electrons on the electrode; 3) Repeated growth of the surface SEI film consumes electrolyte and lithium source, resulting in poor cycle performance; 4) The SEI thickness increases continuously with electrochemical cycling, and an excessively thick SEI layer hinders electron transfer and Li-ion exchange. + 5) Diffusion, increased internal resistance, and increased polarization; 6) Poor contact between active material and conductive agent and binder, leading to capacity decay; 7) Low initial coulombic efficiency and energy density.

[0005] Therefore, how to effectively solve the problems caused by the volume expansion effect and initial capacity loss of silicon materials has become a hot topic in technological research. Utility Model Content

[0006] In view of this, this application provides a current collector, a negative electrode, and a lithium-ion battery. This current collector effectively solves the problems caused by the volume expansion effect and initial capacity loss of silicon materials, and can improve the cycle stability and lifespan of the silicon negative electrode.

[0007] To achieve the aforementioned objectives of this utility model, this application provides the following technical solution:

[0008] This application provides a current collector, which includes a current collector matrix and a lithium supplement agent;

[0009] Along the thickness direction of the current collector substrate, the current collector substrate is divided into a first region, a second region, and a third region from one side surface to the other side surface;

[0010] The first region, the second region, and the third region all have porous structures;

[0011] The diameter of the hole in the first region is smaller than the diameter of the hole in the second region, and the diameter of the hole in the third region is smaller than the diameter of the hole in the second region;

[0012] The lithium replenishing agent fills the holes in the first region, the second region, and the third region.

[0013] In some specific embodiments, the aperture of the holes in the first region is 5μm to 8μm.

[0014] In some specific embodiments, the aperture of the holes in the third region is 5μm to 8μm.

[0015] In some specific embodiments, the aperture of the holes in the second region is 10μm to 15μm.

[0016] In some specific embodiments, the thickness ratio of the first region and the second region is 1:(3-4).

[0017] In some specific embodiments, the thickness ratio of the third region to the second region is 1:(3-4).

[0018] In some specific embodiments, the current collector matrix includes copper foam, nickel foam, or aluminum foam.

[0019] In some specific embodiments, the lithium replenishing agent includes a first lithium replenishing agent, a second lithium replenishing agent, and a third lithium replenishing agent;

[0020] The first lithium replenishing agent fills the pores in the first region, the second lithium replenishing agent fills the pores in the third region, and the third lithium replenishing agent fills the pores in the second region.

[0021] In some specific embodiments, the first lithium replenishing agent and the second lithium replenishing agent each independently include Li2O, Li2O2, Li3N, Li2O / M, LiF / Co or Li2S / Co; wherein M is Fe, Co, Mn or Ni.

[0022] In some specific embodiments, the third lithium supplement includes Li5FeO4, Li6CoO4, Li2NiO2, Li2CuO2 or metallic lithium.

[0023] In some specific embodiments, the thickness of the current collector is 100–800 μm.

[0024] A second aspect of this application provides a negative electrode sheet, the negative electrode sheet comprising the current collector described above.

[0025] A third aspect of this application provides a lithium-ion battery, the lithium-ion battery comprising the negative electrode sheet described above.

[0026] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0027] 1. The current collector provided in this application includes a current collector substrate and a lithium replenishing agent. The current collector substrate is divided into a first region, a second region, and a third region along its thickness direction from one side surface to the other. The pore diameter in the first region is smaller than that in the second region, and the pore diameter in the third region is smaller than that in the second region. That is, the current collector substrate has a gradient pore structure. The smaller pore diameters in the first and third regions improve the fixation efficiency of the lithium replenishing agent and reduce its shedding. The larger pore diameter in the second region can accommodate the volume expansion of the silicon anode material, reducing stress concentration. Simultaneously, it reduces the weight of the metal foil on the battery, lowers the cost of the metal foil raw materials, and provides higher energy density.

[0028] 2. The electrode prepared by the method of this invention has extremely low impedance and excellent conductivity, which can promote ion and electron transport. Compared with electrochemical methods, it reduces the increased internal resistance caused by the loose connection between lithium metal and the matrix. Attached Figure Description

[0029] The accompanying drawings are provided to further illustrate the present invention and form part of the specification. They are used together with the following detailed description to explain the present invention, but do not constitute a limitation thereof.

[0030] Figure 1 The diagram shown is a structural schematic of the current collector of this utility model.

[0031] Explanation of reference numerals in the attached figures:

[0032] 10 - Current collector matrix;

[0033] 20-First Zone;

[0034] 30 - Second Zone;

[0035] 40 - Third Region;

[0036] 50 - Holes in the first area;

[0037] 60 - Holes in the second area;

[0038] 70 - Holes in the third region. Detailed Implementation

[0039] This utility model discloses a current collector, a negative electrode, and a lithium-ion battery. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this utility model. The methods and applications of this utility model have been described through preferred embodiments. Those skilled in the art can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this utility model to realize and apply the technology of this utility model.

[0040] In the description of this utility model, it should be noted that the terms "first," "second," etc., are used for descriptive purposes only and are not intended to indicate or imply relative importance.

[0041] In the description of this utility model, the list of items connected by the term "at least one of" or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0042] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0043] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0044] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0045] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0046] The negative electrode in a lithium-ion battery comprises the current collector and the negative electrode material. Silicon anode materials have become a research hotspot due to their high capacity, abundant reserves, and good cycle performance. However, during charging and discharging, the silicon anode material undergoes volume expansion due to lithium-ion insertion and extraction, leading to structural damage, capacity decay, and loss of cycle performance. Ultimately, this results in increased internal resistance, excessive lithium source consumption, and an excessively thick solid electrolyte interface film. The current collector is also a crucial component of lithium-ion batteries. Traditional electrolytic copper foil and composite copper foil possess excellent conductivity, collecting the current generated by the battery's active materials to form a larger output current.

[0047] In view of this, through long-term research and experimentation, it has been found that by designing a special structure for the current collector and supplementing it with a lithium source, the improved current collector can reduce the volume expansion of the silicon anode material and the consumption of the lithium source, thereby improving the cycle stability and lifespan of the battery. Therefore, this application provides a current collector, as well as an anode sheet and a lithium-ion battery incorporating the current collector. The following is a detailed description of this application.

[0048] [current collector]

[0049] In some embodiments, such as Figure 1 As shown, this application provides a current collector, which includes a current collector substrate 10 and a lithium replenishing agent;

[0050] Along the thickness direction of the current collector substrate 10, the current collector substrate 10 is divided into a first region 20, a second region 30 and a third region 40 from one side surface to the other side surface.

[0051] The first region 20, the second region 30 and the third region 40 all have porous structures;

[0052] The aperture of the hole in the first region 20 is smaller than the aperture of the hole in the second region 30, and the aperture of the hole in the third region 40 is smaller than the aperture of the hole in the second region 30.

[0053] The lithium replenishing agent is filled in the holes 50 in the first region 20, the holes 60 in the second region 30, and the holes 70 in the third region 40.

[0054] In this application, the direction from one side surface of the current collector substrate 10 to the other side surface can be either from the upper surface to the lower surface of the current collector substrate or from the lower surface to the upper surface of the current collector substrate.

[0055] The current collector provided in this application includes a current collector substrate 10 and a lithium replenisher. The current collector substrate 10 is divided into a first region 20, a second region 30, and a third region 40 along its thickness direction from one side surface to the other. The pore diameter in the first region 20 is smaller than that in the second region 30, and the pore diameter in the third region 40 is smaller than that in the second region 30. That is, the current collector substrate 10 has a gradient pore structure. The smaller pore diameters in the first region 20 and the third region 40 improve the fixation efficiency of the lithium replenisher and reduce its shedding. The larger pore diameter in the second region 30 can accommodate the volume expansion of the silicon anode material, reducing stress concentration. Simultaneously, it reduces the weight of the metal foil on the battery, lowers the cost of the metal foil raw materials, and provides higher energy density.

[0056] Therefore, the current collector provided in this application includes a current collector substrate 10 and a lithium replenishing agent, wherein the current collector substrate 10 has a gradient porous structure, and the lithium replenishing agent is disposed in the porous structure. This current collector, while providing lithium replenishment, also suppresses the volume expansion of the silicon anode material, compensating for the capacity loss caused by repeated growth of the solid electrolyte interface film, thereby improving the initial coulombic efficiency of the battery, and enhancing the cycle stability and lifespan of the anode sheet, as well as achieving higher energy density.

[0057] In some embodiments, the aperture of the holes in the first region 20 is 5 μm to 8 μm. As an example, the aperture of the holes in the first region 20 can be any one of 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm and 8 μm or a range between any two.

[0058] In some embodiments, the aperture of the holes in the third region 40 is 5 μm to 8 μm. As an example, the aperture of the holes in the third region 40 can be any one of 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm and 80 μm or a range between any two.

[0059] In some embodiments, the aperture of the holes in the second region 30 is 10 μm to 15 μm. As an example, the aperture of the holes in the second region 30 can be any one of 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm and 15 μm or a range between any two.

[0060] In this application, by controlling the aperture of the holes in the first region 20, the aperture of the holes in the second region 30, and the aperture of the holes in the third region 40 to be within the above-mentioned range, wherein the aperture of the holes in the first region 20 and the aperture of the holes in the third region 40 are both smaller than the aperture of the holes in the second region 30, the pore structure of the current collector substrate 10 is distributed in a gradient void structure from the surface layer to the middle layer. The smaller pore sizes in the first region 20 and the third region 40 of the surface layer of the current collector substrate 10 significantly improve the adhesion and loading uniformity of the lithium replenishing agent by increasing the specific surface area and mechanical interlocking force, reducing the risk of detachment due to volume changes during charging and discharging. Simultaneously, the smaller pore sizes in the first region 20 and the third region 40 allow the lithium replenishing agent to tightly fill and form a dense interface layer, inhibiting excessive electrolyte decomposition, reducing active lithium loss caused by repeated growth of the solid electrolyte interface film, and ensuring efficient lithium ion diffusion. The larger pore sizes in the second region 30 of the middle layer of the current collector substrate 10 provide a buffer space for volume expansion of the silicon anode material, reducing stress concentration. The large pore size can also load more lithium replenishing agent, continuously releasing lithium ions during cycling to compensate for lithium loss caused by the rupture of the solid electrolyte interface film. In other words, the small pores in the surface layer preferentially release lithium replenishing agent to compensate for the initial cycle loss, while the large pores in the middle layer provide long-term lithium replenishment capability, and also inhibit the volume expansion of the silicon anode material.

[0061] In some embodiments, the thickness ratio of the first region 20 and the second region 30 is 1:(3-4). As an example, the thickness ratio of the first region 20 and the second region 30 can be any one of 1:3, 1:3.2, 1:3.5, 1:3.6, 1:3.8 and 1:4 or any range between the two.

[0062] In some embodiments, the thickness ratio of the third region 40 and the second region 30 is 1:(3-4). As an example, the thickness ratio of the third region 40 and the second region 30 can be any one of 1:3, 1:3.2, 1:3.5, 1:3.6, 1:3.8 and 1:4, or a range between any two.

[0063] In this application, by controlling the thickness ratio of the first region 20, the second region 30, and the third region 40 within the aforementioned range, i.e., the first region 20 and the third region 40 on the surface are thinner, while the second region 30 is thicker, the volume expansion stress of the silicon anode material can be absorbed through the pores in the second region 30, reducing stress concentration; at the same time, the design of the large pore size and thickness in the second region 30 can provide long-term lithium replenishment, continuously compensating for lithium loss caused by the rupture of the solid electrolyte interface film; the thin-layer design of the first region 20 and the third region 40 can achieve high-density loading of the lithium replenishing agent, preferentially releasing lithium to compensate for the consumption in the first cycle.

[0064] In some embodiments, the current collector substrate 10 includes, but is not limited to, copper foam, nickel foam, or aluminum foam.

[0065] In some embodiments, the method for preparing the current collector substrate 10, taking copper foam as an example, includes the following steps:

[0066] Material preparation: copper powder (particle size 1-10μm) and pore-forming agent (such as ammonium bicarbonate, available in three particle sizes: small, medium and large: 5μm, 10μm and 15μm);

[0067] First zone 20: Copper powder is mixed with a small-particle-size pore-forming agent (5μm) and spread at the bottom of the mold;

[0068] Second region 30: Copper powder is mixed with a large-particle-size pore-forming agent (15μm) and used to cover the first layer;

[0069] Third zone 40: Copper powder is mixed with a small-particle-size pore-forming agent (5μm) and spread on top; it is pressed into a green body under a pressure of 200-400MPa to ensure interlayer bonding;

[0070] Heat to 60-80℃ and hold for 2 hours to completely decompose the pore-forming agent. Sinter at 900-1000℃ for 1-3 hours in a hydrogen atmosphere to allow copper particles to diffuse and combine, forming gradient pores. Remove burrs by mechanical polishing to optimize surface contact.

[0071] In some embodiments, the lithium replenishing agent includes a first lithium replenishing agent, a second lithium replenishing agent, and a third lithium replenishing agent;

[0072] The first lithium replenishing agent is filled in the holes 50 of the first region 20, the second lithium replenishing agent is filled in the holes 60 of the third region 40, and the third lithium replenishing agent is filled in the holes 70 of the second region 30.

[0073] In some embodiments, the first lithium replenisher and the second lithium replenisher each independently comprise Li2O, Li2O2, Li3N, Li2O / M, LiF / Co, or Li2S / Co; wherein M is Fe, Co, Mn, or Ni.

[0074] In some embodiments, the third lithium supplement includes Li5FeO4, Li6CoO4, Li2NiO2, Li2CuO2, or metallic lithium.

[0075] In this application, a first lithium replenishing agent and a second lithium replenishing agent are filled into the pores of the first region 20 and the third region 40, respectively. Both the first and second lithium replenishing agents are highly active lithium replenishing agents, which can quickly replenish the lithium consumed in the first cycle. A third lithium replenishing agent is filled into the second region 30. The third lithium replenishing agent is a slow-release lithium replenishing agent, which can continuously repair the lithium loss caused by the rupture of the solid electrolyte interface film during the cycle. This can balance the high efficiency of the first lithium replenishment and the stability of long-term cycling, and reduce the side reactions between the lithium replenishing agent and the electrolyte.

[0076] In some embodiments, the thickness of the current collector is 100–800 μm. As an example, the thickness of the current collector can be any one of 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, and 800 μm, or a range between any two.

[0077] In this application, by controlling the thickness of the current collector within the above-mentioned range, and combining the gradient pore structure design with the specific thickness ratio of each layer region, it can not only have the function of lithium replenishment, but also suppress the volume expansion of silicon anode material, thereby compensating for the capacity loss caused by repeated growth of solid electrolyte interface film, thus improving the first coulombic efficiency of the battery, and improving the cycle stability and life of the anode sheet as well as higher energy density.

[0078] In some embodiments, the method for preparing a current collector includes the following steps:

[0079] S1. Under an inert atmosphere, the third lithium replenishing agent is dispersed in molten ethylene carbonate to obtain a mixture. The mixture is coated on the surface of the current collector substrate 10 and allowed to stand to allow the mixture to wet the second region 30 of the current collector. Then, a cooling treatment is performed to remove the residue on the surface of the current collector substrate 10, and then a heating treatment is performed to fill the pore 60 structure of the second region 30 of the current collector substrate 10 with the third lithium replenishing agent.

[0080] S2. Under an inert atmosphere, the first lithium replenishing agent is dispersed in molten ethylene carbonate to obtain a mixture. The mixture is coated on the surface of the current collector substrate 10 and allowed to stand to allow the mixture to wet the first region 20 of the current collector. Then, a cooling treatment is performed to remove the residue on the surface of the current collector substrate 10, and then a heating treatment is performed to fill the pore 50 structure of the first region 20 of the current collector substrate 10 with the first lithium replenishing agent.

[0081] S3. Under an inert atmosphere, the second lithium replenishing agent is dispersed in molten ethylene carbonate to obtain a mixture. The mixture is coated on the surface of the current collector substrate 10 and allowed to stand to allow the mixture to wet the third region 40 of the current collector. Then, a cooling treatment is performed to remove the residue on the surface of the current collector substrate 10, and a heating treatment is performed to fill the pore 70 structure of the third region 40 of the current collector substrate 10 with the second lithium replenishing agent.

[0082] A second aspect of this application provides a negative electrode sheet, the negative electrode sheet comprising the current collector described above.

[0083] The current collector includes a coated area, that is, an area coated with an active material layer, which is divided into the three regions mentioned above: the first region 20, the second region 30, and the third region 40.

[0084] Because the negative electrode includes the current collector provided in the embodiments of this application, it can exhibit good electrochemical performance, such as high initial charge-discharge capacity and excellent initial coulombic efficiency.

[0085] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on the two opposite surfaces of the negative electrode current collector. It is understood that the negative electrode active material layer may also be stacked on either of the two surfaces of the negative electrode current collector.

[0086] This application does not impose any particular restrictions on the material of the negative electrode current collector, as long as it can achieve the purpose of this application, and can be selected according to actual needs. As an example, the negative electrode current collector can be made of metal materials such as aluminum, copper, nickel, stainless steel, nickel-plated steel, or foil with a surface coating.

[0087] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. Furthermore, the negative electrode active material layer may optionally include a binder. This application does not impose any particular limitation on the types of conductive agents and binders in the negative electrode active material layer, as long as they achieve the purpose of this application.

[0088] A third aspect of this application provides a lithium-ion battery, the lithium-ion battery comprising the negative electrode sheet described above.

[0089] In some embodiments, the battery structure includes, but is not limited to, coin cell batteries, pouch cells, cylindrical batteries, etc.

[0090] This application does not impose any particular restrictions on the negative electrode, separator, and electrolyte in the battery. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0091] The reagents, instruments, or materials used in this invention can all be obtained through commercial channels.

[0092] The present invention will be further illustrated below with reference to the embodiments:

[0093] Example 1:

[0094] 1. Current collector

[0095] The current collector includes a current collector substrate 10 and a lithium replenishing agent; wherein, along the thickness direction of the copper foil of the current collector substrate 10, the current collector substrate 10 is divided into a first region 20 with a thickness of 20 μm, a second region 30 with a thickness of 70 μm, and a third region 40 with a thickness of 20 μm from one side surface to the other side surface. The pore size in the first region 20 is 5 μm to 8 μm, the pore size in the second region 30 is 10 μm to 15 μm, and the pore size in the third region 40 is 5 μm to 8 μm; the pores 50 of the first region 20 are filled with Li2O lithium replenishing agent nanoparticles with an average particle size of 100 nm, the pores 60 of the second region 30 are filled with Li5FeO4 lithium replenishing agent nanoparticles with an average particle size of 150 nm, and the pores 70 of the first region 20 are filled with Li2O lithium replenishing agent nanoparticles with an average particle size of 100 nm;

[0096] 2. Preparation of silicon anode sheets:

[0097] The negative electrode active material is made of artificial graphite and silicon oxide (artificial graphite: silicon oxide = 9:1), the conductive agent is made of conductive carbon black and carbon nanotubes, and the binder is made of polyacrylic acid and styrene-butadiene rubber. The negative electrode active material, styrene-butadiene rubber, polyacrylic acid, conductive carbon black and carbon nanotubes are mixed in a mass ratio of 94.3:1.4:2.8:0.06:1.44. The negative electrode active material and conductive carbon black are pre-stirred, then 1 / 2 part of polyacrylic acid and deionized water are added and stirred. Then carbon nanotubes, 1 / 2 part of polyacrylic acid, styrene-butadiene rubber and deionized water are added and stirred. By adjusting the content of deionized water, the final output solid content is about 50%, thus obtaining the negative electrode slurry.

[0098] The negative electrode current collector is a pre-prepared current collector. The negative electrode slurry is coated onto the current collector, with a coating surface density of 95 g / m². 2 Drying, cold pressing (compacted density 1.55 g / cm³) 3 ), which is the negative electrode.

[0099] 3. Preparation of the positive electrode:

[0100] The positive electrode active material is lithium nickel cobalt manganese oxide (LiNi). 0.8 Co 0.1 Mn 0.1O2, conductive carbon black SP was selected as the conductive agent, PVDF5130 was selected as the binder, and 13μm aluminum foil was selected as the positive electrode current collector. The positive electrode active material, SP, and binder were mixed in a ratio of 97:2:1, and NMP was added and stirred to form a uniform and stable positive electrode slurry. The positive electrode slurry was then uniformly coated onto the positive electrode current collector, with a coating surface density of 195 g / m². 2 After drying and cold pressing, a positive electrode sheet is obtained with a compaction density of 3.4 g / cm³. 3 .

[0101] 4. Selection of the separator membrane:

[0102] Polypropylene film with a thickness of 12μm was selected as the separator.

[0103] 5. Electrode and diaphragm cutting:

[0104] Cut the positive and negative electrode plates and the separator into pieces, with the specific dimensions as follows:

[0105] Positive electrode plate: 42.0mm long, 32.0mm wide, tab length 10.0mm, tab width 5.0mm.

[0106] Negative electrode: 46.0mm long, 36.0mm wide, tab length 8.0mm, tab width 5.0mm.

[0107] Separator membrane: 53.0 mm long, 42.0 mm wide.

[0108] 6. Cell assembly:

[0109] Arrange the positive electrode, separator, and negative electrode in sequence, and use stacking as the assembly method.

[0110] 7. Electrolyte preparation:

[0111] LiPF6 was dissolved in a solvent containing ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1, at a concentration of 1.2 mol / L.

[0112] 8. Injection:

[0113] The electrolyte is injected into the dry cell, aged at room temperature for 24 hours, and then aged at 45°C for 8 hours to obtain a lithium-ion battery.

[0114] Example 2:

[0115] The only difference between this embodiment and Embodiment 1 is that the thickness of the current collector is different. The thickness of the current collector is 240 μm, the thickness of the first region 20 is 40 μm, the thickness of the second region 30 is 160 μm, and the thickness of the third region 40 is 40 μm.

[0116] Example 3:

[0117] The only difference between this embodiment and Embodiment 1 is that the thickness of the current collector is different. The thickness of the current collector is 360 μm, the thickness of the first region 20 is 70 μm, the thickness of the second region 30 is 220 μm, and the thickness of the third region 40 is 70 μm.

[0118] Example 4:

[0119] The only difference between this embodiment and Embodiment 1 is that the thickness of the current collector is different. The thickness of the current collector is 600 μm, the thickness of the first region 20 is 100 μm, the thickness of the second region 30 is 400 μm, and the thickness of the third region 40 is 100 μm.

[0120] Comparative Example 1:

[0121] The only difference between this comparative example and Example 1 is that the current collector uses a conventional 6μm copper foil and does not contain lithium replenishing agent.

[0122] Comparative Example 2:

[0123] The only difference between this comparative example and Example 1 is that the current collector does not contain lithium replenishing agent.

[0124] Comparative Example 3:

[0125] The only difference between this comparative example and Example 1 is that the current collector uses a 6μm conventional copper foil coated with a lithium replenishing agent.

[0126] Comparative Example 4

[0127] The only difference between this comparative example and Example 1 is that the pore size in the first region 20, the second region 30 and the third region 40 of the current collector substrate 10 is 5-8 μm.

[0128] Comparative Example 5

[0129] The only difference between this embodiment and Embodiment 1 is that in the current collector substrate 10, the pore diameter of the first region 20 is 10-15 μm, the pore diameter of the second region 30 is 5-8 μm, and the pore diameter of the third region 40 is 10-15 μm.

[0130] Comparative Example 6

[0131] The only difference between this embodiment and Embodiment 1 is that in the current collector substrate 10, the thickness of the first region 20 is 40 μm, the thickness of the second region 30 is 15 μm, and the thickness of the third region 40 is 40 μm.

[0132] Comparative Example 7

[0133] The only difference between this comparative example and Example 1 is that the lithium replenishing agent in the first region 20, the second region 30 and the third region 40 of the current collector matrix 10 is Li5FeO4.

[0134] Comparative Example 8

[0135] The only difference between this comparative example and Example 1 is that the lithium replenishing agent in the first region 20, the second region 30 and the third region 40 of the current collector matrix 10 is Li2O.

[0136] Performance testing:

[0137] 1. Diaphragm resistance test:

[0138] The film resistance of the negative electrode sheets in the examples and comparative examples was tested using the following methods:

[0139] (1) Experimental equipment: diaphragm resistance meter, model BER1300 (IEST Yuaneng Technology), electrode diameter 14mm.

[0140] (2) Zeroing: Without placing the electrode, set the test pressure on the MRMS software, apply a pressure of 25MPa, hold the pressure for 25s, click Start Test, and the electrode will be zeroed after the result appears.

[0141] (3) Membrane resistance test: Cut the rolled membrane into a rectangle of approximately 5cm × 10cm and place it between the two electrodes of the membrane resistance meter. Set the test parameters on the MRMS software and start the test. The software will automatically read the membrane thickness, resistance, resistivity, conductivity and other data. Six positions are randomly selected for testing on each membrane, and the average value is the membrane resistance value of the electrode.

[0142] 2. Battery performance test:

[0143] (1) First Coulomb efficiency (first effect) test: In a constant temperature chamber at 25℃, charge to 3.75V with a current of 0.1C, let stand for 30 minutes, then charge to 4.25V with a current of 0.5C, and record the total charging capacity A; after standing for 30 minutes, discharge to 2.8V with a current of 0.5C, and record the discharge capacity B; first effect = B / A.

[0144] (2) Cyclic performance test: Each example and comparative example was placed at 25°C for 30 minutes; constant current charging at 1C to 4.4V + constant voltage charging at 0.05C; constant current discharge at 2.5V after 30 minutes; repeat the above steps after 30 minutes and record the ×th cycle (× = 1, 2, 3, 4...) (Note: the more cycles, the longer the service life of the electrode). The test was stopped when the discharge capacity of the battery was lower than 80% of the initial capacity.

[0145] (3) Full charge rebound rate test: Use a micrometer to measure the negative electrode sheet after rolling and record the electrode sheet thickness as C1; Charge the battery after capacity division to 100% SOC according to the standard test procedure 1C charging current, disassemble the fully charged battery, use a micrometer to measure the fully charged negative electrode sheet and record the electrode sheet thickness as C2; Full charge rebound rate = (C2-C1) / C1.

[0146] The first-efficiency and cycle performance shown in Table 1 are the average values ​​of three parallel samples.

[0147] Table 1. Diaphragm resistance and battery performance data

[0148]

[0149] As shown in Table 1, Examples 1-4 exhibit excellent cycle performance, superior to Comparative Examples 1-3. The film resistance of Examples 1-4, Comparative Examples 2, 7, and 8 is lower than that of Comparative Examples 1, 3, 4, and 5, demonstrating that the current collector matrix with a gradient pore structure combined with the lithium replenishing agent can effectively improve the charge transport network integrity of the electrode. Furthermore, the full-charge rebound ratio of the negative electrode in Examples 1-4, Comparative Example 5 (with altered current collector pore diameter), Comparative Example 6 (with altered current collector thickness in different pore diameter regions), and Comparative Example 2 is significantly higher than that in Comparative Examples 1 and 3 (using conventional copper foil). The reduction demonstrates that the current collector matrix with a gradient pore structure (the pore diameter of the second region of the current collector is larger than that of the first and third regions; the thickness of the second region of the current collector is larger than that of the first and third regions) combined with the lithium replenishing agent can effectively reduce the structural degradation of the electrode layer caused by the volume expansion and contraction due to silicon lithium insertion and extraction, and improve the structural stability of the negative electrode during cycling. The initial coulombic efficiency of Examples 1-4 and Comparative Examples 3, 5, and 7 is higher than that of Comparative Examples 1-2, mainly because the lithium replenishing agent Li2O / Li5FeO4 compensates for the capacity loss caused by the repeated growth of the SEI film, thus improving the initial efficiency.

[0150] The conventional copper current collector used in Comparative Example 1 has relatively high diaphragm resistance due to its structural and characteristic limitations, and Comparative Example 1 has low initial coulombic efficiency and poor cycle performance.

[0151] Comparative Example 2 shows a slight improvement in circulation performance due to the presence of gradient pore structure in the current collector matrix, but the initial coulombic efficiency is low and the capacity loss is significant.

[0152] The conventional copper current collector used in Comparative Example 3 has a relatively high diaphragm resistance due to its structural and characteristic limitations; the initial coulombic efficiency is increased by the addition of lithium supplement, but the cycle performance is poor because the silicon volume expansion is not alleviated.

[0153] The initial coulombic efficiency of Comparative Example 4 increased due to the addition of lithium replenishment. However, the current collector matrix lacked a gradient pore structure and had a relatively small overall pore size, resulting in a smaller buffer space for silicon expansion and poorer cycle performance.

[0154] Comparative Examples 5 and 6 altered the gradient pore structure of the current collector, resulting in higher diaphragm resistance and an inability to effectively reduce the structural degradation of the electrode layers caused by the volume expansion and contraction resulting from silicon lithium insertion / extraction.

[0155] Comparative Example 7, due to the addition of only the slow-release lithium replenishing agent Li5FeO4 to the gradient pore structure of the current collector matrix, showed poor performance in rapidly compensating for the first lithium loss and had a low first coulombic efficiency.

[0156] Comparative Example 8, due to the addition of only the highly active lithium replenishing agent Li2O to the gradient pore structure of the current collector matrix, showed poor performance in terms of the loss caused by SEI film rupture during continuous repair cycling, resulting in significant capacity loss and poor cycling performance.

[0157] The above description is only a preferred embodiment of the present utility model. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present utility model, and these improvements and modifications should also be considered within the protection scope of the present utility model.

Claims

1. A current collector characterized by comprising: The current collector includes a current collector matrix and a lithium supplement agent; Along the thickness direction of the current collector substrate, the current collector substrate is divided into a first region, a second region, and a third region from one side surface to the other side surface; The first region, the second region, and the third region all have porous structures; The diameter of the hole in the first region is smaller than the diameter of the hole in the second region, and the diameter of the hole in the third region is smaller than the diameter of the hole in the second region; The lithium replenishing agent fills the holes in the first region, the second region, and the third region.

2. The current collector of claim 1, wherein The pore diameter in the first region is 5μm~8μm; And / or, the aperture of the holes in the third region is 5μm~8μm; And / or, the aperture of the holes in the second region is 10μm~15μm.

3. The current collector of claim 1, wherein The thickness ratio of the first region to the second region is 1:(3~4).

4. The current collector of claim 1, wherein The thickness ratio of the third region to the second region is 1:(3~4).

5. The current collector of claim 1, wherein The current collector matrix includes copper foam, nickel foam, or aluminum foam.

6. The current collector of claim 1, wherein The lithium replenishing agent includes a first lithium replenishing agent, a second lithium replenishing agent, and a third lithium replenishing agent; The first lithium replenishing agent fills the pores in the first region, and the second lithium replenishing agent fills the pores in the third region.

7. The current collector of claim 6, wherein The first lithium replenishing agent and the second lithium replenishing agent each independently comprise Li2O, Li2O2, Li3N, Li2O / M, LiF / Co, or Li2S / Co; wherein M is Fe, Co, Mn, or Ni; And / or, the third lithium supplement includes Li5FeO4, Li6CoO4, Li2NiO2, Li2CuO2 or metallic lithium.

8. The current collector of any one of claims 1-7, wherein, The thickness of the current collector is 100~800μm.

9. A negative electrode sheet characterized by comprising: The negative electrode includes the current collector as described in any one of claims 1 to 8.

10. A lithium-ion battery, characterized by, The lithium-ion battery includes the negative electrode sheet as described in claim 9.

Images