Composite anode materials, their preparation methods and applications

Abstract

This invention provides a composite anode material, its preparation method, and its application. The preparation method includes the following steps: mixing and lithiating graphene material and lithium metal material in a protective atmosphere to obtain lithiated graphene material; wherein both the graphene material and the lithium metal material are in particulate form; mixing the metal material and the lithiated graphene material and heating to obtain the composite anode material. The composite anode material obtained by the preparation method of this invention is a lithium alloyed graphene material, which can guide the uniform deposition of metallic lithium, reduce the probability of lithium dendrite formation, and provide more electron pathways, enhancing lithium diffusion, thereby reducing the gap between the anode material and the solid electrolyte, reducing battery impedance, and improving battery cycle performance and rate performance.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a composite negative electrode material, its preparation method and application. Background Technology

[0002] Lithium metal has attracted widespread attention as an ideal candidate for next-generation energy storage materials. Its theoretical capacity is as high as 3860 mAh·g. -1 Furthermore, lithium metal offers the advantage of high energy density, making it considered the best material to replace graphite electrodes. In addition, new electrolyte systems such as solid-state batteries have garnered significant attention in recent years. However, before practical application, lithium metal must overcome a series of challenges, including lithium plating, the instability of active Li, and uncontrollable charge transfer.

[0003] Specifically, in order to prevent lithium dendrite growth, safety risks caused by overcharging, extend battery life, and reduce the gap between the negative electrode and the solid electrolyte, it is necessary to establish a controllable and reversible process in the negative electrode to control the release and collection of lithium ions. Summary of the Invention

[0004] The purpose of this invention is to provide a composite anode material, its preparation method, and its application. The composite anode material obtained by the preparation method can guide the uniform deposition of metallic lithium, reduce the probability of lithium dendrite formation, and provide more electron pathways to enhance lithium diffusion. This reduces the gap between the anode material and the solid electrolyte, lowers the battery impedance, and improves the battery's cycle performance and rate performance.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a method for preparing a composite anode material, the method comprising the following steps:

[0007] (1) In a protective atmosphere, graphene material and lithium metal material are mixed and lithiated to obtain lithiated graphene material, wherein both graphene material and lithium metal material are in particulate state.

[0008] (2) Mix and heat the metal material and the lithium graphene material described in step (1) to obtain the composite negative electrode material.

[0009] Preferably, the molar ratio of the lithium metal material in step (1) to the metal material in step (2) is (15-19):(1-5).

[0010] Preferably, the particle size D50 of the graphene material in step (1) is 5-20 μm.

[0011] Preferably, the particle size D50 of the lithium metal material in step (1) is 4-7 μm.

[0012] Preferably, the particle size D50 of the graphene material in step (1) is more than twice the particle size D50 of the lithium metal material.

[0013] Preferably, the protective atmosphere in step (1) includes any one or a combination of at least two of nitrogen, argon, or neon.

[0014] Preferably, the lithiation time in step (1) is 20 hours or more.

[0015] Preferably, the lithiation temperature in step (1) is 20-35°C.

[0016] Preferably, the lithiation method in step (1) includes standing.

[0017] Preferably, the mass ratio of graphene material to lithium metal material in step (1) is (0.5-2):(0.5-2).

[0018] Preferably, the graphene material in step (1) includes reduced graphene oxide.

[0019] Preferably, the method for preparing the graphene material in step (1) includes the Hummer method and the spray drying method.

[0020] Preferably, the method of mixing the graphene material and the lithium metal material in step (1) includes ball milling.

[0021] Preferably, the ball mill operates at a rotation speed of 400-600 rpm for 12-36 hours.

[0022] Preferably, the time for mixing the graphene material and the lithium metal material in step (1) is 12-36 hours.

[0023] Preferably, the metallic material in step (2) includes any one or a combination of at least two of Ag, Zn, Mg, Al or Ge, with Zn being the most preferred.

[0024] Preferably, step (2) involves heating the metal material to a point above its melting point.

[0025] In a second aspect, the present invention provides a composite anode material, which is prepared by the preparation method described in the first aspect;

[0026] The composite anode material includes graphene, lithium alloy, and lithium metal, or the composite anode material includes graphene and lithium alloy.

[0027] Thirdly, the present invention provides a negative electrode sheet, the negative electrode sheet comprising a current collector and a negative electrode active material layer on at least one side surface of the current collector, the negative electrode active material layer comprising the composite negative electrode material as described in the second aspect.

[0028] Fourthly, the present invention provides a battery comprising a negative electrode as described in the third aspect.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] This invention prepares lithiated graphene by first lithiating graphite material, and then reacts the lithiated graphene with a metal material to convert the lithium metal material into a lithium alloy. The lithiation process allows the graphene to be fully intercalated with lithium, which enhances the bonding ability between the graphene material and the lithium metal alloy, resulting in a lithium alloyed graphene material with uniform component distribution and strong interaction force.

[0031] In the composite anode material prepared by the method of the present invention, both graphene and lithium alloy are materials with good conductivity, which can effectively reduce the internal resistance of the battery and improve the cycle and rate performance of the battery. Furthermore, the lithium alloyed graphene material with uniform component distribution and strong interaction force also increases the lithium pathway, enhances the lithium diffusion ability, promotes the uniform deposition of lithium ions, further improves the rate performance of the battery, and reduces the gap between the anode and electrolyte layer, thus slowing down the precipitation of lithium dendrites. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the structure of the composite negative electrode material described in Embodiment 1 of the present invention;

[0033] Figure 2 This is a SEM image of the reduced graphene oxide described in Example 1 of the present invention;

[0034] Figure 3 This is a schematic diagram of the structure of the battery cell according to a specific embodiment of the present invention;

[0035] Among them, 101-lithium atom, 102-M metal atom, 103-lithium alloy, 104-solid electrolyte, 105-monolayer reduced graphene oxide, 106-reduced graphene oxide, 201-aluminum current collector, 202-copper current collector, 203-positive electrode active material layer, 204-negative electrode active material layer, and 205-solid electrolyte layer. Detailed Implementation

[0036] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0037] When lithium metal is used as the negative electrode, there is a problem of uneven lithium deposition and the formation of lithium dendrites, which affects the safety performance of the battery. Furthermore, when lithium metal negative electrodes are used in solid-state or semi-solid-state batteries, they can also affect the contact between the negative electrode and the solid electrolyte, creating a gap between the solid electrolyte and the negative electrode.

[0038] To address the aforementioned technical problems, in a specific embodiment of the present invention, a method for preparing a composite negative electrode material is provided, the method comprising the following steps:

[0039] (1) Graphene material and lithium metal material are mixed and lithiated to obtain lithiated graphene material;

[0040] (2) Mix and heat the metal material and the lithium graphene material described in step (1) to obtain the composite negative electrode material.

[0041] The composite anode material of this invention is prepared by first thoroughly mixing graphene and lithium metal, and then lithiating the graphene with lithium metal. This lithiation allows the functional groups on the graphene surface to react spontaneously with the lithium metal, enabling the graphene to fully intercalate lithium and enhancing the bonding ability between the graphene and the lithium metal alloy. This results in a lithium-alloyed graphene material with strong component bonding ability. After lithiation, the lithiated graphene material is mixed with the metal material and heated, which allows the lithium metal material to react with the metal material to form a lithium metal alloy.

[0042] Therefore, the composite material obtained by the present invention includes graphene material, lithium metal material and lithium metal material alloy with good conductivity, or only graphene material and lithium metal material alloy, which can increase the lithium diffusion pathway, enhance the lithium diffusion ability, promote the uniform deposition of lithium ions, further reduce the gap between the negative electrode and the electrolyte layer, slow down the precipitation of lithium dendrites, effectively reduce the battery internal resistance and improve the battery cycle and rate performance.

[0043] Furthermore, this invention employs particulate graphene and lithium metal materials. Since the particles have a small size and a high specific surface area, this helps to increase the contact area between the graphene material and the lithium metal material, thereby improving the rate and efficiency of lithiation.

[0044] Further, the molar ratio of the lithium metal material in step (1) to the metal material in step (2) is (15-19):(1-5), for example, it can be 15:5, 16:4, 17:3, 18:2 or 19:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] This invention can regulate the composition of the composite anode material by adjusting the molar ratio of the lithium metal material to the metal material in step (2), further guiding the uniform deposition of lithium, reducing the probability of lithium dendrite formation, and improving the electrochemical performance of the battery. If the metal material is too small compared to the lithium metal material, the lithium content in the lithium metal alloy will be relatively too large, which will reduce the uniformity of lithium deposition. If the metal material is too large compared to the lithium metal material, the lithium content in the lithium metal alloy will be too small, which will reduce the conductivity and lithium ion diffusion ability of the composite anode material.

[0046] Preferably, the particle size D50 of the graphene material in step (1) is 5-20 μm, for example, it can be 5 μm, 10 μm, 15 μm or 20 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] The D50 particle size of the graphene material of this invention is within a specific range, which is beneficial to its function. If the particle size is too large, it is not conducive to the intercalation of lithium ions, thus hindering the lithiation process, affecting the degree of lithiation, and ultimately affecting the rate performance of the battery. If the D50 particle size of the graphene material is too small, agglomeration will occur, which is not conducive to the lithiation process. At the same time, there will also be discontinuity in the graphene sheets, affecting its conductivity.

[0048] Preferably, the particle size D50 of the lithium metal material in step (1) is 4-7 μm, for example, it can be 4 μm, 5 μm, 6 μm or 7 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0049] The selection of the particle size D50 of the lithium metal material described in this invention needs to match the particle size D50 of the graphene material. If the particle size D50 of the lithium metal material is too large, it will be detrimental to the diffusion of lithium ions, thus hindering lithiation. If the particle size D50 of the lithium metal material is too small, the preparation environment for smaller lithium metal materials will be more demanding, increasing the cost of the preparation method described in this invention. Smaller lithium metal materials have lower stability and are also prone to agglomeration, which will affect the lithiation process and the conductivity of the composite anode material, thereby affecting battery performance.

[0050] Preferably, the particle size D50 of the graphene material in step (1) is more than twice the particle size D50 of the lithium metal material, for example, it can be two, three, four or five times, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0051] In step (1) of this invention, the particle size D50 of the graphene material is more than twice that of the lithium metal material, which can promote full contact between the lithium metal material and the graphene material, so that multiple lithium metal material particles are evenly distributed on the surface of the graphene material, thereby increasing the contact area between the lithium metal material and the graphene material, thus promoting lithiation and full lithium intercalation.

[0052] Preferably, the protective atmosphere in step (1) includes any one or a combination of at least two of nitrogen, argon, or neon.

[0053] Furthermore, the lithiation time in step (1) is more than 20 hours, for example, it can be 20 hours, 22 hours, 24 hours, 26 hours, 28 hours or 30 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0054] The lithiation time in step (1) of this invention affects the degree of lithiation of the graphene material. Preferably, the lithiation time in step (1) of this invention is more than 20 hours, which can enable all benzene rings of the graphene material to react with lithium, thereby making the graphene material completely lithiated, further enhancing the lithium storage capacity of graphene, and improving the problem of charge-discharge diffusion restriction caused by the slow mass transfer of Li. If the lithiation time is too short, the degree of lithiation will decrease, the lithium ion mass transfer will slow down, thereby affecting the lithium ion transport capacity.

[0055] Furthermore, the lithiation temperature in step (1) is 20-35°C, for example, it can be 20°C, 25°C, 30°C or 35°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0056] The lithiation of this invention is carried out at around room temperature, which can ensure the stability of lithium metal materials and promote the spontaneous occurrence of the lithiation reaction. If the lithiation temperature is too high, the stability of lithium metal materials will decrease due to their active nature, thus reducing the safety of the preparation process. If the lithiation temperature is too low, it will be detrimental to the lithiation reaction and lead to a decrease in the degree of lithiation.

[0057] Furthermore, the lithiation method described in step (1) includes standing.

[0058] The lithiation method described in step (1) of this invention only requires standing and does not require mechanical stirring, which not only saves energy; in addition, the lithiation method of this invention avoids the damage to the graphene material structure caused by long-term stirring, and also avoids the increase of defects in the graphene material. Furthermore, long-term mechanical stirring may increase the side reactions between graphene and lithium powder, while standing lithiation can reduce the occurrence of side reactions.

[0059] Further, the mass ratio of graphene material to lithium metal material in step (1) is (0.5-2):(0.5-2), for example, it can be 0.5:1, 0.5:1.5, 0.5:2, 1:1, 1.5:0.5, 1.5:1, 1.5:2, 2:0.5, 2:1 or 2:1.5, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0060] The mass ratio of graphene material to lithium metal material described in this invention is within a specific range, which is conducive to lithiation. If the amount of lithium metal material is less than that of graphene material, the lithiation of graphene material will be insufficient, the degree of lithiation will be low, and the diffusion channels of lithium ions will be reduced. If the amount of lithium metal material is more than that of graphene material, the conductivity of the resulting composite anode material will be reduced.

[0061] Furthermore, the graphene material in step (1) includes reduced graphene oxide.

[0062] Furthermore, the methods for preparing the graphene material in step (1) include the Hummer method and the spray drying method.

[0063] The Hummer process described in this invention is a commonly used method for preparing graphene oxide. Its basic principle is to treat graphite with strong acid, causing it to oxidize and be exfoliated into single or multiple layers of graphene oxide. The Hummer process mainly includes three stages: low-temperature reaction, medium-temperature reaction, and high-temperature reaction. All operations are carried out in a glove box, and the water and oxygen levels are below 0.01 ppm.

[0064] The methods for preparing the reduced graphene oxide of the present invention include, but are not limited to, the Hummer method, vitamin C reduction method, ethanethiol-aluminum chloride reduction method, quercetin reduction method, ethylenediamine disuccinic acid reduction method, electrochemical reduction method, or thermal reduction method.

[0065] For example, the preparation of reduced graphene oxide using the Hummer method combined with spray drying specifically includes the following steps:

[0066] (1) Graphite pre-oxidation:

[0067] Add 30 mL of concentrated sulfuric acid (H2SO4) to a 400 mL beaker and mechanically stir in an oil bath. Then, add 1.0 g of natural flake graphite, 0.5 g of potassium persulfate, and 0.5 g of phosphorus pentoxide in sequence. After stirring evenly, react at 80 °C for 4 hours. After cooling to room temperature, slowly add 300 mL of distilled water to the beaker, controlling the temperature inside the beaker to not exceed 80 °C. Vacuum filter the mixed solution at 80 °C. Place the resulting filter cake in a clean beaker, add another 300 mL of water to dilute, and filter again until the filtrate is neutral. Finally, place the filter cake in an 80 °C forced-air drying oven and dry for 12 hours to obtain the pre-oxidized product.

[0068] (2) Preparation of graphene oxide:

[0069] Under ice bath conditions (0℃), 30 mL of concentrated sulfuric acid was added to a 400 mL beaker. The pre-oxidized product was ground and added to the beaker, stirred evenly, and 5 g of finely ground potassium permanganate was slowly added. The reaction was allowed to proceed for 4 hours. Then, the beaker was transferred to an oil bath preheated to 35℃ and mechanically stirred for 2 hours. After the reaction was completed, 130 mL of distilled water was slowly added to the beaker using a titration flask, keeping the temperature in the beaker below 80℃. The solution turned brownish-yellow. 10 mL of hydrogen peroxide was added to the beaker, and the solution changed from pale yellow to bright yellow, yielding graphene oxide.

[0070] (3) Preparation of reduced graphene oxide:

[0071] The graphene oxide solution was transferred to a 500 mL three-necked flask, and 50 mL of 80% hydrazine hydrate solution (35% by mass aqueous solution) was added. The temperature was maintained at 80 °C, and the reaction was continued for more than 36 hours. After the reaction was completed, the sample was filtered through a 220 nm aqueous filter membrane, washed three times with 50 mL of distilled water, and then washed three times with 50 mL of methanol. The filtered sample was placed in a petri dish and dried in a vacuum drying oven at 60 °C for 8 hours to obtain the graphene oxide sample.

[0072] The obtained graphene oxide sponge was placed in a tube furnace and heated to 1000℃ in an H2 / Ar (containing 5% H2) mixture for 6 hours to obtain reduced graphene oxide.

[0073] Graphite is dispersed and mixed with an appropriate amount of water to form a uniform suspension. The hot air temperature is set between 250-300℃, and spray drying is performed to obtain small molecule reduced graphene oxide.

[0074] Furthermore, the method of mixing the graphene material and the lithium metal material in step (1) includes ball milling.

[0075] Furthermore, the ball milling speed is 400-600 rpm, for example, 400 rpm, 500 rpm or 600 rpm, and the time is 12-36 h, for example, 12 h, 15 h, 20 h, 25 h, 30 h or 36 h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0076] The graphene material and lithium metal material described in this invention are mixed evenly by ball milling. If the ball milling speed is too low or the ball milling time is too short, it will affect the uniformity of the mixing, thereby affecting the subsequent lithiation process and resulting in a lower degree of lithiation. If the ball milling speed is too high or the ball milling time is too long, there is a risk of damaging the graphene material structure and increasing the defects in the graphene material.

[0077] Further, the metallic material in step (2) includes any one or a combination of at least two of Ag, Zn, Mg, Al or Ge, preferably Zn.

[0078] The metal material described in this invention can form an alloy with lithium metal material. The preferred metal material is Zn. Since the solid solution formed by lithium metal material and zinc can reduce the deposition interface energy between lithium and the current collector, it can induce the uniform deposition of lithium metal material on its surface, thereby improving battery performance and stability, and further enhancing the cycle performance and rate performance of the composite anode material.

[0079] Furthermore, step (2) involves heating the metal material above its melting point.

[0080] Since different metal materials have different melting points, the present invention does not specify the specific temperature of heating in step (2). It is sufficient to heat the material to a temperature above the melting point of the corresponding metal material, thereby promoting the formation of lithium metal alloy.

[0081] For example, the heating to 450-700°C in step (2) can be, for example, 450°C, 500°C, 550°C, 600°C, 650°C or 700°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0082] In one specific embodiment, a composite anode material is also provided, which is prepared by the preparation method described above;

[0083] The composite anode material includes graphene, lithium alloy, and lithium metal, or the composite anode material includes graphene and lithium alloy.

[0084] The present invention can determine whether the composite anode material contains lithium metal material based on the amount of lithium metal material added during the preparation process.

[0085] In one specific embodiment, a negative electrode sheet is also provided, the negative electrode sheet including a current collector and a negative electrode active material layer on at least one side surface of the current collector, the negative electrode active material layer including the composite negative electrode material.

[0086] In one embodiment, a battery is also provided, the battery including, for example, a negative electrode.

[0087] The battery includes a cell, and a structural schematic diagram of the cell is shown below. Figure 3 As shown, it includes an aluminum current collector 201, a positive electrode active material layer 203, a solid electrolyte layer 205, a negative electrode active material 204, and a copper current collector 202, which are stacked in sequence.

[0088] Example 1

[0089] This embodiment provides a method for preparing a composite anode material, the method comprising the following steps:

[0090] (1) In a nitrogen atmosphere, reduced graphene oxide material and lithium powder were ball-milled at 500 rpm for 25 h at a mass ratio of 1:1, and then lithiated at 25 °C for 24 h to obtain lithiated graphene material; the SEM image of the reduced graphene oxide is shown below. Figure 2 As shown;

[0091] The graphene material has a particle size D50 of 10 μm, the lithium powder has a particle size D50 of 5 μm, and the graphene material has a particle size D50 that is twice that of the lithium powder.

[0092] (2) Place the lithium-ion graphene material described in step (1) into a nickel crucible (purity R is 99.99%), heat to 450°C, and then add metal M (M is Zn, and the molar ratio of lithium powder to Zn is 19:1) until the metal particles are completely melted. After cooling to room temperature, the composite anode material (denoted as Li) is obtained. 95 Zn5 alloy (rGO);

[0093] A schematic diagram of the structure in contact between the composite negative electrode material and the solid electrolyte 104 is shown below. Figure 1 As shown, the composite anode material includes lithium atoms 101, M metal atoms 102, lithium alloy 103, single-layer reduced graphene oxide 105, and reduced graphene oxide 106. Figure 1 It can be seen that the reduced graphene oxide 106, lithium atoms 101 and M metal atoms 102 are evenly distributed, and the composite anode material has a large number of lithium-ion diffusion channels.

[0094] Example 2

[0095] This embodiment provides a method for preparing a composite anode material, the method comprising the following steps:

[0096] (1) In a nitrogen atmosphere, reduced graphene oxide material and lithium powder were ball-milled at 500 rpm for 12 h at a mass ratio of 1:1, and then lithiated at 25 °C for 20 h to obtain lithiated graphene material; the particle size D50 of the graphene material was 20 μm, the particle size D50 of the lithium powder was 7 μm, and the particle size D50 of the graphene material was 2.85 times that of the lithium powder.

[0097] (2) Place the lithium-ion graphene material described in step (1) into a nickel crucible (purity R is 99.99%), heat to 700°C, and then add metal M (M metal is Al, and the molar ratio of lithium powder to Al is 19:1) until the metal particles are completely melted. After cooling to room temperature, the composite anode material (denoted as Li) is obtained. 95 Al5 alloy-rGO);

[0098] Example 3

[0099] This embodiment provides a method for preparing a composite anode material, the method comprising the following steps:

[0100] (1) In a nitrogen atmosphere, the reduced graphene oxide material and lithium powder were ball-milled at 500 rpm for 36 h at a mass ratio of 1:1, and then lithiated at 25 °C for 24 h to obtain the lithiated graphene material.

[0101] The graphene material has a particle size D50 of 8 μm, the lithium powder has a particle size D50 of 4 μm, and the graphene material has a particle size D50 that is twice that of the lithium powder.

[0102] (2) Place the lithium-ion graphene material described in step (1) into a nickel crucible (purity R is 99.99%), heat to 700°C, and then add metal M (the metal M is Mg, and the molar ratio of lithium powder to Mg is 19:1) until the metal particles are completely melted. After cooling to room temperature, the composite anode material (denoted as Li) is obtained. 95 Mg5 alloy - rGO).

[0103] Example 4

[0104] This embodiment provides a method for preparing a composite anode material. The method, except that in step (2) the molar ratio of lithium powder to Zn is 15:5, yields a composite anode material denoted as Li. 75 Zn 25 Except for -rGO, everything else is the same as in Example 1.

[0105] Example 5

[0106] This embodiment provides a method for preparing a composite anode material. The method, except that in step (2) the molar ratio of lithium powder to Al is 15:5, results in a composite anode material denoted as Li. 75 Al 25 Except for -rGO, everything else is the same as in Example 2.

[0107] Example 6

[0108] This embodiment provides a method for preparing a composite anode material. The method, except that in step (2) the molar ratio of lithium powder to Mg is 15:5, yields a composite anode material denoted as Li. 75 Mg 25 Except for -rGO, everything else is the same as in Example 3.

[0109] Example 7

[0110] This embodiment provides a method for preparing a composite anode material. The method, except that in step (2) the molar ratio of lithium powder to Zn is 9:1, yields a composite anode material denoted as Li. 90 Zn 10 Except for -rGO, everything else is the same as in Example 1.

[0111] Example 8

[0112] This embodiment provides a method for preparing a composite anode material. The method, except that in step (2) the molar ratio of lithium powder to Al is 9:1, results in a composite anode material denoted as Li. 90 Al 10 Except for -rGO, everything else is the same as in Example 2.

[0113] Example 9

[0114] This embodiment provides a method for preparing a composite anode material. The method, except that in step (2) the molar ratio of lithium powder to Mg is 9:1, yields a composite anode material denoted as Li. 90 Mg 10 Except for -rGO, everything else is the same as in Example 3.

[0115] Example 10

[0116] This embodiment provides a method for preparing a composite negative electrode material. Except for the molar ratio of lithium powder to Zn of 12:8 in step (2), the preparation method is the same as in Example 1.

[0117] Example 11

[0118] This embodiment provides a method for preparing a composite negative electrode material. Except for the molar ratio of lithium powder to Zn of 30:1 in step (2), the preparation method is the same as in Example 1.

[0119] Example 12

[0120] This embodiment provides a method for preparing a composite anode material. Except for the lithiation time of step (1) being 20 hours, the preparation method is the same as that in Example 1.

[0121] Example 13

[0122] This embodiment provides a method for preparing a composite anode material. Except for the lithiation time of 15h in step (1), the preparation method is the same as that in Example 1.

[0123] Example 14

[0124] This embodiment provides a method for preparing a composite anode material. Except for step (1), where the lithiation is carried out by ball milling at 500 rpm for 24 hours instead of standing, the preparation method is the same as in Example 1.

[0125] Example 15

[0126] This embodiment provides a method for preparing a composite negative electrode material. Except for step (1), where the particle size D50 of the graphene material is 5 μm and the particle size D50 of the graphene material is the same as that of the lithium powder, the preparation method is the same as in Example 1.

[0127] Comparative Example 1

[0128] This comparative example provides a negative electrode material, wherein the negative electrode material is a graphite material.

[0129] Comparative Example 2

[0130] This comparative example provides a method for preparing a composite anode material. The preparation method is the same as that in Example 1, except that step (1) is not lithiation.

[0131] Comparative Example 3

[0132] This comparative example provides a method for preparing a composite negative electrode material. The preparation method is the same as that in Example 1 except that step (2) is not performed.

[0133] The negative electrode materials obtained in the above embodiments and comparative examples are used to prepare negative electrode sheets. The method for preparing negative electrode sheets includes the following steps: rolling the obtained composite negative electrode material into a 20μm lithium strip onto a copper current collector; then preparing the prepared negative electrode sheet, positive electrode sheet, and separator into a battery. The positive electrode sheet includes a positive current collector layer and a positive active material layer covering the surface of the positive current collector layer. The positive active material layer includes Ni in a mass ratio of 96:1.5:2.5. 0.8 Co 0.1 Mn 0.1 The separator comprises a 9μm PE base film and 2μm ceramic layers on both sides of the base film. The obtained battery was subjected to 0.5C / 0.5C cycle and 0.5C, 1C and 2C rate charge and discharge electrochemical performance tests at 25℃±5℃. The test results are shown in Table 1.

[0134] Table 1

[0135]

[0136]

[0137] As can be seen from Table 1:

[0138] (1) As can be seen from Examples 1-14 and Comparative Example 1, the composite negative electrode material of the present invention can significantly reduce the DCR of the battery and improve the capacity retention rate at 0.5C cycle and 2C rate compared with traditional graphite materials. This indicates that the addition of alloy and graphene helps to reduce battery impedance, increase lithium pathways, and enhance lithium diffusion. As can be seen from Examples 1 and Comparative Example 2, the static lithiation of the present invention can enable the graphene material to be lithiated, enhance the interaction between the graphene material and the lithium alloy, thereby improving the electrochemical performance of the battery. As can be seen from Examples 1 and Comparative Example 3, the formation of the lithium alloy of the present invention can effectively increase the electron pathways and improve the uniformity of lithium deposition, thereby improving the electrochemical performance of the battery.

[0139] (2) As can be seen from Examples 1-3, the metal material in step (2) of the present invention is preferably Zn, which can promote the alloying effect of lithium metal materials, thereby further improving the cycle performance, rate performance and first coulombic efficiency of the battery; As can be seen from Examples 1, 4 and 7, Examples 2, 5 and 8, Examples 3, 6 and 9, the molar ratio of the lithium metal material in step (1) to the metal material in step (2) of the present invention is preferably 19:1. At the same time, as can be seen from Examples 1, 4, 7 and 10-11, the molar ratio of the lithium metal material in step (1) to the metal material in step (2) of the present invention is preferably (15- 19): (1-5), can promote uniform lithium deposition and improve the electrochemical performance of the battery; As can be seen from Examples 1 and 12-13, the time of static lithiation in step (1) of the present invention will affect the degree of lithiation of graphene material, thereby affecting the performance of composite anode material; As can be seen from Examples 1 and 14, the lithiation method of the present invention is static lithiation, which can not only save energy consumption, but also does not affect the role of graphene material and lithium metal alloy; As can be seen from Examples 1 and 15, the preferred particle size D50 of graphite material in the present invention is more than twice the particle size D50 of lithium metal material, which can promote the full contact between lithium metal material and graphene material, thereby promoting the lithiation process.

[0140] In summary, this invention provides a composite anode material, its preparation method, and its application. The composite anode material obtained by the preparation method can guide the uniform deposition of metallic lithium, reduce the probability of lithium dendrite formation, provide more electron pathways, enhance lithium diffusion, thereby reducing the gap between the anode material and the solid electrolyte, reducing battery impedance, and improving battery cycle performance and rate performance.

[0141] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a composite negative electrode material, characterized in that, The preparation method includes the following steps: (1) In a protective atmosphere, graphene material and lithium metal material are mixed and lithiated to obtain lithiated graphene material, wherein both graphene material and lithium metal material are in particulate state. (2) Mix and heat the metal material and the lithium graphene material described in step (1) to obtain the composite negative electrode material.

2. The preparation method according to claim 1, characterized in that, The molar ratio of the lithium metal material in step (1) to the metal material in step (2) is (15-19):(1-5); Preferably, the particle size D50 of the graphene material in step (1) is 5-20 μm; Preferably, the particle size D50 of the lithium metal material in step (1) is 4-7 μm; Preferably, the particle size D50 of the graphene material in step (1) is more than twice the particle size D50 of the lithium metal material; Preferably, the protective atmosphere in step (1) includes any one or a combination of at least two of nitrogen, argon, or neon.

3. The preparation method according to claim 1 or 2, characterized in that, The lithiation time in step (1) is more than 20 hours; Preferably, the lithiation temperature in step (1) is 20-35°C; Preferably, the lithiation method in step (1) includes standing.

4. The preparation method according to claim 1 or 2, characterized in that, The mass ratio of graphene material to lithium metal material in step (1) is (0.5-2):(0.5-2); Preferably, the graphene material in step (1) includes reduced graphene oxide; Preferably, the method for preparing the graphene material in step (1) includes the Hummer method and the spray drying method.

5. The preparation method according to claim 1 or 2, characterized in that, The method of mixing graphene material and lithium metal material in step (1) includes ball milling; Preferably, the ball mill rotates at a speed of 400-600 rpm for 12-36 hours. Preferably, the time for mixing the graphene material and the lithium metal material in step (1) is 12-36 hours.

6. The preparation method according to claim 1 or 2, characterized in that, The metallic material in step (2) includes any one or a combination of at least two of Ag, Zn, Mg, Al or Ge, preferably Zn.

7. The preparation method according to claim 1 or 2, characterized in that, Step (2) involves heating the metal material to above its melting point.

8. A composite negative electrode material, characterized in that, The composite negative electrode material is prepared by the preparation method described in any one of claims 1-7; The composite anode material includes graphene, lithium alloy, and lithium metal, or the composite anode material includes graphene and lithium alloy.

9. A negative electrode sheet, characterized in that, The negative electrode sheet includes a current collector and a negative electrode active material layer on at least one side surface of the current collector, wherein the negative electrode active material layer includes the composite negative electrode material as described in claim 8.

10. A battery, characterized in that, The battery includes the negative electrode as described in claim 9.

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