Core-shell structure silicon negative electrode material, preparation method and application

Abstract

The application relates to the technical field of lithium ion batteries, and discloses a core-shell structure silicon negative electrode material, a preparation method and application, which comprises a core, the material of the core is elemental silicon; and a shell, the shell is provided with a C-SiO x layer, a Ti n Si (1‑n) O x layer, a lithium titanium layer and a carbon layer from inside to outside. The application provides the silicon negative electrode material with the multilayer core-shell structure, the shell precursor is crosslinked and anchored on the surface of the elemental silicon in a sintering process. The core-shell structure is crosslinked and exists, and is not independent of each other, but is combined together through the valence bond action of Si-O, Si-C and Si-O-Ti. The ion conductivity can be improved, the volume expansion force of the silicon particles can be played a certain role, the generation of electrode cracks can be reduced, the consumption of electrolyte is reduced, and the cycle stability of the whole electrode is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a core-shell structure silicon negative electrode material, a preparation method and application thereof. BACKGROUND

[0002] The future development direction of global automobiles is new energy or electrification, which has become the consensus of countries and enterprises all over the world. With the rapid development of electronic products, large-scale energy storage and electric vehicles, the development of lithium ion batteries with high energy density, high power density, long cycle life and high safety has become a research hotspot in the field of energy storage, and the development of electrode materials with high capacity, high rate and high stability is an important way to achieve this goal.

[0003] Graphite, as a widely used negative electrode material for lithium ion batteries, has an actual specific capacity close to the theoretical specific capacity limit of 372 mAh / g, and has limited room for further improvement, which cannot meet the high energy density requirements of future power batteries. Therefore, it is urgent to study negative electrodes with high specific capacity (>1000 mAh / g), safety and excellent performance. At present, the industry generally believes that silicon-based negative electrode materials are the first choice to replace graphite negative electrode materials. This is mainly because silicon has a high specific capacity (theoretical specific capacity of 4200 mAh / g), which is about 10 times that of graphite negative electrode, and has a lower lithium extraction potential (about 0.4V), which avoids lithium dendrites caused by lithium deposition in the case of over-discharge, and has better safety performance than graphite negative electrode materials. However, Si negative electrode has poor cycle stability and first efficiency due to its large volume expansion effect (nearly 300%), low electrical conductivity, and continuous growth of SEI film on the electrode surface, which hinders its large-scale use in lithium ion batteries. SUMMARY

[0004] <Technical problems solved by the present application>

[0005] To solve the problems of cycle stability and volume expansion of silicon negative electrode in the prior art.

[0006] <Technical solutions adopted by the present application>

[0007] In view of the above technical problems, the present application aims to provide a core-shell structure silicon negative electrode material, a preparation method and application thereof.

[0008] The specific content is as follows:

[0009] Firstly, the present application provides a core-shell structure silicon negative electrode material, which comprises

[0010] The material of the inner core is elemental silicon;

[0011] The outer shell is provided with C-SiO xlayer, Ti n Si (1-n) O y layer, lithium titanium layer and carbon layer; C-SiO x layer, Ti n Si (1-n) O y layer, wherein 0.5≤n<1, 1

[0012] Secondly, the application provides a preparation method of the aforementioned core-shell structure silicon negative electrode material, comprising the following steps:

[0013] The precursor particles of the elemental silicon composite shell layer and the carbon source are sequentially subjected to high-speed dispersion, compounding, heat pretreatment and sintering to obtain; the sintering temperature is 700-1200℃, and the sintering time is 5-15℃; the sintering atmosphere is air, nitrogen, argon, nitrogen-hydrogen mixed gas or methane-nitrogen mixed gas.

[0014] Thirdly, the application provides an application of the aforementioned core-shell structure silicon negative electrode material in a lithium ion battery negative electrode.

[0015] <Advantages of the application>

[0016] The application provides a silicon negative electrode material with a multilayer core-shell structure, and the shell precursor is crosslinked and anchored to the surface of the elemental silicon in the post-treatment process. The core-shell structure is crosslinked and exists, and is not independent of each other, but is combined together through the valence bond action of Si-O, Si-C and Si-O-Ti. The ion conductivity can be improved, the volume expansion force of the silicon particles can be reduced, the generation of electrode cracks can be reduced, the consumption of electrolyte can be reduced, and the cycle stability of the entire electrode can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 SEM image of the composite material;

[0018] Figure 2 AC impedance diagram of the composite material;

[0019] Figure 3 Cycle performance test diagram (0.5 A g -1 ) of the composite material;

[0020] Figure 4 Cycle performance test diagram (1.0 A g -1 ) of the composite material. DETAILED DESCRIPTION

[0021] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. If specific conditions are not specified in the embodiments, the conventional conditions or the conditions suggested by the manufacturers are adopted. If the manufacturers of the reagents or instruments are not specified, the conventional products that can be purchased in the market are adopted.

[0022] <TECHNICAL SCHEME>

[0023] Firstly, the present application provides a core-shell structure silicon negative electrode material, comprising

[0024] an inner core, the material of the inner core is elemental silicon;

[0025] an outer shell, the outer shell is provided with a C-SiO x layer, a Ti n Si (1-n) O y layer, a lithium titanium layer and a carbon layer from inside to outside; the C-SiO x layer, wherein 1 < x < 2; the Ti n Si (1-n) O y layer, wherein 0.5 ≤ n < 1; 1 < y < 2;

[0026] Further, the lithium titanium layer is a lithium-containing titanate.

[0027] Further, the negative electrode material is formed by mixing elemental silicon and a precursor blend to form a precursor particle, and the precursor particle is sintered with a carbon source;

[0028] The precursor blend comprises organic silicon, lithium salt, organic titanium and solvent.

[0029] Further, the elemental silicon, the organic silicon and the lithium salt are dispersed in the solvent to obtain a dispersion A; the organic titanium is added to the dispersion A to obtain a dispersion B; and the dispersion B is dried to obtain the precursor particle.

[0030] In the dispersion, due to the existence of the active sites on the surface of silicon, the added organic silicon and organic titanium are condensed on the surface, thereby forming different layers. In the drying process, the lithium salt is precipitated and reacts with the titanium on the surface of the precursor particle, thereby forming a lithium-titanium layer. The sintering process is to complete the solidification. Under the action of thermodynamics, the elements between the layers will penetrate each other, thereby completing the gradient diffusion.

[0031] Further, the weight ratio of the elemental silicon, the organic silicon, the lithium salt and the organic titanium is 1:0.01-0.2:0.002-0.1:0.01-0.2.

[0032] Further, the particle size of the nanosilicon is in the range of 1-50 μm, and the silicon purity is >99 %.

[0033] Further, the organic silicon includes at least one of tetraethyl orthosilicate, methyltrimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, (methoxymethyl)trimethoxysilane, ethyltrimethoxysilane or ethyltriethoxysilane.

[0034] Further, the lithium salt includes at least one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate, lithium oxalate or lithium citrate.

[0035] Further, the organic titanium includes at least one of tetraethyl titanate, tetrabutyl titanate, isopropyl titanate, n-propyl titanate or octyl titanate.

[0036] The mass percentage of elemental silicon in the solvent is 5-30%.

[0037] Further, the solvent is ethanol, and the ethanol concentration is greater than 80%.

[0038] Further, the carbon source includes at least one of starch, glucose, sucrose, graphene, carbon nanotube, pitch, petroleum coke or paraffin wax.

[0039] In the present application, it is difficult to prepare true anhydrous ethanol due to the characteristics of the solvent itself. The presence of organic silicon and organic titanium consumes the water in ethanol during crosslinking and changes the surface state of nano-silicon particles, solving the problems of dispersion and grinding efficiency of silicon particles during grinding.

[0040] Further,

[0041] S1 disperses micron silicon particles, organic silicon and lithium salt in a solvent solution, uniformly disperses the mixed slurry in a reaction kettle, and then performs primary grinding to form dispersion liquid A;

[0042] S2 gradually adds organic titanium to the dispersion liquid A, performs secondary grinding after dispersion, and forms dispersion liquid B;

[0043] S3 sprays and dries the dispersion liquid B to obtain dry powder, and obtains precursor particles after sintering and mechanical shaping of the dry powder;

[0044] S4 performs high-temperature fusion of the precursor particles and the carbon source in a fusion machine, and obtains the finished product after secondary sintering of the product after fusion.

[0045] The foregoing grinding equipment is one of a ball mill, a vertical sand mill, a horizontal sand mill or a double-power sand mill; preferably a horizontal sand mill; and the grinding time is 2-8h.

[0046] The sintering equipment is one of a tube furnace, a muffle furnace, a bell jar furnace, a roller kiln, a chain furnace, a tube furnace or a box furnace; preferably a tube furnace.

[0047] The spraying adopts a closed spraying tower.

[0048] Secondly, the application provides a preparation method of the aforementioned core-shell structure silicon negative electrode material, comprising the following steps:

[0049] The elemental silicon and the precursor of the shell material are dispersed and then sintered to obtain; the sintering temperature is 700-1200℃, the sintering time is 5-15℃, and the sintering atmosphere is air, nitrogen, argon, nitrogen-hydrogen mixed gas (hydrogen content 0.2-1%) or methane-nitrogen mixed gas (hydrogen content 0.5-5%).

[0050] Thirdly, the application provides an application of the aforementioned core-shell structure silicon negative electrode material in a lithium ion battery negative electrode.

[0051] <EMBODIMENT>

[0052] Example 1

[0053] 20 g of micron silicon particles, 0.1 g of lithium hydroxide and 2 g of methyl triethoxysilane were weighed and dispersed in 500 ml of an ethanol solution with a purity of 99.9%, stirred and dispersed at 25℃ for 4 h. The dispersion mixture was prepared by grinding in a 500 ml ball mill jar for 6 h. Then 0.5 g of n-butyl titanate was added to the dispersion mixture, and the ball mill jar was continuously ground for 4 h. Spray drying was performed using a closed spray tower to obtain a mixed dry powder, which was placed in a tube furnace for high-temperature sintering. The sintering temperature was 900℃, the sintering atmosphere was nitrogen, and the sintering time was 10 h. The sintered product was taken out and fused with 2 g of USP low-temperature pitch, and then secondary sintering was performed in a tube furnace, with a sintering temperature of 500℃, a sintering atmosphere of nitrogen and a sintering time of 5 h. A composite material was obtained.

[0054] Example 2

[0055] 20 g of micron silicon particles, 0.1 g of lithium hydroxide and 2 g of methyl triethoxysilane were weighed and dispersed in 500 ml of an ethanol solution with a purity of 99.9%, stirred and dispersed at 25℃ for 4 h. The dispersion mixture was prepared by grinding in a 500 ml ball mill jar for 6 h. Then 0.5 g of n-butyl titanate was added to the dispersion mixture, and the ball mill jar was continuously ground for 4 h. Spray drying was performed using a closed spray tower to obtain a mixed dry powder, which was placed in a tube furnace for high-temperature sintering. The sintering temperature was 900℃, the sintering atmosphere was nitrogen, and the sintering time was 10 h. The sintered product was taken out and fused with 2 g of USP low-temperature pitch, and then secondary sintering was performed in a tube furnace, with a sintering temperature of 500℃, a sintering atmosphere of nitrogen and a sintering time of 5 h. A composite material was obtained.

[0056] <COMPARATIVE EXAMPLE>

[0057] Comparative Example 1

[0058] The difference between the present comparative example and Example 1 is that 20 g of micron silicon particles, 0.1 g of lithium hydroxide, 2 g of methyl triethoxysilane and 0.5 g of n-butyl titanate are dispersed in 500 ml of ethanol solution with a purity of 99.9% to obtain a mixed solution; the dispersion is subjected to grinding treatment; and then the mixed solution is subjected to spray drying treatment.

[0059] Comparative Example 2

[0060] The difference between the present comparative example and Example 1 is that the dispersion obtained without grinding is subjected to spray drying treatment.

[0061] <TEST EXAMPLE>

[0062] The composite material prepared in Example 1 is used as a sample for testing.

[0063] SEM

[0064] Figure 1 The SEM image of the composite material.

[0065] Figure 1 It is shown that the crosslinking of organosilicon and organotitanium is anchored on the silicon nanoparticles. Due to the crosslinking, the nanosilicon forms composite secondary agglomerates with micron and sub-micron sizes. The gaps between the agglomerates provide a buffer for the volume expansion of the silicon particles during the charging and discharging process, and the coating layer inhibits the mechanical fracture of the material, thereby improving the electrochemical performance of the composite material.

[0066] AC impedance

[0067] Figure 2 The AC impedance diagram of the composite material.

[0068] The AC impedance test is an effective means for characterizing the properties of chemical modification and understanding the rate of chemical reaction. In the present test, the electrochemical AC impedance test system contained in the Autolab electrochemical workstation is used, 5 mV AC voltage amplitude is selected, and the test frequency range is 20 mHz~100 KHz. Before testing, the battery is in a delithiated state, i.e. the voltage = 2.5 V. The open circuit voltage of the same batch of batteries is kept approximately.

[0069] Figure 2 It is shown that the electrochemical impedance value of the pure silicon electrode is significantly higher than that of the modified silicon-carbon composite negative electrode material prepared after multiple cycles, indicating that the modified material has good electrical conductivity.

[0070] The composite materials prepared in Example 1 and Comparative Examples 1-2 are used as samples for testing.

[0071] Cycle performance test

[0072] According to different systems, the present test adopts a multi-channel battery test system to perform constant current charge-discharge test on button type simulation batteries at a set current density. The NEWARE 4000 (Shenzhen, China) is used to test the charge-discharge performance and long cycle performance at different rates at room temperature, wherein the charge-discharge voltage interval is 0.01-2.5 V, and the current density 1 C = 4200 mA / g.

[0073] The results are shown in Table 1.

[0074] Table 1. Cycle performance test table

[0075]

[0076] Figure 3 The cycle performance test graph of the composite material prepared for Example 1 (0.5 A g -1 ).

[0077] Figure 4 The cycle performance test graph of the composite material prepared for Example 1 (1.0 A g -1 ).

[0078] The results show that the material has a high reversible specific capacity and good cycle stability, and has a specific capacity of nearly 830 mAh / g after 300 cycles at a large current density of 1 A / g.

[0079] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A core-shell structured silicon anode material, characterized in that, include The core is made of elemental silicon. The outer casing, from the inside out, is provided with C-SiO₂. x Layer, Ti n Si (1-n) O y Layer, lithium titanium layer and carbon layer; C-SiO x Layer, where 1 < x < 2; Ti n Si (1-n) O y Layer, where 0.5 ≤ n < 1; 1＜y＜2； The negative electrode material is obtained by sintering precursor particles formed from a blend of elemental silicon and a precursor with a carbon source. Precursor blends include organosilicon, lithium salts, organotitanium, and solvents; Elemental silicon, organosilicon, and lithium salt are dispersed in a solvent and ground to obtain dispersion A. Organotitanium is added to dispersion A to obtain dispersion B. Dispersion B is ground and dried to obtain precursor particles.

2. The core-shell structured silicon anode material according to claim 1, characterized in that, The weight ratio of elemental silicon, organosilicon, lithium salt, and organotitanium is 1:0.01~0.2:0.002~0.1:0.01~0.

2.

3. The core-shell structured silicon anode material according to any one of claims 1 to 2, characterized in that, Organosilicones include at least one of tetraethyl orthosilicate, methyltrimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, (methoxymethyl)trimethoxysilane, ethyltrimethoxysilane, or ethyltriethoxysilane.

4. The core-shell structured silicon anode material according to any one of claims 1 to 2, characterized in that, Lithium salts include at least one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate, lithium oxalate, and lithium citrate.

5. The core-shell structured silicon anode material according to any one of claims 1 to 2, characterized in that, Organic titanium includes at least one of tetraethyl titanate, tetrabutyl titanate, isopropyl titanate, n-propyl titanate, and octyl titanate.

6. The core-shell structured silicon anode material according to claim 1, characterized in that, Carbon sources include at least one of starch, glucose, sucrose, graphene, carbon nanotubes, pitch, petroleum coke, or paraffin.

7. A method for preparing a core-shell structured silicon anode material as described in any one of claims 1 to 6, characterized in that, Includes the following steps: The precursor materials of elemental silicon and shell material are dispersed and then sintered; the sintering temperature is 700~1200℃, the sintering time is 5~15℃; the sintering atmosphere is air, nitrogen, argon, nitrogen-hydrogen mixture or methane-nitrogen mixture.

8. The application of a core-shell structured silicon anode material as described in any one of claims 1 to 6, or a core-shell structured silicon anode material obtained by the preparation method described in claim 7, in a lithium-ion battery anode.

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