CN118136794A - Lithium negative electrode material and preparation method thereof, negative electrode and lithium battery - Google Patents

Abstract

The application relates to the technical field of battery materials, and discloses a lithium anode material, a preparation method thereof, an anode and a lithium battery. A lithium negative electrode material is disclosed, comprising a porous lithium matrix and a protective layer of lithium compound bonded to the walls of the pores of the porous lithium matrix. The preparation method of the disclosed lithium anode material comprises the following steps: heating by taking a lithium composite material as a heating object, wherein the lithium composite material is a material in which a decomposition matrix is distributed in a lithium matrix; the lithium composite material is heated to decompose the decomposition matrix therein into a gas, and at least a portion of the generated gas reacts with the lithium matrix to produce a lithium compound. The disclosed negative electrode is prepared from the lithium negative electrode material. The disclosed lithium battery comprises the negative electrode. Compared with the common metal lithium material, the lithium anode material provided by the application has more excellent electrochemical performance.

Description

Lithium negative electrode material and preparation method thereof, negative electrode and lithium battery

Technical Field

The present application relates to the technical field of battery materials, and in particular to lithium negative electrode materials and preparation methods thereof, negative electrodes and lithium batteries.

Background technique

Lithium metal faces the following challenges as the negative electrode of lithium-ion batteries: (i) Lithium dendrites are formed during operation, resulting in dead lithium or battery short circuit. (ii) Excessive solid electrolyte interface (SEI) film is produced, which consumes lithium. (iii) Large volume changes occur during the cycle. These phenomena lead to a short cycle life of lithium metal anodes and safety and other issues. The above challenges still need to be overcome to apply them to reliable commercial lithium-ion batteries.

In order to solve the above-mentioned defects, various Li metal anode interface protection and structural design modification schemes have been proposed. Unlike the graphite anode that has been successfully commercialized, the Li metal anode has no internal skeleton support during the charge and discharge process. Therefore, the traditional Li metal anode interface protection schemes, such as the design and development of electrolyte additives, in-situ modification of natural SEI films, and functional construction of artificial interface layers, cannot fundamentally solve the huge volume strain of the Li metal anode and its battery failure.

In view of this, this application is hereby filed.

Summary of the invention

The purpose of the present application is to provide a lithium negative electrode material and a preparation method thereof, a negative electrode and a lithium battery.

This application is implemented as follows:

In a first aspect, the present application provides a lithium negative electrode material, comprising a porous lithium matrix and a lithium compound protective layer,

The porous lithium matrix comprises a pore structure;

The lithium compound protective layer is bonded to the pore walls of the pore structure of the porous lithium matrix.

In an optional embodiment, the lithium compound protective layer is lithium nitride;

Optionally, the lithium compound protective layer is obtained by in-situ reaction of nitrogen with lithium on the pore walls of the porous lithium matrix;

Optionally, the thickness of the lithium compound protective layer is 5 nm to 100 nm, preferably 20 to 30 nm;

Optionally, the pores of the porous lithium matrix have a pore size of 20 to 100 μm, preferably 70 to 80 μm;

Optionally, the porosity of the porous lithium matrix is 20% to 60%, preferably 30% to 50%.

In a second aspect, the present application provides a method for preparing a lithium negative electrode material, comprising:

A lithium composite material is used as a heating object for heating, wherein the lithium composite material is a material in which a decomposition matrix is distributed in a lithium matrix;

The lithium composite material is heated to decompose the decomposition matrix therein into gas, and at least a part of the generated gas reacts with the lithium matrix to generate lithium compounds.

In an optional embodiment, the decomposition substrate is azodicarbonamide particles, the lithium compound is lithium nitride, and the heating temperature is 190-250°C;

Optionally, the heating method is:

The first stage is heating: the lithium composite material is heated at 190-210°C to decompose the azodicarbonamide particles into urea and gases including nitrogen;

Second stage heating: After the first stage heating is completed, the temperature is raised to 230-250°C to decompose urea into gas;

Optionally, the heating time of the first heating stage is 40 to 80 minutes;

Optionally, the heating time of the second heating stage is 20 to 40 minutes.

In an optional embodiment, the azodicarbonamide particles are uniformly distributed in the lithium composite material;

Optionally, the mass ratio of the azodicarbonamide particles to the lithium matrix is 0.1 to 5:50; preferably, the mass ratio of the azodicarbonamide particles to the lithium matrix is 2 to 4:50.

In an optional embodiment, the particle size of the azodicarbonamide particles is 5 to 8 μm.

In an optional embodiment, the method for preparing the lithium composite material comprises:

Dispersing azodicarbonamide in a solvent to prepare a slurry;

The slurry is coated on the surface of the lithium foil, and then the solvent of the slurry is volatilized, and then the lithium foil is folded at least once and rolled after folding; after rolling, it is folded at least once again and rolled after folding, and this cycle is repeated at least once to obtain a lithium composite material.

In an optional embodiment, the thickness of the lithium foil is 12 to 14 μm;

Optionally, the solvent is 1,2-dimethoxyethane or dimethyl ether;

The method of dispersing azodicarbonamide in a solvent includes: mixing azodicarbonamide with the solvent and then performing ultrasonic dispersion.

In a third aspect, the present application provides a negative electrode, which is made of the lithium negative electrode material as described in the aforementioned embodiment, or the lithium negative electrode material prepared by the preparation method of any one of the aforementioned embodiments.

In a fourth aspect, the present application provides a lithium battery, comprising a negative electrode as described in the aforementioned embodiment.

This application has the following beneficial effects:

The lithium negative electrode material provided in the embodiment of the present application includes a porous lithium matrix and a lithium compound protective layer bonded to the pore wall of the porous lithium matrix. The pores of the porous lithium matrix can provide deposition space for the deposited lithium and reduce the volume change during the charge and discharge cycle; since lithium nitride has ultra-high room temperature ionic conductivity (6× ^10-3 S/cm) and very low lithium ion diffusion energy barrier (0.007eV～0.038eV), the lithium compound protective layer on the pore wall can effectively inhibit the growth and side reactions of lithium dendrites. Compared with pure lithium metal negative electrode, the lithium negative electrode material provided in the embodiment of the present application has better cycle stability.

The preparation method of the lithium negative electrode material provided in the embodiment of the present application is to heat the decomposition matrix to decompose it into gas, and the gas overflows to form a pore structure, and the generated part of the gas reacts with the lithium matrix to form a lithium compound protective layer on the pore wall. Therefore, the preparation method provided in the embodiment of the present application can prepare the lithium negative electrode material provided in the embodiment of the present application.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

FIG1 is a schematic cross-sectional view of a lithium negative electrode material provided in an embodiment of the present application;

FIG2 is a SEM image of the lithium negative electrode material prepared in Example 1 of the present application;

FIG3 is a Raman spectrum of the porous material obtained in Example 1;

FIG4 is a graph showing the first charge and discharge curves of the half-cells prepared in Example 1 and the comparative example;

FIG5 is a cycle performance curve diagram of the half-cells prepared in Example 1 and the comparative example.

Detailed ways

In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

Based on the series of problems existing in the prior art mentioned in the background technology, the inventors have made the following considerations:

The construction of a Li metal composite negative electrode with a three-dimensional skeleton structure, that is, the composite of Li metal and a three-dimensional supporting skeleton material, can effectively buffer the huge volume strain of the Li metal negative electrode and is a solution with great application prospects. First, the three-dimensional porous skeleton material has a high specific surface area, which can reduce the local current density and delay the initial formation time of lithium dendrites. Secondly, the three-dimensional porous structure of the supporting skeleton material can accommodate the huge volume strain of the Li metal negative electrode, thereby improving the structural stability of the Li metal negative electrode. Foam metals (such as copper foam, nickel foam) and three-dimensional carbonaceous current collectors (such as graphene film, carbon nanotube film, carbon fiber cloth) can be used as three-dimensional supporting skeleton materials to improve the performance of Li metal negative electrodes. However, most commercially available foam metals or three-dimensional carbonaceous skeleton material interfaces are almost lithium-phobic, which makes the nucleation potential and electrodeposition resistance of Li metal on the skeleton surface large, resulting in uneven deposition of Li metal, and the problem of long-term cycle Li metal dendrite growth still exists. In addition, the introduction of three-dimensional skeleton materials will inevitably reduce the overall gram capacity and energy density of the Li metal anode, and will also increase the synthesis steps and production cost of the three-dimensional skeleton structured Li metal anode. Therefore, it is necessary to prepare a highly conductive, stable and lightweight three-dimensional skeleton material to ensure the high capacity of the Li metal anode while improving its cycle stability.

The features and performance of the present application are further described in detail below in conjunction with the embodiments.

As shown in FIG. 1 , a lithium negative electrode material provided in an embodiment of the present application includes a porous lithium matrix and a lithium compound protective layer bonded to the pore walls of the pore structure of the porous lithium matrix.

The pores of the porous lithium matrix can provide deposition space for the deposited lithium and reduce the volume change during the charge and discharge cycle; due to the ultra-high room temperature ionic conductivity of lithium nitride (the room temperature ionic conductivity is 6× ^10-3 S/cm) and the very low lithium ion diffusion barrier (the lithium ion diffusion barrier is 0.007eV to 0.038eV), the lithium compound protective layer on the pore wall can effectively inhibit the growth and side reactions of lithium dendrites. Compared with pure lithium metal negative electrode, the lithium negative electrode material provided in the embodiment of the present application has better cycle stability.

In some optional embodiments of the present application, the lithium compound protective layer is lithium nitride.

Optionally, the lithium compound protection layer is obtained by an in-situ reaction between nitrogen and lithium on the pore walls of the porous lithium matrix.

The lithium that reacts with the nitrogen is provided by the lithium matrix, and the nitrogen can generate a dense and uniform lithium compound protective layer by reacting with the lithium in situ.

To ensure that the lithium negative electrode material has better electrochemical performance, in some optional embodiments of the present application, the pore size of the pores of the lithium porous lithium matrix is 20-100 μm, preferably 70-80 μm; the porosity of the porous lithium matrix is 20%-60%. Since the porosity is greater than 50%, the pores are too large and the structure is relatively fluffy, which is not conducive to the structural stability of the negative electrode material during the cycle, and the porosity is less than 30% is not conducive to the electrolyte infiltration. Therefore, the porosity is preferably 30%-50%.

The present invention provides a method for preparing a lithium negative electrode material, comprising:

Lithium composite materials are materials with a decomposition matrix distributed in a lithium matrix;

The lithium composite material is heated to decompose the decomposition matrix therein into gas, and at least a part of the generated gas reacts with the lithium matrix to generate lithium compounds.

The preparation method provided in the embodiment of the present application heats the decomposition matrix to decompose it into gas, and the gas overflows to form a pore structure, and part of the generated gas reacts with the lithium matrix to form a lithium compound protective layer on the pore wall. Therefore, the preparation method provided in the embodiment of the present application can produce the lithium negative electrode material provided in the embodiment of the present application.

Optionally, the decomposition matrix is azodicarbonamide particles, the lithium compound is lithium nitride, and the heating temperature is 190-250° C. (eg, 190° C., 200° C., 210° C., 230° C., 240° C., or 250° C.).

When heated at the above temperature, azodicarbonamide particles can decompose to generate gas, thereby forming a pore structure in the lithium composite material. After the azodicarbonamide particles are decomposed, nitrogen is generated. Within the above temperature range, the nitrogen can react with the lithium matrix to produce a lithium nitride protective layer on the pore wall.

Specifically, the heating method is:

The first stage is heating: heating the lithium composite material at 190 to 210° C. (e.g., 190° C., 200° C., or 210° C.) to decompose the azodicarbonamide particles into urea and gases including nitrogen;

Second stage heating: After the first stage heating is completed, the temperature is raised to 230-250°C (eg, 230°C, 240°C or 250°C) to decompose the urea into gas.

In the first stage of the heating process, the azodicarbonamide particles are heated at 190-210° _C to decompose into ( _H2NCONH2 ), nitrogen ( _N2 ) and carbon monoxide (CO). The decomposition of the azodicarbonamide particles will foam the lithium composite material, forming pores in the lithium composite material, and the generated nitrogen will react with lithium to generate lithium nitride in situ; in the second stage of the heating process, at 230-250°C, the non-gaseous urea is fully decomposed into hydrocyanic acid (HNCO) and ammonia ( _NH3 ), and the decomposed hydrocyanic acid and nitrogen will be discharged after breaking through the pore wall along with a part of the nitrogen that does not participate in the reaction, and finally a Li porous skeleton with pore channel connection decorated with lithium nitride interface can be obtained.

Preferably, the azodicarbonamide particles are evenly distributed in the lithium matrix. The porous structure can adapt to the volume fluctuation of the deposited lithium. The dense lithium nitride protective layer can inhibit the deposition of lithium dendrites and side reactions. When the azodicarbonamide particles are evenly distributed, the pores of the obtained lithium negative electrode material are evenly distributed, so that each area of the material has a more balanced effect on inhibiting the deposition of lithium dendrites and inhibiting side reactions.

Optionally, to ensure that a lithium negative electrode material with good electrochemical properties can be obtained, the mass ratio of azodicarbonamide particles to lithium matrix is 0.1 to 5:50 (eg, 0.1:50, 0.5:50, 1:50, 3:50 or 5:50), preferably 2 to 4:50, more preferably 3:50.

Optionally, to ensure that a lithium negative electrode material with a suitable pore size can be obtained, the particle size of the azodicarbonamide particles is 5 to 10 μm.

The preparation method of the lithium negative electrode material provided in the embodiment of the present application is specifically as follows:

S1. Preparation of azodicarbonamide slurry

First, a required amount of azodicarbonamide is weighed and placed in a planetary ball mill and mixed with deionized water for ball milling, and then filtered and dried at 100° C. to obtain azodicarbonamide fine powder with a particle size of 2 to 6 μm;

The fine powder of azodicarbonamide is mixed with a solvent and dispersed evenly in ultrasound to obtain a slurry.

Optionally, the solvent is ethylene glycol dimethyl ether or dimethyl sulfoxide.

S2. Preparation of lithium composite materials

The slurry is evenly coated on the surface of the lithium foil to volatilize the solvent in the slurry, and then the lithium foil is folded at least once and rolled after folding; after rolling, it is folded at least once again and rolled after folding, and this cycle is repeated at least once to obtain a lithium composite material.

Optionally, the thickness of the lithium foil is 40-60 μm (eg, 40 μm, 50 μm, or 60 μm). The lithium foil within this thickness range has sufficient physical strength to prevent it from breaking, and is not too thick to cause poor pore distribution.

It should be noted that the method provided in S1 to S2 above is one of the methods for preparing lithium composite materials. In some embodiments, lithium powder and azodicarbonamide powder may be mixed evenly and then pressed into a lithium composite material of a preset size or shape.

S3, heating to generate pores

The first step of heating is to place the composite material in a heating furnace, heat it at 190-210° C., and keep it warm for 40-80 minutes (e.g., 40 minutes, 60 minutes, or 80 minutes) to fully decompose azodicarbonamide into urea, nitrogen, and carbon monoxide.

The second step is heating: after heating at the above temperature, the temperature is further raised to 230-250° C. and kept warm for 25-35 minutes (eg, 25 minutes, 30 minutes or 35 minutes) to fully decompose the urea into hydrocyanic acid (HNCO) and ammonia (NH ₃ ).

After the second step of heating, cool down to room temperature.

A negative electrode provided in an embodiment of the present application is made using the lithium negative electrode material provided in an embodiment of the present application, or a lithium negative electrode material prepared by the provided preparation method.

A lithium battery provided in an embodiment of the present application includes the negative electrode provided in an embodiment of the present application.

Example 1

5 g of azodicarbonamide was placed in a planetary ball mill with 100 g of deionized water and ball-milled for 8 hours. The solid was filtered and baked in an oven at 100° C. for 24 hours to remove moisture and obtain azodicarbonamide fine powder.

Take 30 mg of ball-milled azodicarbonamide and ultrasonically disperse it in 6 mL of ethylene glycol dimethyl ether (1,2-Dimethoxyethane, DME) for 4 hours to obtain a DME dispersion of azodicarbonamide, and then evenly coat the DME dispersion of azodicarbonamide on the surface of a lithium foil with a thickness of 50 μm and a mass of 500 mg. When the dimethyl ether is completely evaporated, the lithium foil is folded three times in a row and then rolled to a thickness of 50 μm. Repeat the above operation many times to finally obtain a lithium composite material with a uniform distribution of azodicarbonamide particles with a thickness of 13 μm for subsequent use. Cut the lithium composite material into small discs of the size used for assembling buckle batteries.

The first stage of heating: the lithium composite material disc is placed in a furnace and heated to 200°C at a heating rate of 3°C/min and kept at this temperature for 60 minutes. In this stage, azodicarbonamide is mainly decomposed into urea (H ₂ NCONH ₂ ), nitrogen (N ₂ ) and carbon monoxide (CO).

Second stage heating: The small disc is then heated to 240°C at a heating rate of 6°C/min and kept at this temperature for 30 min. In this stage, urea is mainly decomposed into hydrocyanic acid (HNCO) and ammonia (NH ₃ ).

Cooling: cooling to room temperature at a cooling rate of 3°C/min to obtain a lithium negative electrode material.

The SEM image of the lithium negative electrode material prepared in Example 1 is shown in Figure 2. The thickness of the lithium nitride protective layer is 20 to 30 nm;

The lithium negative electrode material prepared in Example 1 was subjected to Raman spectroscopy test, and the test result is shown in FIG3 , which indicates that lithium nitride exists in the prepared lithium negative electrode material.

Example 2

This example is basically the same as Example 1, except that 50 mg of ball-milled small-particle azodicarbonamide is ultrasonically dispersed in 6 mL of 1,2-dimethoxyethane (DME) to obtain a DME dispersion of azodicarbonamide.

Example 3

This example is basically the same as Example 1, except that 1 mg of ball-milled small-particle azodicarbonamide is ultrasonically dispersed in 6 mL of 1,2-dimethoxyethane (DME) to obtain a DME dispersion of azodicarbonamide.

Example 4

This embodiment is basically the same as Embodiment 1, except that: there is no first-stage heating step, and the second-stage heating is directly performed, and the second-stage heating time is 90 minutes.

Example 5

This comparative example is basically the same as Example 2, except that 100 mg of ball-milled small-particle azodicarbonamide is ultrasonically dispersed in 6 mL of 1,2-dimethoxyethane (DME) to obtain a DME dispersion of azodicarbonamide.

Comparative Example

A lithium negative electrode material having the same volume and shape as that of Example 1 without any treatment.

Experimental example

Button preparation and testing:

The lithium negative electrode material provided in each embodiment and comparative example is used as the negative electrode;

Commercial LiFePO4 was used as the positive electrode, and the positive electrode formula was 95.5% active material (i.e. LiFePO ₄ ), 2% SP (Super P Conductive Carbon Black) and 2.5% PVDF (polyvinylidene difluoride). After adding NMP (N-methylpyrrolidone, chemical formula C ₅ H ₉ NO), it was stirred for 12 hours. The positive electrode slurry was coated on carbon-coated aluminum foil with a coating surface density of 14 mg/cm ² to obtain the positive electrode;

After vacuum drying at 80°C for 12 h, the electrolyte used was a DMC-EC mixed solvent containing 1.0 M LiPF ₆ and 5% FEC, and a LiFePO ₄ || Li button half-cell was assembled.

The button half-cell was first charged and discharged for 5 times at a current density of 0.1C (1C = 170 mA/g), and then charged and discharged at a constant current density. The charge and discharge cut-off voltage of the cycle test was set to 2.0-3.8V to test its electrochemical performance.

Discussion and Analysis:

The test results are shown in Figures 4 and 5 and Tables 1 and 2:

Table 1 Half-cell impedance fitting results

sample Rs(Ω) Rct(Ω) DLi ⁺ (cm ² /s) Example 1 2.9 12 1.82*10 ^-11 Example 2 2.7 8 1.02*10 ^-11 Example 3 2.7 25 3.28*10 ^-12 Example 4 2.8 twenty two 3.56*10 ^-12 Example 5 2.6 15 1.67*10 ^-12 Comparative Example 2.6 33 5.23*10 ^-12

Note: In Table 1, Rs: ohmic resistance of electrolyte; Rct: charge transfer resistance; DLi ⁺ , Li ⁺ diffusion coefficient value.

Table 2 Rate performance of half cells prepared in various embodiments and comparative examples

Table 3 Half-cell cycle capacity retention rate obtained in each embodiment and comparative example

Tables 1 and 2 show that the Li ⁺ diffusion coefficient value (DLi ⁺ ) and gram capacity of the _LiFePO4 ||Li porous button half-cell (Example 1) are significantly higher than those of the half-cell with pure metal Li negative electrode (Comparative Example). The _LiFePO4 ||Li porous button half-cell has a faster electrochemical reaction kinetic rate, which is due to the excellent conductivity of the porous lithium skeleton and the stable electrode/electrolyte interface ( _Li3N effectively inhibits side reactions). Comparing Example 5 with Example 2, the lithium ion diffusion coefficient and gram capacity of Example 5 are lower, and the amount of azodicarbonamide used in Example 5 is relatively large, indicating that the amount of azodicarbonamide used in the preparation should not be too much, which exceeds the preferred range required by the present application (mass ratio of azodicarbonamide particles to lithium matrix 0.1 to 5:50). The excessively thick _Li3N coating layer formed will also affect the lithium ion migration rate, thereby affecting the gram capacity of the battery. Comparing Example 4 with Example 1, Example 4 has a lower lithium ion diffusion coefficient and a lower gram capacity, indicating that directly heating to a higher temperature may cause incomplete decomposition of azodimethylamide, resulting in incomplete coverage of Li ₃ N on the pore wall, making it difficult to achieve the best effect.

The rate performance test results in Table 2 show that when the current density increases continuously to 1C, 2C and 5C, the discharge capacity of the LiFePO ₄ || Li porous button half cell (Example 1) is significantly higher than that of the LiFePO ₄ || Li button half cell (Comparative Example), showing good rate performance.

As can be seen from FIG4 , during 0.1C constant current charge and discharge, the charge and discharge curve of the LiFePO4||Li porous button half-cell (Example 1) has a very flat charge and discharge voltage platform at about 3.4V, which is completely consistent with the charge and discharge curve of the _LiFePO4 ||Li button half-cell (Comparative Example). The first discharge capacities of _{the LiFePO4} ||Li porous button half-cell and the LiFePO4||Li button half-cell at 0.1C are not much different, which are 156.0 and 155.8 mAh·g ^-1 respectively. At 0.5C, the discharge capacities of the _LiFePO4 ||Li porous button half-cell and the _LiFePO4 ||Li button half-cell are 147 mAh·g ^-1 and 138.7 mAh·g ^-1 respectively.

The cycle stability test results in Table 3 and Figure 5 show that the LiFePO ₄ || Li foam button half-cell (Example 1) exhibits better long-term cycle stability than the LiFePO ₄ || Li button half-cell (Comparative Example). After 300 charge and discharge cycles at 0.5C, the capacity retention rate of the LiFePO ₄ || Li foam button half-cell is 73.6%, which is higher than the 55.9% of the LiFePO ₄ || Li button half-cell, showing good cycle performance. Comparing Example 4 with Example 1, the capacity retention rate of Example 4 is poor, indicating that direct heating to a higher temperature may cause incomplete decomposition of azodimethylamide, resulting in incomplete coverage of Li ₃ N on the pore wall, making it difficult to achieve a better effect of improving the capacity retention rate. Comparing Example 5 with Example 2, the capacity retention rate of Example 5 is poor, which may be because the formed lithium nitride protective layer is thicker, resulting in poor electrolyte infiltration and large internal resistance, resulting in poor cycle performance.

In summary, the lithium negative electrode material provided in the embodiment of the present application includes a porous lithium matrix and a lithium compound protective layer bonded to the pore wall of the porous lithium matrix. The pores of the porous lithium matrix can provide deposition space for the deposited lithium and reduce the volume change during the charge and discharge cycle; due to the ultra-high room temperature ionic conductivity of lithium nitride (6× ^10-3 S/cm) and the very low lithium ion diffusion energy barrier (0.007~0.038eV), the lithium compound protective layer on the pore wall can effectively inhibit the growth and side reactions of lithium branched crystals. Compared with pure lithium metal negative electrode, the lithium negative electrode material provided in the embodiment of the present application has better cycle stability.

The preparation method of the lithium negative electrode material provided in the embodiment of the present application is to heat the decomposition matrix to decompose it into gas, and the gas overflows to form a pore structure, and the generated part of the gas reacts with the lithium matrix to form a lithium compound protective layer on the pore wall. Therefore, the preparation method provided in the embodiment of the present application can prepare the lithium negative electrode material provided in the embodiment of the present application.

The above are only preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims (10)

1. A lithium negative electrode material, characterized in that it comprises a porous lithium matrix and a lithium compound protective layer, The porous lithium matrix comprises a pore structure; The lithium compound protection layer is bonded to the pore walls of the pore structure of the porous lithium matrix. 2. The lithium negative electrode material according to claim 1, characterized in that the lithium compound protective layer is lithium nitride; Optionally, the lithium compound protective layer is obtained by in-situ reaction of nitrogen with lithium on the pore walls of the porous lithium matrix; Optionally, the thickness of the lithium compound protective layer is 5 nm to 100 nm, preferably 20 to 30 nm; Optionally, the pores of the porous lithium matrix have a pore size of 20 to 100 μm, preferably 70 to 80 μm; Optionally, the porosity of the porous lithium matrix is 20% to 60%, preferably 30% to 50%. 3. A method for preparing a lithium negative electrode material, characterized by comprising: A lithium composite material is used as a heating object for heating, wherein the lithium composite material is a material in which a decomposition matrix is distributed in a lithium matrix; The lithium composite material is heated to decompose the decomposition matrix therein into gas, and at least a part of the generated gas reacts with the lithium matrix to generate a lithium compound. 4. The preparation method according to claim 3, characterized in that the decomposition matrix is azodicarbonamide particles, the lithium compound is lithium nitride, and the heating temperature is 190-250°C; Optionally, the heating method is: The first stage of heating: heating the lithium composite material at 190-210° C. to decompose the azodicarbonamide particles into urea and gases including nitrogen; The second stage of heating: after the first stage of heating is completed, the temperature is raised to 230-250° C. to decompose the urea into gas; Optionally, the heating time of the first heating stage is 40 to 80 minutes; Optionally, the heating time of the second heating stage is 20 to 40 minutes. 5. The preparation method according to claim 4, characterized in that the azodicarbonamide particles are uniformly distributed in the lithium composite material; Optionally, the mass ratio of the azodicarbonamide particles to the lithium matrix is 0.1 to 5:50; preferably, the mass ratio of the azodicarbonamide particles to the lithium matrix is 2 to 4:50. 6 . The preparation method according to claim 4 , characterized in that the particle size of the azodicarbonamide particles is 5 to 8 μm. 7. The preparation method according to claim 4, characterized in that the preparation method of the lithium composite material comprises: Dispersing azodicarbonamide in a solvent to prepare a slurry; The slurry is coated on the surface of a lithium foil, and then the solvent of the slurry is volatilized, and then the lithium foil is folded at least once, and then rolled; after rolling, it is folded at least once again, and then rolled, and this cycle is repeated at least once to obtain the lithium composite material. 8. The preparation method according to claim 7, characterized in that the thickness of the lithium foil is 12 to 14 μm; Optionally, the solvent is 1,2-dimethoxyethane or dimethyl ether; The method of dispersing azodicarbonamide in a solvent includes: mixing azodicarbonamide with the solvent and then performing ultrasonic dispersion. 9. A negative electrode, characterized in that it is made of the lithium negative electrode material as described in claim 1 or 2, or the lithium negative electrode material prepared by the preparation method as described in any one of claims 3 to 8. 10. A lithium battery, comprising the negative electrode as claimed in claim 9.