Magnesium-based composite material, pre-magnesium silicon monoxide material, preparation method, application and lithium ion battery

Abstract

The present application relates to a kind of magnesium-based composite material, pre-magnesium silicon monoxide material and its preparation method, application and lithium ion battery.The magnesium-based composite material is composed of magnesium matrix and MgO and Mg2Si distributed on the outer surface of magnesium matrix;MgO and Mg2Si are evenly distributed in the form of particles on the outer surface of magnesium matrix;The mass ratio of magnesium matrix and MgO is greater than 1.71:1;The mass ratio of magnesium matrix and Mg2Si is greater than 2.45:1.The magnesium-based composite material of the present application as magnesium source greatly improves the uniformity of pre-magnesium silicon monoxide reaction, and can effectively improve the specific capacity and structural stability of the material.The magnesium-based composite material and pre-magnesium silicon monoxide material preparation method of the present application is simple, reaction controllable, without special environment, with good operability and industrialization potential.

Description

TECHNICAL FIELD

[0001] The present application relates to a magnesium-based composite material, a pre-magnesium silicon monoxide material, a preparation method and application thereof, and a lithium ion battery. BACKGROUND

[0002] Silicon-based materials are widely considered as the most promising next-generation negative electrode materials due to their high theoretical specific capacity (1700-4200 mAh / g) and low electrochemical lithium intercalation potential (about 0.4 V vs. Li / Li + ), as well as their abundant resource reserves. Compared with traditional graphite negative electrode materials, silicon-based materials have a significant energy density advantage, which is expected to promote the development of battery technology towards higher performance and longer endurance. However, despite the theoretical advantages of silicon-based materials, they still face a series of technical challenges in practical applications, mainly in terms of low first coulomb efficiency and high expansion rate.

[0003] Low first coulomb efficiency refers to the fact that during the first charge and discharge process of the battery, due to the irreversible capacity loss of silicon-based materials, the actual available electric quantity is much lower than the theoretical value. High expansion rate is due to the significant volume expansion of silicon during lithium ion intercalation, which not only causes damage to the internal structure of the battery, but also seriously affects the cycle stability and life of the battery. Therefore, solving the problems of first coulomb efficiency and expansion of silicon-based negative electrode materials is the key to improving their application performance.

[0004] To solve these problems, pre-magnesium technology has emerged. Pre-magnesium technology can improve the electrochemical performance of silicon-based materials to some extent by introducing magnesium elements on the surface of silicon-based materials. Specifically, pre-magnesium technology can effectively improve the first coulomb efficiency of silicon-based materials, reduce irreversible capacity loss by improving the initial charge-discharge process of the material. In addition, pre-magnesium can also inhibit the expansion of silicon-based materials to some extent, reduce the volume change during charge and discharge, and thus improve the cycle life and stability of the battery.

[0005] Pre-magnesium technology mainly includes gas-phase-gas-phase pre-magnesium, gas-phase-solid-phase pre-magnesium, and solid-phase-solid-phase pre-magnesium, and gas-phase-gas-phase pre-magnesium is further divided into front-end pre-magnesium and back-end pre-magnesium according to different silicon-oxygen materials. The uniformity of gas-phase-gas-phase pre-magnesium is higher than that of gas-phase-solid-phase pre-magnesium and solid-phase-solid-phase pre-magnesium, so it has good inhibition of the expansion of silicon-based materials, but there is little difference in the improvement of the first coulomb efficiency among the several ways. Although the uniformity of gas-phase-gas-phase pre-magnesium is good, its harsh process conditions are not conducive to its large-scale production. In addition, although pre-magnesium technology improves the first coulomb efficiency, it also causes a decrease in specific capacity.

[0006] Based on the industrialization angle, how to improve the uniformity of gas-solid pre-magnesium and solid-solid pre-magnesium, and how to reduce the specific capacity loss after pre-magnesium are the most important steps to promote silicon-based materials. SUMMARY

[0007] The technical problem to be solved by the present application is to overcome the defects of low initial coulomb efficiency and high expansion rate of the existing silicon-based negative electrode material. Although the pre-magnesium technology can improve the initial coulomb efficiency and inhibit the expansion, there are still problems of specific capacity reduction and complex large-scale production process. The present application provides a magnesium-based composite material, a pre-magnesium silicon monoxide material, a preparation method, an application and a lithium ion battery. The magnesium-based composite material as a magnesium source greatly improves the uniformity of the pre-magnesium reaction of silicon monoxide, and can effectively improve the specific capacity and structural stability of the material. The pre-magnesium silicon monoxide material has excellent volume stability and cycle performance, significantly improves the initial coulomb efficiency and specific capacity. The preparation method of the magnesium-based composite material and the pre-magnesium silicon monoxide material is simple, the reaction is controllable, and no special environment is needed, which has good operability and industrialization potential.

[0008] The present application solves the above technical problems by the following technical solutions:

[0009] The present application provides a magnesium-based composite material, which comprises a magnesium matrix and MgO and Mg2Si distributed on the outer surface of the magnesium matrix.

[0010] The MgO and the Mg2Si are uniformly distributed on the outer surface of the magnesium matrix in the form of particles.

[0011] The mass ratio of the magnesium matrix to the MgO is greater than 1.71:1.

[0012] The mass ratio of the magnesium matrix to the Mg2Si is greater than 2.45:1.

[0013] As a preferred embodiment, the mass ratio of the magnesium matrix to the MgO is 29.1:1.

[0014] As a preferred embodiment, the mass ratio of the magnesium matrix to the Mg2Si is 41.5:1.

[0015] The present application also provides a preparation method of a magnesium-based composite material, which comprises the following steps: uniformly mixing magnesium powder and SiO2 powder, and heating to react.

[0016] The mass ratio of the magnesium powder to the SiO2 powder is greater than 2.3:1.

[0017] The temperature of the heating reaction is ≤900℃.

[0018] The magnesium matrix is a magnesium matrix commonly selected in the art, such as pure magnesium.

[0019] Preferably, the method for preparing the magnesium-based composite material satisfies one or more of the following conditions:

[0020] (1) the mass ratio of the magnesium powder to the SiO2 powder is (20-100): 1, further preferably (24-99): 1, such as 39: 1;

[0021] (2) the temperature of the heating reaction is 200-900℃, further preferably 400-600℃;

[0022] (3) the operation of mixing uniformly is performed in a mixer;

[0023] (4) the heating reaction is performed in a vacuum furnace;

[0024] (5) the time of the heating reaction is 2-6h, such as 4h;

[0025] (6) the vacuum degree of the heating reaction is ≤10 -5 Pa.

[0026] In this scheme, the mass ratio of the magnesium powder to the SiO2 powder aims to achieve better structure control. This ratio ensures that the magnesium powder and the SiO2 powder can fully react during the reaction process, forming a uniform magnesium-based composite material structure, optimizing the microstructure of the material, and improving the mechanical properties, thermal stability, and electrochemical properties of the composite material.

[0027] The application also provides a magnesium-based composite material prepared by the above method for preparing a magnesium-based composite material.

[0028] The application also provides a pre-magnesium silicon monoxide material, which comprises an inner core, and a carbon coating layer coated outside the inner core. The inner core comprises a magnesium-based composite material, a magnesium silicate compound, and silicon monoxide as described above. The carbon coating layer is an amorphous carbon layer.

[0029] The magnesium-based composite material and the magnesium silicate compound are deposited in the pores and on the surface of the silicon monoxide.

[0030] The magnesium silicate compound is MgSiO3 and Mg2SiO4.

[0031] The weight percentage of silicon in the pre-magnesium silicon monoxide material is 49 wt%-54 wt%, such as 49.6 wt%.

[0032] and / or, the weight percentage of magnesium element in the pre-magnesia silicon monoxide material is 2.5 wt%-12.5 wt%, for example, 7.5 wt%;

[0033] and / or, the weight percentage of oxygen element in the pre-magnesia silicon monoxide material is 34 wt%-41.5 wt%, for example, 39.8 wt%;

[0034] and / or, the weight percentage of carbon element in the pre-magnesia silicon monoxide material is 2.5 wt%-4 wt%, for example, 3.1 wt%;

[0035] wherein, wt% is the percentage of the weight of each element in the total weight of the pre-magnesia silicon monoxide material.

[0036] The application also provides a preparation method of the pre-magnesia silicon monoxide material, mixing the magnesium-based composite material as described above with silicon monoxide uniformly, baking to obtain a mixture A;

[0037] Then, the mixture A is pickled in an acidic solution to obtain a mixture B;

[0038] Then, the mixture B is carbon-coated in a mixed gas containing a carbon source gas and an inert gas.

[0039] In this scheme, by introducing the magnesium-based composite material, the uniformity of the pre-magnesia reaction of silicon monoxide is effectively improved, and the performance decline caused by uneven reaction in the traditional method is avoided. Compared with the traditional solid-solid pre-magnesia method, the use of magnesium-based composite material significantly improves the uniformity in the reaction process, making the reaction product more stable, thereby improving the overall performance of the material.

[0040] As preferred, the preparation method of the pre-magnesia silicon monoxide material satisfies one or more of the following conditions:

[0041] (1) the mass ratio of the silicon monoxide to the magnesium-based composite material is greater than 2.3:1, for example, 9:1;

[0042] (2) the uniform mixing operation is carried out in a mixer;

[0043] (3) after the uniform mixing, the step of inert gas replacement before the baking is further included;

[0044] Further preferably, the inert gas is one or a combination of argon, helium or nitrogen, for example, argon;

[0045] Further preferably, the inert gas replacement is carried out in a rotary furnace, wherein the rotation speed of the rotary furnace is more preferably 0.5 r / min-2 r / min, for example, 1 r / min;

[0046] Further preferably, the flow rate of the inert gas is 0.5 L / min-2 L / min, for example 1 L / min;

[0047] Further preferably, the time for the inert gas to replace is 1 h-4 h, for example 2 h;

[0048] (4) the reaction temperature of the calcination is ≤900℃, further preferably 600-900℃, for example 750℃;

[0049] (5) the reaction time of the calcination is 4 h-8 h, for example 6 h;

[0050] (6) the heating rate from normal temperature to the reaction temperature of the calcination is 5℃ / min-15℃ / min, for example 10℃ / min;

[0051] (7) the acid solution is a combination of one or more of hydrochloric acid, acetic acid or sulfuric acid;

[0052] Further preferably, the concentration of the acid solution is 3%-8%, for example 3%-6%, as mass percentage concentration;

[0053] Further preferably, the volume ratio of the mixture A and the acid solution is less than or equal to 2:1, more further preferably (0.5-2):1;

[0054] (8) the pickling further includes a process of water washing;

[0055] (9) the pickling further includes a process of drying;

[0056] Further preferably, the temperature of the drying is ≤200℃, more further preferably 120℃-200℃, and the time of the drying is ≤48 h, more further preferably 3 h-48 h;

[0057] (10) the carbon source gas is acetylene;

[0058] (11) the inert gas is a combination of one or more of argon, helium or nitrogen, for example argon;

[0059] (12) the flow rate ratio of the inert gas and the carbon source gas is 1:(1-1.5);

[0060] Further preferably, the flow rate of the inert gas is 2 L / min, and the flow rate of the carbon source gas is 2.5 L / min;

[0061] (13) the reaction temperature of the carbon coating is 600℃-1000℃, for example 800℃;

[0062] (14) the heating rate from room temperature to the carbon-coating reaction temperature is 1℃ / min-10℃ / min, for example 5℃ / min;

[0063] (15) the carbon-coating reaction time is 0.5 h-2h, for example 1h;

[0064] (16) the ratio of the amount of the mixed gas to the mixed material B is 0.010L / g-0.200L / g, wherein L / g refers to the volume of the mixed gas required per gram of the mixed material B;

[0065] Further preferably, the ratio of the amount of the mixed gas to the mixed material B is 0.135L / g.

[0066] The application also provides a pre-magnesium silicon monoxide material prepared by the above method.

[0067] The application also provides a use of the pre-magnesium silicon monoxide material as described above in the preparation of an electrode sheet.

[0068] Preferably, the electrode sheet is a negative electrode sheet.

[0069] Preferably, the method for preparing the electrode sheet comprises mixing the pre-magnesium silicon monoxide material, a binder and a conductive agent, coating on a copper foil, vacuum drying, rolling, and slitting.

[0070] The application also provides a lithium ion battery comprising the pre-magnesium silicon monoxide material as described above.

[0071] The positive progress of the application is that:

[0072] (1) solving the problem of uniformity of solid-solid pre-magnesium reaction: the traditional method usually reduces the temperature and forms an inert protective layer by coating a carbon layer on the surface of a silicon-based material or adding a molten salt, so as to improve the reaction uniformity. The application uses a magnesium-based composite material to realize one-step regulation of reaction uniformity, effectively avoiding the problems caused by non-uniform reaction in the traditional method.

[0073] (2) Solid-solid and gas-solid combined pre-magnesium reaction optimization: The present application forms a passivation layer by first performing a solid phase reaction, i.e. the MgO on the surface of the magnesium matrix and Mg2Si and part of the magnesium matrix react with silicon monoxide to form a passivation layer to inhibit the violent reaction and improve the generation of MgSiO3. This solid phase reaction stage helps to reduce the severity of the reaction. Subsequently, the solid-gas reaction stage is entered, in which the unreacted magnesium matrix is gasified and reacts with silicon monoxide in a gas-solid reaction to further promote the generation of MgSiO3 and increase its content. By such a combination, not only is the control of the reaction process optimized, but the MgSiO3 content of the final product is also significantly improved, thereby improving the performance of the pre-magnesium silicon monoxide material.

[0074] (3) Improve the specific capacity and material structure of the pre-magnesium silicon monoxide material: The introduction of Mg2Si effectively makes up for the loss of specific capacity after pre-magnesium, and the introduction of MgO increases the content of MgSiO3 generated in the subsequent reaction, filling the structural pores generated by porous Si, thereby inhibiting the deterioration of particle aggregation and expansion, and significantly improving the volume stability and performance of the material. BRIEF DESCRIPTION OF DRAWINGS

[0075] Figure 1 XRD pattern of the pre-magnesium silicon monoxide material of Example 1.

[0076] Figure 2 XRD pattern of the pre-magnesium silicon monoxide material of Comparative Example 3. DETAILED DESCRIPTION

[0077] The present application will be further described by way of examples, but the present application is not limited to the scope of the examples. The reagents and raw materials used in the following examples, such as magnesium powder, are commercially available.

[0078] In the following examples, the D50 of silicon monoxide is 5 μm; the D50 of silicon dioxide is 5 μm, and the purity is > 99%; the purity of magnesium powder is > 99%.

[0079] In the following examples, the mixer is from Wuxi Qingxin Powder Equipment Co., Ltd., and the model is VC-10L.

[0080] Example 1

[0081] (1) Preparation of magnesium-based composite material:

[0082] A total of 2 kg of magnesium powder and SiO2 powder was weighed, of which SiO2 accounted for 2.5% of the total mass, and the mixture was placed in a mixer and mixed uniformly, then transferred to a vacuum furnace, vacuumed to 10 -5 Pa or less, heated to 400°C for reaction, constant temperature reaction for 4 h, cooling and collecting the material to obtain a magnesium-based composite material.

[0083] The magnesium-based composite material is composed of a magnesium matrix and MgO and Mg2Si distributed on the outer surface of the magnesium matrix; the MgO and Mg2Si are in a granular form and uniformly distributed on the outer surface of the magnesium matrix; the mass ratio of the magnesium matrix to the MgO is 29.1:1; and the mass ratio of the magnesium matrix to the Mg2Si is 41.5:1.

[0084] (2) Preparation of the pre-magnesium silicon monoxide material:

[0085] 5 kg of the magnesium-based composite material and silicon monoxide powder in total, wherein the magnesium-based composite material accounts for 10% of the total mass, are uniformly mixed by using a mixer and then placed in a rotary furnace tube, rotation of the furnace tube is ensured at 1 r / min, replacement is performed for 2 h by using 1 L / min of Ar; after the replacement is completed, heating is started, the temperature is raised to 750 ℃ at a rate of 10 ℃ / min, the temperature is kept constant at 750 ℃ for 6 h, the temperature is lowered, the material is taken out, and mixture A is obtained; mixture A is washed in a 3% hydrochloric acid solution, wherein the volume ratio of mixture A to the hydrochloric acid solution is 0.5:1, after the washing, mixture A is washed in water, filtered, dried at 120 ℃ for 3 h, scattered, and mixture B is obtained; 3 kg of mixture B is placed in a rotary furnace, the temperature is raised to 800 ℃ at a rate of 5 ℃ / min, the temperature is kept constant at 800 ℃ for 90 min, a mixed gas of argon and acetylene is introduced, the ratio of the amount of the mixed gas to the amount of mixture B is 0.135 L / g, the temperature is lowered, and a pre-magnesium silicon monoxide material is obtained.

[0086] Example 2

[0087] Only the heating reaction in step (1) is raised to 400 ℃, and the rest of the conditions are the same as in Example 1.

[0088] Example 3

[0089] Only the heating reaction in step (1) is raised to 600 ℃, and the rest of the conditions are the same as in Example 1.

[0090] Example 4

[0091] Only SiO2 accounts for 1% of the total mass in step (1), and the rest of the conditions are the same as in Example 1.

[0092] Example 5

[0093] Only SiO2 accounts for 4% of the total mass in step (1), and the rest of the conditions are the same as in Example 1.

[0094] Example 6

[0095] Only the magnesium-based composite material accounts for 5% of the total mass in step (2), and the rest of the conditions are the same as in Example 1.

[0096] Example 7

[0097] Only the magnesium-based composite material in step (2) accounts for 15% of the total mass, and the other conditions are the same as in Example 1.

[0098] Example 8

[0099] Only step (2) is heated to 600℃ at a rate of 10℃ / min, and the other conditions are the same as in Example 1.

[0100] Example 9

[0101] Only step (2) is heated to 900℃ at a rate of 10℃ / min, and the other conditions are the same as in Example 1.

[0102] Comparative Example 1

[0103] Preparation of the pre-magnesium silicon monoxide material:

[0104] Take 5kg of magnesium powder and silicon monoxide powder, of which the magnesium powder accounts for 10% of the total mass, mix them uniformly using a mixer, and then place them in a rotary furnace tube. Turn on the rotation to ensure that the furnace tube rotates at 1r / min, and use 1L / min of Ar to displace, displace for 2h. After displacement is complete, turn on the heating, and heat to 750℃ at a rate of 10℃ / min. Keep the temperature at 750℃ for 6h, cool down, take the material, and obtain mixture A. Place mixture A in a 3% hydrochloric acid solution, and the volume ratio of mixture A to the hydrochloric acid solution is 0.5:1. After washing, place it in water, filter, dry at 120℃ for 3h, break up, and obtain mixture B. Take 3kg of mixture B and place it in a rotary furnace, heat to 800℃ at a rate of 5℃ / min, and keep the temperature constant for 90min. At the same time, introduce a mixed gas of argon and acetylene (argon 2L / min, acetylene 2.5L / min), and the ratio of the amount of mixed gas to the amount of mixture B is 0.135L / g. Cool down to obtain the pre-magnesium silicon monoxide material.

[0105] Comparative Example 2

[0106] (1) Preparation of the mixture material:

[0107] Take 2kg of Mg powder and SiO2 powder, of which SiO2 accounts for 2.5% of the total mass, mix the mixture material uniformly using a mixer, and obtain the mixture material.

[0108] (2) Preparation of the pre-magnesium silicon monoxide material:

[0109] Take the above mixture and silicon monoxide powder totaling 5 kg, wherein the mixture accounts for 10% of the total mass, mix uniformly with a mixer, then place in a rotary furnace tube, open the rotation to ensure the tube rotates at 1 r / min, use 1 L / min of Ar to displace, displace for 2 h; after displacement is complete, open the heating, increase the temperature to 750°C at a rate of 10°C / min, hold at 750°C for 6 h, cool, take the material, to obtain mixture A; place mixture A in a 3% hydrochloric acid solution, wherein the volume ratio of mixture A and the hydrochloric acid solution is 0.5:1, after washing, place in water, filter, dry at 120°C for 3 h, break up, to obtain mixture B; take 3 kg of mixture B and place in a rotary furnace, increase the temperature to 800°C at a rate of 5°C / min, hold at 800°C for 90 min, while passing a mixed gas of argon and acetylene (argon 2 L / min, acetylene 2.5 L / min), pass the gas until the ratio of the amount of mixed gas to mixture B is 0.135 L / g, cool, to obtain the pre-magnesium silicon monoxide material.

[0110] Comparative Example 3

[0111] Take 2 kg of Mg powder, mix uniformly with a mixer, then transfer to a vacuum furnace, vacuum to 10 -5 Pa, increase the temperature to 400°C to heat and react, hold at temperature for 4 h, cool, take the material, to obtain the mixture.

[0112] Take the above mixture and silicon monoxide powder totaling 5 kg, wherein the mixture accounts for 10% of the total mass, mix uniformly with a mixer, then place in a rotary furnace tube, open the rotation to ensure the tube rotates at 1 r / min, use 1 L / min of Ar to displace, displace for 2 h; after displacement is complete, open the heating, increase the temperature to 750°C at a rate of 10°C / min, hold at 750°C for 6 h, cool, take the material, to obtain mixture A; place mixture A in a 3% hydrochloric acid solution, wherein the volume ratio of mixture A and the hydrochloric acid solution is 0.5:1, after washing, place in water, filter, dry at 120°C for 3 h, break up, to obtain mixture B; take 3 kg of mixture B and place in a rotary furnace, increase the temperature to 800°C at a rate of 5°C / min, hold at 800°C for 90 min, while passing a mixed gas of argon and acetylene (argon 2 L / min, acetylene 2.5 L / min), pass the gas until the ratio of the amount of mixed gas to mixture B is 0.135 L / g, cool, to obtain the pre-magnesium silicon monoxide material.

[0113] Comparative Example 4

[0114] Preparation of the pre-magnesium silicon monoxide material:

[0115] Silicon monoxide powder was mixed with Mg2Si-4Mg (mass fraction 97% Mg2Si and 3% Mg, D50 = 5 μm) in a mass ratio of 59:41 in a mixer, then transferred to a tablet press for briquetting, and the product was calcined in a tube furnace under argon at a temperature of 650 ℃, with a heating rate of 5 ℃ / min and a holding time of 3 h. After cooling, the product was crushed to D50 = 1 μm to obtain the pre-magnesium silicon monoxide material.

[0116] Effect implementation example

[0117] (1) Element content test

[0118] The pre-magnesium silicon monoxide materials of the above examples and comparative examples were subjected to element content tests (ICP-5000 from Beijing Jitian Instrument Co., Ltd.), to test the silicon content and magnesium content of the pre-magnesium silicon monoxide materials. The oxygen content of the materials was tested by an oxygen-nitrogen analyzer (LECO ONH836 from LECO, USA), and the carbon content of the materials was tested by a carbon-sulfur analyzer (SES-802 from Sains Environmental Protection Co., Ltd.). The test results are shown in Table 1.

[0119] (2) XRD test

[0120] The XRD patterns of the pre-magnesium silicon monoxide materials of Example 1 and Comparative Example 3 are shown in Figure 1 and Figure 2 Comparing Figure 1 and Figure 2 it can be seen that the pre-magnesium silicon monoxide material prepared using the magnesium-based composite material of Example 1 has a high magnesium metasilicate content, which is beneficial to improving the cycle life of the battery as a pole piece, while the pre-magnesium silicon monoxide material prepared by reacting the magnesium powder of Comparative Example 3 with silicon monoxide has a low magnesium metasilicate content, which will make the battery cycle efficiency lower as a pole piece.

[0121] (3) Electrochemical performance test

[0122] The pre-magnesium silicon monoxide materials of the above examples and comparative examples were prepared into negative electrode sheets: the preparation method of the negative electrode sheets is conventional in the art, including the following steps: a mixture of the pre-magnesium silicon monoxide material, a binder and a conductive agent was uniformly grinded and coated on a copper foil, vacuum dried, rolled, and cut to obtain the negative electrode sheet.

[0123] The preparation method of the lithium ion battery is conventional in the art, including the following steps: 1 mol / L LiPF6 mixed solvent as electrolyte, the mixed solvent is mixed according to the volume ratio of ethyl carbonate: dimethyl carbonate: methyl carbonate = 1:1:1, polypropylene microporous membrane is used as the separator, lithium sheet is used as the counter electrode, and the above electrode prepared from the pre-magnesium silicon monoxide is assembled into a button cell in an argon-filled inert gas glove box system. The capacity, initial coulombic efficiency and cycle of the assembled half-cell are obtained by using the LAND battery test system of Wuhan Blue Electronic Co., Ltd. at 25 DEG C. The test results are shown in Table 1.

[0124] Table 1 Test results of examples 1-9 and comparative examples 1-4

[0125]

[0126] By comparing the performance data of examples 1-9 and comparative examples 1-4, it can be seen that the pre-magnesium silicon monoxide material prepared in examples 1-9 has a significant advantage in electrochemical performance.

[0127] Firstly, in terms of capacity, the electrode of examples 1-9 shows higher specific capacity. The capacity of examples 1-9 ranges from 940-1510 mAh / g, and the capacity of most samples exceeds 1200 mAh / g. While the capacity of comparative examples 1-3 is only 1091-1114 mAh / g, which is significantly lower than the average level of examples. Especially example 6, its capacity is as high as 1510 mAh / g.

[0128] Secondly, in terms of initial coulombic efficiency, the electrode prepared in examples 1-9 also has obvious advantages. The initial coulombic efficiency of examples 1-9 ranges from 90.1%-95.3%, which is significantly higher than the initial efficiency range of 81.7%-84.5% of comparative examples 1-3. For example, the initial efficiency of example 7 reaches 95.3%, which is 10.8% higher than the highest value 84.5% of comparative example 1, indicating that the material of examples has higher efficiency in the first charge-discharge process.

[0129] In addition, in terms of cycle performance, the electrode prepared in examples 1-9 shows more excellent capacity retention rate. The 100-cycle cycle capacity retention rate of examples 1-9 is between 79.4%-93.7%, while the retention rate of comparative examples 1-3 is only 68.6%-71.7%. In comparative example 4, too much magnesium silicide is added, causing part of the silicon to be aggregated. Although only 3% is added, the aggregation of this part of silicon will cause the performance of the whole battery to decrease significantly, and its 100-cycle cycle capacity retention rate is only 63.3%. Among them, the cycle capacity retention rate of example 7 reaches 93.7%, which is significantly higher than 71.7% of comparative example 1, showing the stability advantage of the material in long cycle use.

Claims

1. A pre-magnesia silicon monoxide material, characterized in that, The pre-magnesium silicon monoxide material comprises an inner core, and a carbon coating layer coated outside the inner core, wherein the inner core comprises a magnesium-based composite material, a magnesium silicate compound and silicon monoxide; and the carbon coating layer is an amorphous carbon layer; The magnesium-based composite material and the magnesium silicate compound are deposited in the pores and on the surface of the silicon monoxide; The magnesium silicate compound is MgSiO3 and Mg2SiO4; The magnesium-based composite material comprises a magnesium matrix and MgO and Mg2Si distributed on the outer surface of the magnesium matrix; The MgO and the Mg2Si are uniformly distributed in the form of particles on the outer surface of the magnesium matrix; The mass ratio of the magnesium matrix to the MgO is greater than 1.71:1; The mass ratio of the magnesium matrix to the Mg2Si is greater than 2.45:1; The weight percentage of silicon in the pre-magnesium silicon monoxide material is 49 wt%-54 wt%; And / or, the weight percentage of magnesium in the pre-magnesium silicon monoxide material is 2.5 wt%-12.5 wt%; And / or, the weight percentage of oxygen in the pre-magnesium silicon monoxide material is 34 wt%-41.5 wt%; And / or, the weight percentage of carbon in the pre-magnesium silicon monoxide material is 2.5 wt%-4 wt%; Wherein, wt% is the percentage of the weight of each element in the total weight of the pre-magnesium silicon monoxide material.

2. The pre-magnesia silica material of claim 1, wherein, The weight percentage of silicon in the pre-magnesium silicon monoxide material is 49.6 wt%.

3. The pre-magnesia silica material of claim 1, wherein, The weight percentage of magnesium in the pre-magnesium silicon monoxide material is 7.5 wt%.

4. The pre-magnesia silica material of claim 1, wherein, The weight percentage of oxygen in the pre-magnesium silicon monoxide material is 39.8 wt%.

5. The pre-magnesia silica material of claim 1, wherein, The weight percentage of carbon in the pre-magnesium silicon monoxide material is 3.1 wt%.

6. The pre-magnesia silica material of claim 1, wherein, The mass ratio of the magnesium matrix to the MgO is 29.1:1; And / or, the mass ratio of the magnesium matrix to the Mg2Si is 41.5:

1.

7. The pre-magnesia silica material of claim 1, wherein, The preparation method of the magnesium-based composite material comprises the following steps: uniformly mixing magnesium powder and SiO2 powder, and heating to react. The mass ratio of the magnesium powder to the SiO2 powder is greater than 2.3:

1. The heating reaction temperature is ≤900℃.

8. The pre-magnesia silica material of claim 7, wherein, The preparation method of the magnesium-based composite material satisfies one or more of the following conditions: (1) The mass ratio of the magnesium powder to the SiO2 powder is (20-100):1; (2) The heating reaction temperature is 200℃-900℃; (3) The uniform mixing operation is carried out in a mixer; (4) The heating reaction is carried out in a vacuum furnace; (5) The heating reaction time is 2h-6h; (6) the vacuum degree of the heating reaction is ≤10 -5 Pa.

9. The pre-magnesia silica material of claim 8, wherein, In the preparation method of the magnesium-based composite material, the mass ratio of the magnesium powder to the SiO2 powder is (24-99):

1.

10. The pre-magnesia silica material of claim 9, wherein, In the preparation method of the magnesium-based composite material, the mass ratio of the magnesium powder to the SiO2 powder is 39:

1.

11. The pre-magnesia silica material of claim 8, wherein, In the preparation method of the magnesium-based composite material, the heating reaction temperature is 400℃-600℃.

12. The pre-magnesia silica material of claim 8, wherein, In the preparation method of the magnesium-based composite material, the heating reaction time is 4h.

13. A method of producing a pre-magnesia silicon monoxide material, characterized by, Mixing the magnesium-based composite material with silicon monoxide uniformly, baking to obtain a mixture A; Then, the mixture A is pickled in an acid solution to obtain a mixture B; Then, the mixture B is carbon-coated in a mixed gas containing a carbon source gas and an inert atmosphere, and the carbon-coated product is obtained. The magnesium-based composite material comprises a magnesium matrix and MgO and Mg2Si distributed on the outer surface of the magnesium matrix. The MgO and the Mg2Si are uniformly distributed in the form of particles on the outer surface of the magnesium matrix. The mass ratio of the magnesium matrix to the MgO is greater than 1.71:

1. The mass ratio of the magnesium matrix to the Mg2Si is greater than 2.45:

1.

14. The method for preparing the pre-magnesium silicon suboxide material as described in claim 13, characterized in that, The mass ratio of the magnesium matrix to the MgO is 29.1:

1. The mass ratio of the magnesium matrix to the Mg2Si is 41.5:

1.

15. The method for preparing the pre-magnesium silicon suboxide material as described in claim 13, characterized in that, The preparation method of the pre-magnesium silicon monoxide material satisfies one or more of the following conditions: (1) The mass ratio of the silicon monoxide to the magnesium-based composite material is greater than 2.3:1; (2) The uniform mixing is performed in a mixer; (3) After the uniform mixing, the step of replacing the inert atmosphere is further included before the baking; (4) The reaction temperature of the baking is ≤900℃; (5) The reaction time of the baking is 4h-8h; (6) The heating rate from the normal temperature to the reaction temperature of the baking is 5℃ / min-15℃ / min; (7) The acid solution is a combination of one or more of hydrochloric acid, acetic acid or sulfuric acid; (8) The process of water washing is further included after the pickling; (9) The process of drying is further included after the pickling; (10) The carbon source gas is acetylene; (11) The inert atmosphere is a combination of one or more of argon, helium or nitrogen; (12) The flow rate ratio of the inert atmosphere to the carbon source gas is 1:(1-1.5); (13) The reaction temperature of the carbon coating is 600℃-1000℃; (14) The heating rate from the normal temperature to the reaction temperature of the carbon coating is 1℃ / min-10℃ / min, (15) The reaction time of the carbon coating is 0.5h-2h; (16) The usage ratio of the mixed gas to the mixture B is 0.010L / g-0.200L / g, wherein L / g refers to the volume of the mixed gas required per gram of the mixture B.

16. The method for preparing the pre-magnesium silicon suboxide material as described in claim 15, characterized in that, The mass ratio of the silicon monoxide to the magnesium-based composite material is 9:

1.

17. The method for preparing the pre-magnesium silicon suboxide material as described in claim 15, characterized in that, In the step of replacing the inert atmosphere, the inert atmosphere is a combination of one or more of argon, helium or nitrogen.

18. The method for preparing the pre-magnesium silicon suboxide material as described in claim 15, characterized in that, In the step of replacing the inert atmosphere, the replacement of the inert atmosphere is performed in a rotary furnace.

19. The method for preparing the pre-magnesium silicon suboxide material as described in claim 18, characterized in that, The rotation speed of the rotary furnace is 0.5 r / min-2 r / min.

20. The method for preparing the pre-magnesium silicon suboxide material as described in claim 19, characterized in that, The rotation speed of the rotary furnace is 1 r / min.

21. The method for preparing the pre-magnesium silicate material as described in claim 15, characterized in that, In the step of replacing the inert atmosphere, the flow rate of the inert atmosphere is 0.5 L / min-2 L / min.

22. The method for preparing the pre-magnesium silicate material as described in claim 21, characterized in that, In the step of replacing the inert atmosphere, the flow rate of the inert atmosphere is 1 L / min.

23. The method for preparing the pre-magnesium silicate material as described in claim 15, characterized in that, In the step of replacing the inert atmosphere, the replacement time of the inert atmosphere is 1h-4h.

24. The method for preparing the pre-magnesium silicate material as described in claim 23, characterized in that, The inert atmosphere replacement time is 2h.

25. The method for preparing the pre-magnesium silicate material as described in claim 15, characterized in that, The reaction temperature of the calcination is 600-900℃.

26. The method for preparing the pre-magnesium silicate material as described in claim 25, characterized in that, The reaction temperature of the calcination is 750℃.

27. The method for preparing the pre-magnesium silicate material as described in claim 15, characterized in that, The reaction time of the calcination is 6h.

28. The method for preparing the pre-magnesium silicon suboxide material as described in claim 15, characterized in that, The temperature rising rate from normal temperature to the reaction temperature of the calcination is 10℃ / min.

29. The method for preparing the pre-magnesium silicon suboxide material as described in claim 15, characterized in that, The concentration of the acid solution is 3%-8%, mass percentage.

30. The method for preparing the pre-magnesium silicate material as described in claim 29, characterized in that, The concentration of the acid solution is 3%-6%, mass percentage.

31. The method for preparing the pre-magnesium silicon suboxide material as described in claim 15, characterized in that, The volume ratio of the mixture A and the acid solution is less than or equal to 2:

1.

32. The method for preparing the pre-magnesium silicate material as described in claim 31, characterized in that, The volume ratio of the mixture A and the acid solution is (0.5-2):

1.

33. The method for preparing the pre-magnesium silicate material as described in claim 15, characterized in that, The drying temperature is ≤200℃.

34. The method for preparing the pre-magnesium silicate material as described in claim 33, characterized in that, The drying temperature is 120℃-200℃.

35. The method for preparing the pre-magnesium silicate material as described in claim 15, characterized in that, The drying time is ≤48h.

36. The method for preparing the pre-magnesium silicate material as described in claim 35, characterized in that, The drying time is 3h-48h.

37. The method for preparing the pre-magnesium silicon suboxide material as described in claim 15, characterized in that, The inert atmosphere in the inert atmosphere replacement step is argon.

38. The method for preparing the pre-magnesium silicate material as described in claim 15, characterized in that, The flow rate of the inert atmosphere in the inert atmosphere replacement step is 2L / min, and the flow rate of the carbon source gas is 2.5L / min.

39. The method for preparing the pre-magnesium silicon suboxide material as described in claim 15, characterized in that, The reaction temperature of the carbon coating is 800℃.

40. The method for preparing the pre-magnesium silicate material as described in claim 15, characterized in that, The temperature rising rate from normal temperature to the reaction temperature of the carbon coating is 5℃ / min.

41. The method for preparing the pre-magnesium silicon suboxide material as described in claim 15, characterized in that, The reaction time of the carbon coating is 1h.

42. The method of claim 15 wherein the pre-magnesia silica material is prepared by the steps of: The dosage ratio of the mixed gas and the mixture B is 0.135L / g.

43. The method for preparing the pre-magnesium silicon suboxide material as described in claim 13, characterized in that, The preparation method of the magnesium-based composite material comprises the following steps: uniformly mixing magnesium powder and SiO2 powder, and heating to react. The mass ratio of the magnesium powder and the SiO2 powder is greater than 2.3:

1. The heating reaction temperature is ≤900℃.

44. The method for preparing the pre-magnesium silicate material as described in claim 43, characterized in that, The preparation method of the magnesium-based composite material satisfies one or more of the following conditions: (1) the mass ratio of the magnesium powder and the SiO2 powder is (20-100):1; (2) the heating reaction temperature is 200℃-900℃; (3) the uniform mixing operation is performed in a mixer; (4) the heating reaction is performed in a vacuum furnace; (5) the heating reaction time is 2h-6h; (6) the vacuum degree of the heating reaction is ≤10 -5 Pa.

45. The method for preparing the pre-magnesium silicon suboxide material as described in claim 44, characterized in that, In the preparation method of the magnesium-based composite material, the mass ratio of the magnesium powder and the SiO2 powder is (24-99):

1.

46. The method of claim 45, wherein the pre-magnesia silica material is prepared by the steps of: In the preparation method of the magnesium-based composite material, the mass ratio of the magnesium powder and the SiO2 powder is 39:

1.

47. The method for preparing the pre-magnesium silicon suboxide material as described in claim 44, characterized in that, In the preparation method of the magnesium-based composite material, the heating reaction temperature is 400℃-600℃.

48. The method for preparing the pre-magnesium silicon suboxide material as described in claim 44, characterized in that, In the preparation method of the magnesium-based composite material, the heating reaction time is 4h.

49. A pre-magnesia silicon monoxide material characterized by, The pre-magnesium silicon monoxide material is prepared by the preparation method in any one of claims 13-48.

50. Use of the pre-magnesium silicon monoxide material in any one of claims 1-12 or 49 in the preparation of an electrode sheet.

51. The use of a pre-magnesia-silicon monoxide material according to claim 50 for the production of a pole piece, characterized in that The electrode sheet is a negative electrode sheet.

52. The use of a pre-magnesia-silicon monoxide material according to claim 50 for the production of a pole piece, characterized in that The preparation method of the electrode sheet is mixing the pre-magnesium silicon monoxide material, a binder and a conductive agent, coating on a copper foil, vacuum drying, rolling, slitting, and then obtaining the electrode sheet.

53. A lithium-ion battery, characterized in that, It comprises the pre-magnesium silicon monoxide material in any one of claims 1-12 or 49.

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