A high-rate battery, its preparation method, and its electrical equipment

Abstract

This disclosure relates to a high-rate battery, its preparation method, and an electrical device. The battery includes an electrolyte and a positive electrode and a negative electrode immersed in the electrolyte. The negative electrode includes a negative current collector and a negative active material layer formed on at least one surface of the negative current collector. A solid electrolyte interface layer is formed on the surface of the negative active material layer. After formation and charge / discharge, X-ray photoelectron spectroscopy (XPS) is performed on the solid electrolyte interface layer. The atomic percentage of Li₂S in the solid electrolyte interface layer is 1-10%, and the atomic percentage of LiF is 9-31%. In the battery provided by this disclosure, the Li₂S and LiF-rich SEI film can accelerate the rate of lithium-ion insertion / extraction at the negative electrode, improve the rate performance of the battery, and simultaneously improve the cycle life of the cell.

Description

Technical Field

[0001] This disclosure relates to the field of batteries, specifically to a high-rate battery, a method for preparing the same, and an electrical device thereof. Background Technology

[0002] During the first charge and discharge cycle of a lithium-ion battery, a solid electrolyte interphase (SEI) film forms at the electrode / electrolyte interface. The stability of the SEI film is closely related to the battery's cycle life and safety. An ideal SEI film should simultaneously possess the following characteristics: electronic insulation to prevent the continuous decomposition of the electrolyte; and ion conductivity to allow Li-ion exchange. + Efficient diffusion provides assurance; mechanical stability adapts to volume changes of the electrode during cycling.

[0003] SEI layers are typically composite structures consisting of an organic outer layer and an inorganic inner layer. The organic layer buffers volumetric deformation, while the inorganic inner layer, containing substances such as LiF and Li₂CO₃, plays a decisive role in the overall performance of the SEI film. The inorganic components, due to their high ionic conductivity (e.g., the lithium-ion diffusion barrier in LiF is below 0.5 eV), good chemical inertness (resistance to high voltage and / or high temperature), and excellent mechanical properties (elastic modulus exceeding 65 GPa), can effectively suppress lithium dendrite growth and reduce interfacial polarization.

[0004] However, the inorganic component content in SEI films formed by conventional technologies is generally low (usually below 40%) and discontinuously distributed. This causes the interface to repeatedly break down and regenerate during cycling, continuously consuming active lithium, increasing ion migration resistance, and thus severely affecting battery performance. Therefore, there is an urgent need to construct SEI films rich in highly stable inorganic components to overcome the current bottleneck in battery performance. Summary of the Invention

[0005] The purpose of this disclosure is to provide a negative electrode rich in Li2S and LiF in the SEI layer, thereby improving the rate performance and cycle life of the battery cell.

[0006] To achieve the above objectives, a first aspect of this disclosure provides a high-rate battery, the battery comprising an electrolyte and a positive electrode and a negative electrode immersed in the electrolyte, the negative electrode comprising a negative current collector and a negative active material layer formed on at least one surface of the negative current collector; a solid electrolyte interface layer is formed on the surface of the negative active material layer; After formation and charging / discharging, X-ray photoelectron spectroscopy was performed on the solid electrolyte interface layer. The atomic percentage of Li2S in the solid electrolyte interface layer was 1-10%, and the atomic percentage of LiF was 9-31%.

[0007] Optionally, after formation and charging / discharging, the solid electrolyte interface layer is subjected to X-ray photoelectron spectroscopy measurement, wherein the atomic percentage of Li2S in the solid electrolyte interface layer is 2-10%, and the atomic percentage of LiF is 13-31%.

[0008] Optionally, the battery is filled with a filling gas containing sulfur hexafluoride; the filling gas makes the internal absolute pressure of the battery 111~200 kPa.

[0009] Optionally, the negative electrode active material layer includes a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent; the weight ratio of the negative electrode active material to the negative electrode binder is 1:(0.01~0.03); the weight ratio of the negative electrode active material to the negative electrode conductive agent is 1:(0.1~1); the electrolyte includes an electrolyte lithium salt and a non-aqueous solvent; the concentration of the electrolyte lithium salt in the electrolyte is 0.5~2 mol / L.

[0010] The second aspect of this disclosure provides a method for preparing a high-rate battery, the method comprising: A positive electrode, a separator, and a negative electrode are stacked sequentially to form a battery core, and an electrolyte is injected into the battery core to obtain a battery cell. The battery cell is aged by injecting fluorinated gas into it to bring the internal absolute pressure of the cell to a target pressure, and then forming and aging are performed to obtain a formed battery. The fluorinated gas includes sulfur hexafluoride gas. The target pressure is 111~400 kPa.

[0011] Optionally, the target pressure is 111~300 kPa.

[0012] Optionally, the fluorinated gas further contains an inert gas; in the fluorinated gas, the volume ratio of the sulfur hexafluoride gas to the inert gas is 1:(0.5~1).

[0013] Optionally, the preparation method further includes: performing capacity testing and venting on the formed battery; confining the vented battery cell to obtain a lower battery cell; injecting sulfur hexafluoride gas into the lower battery cell and sealing it to obtain a core battery; the internal absolute pressure of the core battery is 111~200 kPa.

[0014] The third aspect of this disclosure provides a battery prepared using the preparation method described in the second aspect of this disclosure.

[0015] A fourth aspect of this disclosure provides an electrical device comprising a battery as described in the first aspect of this disclosure or a battery as described in the third aspect of this disclosure.

[0016] Through the above technical solution, after the battery is formed and charged and discharged, the atomic percentage of Li2S in the solid electrolyte interphase (SEI) layer is 1~10%, and the atomic percentage of LiF is 9~31%. The Li2S- and LiF-rich SEI film can accelerate the rate of lithium ion insertion and extraction at the negative electrode and improve the rate performance of the battery. At the same time, the Li2S- and LiF-rich SEI film has higher thermal stability and electrochemical stability, which can better protect the negative electrode, reduce the reaction between lithium and electrolyte at the negative electrode, avoid deterioration of battery performance, and thus improve the cycle life of the cell.

[0017] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings: Figure 1 This is the XPS-detected Li spectrum of the negative electrode SEI layer in Example 3.

[0019] Figure 2 This is the XPS-detected Li spectrum of the negative electrode SEI layer in Comparative Example 1.

[0020] Figure 3 This is a schematic diagram of introducing fluorine-containing gas into the battery cell in some embodiments of this disclosure. Detailed Implementation

[0021] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure.

[0022] The first aspect of this disclosure provides a high-rate battery, the battery including an electrolyte and a positive electrode and a negative electrode immersed in the electrolyte, the negative electrode including a negative current collector and a negative active material layer formed on at least one surface of the negative current collector; a solid electrolyte interface layer is formed on the surface of the negative active material layer; After formation and charging / discharging, X-ray photoelectron spectroscopy was performed on the solid electrolyte interface layer. The atomic percentage of Li2S in the solid electrolyte interface layer was 1-10%, and the atomic percentage of LiF was 9-31%.

[0023] The battery disclosed herein, after formation and charging / discharging, has a Li2S atomic percentage of 1-10% and a LiF atomic percentage of 9-31% in the solid electrolyte interphase (SEI) layer. The Li2S and LiF-rich SEI film can accelerate the rate of lithium ion insertion / extraction at the negative electrode and improve the rate performance of the battery. At the same time, the Li2S and LiF-rich SEI film has higher thermal stability and electrochemical stability, which can better protect the negative electrode, reduce the reaction between lithium and electrolyte at the negative electrode, effectively avoid the degradation of battery performance, and thus improve the cycle life of the cell.

[0024] In some embodiments of this disclosure, the atomic percentage of Li₂S in the solid electrolyte interphase (SEI) layer can be 1%, 1.8%, 2%, 2.2%, 3%, 4%, 4.2%, 5%, 5.1%, 5.2%, 5.3%, 6%, 7%, 8%, 9%, 9.5%, 9.7%, 9.9%, 10%, or any value within the aforementioned range. In some embodiments of this disclosure, the atomic percentage of LiF in the solid electrolyte interphase (SEI) layer can be 9%, 10%, 12%, 13.5%, 13.8%, 15%, 19.5%, 19.7%, 19.8%, 19.9%, 20%, 25%, 28.3%, 29.0%, 29.9%, 30%, 31%, or any value within the aforementioned range.

[0025] In some embodiments of this disclosure, in order to balance the capacity and cycle performance of the battery cell, X-ray photoelectron spectroscopy is performed on the solid electrolyte interface layer after formation and charging / discharging. The atomic percentage of Li2S in the solid electrolyte interface layer is 2-10%, and the atomic percentage of LiF is 13-31%.

[0026] In some embodiments of this disclosure, the battery is filled with a filling gas containing sulfur hexafluoride. By sealing the sulfur hexafluoride gas within the cell, the cycle stability of the cell can be further improved during subsequent use. Specifically, the volume percentage of sulfur hexafluoride gas in the filling gas can be 99.9% to 100% by volume. Alternatively, a mixture of sulfur hexafluoride gas and an inert gas can be injected into the battery to further improve the cycle stability of the cell. The inert gas can be selected from argon and / or argon gas.

[0027] In some embodiments of this disclosure, the filling gas causes the internal absolute pressure of the battery to be 111-200 kPa. For example, in some embodiments, the internal absolute pressure of the battery can be 111 kPa, 120 kPa, 130 kPa, 140 kPa, 150 kPa, 160 kPa, 170 kPa, 180 kPa, 190 kPa, 200 kPa, or any value within the aforementioned range.

[0028] In some embodiments of this disclosure, the negative electrode active material layer includes a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent. The negative electrode active material can be one or more common negative electrode active materials in the art, including but not limited to carbon-based materials, silicon-based materials, tin-based materials, germanium-based materials, phosphorus-based materials, lithium titanate, lithium titanium phosphate, titanium dioxide, and iron oxide. Specifically, the carbon-based material can include graphite (such as natural graphite and artificial graphite), non-graphitized carbon (soft carbon, hard carbon), etc.; the silicon-based material can include one or more of elemental silicon, silicon-based alloys, silicon oxides, and silicon-carbon composite materials; the tin-based material can include one or more of elemental tin, tin alloys, tin oxides, and tin-carbon composite materials; the germanium-based material can include elemental germanium, germanium-carbon composite materials, germanium oxides, and sulfides; and the phosphorus-based material can include red phosphorus, black phosphorus, and phosphorus-carbon composite materials.

[0029] In some specific embodiments, the negative electrode binder may be selected from one or more of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyacrylamide (PAM), polyacrylic acid (PAA), polyacrylate, polyvinyl alcohol (PVA), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR).

[0030] In some embodiments of this disclosure, the weight ratio of the negative electrode active material to the negative electrode binder can be 1:(0.01~0.03), which makes the battery of this disclosure have a high capacity.

[0031] The negative electrode conductive agent can be one or more of acetylene black, Ketjen black, Super P conductive carbon black, furnace black, graphite, carbon fiber and carbon nanotubes (CNTs).

[0032] In some embodiments of this disclosure, the weight ratio of the negative electrode active material to the negative electrode conductive agent can be 1:(0.1~1) to improve the rate performance of the battery of this disclosure.

[0033] In this disclosure, a negative electrode slurry can be obtained by mixing a negative electrode active material, a negative electrode binder, a negative electrode conductive agent and a solvent in a certain proportion; the obtained negative electrode slurry is coated on a negative electrode current collector, dried to form a negative electrode material layer, and then rolled and slit to obtain a negative electrode sheet.

[0034] The solvent in the negative electrode slurry can be one or more of N-methylpyrrolidone (NMP), dimethylformamide (DMF), diethylformamide (DEF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), alcohol solvents, and water.

[0035] In some embodiments of this disclosure, the electrolyte comprises an electrolyte lithium salt and a non-aqueous solvent. To achieve high battery capacity and good cycle stability, the electrolyte lithium salt may be selected from one or more of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorosilicate, lithium tetraphenylborate, lithium chloride, lithium bromide, lithium chloroaluminate, lithium fluorocarbon sulfonate, LiCH3SO3, LiN(SO2CF3)2, and LiN(SO2C2F5)2. The non-aqueous solvent may be selected from one or more of chain esters, cyclic esters, chain ethers, and cyclic ethers. Specifically, the non-aqueous solvent may be selected from one or more of propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, vinylene carbonate, fluoroethylene carbonate, methyl formate, ethyl acetate, ethyl propionate, propyl propionate, methyl butyrate, methyl acrylate, ethylene sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, ethylene sulfate, acid anhydride, and 1,3-propanesulfonate lactone.

[0036] In some embodiments, the positive electrode and the negative electrode are separated by a separator. In order to promote the rapid movement of ions in the electrolyte between the positive and negative electrodes of the battery, the separator may be selected from polyethylene separator and / or polypropylene separator.

[0037] In some embodiments of this disclosure, the concentration of the electrolyte lithium salt in the electrolyte can be 0.5~2 mol / L to enable the battery to have high capacity and good cycle stability. When the concentration of the electrolyte lithium salt in the electrolyte is below 0.5 mol / L, the impedance of the electrolyte is too high, while when the concentration of the electrolyte lithium salt in the electrolyte is above 2 mol / L, the viscosity of the electrolyte is too high.

[0038] In some embodiments of this disclosure, the negative electrode sheet can also be a lithium-replenishing negative electrode to reduce the irreversible consumption of active lithium extracted from the positive electrode by the negative electrode, thereby improving the energy density of the battery. The lithium-replenishing negative electrode can be prepared by methods such as lithium foil lithium replenishment, lithium powder lithium replenishment, evaporation lithium replenishment, and electrochemical lithium replenishment.

[0039] In some embodiments of this disclosure, the positive electrode sheet includes a positive current collector and a positive active material layer. The active material in the positive active material layer can be any positive active material, such as layered oxide materials, polyanionic materials, spinel-type materials, etc. Specifically, the positive active material can be selected from one or more of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, high-voltage lithium nickel manganese oxide, and lithium-rich manganese-based materials.

[0040] In some embodiments of this disclosure, the positive current collector is an aluminum foil, and the thickness of the positive current collector can be 15-18 μm. For example, the thickness of the positive current collector can be 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, and 18 μm, or any thickness within the aforementioned range.

[0041] In some embodiments of this disclosure, the positive electrode may further include a lithium replenishing agent to replenish the lithium consumed in the formation of the SEI film, promoting the formation of a more stable and high-performance SEI film, thereby improving the ionic conductivity and mechanical stability of the SEI film. The lithium replenishing agent may be selected from lithium oxide, lithium carbonate, lithium-rich manganese-based materials, lithium ferrite, and lithium nickel oxide, among other lithium replenishing materials.

[0042] The second aspect of this disclosure also relates to a method for preparing a high-rate battery, the method comprising: A positive electrode, a separator, and a negative electrode are stacked sequentially to form a battery core, and an electrolyte is injected into the battery core to obtain a battery cell. The battery cell is aged by injecting fluorinated gas into it to bring the internal absolute pressure of the cell to a target pressure, and then forming and aging are performed to obtain a formed battery. The fluorinated gas includes sulfur hexafluoride gas. The target pressure is 111~400 kPa.

[0043] This disclosure introduces a certain amount of SF6 gas into the battery cell after electrolyte injection and aging, and then seals the cell, allowing it to be pressurized and formed under SF6 atmosphere. This process helps to increase the atomic percentage of Li2S and LiF in the SEI film formed during cell formation, accelerates the rate of lithium ion insertion / extraction at the negative electrode, better protects the negative electrode, reduces the reaction between lithium and electrolyte at the negative electrode, thus avoiding degradation of battery performance, and further improves the rate performance and cycle stability of the battery cell.

[0044] In this disclosure, the absolute pressure of the SF6 gas injected into the battery cell can be between 111 and 400 kPa, for example, 111 kPa, 130 kPa, 150 kPa, 180 kPa, 200 kPa, 220 kPa, 250 kPa, 280 kPa, 300 kPa, 350 kPa, 400 kPa, or any value within the aforementioned range. The inventors of this disclosure have discovered through research that as the concentration of SF6 in the battery cell increases during formation, the contents of Li2S and LiF show a significant increasing trend, and the high-temperature cycling and rate performance of the battery cell also improve accordingly. However, when the internal absolute pressure exceeds 400 kPa, due to the influence of the reaction rate, the improvement effect of SF6 on the battery cell formation is not significant.

[0045] When the absolute pressure inside the cell exceeds 300 kPa during formation, the Li2S and LiF in the SEI film will not change significantly compared to 300 kPa due to the influence of the reaction rate. In some embodiments of this disclosure, the target pressure is 111~300 kPa in order to better improve the high-temperature cycling performance and rate performance of the cell.

[0046] This disclosure uses an external flow meter to introduce SF6 gas into the battery cell. The specific structure is as follows: Figure 3 As shown, this flow meter can record gas flow rate, total ventilation volume, and pressure in real time.

[0047] In some embodiments of this disclosure, the fluorinated gas may also contain an inert gas; the presence of a certain internal pressure within the battery cell improves the battery's cycle performance. The inert gas is selected from argon and / or argon gas.

[0048] To enhance the effect of SF6 gas on cell formation, the volume ratio of sulfur hexafluoride gas to the inert gas in the fluorinated gas can be 1:(0.5~1). Specifically, the volume ratio of sulfur hexafluoride gas to the inert gas can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, or any ratio within the aforementioned range.

[0049] According to this disclosure, the method for cell formation is not specifically limited. Formation by injecting fluorinated gas into the aged cell can increase the atomic percentage of Li₂S and LiF in the SEI film. For example, in some specific embodiments, the formation method may include: polarizing the original cell at a constant current density of 0.05-5C for up to 5 formation cycles within the full voltage window of the battery, thereby generating the formed SEI by reducing the electrolyte on the negative electrode, thus producing the target battery.

[0050] In some embodiments of this disclosure, the aging time can be 20 to 50 hours.

[0051] In some embodiments of this disclosure, the aging process can be carried out at 20~30°C.

[0052] In some embodiments of this disclosure, the preparation method further includes: The formed battery is then subjected to capacity testing and degassing; the degassed cells are then bound together to obtain the downstream cells. Sulfur hexafluoride gas is injected into the lower-line battery cell and then sealed to obtain the core battery.

[0053] After the battery cell is produced, SF6 is introduced into the cell to a certain internal absolute pressure to continuously improve the SEI membrane during subsequent cycles.

[0054] In some embodiments of this disclosure, the internal absolute pressure of the battery cell is 111-200 kPa. In this disclosure, introducing a certain amount of SF6 gas into the cell during its production process is beneficial for further improving the cell's cycle stability during subsequent use, and the improvement in cycle performance becomes more significant with increasing SF6 injection. However, when the internal absolute pressure of the produced cell exceeds 200 kPa, excessive SF6 will consume more lithium ions, leading to cell capacity loss and affecting cell cycle performance.

[0055] This disclosure also relates to a battery prepared using the above-described preparation method.

[0056] This disclosure introduces a certain amount of SF6 gas into the battery cell after electrolyte injection and aging, and then seals the battery cell, allowing it to be pressurized and formed in an SF6 atmosphere. This is beneficial for increasing the atomic percentage of Li2S and LiF in the SEI film formed by the battery cell formation, thereby further improving the rate performance and cycle stability of the battery cell.

[0057] A fourth aspect of this disclosure also provides an electrical device comprising the battery described in the first aspect of this disclosure or a battery prepared using the above-described preparation method.

[0058] In some embodiments of the electrical equipment disclosed herein, the electrical equipment may be, for example, an electric vehicle, a portable device, an energy storage cabinet, etc.

[0059] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited thereto.

[0060] In the following examples, the positive electrode active material used to prepare the battery is lithium iron phosphate (LFP), the D50 of the lithium iron phosphate particles is 0.8-1.4 μm, and the specific capacity is 142 mAh / g; the conductive agents used in the positive electrode include carbon nanotubes (CNT) and conductive carbon black (Super P, SP), the binder is polyvinylidene fluoride (PVDF), and the solvent is N-methylpyrrolidone (NMP).

[0061] The positive electrode sheet can be prepared by the following steps: a positive electrode slurry prepared by mixing LFP, CNT:SP:PVDF:NMP in a mass ratio of 100:12:0.3:2.5:55 is coated on both sides of a 16 μm thick aluminum foil, and then dried and pressed to obtain the positive electrode sheet.

[0062] In the following examples, the negative electrode active material used to prepare the battery is natural graphite, with an initial specific capacity of 355 mAh / g; the conductive agent used in the negative electrode is conductive carbon black (SP), the binder is sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR), and the solvent is water.

[0063] The negative electrode sheet can be prepared by the following steps: graphite, SP, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber and water are mixed and stirred evenly in a ratio of 100:1:1.5:3:130 to obtain a negative electrode slurry; the negative electrode slurry is coated on both sides of an 8 μm thick conductive copper foil, dried at 110℃, rolled, and then slit and die-cut to obtain the negative electrode sheet.

[0064] Example 1 This embodiment illustrates the preparation method of the high-rate battery disclosed herein, including the following steps: (1) The positive electrode, polypropylene separator and negative electrode are stacked in a Z-shaped stacking manner to form a lithium-ion battery core facing one direction; the battery core is housed in the battery casing and electrolyte is injected under vacuum conditions at an injection coefficient of 2.8 g / Ah, and the battery casing is sealed to obtain the battery cell; the electrolyte is prepared according to the weight ratio of LiPF6:DMC:EMC:EC:VC=12.3:23.73:33.42:29.92:3; (2) The battery cell was aged at 25°C for 1 hour to obtain an aged battery cell. SF6 gas was injected into the aged battery cell to make the internal absolute pressure of the battery cell reach 111 kPa. The battery cell was sealed with a sealing nail and formed at a temperature of 25°C. Then it was left to stand (age) for 12 hours. After the internal absolute pressure of the battery cell stabilized, it was formed to obtain a formed battery. SF6 gas was injected into the aged battery cell by using an external flow meter. (3) The formed battery is subjected to capacity testing and degassing, and the degassed cells are bound to obtain the lower cell; the lower cell is degassed and sealed to obtain the internal absolute pressure of the core battery, which is 101 kPa.

[0065] The prepared long-cell battery has a length of 500 mm, a width of 12 mm, a cell capacity of 86 Ah, and an explosion-proof valve opening pressure of 0.5 ± 0.1 MPa.

[0066] The specific method of formation in step (2) is as follows: the battery cell is first charged with a constant current density of 0.05C for 145 min, then charged with a constant current density of 0.33C for 40 min, then charged with a constant current density of 0.5C for 43 min, then charged with a constant current density of 0.2C to 3.8V, then charged with a constant current density of 0.1C to 3.8V, and finally charged with a constant current density of 0.05C to 4.0V to cut off, thus completing the formation.

[0067] Example 2 The method for preparing the battery in this embodiment is similar to that in Example 1, except that: In step (2), SF6 gas is injected into the aged battery cell until the internal absolute pressure of the cell reaches 150 kPa before formation. The internal absolute pressure of the battery cell is 101 kPa.

[0068] Example 3 The method for preparing the battery in this embodiment is similar to that in Example 1, except that: In step (2), SF6 gas is injected into the aged battery cell until the internal absolute pressure of the cell reaches 300 kPa before formation. The internal absolute pressure of the battery cell is 101 kPa.

[0069] Example 4 The method for preparing the battery in this embodiment is similar to that in Example 1, except that: In step (2), SF6 gas is injected into the aged battery cell until the internal absolute pressure of the cell reaches 320 kPa before formation. The internal absolute pressure of the battery cell is 101 kPa.

[0070] Example 5 The method for preparing the battery in this embodiment is similar to that in Example 1, except that: In step (2), SF6 gas is injected into the aged battery cell until the internal absolute pressure of the cell reaches 400 kPa before formation. The internal absolute pressure of the battery cell is 101 kPa.

[0071] Example 6 The method for preparing the battery in this embodiment is similar to that in Example 3, except that: Instead of directly evacuating and sealing the battery cells, sulfur hexafluoride gas is introduced through an external flow meter before sealing, resulting in an internal absolute pressure of 111 kPa for the battery cells.

[0072] Example 7 The battery preparation method in this embodiment is similar to that in Example 6, except that: after filling the cell with sulfur hexafluoride gas, it is sealed, and the internal absolute pressure of the resulting battery cell is 150 kPa.

[0073] Example 8 The battery preparation method in this embodiment is similar to that in Example 6, except that: after filling the lower cell with sulfur hexafluoride gas and sealing it, the internal absolute pressure of the resulting cell battery is 200 kPa.

[0074] Example 9 The battery preparation method in this embodiment is similar to that in embodiment 1, except that in step (2), fluorine-containing gas is injected into the aged battery cell through an external flow meter until the absolute pressure inside the battery cell is 300 kPa. The fluorine-containing gas includes high-purity argon and SF6 gas, and the volume ratio of argon and SF6 gas is 1:1.

[0075] Comparative Example 1 The method for preparing the battery in this comparative example includes the following steps: (1) The positive electrode, polypropylene separator and negative electrode are stacked in a Z-shaped stacking manner to form a lithium-ion battery core facing one direction; the battery core is housed in the battery casing and electrolyte is injected under vacuum conditions at an injection coefficient of 2.8 g / Ah, and the battery casing is sealed to obtain the battery cell; the electrolyte is prepared according to the weight ratio of LiPF6:DMC:EMC:EC:VC=12.3:23.73:33.42:29.92:3; (2) The battery cell was aged at 25°C for 1 hour to obtain the aged battery cell. The aged battery cell was sealed with a sealing nail and formed at 25°C; then it was left to stand (age) for 12 hours to obtain the formed battery. (3) The formed battery is subjected to capacity testing and degassing, and the degassed cells are bound to obtain the lower cell; the lower cell is degassed and sealed to obtain the internal absolute pressure of the core battery, which is 101 kPa.

[0076] The prepared long-cell battery has a length of 500 mm, a width of 12 mm, a cell capacity of 86 Ah, and an explosion-proof valve opening pressure of 0.5 ± 0.1 MPa.

[0077] Comparative Example 2 The method for preparing the battery in this comparative example is basically similar to that in comparative example 1, except that: In step (2), high-purity argon gas is injected into the cell after liquid injection and aging by using an external flow meter to make the absolute pressure inside the cell reach 111 kPa. The cell is then sealed with a sealing nail and formed at a temperature of 25°C. After that, the cell is left to stand (age) for 12 hours. Once the absolute pressure inside the cell has stabilized, the cell is then formed to obtain the formed battery.

[0078] Comparative Example 3 The method for preparing the battery in this comparative example is basically similar to that in comparative example 1, except that: In step (2), high-purity argon gas is injected into the cell after liquid injection and aging by using an external flow meter to make the absolute pressure inside the cell reach 111 kPa. The cell is then sealed with a sealing nail and formed at a temperature of 25°C. After that, the cell is left to stand (age) for 12 hours. Once the absolute pressure inside the cell has stabilized, the cell is then formed to obtain the formed battery.

[0079] In step (3), the formed battery is subjected to capacity testing and venting, and the vented battery cell is constrained to obtain the lower battery cell; high-purity argon gas is filled into the lower battery cell by the external flow meter and then sealed, and the internal absolute pressure of the obtained core battery is 200 kPa.

[0080] Comparative Example 4 The method for preparing the battery in this comparative example is basically similar to that in comparative example 1, except that: In step (3), the formed battery is subjected to capacity testing and venting, and the vented battery cell is constrained to obtain the lower battery cell; sulfur hexafluoride gas is filled into the lower battery cell to a certain internal absolute pressure by using an external flow meter and then sealed. The internal absolute pressure of the obtained core battery is 200 kPa.

[0081] Comparative Example 5 The method for preparing the battery in this comparative example is similar to that in Example 1, except that: In step (2), SF6 gas is injected into the aged battery cell until the internal absolute pressure of the cell reaches 105 kPa before formation. The internal absolute pressure of the battery cell is 101 kPa.

[0082] (1) XPS test XPS tests were performed on the SEI layers of the battery anodes obtained during the preparation processes of Examples 1-9 and Comparative Examples 1-5.

[0083] Test method: After cell formation and 500 cycles of high-temperature cycling of the battery core, the cells were discharged at constant current to 2.0 V, and then disassembled. The disassembled cells were immersed in DMC to obtain the negative electrode SEI layer. XPS test analysis was performed on the negative electrode SEI layer, and the obtained Li spectrum was refined and peaked. The proportion of the peaks corresponding to Li2S and LiF in the total Li spectrum was recorded.

[0084] The method for cycling the battery cell at high temperature for 500 cycles is the same as the subsequent high-temperature cycling performance test of lithium-ion batteries.

[0085] Figure 1 This is the XPS-detected Li spectrum of the negative electrode SEI layer in Example 3. Figure 2 This is the XPS-detected Li spectrum of the negative electrode SEI layer in Comparative Example 1.

[0086] The XPS spectra of the formed negative electrode SEI layer obtained in Example 3 and Comparative Example 1 are used as examples for analysis. The specific operation is as follows: Peak fitting was performed on the Li spectrum to obtain the sum of peak areas S for each component.

[0087] If the peak area of ​​Li2S is S1 and the peak area of ​​LiF is S2, then the atomic percentage of Li2S in the negative electrode SEI layer is (S1 / S)*100% and the atomic percentage of LiF is (S2 / S)*100%.

[0088] Table 1 shows the battery's capacity and the atomic percentages of Li2S and LiF in the negative electrode SEI after formation and 500 cycles.

[0089] (2) Performance testing (i) High-temperature cycle performance test of lithium-ion battery: At 25℃, the battery cell was charged and discharged three times at 0.33C, with a voltage range of 2.0-3.8V. The capacity of the third discharge was calibrated as the battery capacity Q. After calibrating the capacity, the battery was charged at 60℃ with a constant current and constant voltage of 1C to 3.8V, with a cutoff current of 0.05C. After resting for 30 minutes, it was discharged at a constant current of 1C to 2.0V, and then rested for 30 minutes. This constitutes one charge-discharge cycle. The lithium-ion battery was cycled 500 times according to the above steps, and the cycle capacity retention rate during the cycle was recorded as: discharge capacity per cycle / discharge capacity of the first cycle * 100%.

[0090] (ii) Discharge rate performance test of lithium-ion battery: At 25 ℃, the battery cell was charged and discharged three times at 0.33C, with a voltage range of 2.0-3.8V. The capacity of the third discharge was calibrated as the battery capacity C0. After calibrating the capacity, the battery was charged to 3.8V at 0.33C0 at 25℃, with a cutoff current of 0.05C. After standing for 30 minutes, it was discharged to 2.0V at 3C0, and the discharge capacity C3 was recorded. The discharge rate performance α = C3 / C0*100%.

[0091] Table 1

[0092] Comparison of Comparative Example 1 and Examples 1-9 shows that cell formation under SF6 atmosphere can significantly increase the atomic percentage of Li2S and LiF in the SEI film. Examples 1-4 show that as the SF6 concentration in the cell increases during formation, the content of Li2S and LiF increases significantly, and the high-temperature cycling and rate performance of the cell also improves. However, when the absolute pressure inside the cell exceeds 300 kPa (e.g., 320 kPa, 400 kPa) during formation (the opening pressure of the explosion-proof valve for this cell is 0.5 ± 0.1 MPa), due to the influence of the reaction rate, the Li2S and LiF content in the SEI film does not change significantly compared to 300 kPa.

[0093] A comparison of Examples 3, 6-8, and Comparative Example 1 reveals that introducing a certain amount of SF6 into the cell during its production process can improve the cell's cycle stability during subsequent use. The improvement in cycle performance becomes more pronounced with increasing SF6 content. However, when the internal absolute pressure of the cell exceeds 150 kPa, such as the 200 kPa pressure in Example 8, the cell's cycle performance deteriorates. For instance, the cell capacity in Example 8 is significantly lower than that in Example 7, possibly because excessive SF6 consumes more lithium ions, leading to capacity loss. Comparing Comparative Examples 1-3 and Example 8 shows that a certain internal pressure within the cell improves cycle performance, but the improvement in cycle performance in Example 8 primarily relies on the effect of SF6.

[0094] According to Comparative Example 5, it can be seen that the formation of the battery cell under SF6 atmosphere and with an internal absolute pressure of 111 kPa to 400 kPa is beneficial to improving the high-temperature cycling performance and rate performance of the battery cell.

[0095] The preferred embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0096] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0097] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A high-rate battery, comprising an electrolyte and a positive electrode and a negative electrode immersed in the electrolyte, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector; a solid electrolyte interface layer is formed on the surface of the negative electrode active material layer. After formation and charging / discharging, X-ray photoelectron spectroscopy was performed on the solid electrolyte interface layer. The atomic percentage of Li2S in the solid electrolyte interface layer was 1-10%, and the atomic percentage of LiF was 9-31%.

2. The battery according to claim 1, wherein, After formation and charging / discharging, X-ray photoelectron spectroscopy was performed on the solid electrolyte interface layer. The atomic percentage of Li2S in the solid electrolyte interface layer was 2-10%, and the atomic percentage of LiF was 13-31%.

3. The battery according to claim 1 or 2, wherein, The battery is filled with a filling gas containing sulfur hexafluoride; the filling gas makes the internal absolute pressure of the battery 111~200 kPa.

4. The battery according to claim 1 or 2, wherein, The negative electrode active material layer includes a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent; the weight ratio of the negative electrode active material to the negative electrode binder is 1:(0.01~0.03); the weight ratio of the negative electrode active material to the negative electrode conductive agent is 1:(0.1~1). The electrolyte includes an electrolyte lithium salt and a non-aqueous solvent; The concentration of the electrolyte lithium salt in the electrolyte is 0.5~2 mol / L.

5. A method for preparing a high-rate battery, characterized in that, The preparation method includes: A positive electrode, a separator, and a negative electrode are stacked sequentially to form a battery core, and an electrolyte is injected into the battery core to obtain a battery cell. The battery cell is aged by injecting fluorinated gas into it to bring the internal absolute pressure of the cell to a target pressure, and then forming and aging are performed to obtain a formed battery. The fluorinated gas includes sulfur hexafluoride gas. The target pressure is 111~400 kPa.

6. The preparation method according to claim 5, wherein, The target pressure is 111~300 kPa.

7. The preparation method according to claim 5 or 6, wherein, The fluorinated gas also contains an inert gas; in the fluorinated gas, the volume ratio of the sulfur hexafluoride gas to the inert gas is 1:(0.5~1).

8. The preparation method according to claim 5, wherein, The preparation method further includes: The formed battery is then subjected to capacity testing and degassing; the degassed cells are then bound together to obtain the downstream cells. Sulfur hexafluoride gas is injected into the lower cell and sealed to obtain a core battery; the internal absolute pressure of the core battery is 111~200 kPa.

9. A battery prepared by the preparation method according to any one of claims 5 to 8.

10. An electrical appliance, characterized in that, The electrical device includes the battery as described in any one of claims 1 to 4 or the battery as described in claim 9.

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