Negative electrode material, and electrochemical device and electronic device comprising same

Abstract

The present application relates to a negative electrode material, and electrochemical devices and electronic devices comprising the same. The negative electrode material of the present application comprises silicon-based particles, which comprise a silicon-containing matrix having at least a portion of its surface having M y SiO z layer; wherein M comprises Li, Mg, Ca, Sr, Ba, Al, Ti, Zn, or any combination thereof; and 0

Description

TECHNICAL FIELD

[0001] The present application relates to the field of energy storage, and in particular to a negative electrode material, an electrochemical device and an electronic device comprising the same, and especially a lithium ion battery. BACKGROUND

[0002] With the popularity of consumer electronics such as notebook computers, mobile phones, tablet computers, mobile power supplies and unmanned aerial vehicles, the requirements for the electrochemical devices therein are becoming more and more stringent. For example, not only is the battery required to be light, but it is also required to have high capacity and long service life. Lithium ion batteries have occupied a dominant position in the market due to their outstanding advantages of high energy density, high safety, no memory effect and long service life. SUMMARY

[0003] The embodiments of the present application provide a negative electrode material and a method for preparing the same in an attempt to solve at least one problem existing in the related art to at least some extent. The embodiments of the present application also provide a negative electrode, an electrochemical device and an electronic device comprising the negative electrode material.

[0004] In one embodiment, the present application provides a negative electrode material, which comprises silicon-based particles, the silicon-based particles comprising a silicon-containing substrate, at least a part of the surface of the silicon-containing substrate having a M y SiO z layer; wherein M y SiO z the layer comprises a combination of Li2SiO3 and at least one of Mg2SiO4, MgSiO3, CaSiO3, SrSiO3, BaSiO3, Al2SiO5, TiSiO4, Zn2SiO4; and 0 < y < 3 and 0.5 < z < 6.

[0005] In one embodiment, the present application provides a method for preparing a negative electrode material, which comprises:

[0006] (1) subjecting the surface of a silicon-containing substrate to thermal oxidation treatment to obtain a silicon material having a silicon dioxide surface; and

[0007] (2) mixing the silicon material having a silicon dioxide surface with a Q source, and subjecting the mixed material to thermal treatment at 400-1600°C for 1-5h;

[0008] (3) mixing the material obtained in step (2) with a lithium source, and subjecting the mixed material to thermal treatment at 400-1600°C for 1-5h to obtain the negative electrode material;

[0009] wherein Q comprises Mg, Ca, Sr, Ba, Al, Ti, Zn or any combination thereof.

[0010] In another embodiment, the present application provides a negative electrode comprising the negative electrode material according to the embodiments of the present application.

[0011] In another embodiment, the present application provides an electrochemical device comprising the negative electrode according to the embodiments of the present application.

[0012] In another embodiment, the present application provides an electronic device comprising the electrochemical device according to the embodiments of the present application.

[0013] The present application avoids the direct contact between the silicon particles and the electrolyte by designing the silicon core-shell composite structure, thereby improving the problem of cycle capacity attenuation caused by the side reaction between the particle surface and the electrolyte during the cycle of the silicon material. The negative electrode material has a high initial coulombic efficiency and good cycle performance.

[0014] Additional layers and advantages of the embodiments of the present application will be described and shown in part in the following description and drawings, or will be understood or apparent to those skilled in the art upon reading and understanding the embodiments of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0015] The drawings necessary for describing the embodiments of the present application or the prior art will be briefly described in the following in order to facilitate the description of the embodiments of the present application. Obviously, the drawings in the following description are only part of the embodiments in the present application. Those skilled in the art can still obtain the drawings of other embodiments according to the structures illustrated in these drawings without creating labor.

[0016] Figure 1 A structure diagram of the silicon-based particles in the negative electrode material in one embodiment of the present application is shown.

[0017] Figure 2 An X-ray diffraction (XRD) diagram of the silicon-based particles in the negative electrode material in Embodiment 1 of the present application is shown.

[0018] Figure 3 A cross-sectional scanning electron microscope (SEM) picture of the silicon-based particles in the negative electrode material in Embodiment 1 of the present application is shown.

[0019] Figure 4 A local magnified view of the cross-sectional scanning electron microscope (SEM) picture of the silicon-based particles in the negative electrode material in Embodiment 1 of the present application is shown.

[0020] Figure 5A A cross-sectional scanning electron microscope (SEM) picture of the silicon-based particles in the negative electrode material in Embodiment 1 of the present application is shown. Figure 5B An energy dispersive spectroscopy (EDS) picture of the silicon-based particles in the negative electrode material in Embodiment 1 of the present application is shown.

[0021] Figure 6 Charge-discharge curves from button cell testing in Example 1 of the present application are shown.

[0022] Figure 7 Cycle curves from button cell testing in Example 1, Comparative Example 1, and Comparative Example 2 of the present application are shown. DETAILED DESCRIPTION

[0023] Embodiments of the present application will be described in detail below. Embodiments of the present application should not be construed as limiting the present application.

[0024] As used in this application, the term "about" is used to describe and account for small variations. When used in connection with a quantity, the term can refer to the exact value or an approximate value within a range of values. For example, when used in connection with a numerical value, the term can refer to a range of variation less than or equal to ± 10% of the numerical value, such as less than or equal to ± 5%, less than or equal to ± 4%, less than or equal to ± 3%, less than or equal to ± 2%, less than or equal to ± 1%, less than or equal to ± 0.5%, less than or equal to ± 0.1%, or less than or equal to ± 0.05%.

[0025] Additionally, amounts, ratios, and other numerical values are sometimes presented herein in a range format. It is to be understood that such range format is used for convenience and brevity and should be understood as having been preceeded by the word "about." Therefore, specifically claimed amounts also include the recited amount in a range from plus or minus the experimental error (or 10% of the recited amount, whichever is greater) to plus or minus 20% of the recited amount.

[0026] In the DETAILED DESCRIPTION and in the claims, a list of items joined by the term "one of" or "one or more of" can mean any single one of the listed items. For example, if a list of items includes A and B, then the phrase "one of A and B" means only A or only B. In another example, if a list of items includes A, B, and C, then the phrase "one of A, B, and C" means only A; only B; or only C. Item A can include a single element or multiple elements. Item B can include a single element or multiple elements. Item C can include a single element or multiple elements.

[0027] In the specific embodiments and claims, a list of items connected by terms such as "at least one of", "at least one in", "at least one kind in" or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0028] I. Anode material

[0029] An embodiment of the present application provides an anode material, which includes silicon-based particles, and the silicon-based particles include a silicon-containing matrix, and at least a part of the surface of the silicon-containing matrix has a M y SiO z layer; where M y SiO z layer includes a combination of Li2SiO3 and at least one of Mg2SiO4, MgSiO3, CaSiO3, SrSiO3, BaSiO3, Al2SiO5, TiSiO4, Zn2SiO4; and 0 < y < 3, and 0.5 < z < 6.

[0030] In some embodiments, Q includes at least one of Mg, Ca, Sr, Ba, Al, Ti or Zn.

[0031] In some embodiments, the M y SiO z layer includes Li2SiO3, Li2Si2O5, Mg2SiO4, MgSiO3, CaSiO3, SrSiO3, BaSiO3, Al2SiO5, TiSiO4, Zn2SiO4 or any combination thereof.

[0032] In some embodiments, when the M y SiO z layer includes Li2SiO3 and / or Li2Si2O5, the M y SiO z layer further includes at least one of Mg2SiO4, MgSiO3, CaSiO3, SrSiO3, BaSiO3, Al2SiO5, TiSiO4 or Zn2SiO4.

[0033] In some embodiments, the M y SiO zThe layer includes Li2SiO3and Mg2SiO4.

[0034] In some embodiments, the M y SiO z The layer has a thickness of about 50-200 nm. In some embodiments, the M y SiO z The layer has a thickness of about 50-150 nm. In some embodiments, the M y SiO z The layer has a thickness of about 70 nm, about 90 nm, about 100 nm, about 120 nm, about 140 nm, about 160 nm, about 180 nm, or a range consisting of any two of these thicknesses.

[0035] In some embodiments, the M y SiO z At least a portion of the surface of the layer has a carbon layer. In some embodiments, the carbon layer includes carbon nanotubes, carbon nanoparticles, carbon fibers, graphene, conductive carbon black, or any combination thereof. In some embodiments, the carbon nanotubes include single-walled carbon nanotubes, multi-walled carbon nanotubes, or any combination thereof.

[0036] In some embodiments, the carbon layer has a thickness of about 1-500 nm. In some embodiments, the carbon layer has a thickness of about 100-400 nm. In some embodiments, the carbon layer has a thickness of about 10 nm, about 50 nm, about 100 nm, about 150 nm, about 200 nm, about 250 nm, about 300 nm, about 350 nm, about 400 nm, about 450 nm, or a range consisting of any two of these thicknesses.

[0037] In some embodiments, the sum of the weight percentages of the Q element and the Li element is about 0.5-15 wt%, based on the total weight of the silicon-based particle. In some embodiments, the sum of the weight percentages of the Q element and the Li element is about 1-12 wt%, based on the total weight of the silicon-based particle. In some embodiments, the sum of the weight percentages of the Q element and the Li element is about 2 wt%, about 3 wt%, about 4 wt%, about 5 wt%, about 6 wt%, about 7 wt%, about 8 wt%, about 9 wt%, about 10 wt%, about 11 wt%, about 12 wt%, about 13 wt%, about 14 wt%, or a range consisting of any two of these weight percentages, based on the total weight of the silicon-based particle.

[0038] In some embodiments, the weight percent of Li element is about 0-5 wt% based on the total weight of the silicon-based particle. In some embodiments, the weight percent of Li element is about 1-4 wt% based on the total weight of the silicon-based particle. In some embodiments, the weight percent of Li element is about 0.5 wt%, about 1 wt%, about 1.5 wt%, about 2 wt%, about 2.5 wt%, about 3 wt%, about 3.5 wt%, about 4 wt%, about 4.5 wt%, or a range consisting of any two of these weight percents, based on the total weight of the silicon-based particle.

[0039] In some embodiments, the weight percent of Mg element is about 0.5-10 wt% based on the total weight of the silicon-based particle. In some embodiments, the weight percent of Mg element is about 1-9 wt% based on the total weight of the silicon-based particle. In some embodiments, the weight percent of Mg element is about 2 wt%, about 2.5 wt%, about 3 wt%, about 3.5 wt%, about 4 wt%, about 4.5 wt%, about 5 wt%, about 6 wt%, about 7 wt%, about 8 wt%, about 9 wt%, or a range consisting of any two of these weight percents, based on the total weight of the silicon-based particle.

[0040] In some embodiments, the weight percent of carbon layer is about 0.1-10 wt% based on the total weight of the silicon-based particle. In some embodiments, the weight percent of carbon layer is about 0.5-8 wt% based on the total weight of the silicon-based particle. In some embodiments, the weight percent of carbon layer is about 1 wt%, about 1.5 wt%, about 2 wt%, about 2.5 wt%, about 3 wt%, about 4 wt%, about 5 wt%, about 6 wt%, about 7 wt%, about 8 wt%, about 9 wt%, or a range consisting of any two of these weight percents, based on the total weight of the silicon-based particle.

[0041] In some embodiments, the silicon-containing matrix comprises SiO x , and 0.6≤x≤1.5.

[0042] In some embodiments, the silicon-containing matrix comprises Si grains, SiO, SiO2, SiC, or any combination thereof.

[0043] In some embodiments, the silicon-containing matrix comprises micron Si, nano Si, or a combination thereof. In some embodiments, the average particle size of the micron Si is about 1-10 μm. In some embodiments, the average particle size of the micron Si is about 1 μm, about 1.5 μm, about 2 μm, about 2.5 μm, about 3 μm, about 3.5 μm, about 4 μm, about 5 μm, about 6 μm, about 7 μm, about 8 μm, about 9 μm, about 10 μm, or a range consisting of any two of these average particle sizes.

[0044] In some embodiments, the average particle size of the nano-Si is about 1-100 nm. In some embodiments, the average particle size of the nano-Si is about 10-80 nm. In some embodiments, the average particle size of the nano-Si is about 5 nm, about 10 nm, about 15 nm, about 20 nm, about 25 nm, about 30 nm, about 40 nm, about 50 nm, about 60 nm, about 70 nm, about 80 nm, about 90 nm, or a range consisting of any two of these average particle sizes.

[0045] In some embodiments, the average particle size of the silicon-based particle is about 500 nm-30 μm. In some embodiments, the average particle size of the silicon-based particle is about 1 μm-25 μm. In some embodiments, the average particle size of the silicon-based particle is about 5 μm, about 10 μm, about 15 μm, about 20 μm, or a range consisting of any two of these values.

[0046] In some embodiments, the specific surface area of the silicon-based particle is about 2.5-15 m 2 / g. In some embodiments, the specific surface area of the silicon-based particle is about 5-10 m 2 / g. In some embodiments, the specific surface area of the silicon-based particle is about 3 m 2 / g, about 4 m 2 / g, about 6 m 2 / g, about 8 m 2 / g, about 10 m 2 / g, about 12 m 2 / g, about 14 m 2 / g, or a range consisting of any two of these values.

[0047] II. Method for preparing negative electrode material

[0048] Embodiments of the present application provide a method for preparing any of the above negative electrode materials, the method comprising:

[0049] (1) subjecting the surface of a silicon-containing substrate to thermal oxidation treatment to obtain a silicon material having silicon dioxide on the surface; and

[0050] (2) mixing the silicon material having silicon dioxide on the surface with a Q source, and subjecting the mixture to thermal treatment at about 400-1600°C for about 1-5 h;

[0051] (3) mixing the material obtained in step (2) with a lithium source, and subjecting the mixture to thermal treatment at 400-1600°C for 1-5 h to obtain the negative electrode material;

[0052] wherein Q comprises Mg, Ca, Sr, Ba, Al, Ti, Zn, or any combination thereof.

[0053] In some embodiments, the anode material comprises silicon-based particles. In some embodiments, the anode material is silicon-based particles.

[0054] In some embodiments, the thermal oxidation process comprises thermally oxidizing the silicon-containing substrate in a gas containing oxygen at a temperature in the range of about 400-1500 °C for a time in the range of about 2-12 h.

[0055] In some embodiments, the gas containing oxygen comprises pure oxygen, water vapor, air, or any combination thereof.

[0056] In some embodiments, the thermal oxidation temperature is in the range of about 400-1100 °C. In some embodiments, the thermal oxidation temperature is in the range of about 600-1000 °C. In some embodiments, the thermal oxidation temperature is about 500 °C, about 600 °C, about 700 °C, about 800 °C, about 900 °C, about 1000 °C, about 1100 °C, about 1200 °C, about 1300 °C, or a range defined by any two of these temperatures.

[0057] In some embodiments, the thermal oxidation time is in the range of about 2-10 h. In some embodiments, the thermal oxidation time is in the range of about 4-8 h. In some embodiments, the thermal oxidation time is about 3 h, about 4 h, about 5 h, about 6 h, about 7 h, about 8 h, about 9 h, about 10 h, or a range defined by any two of these times.

[0058] In some embodiments, the thermal oxidation process is performed in a tube furnace, a box furnace, or a rotary kiln.

[0059] In some embodiments, the weight ratio of the silicon-containing substrate to the Q source is in the range of about 10: 1-120: 1. In some embodiments, the weight ratio of the silicon-containing substrate to the Q source is in the range of about 10: 1-50: 1. In some embodiments, the weight ratio of the silicon-containing substrate to the Q source is about 15: 1, about 20: 1, about 25: 1, about 30: 1, about 35: 1, about 40: 1, about 50: 1, about 55: 1, about 60: 1, about 70: 1, about 80: 1, about 90: 1, about 100: 1, about 110: 1, about 120: 1, or a range defined by any two of these values.

[0060] In some embodiments, the Q source comprises a magnesium source, an aluminum source, or any combination thereof. In some embodiments, the magnesium source comprises magnesium chloride, magnesium acetate, magnesium sulfate, magnesium hydroxide, magnesium carbonate, magnesium powder, or any combination thereof.

[0061] In some embodiments, the aluminum source comprises aluminum oxide, aluminum chloride, aluminum ethoxide, aluminum sulfate, aluminum nitrate, or any combination thereof.

[0062] In some embodiments, the lithium source comprises lithium powder, lithium hydride, lithium oxide, lithium hydroxide, lithium carbonate, lithium aluminum hydride, lithium borohydride, or any combination thereof.

[0063] In some embodiments, the heat treatment in step (2) is performed under an inert gas. In some embodiments, the inert gas comprises helium, argon, nitrogen, or any combination thereof.

[0064] In some embodiments, the heat treatment in step (2) is performed in a tube furnace, a box furnace, or a rotary kiln.

[0065] In some embodiments, the heat treatment temperature in step (2) is about 500-1600 °C. In some embodiments, the heat treatment temperature is about 800-1300 °C. In some embodiments, the heat treatment temperature is about 600 °C, about 700 °C, about 800 °C, about 900 °C, about 1000 °C, about 1100 °C, about 1200 °C, about 1300 °C, about 1400 °C, about 1500 °C, or a range consisting of any two of these temperatures.

[0066] In some embodiments, the heat treatment time in step (2) is about 1-5 h. In some embodiments, the heat treatment time in step (2) is about 1.5-4 h. In some embodiments, the heat treatment time in step (2) is about 1.2 h, about 1.4 h, about 1.6 h, about 1.8 h, about 2 h, about 2.5 h, about 3 h, about 4 h, or a range consisting of any two of these times.

[0067] In some embodiments, the method comprises a step of mixing the silicon material having a surface with silicon dioxide with a carbon source between step (1) and step (2). In some embodiments, further comprising ball milling after the mixing. In some embodiments, the silicon material having a surface with silicon dioxide and a carbon layer is obtained after the ball milling.

[0068] In some embodiments, the weight ratio of the silicon material having a surface with silicon dioxide to the carbon source is about 20: 1-120: 1. In some embodiments, the weight ratio of the silicon material having a surface with silicon dioxide to the carbon source is about 20: 1, about 25: 1, about 30: 1, about 35: 1, about 40: 1, about 45: 1, about 50: 1, about 60: 1, about 70: 1, about 80: 1, about 90: 1, about 100: 1, about 110: 1, about 120: 1, or a range consisting of any two of these ratios.

[0069] In some embodiments, the carbon source comprises carbon nanotubes, carbon nanoparticles, carbon fibers, graphene, conductive carbon black, or any combination thereof. In some embodiments, the carbon nanotubes comprise single-walled carbon nanotubes, multi-walled carbon nanotubes, or any combination thereof.

[0070] In some embodiments, the ball milling is a liquid phase ball milling in a ball milling jar. In one embodiment, a drying step is further included after the ball milling.

[0071] In some embodiments, when Q is Mg, Ca, Sr, Ba, Al, Ti, Zn or any combination thereof, step (2) has only one doping step.

[0072] The failure of silicon as an anode material is mainly due to a series of problems caused by the huge volume expansion after lithium intercalation, and the continuous thickening of the solid electrolyte interface (SEI) film caused by the high reactivity of the silicon surface with the electrolyte. The thickening of the SEI film continuously consumes reversible lithium, thereby causing capacity decay. The present application designs and synthesizes a silicon core-shell composite structure to avoid direct contact between silicon particles and electrolyte, thereby improving the problem of cycle capacity decay caused by side reactions between the particle surface and electrolyte during the cycle of silicon material.

[0073] The shell layer in the silicon core-shell composite structure can be Li2SiO3, Li2Si2O5, Mg2SiO4, MgSiO3, CaSiO3, SrSiO3, BaSiO3, Al2SiO5, TiSiO4, Zn2SiO4 or any combination thereof. When Li2SiO3, Li2Si2O5 or a combination thereof is present in the shell layer, in order to enhance the stability of the silicon core-shell composite structure to water, the shell layer can also contain at least one of Mg2SiO4, MgSiO3, CaSiO3, SrSiO3, BaSiO3, Al2SiO5, TiSiO4 or Zn2SiO4.

[0074] The shell layer of the present application can also have a carbon layer. In this case, the present application first performs carbon coating after the silicon material is oxidized, and then performs Q element and Li element doping. At this time, the Q element and Li element can perform doping reaction on the oxidized silicon shell layer through solid phase diffusion during thermal doping, thereby retaining the outermost carbon layer.

[0075] The anode material of the present application can significantly improve the cycle performance of the lithium ion battery prepared therefrom, while the specific capacity and the first coulombic efficiency do not change significantly.

[0076] Figure 1 A structural schematic diagram of a silicon-based particle in the anode material in one embodiment of the present application is shown. The inner layer 1 is a silicon-containing matrix, the middle layer 2 is a M y SiO z layer, and the outer layer 3 is a carbon layer.

[0077] Figure 2 An X-ray diffraction (XRD) pattern of a silicon-based particle in the anode material in Example 1 of the present application is shown. The Figure 2It can be seen that the silicon-based particles in the negative electrode material in Example 1 contain both Li2SiO3and Mg2SiO4. It is illustrated that the silicon-based core-shell composite structure contains Li2SiO3and Mg2SiO4components.

[0078] Figure 3 A cross-sectional scanning electron microscope (SEM) picture of the silicon-based particles in the negative electrode material in Example 1 of the present application is shown. It can be seen that the silicon-based particles have a core-shell structure. Figure 3 It can be seen that the composite shell layer exists in the silicon-based core-shell composite particles.

[0079] Figure 4 A local magnified picture of the cross-sectional scanning electron microscope (SEM) picture of the silicon-based particles in the negative electrode material in Example 1 of the present application is shown. It can be seen more clearly that the composite shell layer exists. Figure 4 It can be seen more clearly that the composite shell layer exists.

[0080] Figure 5A A cross-sectional scanning electron microscope (SEM) picture of the silicon-based particles in the negative electrode material in Example 1 of the present application is shown. Figure 5B A cross-sectional element distribution line scanning (EDS) picture of the silicon-based particles in the negative electrode active material in Example 1 of the present application is shown. Figure 5B It is shown that the magnesium content is higher in the edge region of the silicon-based particles, which illustrates that the magnesium silicate shell layer exists. At the same time, the carbon element signal of the outermost layer shows that the carbon layer exists on the surface of the silicon-based particles.

[0081] III. Negative electrode

[0082] The present application provides a negative electrode. The negative electrode comprises a current collector and a negative electrode material layer on the current collector. The negative electrode material layer comprises the negative electrode material according to the embodiments of the present application.

[0083] In some embodiments, the negative electrode active material layer comprises a binder. In some embodiments, the binder comprises, but is not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, butadiene rubber, acrylic butadiene rubber, epoxy resin or nylon.

[0084] In some embodiments, the negative electrode active material layer comprises a conductive material. In some embodiments, the conductive material comprises, but is not limited to, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, metal powder, metal fiber, copper, nickel, aluminum, silver or polyphenylene derivative.

[0085] In some embodiments, the current collector comprises, but is not limited to, copper foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper or polymer substrate coated with conductive metal.

[0086] In some embodiments, the negative electrode can be obtained by mixing a negative electrode active material, a conductive material, and a binder in a solvent to obtain a slurry, and coating the slurry on a current collector.

[0087] In some embodiments, the solvent can include, but is not limited to, deionized water or N-methylpyrrolidone.

[0088] IV. Positive Electrode

[0089] Materials, compositions, and methods of manufacturing thereof that can be used for the positive electrode in embodiments of the present application include any of the techniques disclosed in the prior art. In some embodiments, the positive electrode is the positive electrode described in U.S. Patent Application US9812739B, which is incorporated herein by reference in its entirety.

[0090] In some embodiments, the positive electrode includes a current collector and a positive electrode active material layer on the current collector.

[0091] In some embodiments, the positive electrode active material includes, but is not limited to, lithium cobalt oxide (LiCo02), lithium nickel cobalt manganese (NCM) ternary material, lithium iron phosphate (LiFeP04), or lithium manganese oxide (LiMn204).

[0092] In some embodiments, the positive electrode active material layer further includes a binder, and optionally, a conductive material. The binder improves the binding of the positive electrode active material particles to each other, and also improves the binding of the positive electrode active material to the current collector.

[0093] In some embodiments, the binder includes, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyethylene oxide-containing polymer, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, or nylon, etc.

[0094] In some embodiments, the conductive material includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0095] In some embodiments, the current collector can include, but is not limited to, aluminum.

[0096] The cathode can be prepared by a method known in the art. For example, the cathode can be obtained by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and coating the active material composition on a current collector. In some embodiments, the solvent can include, but is not limited to, N-methylpyrrolidone.

[0097] V. Electrolyte

[0098] The electrolyte that can be used in the embodiments of the present application can be an electrolyte known in the art.

[0099] In some embodiments, the electrolyte includes an organic solvent, a lithium salt, and an additive. The organic solvent of the electrolyte according to the present application can be any organic solvent known in the art that can be used as a solvent of an electrolyte. The electrolyte used in the electrolyte according to the present application is not limited, and can be any electrolyte known in the art. The additive of the electrolyte according to the present application can be any additive known in the art that can be used as an additive of an electrolyte.

[0100] In some embodiments, the organic solvent includes, but is not limited to, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, or ethyl propionate.

[0101] In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt.

[0102] In some embodiments, the lithium salt includes, but is not limited to, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis-trifluoromethanesulfonimide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalato)borate LiB(C2O4)2 (LiBOB), or lithium difluoro(oxalato)borate LiBF2(C2O4) (LiDFOB).

[0103] In some embodiments, the concentration of the lithium salt in the electrolyte is about 0.5-3 mol / L, about 0.5-2 mol / L, or about 0.8-1.5 mol / L.

[0104] VI. Separation film

[0105] In some embodiments, a separation film is provided between the cathode and the anode to prevent short circuiting. The material and shape of the separation film that can be used in the embodiments of the present application are not particularly limited, and can be any of the techniques disclosed in the art. In some embodiments, the separation film includes a polymer or an inorganic material formed of a material stable to the electrolyte of the present application, etc.

[0106] For example, the separator film can include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, a film, or a composite film having a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used.

[0107] The surface treatment layer is provided on at least one surface of the substrate layer, and can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

[0108] The inorganic layer includes inorganic particles and a binder, and the inorganic particles are selected from one or a combination of several of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from one or a combination of several of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0109] The polymer layer includes a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0110] Seven, electrochemical device

[0111] Embodiments of the present application provide an electrochemical device, which includes any device in which an electrochemical reaction occurs.

[0112] In some embodiments, the electrochemical device of the present application includes a positive electrode sheet having a positive electrode active material capable of occluding and releasing metal ions; a negative electrode according to embodiments of the present application; an electrolyte; and a separator film disposed between the positive electrode and the negative electrode.

[0113] In some embodiments, the electrochemical device of the present application includes, but is not limited to, a primary battery, a secondary battery, a fuel cell, a solar cell, or a capacitor of all kinds.

[0114] In some embodiments, the electrochemical device is a lithium ion battery. In some embodiments, the electrochemical device is a lithium secondary battery.

[0115] In some embodiments, the lithium secondary battery includes, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0116] Eight, electronic device

[0117] The electronic device of the present application can be any device using the electrochemical device according to the embodiments of the present application.

[0118] In some embodiments, the electronic device includes, but is not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, portable telephones, portable facsimile machines, portable copying machines, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, portable cleaners, portable CD players, mini-disc players, transceivers, electronic organizers, calculators, memory cards, portable audio recorders, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, bicycles, lighting appliances, toys, game machines, timepieces, power tools, flashlights, cameras, home-use large storage batteries or lithium-ion capacitors, etc.

[0119] The preparation of lithium-ion batteries is described below using lithium-ion batteries as an example and in conjunction with specific embodiments. Those skilled in the art will understand that the preparation methods described in the present application are merely examples, and any other suitable preparation method is within the scope of the present application.

[0120] Embodiments

[0121] The following describes performance evaluation according to the embodiments and comparative examples of the coin-type batteries of the present application.

[0122] I. Test method for negative electrode material powder properties

[0123] (1) XRD test: 1.0-2.0 g of the sample was weighed into the recess of a glass sample holder and compacted and ground flat with a glass sheet. The X-ray diffractometer (Bruker, D8) was used to perform the test according to JJS K 0131-1996 "General rules for X-ray diffraction analysis". The test voltage was set to 40 kV, the current was 30 mA, the scanning angle range was 10-40°, the scanning step was 0.0167°, and the time set for each step was 0.24 s. The XRD diffraction pattern was obtained.

[0124] (2) EDS line scanning test method: EDS line scanning was performed using OXFORD-EDS, and the voltage was 20 kV.

[0125] (3) Scanning electron microscope (SEM) test: The scanning electron microscope characterization was recorded by a Philips XL-30 field emission scanning electron microscope under the conditions of 10 kV and 10 mA.

[0126] (4) Shell thickness test method: The shell thickness was obtained by measuring the shell thickness of the particle surface in the SEM cross-sectional view of the particle.

[0127] (5) Method for determining the content of each element in silicon-based negative electrode active material:

[0128] About 0.2 g of silicon-based negative electrode active material was weighed into a beaker made of polytetrafluoroethylene (PTFE), and the sample weight was recorded after the digital balance measurement stabilized to 0.0001 g. About 10 mL of concentrated HNO3 and about 2 mL of HF were slowly added to the sample, which was placed on a flat heater at about 220°C and heated and digested until almost evaporated. About 10 mL of nitric acid was slowly added, and the heating and digestion was continued for about 15 min to fully dissolve the sample. The dissolved sample was placed in a fume hood and cooled to room temperature. The sample solution was shaken well and slowly poured into a funnel with a single layer of filter paper, and the beaker and filter residue were rinsed 3 times. The volume was adjusted to about 50 mL at about 20±5°C, and shaken well. The ion spectral intensity of the filtrate was tested using an inductively coupled plasma (ICP) emission spectrometer (PE 7000), and the ion concentration was calculated according to the standard curve, so as to calculate the content of elements contained in the sample.

[0129] II. Method for testing the electrical properties of negative electrode active material

[0130] 1. Method for preparing button cell and testing charge and discharge capacity:

[0131] Under a dry argon environment, LiPF6 was added to a solvent mixed from propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) (weight ratio about 1:1:1) and mixed uniformly, wherein the concentration of LiPF6 was about 1.15 mol / L. After adding about 7.5 wt% of fluoroethylene carbonate (FEC) and mixing uniformly, an electrolyte was obtained.

[0132] The silicon-based negative electrode active material obtained in the examples and comparative examples, conductive carbon black, and binder PAA (modified polyacrylic acid, PAA) were added to deionized water in a weight ratio of about 80:10:10, stirred to form a slurry, and coated with a doctor blade to form a coating layer with a thickness of about 100 μm. The coating layer was dried in a vacuum drying oven at about 85°C for about 12 hours, cut into a circular piece with a diameter of about 1 cm in a dry environment using a punch press, and assembled into a button cell in a glove box using a lithium metal sheet as the counter electrode, a ceglard composite membrane as the separator membrane, and an electrolyte. The button cell was tested for charge and discharge by using a LAND series battery tester.

[0133] The button cell was discharged at a rate of 0.05C to 5 mV, then changed to 5 mV constant voltage discharge until the current dropped to 10 uA; then charged at a rate of 0.05C to 2V to complete the charge and discharge capacity test, and the initial coulombic efficiency was the ratio of the charge capacity to the discharge capacity.

[0134] 2. Cycle performance test:

[0135] The button cell prepared above was discharged at a rate of 0.05C to 5 mV at 25°C, and then changed to 5 mV constant voltage discharge until the current dropped to 10 μA; then charged at a rate of 0.05C to 2V to complete one charge-discharge cycle. The above charge-discharge cycle was repeated to test the cycle performance of the button cell.

[0136] III. Preparation of silicon-based negative electrode active material

[0137] 1. The silicon-based negative electrode active material in Example 1 was prepared according to the following method:

[0138] (1) Micron silicon particles (average particle size Dv50 = 4 μm) were placed in a tube furnace with air, heat treated at 800°C for 5 hours to obtain silicon material with a silicon oxide shell;

[0139] (2) The above oxidized silicon particles (hereinafter referred to as "A1") were mixed with carbon nanotubes at a weight ratio of 99:1, and then ball milled in a ball mill tank for 4 hours at a speed of 300 revolutions per minute;

[0140] (3) The silicon material after ball milling in step (2) (hereinafter referred to as "A2") was mixed with nano-magnesium oxide at a weight ratio of 95:5 using a V-type mixer, and then heat treated at 1100°C for 2 hours in a tube furnace with argon;

[0141] (4) The silicon material obtained in step (3) (hereinafter referred to as "A3") was mixed with lithium hydride powder at a weight ratio of 98:2, and then heat treated at 600°C for 2 hours in a tube furnace with argon to obtain silicon-based particles as a silicon-based negative electrode active material.

[0142] The preparation methods of the silicon-based negative electrode active materials in Examples 2-9 and Comparative Examples 2 and 3 were similar to that in Example 1, except that the amounts of carbon nanotubes, nano-magnesium oxide or lithium hydride powder were different, as shown in Table 1. When the content of carbon nanotubes, nano-magnesium oxide or lithium hydride powder was 0, it meant that the corresponding step was not performed. The silicon-based negative electrode active material in Comparative Example 1 was micron silicon itself.

[0143] Table 1 shows the weight ratio of the amounts of each substance used in the preparation methods of the silicon-based negative electrode active materials in Examples 1-9 and Comparative Examples 1-3.

[0144] Table 1

[0145]

[0146]

[0147] Table 2 shows the composition of the silicon-based negative electrode active materials in Examples 1-9 and Comparative Examples 1-3.

[0148] Table 2

[0149]

[0150] Table 3 shows the performance test results of the button cells prepared from the silicon-based negative active materials in Examples 1-9 and Comparative Examples 1-3.

[0151] Table 3

[0152]

[0153]

[0154] From the performance test results of Examples 1-9 and Comparative Examples 1-3, it can be seen that the cycle performance of the micron silicon can be significantly improved after the micron silicon is oxidized, then a carbon layer is prepared on the surface of the micron silicon, and then the micron silicon is doped with magnesium and / or lithium, while the first coulombic efficiency does not change significantly.

[0155] Figure 6 The charge-discharge curve obtained from the button cell test in Example 1 of the present application is shown, and it can be seen that the silicon-based negative active material in Example 1 has a high discharge specific capacity and a high first coulombic efficiency.

[0156] Figure 7 The cycle curve obtained from the button cell test in Example 1, Comparative Example 1 and Comparative Example 2 of the present application is shown. Figure 7 It can be seen that the cycle performance of the button cell in Example 1 is significantly better than that of the button cell in Comparative Example 1.

[0157] The reference to “some embodiments”, “particular embodiments”, “one embodiment”, “another embodiment”, “an embodiment”, “the embodiment”, “particular embodiments” or “some embodiments” throughout the specification, means that at least one embodiment of the application or example contains the particular feature, structure, material, or characteristic being described in connection with that reference. Therefore, appearances of the phrases such as “in some embodiments”, “in embodiments”, “in one embodiment”, “in another embodiment”, “in the embodiment”, “in an embodiment”, “in particular embodiments” or “in some embodiments” throughout this specification do not necessarily refer to the same embodiment or example of the application, unless otherwise indicated. Additionally, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples.

[0158] Although illustrative embodiments have been shown and described, a person of ordinary skill in the art will understand that the above-described embodiments are not to be construed as limiting, and that changes, alternatives, and modifications can be made to the embodiments without departing from the spirit, principles, and scope of the application.

Claims

1. A method for preparing a negative electrode material, the method comprising: (1) subjecting a surface of a silicon-containing substrate to a thermal oxidation treatment to obtain a silicon material having a surface with silicon dioxide; and (2) subjecting the silicon material having a surface with silicon dioxide to ball milling after mixing with a carbon source to obtain a silicon material having a surface with silicon dioxide and a carbon layer; (3) subjecting the silicon material having a surface with silicon dioxide and a carbon layer to mixing with a Q source, and subjecting the mixed material to a heat treatment at 400-1600℃ for 1-5h; (4) subjecting the material obtained in step (3) to mixing with a lithium source, and subjecting the mixed material to a heat treatment at 400-1600℃ for 1-5h to obtain the negative electrode material; wherein Q comprises at least one of Mg, Ca, Sr, Ba, Al, Ti or Zn; the negative electrode material comprises silicon-based particles having a core-shell composite structure, the inner layer of the silicon-based particles is a silicon-containing substrate, the intermediate layer of the silicon-based particle is a layer of M y SiO z wherein the M y SiO z layer comprises a combination of Li2SiO3 and at least one of Mg2SiO4, MgSiO3, CaSiO3, SrSiO3, BaSiO3, Al2SiO5, TiSiO4, Zn2SiO4; 0<y<3, and 0.5<z<6; and The outer layer of the silicon-based particle is a carbon layer on at least a portion of the surface of the M y SiO z layer; and The specific surface area of the silicon-based particles is 5-15 m 2 / g. 2.The method of claim 1, wherein the weight percentage of Li element is 0.5-5wt% based on the total weight of the silicon-based particles.

3. The method of claim 1, wherein the M y SiO z thickness of the layer is 50-200 nm. 4.The method of claim 1, wherein the thickness of the carbon layer is 1-500nm; and / or, wherein the weight percentage of the carbon layer is 0.1-10wt% based on the total weight of the silicon-based particles. 5.The method of claim 1, wherein the sum of the weight percentages of Q element and Li element is 0.5-15wt% based on the total weight of the silicon-based particles. 6.The method of claim 1, wherein the silicon-containing substrate comprises micro-Si, nano-Si or a combination thereof. 7.A negative electrode comprising the negative electrode material prepared by the method of any one of claims 1-6. 8.An electrochemical device comprising the negative electrode of claim 7. 9.An electronic device comprising the electrochemical device of claim 8.

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