A doped silicon oxide negative electrode material and preparation method thereof

Abstract

The present invention provides a doped silicon oxide negative electrode material and a preparation method thereof. The aforementioned silicon oxide negative electrode material has the following characteristics: copper target X-ray diffraction analysis can be performed on it to determine that it contains Si and a general formula of M x Si y O z The physical phase, where M x Si y O z The representative phase must contain SrSiO3, and the grain size of the silicon (111) crystal plane calculated by the Scherrer formula is ≤10nm. Elemental analysis can be performed to determine that M is a metal element. Preferably, in addition to Sr, it also contains Li, and the mass fraction A of M in the entire material satisfies 3%≤A≤15%, wherein the molar proportion B of Sr in the metal element M satisfies 30%≤B≤70%. The negative electrode material has a high first efficiency and good cycle stability, and the preparation method is safe and reliable.

Description

Technical Field

[0001] The invention relates to a doped silicon monoxide negative electrode material and a preparation method thereof. Background Art

[0002] In recent years, under the backdrop of the dual carbon goals of "carbon peak and carbon neutrality", the electrification of automobiles has accelerated significantly. At the same time, range anxiety has also brought about the demand for higher energy density batteries.

[0003] For systems with higher energy densities, major power battery manufacturers have prioritized the combination of high-nickel cathodes and silicon-based anodes. Silicon-based anodes offer higher specific capacity than graphite anodes, but they also face the issue of volume expansion during alloying and lithium insertion. Of the two silicon-based anode process routes, silicon oxide expands slightly less after lithium insertion than pure silicon systems, resulting in superior cycling performance and making it more suitable for power battery applications.

[0004] However, silicon oxide also suffers from a low initial efficiency, stemming from the formation of electrochemically inert phases such as lithium silicate and lithium oxide during the initial lithium insertion process. Furthermore, while silicon oxide's cycling performance is superior to pure silicon, it still leaves much room for improvement compared to graphite. Furthermore, silicon oxide exhibits poor conductivity, with resistivity even exceeding the upper limit of powder resistivity instruments.

[0005] In order to improve the initial efficiency of silicon oxide, both industry and academia have conducted extensive attempts. At present, there are two typical process routes, namely pre-lithiation and pre-magnesiation. The principles of the two methods are similar, that is, to generate an electrochemically inert phase in advance during the material preparation process. Among them, pre-lithiation is represented by Shin-Etsu Chemical, and the raw materials used involve lithium-containing organic reagents, and pre-magnesiation is represented by Dazhou Electronics, and the raw materials used involve magnesium metal. Although both have successfully prepared silicon oxide with high initial efficiency, due to the relatively dangerous raw materials used, many bottlenecks have been encountered in the industrialization process. Therefore, there is an urgent need for a safe and reliable method to improve the initial efficiency of silicon oxide.

[0006] To improve the cycling stability of silicon oxide, industry and academia typically amorphize it, reducing the size growth of silicon grains during cycling and thereby slowing their expansion and cracking. Other studies have found that the presence of a magnesium silicate phase can improve the cycling performance of silicon oxide to some extent. However, these methods have limited effects on the cycling performance of silicon oxide. Therefore, a new and more advanced method is needed.

[0007] In order to improve the conductivity of silicon monoxide, industry and academia have reached a consensus on carbon coating it. Summary of the Invention

[0008] As mentioned above, the range anxiety of electric vehicles has brought about the demand for higher energy density power batteries. On the negative electrode material side, it is necessary to develop a silicon oxide negative electrode material with high initial efficiency and good cycle performance, and its preparation process must be safe and reliable.

[0009] The present invention was developed in response to the above-mentioned problems, and its purpose is to provide a silicon oxide negative electrode material with high initial efficiency and good cycle performance, and a preparation method thereof. The negative electrode material can improve the energy density and cycle stability of power batteries, and the preparation process is safe and reliable.

[0010] In order to achieve the above object, the present invention provides a doped silicon oxide negative electrode material, which is subjected to copper target X-ray diffraction analysis to determine that it contains Si and a general formula of M x Si y O z phase, where 1≤x≤8, 1≤y≤4, 1≤z≤7, and M is a metal element M x Si y O z The represented phase must contain SrSiO3, and the grain size of the silicon (111) crystal plane calculated by the Scherrer formula is ≤10nm. Elemental analysis can be performed to determine that M is a metal element, and its simple substance has a boiling point of ≤1673K at normal pressure. Preferably, in addition to Sr, it also contains Li, and the mass fraction A of M in the entire material satisfies 3%≤A≤15%, wherein the mass fraction B of Sr in the metal element M satisfies 30%≤B≤70%.

[0011] In this way, the negative electrode material has generated an electrochemically inert phase M x Si y O z , the first effect is significantly improved. x Si y O z The phase of M must contain SrSiO3, and the cycle stability of the negative electrode material is also improved. This is because SrSiO3 has good structural stability, which closely connects different phases and improves the stability of the matrix. Preferably, in addition to Sr, M also contains Li, because the silicate phase of Li is also relatively stable and has lithium ion conductivity. In addition to SrSiO3, the general formula M x Si y O zThe representative phase is preferably a silicate phase of Sr and Li such as Sr2SiO4, Li4SiO4, Li2SiO3, and Li2Si2O5. At the same time, the mass fraction A of the metal element M in the whole material should be ≥3%, otherwise it will hardly help to improve the first efficiency of the material, and A should be ≤15%, otherwise the mass specific capacity of the material will drop seriously. At this time, it is preferably 5%≤A≤10%. The mass fraction B of Sr in the metal element should be ≥30% to provide sufficient matrix stability, and B should be ≤70% to ensure the conduction of lithium ions. Preferably, 40%≤B≤60%. In addition, the grain size of the silicon (111) crystal plane calculated by the Scherrer formula is ≤10nm, otherwise even if SrSiO3 exists, the cycle performance of the material will also decrease. At this time, it is preferably: the grain size of the silicon (111) crystal plane calculated by the Scherrer formula is ≤6nm.

[0012] The negative electrode material of the present invention further has a carbon coating layer on its surface. The mass fraction of the carbon coating layer should be ≥0.5% to provide sufficient conductivity, and the mass fraction of the carbon coating layer should be ≤10%, otherwise the specific capacity of the material will decrease.

[0013] Preferably, the mass fraction of the carbon coating layer is 2%≤5%.

[0014] The powder resistivity of the negative electrode material of the present invention should be ≤10Ω·mm, otherwise the conductivity of the material will be insufficient.

[0015] Preferably, the powder resistivity of the negative electrode material is ≤5Ω·mm.

[0016] The negative electrode material of the present invention has a specific surface area of ​​≤5m2 as measured by nitrogen adsorption-desorption method. 2 / g, otherwise more side reactions will be triggered due to the higher specific surface area, resulting in a decrease in the initial efficiency of the material.

[0017] Preferably: the specific surface area of ​​the negative electrode material measured by nitrogen adsorption desorption method is ≤ 2m 2 / g.

[0018] The negative electrode material described in the present invention should have a median particle size of 1 micron or larger. Otherwise, processing difficulties will increase material costs, and the increased specific surface area will also lead to increased side reactions when used as a negative electrode material. Furthermore, the median particle size should be 8 microns or smaller. Otherwise, the material's cycling performance will deteriorate due to volume expansion.

[0019] Preferably, the median particle size of the negative electrode material is 2 microns or less and 6 microns or less.

[0020] The method for preparing the negative electrode material of the present invention comprises the following steps:

[0021] 1. Mix silicon powder and silicon dioxide powder in a certain proportion and granulate them.

[0022] Preferably, the median particle size of the silicon powder should be between 1 micron and 10 microns. If the median particle size is less than 1 micron, the material cost will increase due to the difficulty in preparing the raw materials, and if the median particle size is greater than 10 microns, the reactivity of the silicon powder will decrease.

[0023] More preferably, the median particle size of the silicon powder is 3 microns or less and 6 microns or less.

[0024] The median particle size of the silica powder should be between 0.1 μm and 5 μm. If the median particle size is smaller than 0.1 μm, the material cost will increase, while if the median particle size is larger than 5 μm, the reactivity of the silica powder will decrease.

[0025] More preferably, the median particle size of the silicon dioxide powder is 0.3 μm ≤ 2 μm.

[0026] Preferably, the molar ratio of silicon powder to silicon dioxide powder should be between 1:4 and 3:1. When the molar ratio is less than 1:4, the oxygen content in the material is too high, resulting in a significant decrease in the specific capacity and first efficiency of the material. When the molar ratio is greater than 3:1, the oxygen content in the material is too low, resulting in a significant volume expansion effect of the material, thereby reducing the cycle performance.

[0027] More preferably, the molar ratio of silicon powder to silicon dioxide powder is 9:11≤11:9.

[0028] 2. Heat to T1 under a vacuum degree of 0.1-20 Pa, where 1573K≤T1≤1873K, to generate silicon dioxide vapor.

[0029] The vacuum degree should not be higher than 20 Pa, otherwise the temperature required to generate silicon dioxide vapor will increase, leading to increased material costs. The vacuum degree should not be lower than 0.1 Pa, otherwise the requirements for the vacuum pump will be too high, leading to increased costs.

[0030] Preferably, the vacuum degree is 0.5Pa≤vacuum degree≤10Pa.

[0031] Temperature T1 should not be lower than 1573K, otherwise the rate of silicon dioxide vapor generation will be significantly reduced, resulting in increased reaction time and reduced production efficiency. Temperature T1 should not be higher than 1873K, otherwise the equipment requirements will be too high, increasing production costs, and the rate of silicon dioxide vapor generation will be too fast and uncontrollable.

[0032] Preferably: 1623K≤T1≤1823K.

[0033] 3. Strontium oxide is thoroughly mixed with silicon powder, calcium oxide powder, and fluorite powder in a certain proportion and pressed into a tablet. The tablet is then heated to T2 (1173k≤T2≤1573k) under a vacuum of 0.1-20Pa to generate metallic strontium vapor. The reaction equation is Si(s) + 2SrO(s) + 2CaO(s) → Ca2SiO4(s) + 2Sr(g), where T1 and T2 satisfy the following relationship: 0.75≤17850 / T1-11786.4 / T2≤1.875. Preferably, the mass ratio of metallic strontium vapor to silicon oxide vapor is within the range of 0.9:97-10.5:85.

[0034] The median particle size of strontium oxide should not be less than 0.1 micrometers, otherwise the material cost will increase, and should not be greater than 10 micrometers, otherwise the reaction activity will be low and it will be difficult to react completely.

[0035] Preferably, the median particle size of strontium oxide is 0.5 microns or less and 5 microns or less.

[0036] The molar ratio of strontium oxide to silicon powder should be less than 1 to ensure that the silicon powder is in excess, thereby ensuring that the strontium oxide can react completely. The molar ratio of strontium oxide to silicon powder should be greater than 0.85 to avoid wasting silicon powder.

[0037] Preferably, the molar ratio of strontium oxide to silicon powder is 0.9≤0.95.

[0038] The molar ratio of silicon powder to calcium oxide powder should also be less than 1 to ensure an excess of calcium oxide powder, thereby ensuring that the silicon dioxide produced by the reaction is completely combined with the calcium oxide, thereby ensuring the purity of the metallic strontium vapor. The molar ratio of silicon powder to calcium oxide powder should also be greater than 0.85 to avoid wasting calcium oxide.

[0039] Preferably, the molar ratio of silicon powder to calcium oxide powder is 0.9≤0.95.

[0040] The mass fraction of fluorite powder in the total mass fraction of strontium oxide, silicon powder, calcium oxide powder and fluorite powder is in the range of 1%-5%. If it is less than 1%, the catalytic activity is insufficient, and if it is greater than 5%, it causes waste of resources.

[0041] Preferably, the mass fraction of fluorite powder is 2%≤3%.

[0042] The vacuum level should not exceed 20 Pa, otherwise the temperature of the generated metallic strontium vapor will increase, leading to increased material costs, and the generation rate of metallic strontium vapor will decrease, ultimately affecting the distribution of the metallic element strontium in the material. Furthermore, the vacuum level should not be lower than 0.1 Pa, otherwise the requirements for the vacuum pump will be too high, leading to increased costs.

[0043] Preferably, the vacuum degree is 0.5Pa≤vacuum degree≤10Pa.

[0044] Temperature T2 should not be lower than 1173K, otherwise the generation rate of metallic strontium vapor will be significantly reduced, resulting in increased costs and affecting the distribution of metallic strontium in the material. Temperature T2 should not be higher than 1573K, otherwise it may cause the sublimation of excessive components in the raw materials, resulting in a decrease in the purity of the metallic strontium vapor, thereby affecting the impurity content in the material.

[0045] Preferably: 1223K≤T2≤1523K.

[0046] At the same time, T1 and T2 satisfy the following relationship: 0.75 ≤ 17850 / T1 - 11786.4 / T2 ≤ 1.875. At this point, the mass of the metallic strontium vapor: the mass of the silicon oxide vapor falls within the range of 0.9:97-10.5:85. This not only ensures that the mass fraction of the metallic element strontium in the overall material falls within the desired range, but also facilitates the uniform distribution of the metallic element strontium within the material. This control method primarily utilizes the relationship between the vapor pressures of different reaction products at different temperatures and is simple and easy to implement.

[0047] 4. Lithium oxide is thoroughly mixed with silicon powder, calcium oxide powder, and fluorite powder in a specific proportion and pressed into a tablet. The tablet is then heated to T3 (1223k≤T3≤1573k) under a vacuum of 0.1-20 Pa to generate metallic lithium vapor. The general reaction formula is Si(s) + 2Li2O(s) + 2CaO(s) → Ca2SiO4(s) + 4Li(g), where T2 and T3 satisfy the following relationship: 4.314≤18646.9 / T3-11786.4 / T2≤5.05. At this point, the mass ratio of lithium vapor to strontium vapor is within the range of 3:7 to 7:3.

[0048] The median particle size of lithium oxide should not be less than 0.1 micrometers, otherwise the material cost will increase, and should not be greater than 10 micrometers, otherwise the reaction activity will be low and it will be difficult to react completely.

[0049] Preferably, the median particle size of lithium oxide is 0.5 micrometers or less and 5 micrometers or less.

[0050] The molar ratio of lithium oxide to silicon powder should be less than 1 to ensure that the silicon powder is in excess and the oxide can react completely. The molar ratio of lithium oxide to silicon powder should be greater than 0.85 to avoid wasting silicon powder.

[0051] Preferably, the molar ratio of lithium oxide to silicon powder is 0.9≤0.95.

[0052] The molar ratio of silicon powder to calcium oxide powder should also be less than 1, so that the calcium oxide powder is in excess, ensuring that the silicon dioxide produced by the reaction is completely combined with the calcium oxide, thereby ensuring the purity of the metallic lithium vapor. The molar ratio of silicon powder to calcium oxide powder should also be greater than 0.85 to avoid wasting calcium oxide.

[0053] Preferably, the molar ratio of silicon powder to calcium oxide powder is 0.9≤0.95.

[0054] The mass fraction of fluorite powder in the total mass fraction of lithium oxide, silicon powder, calcium oxide powder and fluorite powder is in the range of 1%-5%. If it is less than 1%, the catalytic activity is insufficient, and if it is greater than 5%, it causes waste of resources.

[0055] Preferably, the mass fraction of fluorite powder is 2%≤3%.

[0056] The vacuum level should not exceed 20 Pa, otherwise the temperature of the lithium metal vapor will increase, leading to increased material costs, and the rate of lithium metal vapor generation will decrease, ultimately affecting the distribution of lithium in the material. The vacuum level should not be lower than 0.1 Pa, otherwise the requirements for the vacuum pump will be too high, leading to increased costs.

[0057] Preferably, the vacuum degree is 0.5Pa≤vacuum degree≤10Pa.

[0058] Temperature T3 should not be lower than 1223K, otherwise the generation rate of metallic lithium vapor will be significantly reduced, resulting in increased costs and affecting the distribution of lithium in the material. Temperature T3 should not be higher than 1573K, otherwise it may cause the sublimation of excessive components in the raw materials, resulting in a decrease in the purity of the metallic lithium vapor, thereby affecting the impurity content in the material.

[0059] Preferably: 1323K≤T3≤1523K.

[0060] At the same time, T2 and T3 satisfy the following relationship: 4.314≤18646.9 / T3-11786.4 / T2≤5.05. At this time, the mass of metallic lithium vapor: the mass of strontium vapor falls within the range of 3:7 to 7:3. In this way, not only can the mass fraction of metallic lithium in the entire material be within the required range, but it is also conducive to achieving a uniform distribution of metallic lithium in the material. This control method mainly utilizes the relationship between the vapor pressures of different reaction products at different temperatures, and the method is simple and easy to implement.

[0061] 5. Silicon dioxide vapor, strontium vapor and lithium vapor are contacted and reacted, and then deposited at a temperature of T4, wherein 773K≤T4≤1073K, and the deposition time is 2-10h to obtain a bulk material.

[0062] Among them, the deposition reaction temperature T4 should not be lower than 773K, otherwise the metal element M will be unevenly distributed in the material due to the excessively fast deposition rate. The deposition temperature T4 should not be higher than 1073K, otherwise not only the deposition rate will be slowed down, but also uncontrollable growth of silicon grains will occur.

[0063] Preferably: 823K≤T4≤973K.

[0064] The deposition time should not be less than 2 hours, otherwise the deposition reaction cannot be completed, and should not be more than 10 hours, otherwise it will cause deposition temperature fluctuations, affect the density and disproportionation degree of the material, and increase costs.

[0065] Preferably, the reaction time is 3h≤reaction time≤6h.

[0066] 6. Crush the block material step by step to obtain powder material.

[0067] Among them, the coarse crushing process can select mechanical crusher, hammer crusher, jaw crusher, roller crusher, etc., preferably mechanical crusher, and the fine crushing process can select air flow crusher, sand mill, ball mill, etc., preferably air flow crusher.

[0068] 7. Carbon coating the powder material by pyrolyzing organic matter in an inert atmosphere at T5 temperature, 873K≤T5≤1173K, reaction time 1-10h.

[0069] The inert atmosphere may be nitrogen, argon, helium or a mixture thereof, and nitrogen is preferred in view of cost.

[0070] T5 should not be lower than 873K, otherwise the organic matter will be incompletely pyrolyzed and the resistivity of the obtained material powder will be too high. It should not be higher than 1173K, otherwise it will cause excessive disproportionation of the material and affect the cyclic performance of the material.

[0071] Preferably: 923K≤T5≤1123K.

[0072] The organic matter can be asphalt, phenolic resin, sucrose, glucose, citric acid, starch, polyvinyl alcohol, cellulose, polyvinyl pyrrolidone, acetylene, methane, propylene, etc., preferably acetylene, methane, propylene and other gaseous carbon sources, because the carbon layer obtained by chemical vapor deposition reaction of the gaseous carbon source has the characteristics of uniformity and density. Acetylene is more preferred because the temperature required for its complete reaction is lower and the deposition process will not cause uncontrollable growth of silicon grains.

[0073] The reaction time should not be less than 1 hour to ensure that the pyrolysis reaction is complete, otherwise the obtained carbon layer may contain unreacted functional groups, resulting in insufficient conductivity of the material. At the same time, the reaction time should not exceed 10 hours, otherwise the obtained carbon coating layer will be too thick, resulting in a decrease in the specific capacity of the material.

[0074] Preferably, the carbon coating reaction time is 1 h ≤ 5 h.

[0075] The positive effect of the present invention is that silicon oxide anode materials are being widely researched to improve the energy density of power batteries. Currently, there is an urgent need to develop a silicon oxide anode material with high initial efficiency and good cycle performance, and its preparation process must be safe and reliable.

[0076] After repeated research, the inventors have proposed a doped silicon oxide negative electrode material with high first efficiency and good cycle performance. Under the optimal process conditions, when the current density is 100mA / g, the reversible capacity is ≥1300mAh / g, the first efficiency is ≥88%, and the capacity retention rate after 50 cycles of power-off is ≥77%, which is significantly better than the undoped silicon oxide negative electrode material, and the preparation process is safe and reliable. DETAILED DESCRIPTION

[0077] Hereinafter, although embodiment of the present invention is described, the present invention is not limited to this embodiment.

[0078] Anode materials

[0079] The negative electrode material is doped silicon oxide, and when it has the following characteristics, the first efficiency is high. The copper target X-ray diffraction analysis can determine that it contains Si and the general formula M x Si y O z The physical phase, where M x Si y O z The represented phase must contain SrSiO3, and the grain size of the silicon (111) crystal plane calculated by the Scherrer formula is ≤10nm. Elemental analysis can determine that M is a metal element. In addition to Sr, it also contains Li. The mass fraction A of M in the entire material satisfies 3%≤A≤15%, among which the mass fraction B of Sr in the metal element M satisfies 30%≤B≤70%.

[0080] The above-mentioned negative electrode material is obtained by in-situ doping of a metal element M during synthesis, wherein the incorporation of the metal element M utilizes the reducibility of silicon under high temperature vacuum conditions. The raw material used is the oxide of the metal M, so the synthesis process is safe and reliable.

[0081] button battery

[0082] A metal lithium sheet was used as the counter electrode and assembled with the above-mentioned negative electrode material into a button cell for testing.

[0083] As the conductive agent of the negative electrode material, Ketjen black, acetylene black, carbon nanotubes, graphene, etc. can be selected.

[0084] As the binder for the negative electrode material, polyvinylidene fluoride, polyimide, polyacrylic acid, CMC, SBR, etc. can be selected.

[0085] As the separator of button batteries, synthetic resin porous membrane or ceramic porous membrane can be selected, and coated separator can also be selected.

[0086] As the electrolyte solvent for button batteries, ethylene carbonate, propylene carbonate, dimethyl carbonate, fluoroethylene carbonate, fluoropropylene carbonate, etc. can be selected. For silicon oxide negative electrode materials, fluorocarbonates are preferred because in this type of solvent, the solid electrolyte interface film formed on the surface of silicon oxide is relatively stable.

[0087] As the electrolyte salt for button batteries, lithium hexafluorophosphate, lithium tetrafluoroborate, LiFSI, etc. can be selected to obtain high lithium ion transport properties.

[0088] Example

[0089] The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[0090] Coin cells were prepared using the following procedure.

[0091] First, the negative electrode material is prepared. Silicon powder and silicon dioxide powder are thoroughly mixed and granulated. The mixture reacts under high-temperature vacuum conditions to produce silicon dioxide vapor. Simultaneously, the silicon powder is mixed with calcium oxide powder, metal M oxide powder, and fluorite powder, and pressed into tablets. The mixture reacts under high-temperature vacuum conditions to produce metal M vapor. Several streams of this vapor are then simultaneously introduced into a deposition chamber for deposition. After complete cooling, a bulk deposit is obtained. Multi-stage pulverization is performed to obtain powdered silicon dioxide with the appropriate particle size and distribution. Finally, this is vapor-phase carbon coated to obtain the negative electrode material.

[0092] The negative electrode material, conductive agent, and binder were mixed in a mass ratio of 8:1:1, diluted with deionized water, and stirred evenly to obtain a negative electrode slurry. The conductive agent was a mixed conductive agent of acetylene black and carbon nanotubes, and the binder was polyacrylic acid.

[0093] The negative electrode slurry is coated on the surface of the copper foil using a coating device and dried to obtain the negative electrode sheet.

[0094] The electrolyte was prepared as follows: 4-fluoro-1,3-dioxolane-2-one (FEC), ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed in a solvent at a volume ratio of 1:2:7, and lithium hexafluorophosphate was dissolved at a ratio of 1.2 mol / kg.

[0095] In a glove box filled with argon, the cut negative electrode sheets, lithium sheets, Cellgard separators, and electrolytes are assembled into button batteries, and the performance of the button batteries is tested in a button test cabinet.

[0096] For the initial charge and discharge characteristics, the first efficiency is calculated as follows: first delithiation capacity / first lithium insertion capacity×100%, and the current density is 100 mA / g.

[0097] The capacity retention rate R was calculated after 50 cycles at a current density of 100 mA / g.

[0098] Among them, the power-on test cabinet is provided by Shenzhen Xinwell, model CT-4008Tn.

[0099] The copper target X-ray diffraction analysis was performed using an Aeris benchtop X-ray diffraction analyzer provided by Malvern Panalytical. The elemental analysis was performed using an inductively coupled plasma optical emission spectrometer provided by Agilent Technologies.

[0100] Example 1

[0101] The silicon powder and silicon dioxide powder were fully mixed in a molar ratio of 1.05:1 and granulated, and reacted under a vacuum degree of 5Pa and T1=1773K to produce silicon dioxide vapor; the silicon powder, calcium oxide powder, strontium oxide powder and fluorite powder were fully mixed in a molar ratio of 1:1.1:0.9:0.06 and pressed into tablets, and reacted under a vacuum degree of 5Pa and T2=1323K to produce metallic strontium vapor; the silicon powder, calcium oxide powder and lithium oxide powder were prepared in a molar ratio of 1:1.1:0.9, and fluorite powder with a mass fraction of 2.5% was added, and the mixture was fully mixed and pressed into tablets, and reacted under a vacuum degree of 5Pa and T3=1373K to produce metal strontium vapor. The vapor of silicon dioxide is lithium; at this time, the mass ratio of silicon dioxide vapor to strontium and lithium vapor is 94.06:2.99:2.95; silicon dioxide vapor and strontium and lithium vapor are then introduced into the deposition chamber simultaneously for reaction and deposition, the temperature is T4 = 873K, the deposition time is 3h, and after complete cooling, block-shaped doped silicon dioxide is obtained; after mechanical crushing and air flow crushing (classifying wheel frequency is 230Hz), doped silicon dioxide with a median particle size of 4.8 microns is obtained; acetylene is used as the carbon source gas for gas-phase carbon coating, the feed amount is 1kg, the flow rate is 1L / min, the temperature is T5 = 1073K, and the time is 2h, and the carbon coating layer has a mass fraction of 3%, a powder resistivity of 4.6Ω·mm, and a specific surface area of ​​1.2m 2 / g of negative electrode material.

[0102] Example 2

[0103] During the process of generating silicon oxide vapor, T1 = 1704K; during the process of generating metallic strontium vapor, T2 = 1267K; at this time, the mass ratio of silicon oxide vapor to strontium and lithium vapor is 90.1:2.96:6.94; silicon oxide vapor and strontium and lithium vapor are then simultaneously introduced into the deposition chamber for reaction and deposition, T4 = 923K, and the deposition time is 2 hours. After complete cooling, bulk doped silicon oxide is obtained; during the air flow milling process, the frequency of the classifier wheel is adjusted to 250Hz; other operations are the same as in Example 1. The final product has a median particle size of 6.2 microns, a powder resistivity of 4.9Ω·mm, and a specific surface area of ​​1.3m 2 / g of negative electrode material.

[0104] Example 3

[0105] During the process of generating silicon oxide vapor, T1 = 1732K; during the process of generating metal strontium vapor, T2 = 1382K; at this time, the mass ratio of silicon oxide vapor to metal strontium and lithium vapor is 85:10.5:4.5; then, silicon oxide vapor and mixed vapor of strontium and lithium are simultaneously introduced into the deposition chamber for reaction and deposition, T4 = 973K, and the deposition time is 2 hours. After complete cooling, bulk doped silicon oxide is obtained; during the air flow milling process, the frequency of the classifying wheel is adjusted to 270Hz; other operations are the same as in Example 1. The final result is a median particle size of 7.6 microns, a powder resistivity of 4.8Ω·mm, and a specific surface area of ​​1.15m 2 / g of negative electrode material.

[0106] Example 4

[0107] During the process of generating silicon oxide vapor, T1 = 1850K; during the process of generating metal strontium vapor, T2 = 1350K; at this time, the mass ratio of silicon oxide vapor to metal strontium and lithium vapor is 97:1.8:1.2; silicon oxide vapor and strontium and lithium vapor are then simultaneously introduced into the deposition chamber for reaction and deposition, T4 = 773K, and the deposition time is 4 hours. After complete cooling, bulk doped silicon oxide is obtained; during the air flow milling process, the frequency of the classifier wheel is adjusted to 240Hz; other operations are the same as in Example 1. The final product has a median particle size of 5.3 microns, a powder resistivity of 4.6Ω·mm, and a specific surface area of ​​1.25m 2 / g of negative electrode material.

[0108] Example 5

[0109] During the process of generating silicon oxide vapor, T1 = 1763K; during the process of generating metal strontium vapor, T2 = 1326K; during the process of generating metal lithium vapor, T3 = 1395K; at this time, the mass ratio of silicon oxide vapor to metal strontium and lithium vapor is 91.33:3.44:5.23; then, silicon oxide vapor and strontium and lithium vapor are simultaneously introduced into the deposition chamber for reaction and deposition, T4 = 1023K, the deposition time is 1 hour, and after complete cooling, block doped silicon oxide is obtained; during the air flow pulverization process, the frequency of the classifying wheel is adjusted to 220Hz; during the gas phase carbon coating process, T5 = 1173K, the time is 1.5 hours; other operations are the same as in Example 1. Finally, the carbon coating layer has a mass fraction of 4.5%, a powder resistivity of 2.1Ω·mm, and a specific surface area of ​​0.95m 2 / g of negative electrode material.

[0110] Comparative Example 1

[0111] During the process of generating silicon oxide vapor, T1 = 1673K; at this time, the mass ratio of silicon oxide vapor to metallic strontium and lithium vapor is 80.7:9.7:9.6; other operations are the same as in Example 1. The final obtained particle size is 4.8 microns, the powder resistivity is 10.2Ω·mm, and the specific surface area is 1.2m 2 / g of negative electrode material.

[0112] Comparative Example 2

[0113] Except for not performing the metal element doping process, other operations were the same as in Example 1. Finally, the obtained median particle size was 4.8 μm, the powder resistivity was 3.8 Ω·mm, and the specific surface area was 1.2 m 2 / g of negative electrode material.

[0114] Comparative Example 3

[0115] In this comparative example, no strontium doping was performed. During the generation of metallic lithium vapor, T3 = 1423K. At this time, the mass ratio of silicon dioxide vapor to metallic lithium vapor was 91.7:8.3. Other operations were the same as in Example 1. The final product had a median particle size of 4.8 μm, a powder resistivity of 4.4 Ω·mm, and a specific surface area of ​​1.2 m 2 / g of negative electrode material.

[0116] Comparative Example 4

[0117] During the process of generating metallic strontium vapor, T2 = 1773K, but due to the high temperature, the excess calcium oxide was also evaporated into vapor; the other operations were the same as in Example 1. The final product had a median particle size of 4.8 μm, a powder resistivity of 20.5 Ω·mm, and a specific surface area of ​​1.2 m 2 / g of negative electrode material.

[0118] Comparative Example 5

[0119] Except for not performing the vapor phase carbon coating, the other operations were the same as in Example 1. Finally, the obtained particles had a median particle size of 4.8 μm, a powder resistivity exceeding the upper limit of the instrument test, and a specific surface area of ​​2.6 m 2 / g of negative electrode material.

[0120] Comparative Example 6

[0121] During the gas phase carbon coating process, T5 = 1273K, the time is 3h, and a negative electrode material with a carbon coating layer mass fraction of 7.8% is obtained; other operations are the same as in Example 1. The final obtained material has a median particle size of 4.8 microns, a powder resistivity of 1.2Ω·mm, and a specific surface area of ​​1.05m 2 / g of negative electrode material.

[0122] The negative electrode materials obtained in the above embodiments and comparative examples were subjected to copper target X-ray diffraction analysis and elemental analysis, and button batteries were assembled for testing. The cutoff voltage was 2 V, and the reversible capacity was obtained. The first effect and 50-cycle capacity retention rate R values ​​were calculated. The results are shown in Table 1.

[0123] Table 1

[0124]

[0125]

[0126] From the results in Table 1, it can be seen that when the negative electrode material contains Si and the general formula M x Si y O z The physical phase, and M x Si y O z The phase represented must contain SrSiO3, the mass fraction A of M in the whole material satisfies 3%≤A≤15%, the mass fraction B of Sr in the metal element M satisfies 30%≤B≤70%, and the grain size of silicon (111) crystal plane is ≤10nm, the negative electrode material has a higher first efficiency and better cycle performance. The higher first efficiency is because M x Si y O z The existence of the physical phase effectively suppresses the irreversible consumption of lithium. It can be found that when the mass fraction A of the metal element M in the whole material satisfies 3%≤A≤15%, the first efficiency of the material is significantly improved, and the degree of improvement of the first efficiency varies with the change of A. When A < 3%, due to the decrease in the oxygen element combined with the metal element M, the material will still produce irreversible lithium consumption during the first lithium insertion process, so the first efficiency is low. When A > 15%, the content of metal element M in the material is too high, and some of it is not based on M. x Si yO z It exists not in the form of SrSiO3, but in the form of oxides, which reduces the conductivity of the material and affects the effect of improving the first efficiency. The better cycle performance is because the presence of the SrSiO3 phase improves the stability of the matrix, and the grain size of the silicon (111) crystal plane is ≤10nm, which ensures that the silicon grains do not grow too fast, thus avoiding the problem of particle cracking to a certain extent. At the same time, the presence of the lithium silicate phase ensures the conduction of lithium ions. When the mass fraction B of Sr in the metal element satisfies 30%≤B≤70%, the material can take into account both matrix stability and stable lithium ion conduction.

[0127] By comparing the embodiment with comparative example 1, it can be found that when A exceeds 15%, the improvement of the first efficiency of the material is less than expected, and the cycle performance is poor. This is because part of M is enriched in the form of metal oxides, and the conductivity of the material decreases, which affects the transmission of lithium ions and electrons in the material.

[0128] By comparing the embodiment with comparative example 2, it can be found that when the material is not doped with the metal element M, the first efficiency and cycle performance are poor.

[0129] By comparing the embodiment with the comparative example 3, it can be found that when the phase M x Si y O z SrSiO3 is not included in the material. Although the initial efficiency of the material is also improved, the cycle performance is still poor. This is because SrSiO3 is the key to improving the stability of the material matrix and thus improving the cycle performance.

[0130] By comparing the embodiment with comparative example 4, it can be found that when metal oxides are introduced into the physical composition of the material due to the high reaction temperature, the first effect and cycle performance of the material are not improved, and the reversible capacity also decreases significantly. The reason for the decrease in the reversible capacity of the material is that the doping is obviously excessive at this time, and a large amount of inactive substances are contained in the system. Among these inactive substances, calcium oxide has poor conductivity, which affects the improvement of the first effect of the material. In addition, excessive doping makes the silicon grain size larger, and dead lithium is easily formed in the area with more inactive substances during the cycle, so the cycle performance deteriorates.

[0131] By comparing the embodiment with comparative example 5, it can be found that the material without carbon coating cannot show high first efficiency and cycle performance even if it is doped with metal elements. This is because the overall electronic conductivity of the material is poor, resulting in the active material losing electrical contact in the first cycle, and this continues to occur during the cycle.

[0132] By comparing the embodiment with comparative example 6, it can be found that when the grain size of the silicon (111) crystal plane is much larger than 10 nm, the cyclic stability of the material decreases significantly. This is because larger silicon grains are more likely to cause particle cracking and thus failure.

[0133] In addition, the present invention is not limited to the above-mentioned embodiments, and any negative electrode material preparation method having substantially the same structure and similar technical concept as described in the claims of the present invention is included in the technical scope of the present invention.

Claims

1. A doped silicon oxide negative electrode material, characterized in that: The copper target X-ray diffraction analysis of the negative electrode material can determine that it contains Si and a general formula of M x Si y O z The physical phase, where 1≤x≤8, 1≤y≤4, 1≤z≤7, M x Si y O z The represented phase must contain SrSiO3, and the grain size of the silicon (111) crystal plane calculated by the Scherrer formula is ≤10nm. The elemental analysis of the negative electrode material: it can be determined that M is a metal element, and its boiling point at normal pressure is ≤1673K; in addition to Sr, it also contains Li, and the mass fraction A of M in the overall negative electrode material satisfies 3%≤A≤15%, wherein the mass fraction B of Sr in M ​​satisfies 30%≤B≤70%.

2. The negative electrode material according to claim 1, wherein: The negative electrode material further comprises a carbon coating layer, wherein the mass fraction of the carbon coating layer is greater than or equal to 0.5% and less than or equal to 10% of the negative electrode material.

3. The negative electrode material according to claim 2, wherein: The mass fraction of the carbon coating layer is greater than or equal to 2% and less than or equal to 5% of the negative electrode material.

4. The negative electrode material according to claim 1, wherein: Its powder resistivity is ≤10Ω·mm; and / or its specific surface area measured by nitrogen adsorption-desorption method is ≤5m 2 / g.

5. The negative electrode material according to claim 1, wherein: The median particle size is greater than 1 micron and less than 8 microns.

6. The method for preparing the negative electrode material according to any one of claims 1 to 5, wherein: The method comprises the following steps: (1) fully mixing silicon powder and silicon dioxide powder and granulating them; (2) heating to T1 under a vacuum degree of 0.1-20 Pa, wherein 1573K≤T1≤1873K, to generate silicon dioxide vapor; (3) fully mixing strontium oxide with silicon powder, calcium oxide powder and fluorite powder and pressing them into tablets, and heating to T2 under a vacuum degree of 0.1-20 Pa, wherein 1173k≤T2≤1573K, to generate metallic strontium vapor, and the reaction formula is Si(s)+2SrO(s)+2CaO(s)→Ca2SiO4(s)+2Sr(g); (4) mixing lithium oxide with silicon powder and oxygen; Calcium chloride powder and fluorite powder are fully mixed and pressed into tablets, and heated to T3 under a vacuum degree of 0.1-20 Pa, 1223k≤T3≤1573K, to generate metallic lithium vapor, and the reaction formula is Si(s)+2Li2O(s)+2CaO(s)→Ca2SiO4(s)+4Li(g); (5) silicon dioxide vapor and metal M vapor containing metal Sr and metal lithium vapor are contacted and reacted, and then deposited at T4 temperature to obtain a bulk material; (6) the bulk material is crushed step by step to obtain a powder material; (7) the powder material is carbon-coated by pyrolyzing organic matter at T5 temperature in an inert atmosphere.

7. The preparation method according to claim 6, wherein T1 and T2 satisfy the following relationship: 0.75≤17850 / T1-11786.4 / T2≤1.

875.

8. The preparation method according to claim 6, wherein T2 and T3 satisfy the following relationship: 3.605≤18646.9 / T3-17850 / T1≤4.

361.

9. The preparation method according to claim 6, wherein 773K≤T4≤1073K, deposition time 2-10h.

10. The preparation method according to claim 6, wherein In step (1), the median particle size of the silicon powder is between 1 μm and 10 μm; and / or the median particle size of the silicon dioxide powder is between 0.1 μm and 5 μm; and / or the molar ratio of the silicon powder to the silicon dioxide powder is between 1:4 and 3:

1.

11. The preparation method according to claim 6 or 7, characterized in that: In step (3): the molar ratio of strontium oxide to silicon powder is 0.85≤≤1, and / or the molar ratio of silicon powder to calcium oxide powder is 0.85≤≤1; and / or the total mass fraction of fluorite powder in the total mass fraction of strontium oxide, silicon powder, calcium oxide powder and fluorite powder is in the range of 1%-5%.

12. The preparation method according to claim 6 or 8, characterized in that: In step (4): the molar ratio of lithium oxide to silicon powder is 0.85≤≤1; and / or the molar ratio of silicon powder to calcium oxide powder is 0.85≤≤1; and / or the mass fraction of fluorite powder in the total mass of lithium oxide, silicon powder, calcium oxide powder and fluorite powder is in the range of 1%-5%.

13. The preparation method according to claim 6, characterized in that The median particle size of the oxide of the metal M used in the preparation process is ≥0.1 micron and ≤10 micron.

14. The preparation method according to claim 6, wherein The temperature of the carbon coating process is 873K≤T5≤1173K, and the reaction time is 1-10h.

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