Coated negative electrode material and preparation method and application thereof

Abstract

The invention belongs to the technical field of battery materials, and discloses a coated negative electrode material as well as a preparation method and application thereof. The coated negative electrode material comprises graphite and a coating layer coated on the surface of the graphite, the coating layer is prepared from alginate and metal salt. The coating layer formed by the alginate and the metal salt can slow down decomposition of sulfide electrolyte on the graphite surface, so that the first coulombic efficiency of the battery is improved. In addition, the interface stability between sulfide and graphite is well improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to a coated negative electrode material and a preparation method and application thereof. Background Art

[0002] At present, the energy density of traditional liquid lithium-ion batteries is close to the limit, and there is also the safety problem of thermal runaway. Solid-state batteries are becoming a research hotspot due to their high energy density and high safety. Solid-state batteries can be divided into polymer solid-state batteries, oxide solid-state batteries and sulfide solid-state batteries according to the different electrolytes. Among them, sulfide solid electrolytes have ultra-high ionic conductivity and good lamination mechanical properties, making them a major research hotspot abroad. Graphite, as the most successful commercial negative electrode material, has good cycle stability. However, as a negative electrode for sulfide solid-state batteries, it faces many challenges: lithium ions form a solid electrolyte interface film (SEI) during the embedding process of graphite, consuming a large amount of Li + , and the sulfide electrolyte decomposes on the surface of the graphite negative electrode, resulting in low first coulombic efficiency, thus affecting the overall performance of the lithium-ion battery.

[0003] Therefore, there is an urgent need to provide a new negative electrode that can inhibit the decomposition of sulfide solid electrolyte on the graphite surface and has a high first coulombic efficiency. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention provides a coated negative electrode material and a preparation method and application thereof. The coated negative electrode material of the present invention can inhibit the decomposition of the sulfide solid electrolyte on the graphite surface and has a high first coulomb efficiency, for example, the first coulomb efficiency is not less than 87%, or even more than 94%.

[0005] The present invention utilizes the fact that the molecular structure of alginate (such as sodium alginate SA) contains abundant -OH functional groups and ether oxygen functional groups that can promote ion transmission, and introduces other metal cations into the alginate solution to enable cross-linking. The present invention utilizes the cross-linking phenomenon to coat a layer of polymer on the surface of graphite to slow down the decomposition of sulfide electrolyte on the graphite surface, thereby improving the first coulomb efficiency of the battery. In addition, this has a good improvement effect on the interface stability between sulfide and graphite.

[0006] A first aspect of the present invention provides a coated negative electrode material.

[0007] Specifically, a coated negative electrode material includes graphite and a coating layer coated on the surface of the graphite;

[0008] The coating layer comprises alginate and metal salt.

[0009] Preferably, the alginate comprises sodium alginate or potassium alginate.

[0010] Preferably, the metal salt comprises aluminum salt, calcium salt, barium salt or zinc salt.

[0011] Preferably, the aluminum salt, calcium salt, barium salt or zinc salt may be a nitrate or a chloride salt, such as aluminum nitrate nonahydrate.

[0012] Preferably, the graphite is one of natural graphite, mesophase carbon microbeads, and composite graphite; more preferably, it is mesophase carbon microbeads.

[0013] Preferably, the mass ratio of alginate to graphite is 0.1-10:100.

[0014] Preferably, the mass ratio of alginate to metal salt is 0.12:(0.01-1).

[0015] Preferably, the graphite may be replaced by silicon or lithium titanate.

[0016] A second aspect of the present invention provides a method for preparing a coated negative electrode material.

[0017] Specifically, a method for preparing a coated negative electrode material comprises the following steps:

[0018] Alginate is mixed with a solvent to form an alginate solution, and graphite is added to the mixture to obtain a suspension; a metal salt is added to the suspension to form a gel solution, and the solution is dried to obtain the coated negative electrode material.

[0019] Preferably, the mass volume ratio of the alginate to the solvent is 0.12 g:(40-100) mL, and more preferably 0.12 g:(40-80) mL.

[0020] Preferably, the mass ratio of alginate to graphite is 0.1-10:100, more preferably 0.12:(3-5), for example 3:100.

[0021] Preferably, the mass ratio of alginate to metal salt is 0.12:(0.01-1), and more preferably 0.12:(0.1-0.8).

[0022] Preferably, the solvent includes water, specifically deionized water.

[0023] Preferably, the metal salt is dissolved in a solvent before being added to obtain a metal salt solution, and the concentration of the metal salt solution is 0.05-0.1 mol / L.

[0024] Preferably, the drying temperature is 80-120° C., and the drying time is 6-12 hours.

[0025] A third aspect of the present invention provides an application of a coated negative electrode material.

[0026] A sulfide battery comprises the above-mentioned coated negative electrode material.

[0027] Preferably, the sulfide battery comprises a sulfide solid-state battery or a sulfide liquid-state battery. The sulfide battery is a lithium-ion battery.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] (1) The coated negative electrode material of the present invention comprises graphite and a coating layer coated on the surface of the graphite; the coating layer comprises alginate and a metal salt. The coating layer formed by the alginate and the metal salt can slow down the decomposition of the sulfide electrolyte on the graphite surface, thereby improving the first coulombic efficiency of the battery. In addition, this has a good improvement effect on the interface stability between the sulfide and the graphite.

[0030] (2) The first coulombic efficiency is an important parameter of lithium-ion battery performance, because Li + During the embedding process of graphite, a SEI film is formed, which consumes Li + , and a stable SEI can reduce the subsequent Li + The consumption of the battery has a great impact on the battery performance. The present invention can reduce the contact resistance of the electrode and form a dense and stable SEI film by coating a layer of polymer on the graphite surface by the sol-gel method, thereby improving the first coulomb efficiency of the battery.

[0031] Compared with the prior art, the present invention provides a new type of graphite negative electrode material, which achieves the result of reducing costs and increasing efficiency. A layer of material is coated on the surface of graphite by the sol-gel method, which can effectively improve the first cycle coulomb efficiency of the battery from 85.25% to 94.37%. In summary, the coated negative electrode material prepared by the present invention has excellent stability for sulfide solid-state batteries, which is of great significance for realizing sulfide solid-state batteries with good cycle stability and safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The first cycle charge and discharge curve of a half-cell assembled with the coated negative electrode material prepared in Example 1;

[0033] Figure 2 This is the first cycle charge and discharge curve of the half-cell assembled with the coated negative electrode material prepared in Comparative Example 1. DETAILED DESCRIPTION

[0034] In order to make the technical scheme of the present invention more clearly understood by those skilled in the art, the following embodiments are listed for illustration. It should be pointed out that the following embodiments do not limit the protection scope of the present invention.

[0035] Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0036] Example 1

[0037] A coated negative electrode material, comprising natural graphite and a coating layer coated on the surface of the natural graphite;

[0038] The coating layer is composed of sodium alginate and aluminum nitrate.

[0039] A method for preparing a coated negative electrode material comprises the following steps:

[0040] Weigh 0.12 g of sodium alginate, put it into 50 mL of deionized water, and stir evenly to obtain solution A;

[0041] Weigh 3.88 g of natural graphite and slowly add it into solution A, stirring at 500 rpm to form a uniform suspension B;

[0042] Weigh 0.2626 g of aluminum nitrate nonahydrate, place it in 10 mL of deionized water and stir evenly, the corresponding concentration is 0.07 mol / L, then add it dropwise into suspension B to obtain a gel solution, and react at room temperature for 4 h;

[0043] The product obtained by the above reaction is filtered to obtain a filter cake D;

[0044] The filter cake D was dried in a vacuum oven at 80° C. for 12 h to obtain a coated negative electrode material.

[0045] Example 2

[0046] A method for preparing a coated negative electrode material comprises the following steps:

[0047] Weigh 0.12 g of sodium alginate, put it into 50 mL of deionized water, and stir evenly to obtain solution A;

[0048] Weigh 3.88 g of natural graphite and slowly add it into solution A, stirring at 500 rpm to form a uniform suspension B;

[0049] Weigh 0.0777 g of calcium chloride, place it in 10 mL of deionized water and stir evenly, the corresponding concentration is 0.07 mol / L, then add it dropwise into suspension B to obtain a gel solution, and react at room temperature for 4 h;

[0050] The product obtained by the above reaction is filtered to obtain a filter cake D;

[0051] The filter cake D was dried in a vacuum oven at 80° C. for 12 h to obtain a coated negative electrode material.

[0052] Example 3

[0053] A method for preparing a coated negative electrode material comprises the following steps:

[0054] Weigh 0.04 g of sodium alginate, put it into 50 mL of deionized water, and stir evenly to obtain solution A;

[0055] Weigh 3.88 g of natural graphite and slowly add it into solution A, stirring at 500 rpm to form a uniform suspension B;

[0056] Weigh 0.2626 g of aluminum nitrate nonahydrate, place it in 10 mL of deionized water and stir evenly, the corresponding concentration is 0.07 mol / L, then add it dropwise into suspension B to obtain a gel solution, and react at room temperature for 4 h;

[0057] The product obtained by the above reaction is filtered to obtain a filter cake D;

[0058] The filter cake D was dried in a vacuum oven at 80° C. for 12 h to obtain a coated negative electrode material.

[0059] Example 4

[0060] A method for preparing a coated negative electrode material comprises the following steps:

[0061] Weigh 0.12 g of sodium alginate, put it into 50 mL of deionized water, and stir evenly to obtain solution A;

[0062] Weigh 3.88 g of natural graphite and slowly add it into solution A, stirring at 500 rpm to form a uniform suspension B;

[0063] Weigh 0.375 g of aluminum nitrate nonahydrate, place it in 10 mL of deionized water and stir evenly, the corresponding concentration is 0.1 mol / L, then add it dropwise into suspension B to obtain a gel solution, and react at room temperature for 4 h;

[0064] The product obtained by the above reaction is filtered to obtain a filter cake D;

[0065] The filter cake D was dried in a vacuum oven at 80° C. for 12 h to obtain a coated negative electrode material.

[0066] Comparative Example 1

[0067] Comparative Example 1 is natural graphite without any other treatment.

[0068] Comparative Example 2

[0069] Compared with Example 1, the difference of Comparative Example 2 is that aluminum nitrate nonahydrate is not added, and the rest of the process is the same as that of Example 1.

[0070] Comparative Example 3

[0071] Compared with Example 1, the difference of Comparative Example 3 is that an equal amount of xanthan gum is used to replace the sodium alginate in Example 1, and the rest of the process is the same as Example 1.

[0072] Product effect testing

[0073] The coated negative electrode materials prepared in the above comparative examples and embodiments were used for the first coulombic efficiency and rate performance tests at different current densities.

[0074] The method for preparing solid-state batteries during the test is: grind the coated negative electrode material and the electrolyte LiP6S5Cl together, then add the binder PTFE (polytetrafluoroethylene), grind it evenly again, cut it into 8mm diameter discs, put it into a mold, add the electrolyte LiP6S5Cl, and the counter electrode is Li-In alloy. The whole is pressed at a pressure of 450MPa to obtain an electrode sheet. When assembling the button battery, stainless steel gaskets are added on both sides of the electrode sheet, and a nickel mesh shrapnel is added to one side for packaging to obtain a half-battery. The test pressure is 5MPa. The charge and discharge range is -0.61 to 1.5V, and the first cycle charge and discharge test is carried out at 0.1C. The test results are shown in Table 1.

[0075] Table 1

[0076]

[0077]

[0078] It can be seen from Table 1 that the first coulombic efficiencies corresponding to Examples 1-4 are significantly higher than those of Comparative Examples 1-3.

[0079] Figure 1 The first cycle charge and discharge curve of a half-cell assembled with the coated negative electrode material prepared in Example 1;

[0080] Figure 2 This is the first cycle charge and discharge curve of the half-cell assembled with the coated negative electrode material prepared in Comparative Example 1.

[0081] Depend on Figure 2It can be seen that the half-cell has a hump near 0.5V, where the voltage first decreases and then increases. This is because the exposed graphite contacts the electrolyte, causing the electrolyte to decompose, resulting in a capacity loss of 50mAh / g before lithium ion insertion, so the first coulombic efficiency is low. In addition, the boundaries between the second and third platforms formed by lithium ion insertion into graphite are blurred, which is unfavorable.

[0082] from Figure 1 It can be seen that the hump at 0.5V of the half-cell corresponding to Example 1 disappears, but a slight side reaction still occurs, and the irreversible loss is reduced to 34mAh / g. Therefore, the first coulombic efficiency is significantly improved to 94.37%, which is a significant improvement.

Claims

1. A coated negative electrode material, characterized in that: It comprises graphite and a coating layer coated on the surface of the graphite; The coating layer comprises alginate and metal salt.

2. The coated negative electrode material according to claim 1, characterized in that: The alginate includes sodium alginate or potassium alginate.

3. The coated negative electrode material according to claim 1, characterized in that: The metal salt includes aluminum salt, calcium salt, barium salt or zinc salt.

4. The coated negative electrode material according to claim 1, characterized in that: The aluminum salt, calcium salt, barium salt or zinc salt may be a nitrate or a chloride salt.

5. The coated negative electrode material according to claim 1, characterized in that: The graphite is one of natural graphite, mesophase carbon microspheres and composite graphite.

6. The coated negative electrode material according to claim 1, characterized in that: The graphite may be replaced by silicon or lithium titanate.

7. The method for preparing the coated negative electrode material according to any one of claims 1 to 6, characterized in that: The following steps are involved: Alginate is mixed with a solvent to form an alginate solution, and graphite is added to the mixture to obtain a suspension; a metal salt is added to the suspension to form a gel solution, and the solution is dried to obtain the coated negative electrode material.

8. The preparation method according to claim 7, characterized in that: The mass ratio of the alginate to the graphite is 0.1-10:100; and / or the mass ratio of the alginate to the metal salt is 0.12:(0.01-1).

9. The preparation method according to claim 7, characterized in that: Before adding, the metal salt is first dissolved in a solvent to obtain a metal salt solution, and the concentration of the metal salt solution is 0.05-0.1 mol / L.

10. A sulfide battery, characterized in that: The invention comprises the coated negative electrode material according to any one of claims 1 to 6.

Images