Battery negative electrode active material and method for producing the same, battery negative electrode, and secondary battery

Abstract

The present invention provides a battery negative electrode active material and a manufacturing method thereof, a battery negative electrode, and a secondary battery. The battery negative electrode active material includes negative electrode active material particles containing a silicon oxide compound and lithium element, and the negative electrode active material particles have a first diffraction peak in the range of 2θ=18.78°±0.2° and a second diffraction peak in the range of 2θ=47.4°±0.3° in X-ray diffraction of Cu-Kα rays, the half width of the first diffraction peak is A>0.34°, the half width of the second diffraction peak is B, and B / A≧1.3. The battery negative electrode active material according to the present application has electrochemical properties with high energy density and good dynamic performance during use. A battery manufactured using such a negative electrode active material has advantages such as high energy density, excellent multiply discharge performance, and fast charge performance.

Description

[Technical Field]

[0001] The present application relates to the field of batteries, and more particularly to a battery negative electrode active material and a method for producing the same, a battery negative electrode, and a secondary battery. [Background technology]

[0002] In recent years, with the development of various portable electronic devices and electric vehicles, the demand for batteries with high energy density and long cycle life has been increasing. Currently, the negative electrode active material of commercially available lithium-ion batteries is mainly graphite, but its low theoretical capacity (372 mAh / g) limits further improvement of the battery's energy density. On the other hand, silicon negative electrode active materials have the characteristic of very high capacity (at room temperature, the lithium intercalation state is Li 15 Si4, with a theoretical lithium storage capacity of approximately 3600mAh / g), which is approximately 10 times the theoretical capacity of currently available graphite anode active materials. This high capacity advantage, which cannot be matched by other anode active materials, has made it the focus of research and development in both academia and industry for many years, and it is gradually moving from laboratory development to market commercialization.

[0003] Currently, there are three main types of silicon anode active materials under development. First, composites of silicon (including nanosilicon, porous silicon, amorphous silicon, etc.) and carbon materials; second, alloys combining silicon with other metals (e.g., iron, manganese, nickel, chromium, cadmium, tin, copper, etc.) or nonmetals (carbon, nitrogen, phosphorus, boron, etc.); and third, composites of silicon oxide compounds and carbon materials. Among these three structures, silicon has the highest theoretical capacity and therefore the highest theoretical energy density. However, silicon anode active materials exhibit a significant volume effect during lithium insertion / extraction, with a volume change rate of approximately 300%, leading to pulverization of the electrode material and separation between the electrode material and the current collector. Furthermore, silicon anode active materials continually expand and contract during battery charging and discharging, resulting in the formation of a new SEI film when the newly formed interface is exposed to the electrolyte, continuously consuming the electrolyte and reducing the cycle performance of the electrode material. The above drawbacks have severely limited the commercial application of elemental silicon negative electrodes.

[0004] Since silicon oxide compounds contain a relatively large amount of inactive materials, their capacity is lower than that of pure silicon as a negative electrode active material. However, due to the presence of these inactive components, the expansion of silicon during cycling is effectively suppressed by the inactive phase, so their cycling stability has obvious advantages.

[0005] Silicon oxide compounds also have their own unique problems. When these materials first intercalate lithium, the particle surface undergoes numerous side reactions with the electrolyte, tending to form a relatively thick SEI film. Furthermore, materials that cannot reversibly de-lithiate lithium, such as lithium silicate and lithium oxide, are formed inside the particles, resulting in the irreversible loss of lithium ions within the battery. These two irreversible reactions result in low initial coulombic efficiency in lithium-ion batteries containing silicon oxide compound anodes, limiting the improvement of the overall battery energy density. Furthermore, silicon oxide compounds have other problems, such as low ionic and electronic conductivity, resulting in relatively low coulombic efficiency during the battery cycling process. To address these issues, researchers have made the following improvements.

[0006] Specifically, to improve the conductivity of silicon oxide compounds and achieve high capacity and better cycle retention, the surface of the silicon oxide compounds can be coated with a conductive material such as a carbon film. To improve the initial charge / discharge efficiency, lithium can be inserted into silicon oxide compounds. This can be achieved by kneading silicon oxide compounds with lithium metal at high temperatures, by electrochemically inserting lithium into silicon oxide compound anodes, by using a high-energy mixer to mix silicon oxide compounds with lithium metal or organolithium compounds as lithiation agents and reacting them in situ, or by reacting lithium-containing compounds with silicon oxide compounds at high temperatures. At the same time, the microstructure and crystalline phase composition of silicon oxide compounds have a significant impact on their electrochemical performance. To achieve better cycle performance, many studies have focused on reducing the size of silicon crystallites within silicon oxide compounds. However, improving the kinetic properties of silicon oxide compounds so that secondary batteries using these anodes can have better discharge and rapid charge performance remains a challenging issue in the industry.

[0007] The content of the background art is based solely on the knowledge of the applicant and does not represent prior art in this technical field. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention provides a battery negative electrode active material that addresses the shortcomings of the prior art. [Means for solving the problem]

[0009] A battery negative electrode active material, comprising negative electrode active material particles including a silicon oxide compound and elemental lithium; the negative electrode active material particles have a first diffraction peak in the range of 2θ=18.78°±0.2° and a second diffraction peak in the range of 2θ=47.4°±0.3° in X-ray diffraction using Cu-Kα rays; The full width at half maximum of the first diffraction peak is A>0.34°, and the full width at half maximum of the second diffraction peak is B, where B / A≧1.3.

[0010] In some embodiments of the present invention, 0.43°≦A≦3° and 1.5≦B / A≦20, preferably 0.55°≦A≦2° and 1.8≦B / A≦15.

[0011] In some embodiments of the present invention, the peak area of ​​the first diffraction peak is defined as C, and the sum of the peak areas of all diffraction peaks in the range of 2θ=10° to 60° in X-ray diffraction of the negative electrode active material particles using Cu-Kα rays is defined as D, where C / D≧0.03, and preferably 0.05≦C / D≦0.2.

[0012] In some embodiments of the present invention, the negative electrode active material particles have a third diffraction peak in the range of 2θ=22° to 23° in Cu-Kα X-ray diffraction, and E / D≦0.02, where E is the peak area of ​​the third diffraction peak.

[0013] In some embodiments of the present invention, the negative electrode active material particles have a fourth diffraction peak in the range of 2θ=23.4° to 25.2° in Cu-Kα X-ray diffraction, and where F is the peak area of ​​the fourth diffraction peak, F / C≦6, preferably F / C≦3, and more preferably F / C≦1.

[0014] In some embodiments of the present invention, the negative electrode active material particles further contain monomeric nanosilicon, and the median particle size of the monomeric nanosilicon dispersed within the negative electrode active material particles is 0.1 to 35 nm, preferably 0.5 to 20 nm, and more preferably 1 to 15 nm.

[0015] In some embodiments of the present invention, the silicon content in the negative electrode active material particles is 30 to 80 wt %, preferably 35 to 65 wt %, and more preferably 40 to 65 wt %.

[0016] In some embodiments of the present invention, the negative electrode active material particles further include a carbon film layer located on the surface thereof.

[0017] In some embodiments of the present invention, the carbon film layer has a thickness of 0.001 to 5 μm, preferably 0.005 to 2 μm, and more preferably 0.01 to 1 μm.

[0018] In some embodiments of the present invention, the mass proportion of the carbon film layer is 0.01 to 20 wt %, preferably 0.1 to 15 wt %, and more preferably 1 to 12 wt %, of the total mass of the negative electrode active material particles.

[0019] The present invention also provides a method for producing a battery negative electrode active material, comprising producing negative electrode active material particles, the method comprising: The negative electrode active material particles are prepared by providing silicon oxide compound particles; and inserting lithium element into the silicon oxide compound particles, the negative electrode active material particles have a first diffraction peak in the range of 2θ=18.78°±0.2° and a second diffraction peak in the range of 2θ=47.4°±0.3° in X-ray diffraction using Cu-Kα rays; The full width at half maximum of the first diffraction peak is A>0.34°, and the full width at half maximum of the second diffraction peak is B, where B / A≧1.3.

[0020] In some embodiments of the present invention, preparing the negative electrode active material particles further comprises coating a part or all of the surfaces of the silicon oxide compound particles with carbon.

[0021] In some embodiments of the present invention, the lithium element is inserted into the silicon oxide compound particles after the surfaces of the silicon oxide compound particles are partially or entirely coated with carbon.

[0022] The present invention also provides a battery negative electrode, a battery negative electrode active material as described above, or The battery negative electrode active material produced by the method described above is included.

[0023] The present invention also provides a secondary battery including the above-described battery negative electrode. [Effects of the Invention]

[0024] The negative electrode active material for a battery according to the present invention has electrochemical properties that provide high energy density and good dynamic performance during use, and batteries manufactured using such negative electrode active material have advantages such as high energy density, excellent multiple discharge performance, and fast charge performance. [Brief explanation of the drawings]

[0025] Additional aspects and advantages of the present invention will be set forth in part in the description that follows, and in part will be obvious from the description, or may be learned by practice of the present invention. [Figure 1] 1 is a process flow chart for manufacturing a negative electrode active material according to an exemplary embodiment of the present application. [Figure 2] 4 is a process flow chart for manufacturing a negative electrode active material according to another exemplary embodiment of the present application. [Figure 3] FIG. 1 is a schematic diagram of half-widths obtained by XRD pattern fitting. [Figure 4] 1 is an XRD pattern of a negative electrode active material produced according to an exemplary embodiment of the present application. [Figure 5] 1 is a SEM photograph of a negative electrode active material produced according to an exemplary embodiment of the present application, magnified 10,000 times; DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, specific embodiments of the present invention will be described in more detail in combination with drawings and embodiments to allow a better understanding of the aspects of the present invention and the advantages of its various aspects. However, the specific embodiments and examples described below are for illustrative purposes only and do not limit the present invention.

[0027] In particular, it goes without saying that all similar substitutions and modifications are apparent to those skilled in the art and are deemed to be included in the present invention. The method and use of the present invention have been described by preferred embodiments, and it is apparent that the techniques of the present invention can be realized and applied by modifying, or appropriately modifying and combining, the method and use described herein without departing from the content, spirit and scope of the present invention.

[0028] [Negative electrode active material] The present invention provides a negative electrode active material for a battery, which has negative electrode active material particles containing a silicon oxide compound and elemental lithium. In the present invention, the silicon oxide compound is preferably in the form of particles.

[0029] The negative electrode active material particles of the present invention have a first diffraction peak in the range of 2θ=18.78°±0.2° in Cu-Kα X-ray diffraction, which is a diffraction peak of the Li2SiO3 phase. In the present invention, the half-value width of the first diffraction peak is A>0.34°.

[0030] Furthermore, the negative electrode active material particles of the present invention have a second diffraction peak in the range of 2θ=47.4°±0.3° in Cu-Kα X-ray diffraction. This diffraction peak is a diffraction peak of the Si(220) crystal plane. In the present invention, the half-width of the second diffraction peak is defined as B, and B / A≧1.3.

[0031] Furthermore, the A value may satisfy 0.43°≦A≦3°, and 0.55°≦A≦2°.

[0032] Furthermore, the B / A value may satisfy 1.5≦B / A≦20. Furthermore, the B / A value may satisfy 1.8≦B / A≦15.

[0033] The present invention selects the FWHMs of the Li2SiO3 phase and Si(220) crystal plane diffraction peaks within the above ranges to obtain anode active materials with appropriate grain size, relatively uniform crystalline domain structure within the particles, and good processability. In the present invention, the larger the FWHMs of the Li2SiO3 and Si phase diffraction peaks (i.e., the larger the A and B values), the more amorphous the Li2SiO3 and Si phases are, resulting in smaller grains and less obstruction to solid-state lithium ion migration within the particles, resulting in better dynamic performance. However, the amorphous Li2SiO3 phase has poor stability and is prone to side reactions with water and air, forming strongly alkaline lithium-containing compounds, which can have a negative impact on the electrochemical performance of the material. Therefore, the A value limited by the present invention is preferably within the range of 0.43°≦A≦3°, more preferably within the range of 0.55°≦A≦2°.

[0034] On the other hand, the Li2SiO3 phase and the Si phase are mutually dispersed. When the grain size ratio of the Li2SiO3 phase to the Si phase is within an appropriate range, the particles can have an appropriate grain size and simultaneously ensure a relatively uniform internal microscale crystalline domain structure. When lithium is repeatedly intercalated and deintercalated and expanded and contracted in the Si phase within the particles, the structure of the present invention is advantageous for uniformly releasing the microscale stress within the particles, reducing particle rupture caused by uneven stress and thereby reducing irreversible capacity loss. By controlling the A value and B / A value within the above ranges, the present invention is advantageous for obtaining a negative electrode active material with good kinetic performance, a uniform internal crystalline domain structure, and high reversible capacity.

[0035] In some embodiments of the present invention, the peak area of ​​the first diffraction peak is defined as C, the sum of the peak areas of all diffraction peaks of the negative electrode active material particles within the 2θ range of 10° to 60° is defined as D (the peak area is obtained by removing the linear background area extending between 2θ of 10° and 60°), and the ratio C / D is ≧0.03. Furthermore, the C / D value can satisfy 0.05≦C / D≦0.2.

[0036] In some embodiments of the present invention, the negative electrode active material particles of the present invention have a third diffraction peak in the range of 2θ=22° to 23° in Cu-Kα X-ray diffraction. The third diffraction peak is a diffraction peak of Li4SiO4. The peak area of ​​the third diffraction peak is E, and E / D≦0.02.

[0037] Furthermore, the negative electrode active material particles of the present invention have a fourth diffraction peak in the range of 2θ=23.4° to 25.2° in Cu-Kα X-ray diffraction. The fourth diffraction peak is a diffraction peak of Li2Si2O5. The peak area of ​​the diffraction peak of Li2Si2O5 is F, and F / C≦6.

[0038] Furthermore, the F / C value may satisfy F / C≦3. Furthermore, the F / C value may satisfy F / C≦1.

[0039] In the present invention, it is preferable to limit the proportions of Li2SiO3, Li4SiO4, and Li2SiO2O5 phases in the negative electrode active material particles to a certain extent. It is preferable for Li2SiO3 and Li2SiO2O5 to be the main phases, and avoid excessively high proportions of the Li4SiO4 phase. This is because a relatively high proportion of the Li4SiO4 phase tends to promote increased Si crystallinity and lead to non-uniform microscale crystalline domain structures within the particles. Controlling the proportions of the Li2SiO3, Li4SiO4, and Li2SiO2O5 phases within the above ranges is advantageous for obtaining a negative electrode active material with high reversible capacity, uniform internal crystalline domain structures, and good dynamic performance.

[0040] In some embodiments of the present invention, the median particle size of the silicon oxide compound particles is 0.2 to 20 microns, preferably 1 to 15 microns, and more preferably 3 to 13 microns.

[0041] In some embodiments of the present invention, the silicon oxide compound particles further contain monomeric nanosilicon, which can be uniformly dispersed within the negative electrode active material particles. The monomeric nanosilicon can be present in the silicon oxide compound particles in the form of nanoparticles, with a median particle size of 0.1 to 35 nm, preferably 0.5 to 20 nm, and more preferably 1 to 15 nm. Particles within this particle size range undergo relatively small particle expansion and are less likely to burst after undergoing cycles of lithium ion insertion and extraction, thereby reducing cycle expansion and stabilizing cycles in lithium ion secondary batteries using this material.

[0042] In some embodiments of the present invention, the silicon content in the negative electrode active material particles is 30 to 80 wt%, preferably 35 to 65 wt%, and more preferably 40 to 65 wt%, so that the material has a high reversible capacity.

[0043] In some embodiments of the present invention, the surface of the negative electrode active material particles is coated with a carbon film layer. The carbon film layer covers part or all of the surface of the silicon oxide compound. The thickness of the carbon film layer is 0.001 to 5 μm, preferably 0.005 to 2 μm, and more preferably 0.01 to 1 μm. The presence of the carbon film layer effectively improves the electrical conductivity of the particles and reduces the contact resistance between the particles in the negative electrode piece and between the negative electrode piece and the current collector, thereby improving the lithium desorption / insertion efficiency of the material, reducing polarization in lithium-ion batteries, and promoting their cycle stability.

[0044] In some embodiments of the present invention, the mass proportion of the carbon film layer is 0.01 to 20 wt %, preferably 0.1 to 15 wt %, and more preferably 1 to 12 wt %, of the total mass of the negative electrode active material particles.

[0045] The negative electrode active material of the battery according to the present invention has electrochemical properties such as high energy density and good dynamic performance during use, and batteries fabricated using such negative electrode active material have advantages such as high energy density, excellent multiple discharge performance, and fast charge performance.

[0046] [Method of manufacturing negative electrode active material] FIG. 1 is a flow chart of the manufacturing process of the above-mentioned negative electrode active material according to an exemplary embodiment of the present application.

[0047] According to some embodiments, silicon oxide compound particles are prepared in step S301. The specific manufacturing process can be carried out by the following steps. First, a mixture of metal silicon powder and silica powder is heated in an inert gas atmosphere or under reduced pressure at a temperature range of 900°C to 1600°C to generate silicon oxide gas, and the molar ratio of metal silicon powder to silica powder can be set to a range of 0.5 to 1.5. The gas generated by the raw material heating reaction is deposited on an adsorption plate. When the temperature in the reactor is lowered to below 100°C, the deposit is removed and pulverized using equipment such as a ball mill or jet mill to obtain silicon oxide compound particles.

[0048] Next, the process proceeds to step S303, where lithium elements are incorporated into the silicon oxide compound particles.

[0049] The present invention can utilize the following lithium element insertion method (lithium doping modification method).

[0050] 1) Electrochemical method The electrochemical cell includes four components: a bath, an anode electrode, a cathode electrode, and a power supply. The anode and cathode electrodes are connected to both ends of the power supply. The anode electrode is connected to a lithium source, and the cathode electrode is connected to a container containing silicon oxide compound particles. The bath is filled with an organic solvent, and the lithium source (anode electrode) and the container containing silicon oxide compound particles (cathode electrode) are immersed in the organic solvent. After power is applied, an electrochemical reaction occurs, during which lithium ions are inserted into the silicon oxide compound structure, resulting in lithium-doped modified silicon oxide compound particles. Examples of the organic solvent include ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, and dimethyl sulfoxide. The organic solvent also contains an electrolyte lithium salt, such as lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), or lithium perchlorate (LiClO4). The lithium source (anode electrode) may be a lithium foil or a lithium compound such as lithium carbonate, lithium oxide, lithium hydroxide, lithium cobalt oxide, lithium iron phosphate, lithium manganate, lithium vanadium phosphate, or lithium nickel oxide.

[0051] 2) Liquid phase doping method Metallic lithium, an electron transfer catalyst, and silicon oxide compound particles are added to an ether-based solvent, and the reaction is maintained at a constant temperature while stirring and heating in a non-oxidizing atmosphere until the metallic lithium in the solution is completely dissolved. The electron transfer catalyst dissolves the metallic lithium in the ether-based solvent, forming a lithium ion coordination compound with a lower reduction potential, which reacts with the silicon oxide compound, allowing the lithium ion to enter the silicon oxide compound structure. The electron transfer catalyst includes biphenyl, naphthalene, etc. The ether-based solvent includes methyl butyl ether, ethylene glycol monobutyl ether, tetrahydrofuran, dimethoxyethane, etc. The reaction temperature is 25 to 200°C. The non-oxidizing atmosphere is provided by at least one gas selected from nitrogen, argon, hydrogen, and helium.

[0052] 3) Thermal doping method Silicon oxide compound particles are uniformly mixed with a lithium-containing compound, followed by heat treatment in a non-oxidizing atmosphere. The lithium-containing compound includes lithium hydroxide, lithium carbonate, lithium oxide, lithium peroxide, lithium hydride, lithium nitrate, lithium acetate, lithium gallate, etc. The mixing method uses any one of a high-speed disperser, high-speed stirrer, ball mill, taper mixer, spiral mixer, stirring mixer, and VC mixer. The heat treatment equipment is any one of a rotary hearth, ladle refining furnace, inner pot furnace, roller kiln, pusher kiln, atmospheric box furnace, and tube furnace. The heat treatment temperature is 400°C to 850°C, preferably 550°C to 800°C, and more preferably 550°C to 750°C. The incubation time is 1 to 12 hours, preferably 2 to 12 hours, and more preferably 4 to 12 hours. The heating rate is greater than 0.1°C / min and less than 10°C / min, preferably 0.1 to 5°C / min, and more preferably 0.1 to 3°C / min. The non-oxidizing atmosphere is provided by at least one gas selected from the group consisting of nitrogen, argon, hydrogen, and helium.

[0053] The inventors have found through research that in the above-mentioned heat treatment lithium doping reaction process, the selection of the heat treatment temperature, the heat-holding time, and the temperature rise rate have a significant impact on the crystalline structure of the resulting negative electrode active material and the uniformity of the micro-scale crystalline domains inside the particles, thereby affecting the dynamic performance and cycle stability of the material. The higher the heat treatment temperature, the stronger the crystallinity of the resulting negative electrode active material becomes, and the more likely it is that the Si phase and lithium silicate phase (Li) with too large a crystal grain size will be formed. X SiO Y ), resulting in poor dynamic performance of the material. Meanwhile, the selection of the heat-up time and heat-up rate significantly affects the uniformity of the crystalline domains within the material. A too-fast heat-up rate can easily result in uneven heating of the particles, resulting in excessive localized grain growth. On the other hand, a too-short heat-up time can easily result in uneven lithium doping within the particles, resulting in lithium-rich outer shells and lithium-poor inner cores, which also result in localized grain growth. Therefore, the above-mentioned heat-treatment temperature, heat-up time, and heat-up rate ranges are preferred, which are advantageous for obtaining a negative electrode active material with a uniform internal crystalline domain structure, appropriate grain size, good dynamic performance, and high reversible capacity.

[0054] In some embodiments of the present invention, the silicon oxide compound particles have a stoichiometric ratio of silicon to oxygen of 1:0.4 to 1:2, optionally 1:0.6 to 1:1.5, and further optionally 1:0.8 to 1:1.2, and contain trace amounts of other impurity elements in addition to silicon and oxygen.

[0055] According to some embodiments, as shown in FIG. 2, step S303 may further include step S302 of coating the surface of the silicon oxide compound particles with a carbon film layer before inserting lithium element.

[0056] The lithium doping step S303 is performed after the carbon film layer is coated, which can suppress the growth of silicon crystal grains in the silicon oxide compound during heat treatment. This allows nanoscale silicon particles to be uniformly dispersed and fixed within the lithium silicate compound or silicone compound matrix, effectively suppressing the expansion of silicon nanoparticles and preventing the silicon particles from gradually melting and becoming larger particles during charging and discharging. This reduces the expansion and deformation during battery cycling, reduces electrical failure of the silicon material, and reduces the cycling expansion and stabilizes the cycles of lithium-ion secondary batteries using this material. Furthermore, performing the carbon film layer coating step before the lithium doping step is advantageous for coating a higher-quality, more complete carbon film layer.

[0057] In some embodiments of the present invention, the silicon oxide compound used may be a non-dispersed silicon oxide compound, or may be a silicon oxide compound that has been heat-treated for dispersing. The heat-treatment temperature for dispersing may be 600°C to 1100°C, preferably 700°C to 1000°C, and more preferably 800°C to 1000°C.

[0058] The carbon film layer is directly obtained by chemical vapor deposition (CVD), and the carbon source used in CVD is a hydrocarbon compound gas, whose decomposition temperature is 600°C to 1100°C, preferably 700°C to 1000°C, and more preferably 800°C to 1000°C.

[0059] The carbon film layer may be obtained by first coating via a carbon reaction, followed by carbonization via heat treatment in a non-oxidizing atmosphere. The carbon reaction coating method can use any one of a mechanical blender, VC mixer, coating kettle, spray dryer, sand mill, or high-speed disperser. The solvent used during coating can be one or a combination of water, methanol, ethanol, isopropyl alcohol, N-butanol, ethylene glycol, ether, acetone, N-methylpyrrolidone, methylbutanone, tetrahydrofuran, benzene, toluene, dimethylbenzene, N,N-dimethylformamide, N,N-dimethylacetamide, and chloroform. The carbon reaction source can be one or a combination of coal tar pitch, petroleum pitch, polyvinyl alcohol, epoxy resin, polyacrylonitrile, polymethylmethacrylate, glucose, sucrose, polyacrylic acid, and polyvinylpyrrolidone. The equipment used for the heat treatment carbonization can be any one of a rotary kiln, ladle refining furnace, roller kiln, pusher kiln, atmospheric box furnace, and tube furnace. The temperature for the heat treatment carbonization is 600°C to 1100°C, preferably 700°C to 1000°C, and more preferably 800°C to 1000°C, and the temperature retention time is 0.5 to 24 hours. The non-oxidizing atmosphere may be provided by at least one gas selected from nitrogen, argon, hydrogen, and helium.

[0060] According to some embodiments, the silicon oxide compound particles may be completely, partially, or not at all coated with a carbon film layer.

[0061] [Method for characterizing negative electrode active materials] 1. Material Testing: The characteristics of the negative electrode active materials prepared in each example and comparative example were evaluated using the following equipment. A Dandong BetterSize 2000 laser granulometer was used to measure the particle size distribution of the negative electrode active material. A Rigaku Miniflex 600 powder X-ray diffractometer (XRD) was used to measure the composition and crystalline structure of the obtained negative electrode material. The 2θ angle range was 10° to 60°, the scanning speed was 1° / min, the step size was 0.02°, and the X-ray source power was 600W. The half-width measurement method used in this application was as shown in Figure 3. After removing the linear background between 10° and 60° from the measured X-ray diffraction spectrum using Jade software, fitting was performed on the corresponding diffraction peak. The fitted peak and the measured spectrum were essentially overlapped, and the half-width of the fitted peak was read as the half-width of the corresponding diffraction peak. At the same time, the peak area of ​​the diffraction peak used in this application was also measured as described above, using the peak area of ​​the fitted peak as the peak area of ​​the diffraction peak. A Hitachi SU8010 scanning electron microscope is used to observe the surface morphology of the negative electrode active material.

[0062] 2. Preparation of homogenate and electrode pieces: 14 parts of the above negative electrode active material, 81 parts of artificial graphite, 2.5 parts of conductive additive, and 2.5 parts of adhesive are taken, and homogenized in an aqueous system, then dried and rolled to obtain negative electrode pieces containing the negative electrode active material of the present invention.

[0063] 3. Whole battery evaluation: The negative electrode pieces of the negative active materials prepared in each example and comparative example were cut, vacuum baked, and wound together with the paired positive electrode pieces and the partition film, then placed in an aluminum shell of the corresponding size, and a certain amount of electrolyte was injected, gas was removed, and the shell was sealed. After formation, a lithium-ion whole battery of approximately 3.2 Ah was obtained. The capacity, energy, and constant current charge rate of the whole battery at 0.2 C and 3 C were measured using a battery tester from Shenzhen Newwill Electronics Co., Ltd.

[0064] The present invention will now be further described with reference to specific examples.

[0065] Example 1-1 1000 grams of silicon oxide compound particles having a median diameter of 5 microns and an atomic ratio of silicon to oxygen of 1:1 were prepared.

[0066] The silicon oxide compound powder, lithium metal ribbon, and biphenyl were placed in a sealable glass container, and methyl butyl ether was added. The mixture was stirred and reacted under an argon atmosphere. After the reaction was completed and the mixture was dried, the resulting powder was heat-treated in an argon atmosphere, heated to 850°C at a rate of 5°C / min, and then allowed to cool for two hours. The resulting lithium-doped silicon oxide compound powder was obtained after natural cooling. The XRD spectrum and SEM image of the material are shown in Figures 4 and 5.

[0067] The spectrum obtained by X-ray diffraction using Cu-Kα ray diffractometry has a diffraction peak of the Li2SiO3 phase in the 2θ range of 18.78° ± 0.2°. The half-width of this diffraction peak is A = 0.34, and the peak area of ​​this diffraction peak is C. At the same time, the material also has a diffraction peak for the Si(220) crystal plane in the 2θ range of 47.4° ± 0.3°. The half-width of this diffraction peak is B, with B / A = 4. The material also has a Li2SiO5 diffraction peak in the 2θ range of 23.4° to 25.2°, and the peak area of ​​this Li2SiO5 diffraction peak is F. The sum of the peak areas of all diffraction peaks in the 2θ range of 10° to 60° in this diffraction spectrum is defined as D (the linear background area between 10° and 60° in 2θ is removed from this peak area). The resulting values ​​are C / D = 0.12 and F / C = 0.4 (see Table 1). Since this material does not contain the diffraction peak of the Li4SiO4 phase in the range of 2θ=22° to 23°, the diffraction peak area E of the Li4SiO4 phase can be considered to be zero.

[0068] 14 parts of the above negative electrode active material, 81 parts of artificial graphite, 2.5 parts of conductive additive, and 2.5 parts of adhesive were homogenized in an aqueous system, and some of the aqueous homogenized slurry was taken for water resistance and stability tests, and the other slurry was applied, followed by drying and rolling to obtain silicon-containing negative electrode pieces.

[0069] In this example, the results of whole-cell evaluation of the negative electrode active material were that the constant current charge ratio (CCCCR) was 75.9% at a 3C rapid charge rate, the mass energy density was 261.5Wh / kg at a 3C discharge rate, and the ratio of the energy density at a 3C discharge rate to the energy density at a 0.2C discharge rate was 86.3%.

[0070] Example 1-2 1000 grams of silicon oxide compound particles with a median diameter of 5 microns were placed in a CVD furnace. A coating reaction was carried out at 950°C using acetylene as the carbon source, resulting in silicon oxide compound particles completely coated with a carbon film layer, the thickness of which was 20 nm.

[0071] Next, lithium metal doping was performed using a thermal doping method. Specifically, the above particles were taken and mixed with a lithium-containing compound (e.g., lithium oxide, lithium hydride, lithium hydroxide, lithium carbonate, etc.), and the mixed powder was heat-treated in an argon atmosphere to heat up to 800°C at a heating rate of 3°C / min, and then kept at that temperature for 3 hours. After natural cooling, a lithium-containing silicon oxide compound coated with a carbon film was obtained.

[0072] As shown in Table 1 below, in this example, A=0.43, B / A=4, C / D=0.12, and F / C=0.4, and the material does not contain any diffraction peaks of the Li4SiO4 phase.

[0073] In this example, the results of whole-cell evaluation of the negative electrode active material were that the constant current charge ratio (CCCCR) was 79.84% at a 3C fast charge rate, the mass energy density was 268.9Wh / kg at a 3C discharge rate, and the ratio of the energy density at a 3C discharge rate to the energy density at a 0.2C discharge rate was 89.4%.

[0074] Examples 1-3 to 1-16 The particle size of the silicon oxide compound was controlled to 5 microns, and a 20 nm thick carbon film layer was coated on the surface of the silicon oxide compound using the aforementioned chemical vapor deposition or carbon reactive coating methods. Lithium doping was then carried out using the aforementioned electrochemical doping, thermal doping, or liquid phase doping methods. By adjusting parameters such as the carbonization temperature during the carbon film coating process, the lithium doping amount during the lithium doping reaction, the heat treatment temperature, the incubation time, and the heating rate, the crystalline structure and uniformity of the microscale crystalline domains of the material were altered, resulting in anode active materials with different A and B / A values.

[0075] The results are shown in Table 1 below, and none of Examples 1-3 to 1-16 contain a diffraction peak of the Li4SiO4 phase. Table 1 shows the 3C rapid charge performance and 3C multiple discharge performance of these example materials.

[0076] Comparative Example 1-1 1000 grams of silicon oxide compound particles with a median diameter of 5 microns and a silicon to oxygen atomic ratio of 1:1 were prepared and subjected to a lithium doping reaction using the liquid phase doping method. The resulting powder was heat-treated in an argon atmosphere, heated to 900°C at a rate of 15°C / min, and then kept at that temperature for 2 hours before being naturally cooled to obtain lithium-doped silicon oxide compound powder.

[0077] Comparative Example 1-2 1000 grams of silicon oxide compound particles with a median diameter of 5 microns were placed in a CVD furnace. A coating reaction was carried out at 1200°C using acetylene as the carbon source. Next, lithium metal doping was carried out using an electrochemical method, resulting in a lithium-containing silicon oxide compound coated with a carbon film.

[0078] Table 1 shows the material structure parameters (A value, B / A value, etc.) of Comparative Examples 1-1 and 1-2, as well as the 3C rapid charge performance and 3C multiply discharge performance.

[0079] [Table 1]

[0080] As can be seen from a comparison with the data of Examples 1-1 to 1-16, the energy density, rapid charge performance, and multiply discharge performance of Comparative Example 1-1 were poor. This was because its A value was 0.25 and the crystal grain size was large, which affected the kinetics of the material. On the other hand, the energy density, rapid charge performance, and multiply discharge performance of Comparative Example 1-2 were also poor. Although its A value was greater than 0.34, its B / A value was only 1, which similarly affected the kinetics of the material.

[0081] Comparing the results of Examples 1-1 to 1-16, when the A value satisfies 0.55°≦A≦2° and the B / A value satisfies 1.8≦B / A≦15, the Li2SiO3 and Si phase grains of the material are small, while the Li2SiO3 phase has a certain degree of crystallinity to maintain material stability. The microcrystalline domain structure within the material particles is more uniform, and the grain sizes of the Li2SiO3 and Si phases are not significantly different. Therefore, the material exhibits less inhibition of solid-state lithium ion migration within the particles, resulting in good dynamic performance. Furthermore, this structure favors uniform release of microscopic stress within the particles, reducing particle rupture caused by stress unevenness and the resulting irreversible capacity loss. Therefore, examples in this range exhibit higher energy density and optimal 3C fast charge and 3C multiply discharge performance.

[0082] Examples 2-1 to 2-6 The particle size of the silicon oxide compound was controlled to 5 microns, and a 20 nm thick carbon film layer was coated on the surface of the silicon oxide compound using the aforementioned chemical vapor deposition or carbon reactive coating method. The lithium doping reaction was then carried out using the aforementioned electrochemical doping method, thermal doping method, or liquid phase doping method. By adjusting parameters during the lithium doping reaction, such as the lithium doping amount, heat treatment temperature, incubation time, and heating rate, negative electrode active materials with different C / D values ​​were obtained. The specific results are shown in Table 2.

[0083] [Table 2]

[0084] As can be seen from a comparison of the data of Examples 2-1 to 2-6, when the C / D value is too small (Example 2-6), the energy density of the battery using the material is affected to some extent, and when the C / D value is between 0.05 and 0.2, the 3C rapid charge performance, 3C multiple discharge performance, and energy density are good.

[0085] Examples 3-1 to 3-4 The particle size of the silicon oxide compound was controlled to 5 microns, and a 20 nm thick carbon film layer was coated on the surface of the silicon oxide compound using the aforementioned chemical vapor deposition or carbon reactive coating method. The lithium doping reaction was then carried out using the aforementioned electrochemical doping method, thermal doping method, or liquid phase doping method. By adjusting parameters such as the lithium doping amount, heat treatment temperature, incubation time, and heating rate during the lithium doping reaction, negative electrode active materials with different E / D values ​​were obtained. The specific results are shown in Table 3.

[0086] [Table 3]

[0087] As can be seen from a comparison of the data in Examples 3-1 to 3-4, when E / D is greater than 0.02, the energy density and fast charge and discharge performance of the battery using this material are affected to some extent. This is because a relatively large proportion of the Li4SiO4 phase tends to enhance the crystallinity of Si and cause non-uniformity in the microscale crystalline domain structure inside the particles.

[0088] Examples 4-1 to 4-5 As in Examples 3-1 to 3-4, negative electrode active materials with different F / C values ​​were obtained by adjusting parameters such as the lithium doping amount during the lithium doping reaction, the heat treatment temperature, the heat-keeping time, and the temperature rise rate, as shown in Table 4.

[0089] [Table 4]

[0090] As can be seen from a comparison of the data of Examples 4-1 to 4-5, when F / C is greater than 6, the energy density, rapid charge performance, and multiply discharge performance of the battery using the material are affected to some extent.

[0091] It is clear that the above examples are only for clarifying the examples described herein and do not limit the embodiments. Those skilled in the art can make various changes and variations based on the above description. It is not necessary to fully describe all the embodiments here, and the description cannot be exhaustive. Any obvious changes or variations brought about thereby still fall within the scope of protection of the present invention.

Claims

1. A battery negative electrode active material, comprising negative electrode active material particles including a silicon oxide compound and elemental lithium; the negative electrode active material particles have a first diffraction peak in the range of 2θ=18.78°±0.2° and a second diffraction peak in the range of 2θ=47.4°±0.3° in X-ray diffraction using Cu—Kα rays; A battery negative electrode active material, wherein the half width of the first diffraction peak is A>0.34°, the half width of the second diffraction peak is B, and B / A≧1.

3.

2. 2. The battery negative electrode active material according to claim 1, wherein 0.43°≦A≦3° and 1.5≦B / A≦20.

3. 2. The battery negative electrode active material according to claim 1, wherein C is a peak area of ​​the first diffraction peak, D is a sum of peak areas of all diffraction peaks in the range of 2θ=10° to 60° in X-ray diffraction of the negative electrode active material particles using Cu-Kα rays, and C / D≧0.

03.

4. 2. The battery negative electrode active material according to claim 1, wherein the negative electrode active material particles have a third diffraction peak in a range of 2θ=22° to 23° in X-ray diffraction with Cu-Kα rays, the peak area of ​​the third diffraction peak is E, the sum of the peak areas of all diffraction peaks in a range of 2θ=10° to 60° in X-ray diffraction with Cu-Kα rays of the negative electrode active material particles is D, and E / D≦0.

02.

5. 2. The battery negative electrode active material according to claim 1, wherein a peak area of ​​the first diffraction peak is defined as C, the negative electrode active material particles have a fourth diffraction peak in the range of 2θ=23.4° to 25.2° in Cu-Kα X-rays, a peak area of ​​the fourth diffraction peak is defined as F, and F / C≦6.

6. 2. The battery negative electrode active material according to claim 1, wherein the negative electrode active material particles further comprise silicon nanoparticles, and the silicon nanoparticles dispersed within the negative electrode active material particles have a median particle size of 0.1 to 35 nm.

7. 2. The battery negative electrode active material according to claim 1, wherein the silicon content in the negative electrode active material particles is 30 to 80 wt %.

8. The battery negative electrode active material of claim 1 , wherein the negative electrode active material particles further comprise a carbon film layer located on the surface thereof.

9. 9. The battery negative electrode active material according to claim 8, wherein the carbon film layer has a thickness of 0.001 to 5 μm.

10. 9. The battery negative electrode active material according to claim 8, wherein the mass ratio of the carbon film layer is 0.01 to 20 wt % of the total mass of the negative electrode active material particles.

11. 1. A method for producing a battery negative electrode active material, comprising: preparing negative electrode active material particles, The preparation of the negative electrode active material particles includes: providing silicon oxide compound particles; and inserting lithium element into the silicon oxide compound particles, the negative electrode active material particles have a first diffraction peak in the range of 2θ=18.78°±0.2° and a second diffraction peak in the range of 2θ=47.4°±0.3° in Cu—Kα X-rays; A method for producing a battery negative electrode active material, wherein the half width of the first diffraction peak is A>0.34°, the half width of the second diffraction peak is B, and B / A≧1.

3.

12. The method according to claim 11, wherein preparing the negative electrode active material particles further comprises coating a part or all of the surfaces of the silicon oxide compound particles with carbon.

13. 13. The method according to claim 12, wherein the lithium element is incorporated into the silicon oxide compound particles after the surfaces of the silicon oxide compound particles are partially or entirely coated with carbon.

14. A battery negative electrode, A battery negative electrode comprising the battery negative electrode active material according to any one of claims 1 to 10.

15. A secondary battery comprising the battery negative electrode according to claim 14.

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