Secondary battery and electric device

Abstract

The application discloses a secondary battery and an electric device, and belongs to the technical field of secondary batteries. The positive electrode material layer in the secondary battery comprises a positive electrode material, and the positive electrode material comprises lithium nickel manganese oxide. After one cycle and 200 cycles of the secondary battery, the lowest peaks of the positive electrode material layer in the infrared spectrum within the range of 550-950 cm ‑1 The application can effectively reduce the side reaction of electrolyte and the positive electrode by introducing carbamate compounds in the positive electrode material layer, can form metal-oxygen bonds by coordinating transition metal ions with N and O containing lone pair electrons in the carbamate group, and can comprehensively control the absolute value (i.e., acm ‑1 ) of the peak difference of peaks A and B, the ratio b between the thickness of the positive electrode material layer and the particle size Dv50 of the positive electrode material, and the viscosity ccP of the electrolyte, so that (a x c) / b is within a suitable range, and the cycle performance and fast charging performance of the secondary battery can be comprehensively improved.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, specifically to a secondary battery and an electrical device. Background Technology

[0002] Currently, the development of high-energy-density cathode materials has become a research hotspot. Spinel-structured lithium nickel manganese oxide (LNMO) has received widespread attention and research in recent years due to its environmental friendliness, safety, and high energy density. However, when the cathode sheet is in large-area contact with the electrolyte, LNMO readily reacts with the electrolyte, generating byproducts and gases, which significantly affects the stability and performance of the cathode sheet. Furthermore, after the transition metal ions in LNMO dissolve, they deposit on the anode. These deposited transition metal ions catalyze the reduction and decomposition reaction of the electrolyte, leading to continuous thickening and reorganization of the solid electrolyte interphase (SEI) film. This continuously consumes the limited active lithium ions in the battery, causing severe capacity decay and affecting battery life.

[0003] In view of this, it is indeed necessary to provide a technical solution to the above problems. Summary of the Invention

[0004] Based on the deficiencies of the existing technology, the purpose of this application is to provide a secondary battery and electrical equipment.

[0005] To achieve the above objectives, the technical solution adopted in this application is as follows: In a first aspect of this application, a secondary battery is provided, including a cell and an electrolyte. The cell includes a positive electrode sheet, the positive electrode sheet includes a positive electrode material layer, the positive electrode material layer includes a positive electrode material, the positive electrode material includes lithium nickel manganese oxide, and the surface of the positive electrode material layer opposite to the positive electrode current collector is covered with a protective layer, the protective layer containing urethane groups. After one cycle of the secondary battery, the infrared spectrum of the positive electrode material layer is in the range of 550~950 cm⁻¹. -1 The lowest peak within the range is peak A; after 200 cycles of the secondary battery, the infrared spectrum of the positive electrode material layer is in the range of 550~950 cm⁻¹. -1 The lowest peak within the range is peak B; The absolute value of the peak position difference between peak A and peak B is acm. -1 ; The ratio between the thickness of the positive electrode material layer and the particle size Dv50 of the positive electrode material is b; The viscosity of the electrolyte at 25°C is cpp; The secondary battery satisfies: 0.2≤(a×c) / b≤35.7.

[0006] In a second aspect of this application, an electrical device is provided, including the secondary battery provided in the first aspect of this application.

[0007] Compared with the prior art, the beneficial effects of this application are as follows: This application introduces urethane compounds into the positive electrode material layer, which not only effectively reduces side reactions between the electrolyte and the positive electrode, but also allows the N and O groups containing lone pairs of electrons in the urethane groups to coordinate with transition metal ions, forming metal-oxygen bonds. This anchors the dissolved transition metal ions to the positive electrode side, reducing their deposition on the negative electrode side. Furthermore, it comprehensively controls the absolute value (i.e., ACM) of the peak position difference of the metal-oxygen bond absorption peaks in the infrared spectrum of the positive electrode material layer after one and 200 cycles of the secondary battery. -1 The ratio b between the thickness of the positive electrode material layer and the particle size Dv50 of the positive electrode material, and the viscosity cpp of the electrolyte at 25℃, ensure that (a×c) / b is within a suitable range, which can comprehensively improve the cycle performance and fast charging performance of the secondary battery. Attached Figure Description

[0008] Figure 1 The infrared spectrum of the cathode material layer provided in Embodiment 1 of this application. Detailed Implementation

[0009] To better illustrate the purpose, technical solution, and advantages of this application, the following description, in conjunction with specific embodiments and comparative examples, aims to provide a detailed understanding of the content of this application, rather than to limit its scope. All other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this application.

[0010] 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.

[0011] 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.

[0012] In the description of this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0013] Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0014] In this application, the terms "secondary battery", "lithium secondary battery", and "lithium-ion secondary battery" all have the same meaning and refer to lithium-ion secondary batteries, which typically include electrode components (such as positive electrode plates, negative electrode plates, and separators), a container (such as a housing) that houses the electrode components, and an electrolyte.

[0015] In a first aspect of this application, a secondary battery is provided, including a cell and an electrolyte. The cell includes a positive electrode sheet, the positive electrode sheet includes a positive electrode material layer, the positive electrode material layer includes a positive electrode material, the positive electrode material includes lithium nickel manganese oxide, and the surface of the positive electrode material layer opposite to the positive electrode current collector is covered with a protective layer, the protective layer containing urethane groups. After one cycle of the secondary battery, the infrared spectrum of the positive electrode material layer is in the range of 550~950 cm⁻¹. -1 The lowest peak within the range is peak A; after 200 cycles of the secondary battery, the infrared spectrum of the positive electrode material layer is in the range of 550~950 cm⁻¹. -1 The lowest peak within the range is peak B; The absolute value of the peak position difference between peak A and peak B is acm. -1 ; The ratio between the thickness of the positive electrode material layer and the particle size Dv50 of the positive electrode material is b; The viscosity of the electrolyte at 25°C is cpp; The secondary battery satisfies: 0.2≤(a×c) / b≤35.7.

[0016] For example, (a×c) / b can be 0.2, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.1, 17.5, 18, 18.5, 19, 19.5, 20, 20.5, 21, 21.5, 22, 22.5, 23, 23.5, 24, 24.5, 25, 25.5, 26, 26.5, 27, 27.5, 28, 28.5, 29, 29.5, 30, 30.5, 31, 31.5, 32, 32.5, 33, 33.5, 34, 34.5, 35, 35.2, 35.5, 35.7, or a range consisting of any two sets of values.

[0017] The inventors discovered that introducing urethane compounds into the positive electrode material layer can not only effectively reduce side reactions between the electrolyte and the positive electrode, but also form metal-oxygen bonds by coordinating the N and O groups containing lone pairs of electrons with transition metal ions. This anchors the dissolved transition metal ions to the positive electrode side, reducing the deposition of transition metal ions on the negative electrode side (the deposition of transition metal ions on the negative electrode side can lead to reduction and deposition, which can damage the negative electrode SEI layer and may also catalyze electrolyte decomposition). This reduces the consumption of active lithium inside the secondary battery, thereby improving the cycle performance of the secondary battery.

[0018] In this application, the infrared spectrum of the positive electrode material layer is 550~950cm. -1 The lowest peak in the range is the vibrational peak of the metal-oxygen bond. The energy change caused by the coordination of the electron-donating urethane group with the transition metal ion leads to the vibration of the metal-oxygen bond, causing a blue shift in the absorption peak. After 200 cycles of the secondary battery, the coordination of the urethane group with the transition metal ion reaches saturation. Therefore, the infrared spectrum of the cathode material layer after one cycle of the secondary battery shows a peak in the range of 550–950 cm⁻¹. -1 The lowest peak (peak A) within the range and its infrared spectrum in the cathode material layer after 200 cycles are in the range of 550~950 cm⁻¹. -1 The absolute value of the peak position difference between the lowest peaks (i.e., peak B) within the range (i.e., acm) -1 This demonstrates the effect of urethane compounds in the cathode material layer on fixing transition metal ions.

[0019] The inventors further discovered that the introduction of carbamate compounds increases the internal impedance of the secondary battery, affecting its fast-charging performance. Therefore, it is necessary to further regulate the ratio (b) between the thickness of the positive electrode layer and the particle size Dv50 of the positive electrode material, as well as the viscosity (ccP) of the electrolyte. On the one hand, regulating the electrolyte viscosity can increase the wetting rate of the electrode, improving lithium-ion transport efficiency and thus enhancing the fast-charging performance of the secondary battery. On the other hand, regulating the ratio (b) between the thickness of the positive electrode layer and the particle size Dv50 of the positive electrode material, appropriately thinning the positive electrode layer and reducing the particle size, shortens the lithium-ion solid-phase diffusion and liquid-phase migration paths, optimizes the electrode pore structure, improves the electrolyte's wetting effect on the positive electrode, reduces charge transfer impedance and concentration polarization, thereby enhancing the battery's fast-charging capability.

[0020] Therefore, by introducing urethane compounds into the positive electrode material layer, this application can not only effectively reduce the side reactions between the electrolyte and the positive electrode, but also anchor the dissolved transition metal ions to the positive electrode side by coordinating the N and O groups containing lone pairs of electrons in the urethane groups with transition metal ions to form metal-oxygen bonds, thereby reducing the precipitation of transition metal ions on the negative electrode side. Furthermore, it comprehensively controls the absolute value (i.e., ACM) of the peak position difference of the metal-oxygen bond absorption peak in the infrared spectrum of the positive electrode material layer after one and 200 cycles of the secondary battery. -1 The ratio b between the thickness of the positive electrode material layer and the particle size Dv50 of the positive electrode material, and the viscosity cpp of the electrolyte at 25℃, ensure that (a×c) / b is within a suitable range, which can comprehensively improve the cycle performance and fast charging performance of the secondary battery.

[0021] In some implementations, 4 ≤ (a×c) / b ≤ 17.1. When (a×c) / b is within this range, the battery's cycle performance and fast charging performance are better.

[0022] In some implementations, acm -1 10~80cm -1 .

[0023] For example, ACM -1 It can be 10cm -1 11cm -1 12cm -1 13cm -1 14cm -1 15cm -1 16cm -1 17cm -1 18cm -1 19cm -1 20cm -1 21cm -1、22cm -1 、23cm -1 、24cm -1 、25cm -1 、26cm -1 、27cm -1 、28cm -1 、29cm -1 、30cm -1 、31cm -1 、32cm -1 、33cm -1 、34cm -1 、35cm -1 、36cm -1 、37cm -1 、38cm -1 、39cm -1 、40cm -1 、41cm -1 、42cm -1 、43cm -1 、44cm -1 、45cm -1 、46cm -1 、47cm -1 、48cm -1 、49cm -1 、50cm -1 、51cm -1 、52cm -1 、53cm -1 、54cm -1 、55cm -1 、56cm -1 、57cm -1 、58cm -1 、59cm -1 、60cm -1 、61cm -1 、62cm -1 、63cm -1 、64cm -1 、65cm -1 、66cm -1 、67cm -1 、68cm -1 、69cm -1 、70cm -1 、71cm -1 、72cm -1 、73cm -1 、74cm -1 、75cm -1 、76cm -1 、77cm-1 78cm -1 79cm -1 80cm -1 Or a range consisting of any two sets of values.

[0024] Research has found that ACM -1 The larger the value, the stronger the complexation ability of the urethane compounds in the positive electrode material layer for transition metal ions. However, the more urethane groups in the positive electrode, the greater the internal resistance of the secondary battery, thus worsening its fast-charging performance. Conversely, a higher value indicates a higher internal resistance. -1 The smaller the value, the lower the internal resistance of the secondary battery will be. However, the weaker the complexation ability of the urethane compounds in the positive electrode material layer for transition metal ions, the easier it is for transition metal ions to migrate to the negative electrode and be deposited there, resulting in a decrease in the cycle performance of the secondary battery.

[0025] This application will pass ACM -1 By adjusting the parameters to a suitable range, it is possible to avoid excessive internal resistance of the battery due to an excessive number of urethane groups in the positive electrode, while also ensuring that the urethane compounds in the positive electrode material layer have a strong complexing ability for transition metal ions, making it difficult for transition metals to be deposited in the negative electrode. This ensures both fast charging performance and improved cycle performance.

[0026] In this application, acm -1 The control methods include, but are not limited to, the following: controlling the ACM by adjusting the type and amount of carbamate compounds in the cathode material layer. -1 The numerical value. For example, the higher the amount of carbamate compounds added, the higher the ACM value. -1 The larger.

[0027] acm -1 A further preferred size is 40~56cm -1 .

[0028] In some implementations, b is 12.5 to 31.8.

[0029] For example, b can be 12.5, 13, 14, 15, 15.2, 15.5, 16, 17, 18, 19, 20, 21, 22, 23, 23.5, 24, 24.5, 25, 26, 27, 28, 29, 30, 31, 31.2, 31.5, 31.8 or a range of any two sets of values.

[0030] Research has shown that the greater the thickness of the cathode material layer and the smaller the particle size (Dv50) of the cathode material, the larger the ratio (b) between the thickness of the cathode material layer and the particle size (Dv50) of the cathode material. Although the diffusion path of lithium ions in the cathode material particles is shorter, a thicker electrode not only makes it difficult to be fully wetted by the electrolyte, but also significantly prolongs the overall ion migration path, leading to increased concentration polarization and thus limiting the fast-charging capability of the secondary battery. On the other hand, small-particle-size cathode materials have a large specific surface area and faster CEI film growth. If the electrode is too thick, uneven ion transport will exacerbate local CEI thickening, leading to a continuous increase in impedance and a decrease in the cycle life of the secondary battery.

[0031] Research revealed that a small ratio (b) between the thickness of the cathode material layer and the particle size Dv50 of the cathode material indicates a thinner cathode material layer and a larger particle size Dv50. While a thinner electrode facilitates ion transport, it also lengthens the solid-phase diffusion path of lithium ions within the cathode material. Furthermore, the larger particles have fewer surface active sites and insufficient interfacial contact, leading to increased charge transfer impedance, severe concentration polarization during charge and discharge, and increased polarization during fast charging as lithium migration cannot keep pace with the current rate. This results in a larger voltage drop, easier lithium plating, and less complete lithium ion insertion / extraction, ultimately increasing the internal impedance of the secondary battery and limiting its fast-charging capability.

[0032] A large ratio (b) between the thickness of the cathode material layer and the particle size Dv50 of the cathode material indicates a large cathode material layer thickness. While a small particle size Dv50 results in a shorter solid-phase diffusion path for lithium ions within the cathode material particles, the thick electrode significantly prolongs the overall ion migration path, leading to increased concentration polarization and limiting the fast-charging capability of the secondary battery. Furthermore, the volume changes during charging and discharging of the thick electrode make it more prone to cracking and delamination. A decrease in the particle size Dv50 increases the specific surface area of ​​the particles, increasing side reactions between the cathode material and the electrolyte, intensifying manganese ion disproportionation and dissolution, and causing numerous surface defects in small particles. Under cyclic stress, these particles are prone to cracking and breakage, continuously exposing fresh interfaces, constantly consuming active lithium, and damaging the electrode structure, thus reducing the cycle performance of the secondary battery.

[0033] Therefore, this application adjusts the ratio (i.e. b) between the thickness of the cathode material layer and the particle size Dv50 of the cathode material to a suitable range, so that the thickness of the cathode material layer is matched with the particle size Dv50 of the cathode material, which can comprehensively improve the cycle and fast charging performance of the battery.

[0034] In this application, the method for controlling the ratio b of the thickness of the cathode material layer to the particle size Dv50 of lithium nickel manganese oxide includes, but is not limited to, the following: By adjusting the coating thickness of the positive electrode slurry and / or the rolling pressure during the preparation of the positive electrode material layer, the thickness of the positive electrode material layer can be changed, thereby achieving the control of the b value; Furthermore, the particle size Dv50 of the cathode material can be changed by adjusting the calcination temperature and / or the gas pressure of the gas flow breakup during the preparation of the cathode material, thereby achieving the control of the b value.

[0035] b is further preferably 15.2~24.

[0036] In some implementations, cCP is 0.5~6 cP.

[0037] For example, ccp can be 0.5cP, 1cP, 1.5cP, 2cP, 2.5cP, 3cP, 3.5cP, 4cP, 4.5cP, 5cP, 5.5cP, 6cP, or a range consisting of any two sets of values.

[0038] Studies have found that the lower the viscosity (ccp) of the electrolyte at 25°C, the weaker the intermolecular forces of the solvent, making it more prone to volatilization or decomposition at high temperatures. This makes it more difficult for the negative electrode to form a dense and stable SEI film, leading to repeated rupture and regeneration of the SEI film during cycling, thus reducing the cycle performance of the secondary battery. Conversely, while a higher viscosity (ccp) of the electrolyte at 25°C provides better high-temperature stability, it slows down the wetting rate of the electrolyte onto the electrode, making lithium-ion transport more difficult and thus reducing the fast-charging performance of the lithium-ion battery.

[0039] This application adjusts the viscosity of the electrolyte at 25°C to a suitable range and keeps (a×c) / b within a suitable range, which can ensure the stability of the electrolyte at high temperatures and improve the lithium-ion transport efficiency, thereby improving the fast-charging performance of the secondary battery while ensuring its cycle performance.

[0040] This application does not impose any particular limitations on the means of controlling the viscosity (i.e., CCP) of the electrolyte at 25°C, including but not limited to the following: controlling the composition and volume ratio of the solvent in the electrolyte to change the viscosity of the electrolyte. For example, the solvent of the electrolyte may include fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), and fluoroethyl methyl carbonate (FEMC). The higher the volume percentage of fluoroethylene carbonate (FEC) in the solvent, the greater the viscosity of the electrolyte at 25°C; the higher the volume percentage of fluoroethyl methyl carbonate (FEMC) in the solvent, the greater the viscosity of the electrolyte at 25°C.

[0041] The cp is further preferably 2~5 cp.

[0042] In some embodiments, the thickness of the positive electrode material layer is 110~130μm.

[0043] For example, the thickness of the positive electrode material layer can be 110μm, 111μm, 112μm, 113μm, 114μm, 115μm, 116μm, 117μm, 118μm, 119μm, 120μm, 120μm, 121μm, 122μm, 123μm, 124μm, 125μm, 126μm, 127μm, 128μm, 129μm, 130μm, or a range consisting of any two sets of values.

[0044] The thickness of the positive electrode material layer is further preferably 114~122μm.

[0045] In some embodiments, the particle size Dv50 of the cathode material is 4~9 μm.

[0046] For example, the particle size Dv50 of the positive electrode material can be 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, or any two sets of values ​​therein.

[0047] Research has shown that by controlling the particle size Dv50 of the cathode material to the above-mentioned range, this application can ensure that the lithium ion transport path inside the cathode material particles is appropriate, thereby guaranteeing the fast charging performance of the secondary battery. It can also make the cathode material have a suitable specific surface area, reducing the contact area between the cathode material and the electrolyte, reducing the side reactions between the cathode material and the electrolyte, and thus improving the cycle performance of the secondary battery.

[0048] The particle size Dv50 of the cathode material is further preferably 5~7.5μm.

[0049] In some embodiments, the particle size Dv90 of the positive electrode material is 9~20μm, and the particle size Dv10 of the positive electrode material is 2~6μm.

[0050] For example, the particle size Dv90 of the positive electrode material can be 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, or any two sets of values ​​therein. The particle size Dv10 of the positive electrode material can be 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, or any two sets of values ​​therein.

[0051] Research has shown that by adjusting the particle size Dv90 and Dv10 of the cathode material to suitable ranges, this application achieves an appropriate difference between the particle size Dv90 and Dv10, resulting in a moderate particle size distribution. This allows for particle gradation and moderate porosity, ensuring the ion transport rate between particles and reducing side reactions between the cathode material and the electrolyte, thereby improving the fast-charging and cycle performance of the secondary battery.

[0052] In some embodiments, the surface of the positive electrode material particles has a coating layer with a thickness of 0.5~10 nm.

[0053] For example, the thickness of the coating layer can be 0.5nm, 1nm, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, or any two of these values.

[0054] Research has shown that by setting a coating layer on the surface of the positive electrode material and controlling the thickness of the coating layer to the above-mentioned range, this application can improve the conductivity of the positive electrode material, reduce the direct contact between the electrolyte and the positive electrode material, reduce the side reactions between the positive electrode material and the electrolyte, and thus improve the fast charging performance and cycle performance of the secondary battery.

[0055] In some embodiments, the thickness of the coating layer is further preferably 1 to 5 nm.

[0056] In some embodiments, the coating layer includes at least one of Al2O3, Li3PO4, ZrO2, TiO2, SiO2, MgF2, lithium lanthanum titanium oxide, and P2O5.

[0057] In some embodiments, the cathode material further includes a doping element, which includes at least one of Y, Nb, P, W, Al, Co, Mg, Zr, Ti, B, and F.

[0058] In some embodiments, the porosity of the positive electrode material layer is 20-40%.

[0059] For example, the porosity of the positive electrode material layer can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, or any two sets of values ​​therein.

[0060] The inventors discovered through research that by adjusting the porosity of the positive electrode material layer to a suitable range, it is possible to ensure the wetting effect of the electrolyte on the positive electrode sheet, promote lithium-ion transport, reduce the internal impedance of the battery, and avoid the increase of side reactions due to excessive wetting of the positive electrode sheet by the electrolyte, thereby improving the cycle life and fast charging performance of the battery.

[0061] In some embodiments, the compaction density of the positive electrode is 2.3 g / cm³. 3 ~3.2g / cm 3 .

[0062] For example, the compaction density of the positive electrode sheet can be 2.3 g / cm³. 3 2.4g / cm 3 2.5g / cm 3 2.6g / cm 3 2.7g / cm 3 2.8g / cm 3 2.85g / cm 3 2.9g / cm 3 2.95g / cm 3 3g / cm 3 3.05g / cm 3 3.1g / cm 3 3.15g / cm 3 3.2g / cm 3 Or a range consisting of any two sets of values.

[0063] Through research, the inventors discovered that controlling the compaction density of the positive electrode sheet within the aforementioned range can give the positive electrode material layer a certain porous structure, ensuring the wetting effect of the electrolyte on the positive electrode material layer, improving ion transport efficiency, and preventing the positive electrode material particles from breaking, pulverizing, or falling off during charge-discharge cycles due to excessive compaction density. It can also prevent the positive electrode from increasing side reactions between the positive electrode and the electrolyte due to insufficient compaction density, thereby improving the fast-charging performance and cycle life of the secondary battery.

[0064] In some embodiments, the positive electrode sheet further includes a positive current collector, and the positive electrode material layer is disposed on at least one side surface of the positive current collector, wherein the peel force between the positive electrode material layer and the positive current collector is 10~50 N / m.

[0065] For example, the peel force between the positive electrode material layer and the positive electrode current collector can be 10 N / m, 15 N / m, 20 N / m, 25 N / m, 30 N / m, 35 N / m, 40 N / m, 45 N / m, 50 N / m or any two of these values.

[0066] Through research, the inventors discovered that by adjusting the peel force between the positive electrode material layer and the positive electrode current collector to the above-mentioned range, the positive electrode material layer tightly covers the foil surface, blocking the direct contact between the electrolyte and the positive electrode current collector, inhibiting the interfacial corrosion side reaction of the electrolyte on the positive electrode current collector, reducing or avoiding the formation of insulating by-product layers, thereby ensuring the cycle life and fast charging performance of the secondary battery.

[0067] In this application, the peel force between the positive electrode material layer and the positive electrode current collector can be determined by the following method: Discharge the secondary battery at 0.33C to the lower limit voltage of 3.5V, remove the empty battery, disassemble the positive electrode, soak the positive electrode in dimethyl carbonate (DMC) solution for 4 hours; then air dry. Cut the dried positive electrode sheet into test samples with an area of ​​25mm wide × 200mm long. Adhere the test sample to a rigid substrate (stainless steel plate) using high-strength double-sided adhesive (peel force > 50 N / m). Use a 2kg standard roller to press the sample back and forth three times at a speed of 300mm / min to ensure tight adhesion, no air bubbles, and no wrinkles. Manually pre-peel the coating from one end of the sample to the current collector by about 20-30mm. Using a universal tensile testing machine, fix the rigid substrate to the lower clamp, fold the pre-peeled coating end 180° back, and clamp it to the upper clamp. Zero the force value, eliminate the clamp gap, and start the tensile test at a peeling speed of 100mm / min. Continuously record the force-displacement curve until the peel length ≥ 100mm. Remove the edge effect segments of the curve at the beginning and end (25mm each), and take the average peel force F (N) of the middle stable segment. Calculate the peel force between the positive electrode material layer and the positive electrode current collector using the following formula: Peel force (N / m) = F / Sample width (m).

[0068] In this application, the preparation method of the lithium nickel manganese oxide includes, but is not limited to, the following methods: S11. Grind and mix the nickel-manganese precursor, lithium source and dopant source to obtain a mixed powder; S12. The mixed powder is pre-calcined at 400~500℃ for 4h, then heated to 750~880℃ at a heating rate of 5℃ / min, and calcined at 750~880℃ for 4~8h. After that, it is cooled to room temperature, and the calcined product is subjected to airflow crushing to obtain lithium nickel manganese oxide. S13. Grind and mix the lithium nickel manganese oxide obtained in step S12 with the coating agent, then pre-calcine the mixed powder at 280~350℃ for 1~3h, then raise the temperature to 600~800℃ at a heating rate of 1~10℃ / min, and keep it at 600~800℃ for 2~8h. After cooling, obtain lithium nickel manganese oxide with a coating layer.

[0069] In step S11, the nickel-manganese precursor is a hydroxide containing nickel and manganese, the lithium source may include at least one of lithium carbonate, lithium hydroxide, lithium oxalate, lithium acetate, and lithium oxide, the doping source is at least one of a hydroxide of a doping element, an oxide of a doping element, a carbonate of a doping element, and an oxalate of a doping element, and the molar ratio of the nickel-manganese precursor to the lithium element in the lithium source is 1:1.

[0070] In step S11, the mass of the dopant element in the dopant source is 0.05 to 1% of the theoretical mass of lithium nickel manganese oxide.

[0071] In steps S11 and S13, the grinding and mixing can be done by ball milling. The ball milling conditions are as follows: rotation speed of 200~500 r / min, time of 4~6 h, abrasive is zirconium balls, and the diameter of the zirconium balls is 1~10 mm.

[0072] In step S12, the air pressure at which the airflow is broken is 0.5~1.1 MPa.

[0073] In step S13, the mass of the coating agent accounts for 0.1 to 5% of the mass of the lithium nickel manganese oxide.

[0074] In some embodiments, the lithium nickel manganese oxide is a cathode material with a spinel structure, abbreviated as LNMO, which has the advantage of high voltage characteristics. The lithium nickel manganese oxide satisfies the general formula: Li 1+x Ni y M z Mn 2-x-y-z O 4-k -0.1≤x≤0.2, 0.4≤y≤0.6, 0≤z≤0.2, 0≤k≤0.1, M is a doping element, M includes but is not limited to at least one of Cr, Mo, Nb, Ru, P, S, Ta, W, Tl and Ti.

[0075] In some embodiments, the cathode material may further include at least one of lithium iron phosphate, nickel-cobalt ternary materials, and lithium manganese iron phosphate.

[0076] Lithium iron phosphate (LFP) is a cathode material with an olivine-type crystal structure, offering advantages such as low cost and high safety. The general chemical formula of lithium iron phosphate can be LiFe. 1-x M x PO y Q z Where x≤0.1, 3.85≤y≤4, 0≤z≤0.05, and the doping element M includes, but is not limited to, at least one of Mn, Ni, Co, Cr, Cu, Bi, and Sb.

[0077] The nickel-cobalt ternary material satisfies the general formula: Lia Ni b Co c M1 d M2 e O f R g Where 0.75≤a≤1.2, 0<b<1, 0<c<1, 0<d<1, b+c+d=1; 0≤e≤0.2, 1≤f≤2.5, 0≤g≤1, f+g≤3; M1 can be Mn or Al, M2 includes but is not limited to at least one of B, Zr, Ti, Si, Mo, La, Ce, Te, Nb, Ta, Si, Al, W, Sr, V, Y, Mg, Co, and Li; R includes but is not limited to at least one of N, F, S, and Cl.

[0078] The lithium manganese iron phosphate is a cathode material with an olivine structure and a hexagonal close-packed structure. The chemical formula of lithium manganese iron phosphate is: Li a N b Fe x Mn y M 1-x-y P 1-m Q m O 4-n R n In the formula, a is 0.9~1.1, b is 0~0.1, x is 0.001~0.999, y is 0.001~0.999, 1-xy is 0~0.1, m is 0~0.1, and n is 0~0.1. In the formula, M represents the doping element at the manganese and / or iron sites of lithium manganese iron phosphate, and M includes, but is not limited to, at least one of Co, Mg, Zn, Ca, Ti, V, Ni, and Cr; N represents the doping element at the lithium site of lithium manganese iron phosphate, and N includes, but is not limited to, at least one of Zn, Al, Na, K, Mg, Nb, Mo, and W; Q represents the doping element at the phosphorus site of lithium manganese iron phosphate, and Q includes, but is not limited to, at least one of B, S, Si, and N; R represents the doping element at the oxygen site of lithium manganese iron phosphate, and R includes, but is not limited to, at least one of S, F, Cl, and Br.

[0079] In some embodiments, the lithium nickel manganese oxide content in the cathode material is 80-100% by mass.

[0080] For example, the mass percentage of lithium nickel manganese oxide in the positive electrode material layer can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, or a range of any two sets of values.

[0081] In some embodiments, the positive electrode material layer further includes a carbamate compound, a positive electrode conductive agent, and a positive electrode binder.

[0082] Specifically, in the positive electrode material layer, the mass percentage of the positive electrode material is 96-98%, the mass percentage of the carbamate compound is 0.1-1%, the mass percentage of the positive electrode conductive agent is 1-2%, and the mass percentage of the positive electrode binder is 0.5-2%.

[0083] In some embodiments, the chemical structural formula of the carbamate compound is as follows: Wherein, R1 is any one of alkenyl or alkynyl groups with ≤4 C atoms, and R2, R3, and R4 each independently include H, alkyl groups with ≤4 C atoms, alkenyl groups with ≤4 C atoms, phenyl groups, methoxy groups, etc. At least one of them.

[0084] The alkenyl group with ≤4 C atoms may include, but is not limited to, any one of vinyl (-CH=CH2), propenyl (-CH2CH=CH2), isopropenyl (-C(CH3)=CH2), butenyl (-CH2CH2CH=CH2), 2-butenyl (-CH2CH=CHCH2), and butadienyl (-CH2CH=CHCH=CH2).

[0085] The alkynyl group with ≤4 C atoms may include, but is not limited to, any one of ethynyl (-C≡CH), propynyl (-CH2C≡CH), 2-propynyl (-C≡CCH2), and butynyl (-CH2CH2C≡CH).

[0086] In some embodiments, the carbamate compound includes at least one of the compounds shown in the following structural formulas: , , .

[0087] The positive electrode conductive agent may include conductive agents conventionally used in the art. For example, the positive electrode conductive agent includes at least one of multi-walled carbon nanotubes, single-walled carbon nanotubes, conductive carbon black, acetylene black, Ketjen black, conductive graphite, graphene, and conductive carbon fiber.

[0088] The positive electrode binder may include positive electrode binders conventionally used in the art. For example, the positive electrode binder includes at least one selected from polytetrafluoroethylene, polyvinylidene fluoride, polyethylene oxide, styrene-butadiene rubber, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyacrylonitrile, polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyvinyl alcohol, polyimide, and polyamide-imide.

[0089] The positive current collector may include positive current collectors conventionally used in the art. For example, the positive current collector includes at least one of aluminum foil and composite foil. The composite foil includes a middle high-density layer and metal layers disposed on both sides of the polymer layer. The polymer layer includes polymer materials, including at least one of polyamide (PA), polyterephthalate, polyimide (PI), polyethylene (PE), polypropylene (PP), polystyrene (PPE), polyvinyl chloride (PVC), aramid, acrylonitrile-butadiene-styrene copolymer (ABS), polybutylene terephthalate (PET), poly(p-phenylene terephthalamide) (PPTA), polypropylene (PPE), polyoxymethylene (POM), epoxy resin, phenolic resin, polytetrafluoroethylene (PTEE), polyvinylidene fluoride (PVDF), silicone rubber, polycarbonate (PC), polyvinyl alcohol (PVA), polyethylene glycol (PEG), cellulose, starch, protein, their derivatives, their crosslinks, and their copolymers. The metal layers may include at least one of aluminum, copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys.

[0090] The positive electrode sheet can be prepared according to conventional methods in the art. For example, the preparation method of the positive electrode sheet includes the following steps: mixing the components of the positive electrode material layer with a solvent to obtain a positive electrode slurry; coating the positive electrode slurry onto two opposite surfaces of the positive electrode current collector aluminum foil, and then drying, rolling, and slitting to obtain the positive electrode sheet.

[0091] In some embodiments, the battery cell further includes a negative electrode and a separator, the separator being located between the positive electrode and the negative electrode.

[0092] In some embodiments, the air permeability of the diaphragm is 100~400s / 100mL.

[0093] For example, the air permeability of the diaphragm can be 100s / 100mL, 120s / 100mL, 150s / 100mL, 180s / 100mL, 200s / 100mL, 220s / 100mL, 250s / 100mL, 280s / 100mL, 300s / 100mL, 320s / 100mL, 350s / 100mL, 380s / 100mL, 400s / 100mL, or a range of any two sets of values ​​therein.

[0094] Through research, the inventors discovered that the membrane selected in this application, with an air permeability within the above-mentioned range, can not only ensure the wetting effect of the electrolyte on the membrane and improve the lithium ion transport rate, but also reduce the side reactions at the interface between the electrolyte and the positive and negative electrodes, thereby improving the fast charging performance and cycle performance of the secondary battery.

[0095] In this application, the air permeability of the diaphragm can be determined by the following method: The secondary battery was discharged at 0.33C to the lower limit voltage of 3.5V. The secondary battery was then disassembled, the separator was removed, and a sample with an area of ​​2.54cm × 2.54cm was prepared. The sample was immersed in DMC (dimethyl carbonate) for 4 hours and then dried at 60℃ for 12 hours. The air permeability (Gurley number) of the separator was measured using a Gurley tester. The sample was placed in the Gurley tester, and the time (in seconds) required for a certain amount of test gas to pass through the 2.54cm × 2.54cm sample at a pressure of 1.22kPa was measured using a timer. The test gas was air, with a volume of 100mL. The time it took for 100mL of air to pass through the sample was calculated to obtain the air permeability of the separator (i.e., s / 100mL). The lower the air permeability, the better the air permeability of the separator; the higher the air permeability, the worse the air permeability of the separator.

[0096] In some embodiments, the thickness of the diaphragm is 8.5~18 μm.

[0097] For example, the thickness of the diaphragm may be 8.5μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm or any two of these values.

[0098] In this application, the thickness of the diaphragm can be determined by the following method: The secondary battery was discharged at 0.33C to the lower limit voltage of 3.5V. The secondary battery was then disassembled, the separator was removed, and dried at 60℃ for 4 hours. The thickness of the separator was then measured with a micrometer.

[0099] In some embodiments, the diaphragm includes a substrate layer comprising at least one of polyethylene, polypropylene, polyamide, and aramid.

[0100] Optionally, the diaphragm may further include an adhesive layer and / or a ceramic layer. The adhesive layer may be made of at least one of polyvinylidene fluoride, polymethyl methacrylate, aramid, polyethylene oxide, polyvinylidene fluoride-hexafluoropropylene copolymer, or polyaniline; the ceramic layer may be made of at least one of boehmite, alumina, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium oxide, zinc oxide, barium sulfate, boron nitride, aluminum nitride, and magnesium nitride.

[0101] In some embodiments, the negative electrode sheet includes a negative electrode material layer, the negative electrode material layer includes a negative electrode material, and the negative electrode material includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microspheres, silicon-oxygen materials, elemental silicon, silicon-carbon composite materials, and lithium titanate.

[0102] Furthermore, the particle size Dv50 of the negative electrode material is 5~16μm.

[0103] For example, the particle size Dv50 of the negative electrode material can be 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm or any two sets of values ​​therein.

[0104] This application improves the cycle life and fast charging performance of the battery by adjusting the particle size Dv50 of the negative electrode material to a suitable range, thereby making the lithium ion transport path moderate and reducing the side reactions between the negative electrode material and the electrolyte.

[0105] In this application, the particle size Dv50 of the negative electrode material can be determined by the following method: The secondary battery was discharged at 0.33C to the lower limit voltage of 3.5V. The battery was then disassembled in a glove box (H2O molar content ≤0.1ppm, O2 molar content ≤0.1ppm), and the negative electrode was removed. The negative electrode was then soaked in dimethyl carbonate (DMC) for 4 hours, and then vacuum dried at 60℃ for 12 hours. The powder on the surface of the dried electrode was scraped off with a scraper to obtain a powder sample. 1g of the powder sample was taken and the volumetric cumulative particle size distribution was measured using a Mastersizer 3000 laser particle size analyzer according to the particle size distribution laser diffraction method (specific steps refer to standard GB / T19077-2016). Dv50 represents the particle size corresponding to a cumulative particle size distribution percentage of 50%.

[0106] Furthermore, the Id / Ig ratio of the negative electrode material is 0.02~0.4, where Id is the value at 1343~1353 cm⁻¹ in the Raman spectrum of the negative electrode material. -1 The peak intensity at 1580-1600 cm⁻¹ is given by Ig, which is the Raman spectrum of the negative electrode material in the range of 1580-1600 cm⁻¹. -1 Peak intensity at that location.

[0107] For example, the Id / Ig ratio of the negative electrode material can be 0.02, 0.05, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3, 0.32, 0.35, 0.38, 0.4, or a range consisting of any two sets of values.

[0108] In this application, the Id / Ig ratio of the negative electrode material can be determined by the following method: The secondary battery was discharged at 0.33C to the lower limit voltage of 3.5V. The battery was then disassembled in a glove box (H₂O molar content ≤ 0.1ppm, O₂ molar content ≤ 0.1ppm), and the negative electrode was removed. It was then soaked in dimethyl carbonate (DMC) for 4 hours, removed, and vacuum dried at 60℃ for 12 hours. Active material powder was scraped from the electrode surface using a ceramic knife. Raman spectroscopy was performed on the scraped active material using a spectrometer (Jobin Yvon Lab RAMHR). The light source wavelength was 532nm, using an Ar ion laser, with an integration time of 10s, a 50X long focal length objective lens, and a measurement wavelength of 1350cm. -1 The nearby peak intensity is Id, with a wavelength of 1580 cm⁻¹. -1 The nearby peak intensity is Ig, and the specific value is calculated using the formula Id / Ig.

[0109] The inventors discovered that the Id / Ig ratio of a negative electrode material can be used to characterize its graphitization degree. A higher Id / Ig ratio indicates a lower graphitization degree, more lattice defects, higher amorphous carbon content, and higher disorder. Conversely, a lower Id / Ig ratio indicates a higher degree of graphitization, fewer lattice defects, and better crystallinity. Adjusting the Id / Ig ratio of the negative electrode material to a suitable range, thus achieving an appropriate graphitization degree, helps reduce lattice defects. Since lattice defects scatter electrons, reducing them improves the conductivity of the negative electrode, lowers the battery's internal resistance, and enhances cycle life and fast-charging performance.

[0110] Furthermore, the porosity of the negative electrode material layer is 28.3~37.2%.

[0111] For example, the porosity of the negative electrode material layer can be 28.3%, 28.5%, 29%, 29.5%, 30%, 30.5%, 31%, 31.5%, 32%, 32.5%, 33%, 33.5%, 34%, 34.5%, 35%, 35.5%, 36%, 36.5%, 37%, 37.2%, or a range of any two sets of values.

[0112] The inventors discovered through research that by adjusting the porosity of the negative electrode material layer to a suitable range, it is possible to ensure the wetting effect of the electrolyte on the negative electrode sheet, promote lithium-ion transport, and reduce the internal impedance of the battery; it is also possible to avoid the increase of side reactions due to excessive wetting of the negative electrode sheet by the electrolyte, thereby improving the cycle life and fast charging performance of the battery.

[0113] In this application, the porosity of the negative electrode material layer can be determined by the following method: The secondary battery was discharged at 0.33C to the lower limit voltage of 3.5V. The battery was disassembled in a glove box (H₂O molar content ≤ 0.1ppm, O₂ molar content ≤ 0.1ppm), and the negative electrode was removed. The negative electrode was then soaked in dimethyl carbonate (DMC) solution for 4 hours and dried. Subsequently, the negative electrode was cut into circular pieces with a radius of 12mm using an electrode punching machine. Simultaneously, the thickness of the positive electrode and the current collector were measured using a thickness gauge, recorded as h1 and h2 respectively. The mass was weighed using a balance with an accuracy of 0.00001g and recorded as m1. The positive electrode... The electrode sheet is immersed in a sealed container with a certain volume of hexadecane for 1 hour (the volume of hexadecane in the sealed solution is not required, but the amount must be sufficient to completely submerge the electrode sheet). After 1 hour, the positive electrode sheet is removed with tweezers and placed on filter paper to absorb the water until a constant weight is reached (generally, 1 hour is sufficient to absorb the water until a constant weight is reached). The mass is then weighed using a balance and recorded as m2. The porosity is calculated using the following formula: Porosity of the positive electrode material layer = X / V × 100%, where X = (m2 - m1) / ρ, and ρ is the density of hexadecane, 0.7734 g / cm³. 3 V=πr 2 ×(h1-h2)

[0114] Optionally, the negative electrode material layer may further include a negative electrode conductive agent and a negative electrode binder.

[0115] In the negative electrode material layer, the mass percentage of the negative electrode material is 94-98%, the mass percentage of the negative electrode conductive agent is 1-3%, and the mass percentage of the negative electrode binder is 1-3%.

[0116] The negative electrode conductive agent may include conductive agents conventionally used in the art. For example, the negative electrode conductive agent includes at least one of multi-walled carbon nanotubes, single-walled carbon nanotubes, conductive carbon black, acetylene black, Ketjen black, conductive graphite, graphene, and conductive carbon fiber.

[0117] The negative electrode binder may include binders conventionally used in the art. For example, the negative electrode binder includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyethylene oxide, styrene-butadiene rubber, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyacrylonitrile, polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyvinyl alcohol, polyimide, and polyamide-imide.

[0118] Furthermore, the negative electrode sheet includes a negative electrode current collector, and at least one side surface of the negative electrode current collector is provided with the negative electrode material layer.

[0119] The negative electrode current collector may include negative electrode current collectors conventionally used in the art. For example, the negative electrode current collector includes at least one of copper foil, chromium foil, nickel foil, and titanium foil.

[0120] The negative electrode sheet can be prepared according to conventional methods in the art. For example, the preparation method of the negative electrode sheet includes the following steps: mixing negative electrode material, negative electrode conductive agent, negative electrode binder and solvent to obtain negative electrode slurry; coating the negative electrode slurry on at least one side surface of the negative electrode current collector, drying and then rolling and cutting to obtain the negative electrode sheet.

[0121] In some embodiments, the electrolyte includes a non-aqueous solvent, which includes at least one of carbonate solvents, carboxylic acid ester solvents, and fluorinated solvents; The carbonate solvent includes at least one of ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, and propylene carbonate, and / or the carboxylic acid ester solvent includes at least one of ethyl acetate, methyl propionate, ethyl propionate, and methyl acetate, and / or the fluorinated solvent includes at least one of ethyl trifluoroacetate, ethyl difluoroacetate, and methyl trifluoroethyl carbonate.

[0122] In some embodiments, the electrolyte comprises a lithium salt.

[0123] In some embodiments, the electrolyte contains 5-20% lithium salt by mass.

[0124] For example, the mass percentage of lithium salt in the electrolyte can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 12.5%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a range of any two sets of values.

[0125] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium perchlorate, lithium dioxalate borate, lithium trifluoromethanesulfonate, lithium difluorodioxalate phosphate, lithium tetrafluorooxalate phosphate, and lithium bis(trifluoromethanesulfonyl)imide.

[0126] In some embodiments, the electrolyte includes additives.

[0127] In some embodiments, the electrolyte contains 0.5% to 5% by mass of the additive.

[0128] For example, the mass percentage of the additive in the electrolyte can be 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, or any range of two sets of values.

[0129] In some embodiments, the additive includes at least one of vinylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonate lactone, propylene sulfite, vinyl ethylene carbonate, vinyl sulfate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide, lithium bis(fluoromethylsulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, methane disulfonate, tri(trimethylsilane) phosphate, tri(trimethylsilane) borate, and tri(trimethylsilane) phosphite.

[0130] In a second aspect, this application provides an electrical device including the aforementioned secondary battery.

[0131] In this application, the electrical equipment may include energy storage devices, electric ships, aircraft, laptops, power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace equipment, etc.

[0132] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments.

[0133] Unless otherwise specified, all components and raw materials used in the embodiments and comparative examples of this application are commercially available, and the same type of components and raw materials are used in each parallel experiment.

[0134] In the following examples and comparative examples, the chemical structural formula of compound 1 is as follows: The chemical structural formula of compound 2 is The chemical structural formula of compound 3 is .

[0135] Example 1 The embodiment of the lithium-ion secondary battery described in this application includes a method for preparing the lithium-ion secondary battery comprising the following steps: S1. Preparation of cathode materials: S11, Ni selected 0.5 Mn 1.5 (OH)4 is used as a nickel-manganese precursor, lithium carbonate as a lithium source, and alumina as a dopant source. The nickel-manganese precursor, lithium source, and dopant source are ball-milled and mixed. The molar ratio of the nickel-manganese precursor to the lithium source is 1:1. The mass percentage of the dopant element in the dopant source is 0.25% of the theoretical mass of lithium nickel manganese oxide. The ball milling speed is 300 r / min. The abrasive used in the ball mill is zirconium balls with a diameter of 5 mm. The ball milling time is 5 h to obtain a mixed powder. S12. The mixed powder is pre-calcined at 450℃ for 4 hours to completely decompose lithium carbonate. Then, the temperature is increased to 810℃ at a rate of 5℃ / min and calcined at 810℃ for 6 hours. After that, it is cooled to room temperature. The calcined product is then subjected to air jet crushing and sieved through a 400-mesh sieve. The air jet crushing pressure is 0.8MPa to obtain lithium nickel manganese oxide. S13. Using Li3PO4 as the coating agent, the lithium nickel manganese oxide obtained in step S12 is ball-milled and mixed with the coating agent. The mass percentage of the coating agent is 1% of the lithium nickel manganese oxide mass. The ball milling speed is 300 r / min, the abrasive is zirconium balls with a diameter of 5 mm, and the ball milling time is 5 h. Then, the mixed powder is pre-calcined at 300℃ for 2 h to remove water. Then, the temperature is increased to 650℃ at a rate of 5℃ / min and calcined at 650℃ for 3 h. After that, it is cooled to room temperature, and the calcined powder is passed through a 400-mesh sieve to obtain lithium nickel manganese oxide with a coating layer.

[0136] S2, Preparation of the positive electrode: Compound 1 is selected as a carbamate compound. The positive electrode material obtained in step S13, conductive carbon black SP, conductive carbon nanotubes, binder polyvinylidene fluoride (PVDF), and carbamate compound are mixed in a mass ratio of X:1.5:1:2.5:Y (X+Y is 95, Y is 0.5). N-methylpyrrolidone (NMP) is added, and the mixture is stirred under vacuum until the system is homogeneous to obtain a positive electrode slurry with a solid content of 70%. The positive electrode slurry is coated on two opposite surfaces of the positive electrode current collector aluminum foil. The coating thickness of the positive electrode slurry is 225 μm. After drying, it is rolled at a pressure of 25 MPa and then slit to obtain the positive electrode sheet.

[0137] S3. Preparation of the negative electrode: Natural graphite, conductive carbon black SP, carboxymethyl cellulose (CMC), binder B1601, and binder LA136D were mixed in a mass ratio of 96.4:0.6:0.6:1.4:1. Deionized water was added, and the mixture was stirred under vacuum until it became homogeneous, thus obtaining a negative electrode slurry. The negative electrode slurry was coated onto two opposing surfaces of a copper foil along its thickness direction. The foil was first dried at 100°C for 2 minutes, and then heated to 120°C at a rate of 3°C / min. After rolling and cutting, the negative electrode sheet was obtained.

[0138] S4. Preparation of electrolyte: Fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), and fluoroethyl methyl carbonate (FEMC) were mixed in the volume percentages shown in Table 2 to obtain an organic solvent. Fully dried lithium salt LiPF6 was added to prepare an electrolyte. The mass percentage of lithium salt LiPF6 in the electrolyte was 12.5%.

[0139] S5. Preparation of the diaphragm: We chose a commercially available PP membrane with a thickness of 14μm.

[0140] S6. Weld tabs onto the positive and negative electrode sheets respectively. Stack the obtained positive electrode sheet, separator, and negative electrode sheet in sequence, so that the separator is placed between the positive and negative electrode sheets to play a role in isolation. Then, wind them to obtain a bare cell. Place the bare cell in an outer packaging shell, dry it, inject electrolyte, and then go through vacuum sealing, standing, formation, shaping and other processes to obtain a secondary battery.

[0141] Examples 2-17 and Comparative Examples 1-5 Examples 2-17 and Comparative Examples 1-5 each provide a secondary battery. The only difference from Example 1 is that the preparation process parameters and characteristic parameters of the secondary battery are different, as shown in Tables 1-2.

[0142] This application uses the secondary batteries obtained in the above embodiments and comparative examples as test objects, and tests their various performance characteristics and effects. The test results are shown in Tables 1-3. The test methods for each performance characteristic and effect are as follows: Primary and secondary battery characteristic parameter testing 1. ACM -1 The testing method is as follows: The secondary battery was charged at a rate of 0.33C to the upper limit voltage of 4.8V, left to stand for 10 minutes, and then discharged at a rate of 0.33C to the lower limit voltage of 3.5V. The battery was disassembled in a glove box (molar content of H2O ≤ 0.1ppm, molar content of O2 ≤ 0.1ppm), the positive electrode was removed, and the positive electrode was soaked in DMC for 4 hours and dried to obtain the positive electrode sample. At room temperature (25°C), cut the original sample into small pieces, clean the surface with compressed air to obtain the sample to be tested; thoroughly wipe the ATR crystal with anhydrous ethanol and dry it, then without placing the sample, first acquire the background spectrum; place the coated surface of the sample to be tested tightly against the crystal, apply moderate pressure to ensure good contact, and set the parameters (e.g., resolution 4 cm⁻¹). -1 Infrared spectra were then acquired; baseline correction was performed on the obtained spectra, and samples were collected from 550 to 950 cm⁻¹. -1 The peak intensity of all peaks within the range is calculated, and the lowest peak (denoted as peak A) is selected. The peak position of this peak is recorded to obtain the infrared spectrum of the cathode material located at 550~950 cm⁻¹ after one cycle of the secondary battery. -1 The position of the lowest peak (i.e., peak A) within the range is determined, and the position of peak A is denoted as a1cm. -1 ; Take another secondary battery and charge it at a rate of 0.33C to the upper limit voltage of 4.8V. Let it stand for 10 minutes, then discharge it at a rate of 0.33C to the lower limit voltage of 3.5V. Let it stand for 10 minutes. Repeat this cycle 200 times. Then, disassemble the secondary battery and remove the positive electrode. Cut the positive electrode to make a small electrode piece and clean the surface with compressed air. Thoroughly wipe the ATR crystal with anhydrous ethanol and dry it. Without placing the sample, first collect the background spectrum. Press the coated surface of the electrode tightly onto the crystal, apply moderate pressure to ensure good contact, and set the parameters (e.g., resolution 4 cm⁻¹). -1 Infrared spectra were then acquired; baseline correction was performed on the obtained spectra, and samples were collected from 550 to 950 cm⁻¹. -1 The peak intensities of all peaks within the range were analyzed, and the lowest peak (denoted as peak B) was selected. The infrared spectrum of the cathode material after 200 cycles of the secondary battery, located between 550 and 950 cm⁻¹, was obtained. -1 The position of the lowest peak (i.e., peak B) within the range is determined, and the position of peak B is denoted as a2cm. -1 ; Calculate a1cm -1 -a2cm -1 And take the absolute value, denoted as acm -1 .

[0143] For example, Figure 1 This is the infrared spectrum of Embodiment 1 of this application.

[0144] 2. The testing methods for the particle sizes Dv50, Dv10, and Dv90 of the cathode material are as follows: The secondary battery was discharged at 0.33C to the lower limit voltage of 3.5V. The battery was disassembled in a glove box (H2O molar content ≤0.1ppm, O2 molar content ≤0.1ppm), and the positive electrode was removed. Then, it was soaked in dimethyl carbonate (DMC) for 4 hours, and then vacuum dried at 60℃ for 12 hours. The powder on the surface of the dried electrode was scraped off with a scraper to obtain a powder sample. 1g of the powder sample was taken and the volume-based cumulative particle size distribution was measured using a Mastersizer 3000 laser particle size analyzer according to the particle size distribution laser diffraction method (specific steps refer to standard GB / T19077-2016). Dv50 represents the particle size corresponding to a cumulative particle size distribution percentage of 50%, Dv10 represents the particle size corresponding to a cumulative particle size distribution percentage of 10%, and Dv90 represents the particle size corresponding to a cumulative particle size distribution percentage of 90%.

[0145] 3. Test method for coating thickness: The secondary battery was discharged at 0.33C to the lower limit voltage of 3.5V. The battery was then disassembled in a glove box (H2O molar content ≤0.1ppm, O2 molar content ≤0.1ppm). The positive electrode was removed and soaked in dimethyl carbonate (DMC) solution for 4 hours. After drying, the powder on the dried electrode surface was scraped off with a scraper, preliminarily crushed in a mortar, and then passed through a 200-mesh sieve to obtain a fine powder sample. A small amount of powder (approximately 1mg) was added to anhydrous ethanol or acetone and ultrasonically dispersed for 10-15 minutes to ensure monodispersity. The powder was then pipetted into the solution. Take the upper dispersion and drop it onto a copper mesh (200 or 300 mesh) with a carbon support film, then let it air dry at room temperature. Thin the mesh using an ion thinner. Fix the copper mesh on the sample stage and bombard it from both sides of the sample with a high-energy argon ion beam (3-5 keV) at an angle, gradually thinning it until electrons can penetrate. Then transfer the sample into an HRTEM to begin testing. The accelerating voltage is 200-300 kV. First, quickly scan the copper mesh in bright-field TEM mode to find monodisperse cathode material particles. Then switch to HRTEM mode, focus on the interface between the coating layer and the substrate, and ensure that the lattice fringes are clearly visible in the image. Open the image with ImageJ or Gatan Digital Micrograph software. On the HRTEM image, measure the thickness of the coating layer along the direction perpendicular to the coating layer interface using the software's "straight line tool". Select 5 different regions for measurement and take the average value.

[0146] 4. Test method for porosity of the positive electrode material layer: The secondary battery was discharged at 0.33C to the lower limit voltage of 3.5V. The battery was disassembled in a glove box (H₂O molar content ≤ 0.1ppm, O₂ molar content ≤ 0.1ppm), and the positive electrode was removed. The positive electrode was then soaked in dimethyl carbonate (DMC) solution for 4 hours and dried. Subsequently, the positive electrode was cut into circular pieces with a radius of 12mm using an electrode punching machine. Simultaneously, the thickness of the positive electrode and the current collector were measured using a thickness gauge, recorded as h1 and h2 respectively. The mass was weighed using a balance with an accuracy of 0.00001g and recorded as m1. The positive electrode... The electrode sheet is immersed in a sealed container with a certain volume of hexadecane for 1 hour (the volume of hexadecane in the sealed solution is not required, but the amount must be sufficient to completely submerge the electrode sheet). After 1 hour, the positive electrode sheet is removed with tweezers and placed on filter paper to absorb the water until a constant weight is reached (generally, 1 hour is sufficient to absorb the water until a constant weight is reached). The mass is then weighed using a balance and recorded as m2. The porosity is calculated using the following formula: Porosity of the positive electrode material layer = X / V × 100%, where X = (m2 - m1) / ρ, and ρ is the density of hexadecane, 0.7734 g / cm³. 3 V=πr 2 ×(h1-h2)

[0147] 5. The test methods for the thickness of the positive electrode material layer and the compaction density of the positive electrode sheet are as follows: The secondary battery was discharged at 0.33C to the lower limit voltage of 3.5V. The battery was then disassembled in a glove box (H2O molar content ≤0.1ppm, O2 molar content ≤0.1ppm). The positive electrode was removed and soaked in dimethyl carbonate (DMC) solution for 4 hours; then air-dried. The pre-treated positive electrode sheet is punched into circular sheets of a fixed area using a punching machine. The area is denoted as S0. Three circular sheets are taken as parallel samples, and the mass of the three circular sheets is weighed using an electronic balance. The average value is recorded as M1. The total thickness of the three circular sheets is measured using a micrometer, and the average value is recorded as H1. The thickness of the positive current collector in the three circular sheets is measured using a micrometer, and the average value is recorded as H2. The thickness of the cathode material layer is calculated using the following formula: H = (H1 - H2) / 2; Finally, add an appropriate amount of deionized water to each of the three discs, gently wipe off the coating on the discs with a lint-free paper to expose the positive current collector, let stand at room temperature (or dry) for 10 minutes, and after the positive current collector is dry, weigh the three positive current collectors respectively, take the average value and record it as M0. The compaction density A of the positive electrode sheet is calculated using the following formula: A = (M1 - M0) / [(H1 - H2) × S0]; 6. The test method for the viscosity of the electrolyte at 25℃ is as follows: The secondary battery was discharged at 0.33C to the lower limit voltage of 3.5V. The battery was then disassembled in a glove box (H2O molar content ≤0.1ppm, O2 molar content ≤0.1ppm) and the electrolyte was collected. There are three methods for collecting the electrolyte: After removing the battery cover, ① if there is free electrolyte, collect it into a 5mL sample tube using a pipette and seal it with sealing tape to prevent leakage; ② if there is no free electrolyte, use a hydraulic press (Beijing Heng'ao Technology Co., Ltd.'s FY-30 hydraulic press) to continuously pressurize until free electrolyte appears, collect it into a sample tube and seal it; ③ add appropriate amounts of [unspecified substance] to the battery. Measure and record the dichloromethane extractant content. After adding dichloromethane, place the battery in an aluminum-plastic bag and seal it with a heat sealer. Transfer it to an ultrasonic oscillator and oscillate for 12 hours to allow the electrolyte in the electrode to mix thoroughly with the dichloromethane. Then, use a pipette to draw the mixture of dichloromethane and electrolyte into a 5mL sample tube and seal the sample tube with sealing adhesive. Take out the electrolyte and test it using a Cambridge viscometer. The design principle of the Cambridge viscometer is mainly based on electromagnetic oscillation viscosity detection technology, using a magnetic levitation probe for viscosity measurement. Specifically, place the electrolyte in a beaker and control the sample temperature at 25℃ for testing. Read the value after the displayed value stabilizes.

[0148] II. Performance Test of Secondary Batteries 1. The test method for the cycle performance of secondary batteries is as follows: At 45℃, 1) Charge at a constant current rate of 1C to 4.8V, and then charge at a constant voltage until the current drops to 0.05C; 2) Let stand for 10 minutes; 3) Discharge to 3.5V at a 1C rate; 4) Let stand for 10 minutes. Perform cycle tests according to steps 1)-4) until the capacity of the lithium-ion battery is less than 80% of the initial capacity, and record the number of cycles.

[0149] 2. The test method for the fast charging performance of secondary batteries is as follows: Using copper wire as a reference electrode, after normalization and calibrating to constant capacity, the battery was charged to 0% SOC. Then, lithium was plated on the three-electrode copper wire at a rate of 0.01C for 10 hours on the positive side. After lithium plating, the following fast charging test was performed. The battery is charged at a constant current of 0.33C to the upper limit voltage of 4.8V, and then charged at a constant voltage until the current is less than or equal to 0.05C; then discharged at 0.33C to the lower limit voltage of 3.5V. The above steps are repeated 3 times, and the capacity discharged in the third cycle is taken as the battery discharge capacity C1. Charge at 0.33C to 10% SOC; then reduce the charge rate to 0.4C, and charge at rates of 4C, 3.6C, 3.2C, 2.8C, 2.4C, 2.0C, 1.6C, 1.2C, and 0.8C in sequence. The cutoff condition for each charge is to charge to the upper limit voltage of 4.8V or the auxiliary voltage of 0mV, with a cutoff current of 0.05C. Record the charging time from 10% SOC to 80% SOC; finally, fully charge at 0.33C (100% SOC).

[0150] Table 1 Table 2 Table 3 As can be seen from Examples 1-17, by introducing urethane compounds into the positive electrode material layer, this application can not only effectively reduce the side reactions between the electrolyte and the positive electrode, but also anchor the dissolved transition metal ions to the positive electrode side by coordinating the N and O groups containing lone pairs of electrons with transition metal ions through the urethane groups, thereby reducing the precipitation of transition metal ions on the negative electrode side. Furthermore, it comprehensively controls the absolute value (i.e., ACM) of the peak position difference of the metal-oxygen bond absorption peak in the infrared spectrum of the positive electrode material layer after one and 200 cycles of the secondary battery. -1 The ratio b between the thickness of the positive electrode material layer and the particle size Dv50 of the positive electrode material, and the viscosity ccp of the electrolyte at 25℃, ensure that (a×c) / b is within a suitable range. This can comprehensively improve the cycle performance and fast-charging performance of the secondary battery, ensuring that the secondary battery can cycle to 80% SOC at 45℃ for no less than 436 cycles, and the charging time required from 10% SOC to 80% SOC is no more than 34.7 min. When (a×c) / b is 4~17.1, acm -1 40~56cm -1 When b is 15.2~24 and cp is 2.1~5cp, the overall improvement effect of the cycle performance and fast charging performance of the secondary battery is better. It was measured that the secondary battery can cycle to 80% SOC at 45℃ for no less than 813 cycles, and the charging time required from 10% SOC to 80% SOC is no more than 24.9 minutes.

[0151] Compared with the embodiments, although a, b, and c in Comparative Example 3 are within the scope of this application, a×c / b is too small, which significantly reduces the fast charging performance of the secondary battery; in Comparative Example 5, no carbamate compound was introduced, and the cycle performance of the secondary battery was even worse than that of Comparative Example 3.

[0152] Compared with the embodiments, although a, b, and c in Comparative Example 4 are within the scope of this application, a×c / b is too large, which significantly reduces the fast charging performance of the secondary battery.

[0153] Compared with the embodiments, in Comparative Example 1, a×c / b is too small, and both a and c are too small, while b is too large, which significantly reduces the cycle performance and fast charging performance of the secondary battery, even worse than the cycle performance and fast charging performance of Comparative Example 3.

[0154] Compared with the embodiments, in Comparative Example 2, a×c / b is too large, and both a and c are too large, while b is too small, which significantly reduces the fast charging performance of the secondary battery. The measured charging time is even significantly longer than that measured in Comparative Example 4.

[0155] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended 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. A secondary battery, characterized in that, The battery includes a battery cell and an electrolyte. The battery cell includes a positive electrode sheet, the positive electrode sheet includes a positive electrode material layer, the positive electrode material layer includes a positive electrode material and a carbamate compound, and the positive electrode material includes lithium nickel manganese oxide. After one cycle of the secondary battery, the infrared spectrum of the positive electrode material layer is in the range of 550~950 cm⁻¹. -1 The lowest peak within the range is peak A; after 200 cycles of the secondary battery, the infrared spectrum of the positive electrode material layer is in the range of 550~950 cm⁻¹. -1 The lowest peak within the range is peak B; The absolute value of the peak position difference between peak A and peak B is acm. -1 ; The ratio between the thickness of the positive electrode material layer and the particle size Dv50 of the positive electrode material is b; The viscosity of the electrolyte at 25°C is ccP; The secondary battery satisfies: 0.2≤(a×c) / b≤35.

7.

2. The secondary battery as described in claim 1, characterized in that, 4≤(a×c) / b≤17.

1.

3. The secondary battery as described in claim 1, characterized in that, acm -1 10~80cm -1 ; And / or, b is 12.5~31.8; And / or, cp is 0.5~6 cp.

4. The secondary battery as described in claim 1, characterized in that, The thickness of the positive electrode material layer is 110~130μm.

5. The secondary battery as described in claim 1, characterized in that, The particle size Dv50 of the cathode material is 4~9μm.

6. The secondary battery as described in claim 1, characterized in that, The particle size Dv90 of the positive electrode material is 9~20μm, and / or the particle size Dv10 of the positive electrode material is 2~6μm.

7. The secondary battery as described in claim 1, characterized in that, The chemical structural formula of the carbamate compound is as follows: Wherein, R1 is any one of alkenyl or alkynyl groups with ≤4 C atoms, and R2, R3, and R4 each independently include H, alkyl groups with ≤4 C atoms, alkenyl groups with ≤4 C atoms, phenyl groups, methoxy groups, etc. At least one of them.

8. The secondary battery as described in claim 1, characterized in that, The mass percentage of carbamate compounds in the cathode material layer is 0.1-1%.

9. The secondary battery as described in claim 1, characterized in that, The surface of the positive electrode material particles has a coating layer; The thickness of the coating layer is 0.5~10nm, and / or the coating layer includes at least one of Al2O3, Li3PO4, ZrO2, TiO2, SiO2, MgF2, lithium lanthanum titanium oxide, and P2O5.

10. The secondary battery as described in claim 1, characterized in that, The porosity of the positive electrode material layer is 20-40%.

11. The secondary battery as described in claim 1, characterized in that, The compaction density of the positive electrode is 2.3 g / cm³. 3 ~3.2g / cm 3 .

12. The secondary battery as described in claim 1, characterized in that, The cathode material further includes doping elements, which include at least one of Y, Nb, P, W, Al, Co, Mg, Zr, Ti, B, and F.

13. The secondary battery as described in claim 1, characterized in that, The positive electrode sheet also includes a positive current collector, and the positive electrode material layer is disposed on at least one side surface of the positive current collector. The peel force between the positive electrode material layer and the positive current collector is 10~50N / m.

14. The secondary battery as described in claim 1, characterized in that, The cathode material also includes at least one of lithium iron phosphate, nickel-cobalt ternary materials, and lithium manganese iron phosphate.

15. The secondary battery as described in claim 14, characterized in that, The cathode material contains 80-100% lithium nickel manganese oxide by mass.

16. The secondary battery according to any one of claims 1 to 15, characterized in that, The battery cell also includes a negative electrode and a separator, with the separator located between the positive electrode and the negative electrode.

17. The secondary battery as described in claim 16, characterized in that, The air permeability of the diaphragm is 100~400s / 100mL.

18. The secondary battery as described in claim 16, characterized in that, The thickness of the diaphragm is 8.5~18μm.

19. The secondary battery as described in claim 16, characterized in that, The negative electrode sheet includes a negative electrode material layer, and the negative electrode material layer includes a negative electrode material, which includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microspheres, silicon-oxygen materials, elemental silicon, silicon-carbon composite materials, and lithium titanate.

20. The secondary battery as described in claim 19, characterized in that, The particle size Dv50 of the negative electrode material is 5~16μm.

21. The secondary battery as described in claim 19, characterized in that, The Id / Ig ratio of the negative electrode material is 0.02~0.4, where Id is the value at 1343~1353 cm⁻¹ in the Raman spectrum of the negative electrode material. -1 The peak intensity at 1580-1600 cm⁻¹ is given by Ig, which is the Raman spectrum of the negative electrode material in the range of 1580-1600 cm⁻¹. -1 Peak intensity at that location.

22. The secondary battery as described in claim 19, characterized in that, The porosity of the negative electrode material layer is 28.3~37.2%.

23. The secondary battery as described in claim 1, characterized in that, The electrolyte includes a non-aqueous solvent, which includes at least one of carbonate solvents, carboxylic acid ester solvents, and fluorinated solvents; The carbonate solvent includes at least one of ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, and propylene carbonate, and / or the carboxylic acid ester solvent includes at least one of ethyl acetate, methyl propionate, ethyl propionate, and methyl acetate, and / or the fluorinated solvent includes at least one of ethyl trifluoroacetate, ethyl difluoroacetate, and methyl trifluoroethyl carbonate.

24. The secondary battery as described in claim 1, characterized in that, The electrolyte includes lithium salt; The electrolyte contains 5-20% lithium salt by mass, and / or the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium perchlorate, lithium dioxalate borate, lithium trifluoromethanesulfonate, lithium difluorodioxalate phosphate, lithium tetrafluorooxalate phosphate, and lithium bis(trifluoromethanesulfonyl)imide.

25. The secondary battery as described in claim 1, characterized in that, The electrolyte includes additives; The electrolyte contains additives at a mass percentage of 0.5-5%, and / or the additives include at least one of the following: vinylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonate lactone, propylene sulfite, vinyl ethylene carbonate, vinyl sulfate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide, lithium bis(fluoromethylsulfonyl)imide, lithium methane disulfonate, tri(trimethylsilane) phosphate, tri(trimethylsilane) borate, and tri(trimethylsilane) phosphite.

26. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1 to 25.

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