A coated LiSi-C material, electrode and battery

Abstract

The present invention relates to the field of battery technology, and in particular to a coated LiSi-C material and a preparation method thereof, a pole piece and a battery comprising the coated LiSi-C material. The coated LiSi-C material has a core-shell structure, wherein the core of the coated LiSi-C material is a LiSi-C particle, the shell of the coated LiSi-C material is an oxygen-containing coating layer, and the LiSi-C particle has a continuous phase structure in which a LiSi phase and a C phase are uniformly doped; there is a characteristic peak in the X-ray diffraction pattern of the LiSi-C particle, and the characteristic peak is attributed to 23°-24° in 2θ and to 41°-42° in 2θ. The coated LiSi-C material of the present invention can improve cycle performance and stability in aqueous slurry; the pole piece of the present invention has better cycle stability and lower expansion performance; the battery of the present invention has higher first charge and discharge efficiency, lower deformation rate and better cycle performance.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a coated LiSi-C material and a preparation method thereof, and a pole piece and a battery comprising the coated LiSi-C material. Background Art

[0002] Traditional lithium cobalt oxide (LCO), lithium iron phosphate (LFP), nickel cobalt manganese (NCM), and nickel cobalt aluminum (NCA) positive electrode materials combined with graphite negative electrode materials are far from meeting the market's growing energy density needs, so the development of new high-energy density positive and negative electrode systems is very necessary.

[0003] Silicon-based anode materials offer excellent properties such as high specific capacity, low cost, and easy processing. Among them, silicon oxide (SiOx, 1.2>x>0.8) materials, while having a lower specific capacity (<1800mAh / g), offer a long cycle life and better meet the anode material requirements of soft-pack batteries, making them increasingly popular with soft-pack battery manufacturers. While more and more manufacturers are shifting their research focus to SiOx materials, their continued volume expansion during cycling remains a major obstacle to their large-scale application.

[0004] Since the lithium insertion mechanism of silicon-based negative electrode materials is different from that of anisotropic graphite-based negative electrode materials, the alloying process is accompanied by a very large isotropic expansion. In actual use, the expanded SiOx material will produce a large expansion in the electrode plane, causing the internal stress of the negative electrode to increase, causing the negative electrode to twist and deform, or even tear the substrate copper foil, which may seriously lead to battery cell failure and safety problems.

[0005] Si and SiC negative electrode materials have the advantages of high specific capacity (~3400mAh / g) and long cycle life. Si composite materials mixed with graphite negative electrodes have been widely used in the field of high energy density cylindrical and steel shell power batteries. Although the new homogeneous SiC can solve the problems of large volume expansion of SiC materials during cycling, easy shedding of particles, which causes effective active substances to separate from the conductive network, particle fragmentation leading to repeated generation and destruction of SEI membranes, accelerated electrolyte consumption, and increased internal resistance, the possibilities and prospects of homogeneous SiC negative electrode materials are broader. However, the problems of low initial efficiency of the entire battery and poor stability in aqueous slurries in actual use of existing homogeneous SiC negative electrode materials still need to be solved.

[0006] Therefore, it is very important to invent a battery with higher initial charge and discharge efficiency, lower deformation rate and better cycle performance. Summary of the Invention

[0007] The purpose of the present invention is to overcome the above-mentioned problems existing in the prior art and provide a coated LiSi-C material and a pole piece and battery comprising the coated LiSi-C material. The coated LiSi-C material of the present invention has a dual-continuous phase structure and an oxygen-containing coating layer. The dual-continuous phase structure is conducive to improving the cycle stability of the coated LiSi-C material. The outer shell of the oxygen-containing coating layer can effectively improve its stability in aqueous slurry and reduce the side reactions of the negative electrode active material and the electrolyte. The preparation method of the coated LiSi-C material of the present invention can prepare a coated LiSi-C material with a core-shell structure. The pole piece obtained from the coated LiSi-C material of the present invention has better cycle stability and lower expansion performance. The battery obtained from the pole piece of the present invention has higher first charge and discharge efficiency, lower deformation rate and better cycle performance.

[0008] Conventional SiC materials are secondary large particles composed of separate silicon nanoparticles and carbon composites. There is obvious phase separation of silicon and carbon in this material, that is, the two components still have a clear boundary in the microstructure. This structure is not conducive to the cyclic stability of SiC materials, and is prone to problems such as SEI film thickening and accelerated attenuation. The more active homogeneous SiC material is easy to react with water in aqueous slurry, increasing the alkalinity of the solution and generating gas, thereby affecting the stability of the slurry.

[0009] The inventors of the present invention have discovered that by improving the cycle performance of the electrode and reducing the expansion performance of the electrode, the initial charge and discharge efficiency and cycle performance of the battery can be improved, and the deformation rate of the battery can be reduced.

[0010] The inventors of the present invention have found through further in-depth research that in order to improve the cycle performance of the electrode and reduce the expansion performance of the electrode, the structure of the SiC material in the negative electrode active material can be changed so that its structure is conducive to improving the cycle performance of the electrode and reducing the expansion performance. After extensive in-depth research, the inventors of the present invention have found that by introducing the Li element into the SiC material so that it has a dual-continuous phase homogeneous structure, and then through an oxygen-containing coating modification treatment to form a coated LiSi-C material with an oxygen-containing coating layer, the dual-continuous phase structure is conducive to improving the cycle stability of the electrode and reducing the expansion performance of the electrode. The outer shell of the oxygen-containing coating layer can effectively improve its stability in aqueous slurry, solve the problem of gas generation when the homogeneous Li-SiC material reacts with water, and at the same time reduces the side reactions of the negative electrode active material and the electrolyte, thereby improving the cycle performance of the battery.

[0011] To achieve the above objectives, the first aspect of the present invention provides a coated LiSi-C material, wherein the coated LiSi-C material has a core-shell structure, wherein the core of the coated LiSi-C material is a LiSi-C particle, the shell of the coated LiSi-C material is an oxygen-containing coating layer, and the LiSi-C particle has a continuous phase structure in which a LiSi phase and a C phase are uniformly doped; the LiSi-C particle has a characteristic peak in the X-ray diffraction pattern, and the characteristic peak is attributed to the range of 23°-24° in 2θ and the range of 41°-42° in 2θ.

[0012] A second aspect of the present invention provides a method for preparing the coated LiSi-C material described in the first aspect, wherein the LiSi-C particles are subjected to an oxygen-containing coating modification treatment; the LiSi-C particles have a continuous phase structure in which a LiSi phase and a C phase are uniformly doped; and the LiSi-C particles have characteristic peaks in an X-ray diffraction pattern, wherein the characteristic peaks fall within the range of 23°-24° at 2θ and within the range of 41°-42° at 2θ.

[0013] A third aspect of the present invention provides an electrode sheet, which includes a negative electrode current collector and a negative electrode active material coated on at least one side of the negative electrode current collector, wherein the negative electrode active material includes graphite, and the coated LiSi-C material described in the first aspect of the present invention and / or the coated LiSi-C material prepared by the method described in the second aspect of the present invention.

[0014] The fourth invention of the present invention provides a battery, the electrode of the battery is the pole piece described in the third aspect of the present invention.

[0015] Through the above technical solution, the present invention has at least the following advantages compared with the prior art:

[0016] (1) The coated LiSi-C material of the present invention has good stability in aqueous slurry;

[0017] (2) The electrode of the present invention has good cycle stability;

[0018] (3) The pole piece expansion rate of the present invention is low;

[0019] (4) The battery of the present invention has high initial charge and discharge efficiency;

[0020] (5) The battery deformation rate of the present invention is low;

[0021] (6) The battery of the present invention has good cycle performance;

[0022] (7) The battery of the present invention has a long service life;

[0023] (8) The battery of the present invention has low production cost.

[0024] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Shown is the TEM image of the coated LiSi-C material provided in Example 1.

[0026] Figure 2 Shown is a schematic structural diagram of the coated LiSi-C material.

[0027] Figure 3 The SEM interface image of the LiSi-C material provided in Example 1 of the present invention shows a homogeneous structure inside the particles at a magnification of 50K.

[0028] Figure 4 Shown is the XRD pattern of the LiSi-C material provided in Example 1 of the present invention.

[0029] Figure 5 Shown is an SEM cross-sectional image of the conventional SiC material in Comparative Example 3, showing the internal Si / C phase at a magnification of 50K (the light color represents the Si phase component, and the dark color represents the carbon phase component).

[0030] Figure 6 Shown is the negative electrode slurry made from the material obtained in Example 1.

[0031] Figure 7 Shown is the negative electrode slurry made from the material obtained in Example 2.

[0032] Figure 8 Shown is the negative electrode slurry made from the material obtained in Comparative Example 1.

[0033] Figure 9 Shown is the negative electrode slurry made from the material obtained in Comparative Example 2. DETAILED DESCRIPTION

[0034] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0035] In a first aspect, the present invention provides a coated LiSi-C material having a core-shell structure, wherein the core of the coated LiSi-C material is a LiSi-C particle, the shell of the coated LiSi-C material is an oxygen-containing coating layer, and the LiSi-C particle has a continuous phase structure in which a LiSi phase and a C phase are uniformly doped; the LiSi-C particle has a characteristic peak in the X-ray diffraction pattern, and the characteristic peak is attributed to the range of 23°-24° at 2θ and the range of 41°-42° at 2θ.

[0036] In the present invention, by adding Li to the silicon-carbon material and simultaneously performing an oxygen-containing coating modification treatment, the coated LiSi-C material has been able to achieve better cycle stability than the existing technology. To further improve the effect, one or more of the technical features can be further optimized.

[0037] The coated LiSi-C material has a core-shell structure, wherein the core of the coated LiSi-C material is a LiSi-C particle and the shell of the coated LiSi-C material is an oxygen-containing coating layer. Figure 1 As shown in FIG, it can be seen that the structure of the coated LiSi-C material is a core-shell structure with a boundary between the core and the shell. Figure 2 shown.

[0038] The LiSi-C particles may be lithium silicon carbon materials.

[0039] The LiSi-C particles have a continuous phase structure in which the LiSi phase and the C phase are uniformly doped. The continuous phase structure means that the LiSi phase and the C phase are continuous in microstructure, and there is no obvious boundary between the two phases.

[0040] For example, the SEM cross-sectional view of the LiSi-C particles at 50K magnification shows the internal structure of the particles as follows: Figure 3 As shown, it can be seen that at a magnification of 50K, the internal structure of the LiSi-C particles is uniform and there is no obvious boundary between the two phases.

[0041] There are characteristic peaks in the X-ray diffraction pattern of the LiSi-C particles, and the characteristic peaks are attributed to the range of 23°-24° in 2θ and the range of 41°-42° in 2θ. That is, there are two characteristic peaks in the X-ray diffraction pattern of the LiSi-C particles, one of which is attributed to the range of 23°-24° in 2θ, and the other is attributed to the range of 41°-42° in 2θ.

[0042] The characteristic peak is a characteristic peak that characterizes the presence of Li. When the characteristic peak exists in the X-ray diffraction pattern of the LiSi-C particles in the range of 2θ belonging to 23°-24° and in the range of 2θ belonging to 41°-42°, it indicates that Li exists in the LiSi-C particles.

[0043] According to a preferred embodiment, the maximum intensity of the characteristic peak in the X-ray diffraction pattern of the LiSi-C particles belonging to the range of 23°-24° at 2θ is I1, and the maximum intensity of the characteristic peak in the range of 41°-42° at 2θ is I2, then I1>I2.

[0044] For example, the X-ray diffraction pattern of the LiSi-C particles is as follows: Figure 4 As shown, I1 is the maximum intensity of the characteristic peak attributable to 23°-24°, and I2 is the maximum intensity of the characteristic peak attributable to 41°-42°. It can be seen that I1>I2.

[0045] In one embodiment, the weight proportions of the C element at any two points A and B in the area 100 nm away from the surface of the LiSi-C particle are C A and C B , and satisfies C A and C B :|C A -C B |≤15%.

[0046] |C A -C B |≤15%, indicating that the internal structure of the LiSi-C particles is uniform and the C element is uniformly distributed at any position in the LiSi-C particles.

[0047] According to a preferred embodiment, inside the LiSi-C particle, in the area 100 nm away from the surface of the LiSi-C particle, the weight proportions of the C element at any two points A and B are C A and C B , and satisfies C A and C B :|C A -C B |≤10%

[0048] In one embodiment, a SEM cross-sectional view of the LiSi-C particles at a magnification of 50 K shows a homogeneous structure inside the particles. The homogeneous structure means that the internal structure of the particles is uniform, without separation of silicon and carbon phases.

[0049] In one example, the porosity of the C phase in the LiSi—C particles is 0.4 to 1.1 cc / g. Preferably, the porosity of the C phase is 0.6 to 0.9 cc / g.

[0050] In the present invention, the term "C phase porosity" is distinct from the commonly used term "porosity." Because the C phase in the LiSi-C particles of the present invention is uniformly dispersed, "C phase porosity" is used to describe the distribution of the C phase in the particles. The porosity of the C phase in the LiSi-C particles can be characterized by measuring the porosity of the remaining C phase skeleton after etching away the Li and Si in the particles (i.e., no actual pores exist between the C phases in the LiSi-C particles).

[0051] In one embodiment, the specific surface area of ​​the C phase in the LiSi-C particles is 700 to 1500 m 2 / g, preferably, the specific surface area is 1000 to 1400m 2 / g.

[0052] In the present invention, the term "C phase specific surface area" differs from the commonly used specific surface area. Because the C phase in the LiSi-C particles of the present invention is uniformly dispersed, "C phase specific surface area" refers to the C phase skeleton within the particles. The specific surface area of ​​the C phase in the LiSi-C particles can be characterized by measuring the remaining C phase skeleton after etching away the Li and Si in the particles (i.e., there are no actual pores between the C phases in the LiSi-C particles).

[0053] Based on the C phase skeleton structure remaining after dissolving the LiSi phase, the porous structure of the C phase is a mixed structure of mesopores and micropores.

[0054] The mesopore diameters are concentrated in the range of 4 nm to 14 nm, preferably in the range of 6 nm to 12 nm.

[0055] The micropore diameters are concentrated in a range of less than or equal to 1 nm.

[0056] The mesopore porosity of the C phase in the LiSi-C particles is 0.1 to 0.4 cc / g, and preferably, the mesopore porosity is 0.15 to 0.35 cc / g.

[0057] The micropore porosity of the C phase in the LiSi-C particles is 0.3-0.9 cc / g, and preferably, the micropore porosity is 0.4-0.6 cc / g.

[0058] According to a specific embodiment, based on the total weight of the LiSi-C particles, the content of the C element in the LiSi-C particles is 30-70 wt% (for example, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%), the content of the Li element is 0.2-5 wt% (for example, 0.2 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%), and the content of the Si element is 29.8-65 wt% (for example, 29.8 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 60 wt%, 65 wt%).

[0059] According to a preferred specific embodiment, based on the total weight of the LiSi-C particles, the content of C element in the LiSi-C particles is 40-60 wt %.

[0060] In one example, at a depth of less than 10 nm on the surface of the oxygen-containing coating layer of the coated LiSi-C material, the content of O element is 01%, and at a depth of more than 100 nm, the content of O element is 02%. Then, O1% ≥ 35% and O1% - O2% ≥ 20%. Preferably, O1% is 40%-60% and O1% - O2% ≥ 25%. For example, at a depth of 10 nm on the surface of the oxygen-containing coating layer of the coated LiSi-C material, the content of O element is 01%, and at a depth of 100 nm, the content of O element is 02%. Then, O1% ≥ 35% and O1% - O2% ≥ 20%. Preferably, O1% is 40%-60% and O1% - O2% ≥ 25%.

[0061] XPS elemental analysis of the oxygen-containing coating layer of the coated LiSi-C material revealed that the oxygen content was 01% at a depth of 10 nm from the surface of the oxygen-containing coating layer, and 02% at a depth of 100 nm. It can be understood that the oxygen content gradually decreases as the depth of the oxygen-containing coating layer increases from the outside to the inside, i.e., 01% > 02%. When the oxygen content reaches a certain depth, 0% ≤ 10%, indicating that the oxygen-containing coating layer ends at this location.

[0062] A second aspect of the present invention provides a method for preparing the coated LiSi-C material described in the first aspect, wherein the LiSi-C particles are subjected to an oxygen-containing coating modification treatment; the LiSi-C particles have a continuous phase structure in which a LiSi phase and a C phase are uniformly doped; and the LiSi-C particles have characteristic peaks in an X-ray diffraction pattern, wherein the characteristic peaks fall within the range of 23°-24° at 2θ and within the range of 41°-42° at 2θ.

[0063] By performing oxygen-containing coating modification treatment on the LiSi-C particles, an oxygen-containing coating layer can be formed on the surface of the LiSi-C particles, thereby forming the coated LiSi-C material.

[0064] In one example, the oxygen-containing coating modification treatment method may include high-temperature sintering, oxygen plasma surface treatment, or oxygen-containing salt surface coating of the LiSi—C particles.

[0065] In one example, the coated LiSi-C material is prepared by heating the LiSi-C particles in air at a temperature of 150-300° C. (e.g., 150° C., 170° C., 200° C., 230° C., 250° C., 280° C., 300° C.) for 0.5-1 h (e.g., 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, 1 h).

[0066] In one example, the coated LiSi—C material is prepared by treating the LiSi—C particles in an oxygen plasma atmosphere for 2-15 minutes (eg, 2 minutes, 5 minutes, 7 minutes, 10 minutes, 13 minutes, 15 minutes).

[0067] The LiSi-C particles can be purchased from commercial sources or prepared by a multi-step CVD vapor deposition method.

[0068] According to a specific embodiment, the LiSi-C particles can be prepared by the following method: under the protection of an inert gas, the porous carbon material is first contacted with a lithium source, second contacted with a silicon source gas or a mixed gas of a silicon source and a first carbon source, and then third contacted with a second carbon source gas.

[0069] In one example, the lithium source is lithium vapor.

[0070] According to a specific embodiment, the conditions for the first contact may include: a temperature of 250° C.-450° C., a time of 5-60 minutes, and a vacuum degree of 0.001-10 Pa.

[0071] In one example, the silicon source is SiH 4 .

[0072] In one example, the first carbon source is selected from one or more of ethane, ethylene, and acetylene.

[0073] According to a specific embodiment, the second contacting conditions may include a temperature of 400-550° C. and a time of 6-24 hours.

[0074] In one example, the second carbon source is selected from one or more of ethane, ethylene, and acetylene.

[0075] According to a specific embodiment, the conditions for the third contact may include a temperature of 500° C. to 650° C. and a time of 20 min to 60 min.

[0076] According to a specific embodiment, after the third contact, the mixture is cooled to room temperature under the protection of an inert atmosphere.

[0077] In one example, the inert gas may be argon.

[0078] A third aspect of the present invention provides an electrode sheet, which includes a negative electrode current collector and a negative electrode active material coated on at least one side of the negative electrode current collector, wherein the negative electrode active material includes graphite, and the coated LiSi-C material described in the first aspect of the present invention and / or the coated LiSi-C material prepared by the method described in the second aspect of the present invention.

[0079] The materials of the electrode sheet except the coated LiSi-C material in the negative electrode active material can be made according to the methods in the art, and can achieve better cycle stability and lower expansion rate.

[0080] The electrode sheet includes a negative electrode current collector and a negative electrode active material coated on at least one surface of the negative electrode current collector. The negative electrode active material may include the coated LiSi-C material and graphite. Because the core LiSi-C particles in the coated LiSi-C material have a continuous phase structure, this structure is beneficial for improving the stability of the electrode sheet during lithium insertion and extraction.

[0081] In one example, the negative electrode current collector is copper foil or porous copper foil.

[0082] According to a specific embodiment, based on the total weight of the coated LiSi-C material and the graphite, the content of the coated LiSi-C material is 1 to 55 wt% (for example, 1 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%).

[0083] According to a specific embodiment, based on the total weight of the coated LiSi-C material and the graphite, the content of the graphite is 45 to 99 wt% (for example, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt%, 99 wt%).

[0084] In one embodiment, the coated LiSi-C material is in granular form, and the median particle size D 50 5μm to 15μm (for example, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm).

[0085] According to a specific embodiment, the coated LiSi-C material has a porous structure.

[0086] In one embodiment, the specific surface area of ​​the coated LiSi-C material is 1 to 5 m 2 / g.

[0087] According to a specific embodiment, the graphite includes artificial graphite and / or natural graphite.

[0088] In one embodiment, the median particle size D of the graphite 50 It is 5μm to 20μm (for example, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm).

[0089] In one example, the negative electrode active material further includes a negative electrode binder and a negative electrode conductor.

[0090] According to a specific embodiment, the negative electrode binder is selected from one or more of styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyurethane, polyacrylic acid, sodium polyacrylate, polyvinyl alcohol, alginic acid, sodium alginate, CMC-Na, CMC-Li, and PVP.

[0091] According to a specific embodiment, the negative electrode conductive agent is selected from one or more of conductive carbon black, carbon fiber, activated carbon, acetylene black, graphene, super P, and carbon nanotubes.

[0092] In one example, based on the total weight of the negative electrode active material, the total content of the coated LiSi-C material and graphite is 80-99.8 wt %, the content of the negative electrode binder is 0.1-10 wt %, and the content of the negative electrode conductor is 0.1-10 wt %.

[0093] Preferably, based on the total weight of the negative electrode active material, the total content of the coated LiSi-C material and graphite is 90-98 wt%, the content of the negative electrode binder is 1-5 wt%, and the content of the negative electrode conductor is 1-5 wt%.

[0094] In one embodiment, the negative electrode active material further comprises a conventional auxiliary agent in the art, such as a dispersant, wherein the content of the dispersant is 0-2 wt % based on the total weight of the negative electrode active material.

[0095] The pole piece can be prepared by the following method:

[0096] (1) adding the coated LiSi-C material, graphite, the negative electrode binder, the negative electrode conductive agent and water into a stirring kettle, stirring at 20-45° C. for 6-18 hours to prepare a negative electrode slurry with a solid content of 30-50 wt%;

[0097] (2) coating the prepared negative electrode slurry on at least one side of the negative electrode current collector, drying and rolling to obtain a negative electrode sheet.

[0098] In one embodiment, the negative electrode slurry is an aqueous slurry. The coated LiSi-C material has an outer shell containing an oxygen-containing coating layer, which improves the stability of the coated LiSi-C material in the aqueous slurry, reduces side reactions between the negative electrode active material and the electrolyte, and improves the battery's cycling performance. Furthermore, aqueous slurries are less expensive than non-aqueous slurries, thereby reducing the production cost of the electrode sheet.

[0099] According to a specific embodiment, the negative electrode slurry is coated on at least one side of the negative electrode current collector with a thickness of 20-100 μm.

[0100] Since the pole piece of the present invention includes the negative electrode active material containing the coated LiSi-C material of the present invention, the cycle stability of the pole piece is improved, and the expansion performance of the pole piece and the production cost of the pole piece are reduced.

[0101] A fourth aspect of the present invention provides a battery, wherein the electrode of the battery is the electrode described in the third aspect of the present invention.

[0102] The materials of the battery except the negative electrode plate can be made according to the methods in the art, and can achieve lower initial charge and discharge efficiency, better rate performance, lower deformation rate and better cycle performance.

[0103] The battery is preferably a lithium-ion battery.

[0104] In one example, the battery further includes a positive electrode sheet, a separator, and an electrolyte.

[0105] In one example, the positive electrode sheet contains positive electrode active material.

[0106] In one embodiment, the positive electrode active material is selected from one or more of lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium iron silicate, lithium cobalt oxide, nickel-cobalt-manganese ternary material, nickel-manganese / cobalt-manganese / nickel-cobalt binary raw materials, lithium manganese oxide, and lithium-rich manganese-based materials.

[0107] In one example, the separator is one of polyethylene polymer, polypropylene polymer and non-woven fabric.

[0108] In one example, the electrolyte is a non-aqueous electrolyte.

[0109] In one example, the non-aqueous electrolyte includes a carbonate solvent and a lithium salt.

[0110] In one example, the carbonate solvent is selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC).

[0111] In one example, the lithium salt is selected from one or more of LiPF6, LiBF4, LiSbF6, LiClO4, LiCF3SO3, LiAlO4, LiAlCl4, Li(CF3SO2)2N, LiBOB and LiDFOB.

[0112] By aging the battery, performing high-temperature formation, or charging and discharging, a fluorine-containing coating layer can be formed outside the oxygen-containing coating layer of the coated LiSi-C material. This fluorine-containing coating layer helps the coated LiSi-C material resist HF corrosion in the electrolyte and reduces the formation of side reaction products on the surface of the coated LiSi-C material during cycling, thereby extending the cycle life of the coated LiSi-C material.

[0113] Since the battery of the present invention contains the pole piece of the present invention, the initial charge and discharge efficiency of the battery is improved, the deformation rate of the battery is reduced, the cycle performance of the battery is improved, and the production cost of the battery is reduced.

[0114] The present invention will be described in detail below through examples. The examples described in the present invention are only some examples of the present invention, not all examples. All other examples obtained by persons of ordinary skill in the art based on the examples of the present invention without creative work are within the scope of protection of the present invention.

[0115] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the reagents, materials, etc. used in the following examples are all commercially available unless otherwise specified.

[0116] The following examples are used to illustrate the coated LiSi-C material of the present invention.

[0117] Example 1

[0118] Preparation of coated LiSi-C materials:

[0119] The purchased mesoporous carbon material FDU-15 was -3 Lithium vapor was continuously introduced at 350°C under vacuum conditions for 60 minutes, then the introduction of lithium vapor was stopped. The furnace pressure was adjusted to 101 kPa, the temperature was raised to 450°C, silane gas (SiH4) was introduced, and the temperature was maintained for 6 hours, then the introduction of silane gas was stopped. The temperature was raised to 650°C, ethylene gas was introduced for 30 minutes, then the introduction of ethylene gas was stopped. LiSi-C particles were naturally cooled under argon protection throughout the process. The obtained LiSi-C particles were heated at 170°C in air for 1 hour to obtain the coated LiSi-C material.

[0120] The weight ratio of the coated LiSi-C material to graphite is 12:88.

[0121] Example 2

[0122] Preparation of coated LiSi-C materials:

[0123] The purchased Jicang nanoporous carbon material MC-1 was -3 Lithium vapor was continuously introduced at 350°C under vacuum conditions for 60 minutes, then the introduction of lithium vapor was stopped. The pressure in the furnace was adjusted to 80 kPa, the temperature was raised to 430°C, a mixture of silane gas (SiH4) and ethylene was introduced, and the mixture was maintained for 12 hours before the introduction of silane gas was stopped. The temperature was raised to 650°C, ethylene gas was introduced for 30 minutes, and then the introduction of ethylene gas was stopped. The mixture was naturally cooled under argon protection throughout the process. The obtained LiSi-C material was treated in an oxygen plasma atmosphere for 5 minutes to obtain a coated LiSi-C material.

[0124] The weight ratio of the coated LiSi-C material to graphite is 30:70.

[0125] Example 3

[0126] The process was carried out in accordance with Example 1, except that the weight ratio of the coated LiSi-C material to graphite was changed to 7:93.

[0127] Comparative Example 1

[0128] The procedure of Example 1 was followed, except that heating in air was not performed.

[0129] Comparative Example 2

[0130] The process was carried out as in Example 2, except that the oxygen plasma treatment was not performed.

[0131] Comparative Example 3

[0132] The process was carried out as in Example 1, except that conventional SiC material was mixed with graphite.

[0133] Preparation Example

[0134] Batteries were prepared using the materials obtained in the examples and comparative examples in the following manners.

[0135] (1) Preparation of negative electrode sheet

[0136] Materials preparation:

[0137] Negative electrode binder: lithium carboxymethyl cellulose (CMC-Li) and styrene-butadiene rubber (SBR);

[0138] Negative electrode conductive agents: super P (SP) and single-walled carbon nanotubes (SWCNTs);

[0139] The composition of the negative electrode active material: (coated LiSi-C material and graphite): the weight ratio of CMC-Li:SBR:SP:SWCNTs is 96:1.5:1.5:0.9:0.1.

[0140] Solvent: water;

[0141] Negative electrode current collector: copper foil;

[0142] Preparation: Add the negative electrode active material and solvent to the dispersant according to the weight ratio and stir at 20°C for 18 hours to prepare a negative electrode slurry with a solid content of 30-50%; apply the negative electrode slurry on both sides of the negative electrode collector, dry and roll-press to obtain a negative electrode sheet.

[0143] (2) Preparation of positive electrode sheet

[0144] Materials preparation:

[0145] Binder: polyvinylidene fluoride (PVDF);

[0146] Solvent: N-methylpyrrolidone (NMP);

[0147] Composite conductive agent: SP (super P) and carbon nanotubes (CNTs);

[0148] Composition of the positive electrode active material: The weight ratio of 4.45V lithium cobalt oxide positive electrode (LiCoO2):PVDF:SP:CNTs is 96:2:1.5:0.5.

[0149] Preparation: The positive electrode active material and solvent are mixed according to the weight ratio, stirred, coated, rolled, cut and sliced ​​to prepare the positive electrode sheet.

[0150] (3) Diaphragm

[0151] The diaphragm is a polyethylene diaphragm.

[0152] (4) Electrolyte

[0153] The electrolyte is a non-aqueous electrolyte including ethylene carbonate (EC) and LiPF6.

[0154] (5) Battery preparation

[0155] The negative electrode sheet is larger than the positive electrode sheet. The negative electrode sheet of step (1) and the positive electrode of step (2) are stacked and assembled, the tabs are welded, the aluminum-plastic film is wrapped, the top and side are sealed, and the moisture is vacuum-baked. After the moisture reaches the standard, the liquid is injected, the battery is allowed to stand, and the battery is formed. After the battery is formed, the battery is vacuum-sealed and sorted.

[0156] Test Case

[0157] Test Example 1

[0158] The coated LiSi-C material obtained in Example 1 was subjected to TEM testing, and the TEM image of the coated LiSi-C material was as follows: Figure 1 shown.

[0159] from Figure 1 It can be seen from the figure that the structure of the coated LiSi-C material includes two parts, light and dark, with a boundary between the light and dark parts. Therefore, the structure of the coated LiSi-C material is a core-shell structure.

[0160] The coated LiSi-C material obtained in Example 1 was subjected to SEM and X-ray diffraction tests, and the SEM cross-sectional images of the coated LiSi-C material were respectively measured as follows: Figure 3 The XRD patterns of the coated LiSi-C materials are shown in Figure 4 shown.

[0161] Figure 3 This is the SEM interface image of the coated LiSi-C material at 50K magnification, where the light color is the internal structure of the coated LiSi-C material and the dark color is the gap between the LiSi-C particles. Figure 3 It can be seen from the figure that at a magnification of 50K, the interior of the coated LiSi-C particles is a homogeneous structure, and there is no obvious boundary between the LiSi phase and the C phase.

[0162] from Figure 4 It can be seen that there are two characteristic peaks in the XRD spectrum of the coated LiSi-C material, namely, characteristic peak 1 at 2θ belonging to the range of 23°-24° and the maximum intensity of the characteristic peak is recorded as I1 and characteristic peak 2 at 2θ belonging to 41°-42° and the maximum intensity of the characteristic peak is recorded as I2, I1>I2.

[0163] Test Example 2

[0164] The negative electrode slurries prepared in the examples and comparative examples were subjected to comparative tests. The negative electrode slurries prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 were respectively as follows: Figure 6 、 Figure 7 、 Figure 8 、 Figure 9 By comparison, it can be seen that the negative electrode slurries obtained in Comparative Examples 1 and 2 have bubbles, especially the negative electrode slurry obtained in Comparative Example 1. Therefore, the negative electrode slurries obtained in Comparative Examples 1 and 2 have low stability. The negative electrode slurries obtained in Examples 1 and 2 are more uniform and have no bubbles. Therefore, the negative electrode slurries obtained in Examples 1 and 2 have higher stability.

[0165] Test Example 3

[0166] The Si-based materials of the examples and comparative examples were tested for carbon content in the Si-based materials and carbon content difference within the Si-based particles. The batteries obtained from the examples and comparative examples were tested for initial charge and discharge efficiency, capacity retention after 500, 600, and 800 cycles, and post-cycle expansion.

[0167] (1) Carbon content test in Si-based materials

[0168] The carbon content of Si-based materials was measured using a sulfur-carbon analyzer.

[0169] (2) Carbon content difference test in Si-based particles

[0170] The cross section of the negative electrode sheet was polished with Ar particles, and SEM and EDS were used to test the cross section of the negative electrode sheet in the embodiment and the comparative example. The mass proportion C of the C element at any four points A, B, C, and D in the area 100 nm from the surface of any five LiSi-C particles was calculated by SEM and EDS. A , C B , C C , C D , pairwise calculation |C n -C m |(n, m are any two points of A, B, C, D), take the Max inside the five particles |Cn-Cm| The average value of .

[0171] (3) Battery cell first charge and discharge efficiency test

[0172] After the battery cell is filled and aged, the charging capacity is obtained by charging at a rate of 0.1C to 4.48V and then cutting off at 0.025C at 25°C; the discharge capacity is obtained by discharging at a rate of 0.1C to 3.0V.

[0173] Initial charge and discharge efficiency = discharge capacity / charge capacity*100%.

[0174] (4) Capacity retention test after 500 / 600 / 800 cycles

[0175] At room temperature, charge the battery to 4.48V at 0.5C or 3C constant current and constant voltage, cut off at 0.05C, and then discharge the battery to 3.0V at 0.5C. Cycle for 500 / 600 / 800 cycles. Calculate the capacity retention rate after 500 / 600 / 800 cycles using the following formula:

[0176] Capacity retention rate = final capacity / initial capacity*100%.

[0177] (5) Post-cycle expansion rate test

[0178] At room temperature, charge the battery to 4.48V at a constant current and constant voltage of 0.5C or 3C, cut off at 0.05C, and then discharge the battery to 3.0V at 0.5C. Cycle for the specified number of cycles (500 / 600 / 800 cycles, as shown in Table 1) and calculate using the following formula:

[0179] Expansion rate = (THK1-THK0) / THK0*100%;

[0180] Among them, THK0 is the thickness of the initial 3.85V battery measured by 600g PPG, and THK1 is the thickness of the fully charged battery after cycling.

[0181] (6) XPS surface analysis and depth profiling

[0182] The surface XPS element analysis of the coated LiSi-C material showed that the content of O element at a depth of 10 nm on the surface of the oxygen-containing coating layer was recorded as O1%, and the content of O element at a depth of 100 nm was recorded as O2%.

[0183] The obtained results are recorded in Table 1.

[0184] Table 1

[0185]

[0186]

[0187] As can be seen from Table 1, from the comparative examples and the examples, it can be seen that the expansion rate of the battery of the examples after cycling is significantly reduced, the capacity retention rate is significantly improved, and the battery has good slurry stability.

[0188] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A coated LiSi-C material, characterized in that: The coated LiSi-C material has a core-shell structure, wherein the core of the coated LiSi-C material is a LiSi-C particle, the shell of the coated LiSi-C material is an oxygen-containing coating layer, and the LiSi-C particle has a continuous phase structure uniformly doped with a LiSi phase and a C phase; the LiSi-C particle has a characteristic peak in the X-ray diffraction pattern, and the characteristic peak is attributed to the range of 23°-24° in 2θ and the range of 41°-42° in 2θ; At a depth of 10 nm on the surface of the oxygen-containing coating layer of the coated LiSi-C material, the content of O element is 01%, and at a depth of 100 nm, the content of O element is 02%, and O1%>O2%.

2. The coated LiSi-C material according to claim 1, wherein: In the X-ray diffraction pattern of the LiSi-C particles, the maximum intensity of the characteristic peak belonging to the range of 23°-24° in 2θ is I1, and the maximum intensity of the characteristic peak belonging to the range of 41°-42° is I2, so I1>I2.

3. The coated LiSi-C material according to claim 1, wherein: Inside the LiSi-C particle, in the area 100 nm away from the surface of the LiSi-C particle, the mass proportion of the C element at any two points A and B is C. A and C B Satisfies: |C A -C B |≤15%; and / or, The SEM cross-sectional view of the LiSi-C particles shows a homogeneous structure inside the particles at a magnification of 50K.

4. The coated LiSi-C material according to any one of claims 1 to 3, wherein: The porosity of the C phase in the LiSi-C particles is 0.4 to 1.1 cc / g; and / or, Based on the total weight of the LiSi-C particles, the content of C element in the LiSi-C particles is 30-70 wt %, the content of Li element is 0.2-5 wt %, and the content of Si element is 29.8-65 wt %.

5. The coated LiSi-C material according to claim 1, wherein: At a surface depth of less than 10 nm, the O content of the oxygen-containing coating layer of the coated LiSi-C material is 01%, and at a depth greater than 100 nm, the O content is 02%. Thus, O1% ≥ 35% and O1% - O2% ≥ 20%.

6. The coated LiSi-C material according to claim 5, wherein: O1% is 40%-60% and O1%-O2% ≥ 25%.

7. A method for preparing the coated LiSi-C material according to any one of claims 1 to 6, characterized in that: LiSi-C particles are subjected to oxygen-containing coating modification treatment; the LiSi-C particles have a continuous phase structure in which a LiSi phase and a C phase are uniformly doped; and characteristic peaks exist in an X-ray diffraction pattern of the LiSi-C particles, and the characteristic peaks fall within the range of 23°-24° at 2θ and within the range of 41°-42° at 2θ.

8. A pole piece, characterized in that: The electrode sheet includes a negative electrode current collector and a negative electrode active material coated on at least one side of the negative electrode current collector, wherein the negative electrode active material includes graphite, and the coated LiSi-C material according to any one of claims 1 to 6 and / or the coated LiSi-C material prepared by the method according to claim 7.

9. The pole piece according to claim 8, wherein: Based on the total weight of the coated LiSi-C material and the graphite, the content of the coated LiSi-C material is 1 to 55 wt%, and the content of the graphite is 45 to 99 wt%.

10. The pole piece according to claim 8, wherein: The coated LiSi-C material is granular, and the median particle size D 50 5 μm to 15 μm; and / or, The coated LiSi-C material has a porous structure and a specific surface area of ​​1 to 5 m 2 / g.

11. A battery, characterized in that: The battery comprises the pole piece according to any one of claims 8 to 10.

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