Electrochemical device and electronic device including the same

Abstract

The invention belongs to the technical field of batteries, and particularly discloses an electrochemical device and electronic equipment comprising the same. In the electrochemical device, the silicon-carbon material in the negative electrode provides high-capacity support, the lithium supplement layer shows lithium supply and buffer volume expansion effects, and meanwhile, the positive electrode active material comprises a P63mc phase-containing matrix, an R-3m phase-containing compound and an amorphous solid electrolyte, so that the ionic conductivity and the interface stability of the material can be obviously improved; therefore, the electrochemical device has high rate capability, first efficiency, high-temperature cycling stability and low volume expansion rate.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, and in particular to electrochemical devices and electronic devices containing the same. Background Technology

[0002] The lithium-ion battery field has increasingly higher requirements for energy density (ED). Silicon-carbon anode materials, composed of silicon and carbon, have received widespread attention and applications due to their high theoretical capacity (silicon's theoretical specific capacity is 4200 mAh / g, and graphite's is 372 mAh / g). However, silicon-carbon anodes suffer from low initial efficiency, typically between 80% and 92%, and their performance depends heavily on the silicon content and material structure. This means that during the first charge, some lithium ions form an SEI film with the anode or are irreversibly embedded, unable to return to the cathode, permanently consuming lithium ions from the cathode and leading to a decline in battery performance. Furthermore, silicon-based anode active materials also suffer from significant volume expansion, resulting in poor battery cycle performance.

[0003] Furthermore, the positive electrode active material is also crucial to battery performance. Currently, the positive electrode active materials used in silicon-carbon anode batteries suffer from poor capacity utilization, rate performance, and high-temperature cycle stability due to their inherent crystal phase structure. For example, the R-3m phase lithium cobalt oxide crystal structure is unstable at high temperatures, making it difficult to fundamentally suppress interfacial side reactions, resulting in poor rate performance and high-temperature cycle stability of the battery. Summary of the Invention

[0004] The purpose of this application is to address the shortcomings of existing batteries, such as low initial efficiency, low rate performance, low high-temperature cycling stability, and high volume expansion rate, and proposes an electrochemical device and an electronic device containing the same.

[0005] To achieve the above objectives, in a first aspect, this application provides an electrochemical device, wherein the negative electrode includes a negative current collector, a negative active material layer disposed on at least one side of the negative current collector, and a lithium replenishment layer disposed on the negative active material layer, the lithium replenishment layer being located on a side away from the thickness direction of the current collector; the negative active material layer includes a silicon-carbon material. The positive electrode includes a positive electrode active material, which includes a matrix, a second compound located on at least a portion of the surface of the matrix, and a third compound. The matrix includes a first compound having a crystal structure belonging to space group P63mc, the second compound having a crystal structure belonging to space group R-3m, and the third compound including an amorphous solid electrolyte. The amorphous solid electrolyte includes a metal element R, which includes at least one of Zr and Ti.

[0006] In the electrochemical device of this application, the P63mc phase matrix in the positive electrode active material exhibits high initial efficiency. Furthermore, the P63mc phase matrix enables the battery to withstand high voltage and possess high capacity and high initial efficiency. Building upon the high capacity of silicon-carbon materials, it compensates for the lower initial efficiency of silicon-carbon anode materials. The synergy between the positive and negative electrode active materials significantly improves the single-cell energy density of the battery. Simultaneously, the ion channels in the amorphous solid electrolyte of the positive electrode active material can simultaneously provide lithium sources with the lithium replenishment layer, forming a "dual ion transport path," further enhancing the lithium-ion migration rate, suppressing dendrite nucleation, and improving the battery's initial efficiency and cycle stability. Moreover, the lithium replenishment layer acts as an elastic buffer for the silicon-carbon-containing negative electrode active material layer. The rigid support of the amorphous solid electrolyte on the positive electrode side indirectly provides a uniform stress distribution on the negative electrode side through mechanical transmission, alleviating local expansion stress. Therefore, the lithium replenishment layer and the amorphous solid electrolyte can jointly alleviate the volume expansion of the silicon anode, preventing interface delamination and thus improving the battery's cycle stability.

[0007] Meanwhile, the surface of the P63mc phase-containing matrix of the positive electrode active material includes a second compound with a crystal structure belonging to space group R-3m. Under high voltage, the near-surface layer of this second compound can form a stable spinel phase transition layer after delithiation, providing good interfacial protection for the P63mc phase-containing matrix, suppressing side reactions and the dissolution of transition metals, and improving interfacial stability. This achieves the goal of improving the battery's rate capability and high-temperature cycle stability. Because the matrix contains the P63mc phase, it has a unique lithium-deficient crystal structure. The irreversible lithium ions extracted from the second compound can enter the lithium vacancies in the matrix during re-intercalation, further improving capacity utilization, slowing down cycle decay, and further enhancing the battery's cycle stability. The second coating layer includes an amorphous solid electrolyte containing Zr and / or Ti, which has high ionic conductivity and can alleviate stress concentration at the interface between the matrix and the second compound during charging and discharging due to volume changes (such as the transition from layered to spinel phase) through a uniform ion transport path, thereby inhibiting interface crack propagation and extending cycle life. It also has good machinability and is stable and not easily decomposed at high voltage. Its coating on the surface of the second compound can significantly improve the overall high-temperature cycle stability of the material and improve the safety and stability of the battery.

[0008] In some implementations, 0.25μm≤L1≤10μm, where L1 is the thickness of the lithium replenishment layer in μm.

[0009] In some implementations, 25μm≤L2≤50μm, where L2 is the thickness of the negative electrode active material layer in μm.

[0010] In some embodiments, 0% < m ≤ 6.5%, where m is the total mass percentage of the third and second compounds in the positive electrode active material.

[0011] In some embodiments, 0.1% ≤ w ≤ 2%, where w is the mass percentage of metal element R in the positive electrode active material.

[0012] In some embodiments, the electrochemical device satisfies the following relationship: 0 < 10 × L1 × (0.03 × m + 2.87 × w + 0.03) / L2 ≤ 0.1, In the formula, L1 is the thickness of the lithium replenishment layer in μm; L2 is the thickness of the negative electrode active material layer in μm; m is the total mass percentage of the third compound and the second compound in the positive electrode active material; and w is the mass percentage of the R metal element in the positive electrode active material.

[0013] In some embodiments, the lithium replenishment layer includes lithium metal, a lithium replenishment layer conductive agent, and a lithium replenishment layer binder, wherein the lithium metal content is 50%-70% by mass based on the total mass of the lithium replenishment layer.

[0014] In some embodiments, the mass percentage of silicon in the negative electrode active material layer is 5%-20% based on the total mass of the negative electrode active material.

[0015] In some embodiments, the D50 of the first compound is d1, where 5 μm ≤ d1 ≤ 15 μm.

[0016] In some embodiments, the D50 of the second compound is d2, where 0 < d2 ≤ 4 μm.

[0017] In some embodiments, the amorphous solid electrolyte includes Li 2+2z RX4O 1+Z R is Zr and / or Ti, X is at least one of F, Cl, and Br, and 0 < z ≤ 0.75.

[0018] In some embodiments, in the X-ray diffraction pattern of the positive electrode active material, 2θ has a first peak with intensity I1 between 18° and 19°, and a second peak with intensity I2 between 18.5° and 20°. The peak position difference between the second peak and the first peak is 0.3~1°, and satisfies the following relationship: 0 <I2 / I1<1。

[0019] In some embodiments, the first compound includes Li n-α Na α Co 1-x M xO2, where 0.7≤n≤1, 0≤α≤0.1, 0≤x≤0.1, and M is one or more of Al, Mg, La, Y, Ni, Mn, W, and V.

[0020] In some embodiments, the second compound includes LiCo. 1-y A y O2, 0≤y≤0.1, A is one or more of Al, Mg, La, Y, Ni, Mn, W, and V.

[0021] In some embodiments, in the positive electrode active material, a third compound located on at least a portion of the surface of the second compound constitutes a second coating layer covering the surface of the second compound; the second compound and the third compound located on at least a portion of the surface of the substrate constitute a first coating layer covering the surface of the substrate.

[0022] In some embodiments, the thickness of the second coating layer is L3, where 0 μm < L3 ≤ 0.4 μm.

[0023] Secondly, this application provides an electronic device including the aforementioned electrochemical device.

[0024] Compared with the prior art, the beneficial effects of this application are as follows: In the electrochemical device of this application, the silicon-carbon material in the negative electrode provides high capacity support, and the lithium replenishment layer exhibits lithium supply and buffering volume expansion effects. At the same time, the positive electrode active material includes a matrix containing P63mc phase, a second compound containing R-3m phase, and an amorphous solid electrolyte, which can significantly improve the ionic conductivity and interfacial stability of the material. Overall, the electrochemical device has high rate performance, first-efficiency and high-temperature cycling stability, and low volume expansion rate. Attached Figure Description

[0025] Figure 1 The image shows the XRD pattern of the positive electrode active material in Example 1. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0028] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0029] In the detailed description and claims, a list of items connected by the terms "one of," "among," "a kind of," or other similar terms may mean any of the listed items. For example, if items A and B are listed, then the phrase "one of A and B" means only A or only B. In another example, if items A, B, and C are listed, then the phrase "one of A, B, and C" means only A; only B; or only C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0030] In a first aspect, this application provides an electrochemical device, including a positive electrode and a negative electrode. The negative electrode includes a negative current collector, a negative active material layer disposed on at least one side of the negative current collector, and a lithium replenishment layer disposed on the negative active material layer. The lithium replenishment layer is located on a side away from the thickness direction of the current collector. The negative active material layer includes a silicon-carbon material. The positive electrode includes a positive electrode active material, which includes a matrix, a second compound located on at least a portion of the surface of the matrix, and a third compound. The matrix includes a first compound having a crystal structure belonging to space group P63mc, the second compound having a crystal structure belonging to space group R-3m, and the third compound including an amorphous solid electrolyte. The amorphous solid electrolyte includes a metal element R, which includes at least one of Zr and Ti.

[0031] In the electrochemical device of this application, the P63mc phase matrix in the positive electrode active material exhibits high initial efficiency. Furthermore, the P63mc phase matrix enables the battery to withstand high voltage and possesses high capacity and high initial efficiency. Building upon the high capacity of silicon-carbon materials, it compensates for the lower initial efficiency of silicon-carbon anode materials. The synergy between the positive and negative electrode active materials significantly improves the single-cell energy density of the battery. Simultaneously, the ion channels in the amorphous solid electrolyte of the positive electrode active material can simultaneously provide lithium sources with the lithium replenishment layer, forming a "dual ion transport path," further enhancing the lithium-ion migration rate, suppressing dendrite nucleation, and improving the battery's initial efficiency and cycle stability. The lithium replenishment layer acts as an elastic buffer for the silicon-carbon anode active material layer, while the amorphous solid electrolyte provides rigid support, jointly mitigating the volume expansion of the silicon anode and preventing interface stripping, thereby improving the battery's cycle stability.

[0032] Furthermore, the surface of the P63mc phase-containing matrix of the positive electrode active material includes a second compound with a crystal structure belonging to space group R-3m. Under high voltage, the near-surface layer of this second compound can form a stable spinel phase transition layer after delithiation, providing good interfacial protection for the P63mc phase-containing matrix, suppressing side reactions and the dissolution of transition metals, and improving interfacial stability. This achieves the goal of improving the battery's rate capability and high-temperature cycle stability. Because the matrix contains the P63mc phase, it possesses a unique lithium-deficient crystal structure. The irreversible lithium ions extracted from the second compound can enter the lithium vacancies in the matrix during re-intercalation, further improving capacity utilization, slowing cycle decay, and further enhancing the battery's cycle stability. The second coating layer includes an amorphous solid electrolyte containing Zr and / or Ti, which has high ionic conductivity and can alleviate stress concentration at the interface between the matrix and the second compound during charging and discharging due to volume changes (such as the transition from layered to spinel phase) through a uniform ion transport path, thereby inhibiting interface crack propagation and extending cycle life. It also has good machinability and is stable and not easily decomposed at high voltage. Its coating on the surface of the second compound can significantly improve the overall high-temperature cycle stability of the material and improve the safety and stability of the battery.

[0033] In some embodiments, the electrochemical device satisfies the following relationship: 0 < 10 × L1 × (0.03 × m + 2.87 × w + 0.03) / L2 ≤ 0.1, In the formula, L1 is the thickness of the lithium replenishment layer in μm; L2 is the thickness of the negative electrode active material layer in μm; m is the total mass percentage of the third compound and the second compound in the positive electrode active material; and w is the mass percentage of the R metal element in the positive electrode active material.

[0034] The inventors of this application discovered that, when the above-mentioned relationship is satisfied, the core objective of lithium replenishment is to balance the total amount of lithium ions in the electrode. During the first cycle, the lithium ions consumed by the formation of the SEI film on the negative electrode and the losses due to side reactions on the positive electrode surface lead to a permanent reduction in active lithium. The role of lithium replenishment is to provide an additional lithium source for the replenishment layer, compensating for this loss and ensuring that the total amount of cyclic lithium equals the design value. When the above formula is satisfied, it can be ensured that the amount of lithium replenished is appropriate, and the lithium inventory is balanced after charging and discharging of the positive and negative electrodes. This can simultaneously improve the battery's rate performance, first-cycle efficiency and high-temperature cycle stability, as well as reduce the volume expansion rate.

[0035] In some implementations, 0.25 μm ≤ L1 ≤ 10 μm. Exemplarily, L1 can be 0.25 μm, 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm, or 10.0 μm. Here, L1 refers only to the thickness of a single lithium-filling layer on one side of the negative electrode. 1。 Within the above range, insufficient lithium replenishment of the lithium replenishment layer can be avoided, which would lead to capacity decay due to residual irreversible lithium loss; and excessive lithium replenishment can also be avoided, which would easily cause lithium plating short circuits due to residual metallic lithium, and increase impedance, thus degrading the performance of the battery.

[0036] In some implementations, 25μm ≤ L2 ≤ 50μm. For example, L2 can be 25μm, 26μm, 27μm, 28μm, 29μm, 30μm, 35μm, 40μm, 45μm, 50μm, or any two of the above values. Here, L2 refers only to the thickness of a single layer of negative electrode active material on one side of the negative electrode sheet. Within the above thickness range, both cell capacity and dynamic window can be considered, and it is also relatively suitable for existing coating or rolling process conditions.

[0037] In some embodiments, 0% < m ≤ 6.5%. Exemplarily, m is 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, or falls within the range of any two of the above values. When m is within the above range, the spinel interface layer formed after delithiation of the second compound synergistically works with the lithium-deficient structure of the matrix, and combined with the surface amorphous solid electrolyte third compound, jointly improves the rate performance and high-temperature cycling stability of the material.

[0038] In some embodiments, 0.1% ≤ w ≤ 2%. Exemplarily, w can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, or within any two of the above values. Within the above range, the surface amorphous solid electrolyte third compound can alleviate stress concentration at the interface between the matrix and the second compound phase during charging and discharging through a uniform ion transport path, thereby suppressing interface crack propagation, extending cycle life, and synergistically improving the cycling stability of the material under high voltage with the second compound.

[0039] In some embodiments, the lithium replenishment layer includes metallic lithium, a lithium replenishment layer conductive agent, and a lithium replenishment layer binder.

[0040] In some embodiments, based on the total mass of the lithium replenishment layer, the mass percentage of metallic lithium in the lithium replenishment layer is 50%-70%; for example, it can be 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, or within any two of the above values. When the mass percentage of metallic lithium in the lithium replenishment layer is within the above range, insufficient lithium replenishment can be avoided, effectively improving the first-time efficiency; it also avoids a large proportion, reducing the binder content, making the adhesion structure of the lithium replenishment layer stable, and avoiding the risk of rolling cracking or material loss, or even the risk of lithium deposition during recycling; therefore, within the above range, it can balance the amount of lithium replenishment and the bonding ability, ensuring sufficient lithium release and a complete interface, with no significant risks.

[0041] In some embodiments, the conductive agent of the lithium replenishment layer includes at least one of carbon black, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon tubes, carbon nanotubes, activated carbon, and mesoporous carbon.

[0042] In some embodiments, the mass percentage of the lithium replenishing layer conductive agent in the lithium replenishing layer is 1%-10%; for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or within any two of the above values.

[0043] In some embodiments, the lithium-supplementing layer adhesive includes at least one of polyvinylidene fluoride, polyacrylic acid, polymethacrylic acid, polyacrylate, polymethacrylate, polyacrylamide, styrene-butadiene rubber, acrylic styrene-butadiene rubber, acrylic acid-acrylonitrile-acrylamide copolymer, acrylic acid-acrylonitrile-acrylate copolymer, acrylonitrile-butadiene rubber, nitrile rubber, acrylonitrile-styrene-butadiene copolymer, acryloyl rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl acetate, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenolic resin, epoxy resin, carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl cellulose, carboxymethyl chitosan, polyester, polyamide, polyether, polyimide, polycarboxylic acid ester, polycarboxylic acid, polyurethane, alginate, polyvinylidene fluoride, and poly(vinylidene fluoride)-hexafluoropropylene.

[0044] In some embodiments, the mass percentage of the lithium-supplementing layer binder in the lithium-supplementing layer is 15%-40%; for example, it can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, or within any two of the above values.

[0045] In some embodiments, the mass percentage of silicon in the negative electrode active material layer is 5%-20% based on the total mass of the negative electrode active material; for example, it can be 5%, 10%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, 20%, or within any two of the above values.

[0046] In some embodiments, the D50 of the first compound is d1, where 5 μm ≤ d1 ≤ 15 μm. Exemplarily, d1 can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or within any two of these ranges. Having d1 within this range allows the first compound to achieve a good balance between compaction density and cycling performance.

[0047] In some embodiments, the D50 of the second compound is d2, where 0 < d2 ≤ 4 μm. Exemplarily, d2 can be 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3.0 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm, 4.0 μm, or within any two of the above values. Having d2 within this range allows the second compound to achieve a good balance between cycle performance and discharge capacity.

[0048] In some embodiments, the amorphous solid electrolyte includes Li 2+2z RX4O 1+Z R is Zr and / or Ti, X is at least one of F, Cl, and Br, and 0 < z ≤ 0.75.

[0049] In some embodiments, in the X-ray diffraction pattern of the positive electrode active material, 2θ has a first peak with intensity I1 between 18° and 19°, and a second peak with intensity I2 between 18.5° and 20°. The peak position difference between the second peak and the first peak is 0.3~1°, and satisfies the following relationship: 0 <I2 / I1<1。

[0050] The first peak represents the characteristic diffraction peak of the (002) crystal plane of the first compound matrix material with a P63mc crystal structure. The second peak represents the characteristic diffraction peak of the (003) crystal plane of the second compound with an R-3m crystal structure. The 2θ difference between the second peak and the first peak is expressed as the difference in 2θ between the second peak and the first peak, i.e., the peak position difference. The intensity of the characteristic diffraction peaks is positively correlated with their content to a certain extent, and the I2 / I1 value is used to represent the content difference between the first compound and the second compound. When the contents of the second compound and the first compound satisfy the above relationship, the positive electrode active material can achieve both good cycle performance and discharge capacity.

[0051] In some implementations, I2 / I1 is 0.2-0.7; for example, it can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.65, 0.7, or within the range of any two of the above values.

[0052] In some implementations, I1 > 5000 cps.

[0053] In some implementations, I1 is 8100-20000 cps. For example, I1 is 8100 cps, 9000 cps, 10000 cps, 11000 cps, 12000 cps, 13000 cps, 14000 cps, 15000 cps, 16000 cps, 17000 cps, 18000 cps, 19000 cps, 20000 cps, 13000 cps, or within the range of any two of the above values.

[0054] In some implementations, I2 is greater than 3000 cps.

[0055] In some implementations, I2 is 3005-8000 cps. For example, I2 is 3005 cps, 4000 cps, 5000 cps, 6000 cps, 7000 cps, 8000 cps, or within the range of any two of the above values.

[0056] In some embodiments, the first compound comprises metal-doped lithium cobalt oxide.

[0057] In some embodiments, the metal-doped lithium cobalt oxide includes Li n-α Na α Co 1-x M x O2, where 0.7≤n≤1, 0≤α≤0.1, 0≤x≤0.1, and M is one or more of Al, Mg, La, Y, Ni, Mn, W, and V. A certain range of Na elements in the matrix can expand the interlayer spacing of the material, which helps to further improve the migration rate of lithium ions, thereby enhancing the rate performance of the battery.

[0058] In some embodiments, the second compound includes LiCo. 1-y A y O2, 0≤y≤0.1, A is one or more of Al, Mg, La, Y, Ni, Mn, W, and V. Under high voltage, the near-surface layer of this second compound can form a stable spinel phase transition layer after delithiation, providing good interfacial protection to the matrix, suppressing side reactions and dissolution of transition metals, improving interfacial stability, and thus improving the high-temperature cycle stability of the battery.

[0059] In some embodiments, in the positive electrode active material, a third compound located on at least a portion of the surface of the second compound constitutes a second coating layer covering the surface of the second compound; the second compound and the third compound located on at least a portion of the surface of the substrate constitute a first coating layer covering the surface of the substrate.

[0060] In some embodiments, the thickness of the second coating layer is L3, where 0 μm < L3 ≤ 0.4 μm; for example, L3 is 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, or within the range of any two of the above values.

[0061] In some embodiments, the thickness of the first coating layer is 0.1 μm to 10 μm. For example, it is 0.1 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or within any two of the above values.

[0062] In some embodiments, the method for preparing the first compound includes the following steps: S1. Sodium source, cobalt source and compound containing element M are mixed and sintered in air or oxygen atmosphere to obtain first compound precursor; S2. The lithium source and the first compound precursor are dispersed in water, ion exchange is performed, and then dried to obtain the first compound.

[0063] In some embodiments, in step S1, the sintering temperature is 600-900°C and the sintering time is 8-50 hours.

[0064] In some embodiments, in step S1, the sodium source includes one or more of sodium oxide, sodium carbonate, sodium nitrate, sodium hydroxide, sodium bicarbonate, and sodium sulfate.

[0065] In some embodiments, in step S1, the cobalt source includes one or more of cobalt hydroxide, cobalt tetroxide, doped cobalt tetroxide, cobalt suboxide, cobalt hydroxyl oxide, cobalt nitrate, and cobalt sulfate.

[0066] In some embodiments, in step S1, the compound containing element M contains one or more of the following: oxide, carbonate, and hydroxide of element M.

[0067] In some embodiments, in step S2, the lithium source includes one or more of lithium chloride, lithium bromide, lithium iodide, lithium nitrate, lithium hydroxide, and lithium fluoride.

[0068] In some embodiments, in step S2, the temperature of the ion exchange is 70-125°C, and the time of the ion exchange is 5-15 hours.

[0069] In some embodiments, in step S2, the mass ratio of the lithium source to the first compound precursor ranges from 1 to 4:1.

[0070] In some embodiments, in step S2, the mass ratio of water to the first compound precursor is 5-150:1.

[0071] In some embodiments, the preparation method of the second compound includes the following steps: mixing a lithium source, a cobalt source and a compound containing element A and sintering them in air or oxygen to obtain the second compound.

[0072] In some embodiments, the sintering temperature is 600-1000°C and the sintering time is 5-50 hours.

[0073] This application does not impose any particular limitation on the preparation method of amorphous solid electrolytes, as long as it achieves the purpose of this application. For example, it can be prepared according to the following solid electrolyte preparation method, which includes the following steps: after mixing RCl4 and lithium source under argon atmosphere protection, the mixture is subjected to a first grinding and a second grinding to obtain a solid electrolyte.

[0074] In some embodiments, the lithium source includes one of LiCl and Li2O.

[0075] In some implementations, R in RCl4 is Zr and / or Ti.

[0076] In some embodiments, the first grinding speed is 50-200 rpm, and the first grinding time is 1-3 hours; the second grinding speed is 400-900 rpm, and the second grinding time is 5-24 hours.

[0077] In some embodiments, the preparation method of the positive electrode active material includes the following steps: S1. The second compound and the third compound are sequentially subjected to a first ball milling and a second ball milling to obtain a coating material; the rotational speed in the first ball milling is lower than the rotational speed in the second ball milling. S2. The first compound and the coating material are sequentially subjected to a third ball milling and a fourth ball milling to obtain the positive electrode active material; the rotation speed in the third ball milling is less than the rotation speed in the fourth ball milling.

[0078] In some embodiments, the rotational speed in the first ball milling, the rotational speed in the second ball milling, the rotational speed in the third ball milling, and the rotational speed in the fourth ball milling are each independently selected from 50 r / min to 400 r / min.

[0079] In some embodiments, the time for the first ball milling mixture, the time for the second ball milling mixture, the time for the third ball milling mixture, and the time for the fourth ball milling mixture are each independently selected from 0.5-10 hours.

[0080] In some embodiments, the time spent in the first ball milling mixture is shorter than the time spent in the second ball milling mixture.

[0081] In some embodiments, the time spent in the third ball milling mixture is less than the time spent in the fourth ball milling mixture.

[0082] In some embodiments, the mass ratio of the first compound, the second compound, and the third compound is (92-99.5):(0.1-3.5):(0.5-5.5).

[0083] In one embodiment, the positive electrode active material has a mass percentage content of 50-99% in the positive electrode sheet.

[0084] In some embodiments, the positive electrode sheet includes a positive current collector and a layer containing positive active material disposed on at least one side of the positive current collector.

[0085] In some embodiments, the positive current collector is a metal foil or a composite current collector.

[0086] In some embodiments, the metal foil is aluminum foil. The composite current collector may include a metal foil substrate and a conductive layer disposed on at least one side of the metal foil substrate.

[0087] In some embodiments, the conductive layer may include at least one of carbon black, graphite, expanded graphite, graphene, graphene nanosheets, carbon fiber, carbon nanofiber, graphitized carbon sheet, carbon tube, carbon nanotube, activated carbon, and mesoporous carbon.

[0088] In some embodiments, the layer containing the positive electrode active material includes the positive electrode active material, a positive electrode binder, and a positive electrode conductive agent.

[0089] In some embodiments, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polyvinyl butyral, polyvinylpyrrolidone (PVP), acrylic acid-acrylonitrile-acrylamide copolymer, and acrylic acid-acrylonitrile-acrylate copolymer. The positive electrode binder of this application is not limited to the above materials, but also includes other materials that can be used as battery positive electrode binders.

[0090] In some embodiments, the positive electrode conductive agent may include at least one of graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon tubes, carbon nanotubes, activated carbon, and mesoporous carbon.

[0091] The positive electrode conductive agent of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as positive electrode conductive agents for batteries.

[0092] Electrochemical devices include any apparatus in which an electrochemical reaction occurs to convert chemical energy into electrical energy and vice versa, including, but not limited to, all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0093] In some embodiments, the negative current collector is a metal foil or a composite current collector.

[0094] In some embodiments, the metal foil is a copper foil. The composite current collector may include a metal foil substrate and a conductive layer disposed on at least one side of the metal foil substrate.

[0095] In some embodiments, the conductive layer may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, carbon fiber, carbon nanofiber, graphitized carbon sheet, carbon tube, carbon nanotube, activated carbon, and mesoporous carbon.

[0096] In some embodiments, the negative electrode active material layer further includes a negative electrode binder and / or a negative electrode conductive agent.

[0097] The silicon-carbon material described in this application is a silicon-carbon composite material. Based on the mass of the silicon-carbon composite material, the mass percentage content of silicon is 30%-70%, and more preferably, the mass percentage content of carbon is 15%-70%. This application does not impose any particular limitation on the silicon-carbon composite material, as long as it can achieve the purpose of this application. For example, the silicon-carbon composite material can be a composite material obtained by deposition. Exemplarily, the silicon-carbon composite material can be silicon material deposited on a carbon skeleton, or carbon material deposited on a silicon skeleton.

[0098] In some embodiments, the negative electrode binder includes at least one of polyacrylic acid, polymethacrylic acid, polyacrylate, polymethacrylate, polyacrylamide, styrene-butadiene rubber, acrylic styrene-butadiene rubber, acrylic acid-acrylonitrile-acrylamide copolymer, acrylic acid-acrylonitrile-acrylate copolymer, acrylonitrile-butadiene rubber, nitrile rubber, acrylonitrile-styrene-butadiene copolymer, acryloyl rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl acetate, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenolic resin, epoxy resin, carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl cellulose, carboxymethyl chitosan, polyester, polyamide, polyether, polyimide, polycarboxylic acid ester, polycarboxylic acid, polyurethane, alginate, fluorinated polymer, chlorinated polymer, polyvinylidene fluoride, and poly(vinylidene fluoride)-hexafluoropropylene. The negative electrode binder of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as battery negative electrode binders.

[0099] In one embodiment, the negative electrode binder has a mass percentage content of 1.5%-20% in the negative electrode sheet.

[0100] In some embodiments, the negative electrode conductive agent may include at least one of carbon, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon nanotubes, activated carbon, and mesoporous carbon. The negative electrode conductive agent of this application is not limited to the above materials, but also includes other materials that can be used as battery negative electrode conductive agents.

[0101] In one embodiment, the negative electrode conductive agent has a mass percentage content of 0.5%-20% in the negative electrode sheet.

[0102] The separator separates the negative and positive electrodes and provides a pathway for lithium-ion migration. The use of the separator is not particularly limited, as long as it is a separator commonly used in lithium-ion secondary batteries. In particular, separators with low resistance to electrolyte ion movement and excellent electrolyte permeability are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes formed from polyolefin-based polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, ethylene / methacrylate copolymers, etc.) or laminated structures with two or more layers. Alternatively, nonwoven fabrics formed from conventional porous nonwoven fabrics (e.g., glass fibers with high melting points, polyethylene terephthalate fibers, etc.) can be used. Furthermore, coated separators containing ceramic components or polymer materials to ensure heat resistance or mechanical strength can be used, and can optionally be used as single-layer or multi-layer structures.

[0103] Generally, a diaphragm includes a substrate and a coating applied to the surface of the substrate.

[0104] In some embodiments, the substrate includes, but is not limited to, at least one of polyolefins, polyesters, polyacetals, polyamides, polyethylene terephthalate, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyacrylonitrile, polyvinylidene fluoride, polyoxymethylene, polyoxymethylene, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polysulfone, and polymethyl methacrylate. Some non-limiting examples of polyolefins include at least one of polyethylene (PE), ultra-high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE), polypropylene (PP), polyethylene-polypropylene copolymer (PE-PP), and polyethylene-polypropylene-polyethylene copolymer.

[0105] In some embodiments, the coating is disposed on one side of the substrate. In some embodiments, the coating is disposed on both sides of the substrate.

[0106] In some embodiments, the coating includes inorganic fillers and diaphragm binders.

[0107] In some embodiments, the inorganic filler comprises Al2O3, SiO2, TiO2, ZrO2, Mg(OH)2, MgO, SnO2, CaCO3, BaSO4, TiN, AlN, Na2OmTiO2, K2OnTiO2, BaOx, MTiO3, and combinations thereof, wherein m is 3 or 6, n is 1, 2, 4, 6, or 8, x is 1 or 2, and M is Ba, Sr, or Ca. In some embodiments, the inorganic filler may be spherical, plate-like, disc-like, needle-like, cylindrical, irregular, or other known particle shapes.

[0108] In some embodiments, the diaphragm adhesive is a water-soluble polymer.

[0109] In some embodiments, the water-soluble polymer is a homopolymer or copolymer.

[0110] In some embodiments, the water-soluble polymer includes at least one of polyamide, polycarboxylate, polycarboxylic acid, polyacrylic acid, polyacrylate, polymethacrylic acid, polymethacrylate, polyvinyl alcohol, polyvinyl acetate, polyacrylamide, cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, carboxymethyl cellulose, cyanoethyl cellulose, acrylonitrile rubber (NBR), styrene-butadiene rubber (SBR), and latex.

[0111] In some embodiments, the chemical apparatus further includes an electrolyte.

[0112] In some embodiments, the electrolyte comprises a non-aqueous solvent and a lithium salt.

[0113] In some embodiments, the lithium salt may include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate.

[0114] In some embodiments, the non-aqueous solvent may be at least one of carbonate compounds, carboxylic acid ester compounds, and ether compounds.

[0115] In some embodiments, the carbonate compound may include at least one of chain carbonate compounds, cyclic carbonate compounds, and fluorocarbonate compounds.

[0116] In some embodiments, the chain carbonate compound may include ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), ethylene carbonate (VC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof.

[0117] In some embodiments, the cyclic carbonate compound may include ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), and combinations thereof.

[0118] In some embodiments, the fluorocarbonate compound may include at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate.

[0119] In some embodiments, the carboxylic acid ester compound may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonate lactone, caprolactone, and methyl formate.

[0120] In some embodiments, the ether compound may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

[0121] In some embodiments, the non-aqueous solvent may further include at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters.

[0122] Secondly, this application provides an electronic device including the aforementioned electrochemical device.

[0123] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. The electrochemical device of this invention is not particularly limited in its application and can be used in any electronic device known in the prior art. According to some embodiments of the invention, the electronic device includes, but is not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robot dogs, industrial robots, and android robots.

[0124] Test method: (1) XRD test: X-ray diffraction (XRD) is primarily used to study the internal crystal structure of materials. Because X-rays have wavelengths close to the interplanar spacing and possess a certain penetrating power, a beam of X-rays passes through a crystal and diffracts. Analyzing the diffraction pattern allows for phase identification and structural analysis. X-ray diffraction (XRD) was performed on the positive electrode active material to obtain its X-ray diffraction pattern, and its crystal phase, peak intensity, and positional differences of different diffraction peaks were analyzed. Testing conditions: The X-ray diffractometer was a Bruker D8 ADVANCE (Cu-Kα1, λ=1.5406Å), operating current 250mA, continuous scanning, operating voltage 40kV, scanning range 2θ 15-90°, step size 0.02, and scanning speed 2°·min. -1 .

[0125] (2) Scanning electron microscopy (SEM): The spherical structure and particle size of the first, second, and third compounds prepared in this application were analyzed by scanning electron microscopy (SEM) at a magnification of 5000-1000x. The instrument used was a JSM-7610Fplus field emission electron microscope.

[0126] Prepare positive electrode active material particle samples with cross sections, observe and photograph the particle cross sections. The positive electrode active material particles can be regarded as spherical particles with a perfect circle cross section. By testing the particle size of each particle, the D50 (d1) of the first compound and the D50 (d2) of the second compound can be calculated.

[0127] (3) The thickness of the lithium replenishment layer and the negative electrode active material layer in the negative electrode sheet prepared in this application were analyzed by scanning electron microscopy (SEM), focused ion beam (FIB) and argon ion cross-section polishing (CP) at magnification of 500-3000 times. The equipment used was a FEI Helios Nanolab 450S focused ion beam scanning electron microscope.

[0128] A cross-sectional sample of the negative electrode sheet was prepared in a glove box, and a Pt protective layer was deposited on the sample surface to prevent oxidation. The boundary between the lithium replenishment layer and the negative electrode active material layer was determined by the difference in brightness under backscattered electrons and the difference in micromorphology under secondary electrons, thereby measuring the thickness of the lithium replenishment layer L1 and the negative electrode active material layer L2.

[0129] (4) The elemental distribution of the positive electrode active material was analyzed by electron probe X-ray micro-area analysis (EPMA) under the following conditions: temperature 20±2℃, relative humidity ≤60%RH, no vibration, no strong magnetic field (<0.1 mT), independent UPS power supply (10 kVA), and field emission X-ray equipment JEOL JXA-8530F Plus was used for EPMA analysis. The thickness (L3) of the second coating layer in the positive electrode active material was analyzed based on its elemental location. The thickness of the first coating layer can also be obtained by referring to the above method.

[0130] (5) The contents of Na, R, and Co in the positive electrode active material were measured by inductively coupled plasma optical emission spectroscopy (ICP-OES). 2 g of powder sample was dissolved in 10 mL of high-purity hydrochloric acid (at least 30 wt% HCl relative to the total weight of the solution) in a conical flask. The flask was covered with a glass cap and heated on a hot plate at 380 °C until the precursor was completely dissolved. After cooling to room temperature, the solution in the conical flask was poured into a 250 mL volumetric flask. The volumetric flask was then filled to the 250 mL mark with deionized water and completely homogenized. A standard curve was plotted based on the analytes and corresponding analytical wavelengths. The contents of Na, R, and Co in the positive electrode active material were analyzed, and the total mass percentage m of the second and third compounds and the mass percentage w of R in the positive electrode active material were calculated using the stoichiometric ratios of the three elements in their respective chemical formulas.

[0131] (6) First-effect test: Five lithium-ion secondary batteries were taken from each of the comparative and example samples. The lithium-ion secondary batteries were subjected to the first charge and discharge process through the following steps, and the first coulombic efficiency of the lithium-ion secondary batteries was calculated.

[0132] First, the first charge and discharge cycle was performed at 45°C. Constant current and constant voltage charging was conducted at a charging current of 0.3C (the current required to completely discharge the theoretical capacity within 3.33 hours) until the upper limit voltage reached 4.55V, and the charging capacity of the first cycle was recorded. Then, constant current discharging was performed at a discharging current of 0.2C until the final voltage reached 2.5V, and the discharging capacity of the first cycle was recorded.

[0133] First-time efficiency = (first discharge capacity / first charge capacity) × 100%.

[0134] (7) Rate discharge test: Five lithium-ion secondary batteries were taken from each of the comparative and example samples. The lithium-ion secondary batteries were repeatedly charged and discharged through the following steps, and the rate discharge performance of the lithium-ion secondary batteries was calculated.

[0135] First, in an environment of 25℃, the first charge and discharge were performed. The device was charged at a constant current of 0.5C (the current value that completely discharges the theoretical capacity within 2 hours) until the voltage reached 4.55V. Then, it was charged at a constant voltage of 4.55V until the current dropped below 0.025C. Finally, it was discharged at a constant current of 0.2C until the final voltage reached 2.5V, and the 0.2C discharge capacity was recorded. Then, the device was charged at a constant current of 0.5C (the current value that completely discharges the theoretical capacity within 2 hours) until the voltage reached 4.55V. Then, it was charged at a constant voltage of 4.55V until the current dropped below 0.025C. Finally, it was discharged at a constant current of 2C until the final voltage reached 2.5V, and the 2C discharge capacity was recorded.

[0136] Rate discharge capacity retention rate = (2C discharge capacity / 0.2C discharge capacity) × 100%.

[0137] (8) Cyclic performance test: Five lithium-ion secondary batteries were taken from each of the comparative and example samples. The lithium-ion secondary batteries were repeatedly charged and discharged through the following steps, and the cycle capacity retention rate of the lithium-ion secondary batteries was calculated.

[0138] First, in an environment of 45℃, the first charge and discharge cycle was performed. Constant current and constant voltage charging was carried out at a charging current of 2C (i.e., the current value that completely discharges the theoretical capacity within 0.5h) until the upper limit voltage is 4.55V. Then, constant current discharging was carried out at a discharging current of 0.7C until the final voltage is 2.5V. The discharge capacity of the first cycle was recorded. Then, 400 charge and discharge cycles were performed, and the discharge capacity of the 400th cycle was recorded.

[0139] Cycle capacity retention = (Discharge capacity of the 400th cycle / Discharge capacity of the first cycle) × 100%.

[0140] (9) Thickness expansion: Five lithium-ion secondary batteries were taken from each of the comparative and example samples. The lithium-ion secondary batteries were repeatedly charged and discharged through the following steps, and the thickness expansion rate of the lithium-ion secondary batteries was calculated.

[0141] First, in an environment of 25℃, the first charge and discharge cycle was performed. Constant current and constant voltage charging was carried out at a charging current of 2C (i.e., the current value that completely discharges the theoretical capacity within 0.5h) until the upper limit voltage is 4.55V. The full-charge thickness of the battery in the first cycle was measured and recorded. Then, constant current discharge was carried out at a discharge current of 0.7C until the final voltage is 2.5V. After that, 500 discharge and charge cycles were performed, and the full-charge thickness of the battery after the 500th cycle was measured and recorded.

[0142] Thickness expansion rate = (Battery full-charge thickness at the 500th cycle / Battery full-charge thickness at the first cycle) × 100%.

[0143] Unless otherwise specified, all reagents or instruments used in this application are commercially available products.

[0144] Example 1 A method for preparing a lithium-ion secondary battery includes the following steps: (1) Preparation of the first compound: Na₂CO₃, Co₃O₄, MnSO₄, and Li₂CO₃ were weighed according to a molar ratio of Li:Na:Co:Mn of 0.985:1:0.95:0.05; Na₂CO₃, Co₃O₄, and MnSO₄ were thoroughly ball-milled for 5 hours and sintered in air at 800°C for 24 hours to obtain the precursor of the first compound. Li₂CO₃ and a first compound precursor were dispersed in deionized water at a mass ratio of 1:100. Ion exchange was performed at 100 rpm and 100 °C for 10 h, followed by drying to obtain the chemical formula Li. 0.985 Na 0.015 Co 0.95Mn 0.05 The first compound of O2.

[0145] (2) Preparation of the second compound: According to LiCo 0.95 Y 0.05 O2 was stoichiometrically weighed Co3O4, Y2O3, and Li2CO3; the above raw materials were ball-milled and mixed thoroughly for 5 hours and then sintered in air at 900°C for 20 hours to obtain the second compound; (3) Preparation of the third compound: According to Li3ZrCl4O 1.5 Weigh out ZrCl4 and anhydrous Li2O, mix them under an argon atmosphere, and then grind them at a low speed (100 r / min) for 2 h and then at a high speed (500 r / min) for 10 h to obtain an amorphous solid electrolyte (third compound).

[0146] (4) Preparation of positive electrode active material: The third compound and the second compound were placed in a mixing device at a certain mass ratio and mixed at 400 r / min for 60 min until homogeneous. The mixture was then ground at a low speed (50 r / min) for 30 min and then at a high speed (350 r / min) for 6 h at a ball milling temperature of 100℃ to obtain a coating material in which the third compound coated the surface of the second compound.

[0147] The first compound is then mixed evenly with the obtained coating material in a certain proportion, and then ground at low speed (50 r / min) for 60 min and then at high speed (400 r / min) for 8 h using a ball mill to obtain the positive electrode active material.

[0148] (5) Preparation of the positive electrode: The obtained positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 95:3:2. The mixture was then coated on both sides of the positive electrode current collector Al foil, dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0149] (6) Preparation of negative electrode: The negative electrode active material, artificial graphite, silicon carbide material, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are thoroughly mixed in a deionized water solvent system at a mass ratio of 77.9:17.1:1:1.5:2.5 to obtain a negative electrode slurry. The negative electrode slurry is coated on both sides of the negative electrode current collector Cu foil, and then dried, cold-pressed, and slit to obtain a double-sided negative electrode active material layer. The thickness of the single-sided negative electrode active material layer is L2.

[0150] Next, lithium metal powder, conductive carbon black, and polyvinylidene fluoride are added to tetrahydrofuran solvent at a mass ratio of 60:5:35 and dispersed evenly, with the solid content controlled at 35%, to obtain a lithium replenishing slurry; the lithium replenishing slurry is uniformly coated on both sides of the negative electrode active material layer to obtain a lithium replenishing layer, with a single-sided lithium replenishing layer thickness of L1; thus, a negative electrode sheet is obtained.

[0151] (7) Selection of the separator: Polyethylene (PE) porous polymer film is used as the separator.

[0152] (8) Preparation of electrolyte: The solution prepared by mixing lithium salt LiPF6 with non-aqueous organic solvent at a mass ratio of 8:92 is used as the electrolyte for lithium-ion secondary batteries. The mass ratio of each solvent in the non-aqueous organic solvent is EC:DEC:PC:PP:VC = 20:30:20:28:2.

[0153] (9) Preparation of lithium-ion secondary batteries: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes for safety isolation. The electrode assembly is then wound to form the final electrode assembly. This assembly is placed in a packaging shell, infused with electrolyte, and sealed to obtain a lithium-ion secondary battery.

[0154] Example 2 The difference between this embodiment and Example 1 is that ZrCl4 is replaced with TiCl4, and the mass percentages of Ti and Zr elements in the positive electrode active material are the same. The chemical formula of the third compound in this embodiment is Li3TiCl4O. 1.5 The rest are the same.

[0155] Examples 3-6 Compared with Example 1, this embodiment differs in that, based on the same total mass of the first compound, the second compound, and the third compound, the mass ratio of the three compounds is changed, so that the mass percentage w of R in the positive electrode active material, the total mass percentage m of the second compound and the third compound in the positive electrode active material, and the thickness L3 of the second coating layer are different, while the rest are the same.

[0156] Examples 7-10 Compared with Example 1, this embodiment differs in that, based on the same total mass of the first compound, the second compound, and the third compound, the mass ratio of the three compounds is changed, so that the mass percentage content w of R in the positive electrode active material / the total mass percentage content m of the second compound and the third compound in the positive electrode active material and the thickness L3 of the second coating layer are different. At the same time, the thickness of the lithium replenishment slurry coating is changed, so that L1 is changed, while the rest are the same.

[0157] Examples 11-12 The difference between this embodiment and Embodiment 1 is that the thickness of the negative electrode slurry coating is changed, thus altering L2; otherwise, they are the same.

[0158] Examples 13-14 Compared with Example 1, the difference in this embodiment is that, based on the same total mass of the first compound, the second compound, and the third compound, the mass ratio of the three compounds is changed, so that the mass percentage content w of R in the positive electrode active material / the total mass percentage content m of the second compound and the third compound in the positive electrode active material and the thickness L3 of the second coating layer are different. At the same time, the thickness of the negative electrode slurry and the lithium replenishment slurry coating is changed, so that L1 and L2 are changed, while the rest are the same.

[0159] Examples 15-16 The difference between this embodiment and Embodiment 1 is that the thickness of the lithium replenishment slurry coating is changed, thus altering L1; otherwise, they are the same.

[0160] Examples 17-19 The difference between this embodiment and Example 1 is that the chemical formulas of the first compounds obtained in Examples 17-19 are Li 0.99 Na 0.01 Co 0.95 Mn 0.05 O2, Li 0.98 Na 0.02 Co 0.95 Mn 0.05 O2, Li 0.956 Na 0.05 Co 0.95 Mn 0.05 O2 was used to alter the stoichiometric ratio of Li and Na elements in the first compound. Specifically, in Example 17, Na₂CO₃, Co₃O₄, MnSO₄, and Li₂CO₃ were weighed according to a Li:Na:Co:Mn molar ratio of 0.99:1:0.95:0.05; in Example 18, Na₂CO₃, Co₃O₄, MnSO₄, and Li₂CO₃ were weighed according to a Li:Na:Co:Mn molar ratio of 0.98:1:0.95:0.05; and in Example 1998, Na₂CO₃, Co₃O₄, MnSO₄, and Li₂CO₃ were weighed according to a Li:Na:Co:Mn molar ratio of 0.956:1:0.95:0.05; the rest were the same.

[0161] Examples 20-21 The difference between this embodiment and Example 1 is that the chemical formula of the second compound is changed. In Examples 20-21, the chemical formula of the second compound is LiCo. 0.95 La 0.05 O2 and LiCo 0.95 Mg0.05 O2, replace Y2O3 with La2O3 and MgO respectively, the rest are the same.

[0162] Examples 22-23 The difference between this embodiment and Example 1 is that the sintering time for preparing the first compound precursor is changed, resulting in different D50 (d1) of the matrix. Specifically, the sintering times for preparing the first compound precursor in Examples 22 and 23 are 16h and 40h, respectively, while the rest are the same.

[0163] Examples 24-25 The difference between this embodiment and Example 1 is that the sintering time for preparing the second compound is changed, so that the second compound D50 (d2) in the first coating layer is different. In Examples 24-25, the sintering times for preparing the second compound are 10h and 30h, respectively, and the rest are the same.

[0164] Example 26 The difference between this embodiment and Example 1 is that the mass ratio of artificial graphite, silicon carbide material, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) in the negative electrode active material is 76:19:1:1.5:2.5, while the rest are the same.

[0165] Example 27 The difference between this embodiment and Example 1 is that the mass ratio of artificial graphite, silicon carbide material, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) in the negative electrode active material is 90.25:4.75:1:1.5:2.5, while the rest are the same.

[0166] Comparative Example 1 Compared with Example 1, this comparative example did not prepare a second coating layer in the positive electrode active material, that is, no third compound was added to the positive electrode active material, but the rest were the same.

[0167] Comparative Example 2 The difference between this comparative example and Example 1 is that no second compound was added to the positive electrode active material in this comparative example; otherwise, they are the same.

[0168] Comparative Example 3 The difference between this comparative example and Example 1 is that no second compound and third compound were added to the positive electrode active material in this comparative example; otherwise, they are the same.

[0169] Comparative Example 4 The difference between this comparative example and Example 1 is that the amorphous solid electrolyte of the third compound in this comparative example is a crystalline solid electrolyte Li3ZrCl4O. 1.5It is obtained by heating the amorphous solid electrolyte obtained in step (3) at 850°C for 12 hours, and the rest is the same.

[0170] Comparative Example 5 The difference between this comparative example and Example 1 is that the process of preparing the lithium replenishment layer in step (6) is omitted in this comparative example, that is, there is no lithium replenishment layer in the negative electrode sheet, and the rest is the same.

[0171] The relevant parameters in the above embodiments and comparative examples are shown in Table 1, and the battery performance test results are shown in Table 2.

[0172] In Table 1-2, w represents the mass percentage of R in the positive electrode active material, m represents the total mass percentage of the second and third compounds in the positive electrode active material, d1 represents the D50 of the first compound, d2 represents the D50 of the second compound, L3 represents the thickness of the second coating layer, L2 represents the thickness of the negative electrode active material layer, L1 represents the thickness of the lithium replenishment layer, and s represents the mass percentage of silicon in the negative electrode active material layer.

[0173] Table 1 Continued from Table 1 Table 2 Continued from Table 2 The XRD patterns of the cathode active material in Example 1 show that the first peak with an intensity of I1 = 16756 cps at 18.6° is 2θ. This first peak corresponds to the characteristic diffraction peak of the (002) crystal plane, indicating that the first compound in the cathode active material has a crystal structure belonging to space group P63mc. The second peak with an intensity of I2 = 8613 cps at 19° is 2θ. This second peak represents the characteristic diffraction peak of the (003) crystal plane of the second compound with an R-3m crystal structure. The peak position difference between the second and first peaks is 0.4°, and I2 / I1 = 0.51. The absence of peaks for the third compound in the XRD pattern further confirms that it is an amorphous solid electrolyte.

[0174] As can be seen from the above embodiments and comparative examples, the battery of this application has an initial efficiency of ≥87%, a thickness expansion rate of less than 13%, a 2C rate discharge rate of ≥89%, and a high temperature (45°C) cycle retention rate of ≥85%. It can be seen that the battery of this application has high battery rate performance, initial efficiency and high temperature cycle stability, as well as a high volume expansion rate.

[0175] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of this application and not to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. An electrochemical device comprising a positive electrode and a negative electrode, characterized in that, The negative electrode sheet includes a negative current collector, a negative active material layer disposed on at least one side of the negative current collector, and a lithium replenishment layer disposed on the negative active material layer, wherein the lithium replenishment layer is located on the side away from the thickness direction of the current collector; the negative active material layer includes silicon-carbon material. The positive electrode includes a positive electrode active material, which includes a matrix, a second compound located on at least a portion of the surface of the matrix, and a third compound. The matrix includes a first compound having a crystal structure belonging to space group P63mc, the second compound having a crystal structure belonging to space group R-3m, and the third compound including an amorphous solid electrolyte. The amorphous solid electrolyte includes a metal element R, which includes at least one of Zr and Ti.

2. The electrochemical device according to claim 1, characterized in that, 0.25μm≤L1≤10μm, where L1 is the thickness of the lithium replenishment layer in μm; And / or, 25μm≤L2≤50μm, where L2 is the thickness of the negative electrode active material layer in μm; And / or, 0% < m ≤ 6.5%, where m is the total mass percentage of the third compound and the second compound in the positive electrode active material; And / or, 0.1%≤w≤2%, where w is the mass percentage of metal element R in the positive electrode active material.

3. The electrochemical device according to claim 1 or 2, characterized in that, The following relationship must be satisfied: 0 < 10 × L1 × (0.03 × m + 2.87 × w + 0.03) / L2 ≤ 0.1, In the formula, L1 is the thickness of the lithium replenishment layer in μm; L2 is the thickness of the negative electrode active material layer in μm; m is the total mass percentage of the third compound and the second compound in the positive electrode active material; and w is the mass percentage of the R metal element in the positive electrode active material.

4. The electrochemical device according to claim 1, characterized in that, The lithium replenishment layer includes lithium metal, a lithium replenishment layer conductive agent, and a lithium replenishment layer binder. Based on the total mass of the lithium replenishment layer, the mass percentage of lithium metal is 50%-70%.

5. The electrochemical device according to claim 1, characterized in that, Based on the total mass of the negative electrode active material, the mass percentage of silicon in the negative electrode active material layer is 5%-20%.

6. The electrochemical device according to claim 1, characterized in that, Includes at least one of the following: The D50 of the first compound is d1, where 5μm≤d1≤15μm; The D50 of the second compound is d2, where 0 < d2 ≤ 4 μm.

7. The electrochemical device according to claim 1, characterized in that, Includes at least one of the following I-IV: I. The amorphous solid electrolyte includes Li 2+2z RX4O 1+Z R is Zr and / or Ti, X is at least one of F, Cl, and Br, and 0 < z ≤ 0.75; II. In the X-ray diffraction pattern of the positive electrode active material, 2θ has a first peak with an intensity of I1 between 18° and 19°, and a second peak with an intensity of I2 between 18.5° and 20°. The peak position difference between the second peak and the first peak is 0.3~1°, and satisfies the following relationship: 0 <I2 / I1<1; III. The first compound includes metal-doped lithium cobalt oxide; IV. The second compound includes LiCo 1-y A y O2, 0≤y≤0.1, A is one or more of Al, Mg, La, Y, Ni, Mn, W, and V.

8. The electrochemical device according to claim 1, characterized in that, A third compound located on at least a portion of the surface of the second compound constitutes a second coating layer covering the surface of the second compound; the second compound and the third compound located on at least a portion of the surface of the substrate constitute a first coating layer covering the surface of the substrate.

9. The electrochemical device according to claim 8, characterized in that, The thickness of the second coating layer is L3, where 0 μm < L3 ≤ 0.4 μm.

10. An electronic device, characterized in that, Includes the electrochemical device according to any one of claims 1-9.

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