Silicon negative electrode material with high-temperature storage performance and preparation method thereof

Abstract

The invention belongs to the field of lithium ion battery negative electrodes, and discloses a silicon negative electrode material with high-temperature storage performance, which comprises silicon monoxide particles, the surfaces of the silicon monoxide particles are coated with silicon nitride and carbon composite layers, and the high-temperature storage performance of the silicon negative electrode material can be obviously improved. The invention also discloses a preparation method of the silicon negative electrode material with the high-temperature storage performance, which comprises the following steps: adding silicon monoxide particles into a closed reaction container, and heating to a preset temperature in a nitrogen protective atmosphere; and introducing a mixed gas of an organic gas, gaseous silicon tetrachloride and nitrogen into the closed reaction container, and carrying out a reaction until a silicon nitride composite carbon layer is formed on the surface of the silicon monoxide particles, thereby obtaining the silicon negative electrode material with the high-temperature storage performance. The method is simple to operate, CVD equipment of an original process can be continuously used, and the high-temperature storage performance of the battery is improved by introducing gaseous SiCl4 and simultaneously forming a silicon nitride composite carbon layer on the surface of a silicon negative electrode material.

Description

Technical Field

[0001] The present invention belongs to the field of lithium ion battery negative electrodes, and in particular relates to a silicon negative electrode material with high temperature storage performance and a preparation method thereof. Background Art

[0002] Recently, with the development of electronic portable devices and electric vehicles, higher requirements have been put forward for the volume, weight, capacity and economy of batteries, so there is an urgent need for high energy density batteries. At present, the way to improve the energy density of batteries is to use silicon oxide as the negative electrode material, and its theoretical capacity reaches 2100mAh / g, which is much higher than the current commercial high-end graphite negative electrode capacity, and has become one of the most promising battery negative electrode materials.

[0003] The existing silicon negative electrode material coating mainly adopts CVD gas phase coating. Under the CVD high temperature process conditions, methane, ethylene, acetylene and other gaseous alkanes, alkenes, alkynes, etc. are used as organic gas sources. After the organic gas decomposes, carbon molecules, hydrogen, intermediate organic decomposition, etc. are generated. The carbon molecules are attached to the surface of the silicon material particles to form a simple coated carbon layer, thereby reducing the occurrence of side reactions between the silicon material and the electrolyte. This type of silicon negative electrode precursor material that has been developed on the market has a high gram capacity of 1300-2000mAh / g, but after being used to make batteries with graphite, the high temperature storage performance is poor. Therefore, how to improve the high temperature storage performance of silicon negative electrode material batteries is a technical problem that needs to be solved urgently in this field. Summary of the invention The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology, improve the high temperature storage performance of silicon negative electrode materials prepared by the original process, and provide a silicon negative electrode material with high temperature storage performance and a preparation method thereof.

[0004] In order to solve the above technical problems, the technical solution proposed by the present invention is: A silicon negative electrode material with high-temperature storage performance comprises silicon oxide particles, the surfaces of which are coated with a composite layer of silicon nitride and carbon.

[0005] The above-mentioned silicon negative electrode material with high temperature storage performance, preferably, in the said silicon negative electrode material with high temperature storage performance, the mass percentage of carbon is 0.1-0.5%, and the mass percentage of nitrogen is 1.5-5%.

[0006] Preferably, the thickness of the composite layer of silicon nitride and carbon is 10-30 nm.

[0007] Based on a general inventive concept, the present invention also provides a method for preparing a silicon negative electrode material with high temperature storage performance, comprising the following steps: (1) Add silicon dioxide particles into a sealed reaction vessel and heat to a predetermined temperature under a nitrogen atmosphere; (2) A mixed gas of organic gas, gaseous silicon tetrachloride and nitrogen is introduced into the closed reaction container to react until a silicon nitride composite carbon layer is formed on the surface of the silicon oxide particles, thereby obtaining the silicon negative electrode material with high temperature storage performance.

[0008] In the above preparation method, preferably, the particle size D50 of the silicon powder is 4-15, and the particle size D50 of the silicon oxide particles is 5 μm.

[0009] Preferably, the closed reaction vessel is a CVD furnace.

[0010] Preferably, the heating temperature is controlled at 800-1100°C.

[0011] Preferably, the organic gas is methane, ethylene or acetylene.

[0012] Preferably, silicon tetrachloride is liquid at room temperature, and the gaseous silicon tetrachloride is obtained by heating liquid silicon tetrachloride to above 100° C. to form a gas.

[0013] Preferably, the reaction time is more than 2 hours.

[0014] SiCl 4 It is liquid at room temperature, becomes gaseous at 100°C, and reacts to produce silicon atoms in a hydrogen-containing environment at 800°C, which then react with nitrogen. 4 (Pre-heated to gaseous state), and with the help of protective atmosphere N 2 H produced by the decomposition of organic gases such as methane 2 , under high temperature conditions, C x H y (High temperature) → C+C m H n (There may be multiple intermediate products) +H 2 , SiCl 4 +2N 2 +6H 2 (High temperature) → Si 3 N 4 +12HCl, carbon and silicon nitride molecules can be formed to coat the surface of silicon negative electrode material at the same time; and through the composite coating layer of carbon and silicon nitride molecules, the high-temperature storage performance of the battery prepared by the obtained silicon negative electrode material is significantly improved.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention forms a composite layer of silicon nitride and carbon on the surface of the silicon negative electrode material, which significantly improves the high-temperature storage performance and cycle performance of the silicon negative electrode material.

[0016] 2. The method of the present invention is simple to operate, and the original CVD equipment can be used. 4 At the same time, a silicon nitride composite carbon layer is formed on the surface of the silicon negative electrode material to improve the high-temperature storage performance and cycle performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 This is an electron microscope image of the composite coating layer of the silicon negative electrode material with high temperature storage performance obtained in Example 1 of the present invention; Figure 2 This is a distribution diagram of silicon, oxygen, carbon and nitrogen elements in the high temperature storage performance silicon negative electrode material obtained in Example 1 of the present invention; Figure 3 This is the XRD diagram of the silicon negative electrode material with high temperature storage performance obtained in Example 1 of the present invention; Figure 4 This is a distribution diagram of silicon, oxygen, carbon and nitrogen elements in the high temperature storage performance silicon negative electrode material obtained in Example 2 of the present invention; Figure 5 This is a distribution diagram of silicon, oxygen, carbon and nitrogen elements in the silicon negative electrode material with high temperature storage performance obtained in the comparative example of the present invention; Figure 6 The graph is a cycle performance diagram of the silicon negative electrode materials obtained in Examples 1-3 of the present invention and the comparative example after being mixed with graphite at 25°C. DETAILED DESCRIPTION

[0019] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and carefully in combination with preferred embodiments below, but the protection scope of the present invention is not limited to the following specific embodiments.

[0020] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0021] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0022] A method for preparing a silicon negative electrode material with better high-temperature storage performance for a secondary battery comprises the following steps: (1) Select silicon oxide negative electrode material with D50 of 5 μm for testing; (2) Add to the CVD furnace, set the heating temperature process, control the heating temperature at 800-1100°C, preferably 1000°C for testing; (3) Prepare methane, silicon tetrachloride (preheated to 100°C to form a gas), and nitrogen. After the CVD is heated to 1000°C, introduce a mixed gas of methane, silicon tetrachloride, and nitrogen; (4) At high temperatures, methane, silicon tetrachloride, and nitrogen decompose to form a silicon nitride composite carbon layer on the surface of silicon oxide particles; (5) After the composite carbon layer is completely formed, a silicon oxide precursor is obtained, which is a silicon negative electrode material with high temperature storage performance.

[0023] Embodiment 1: A method for preparing a silicon negative electrode material with high temperature storage performance comprises the following steps: A silicon oxide negative electrode material with a D50 of 5μm was selected for the experiment. 700g of silicon oxide negative electrode material was added into the CVD furnace, and the heating temperature was set to 1000℃ for the experiment. After the temperature in the CVD furnace was heated to 1000℃ under a nitrogen protective atmosphere, 50g of silicon tetrachloride was prepared (heated to 100℃ to form a gas, the heating method was set, and it evaporated in 2h), 1L / min of methane and 1L / min of nitrogen were introduced, and a mixed gas of methane, silicon tetrachloride and nitrogen was introduced. After maintaining a constant temperature at 1000℃ for 2h, the introduction of methane and silicon tetrachloride was stopped, and the silicon oxide precursor was obtained after cooling, which is the silicon negative electrode material with high temperature storage performance.

[0024] like Figure 1 As shown, the thickness of the composite coating layer is about 20 nm.

[0025] like Figure 2 As shown, this embodiment successfully forms a composite layer of silicon nitride and carbon on the surface of the silicon negative electrode material, and the N and C elements in the silicon negative electrode material particles are evenly distributed.

[0026] like Figure 3 As shown, the high temperature storage performance silicon negative electrode material of this embodiment contains a small protrusion of silicon nitride peak in addition to conventional silicon dioxide and silicon peaks, indicating the presence of silicon nitride compounds.

[0027] Embodiment 2: A method for preparing a silicon negative electrode material with high temperature storage performance comprises the following steps: A silicon oxide negative electrode material with a D50 of 5μm was selected for the experiment. 700g of silicon oxide negative electrode material was added into the CVD furnace, and the heating temperature was set to 1000℃ for the experiment. After the temperature in the CVD furnace was heated to 1000℃ under a nitrogen protective atmosphere, 100g of silicon tetrachloride was prepared (heated to 100℃ to form a gas, the heating method was set, and it evaporated in 2h), 1L / min of methane and 1L / min of nitrogen were introduced, and a mixed gas of methane, silicon tetrachloride and nitrogen was introduced. After maintaining a constant temperature at 1000℃ for 2h, the introduction of methane and silicon tetrachloride was stopped, and the silicon oxide precursor was obtained after cooling, which is the silicon negative electrode material with high temperature storage performance.

[0028] like Figure 4 As shown, this embodiment successfully forms a silicon nitride composite carbon layer on the surface of the silicon negative electrode material, and the N and C elements in the silicon negative electrode material particles are evenly distributed.

[0029] Embodiment 3: A method for preparing a silicon negative electrode material with high temperature storage performance comprises the following steps: A silicon oxide negative electrode material with a D50 of 5μm was selected for the experiment. 700g of silicon oxide negative electrode material was added into the CVD furnace, and the heating temperature was set to 1000℃ for the experiment. After the temperature in the CVD furnace was heated to 1000℃ under a nitrogen protective atmosphere, 100g of silicon tetrachloride was prepared (heated to 100℃ to form a gas, the heating method was set, and it evaporated in 2h), 0.5L / min of methane and 1L / min of nitrogen were introduced, and a mixed gas of methane, silicon tetrachloride and nitrogen was introduced. After maintaining a constant temperature at 1000℃ for 2h, the introduction of methane and silicon tetrachloride was stopped, and the silicon oxide precursor was obtained after cooling, which is the silicon negative electrode material with high temperature storage performance.

[0030] Comparative Example 1: A method for preparing a silicon negative electrode material comprises the following steps: A silicon oxide negative electrode material with a D50 of 5μm was selected for the experiment. 700g of silicon oxide negative electrode material was added into the CVD furnace, and the heating temperature was set to 1000℃ for the experiment. After the temperature in the CVD furnace was heated to 1000℃ under a nitrogen protective atmosphere, 1L / min of methane and 1L / min of nitrogen were introduced, and a mixed gas of methane and nitrogen was introduced. After maintaining a constant temperature at 1000℃ for 2h, the introduction of methane was stopped, and the silicon oxide precursor was obtained after cooling down.

[0031] like Figure 5 As shown, in the comparative example, no N element is present in the silicon negative electrode material particles prepared without adding silicon tetrachloride.

[0032] The silicon dioxide precursor materials prepared in Examples 1-3 and the comparative example were added with 8% by mass of mixed graphite to obtain negative electrode materials, and cylindrical batteries were prepared for high temperature storage performance test and evaluation. The comparison results are shown in Table 1.

[0033] Test method: (1) At 25±2℃, use 0.5C constant current and constant voltage to charge to 4.2V full charge, then discharge to 2.5V with 1C current, cycle 3 times, then charge to 4.2V with 0.5C constant current and constant voltage, and use the last discharge capacity as the capacity benchmark; (2) Place the battery in a 55±1℃ constant temperature box and keep it warm for 27h×7 days. After the time is reached, take out the battery and leave it at 25±2℃ for 2h; (3) Use 0.5C current to discharge to 2.5V, then charge to 4.2V with 0.5C constant current and constant voltage, and use 0.5C current to discharge to 2.5V. Use the first discharge capacity to maintain the capacity and the second discharge capacity to recover the capacity. Calculate the battery retention rate and recovery rate.

[0034] Table 1 Comparison of high temperature storage performance of the precursors obtained in Examples 1-3 and the comparative example after mixing with graphite

[0035] As shown in the table above, the silicon anode material coated with silicon nitride and carbon composite layer prepared in Examples 1-3 has significantly improved battery high temperature storage performance compared with the silicon 2 Oxide anode material prepared in the comparative example.

[0036] like Figure 6 As shown, compared with the comparative example without silicon nitride coating, the cycle performance of the silicon negative electrode material coated with silicon nitride and carbon composite layer in Examples 1-3 is better.

Claims

1. A silicon negative electrode material with high temperature storage performance, characterized in that: The invention comprises silicon oxide particles, on the surface of which a composite layer of silicon nitride and carbon is coated.

2. The high temperature storage performance silicon negative electrode material according to claim 1, characterized in that: In the silicon negative electrode material with high temperature storage performance, the mass percentage of carbon is 0.1-0.5%, and the mass percentage of nitrogen is 1.5-5%.

3. The high temperature storage performance silicon negative electrode material according to claim 1 or 2, characterized in that: The thickness of the composite layer of silicon nitride and carbon is 10-30 nm.

4. A method for preparing a silicon negative electrode material with high temperature storage performance as claimed in claim 1, characterized in that: The steps include: (1) Add silicon dioxide particles into a sealed reaction vessel and heat to a predetermined temperature under a nitrogen atmosphere; (2) A mixed gas of organic gas, gaseous silicon tetrachloride and nitrogen is introduced into the closed reaction container to react until a silicon nitride composite carbon layer is formed on the surface of the silicon oxide particles, thereby obtaining the silicon negative electrode material with high temperature storage performance.

5. The preparation method according to claim 4, characterized in that: The particle size D50 of the silicon oxide particles is 4-9 μm.

6. The preparation method according to claim 4, characterized in that: The closed reaction container is a CVD furnace.

7. The preparation method according to claim 4, characterized in that: The heating temperature is controlled at 800-1100°C.

8. The preparation method according to claim 4, characterized in that: The organic gas is methane, ethylene or acetylene.

9. The preparation method according to claim 4, characterized in that: The gaseous silicon tetrachloride is obtained by heating silicon tetrachloride liquid to above 100° C. to form a gaseous state.

10. The preparation method according to claim 4, characterized in that: The reaction time is more than 2 hours.

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