Lithium battery cathode and lithium battery
阅读说明：本技术 一种锂电池负极及锂电池 (Lithium battery cathode and lithium battery ) 是由 张露露 江文锋 郭姿珠 谢静 于 2020-06-24 设计创作，主要内容包括：一种锂电池负极,包括负极集流体和设置在负极集流体表面上的保护层,保护层包括掺杂的碳材料基体和过渡金属化合物颗粒,且至少部分过渡金属化合物颗粒被掺杂的碳材料基体包覆,其中,掺杂的碳材料基体中的掺杂元素为钴元素和氮元素。保护层的设置,有助于锂离子在负极中的均匀沉积,可有效阻止锂枝晶朝着正极侧的方向生长,避免了电池短路的现象发生。(A lithium battery negative electrode comprises a negative electrode current collector and a protective layer arranged on the surface of the negative electrode current collector, wherein the protective layer comprises a doped carbon material matrix and transition metal compound particles, at least part of the transition metal compound particles are coated by the doped carbon material matrix, and doping elements in the doped carbon material matrix are cobalt elements and nitrogen elements. The protective layer is beneficial to the uniform deposition of lithium ions in the negative electrode, can effectively prevent the growth of lithium dendrites towards the direction of the positive electrode side, and avoids the occurrence of the phenomenon of short circuit of the battery.)
1. The negative electrode of the lithium battery is characterized by comprising a negative electrode current collector and a protective layer arranged on the surface of the negative electrode current collector, wherein the protective layer comprises a doped carbon material matrix and transition metal compound particles, at least part of the transition metal compound particles are coated by the doped carbon material matrix, and doping elements in the doped carbon material matrix are cobalt elements and nitrogen elements.
2. The lithium battery negative electrode as claimed in claim 1, wherein the cobalt element is contained in an amount of not less than 1% by mass and the nitrogen element is contained in an amount of not less than 1% by mass, based on the total mass of the doped carbon material matrix; preferably, the mass content of the cobalt element is 1-15%, and the mass content of the nitrogen element is 1-15%.
3. The lithium battery negative electrode as claimed in claim 2, wherein the cobalt element is contained in an amount of 5 to 10% by mass and the nitrogen element is contained in an amount of 5 to 12% by mass, based on the total mass of the doped carbon material matrix.
4. The lithium battery negative electrode as claimed in claim 1, wherein a molar ratio of the cobalt element to the nitrogen element in the carbon material matrix is 1:3 to 1: 6.
5. The negative electrode for a lithium battery as claimed in claim 1, wherein the transition metal compound particles are coated in an amount of at least 60% based on the total amount of the transition metal compound particles.
6. The negative electrode for a lithium battery as claimed in claim 1, wherein the transition metal compound particles have a particle size of 10 to 30nm, preferably 15 to 20 nm.
7. The negative electrode for a lithium battery as claimed in claim 1, wherein the mass ratio of the carbon material matrix is 85 to 95% and the mass ratio of the transition metal compound particles is 5 to 15% based on the total mass of the protective layer.
8. The lithium battery negative electrode as claimed in claim 1, wherein a mass ratio of the carbon material matrix to the transition metal compound particles in the protective layer is 5.6:1 to 19: 1.
9. The lithium battery negative electrode as claimed in claim 1, wherein the transition metal compound particles are selected from Co9S8、Co3O4、Fe3C、MoS2、ZnO、CoCl3One or more of (a).
10. The lithium battery negative electrode according to claim 1, wherein a thickness of the protective layer is 3 to 15 μm.
11. The negative electrode for a lithium battery as claimed in claim 1, wherein the carbon material is selected from at least one of carbon nanofibers, carbon nanotubes, carbon nanorods and graphene, preferably the carbon material is selected from graphene.
12. The lithium battery negative electrode as claimed in claim 1, further comprising a negative active material layer between the negative current collector and the protective layer.
13. The negative electrode for a lithium battery as claimed in claim 12, wherein the negative active material layer is a lithium metal layer.
14. A lithium battery comprising a negative electrode for a lithium battery as claimed in any one of claims 1 to 13.
Technical Field
The application relates to the field of lithium batteries, in particular to a lithium battery cathode and a lithium battery.
Background
Lithium ion batteries are widely used in portable electronic products such as digital cameras, mobile phones and notebook computers, as well as electric bicycles and electric automobiles due to their advantages of high reversible capacity, high energy density, long cycle life, environmental protection, and the like. With the popularization of new energy automobiles, the requirements on batteries are higher and higher, and people are dedicated to the research on high-energy density lithium batteries in order to meet the requirements of long driving mileage. The theoretical capacity of the conventional graphite cathode is low, and the requirement of a high-energy density battery cannot be met. The lithium metal has low electrode potential and can improve the energy density of the battery when used as a negative electrode material, however, the lithium metal has active chemical properties, and lithium dendrite is easily generated when used as a negative electrode in the charge-discharge cycle of the battery, and the generation of the lithium dendrite not only causes the loss of active lithium, namely the attenuation of the battery capacity, but also has hidden troubles in the aspect of the safety performance of the battery.
Disclosure of Invention
For the technical problem of the lithium dendrite that exists among the lithium cell negative pole among the solution prior art, this application provides a lithium cell negative pole and lithium cell, but lithium ion uniform deposition in this negative pole effectively prevents the growth of lithium dendrite towards the direction of anodal, has avoided the phenomenon of battery short circuit to take place.
In a first aspect, the present application provides a lithium battery negative electrode, including a negative electrode current collector and a protective layer disposed on a surface of the negative electrode current collector, where the protective layer includes a doped carbon material matrix and transition metal compound particles, at least a portion of the transition metal compound particles are coated by the doped carbon material matrix, and doping elements in the doped carbon material matrix are cobalt element and nitrogen element.
In order to avoid the situation that lithium dendrites generated by a negative electrode continue to grow towards the direction of a positive electrode side, a negative electrode protective layer is usually arranged on the surface of the negative electrode in the prior art, the negative electrode protective layer is usually a carbon-containing material, and because deposition sites of lithium ions in the carbon-containing material are few and lithium affinity is weaker than that of the lithium dendrites, when the lithium dendrites grow into the protective layer, the lithium ions can be preferentially deposited at the lithium dendrite positions, so that the lithium dendrites continue to grow, namely the negative electrode protective layer in the prior art can not effectively prevent the growth of the lithium dendrites.
According to the lithium battery cathode provided by the application, the protective layer contains the carbon material matrix doped with the nitrogen element and the cobalt element together, and the introduction of the nitrogen element and the cobalt element enables a Co-N-C structure Co-doped with cobalt and nitrogen to be formed in the carbon material. In addition, one cobalt atom is co-coordinately doped with nitrogen atoms around the cobalt atom in the carbon material structure, so that CoN can be formedxThe cobalt atom in the site acts as an effective active site for lithium deposition, helping to guide lithium ions to proceed at the siteThe carbon material after deposition and element doping has more lithium ion deposition sites, and the distribution of the deposition sites is uniform, so that lithium ions are uniformly deposited in the protective layer. Moreover, the negative electrode protection layer also contains transition metal compound particles, and the transition metal compound particles also have good lithium affinity, so that lithium ions can be deposited at the particles, namely, the transition metal compound is introduced, the deposition sites of the lithium ions in the protection layer are further increased, the deposition sites are increased, the distribution of the deposition sites is uniform, and the more uniform deposition of the lithium ions in the protection layer is facilitated. In addition, at least part of the transition metal compound particles are coated by the carbon material matrix, so that the electron cloud density of the transition metal compound particles and the electron cloud density of CoNx sites in the carbon material matrix can influence each other, the lithium affinity effect of the protective layer is better, and lithium ions are favorably deposited in each position of the protective layer. When lithium dendrite generated by the negative electrode enters the protective layer, lithium ions are not only deposited at the lithium dendrite, but also deposited in the whole protective layer, so that the lithium dendrite is effectively prevented from continuously growing towards the direction of the positive electrode side, the occurrence of short circuit in the battery is avoided, and the safety performance of the battery is greatly improved.
In a second aspect, the present application provides a lithium battery comprising a negative electrode for a lithium battery as described above.
Compared with the prior art, the lithium battery negative electrode provided by the application contains the protective layer, and the protective layer contains the carbon material matrix and the transition metal compound particles which are doped with nitrogen elements and cobalt elements together, so that the lithium affinity of the protective layer is effectively improved, lithium affinity active sites in the protective layer are increased, and the lithium affinity active sites are uniformly distributed in the protective layer, so that lithium ions can be uniformly deposited in the protective layer, and even if lithium dendrite generated by the negative electrode reaches the protective layer, the lithium affinity active sites in the protective layer are more and uniformly distributed, so that the phenomenon that the lithium ions are only deposited at the lithium dendrite is avoided, the lithium ions can be uniformly deposited at each part of the protective layer, and the growth of the lithium dendrite towards the positive electrode side is effectively prevented; moreover, the lithium ions uniformly deposited are not easy to generate dead lithium, so that the loss of the active capacity of the battery is avoided, and the safety performance and the cycle performance of the battery are greatly improved.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects solved by the present application more clear, the present application is further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
In a first aspect, the present application provides a negative electrode for a lithium battery, including a negative electrode current collector and a protective layer disposed on a surface of the negative electrode current collector, where the protective layer includes a doped carbon material matrix and transition metal compound particles, at least a portion of the transition metal compound particles are coated with the doped carbon material matrix, and doping elements in the doped carbon material matrix are cobalt and nitrogen.
By introducing nitrogen element and cobalt element into the carbon material matrix at the same time, a Co-N-C structure can be formed, the lithium affinity of the carbon material matrix can be effectively improved, and a cobalt atom and the surrounding N atom are Co-coordinately doped in the carbon material structure to form CoNxSite, CoNxThe formation of the sites increases the number of lithium-philic active sites in the carbon material matrix, and the sites are uniformly distributed, thereby being beneficial to the uniform deposition of lithium ions in the protective layer, avoiding the occurrence of the phenomenon that a large number of lithium ions are deposited at the position of lithium dendrite, further preventing the continuous growth of the lithium dendrite and greatly improving the safety performance of the battery. In addition, the protective layer also contains transition metal compound particles, and the transition metal compound particles have better lithium affinity, so that active sites deposited by lithium ions in the protective layer are further increased, and at least one part of the transition metal compound particles are coated in the carbon material matrix, so that the transition metal compound particles can be better dispersed on the carbon material matrix, the agglomeration of the transition metal compound particles is prevented, and the transition metal compound particles can also generate synergistic action with CoNx sites in the carbon material matrix, namely the electron cloud density of the transition metal compound particles and the CoNx sites can be influenced by each other to a greater extent, compared with the situation that the CoNx sites are independently introduced, the CoNx sites can be better introducedOr the transition metal compound particles and the transition metal compound particles have the synergistic effect simultaneously, so that the lithium affinity of the protective layer is higher, the uniform deposition of lithium ions in the protective layer is guided, the inhibition effect of the protective layer on the growth of lithium dendrites is better, and the safety performance of the battery is further improved. Because of the uniform deposition of lithium ions in the protective layer, the generation of dead lithium can be effectively avoided, thereby being beneficial to improving the cycle performance of the battery.
Further, the number of coated transition metal compound particles is at least 60% based on the total number of transition metal compound particles in the protective layer.
The transition metal compound particles coated by the carbon material matrix in the protective layer can generate a synergistic effect with CoNx sites in the carbon material matrix, namely, the electron cloud density of the transition metal compound particles and the CoNx sites in the carbon material matrix can be influenced mutually, so that the deposition behavior of lithium ions in the protective layer can be improved, and the quantity ratio of the coated transition metal compound particles in the range can better guide the lithium ions to be uniformly deposited in the protective layer.
Preferably, in the protective layer, all of the transition metal compound particles are coated with the graphene substrate.
When the transition metal compound particles are completely coated by the carbon material matrix, the synergistic effect between the transition metal compound particles and the carbon material matrix can be exerted to the greatest extent, namely, the electron cloud density of the transition metal compound particles and the carbon material matrix can be influenced by each other to the greatest extent, so that the protective layer can achieve a better lithium precipitation effect.
Further, based on the total mass of the doped carbon material matrix, the mass content of cobalt is not less than 1%, and the mass content of nitrogen is not less than 1%; preferably, the mass content of the cobalt element is 1-15%, and the mass content of the nitrogen element is 1-15%.
The introduction of cobalt element and nitrogen element in the carbon material matrix can not only increase the lithium ion deposition sites in the carbon material matrix, so that the lithium ion deposition sites in the carbon material matrix are uniformly distributed, but also improve the lithium affinity of the carbon material matrix, thereby being beneficial to the uniform deposition of lithium ions in the protective layer, and therefore, when the content of cobalt element and nitrogen element in the carbon material matrix is in the range, the carbon material matrix can achieve a better lithium deposition effect.
Preferably, the mass content of cobalt element is 5-10% and the mass content of nitrogen element is 5-12% based on the total mass of the doped carbon material matrix.
Further, the molar ratio of the cobalt element to the nitrogen element in the carbon material matrix is 1:3 to 1: 6.
As the effective lithium deposition active site is a CoNx site in the co-doped carbon material matrix of the cobalt element and the nitrogen element, namely, one cobalt atom and 3-4 nitrogen atoms around the cobalt atom are co-coordinated and doped in the carbon material structure, for the carbon material matrix of the structure, when the molar ratio of the cobalt element to the nitrogen element is in the range, the carbon material matrix can achieve a better lithium deposition effect.
Further, the particle diameter of the transition metal compound particles is 10 to 30nm, and preferably, the particle diameter of the transition metal compound particles is 15 to 20 nm.
The size of the transition metal compound particles can influence the synergistic effect of the transition metal compound particles and CoNx sites in the carbon material matrix, and if the particles are too small, the influence of the coating layer on the surfaces of the particles is larger, so that the electron cloud of the transition metal compound particles can not effectively influence the electron cloud of the CoNx sites in the protective layer; the particles are too large, the specific surface area of the particles is small, atoms in the particles cannot effectively generate a synergistic effect with graphene, and the effect of a protective layer per unit mass is poor, so that the transition metal compound particles in the particle size range are selected, the synergistic effect between the transition metal compound particles and CoNx sites in a graphene matrix is better, the hydrophilicity performance of the protective layer is better, and the effect of inhibiting the growth of lithium dendrites is better.
Further, the mass ratio of the carbon material matrix is 85 to 95% and the mass ratio of the transition metal compound particles is 5 to 15% based on the total mass of the protective layer.
The active sites for lithium ion deposition in the protective layer are mainly provided by the carbon material matrix, and the introduction of the transition metal compound particles can generate a synergistic effect with the carbon material matrix to further improve and improve the lithium affinity of the carbon material matrix, so that the mass ratio of the carbon material matrix and the transition metal compound particles in the protective layer is selected within the range, sufficient and uniformly distributed lithium deposition sites in the protective layer can be ensured, and the sufficient synergistic effect of the transition metal compound particles and the carbon material matrix can be satisfied to improve the lithium affinity of the protective layer, so that the protective layer can achieve a better lithium deposition effect.
Further, in the protective layer, the mass ratio of the carbon material matrix to the transition metal compound particles is 5.6:1 to 19: 1.
The transition metal compound particles coated with the carbon material matrix can interact with the carbon material matrix to a large extent, that is, electron clouds of the transition metal compound particles and electron clouds of the CoNx sites in the carbon material matrix affect each other, so that the hydrophilicity of the protective layer is improved, and lithium ions are uniformly deposited in the protective layer. Therefore, when the mass ratio of the carbon material matrix to the transition metal compound particles in the protective layer is in the above range, the protective layer can effectively inhibit the continuous growth of lithium dendrites, improve the safety performance of the battery, and also can effectively avoid the generation of dead lithium, thereby improving the cycle performance of the battery.
Further, the transition metal compound particles are selected from Co9S8、Co3O4、Fe3C、MoS2、ZnO、CoCl3Preferably, the transition metal compound particles are selected from Co9S8。
Further, the thickness of the protective layer is 3-15 [ mu ] m.
The protective layer should provide enough space for lithium deposition, and the thickness of the protective layer is within the above range, so that the sufficient space for lithium ion deposition can be ensured, and the volumetric energy density of the battery cannot be reduced due to the introduction of the protective layer.
Further, the carbon material is selected from at least one of carbon nanofibers, carbon nanotubes, carbon nanorods and graphene, and preferably, the carbon material is selected from graphene.
Further, the lithium metal negative electrode includes a negative electrode current collector and a negative electrode active material layer and a protective layer sequentially disposed on a surface thereof.
The negative active material layer contains a negative active material, further the negative active material is selected from one or more of carbon materials, tin alloys, silicon, tin, germanium, lithium metal and lithium alloys, when the carbon materials are selected, the carbon materials can adopt non-graphitized carbon, graphite or carbon obtained by high-temperature oxidation of polyacetylene polymer materials or one or more of pyrolytic carbon, coke, organic polymer sinter and activated carbon; preferably, the anode active material is lithium metal.
Further, the anode active material layer is a lithium metal layer.
The preparation method of the lithium battery negative electrode does not have a strong requirement, and the lithium battery negative electrode can be obtained by coating protective layer slurry on the surface of a negative electrode current collector; the negative electrode of the lithium battery can also be obtained by coating the negative active material slurry and the protective layer slurry on the surface of the negative current collector in sequence.
The preparation of the protective layer slurry comprises the following steps:
(1) dissolving a cobalt source, a nitrogen source and a transition metal source in a solvent, and stirring to react to obtain a reaction solution;
(2) treating a carbon source in acid, adding the treated carbon source into the reaction liquid obtained in the step (1), stirring and evaporating to obtain black powder;
(3) calcining the black powder obtained in the step (2) at high temperature in an inert atmosphere, and then carrying out acid washing and drying to obtain a composite material;
(4) and mixing the composite material with a binder and an organic solvent to obtain the protective layer slurry.
The composite material comprises transition metal compound particles and a doped carbon material matrix, wherein the carbon material matrix wraps at least part of the transition metal compound particles, and the doping elements in the doped carbon material matrix are cobalt elements and nitrogen elements.
In one embodiment, the cobalt source and the transition metal source in step (1) are both Co (NO)3)2﹒6H2O, the nitrogen source is aniline and (NH)4）2S2O8The solvent is hydrochloric acid; the carbon source in the step (2) is carbon black, and the acid is nitric acid and hydrochloric acid.
In a second aspect, the present application provides a lithium battery comprising a negative electrode for a lithium battery as described above.
Because the negative pole of the lithium battery is provided with the negative pole protective layer, the protective layer contains transition metal compound particles and a doped carbon material matrix, the doped carbon material matrix is a carbon material matrix doped with cobalt element and nitrogen element together, the introduction of the cobalt element and the nitrogen element can not only increase the lithium ion deposition sites in the carbon material matrix, but also form uniformly distributed CoNx sites in the carbon material matrix, and the sites can not only effectively improve the lithium affinity of the carbon material matrix, so that the lithium ions can be deposited in the protective layer more easily and uniformly; in addition, the introduction of the transition metal compound particles can also increase lithium ion deposition sites in the protective layer, and moreover, electron clouds of the transition metal compound particles and CoNx sites can influence each other, and under the synergistic effect of the transition metal compound particles and the CoNx sites, the lithium affinity of the protective layer is further promoted, so that the lithium ions can be deposited in the protective layer more uniformly, the growth of lithium dendrites can be effectively prevented, and the safety performance of the lithium battery is greatly improved.
Further, the lithium battery further comprises a positive electrode, the positive electrode comprises a positive active material, wherein the positive active material is selected from LiFexMnyMzPO4(x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, and x + y + z =1, wherein M is at least one of Al, Mg, Ga, Ti, Cr, Cu, Zn and Mo), Li3V2(PO4)3、Li3V3(PO4)3、LiNi0.5-xMn1.5-yMx+yO4X is more than or equal to 0.1 and less than or equal to 0.5, y is more than or equal to 0 and less than or equal to 1.5, M is at least one of Li, Co, Fe, Al, Mg, Ca, Ti, Mo, Cr, Cu and Zn), and LiVPO4F、Li1＋xL1－y－zMyNzO2(L, M, N is at least one of Li, Co, Mn, Ni, Fe, Al, Mg, Ga, Ti, Cr, Cu, Zn, Mo, F, I, S and B-0.1-0.2 x, 0-1 y, 0-1 z, 0-1 + z 1.0), Li2CuO2、Li5FeO4One or more of; preferably, the positive active material is selected from LiAl0.05Co0.15Ni0.80O2、LiNi0.80Co0.10Mn0.10O2、LiNi0.60Co0.20Mn0.20O2、LiCoO2、LiMn2O4、LiFePO4、LiMnPO4、LiNiPO4、LiCoPO4、LiNi0.5Mn1.5O4、Li3V3(PO4)3One or more of (a).
Further, the lithium battery further comprises an electrolyte comprising a solvent and a lithium salt, wherein the solvent is selected from compounds having one or more of the following groups: ether groups, nitrile groups, cyanide groups, fluorine ester groups, tetrazolyl groups, fluorosulfonyl groups, chlorosulfonyl groups, nitro groups, carbonate groups, dicarbonate groups, nitrate groups, fluoroamide groups, diketone groups, azole groups, and triazine groups. The lithium salt may be conventionally employed by those skilled in the art, and is selected from, for example, LiPF6、LiAsF6、LiClO4、LiBF6、LiN(CF3SO3)2、LiCF3SO3、LiC(CF3SO3)2And LiN (C)4F9SO2)(CF3SO3) One or more of (a).
The specific preparation method of the lithium battery is not particularly limited, and may be a preparation method of a lithium battery that is conventional in the art, for example, a battery cell may be obtained by sealing a battery cell in a battery case, and the preparation of the battery cell is a preparation method of a battery cell in a lithium battery that is conventional in the art, and is not particularly limited. The specific form of the lithium battery is not limited, and the lithium battery can be a button battery, a square battery or a soft package battery.
The present application is further illustrated by the following specific examples, which are provided only for illustrating and explaining the present application and are not intended to limit the present application.
Example 1
(1) 0.75ml of aniline, 218g of Co (NO)3)2﹒6H2O、1.25g（NH4）2S2O8Adding into 125ml 1M hydrochloric acid solutionStirring the mixture in the solution to react to obtain reaction solution;
(2) pretreating 0.1g of carbon black in 70% nitric acid, dispersing in 10ml of 1M hydrochloric acid solution, adding into the reaction solution obtained in the step (1), stirring for 48 hours, stirring on a heating plate at 90 ℃ to evaporate the solution to obtain black powder, and grinding by using a mortar;
(3) calcining and carbonizing the powder obtained in the step (2) for one hour at the high temperature of 800 ℃ in a tube furnace under the atmosphere of argon, and putting the calcined powder at 0.5M H2SO4Pickling the solution at 80-90 deg.c for 8 hr, and drying in a vacuum drying oven at 100 deg.c for 12 hr. Then, carrying out secondary calcination in a tube furnace to obtain a composite material, wherein the composite material is a graphene matrix doped with cobalt and nitrogen and Co completely wrapped by the graphene matrix9S8The particle comprises a graphene matrix, wherein the mass content of cobalt element is 7%, the mass content of nitrogen element is 8%, the mass ratio of the graphene matrix in the composite material is 90%, and Co is9S8The mass ratio of the particles is 10 percent, and Co9S8The particle size of the particles is 17 nm;
(4) and (4) mixing the composite material obtained in the step (3) with PVDF and NMP to prepare protective layer slurry, and coating the protective layer slurry on a lithium foil to obtain the lithium foil with a protective layer, namely the lithium battery cathode.
Example 2
Unlike example 1, the temperature of the high-temperature calcination in step (3) was 750 ℃; the obtained composite material comprises a graphene matrix doped with cobalt and nitrogen and Co completely wrapped by the graphene matrix9S8The particle comprises 10% of cobalt element by mass and 12% of nitrogen element by mass in a graphene matrix, and in the composite material, the mass ratio of the graphene matrix is 90%, and the Co is9S8The mass ratio of the particles is 10 percent, and Co9S8The particle size of the particles was 17 nm.
Example 3
Different from the embodiment 1, the temperature of the high-temperature calcination in the step (3) is 600 ℃; the obtained composite material is cobalt element and nitrogen elementGraphene matrix doped with graphene and Co completely wrapped by graphene matrix9S8The particle comprises 15% of cobalt element by mass and 15% of nitrogen element by mass in a graphene matrix, and in the composite material, the mass ratio of the graphene matrix is 90%, and the Co is9S8The mass ratio of the particles is 10 percent, and Co9S8The particle size of the particles was 15 nm.
Example 4
Different from the example 1, the temperature of the high-temperature calcination in the step (3) is 900 ℃; the obtained composite material comprises a graphene matrix doped with cobalt and nitrogen and Co completely wrapped by the graphene matrix9S8The particle comprises a graphene matrix, wherein the mass content of cobalt element is 5%, the mass content of nitrogen element is 5%, the mass ratio of the graphene matrix in the composite material is 90%, and Co is9S8The mass ratio of the particles is 10 percent, and Co9S8The particle size of the particles was 17 nm.
Example 5
Unlike example 1, the temperature of the high-temperature calcination in step (3) was 950 ℃; the obtained composite material comprises a graphene matrix doped with cobalt and nitrogen and Co completely wrapped by the graphene matrix9S8The particle comprises a graphene matrix, wherein the mass content of cobalt element is 1%, the mass content of nitrogen element is 1%, the mass ratio of the graphene matrix in the composite material is 90%, and Co is9S8The mass ratio of the particles is 10 percent, and Co9S8The particle size of the particles was 30 nm.
Example 6
Different from the embodiment 1, the temperature of the high-temperature calcination in the step (3) is 1000 ℃; the obtained composite material comprises a graphene matrix doped with cobalt and nitrogen and Co completely wrapped by the graphene matrix9S8The particle comprises a graphene matrix, wherein the mass content of cobalt element in the graphene matrix is 0.5%, the mass content of nitrogen element in the graphene matrix is 0.5%, the mass ratio of the graphene matrix in the composite material is 90%, and Co is9S8The mass ratio of the particles is 10 percent, and Co9S8The particle size of the particles was 17 nm.
Example 7
Unlike example 1, the precursor Co (NO) in step (1)3)2﹒6H2The amount of O was changed to 250 g; the obtained composite material comprises a graphene matrix doped with cobalt and nitrogen and Co completely wrapped by the graphene matrix9S8The particle comprises a graphene matrix, wherein the mass content of cobalt element is 6%, the mass content of nitrogen element is 10%, the mass percentage of the graphene matrix in the composite material is 85%, and Co is9S8The mass ratio of the particles is 15 percent, and Co9S8The particle size of the particles was 17 nm.
Example 8
Unlike example 1, Co (NO) in step (1)3)2﹒6H2The dosage of O is 190 g; the obtained composite material comprises a graphene matrix doped with cobalt and nitrogen and Co completely wrapped by the graphene matrix9S8The particle comprises a graphene matrix, wherein the mass content of cobalt element is 6%, the mass content of nitrogen element is 10%, the mass percentage of the graphene matrix in the composite material is 95%, and Co is9S85% of particles by mass, Co9S8The particle size of the particles was 17 nm.
Example 9
Unlike example 1, the precursor Co (NO) in step (1)3)2﹒6H2The amount of O was changed to 290 g; the obtained composite material comprises a graphene matrix doped with cobalt and nitrogen and Co completely wrapped by the graphene matrix9S8The particle comprises a graphene matrix, wherein the mass content of cobalt element is 6%, the mass content of nitrogen element is 10%, the mass percentage of the graphene matrix in the composite material is 80%, and Co is9S8The mass percentage of the particles is 20 percent, and Co9S8The particle size of the particles was 17 nm.
Example 10
Unlike example 1, the evaporation temperature in step (2) was 100 ℃; the obtained composite material comprises a graphene matrix doped with cobalt and nitrogen and Co completely wrapped by the graphene matrix9S8The particle comprises a graphene matrix, wherein the mass content of cobalt element in the graphene matrix is 6%, the mass content of nitrogen element in the graphene matrix is 10%, and the mass ratio of the graphene matrix in the composite material is 90%, and Co9S8The mass ratio of the particles is 10 percent, and Co9S8The particle size of the particles was 20 nm.
Example 11
Unlike example 1, the evaporation temperature in step (2) was 80 ℃; the obtained composite material comprises a graphene matrix doped with cobalt and nitrogen and Co completely wrapped by the graphene matrix9S8The particle comprises a graphene matrix, wherein the mass content of cobalt element in the graphene matrix is 6%, the mass content of nitrogen element in the graphene matrix is 10%, and the mass ratio of the graphene matrix in the composite material is 90%, and Co9S8The mass ratio of the particles is 10 percent, and Co9S8The particle size of the particles was 10 nm.
Example 12
Unlike example 1, the evaporation temperature in step (2) was 120 ℃; the obtained composite material comprises a graphene matrix doped with cobalt and nitrogen and Co completely wrapped by the graphene matrix9S8The particle comprises a graphene matrix, wherein the mass content of cobalt element in the graphene matrix is 6%, the mass content of nitrogen element in the graphene matrix is 10%, and the mass ratio of the graphene matrix in the composite material is 90%, and Co9S8The mass ratio of the particles is 10 percent, and Co9S8The particle size of the particles was 40 nm.
Example 13
Unlike example 1, the secondary calcination temperature in the tube furnace in step (3) was 800 ℃; the obtained composite material is a graphene matrix and Co which are doped with cobalt element and nitrogen element together9S8Particles of which 80% of Co9S8The particles are coated with graphene matrix, the remainder being Co9S8The particles are dispersed in graphene and not coated, the mass content of cobalt element in the graphene matrix is 6%, the mass content of nitrogen element in the graphene matrix is 10%, the mass ratio of the graphene matrix in the composite material is 90%, and Co is used as a binder9S8The mass ratio of the particles is 10 percent, and Co9S8GranulesHas a particle diameter of 17 nm.
Example 14
Unlike example 1, the secondary calcination temperature in the tube furnace in step (3) was 700 ℃; the obtained composite material is a graphene matrix and Co which are doped with cobalt element and nitrogen element together9S8Particles of which 60% of Co9S8The particles are coated with graphene matrix, the remainder being Co9S8The particles are dispersed in graphene and not coated, the mass content of cobalt element in the graphene matrix is 6%, the mass content of nitrogen element in the graphene matrix is 10%, the mass ratio of the graphene matrix in the composite material is 90%, and Co is used as a binder9S8The mass ratio of the particles is 10 percent, and Co9S8The particle size of the particles was 17 nm.
Example 15
Unlike example 1, the secondary calcination temperature in the tube furnace in step (3) was 500 ℃; the obtained composite material is a graphene matrix and Co which are doped with cobalt element and nitrogen element together9S8Particles of which 30% of Co9S8The particles are coated with graphene matrix, the remainder being Co9S8The particles are dispersed in graphene and not coated, the mass content of cobalt element in the graphene matrix is 6%, the mass content of nitrogen element in the graphene matrix is 10%, the mass ratio of the graphene matrix in the composite material is 90%, and Co is used as a binder9S8The mass ratio of the particles is 10 percent, and Co9S8The particle size of the particles was 17 nm.
Example 16
Unlike example 1, the secondary high-temperature calcination was not performed in step (3); the obtained composite material is a graphene matrix and Co which are doped with cobalt element and nitrogen element together9S8Particles of which Co9S8The particles are dispersed in graphene and not coated, the mass content of cobalt element in the graphene matrix is 6%, the mass content of nitrogen element in the graphene matrix is 10%, the mass ratio of the graphene matrix in the composite material is 90%, and Co is used as a binder9S8The mass ratio of the particles is 10 percent, and Co9S8The particle size of the particles was 17 nm.
Comparative example 1
Different from the embodiment 1, the calcined powder in the step (3) is subjected to acid washing in 70% concentrated nitric acid, and the obtained composite material is a graphene matrix doped with cobalt and nitrogen together, wherein the mass content of the cobalt in the graphene matrix is 6%, and the mass content of the nitrogen in the graphene matrix is 7%.
Comparative example 2
(1) 2.49g of Co (CH)3COO)2﹒4H2Adding O and 0.76g of thiourea into 60ml of ethylene glycol, reacting for 8 hours in a hydrothermal kettle at the temperature of 200 ℃, centrifugally collecting a reaction product, and drying for 6 hours in a vacuum drying oven to obtain Co9S8Particles having a particle size of 17 nm;
(2) co obtained in the step (1)9S8The particles are mixed with PVDF and NMP to prepare slurry, and the slurry is coated on a lithium foil to obtain the lithium foil with a protective layer, namely the lithium battery cathode.
Comparative example 3
Different from the comparative example 2, the reaction product obtained in the step (1) is collected by centrifugation and then is subjected to ultrasonic treatment for 4 hours together with the dispersed graphene to obtain pure graphene-coated Co9S8And (4) preparing particles, and further preparing the lithium battery cathode.
Comparative example 4
And directly mixing the graphene subjected to ultrasonic dispersion with PVDF and NMP to prepare slurry, and coating the slurry on copper foil to prepare the lithium battery cathode.
Comparative example 5
And directly using copper foil as a negative electrode, and assembling the copper foil and a lithium sheet into a half cell for testing. Or directly using a lithium sheet to assemble the positive plate for full battery test.
The compositions of the lithium battery negative electrode protective layers in the examples and comparative examples are shown in table 1.
TABLE 1
And (3) performance testing:
Li vspreparation and testing of the Cu button cell: cutting the copper foil with the protective layer into a size of 17mmAdding two PE diaphragms with the diameter of 19mm into the pole piece, adding a lithium foil with the diameter of 15mm, applying the pressure of 0.1-1 Mpa to compact the two diaphragms, and packaging and buckling the two diaphragms into a battery case to obtain the LivsA Cu cell. Using 1mA cm-2The coulomb efficiency of the battery was tested by performing cyclic charge and discharge for 1.5 hours each time. The effect of the protective layer on the stability of the metallic lithium negative electrode was evaluated by calculating the average coulombic efficiency per 10 cycles of charge-discharge cycles up to 100 cycles, and the results are shown in table 2.
Positive electrodevs Preparation and testing of Li laminated batteries: the cathode is a lithium foil cathode with a protective layer prepared in the above examples and comparative examples, and the anode is a ternary material anode which are assembled together into a laminated battery with 1 mA.cm-2The current density of (2) was cycled between 2.7 and 4V to evaluate the cycle life of the battery, and the effect of the protective layer on the battery life was investigated, the results of which are shown in Table 2.
TABLE 2
Experiment number
Average coulomb efficiency,%
Capacity retention 80% cycle count
Example 1
99.47
155
Example 2
99.45
136
Example 3
99.44
125
Example 4
99.43
122
Example 5
99.42
120
Example 6
99.39
114
Example 7
99.46
140
Example 8
99.43
121
Example 9
99.39
113
Example 10
99.44
126
Example 11
99.43
124
Example 12
99.39
114
Example 13
99.45
137
Example 14
99.43
122
Example 15
99.41
119
Example 16
99.40
117
Comparative example 1
99.38
108
Comparative example 2
99.37
105
Comparative example 3
99.38
109
Comparative example 4
99.36
104
Comparative example 5
99.35
100
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