Secondary battery and electric device

Abstract

The application provides a secondary battery and a power utilization device. The secondary battery comprises a positive electrode, a negative electrode and an electrolyte, the electrolyte comprises an ethoxy-containing additive and a nitrogen-containing additive; in a solid electrolyte interface film, 3≤2W O +W N ≤10. The application controls the type of the electrolyte in the secondary battery, and controls the content of nitrogen elements and oxygen elements in the solid electrolyte interface film formed on the surface of the negative electrode active material layer within a specific range. The nitrogen-containing compound and the ethoxy-containing compound synergistically act in structure, improve the fast charging performance and low temperature performance of the battery, inhibit the rupture of the SEI film in the high temperature cycle process, and further prolong the cycle performance of the secondary battery, especially the cycle life and storage performance at high temperature.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries. Specifically, the present application relates to a secondary battery and a power utilization device. BACKGROUND

[0002] Lithium ion batteries, with their outstanding energy density, excellent cycle life, and no memory effect, have become an indispensable energy supplier for 3C products such as mobile phones and laptops, and have occupied a core position in the field of electric vehicles, driving the trend of green travel. In recent years, electric vehicles have made significant progress in energy density, cycle performance, safety, and cost control, and lithium ion batteries have played an important role. However, the long charging time of electric vehicles is a difficult problem that limits their widespread popularity and application in the market. The breakthrough of fast charging technology is crucial for the future development of electric vehicles, as it not only shortens the charging waiting time and improves user experience, but also accelerates the market penetration of electric vehicles and promotes the green energy revolution.

[0003] However, existing commercialized lithium ion batteries are difficult to balance fast charging and cycle performance when facing the performance challenges of high temperature and low temperature environments. In order to improve the fast charging ability and low temperature adaptability, existing technologies tend to use low boiling point carboxylic acid ester solvents to reduce the viscosity of the electrolyte and improve the ionic conductivity. However, this approach, while improving certain performance indicators of the battery in the short term, poses a serious threat to the high temperature safety and cycle life of the battery in the long term, and the frequent side reactions of carboxylic acid ester solvents with negative electrode materials not only reduce the high temperature safety performance of the battery, but also exacerbate the internal loss of the battery and shorten its service life.

[0004] Therefore, finding a solution that can meet the fast charging demand, maintain stable operation of the battery at extreme temperatures, and extend the cycle life of the battery has become one of the urgent tasks for technical researchers. SUMMARY

[0005] The main purpose of the present application is to provide a secondary battery and a power utilization device, especially a fast charging type long life secondary battery and a power utilization device, to solve the problem that the battery in the prior art is difficult to balance high temperature performance, low temperature performance, fast charging, and cycle performance.

[0006] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a secondary battery is provided, comprising a positive electrode, a negative electrode and an electrolyte, the electrolyte comprising an ethoxy-containing additive and a nitrogen-containing additive; the negative electrode comprising a negative electrode active material layer and a solid electrolyte interface film on the surface of the negative electrode active material layer, the solid electrolyte interface film comprising an ethoxy compound and lithium nitride, the ethoxy compound being derived from the ethoxy-containing additive, and the lithium nitride being derived from the nitrogen-containing additive; the weight percentage of oxygen element from the ethoxy compound in the solid electrolyte interface film is defined as W O %, and the weight percentage of nitrogen element from the lithium nitride in the solid electrolyte interface film is defined as W N %, wherein 3≤2W O +W N ≤10. Under the above conditions, the lithium nitride and the ethoxy compound in the SEI film have a good synergistic effect, in which the lithium nitride improves ion transmission, and the ethoxy compound can improve the flexibility of the SEI film, improve the structural stability of the interface film of the electrode during fast charging, improve the kinetic characteristics of lithium ion transmission at the interface, reduce impedance, and improve the fast charging performance and low temperature performance of the battery; it can further improve the compactness and flexibility of the SEI film, thereby effectively inhibiting the rupture of the SEI film during high temperature cycling, and further reducing the negative effects of continuous side reactions of electrolyte and negative electrode, prolonging the cycle performance of the secondary battery, especially the cycle life and storage performance at high temperature.

[0007] Further, 0.05 O <5, preferably, 1≤W O ≤3; under the above conditions, the formation of a stable and flexible SEI film can be more effectively promoted, and the fast charging performance and cycle stability of the lithium ion battery can be more effectively improved; and / or, 1 N <10, preferably, 2≤W N ≤8; under the above conditions, the lithium ion conductivity and high temperature stability of the SEI film can be further enhanced, and the fast charging capacity and cycle life of the battery can be more effectively improved.

[0008] Further, the tortuosity of the electrode tab of the negative electrode is defined as τ, wherein 0 N ×W O <1. Under the above conditions, the lithium ion conductivity in the electrode is faster, the electrolyte can be more fully infiltrated into the voids, and the side reaction between the electrolyte and the electrode is less, so that the high temperature performance, low temperature performance, fast charging and cycle performance of the battery can be more effectively balanced, and the comprehensive performance of the battery is better.

[0009] Further, 2.5 < τ < 9. Under the above conditions, the ion transport path of the secondary battery is shorter, the transport efficiency is faster, the current distribution is more uniform, the SEI film is more stable, the generated heat is dissipated faster, and the mechanical stability and chemical stability are better, and the high-temperature performance, low-temperature performance, fast charging and cycle performance of the battery are better.

[0010] Further, the ethoxy-containing additive includes one or more of ethoxy acrylate, ethoxy vinylene carbonate and ethoxy vinylene sulfite; preferably, the ethoxy acrylate has a structure shown in general formula (I-1):

[0011]

[0012] In general formula (I-1), n is an integer from 1 to 4, R 11 selected from hydrogen, C1-C3 alkyl, vinyl carboxylate or propenyl carboxylate, R 12 selected from hydrogen, C1-C3 alkyl;

[0013] Preferably, the ethoxy vinylene carbonate has a structure shown in general formula (I-2):

[0014]

[0015] In general formula (I-2), m is an integer from 1 to 4, R 13 selected from hydrogen, C1-C3 alkyl, vinyl carboxylate or propenyl carboxylate;

[0016] Preferably, the ethoxy vinylene sulfite has a structure shown in general formula (I-3):

[0017]

[0018] In general formula (I-3), p is an integer from 1 to 4, R 14 selected from hydrogen, C1-C3 alkyl, vinyl carboxylate or propenyl carboxylate; the ethoxy-containing additive with the above structure can more significantly improve the transport of lithium ions, and can further improve the flexibility of the SEI film and the structural stability of the interface film of the electrode during fast charging;

[0019] and / or, the nitrogen-containing additive includes one or more of nitrile compounds, phosphazene, amide, organic nitrogen-containing lithium salt, inorganic nitrogen-containing alkali metal salt, nitrate and nitro ester;

[0020] Preferably, the nitrile compound has a structure shown in general formula (II-1):

[0021]

[0022] In general formula (II-1), R 21R is selected from C2-C10alkylene or nitrile-substituted C2-C10alkylene, R 22 R is selected from hydrogen, nitrile, C1-C6alkyl or carboxylate;

[0023] Preferably, the phosphazene has the structure according to general formula (II-2):

[0024]

[0025] In general formula (II-2), R 23 R is selected from C1-C6alkyl or fluoro-C1-C6alkyl, R 24 , R 25 , R 26 , R 27 and R 28 are each independently selected from hydrogen, fluorine, C1-C6alkyl or fluoro-C1-C6alkyl, and R 24 , R 25 , R 26 , R 27 and R 28 at least one of R, R, R, R, R and R is fluoro-C1-C6alkyl;

[0026] Preferably, the amide has the structure according to general formula (II-3):

[0027]

[0028] In general formula (II-3), R 29 , R 210 , R 211 are each independently selected from hydrogen, C1-C6alkyl or fluoro-C1-C6alkyl, and R 29 , R 210 , R 211 at least one of R, R, R and R is fluoro-C1-C6alkyl;

[0029] Preferably, the organic nitrogen-containing lithium salt has the structure according to general formula (II-4) or general formula (II-5):

[0030]

[0031] In general formula (II-4), R 212 , R 213 , R 214 are each independently selected from hydrogen, fluorine, C1-C6alkyl, fluoro-C1-C6alkyl or nitrile, and R 212 , R 213 , R 214 at least one of R, R, R and R is selected from fluorine, fluoro-C1-C6alkyl or nitrile;

[0032]

[0033] In general formula (II-5), R 215 , R 216 are each independently selected from fluorine, C1-C6 alkyl or fluorinated C1-C6 alkyl, and R 215 and R 216 are at least one selected from fluorine or fluorinated C1-C6 alkyl;

[0034] Preferably, the inorganic nitrogen-containing alkali salt has a structure represented by general formula (II-6):

[0035] R 217 NO t general formula (II-6);

[0036] In general formula (II-6), t is selected from 2 or 3; R 217 is selected from lithium, sodium or potassium;

[0037] Preferably, the nitrate ester has a structure represented by general formula (II-7):

[0038] R 218 NO r general formula (II-7);

[0039] In general formula (II-7), r is 3; R 218 is selected from C1-C4 alkyl;

[0040] Preferably, the nitro ester has a structure represented by general formula (II-8):

[0041] R 219 NO r general formula (II-8);

[0042] In general formula (II-8), s is 2; R 219 is selected from C1-C4 alkyl. The nitrogen-containing base additive having the above structure can further improve the lithium ion transmission property and structural stability at high temperature of the SEI film, thereby being more beneficial to improve the fast charging performance and high-temperature cycle storage performance of the negative electrode.

[0043] Further, the ethoxy-containing acrylate includes one or more of ethoxyethoxyethyl acrylate, 2-methoxyethyl acrylate, and triethylene glycol diacrylate; and / or, the ethoxy-containing vinylene carbonate includes one or more of methyl ethoxyvinylene carbonate, methyl ethoxyvinylene sulfite, and methoxyethoxymethyl vinylene carbonate; and / or, the ethoxy-containing vinylene sulfite includes ethoxymethyl vinylene sulfite; and / or, the nitrile compound includes one or more of butanedinitrile, hexanedinitrile, pentanedinitrile, hexanetristitnitrile, ethylene glycol (bis) propionitrile ether, methoxypropionitrile, 2,3-dimethoxypropionitrile, and methyl cyanoacetate; and / or, the phosphazene includes one or more of methoxy-pentafluorocyclotriphosphazene, trifluoromethoxy-pentafluorocyclotriphosphazene, ethoxy-pentafluorocyclotriphosphazene, and trifluoroethoxy-pentafluorocyclotriphosphazene; and / or, the amide includes trifluoromethylamide or trifluoroethylamide; and / or, the organic nitrogen-containing lithium salt includes one or more of lithium 4,5-dicyano-2-(trifluoromethyl)imidazole, lithium (fluorosulfonyl)(perfluorobutylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(pentafluoroethylsulfonate)imide; and / or, the inorganic nitrogen-containing alkali metal salt includes one or more of lithium nitrate, lithium nitrite, sodium nitrate, and sodium nitrite; and / or, the nitrate ester includes ethyl nitrate and / or propyl nitrate; and / or, the nitro ester includes nitromethane and / or nitroethane. The above-mentioned specific types of ethoxy-containing additives and nitrogen-containing additives can synergize, and are more conducive to the construction of a dense, flexible, and high-ionic-conductivity SEI film, thereby greatly reducing side reactions during fast charging and improving the performance of the battery in high- and low-temperature environments.

[0044] Further, the weight percentage content of the ethoxy-containing additive in the electrolyte is 0.05-4%; and / or, the weight percentage content of the nitrogen-containing additive in the electrolyte is 0.5-10%; preferably, the weight ratio of the ethoxy-containing additive to the nitrogen-containing additive is (0.05-4):1. Under the above conditions, the ethoxy-containing additive and the nitrogen-containing additive synergize, which can further optimize the SEI film structure and is more conducive to improving the fast-charging performance and cycle stability of the battery, while also maintaining good safety and electrochemical efficiency.

[0045] Further, the electrolyte comprises a mixture of ethoxyethoxyethyl acrylate and lithium bis(fluorosulfonyl)imide, the weight ratio of the two being (0.05-4):1; or the electrolyte comprises a mixture of ethoxyethoxyethyl acrylate and ethoxy pentafluorocyclotriphosphazene, the weight ratio of the two being (2-4):1; or the electrolyte comprises a mixture of ethoxyethoxyethyl acrylate and ethyl nitrate, the weight ratio of the two being (1-4):1. The synergistic effect of the above-mentioned combination of electrolyte additives is more conducive to the construction of an SEI film with high lithium ion transmission and structural stability, thereby more significantly improving the fast-charging capability and high-temperature cycle performance of the secondary battery, reducing gas production, and strengthening the safety of the battery.

[0046] Further, the electrolyte further comprises other additives, the other additives comprising one or more of vinylene carbonate, vinyl ethylene carbonate, lithium difluorophosphate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, fluorinated vinyl carbonate, difluorinated vinyl carbonate, trifluorinated propylene carbonate, 2,2,2-trifluoromethyl ethyl carbonate, 2,2,2-trifluorodiethyl carbonate, tris(trifluoroethyl) phosphate, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether; the weight percentage content of the other additives in the electrolyte being 0.1-10%; the above-mentioned other additives can participate in the formation of the SEI film, cooperate with the ethoxy-containing additives and the nitrogen-containing additives, and construct a composite SEI film, which is more conducive to maintaining the structural integrity of the SEI film during fast charging, thereby further reducing electrolyte consumption, improving the cycle life and safety of the battery; and / or the positive electrode comprises a positive electrode active material, the positive electrode active material comprising a lithium nickel transition metal oxide, the chemical formula of the lithium nickel transition metal oxide being: LiNi x Co y A (1-x-y) O2, wherein A comprises one or more of manganese, aluminum, magnesium, chromium, calcium, zirconium, molybdenum, silver, and niobium, 0.5≤x≤1, 0≤y≤0.5, x+y≤1; the stable and highly conductive interface layer formed by the additive of the present application can more effectively slow down the structural degradation of the above-mentioned positive electrode material during charging and discharging, thereby further prolonging the cycle life of the battery; and / or the negative electrode active material in the negative electrode active material layer comprises a silicon-based material, the silicon-based material comprising one or more of silicon, silicon alloy, silicon oxide compound, and silicon carbide compound; preferably, in the negative electrode active material, the weight percentage content of the silicon-based material is 10-100%, the additive of the present application can interact with the above-mentioned negative electrode active material to form a more stable SEI film, protect the negative electrode material from the corrosion of the electrolyte, more effectively buffer the volume change of the silicon-based material during charging and discharging, and improve the conductivity of the negative electrode, thereby more conducive to improving the charging and discharging efficiency, cycle stability, and safety of the battery.

[0047] According to another aspect of the present application, a power consuming device is provided, comprising the above-mentioned secondary battery. The power consuming device adopting the secondary battery of the present application can enhance the fast charging and cycle performance of the power consuming device through the optimized SEI film, significantly improve the overall energy density, power output and durability, and is suitable for application scenarios requiring high energy, fast charging and long-term stable operation.

[0048] The present application controls the type of electrolyte in the secondary battery, and controls the content of nitrogen element and oxygen element in the solid electrolyte interface film (SEI film) formed on the surface of the negative electrode active material layer within a specific range. The nitrogen element from the nitrogen-containing additive improves the lithium ion transportability and structural stability of the SEI film at high temperature, thereby improving the fast charging performance and high-temperature cycle storage performance of the negative electrode. The oxygen element from the ethoxyl-containing additive exists in the form of -(CH2-CH2O)-, which improves the transport of lithium ions and improves the flexibility of the SEI film, thereby ensuring the structural stability of the interface film when the electrode is fast charged. Moreover, the nitrogen-containing compound and the ethoxyl-containing compound have a good synergistic effect in structure, which improves the kinetic characteristics of lithium ion transport at the interface, reduces the impedance, and improves the fast charging performance and low-temperature performance of the battery; further improves the compactness and flexibility of the SEI film, thereby effectively inhibiting the rupture of the SEI film during high-temperature cycling, and further reducing the negative effects such as continuous side reactions of electrolyte and negative electrode, prolonging the cycle performance of the secondary battery, especially the cycle life and storage performance at high temperature.

[0049] Based on the above improvements, the SEI film of the secondary battery of the present application is compact and stable, effectively inhibiting the continuous decomposition of electrolyte and gas generation, and the secondary battery has excellent fast charging performance, and at the same time, has good cycle performance, storage performance and safety performance at high temperature and low temperature. DETAILED DESCRIPTION

[0050] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the embodiments.

[0051] For the sake of brevity, only some numerical ranges are specifically disclosed in the present application. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and likewise any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, each individually disclosed point or single numerical value can itself be combined as a lower limit or an upper limit with any other point or single numerical value or with other lower limits or upper limits to form a range not explicitly recited.

[0052] The terms used in this application have the commonly understood meanings as understood by one of ordinary skill in the art, unless otherwise indicated. The values of each parameter mentioned in this application can be measured by various measuring methods commonly used in the art (for example, can be tested according to the methods given in the examples of this application), unless otherwise indicated.

[0053] The list of items connected by the phrase "one or more of' or other similar phrases can mean any combination of the listed items. For example, if the items A and B are listed, the phrase "one or more of A and B" means only A; only B; or A and B. In another example, if the items A, B, and C are listed, the phrase "one or more of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A can include a single component or multiple components. Item B can include a single component or multiple components. Item C can include a single component or multiple components.

[0054] As described in the background of the application, the prior art has the problem that it is difficult to simultaneously achieve high-temperature performance, low-temperature performance, fast charging, and cycle performance. In order to solve the above problem, in a typical embodiment of the present application, a secondary battery is provided, which comprises a positive electrode, a negative electrode, and an electrolyte, the electrolyte comprising an ethoxy-containing additive and a nitrogen-containing additive; the negative electrode comprises a negative electrode active material layer, and a solid electrolyte interface film located on the surface of the negative electrode active material layer, the solid electrolyte interface film containing an ethoxy compound and lithium nitride, the ethoxy compound being derived from the ethoxy-containing additive, and the lithium nitride being derived from the nitrogen-containing additive; using an X-ray photoelectron spectrometer, the weight percentage content of oxygen element from the ethoxy compound in the solid electrolyte interface film is defined as W O %, and the weight percentage content of nitrogen element from the lithium nitride in the solid electrolyte interface film is defined as W N %, wherein 3≤2W O +W N ≤10. In some embodiments, 4≤2O+N≤8.

[0055] In the solid electrolyte interface film SEI on the surface of the negative electrode, the nitrogen element from the nitrogen-containing additive can form lithium nitride to improve the lithium ion transportability and structural stability of the SEI film at high temperature, thereby facilitating the improvement of the fast charging performance and high-temperature cycle storage performance of the negative electrode; however, due to the high activity of nitrogen element, when the content of nitrogen element is high, it will affect the initial efficiency and capacity of the electrode; and nitrogen element usually exists in the form of Li3N, and has low adhesion to the electrode, and is easy to cause the rupture of the SEI due to the change in the volume of the electrode during fast charging, thereby affecting the electrochemical performance of the battery.

[0056] The oxygen element from the ethoxyl group-containing additive exists in the form of -(CH2-CH2O)- in the solid electrolyte interface film SEI on the negative electrode surface, which can improve the transmission of lithium ions and improve the flexibility of the SEI film, and improve the structural stability of the interface film of the electrode during fast charging; however, when the content is too high, the SEI film on the surface of the negative electrode active material layer has too high a swelling rate, which leads to unstable interface film structure, thereby increasing the side reaction of the electrolyte on the negative electrode side, and finally degrading the cycle life of the battery.

[0057] The inventors found through a large number of experimental verification and theoretical research that when the content of nitrogen element and oxygen element meets the relationship of "3≤2W O +W N ≤10", the SEI film is dense and stable, which can effectively inhibit the continuous decomposition of the electrolyte caused by the contact between the electrolyte and the negative electrode active material, and inhibit gas production, thereby improving the cycle performance and safety performance of the secondary battery, especially the cycle performance and storage performance at high temperature.

[0058] In addition, lithium nitride and ethoxyl compounds in the SEI film have a good synergistic effect, in which lithium nitride improves ion transmission, and ethoxyl compounds can improve the flexibility of the SEI film, improve the structural stability of the interface film of the electrode during fast charging, improve the kinetic characteristics of lithium ion transmission at the interface, reduce impedance, and improve the fast charging performance and low temperature performance of the battery; it can further improve the density and flexibility of the SEI film, thereby effectively inhibiting the rupture of the SEI film during high temperature cycling, and thereby reducing the negative effects of continuous side reactions of the electrolyte and the negative electrode, prolonging the cycle performance of the secondary battery, especially the cycle life and storage performance at high temperature.

[0059] Based on the above improvements, the secondary battery of the application has excellent fast charging performance, and at the same time, has good cycle performance, storage performance and safety performance at high temperature and low temperature.

[0060] Typically but not limitedly, 2W O +W N is 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10 or a range composed of any two numerical values.

[0061] The inventors further preferred the range of W O and W N . In a preferred embodiment, 0.05 O < 5, preferably 0.5 O ≤ 4, more preferably 1 O ≤ 3. Typically but not limitedly, W O0.1, 0.2, 0.5, 0.8, 1, 1.1, 1.3, 1.4, 1.5, 1.6, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 4.9, or any range of two numerical values. Under the above conditions, the formation of stable and flexible SEI film can be more effectively promoted, thereby more favorably improving the fast-charging performance and cycle stability of the lithium-ion battery. However, if W O is too low or too high, it can lead to poor SEI film structure, thereby affecting the transport of lithium ions and the performance of the battery, especially under fast-charging and high-temperature cycling conditions, which can accelerate the degradation of the battery.

[0062] In a preferred embodiment, 1 < W N < 10, preferably, 2 < W N < 8. In a preferred embodiment, 2 < W N < 6. In a preferred embodiment, 3 < W N < 6. Typically but not limitedly, W N 1.6, 1.7, 2, 2.3, 2.5, 2.7, 3, 3.3, 3.5, 3.7, 4, 4.3, 4.5, 4.8, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, or any range of two numerical values. Under the above conditions, the lithium ion conductivity and high-temperature stability of the SEI film can be further enhanced, thereby more favorably improving the fast-charging capability and cycle life of the battery. However, if W N is too low, it can be insufficient to optimize the SEI film, and if W N is too high, it can trigger additional side reactions, even damaging the performance of the battery, especially the initial efficiency and the electrochemical stability at high temperature.

[0063] Tortuosity is a parameter reflecting the degree of winding and turning of the path of the pores in the porous medium from one end to the other, that is, the ratio of the actual flow path length to the straight-line distance between the flow path ends. In the electrode structure, the electrolyte is fully infiltrated into the pores, and the transport of lithium ions needs to migrate along the pores through the electrolyte, so the electrode tortuosity has an important influence on the lithium ion conductivity and electrolyte diffusion in the electrode, and also has important significance for the construction of the relationship between the performance of the battery and the interface composition of the electrode and the structural characteristics of the electrode. In the present application, the tortuosity can be adjusted according to the characteristics of the selected negative active material by conventional technical means in the art, for example, by controlling the roll pressure, roll temperature, roll speed, and roll number.

[0064] In a preferred embodiment, the tortuosity of the electrode sheet defining the negative electrode is τ, wherein 0 < 2(W N x WO ) - τ < 1; preferably, 0.2 < 2(W N × W O ) - τ < 0.8; more preferably, 0.3 < 2(W N × W O ) - τ < 0.6. Under the above conditions, the lithium ion conductivity in the electrode is faster, the electrolyte can be more fully infiltrated into the voids, and the side reactions between the electrodes are less, so that the high-temperature performance, low-temperature performance, fast charging and cycle performance of the battery can be more effectively balanced, and the comprehensive performance of the battery is better. When the value of 2(W N × W O ) - τ is too large, correspondingly, the content of nitrogen and oxygen elements in the SEI film is too high, or the tortuosity of the negative electrode sheet is too small, which may cause the reaction between the electrolyte and the electrode to increase, thereby increasing the consumption of the electrolyte and reducing the cycle life of the battery, and may also increase the gas production of the battery. When the value of 2(W N × W O ) - τ is too small, correspondingly, the content of nitrogen and oxygen elements in the SEI film is too low, or the tortuosity of the negative electrode sheet is too large, which may cause the negative electrolyte to reduce the wettability, thereby making the kinetics of the secondary battery worse, the polarization larger, the capacity lower, and further affecting the electrochemical performance. Typically but not limited to, the value of 2(W N × W O ) - τ is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or a range composed of any two numerical values.

[0065] In a preferred embodiment, 2.5 < τ < 9; preferably, 3 < τ < 8; more preferably, 4 < τ < 7. Typically but not limitedly, τ is 2.6, 2.8, 3, 3.2, 3.4, 3.6, 3.8, 4, 4.2, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.8 or any range between any two of the values. If the sheet winding degree of the negative electrode is too large, it can cause uneven heat dissipation inside the battery, exacerbate the swelling of the electrode material, affect the stability and safety of the battery under high temperature conditions, and also cause low ion mobility, long ion transport path, increased resistance, and poor low-temperature performance. In addition, it can also cause uneven current distribution, making it difficult to quickly dissipate the heat generated during fast charging, thereby affecting the fast-charging performance, safety of the battery, and possibly affecting the stability of the SEI film on the negative electrode surface, thereby affecting the cycle life of the battery. If the sheet winding degree of the negative electrode is too small, it will also affect the life, electrochemical performance and safety of the battery. Under the above conditions, the ion transport path of the secondary battery is shorter, the transport efficiency is faster, the current distribution is more uniform, the SEI film is more stable, the heat generated is dissipated faster, and the mechanical and chemical stability is better, and the high-temperature performance, low-temperature performance, fast-charging and cycle performance of the battery are better.

[0066] In a preferred embodiment, the ethoxylated additive includes one or more of ethoxylated acrylate, ethoxylated vinylene carbonate and ethoxylated vinylene sulfite. The above oxygen-containing additive can more effectively improve the flexibility and lithium ion conduction efficiency of the SEI film, thereby more favorably strengthening the fast-charging performance and cycle stability of the battery; and can also synergize with the nitrogen-containing additive to jointly optimize the SEI film structure, thereby more significantly inhibiting the occurrence of side reactions and prolonging the life of the battery.

[0067] Preferably, the ethoxylated acrylate has a structure represented by general formula (I-1):

[0068]

[0069] In general formula (I-1), n is an integer from 1 to 4, R 11 selected from hydrogen, C1-C3 alkyl, vinyl carboxylate or propenyl carboxylate, such as H, C2H5 or vinyl propionate, R 12 selected from hydrogen, C1-C3 alkyl, such as H, CH3 or C2H5.

[0070] Preferably, the ethoxylated vinylene carbonate has a structure represented by general formula (I-2):

[0071]

[0072] In general formula (I-2), m is an integer from 1 to 4, R 13selected from hydrogen, C1-C3 alkyl, vinyl carboxylate or propenyl carboxylate, for example H, C2H5 or vinyl propionate;

[0073] Preferably, the ethoxylated vinylene sulfite has a structure represented by general formula (I-3):

[0074]

[0075] In general formula (I-3), p is an integer from 1 to 4, R 14 selected from hydrogen, C1-C3 alkyl, vinyl carboxylate or propenyl carboxylate.

[0076] The ethoxylated additive having the above structure can further significantly improve the transport of lithium ions, and can further improve the flexibility of the SEI film and the structural stability of the interface film of the electrode during fast charging.

[0077] In a preferred embodiment, the nitrogen-containing additive includes one or more of nitrile compounds, phosphazene, amide, organic nitrogen-containing lithium salt, inorganic nitrogen-containing alkali metal salt, nitrate and nitro ester. The above-mentioned nitrogen-containing additive can further improve the ionic conductivity of the electrolyte, improve the composition and structure of the interface film, make it more effectively play the above-mentioned effect, and further improve the fast charging performance and cycle storage performance of the secondary battery.

[0078] Preferably, the nitrile compound has a structure represented by general formula (II-1):

[0079]

[0080] In general formula (II-1), R 21 selected from C2-C10 alkylene or C2-C10 alkylene substituted with nitrile group, more preferably, R 21 selected from C1-C6 alkylene or C2-C6 alkylene substituted with nitrile group, for example ethylene, propylene, butylene, pentylene, hexylene, or ethylene, propylene, butylene, pentylene, hexylene substituted with nitrile group; R 22 selected from hydrogen, nitrile group, C1-C6 alkyl or carboxylate group, more preferably, R 22 selected from hydrogen, C1-C6 alkyl or nitrile group.

[0081] Preferably, the phosphazene has a structure represented by general formula (II-2):

[0082]

[0083] In general formula (II-2), R 23 selected from C1-C6 alkyl or fluorinated C1-C6 alkyl, R 24 , R 25 , R 26 , R27 and R 28 are each independently selected from hydrogen, fluorine, C1-C6alkyl or fluorinated C1-C6alkyl, and at least one of R 24 , R 25 , R 26 , R 27 and R 28 is fluorine or fluorinated C1-C6alkyl; more preferably, R 23 is selected from C1-C4alkyl or fluorinated C1-C4alkyl, R 24 , R 25 , R 26 , R 27 and R 28 are each independently selected from fluorine, C1-C4alkyl or fluorinated C1-C4alkyl, or R 28 is selected from methyl, ethyl, n-propyl, i-propyl, trifluoromethyl or 2,2,2-trifluoroethyl, R 23 , R 24 , R 25 , R 26 , R 27 are each independently selected from fluorine or fluorinated C1-C4alkyl, and at least one of R 23 , R 24 , R 25 , R 26 and R 27 is fluorine.

[0084] Preferably, the amide has the structure according to general formula (II-3):

[0085]

[0086] In general formula (II-3), R 29 , R 210 , R 211 are each independently selected from hydrogen, C1-C6alkyl or fluorinated C1-C6alkyl, and at least one of R 29 , R 210 , R 211 is fluorinated C1-C6alkyl; more preferably, R 29 , R 210 , R 211 are each independently selected from hydrogen, C1-C4alkyl or fluorinated C1-C4alkyl, and at least one of R 29 , R 210 , R 211 is fluorinated C1-C4alkyl.

[0087] Preferably, the organic nitrogen-containing lithium salt has the structure according to general formula (II-4) or general formula (II-5):

[0088] Preferably, the organic nitrogen-containing lithium salt has the structure according to general formula (II-4) or general formula (II-5):

[0088]

[0089] In general formula (II-4), R 212 , R 213 , R 214 are each independently selected from hydrogen, fluorine, C1-C6 alkyl, fluorinated C1-C6 alkyl or nitrile, and R 212 , R 213 , R 214 at least one of which is selected from fluorine, fluorinated C1-C6 alkyl or nitrile; more preferably, R 212 , R 213 , R 214 are each independently selected from fluorine or fluorinated C1-C4 alkyl, and R 212 , R 213 , R 214 at least one of which is nitrile;

[0090]

[0091] In general formula (II-5), R 215 , R 216 are each independently selected from fluorine, C1-C6 alkyl or fluorinated C1-C6 alkyl, and R 215 and R 216 at least one of which is selected from fluorine or fluorinated C1-C6 alkyl; more preferably, R 215 , R 216 are each independently selected from fluorine, C1-C4 alkyl or fluorinated C1-C4 alkyl, and R 215 and R 216 at least one of which is selected from fluorine or fluorinated C1-C4 alkyl.

[0092] Preferably, the inorganic nitrogen-containing alkali salt has the structure of general formula (II-6):

[0093] R 217 NO t general formula (II-6);

[0094] In general formula (II-6), t is selected from 2 or 3; R 217 is selected from lithium, sodium or potassium.

[0095] Preferably, the nitrate ester has the structure of general formula (II-7):

[0096] R 218 NO r general formula (II-7);

[0097] In general formula (II-7), r is 3; R 218 is selected from C1-C4 alkyl.

[0098] Preferably, the nitro ester has a structure represented by general formula (II-8):

[0099] R 219 NO s general formula (II-8);

[0100] In general formula (II-8), s is 2; R 219 selected from C1-C4 alkyl.

[0101] The nitrogen-containing base additive having the above structure can further improve the lithium ion transmission property and structural stability of the SEI film at high temperature, thereby being more conducive to improving the fast-charging performance and high-temperature cycle storage performance of the negative electrode.

[0102] The inventors further optimize the composition and type of the ethoxylated additive and the nitrogen-containing additive. In a preferred embodiment, the ethoxylated acrylate includes one or more of ethoxylated ethoxylated ethyl acrylate EOEA, 2-methoxyethyl acrylate MOEA, and triethylene glycol diacrylate TGD; and / or, the ethoxylated vinylene carbonate includes one or more of methyl ethoxylated vinylene carbonate, methyl ethoxylated vinylene sulfite, and methoxyethoxymethyl vinylene carbonate; and / or, the ethoxylated vinylene sulfite includes ethoxylated methyl vinylene sulfite, the above ethoxylated compounds having a rich -(CH2O-CH2O) n structure, which can further improve the flexibility and lithium ion conductivity of the SEI film, thereby being able to more effectively inhibit the decomposition of the electrolyte and prolong the battery life.

[0103] In a preferred embodiment, the nitrile compound includes one or more of succinonitrile SN, adiponitrile ADN, glutaronitrile GLN, hexanetristrinitrile HTN, ethylene glycol (bis) propionitrile ether DENE, methoxypropionitrile MOPN, 2,3-dimethoxypropionitrile DMOPN, and methyl cyanoacetate MOCA; and / or, the phosphazene includes one or more of methoxy-pentafluorocyclotriphosphazene, trifluoromethoxy-pentafluorocyclotriphosphazene, ethoxy-pentafluorocyclotriphosphazene PFPN, and trifluoroethoxy-pentafluorocyclotriphosphazene TFPN; and / or, the amide includes trifluoromethylamide or trifluoroethylamide; and / or, the organic nitrogen-containing lithium salt includes one or more of 4,5-dicyano-2-(trifluoromethyl)imidazolide LiTDI, lithium (fluorosulfonyl)(perfluorobutylsulfonyl)imide LiFNFSI, lithium bis(fluorosulfonyl)imide LiFSI, lithium bis(trifluoromethylsulfonyl)imide LiTFSI, and lithium bis(pentafluoroethylsulfonyl)imide LiBETI; and / or, the inorganic nitrogen-containing alkali metal salt includes one or more of lithium nitrate LiNO3, lithium nitrite LiNO2, sodium nitrate NaNO3, and sodium nitrite NaNO2; and / or, the nitrate ester includes ethyl nitrate and / or propyl nitrate; and / or, the nitro ester includes nitromethane and / or nitroethane. The above-mentioned nitrogen-containing compounds are more conducive to the formation of compounds such as Li3N, thereby more conducive to enhancing the thermal stability and lithium ion transmission speed of the film.

[0104] The above-mentioned specific kinds of ethoxy-containing additives and nitrogen-containing additives can synergize, and are more conducive to constructing a dense, flexible, and high-ionic-conductivity SEI film, thereby being able to greatly reduce side reactions during fast charging and improve the performance of the battery in high- and low-temperature environments.

[0105] The inventors have optimized the content range of the ethoxy-containing additive and the nitrogen-containing additive through a large number of experiments. In a preferred embodiment, the weight percentage content of the ethoxy-containing additive in the electrolyte is 0.05-4%, preferably 0.2-3%; and / or, the weight percentage content of the nitrogen-containing additive in the electrolyte is 0.5-10%, preferably 1-5%. In a preferred embodiment, the weight ratio of the ethoxy-containing additive to the nitrogen-containing additive is (0.05-4):1. Under the above conditions, the ethoxy-containing additive and the nitrogen-containing additive synergize to further optimize the SEI film structure, which is more conducive to improving the fast-charging performance and cycle stability of the battery, while also maintaining good safety and electrochemical efficiency. If the content of the ethoxy-containing additive is too high, it may cause the SEI film on the surface of the negative active material layer to have too high a swelling rate, resulting in unstable interface film structure, thereby increasing the side reactions of the electrolyte on the negative side, ultimately degrading the cycle life of the battery. If the content of the ethoxy-containing additive is too low, it may result in no obvious improvement of the SEI film; if the content of the nitrogen-containing additive is too high, it may result in a decrease in the initial efficiency and capacity of the electrode, and the nitrogen element usually exists in the form of Li3N, which has low adhesion to the electrode, and is prone to cause the SEI to crack due to the volume change of the electrode during fast charging, thereby affecting the electrochemical performance of the battery, and if the content of the nitrogen-containing additive is too low, it may also result in poor improvement of the SEI film.

[0106] Typically but not limitedly, the weight percentage content of the ethoxy-containing additive in the electrolyte is 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, or a range formed by any two of the above values, the weight percentage content of the nitrogen-containing additive is 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10%, or a range formed by any two of the above values, and the weight ratio of the ethoxy-containing additive to the nitrogen-containing additive is 0.05:1, 0.1:1, 0.5:1, 1:1, 2:1, 3:1, 4:1, or a range formed by any two of the above values.

[0107] In a preferred embodiment, the electrolyte comprises a mixture of ethoxyethoxyethyl acrylate and lithium bis(fluorosulfonyl)imide, with a weight ratio of (0.05-4):1; or, the electrolyte comprises a mixture of ethoxyethoxyethyl acrylate and ethoxy pentafluorocyclotriphosphazene, with a weight ratio of (2-4):1; or, the electrolyte comprises a mixture of ethoxyethoxyethyl acrylate and ethyl nitrate, with a weight ratio of (1-4):1. The electrolyte additives in the above combinations synergize with each other, which is more conducive to the construction of SEI film with high lithium ion transmission and structural stability, thereby more significantly improving the fast-charging capability and high-temperature cycle performance of the secondary battery, reducing gas production, and strengthening the safety of the battery.

[0108] The inventors further optimized the types and compositions of electrolyte additives. In a preferred embodiment, the electrolyte further comprises other additives, which include one or more of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), lithium difluorophosphate (LiDFP), tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, fluorinated vinyl carbonate, difluorinated vinyl carbonate, trifluorinated propylene carbonate, 2,2,2-trifluoromethyl ethyl carbonate, 2,2,2-trifluorodiethyl carbonate, tris(trifluoroethyl)phosphate, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, preferably one or more of vinylene carbonate, vinyl ethylene carbonate, and lithium difluorophosphate. In a preferred embodiment, the weight percentage of the other additives in the electrolyte is 0.1-10%, preferably 0.1-5%. The other additives of the above types can participate in the formation of SEI film, cooperate with the ethoxy-containing additives and nitrogen-containing additives, and construct a composite SEI film, which is more conducive to maintaining the structural integrity of the SEI film during fast charging, thereby further reducing electrolyte consumption, improving battery cycle life and safety.

[0109] In a preferred embodiment, the electrolyte further comprises other lithium salts, which include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium triflate (LiOTF), lithium bis(oxalato)borate (LiBOB), lithium bis(fluoromalonato)borate (LiBFMB), and lithium difluoro(oxalato)borate (LiDFOB). The lithium salts of the above types can synergize with the ethoxy-containing additives and nitrogen-containing additives of the present application, regulate the composition of SEI film, further enhance the stability and lithium ion conduction of the film, inhibit side reactions, and collectively improve the fast-charging capability, cycle life, and safety of the battery.

[0110] Typically but not exclusively, the electrolyte includes other additives in a weight percentage of 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10%, or a range between any two of the values.

[0111] In a preferred embodiment, the electrolyte further includes a solvent, the solvent including one or more of a chain carbonate, a cyclic carbonate, and a carboxylate. The chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and a fluorinated chain carbonate; and / or, the cyclic carbonate includes one or more of ethylene carbonate, propylene carbonate, and butylene carbonate; and / or, the carboxylate includes one or more of methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, gamma-butyrolactone, and a fluorinated carboxylate. The above-mentioned types of solvents are able to synergize with the additives of the present application to stabilize the additives, to disperse the additives uniformly, to enhance the effects of the additives, to form a more stable SEI layer, to further reduce side reactions during battery cycling, to improve the safety of the battery, and to prevent thermal runaway caused by overcharging.

[0112] The inventors further optimized the types and compositions of the cathode materials. In a preferred embodiment, the cathode includes a cathode active material, the cathode active material including a lithium nickel transition metal oxide, the lithium nickel transition metal oxide having a chemical formula of LiNi x Co y A (1-x-y) O2, where A includes one or more of manganese, aluminum, magnesium, chromium, calcium, zirconium, molybdenum, silver, and niobium, 0.5≤x≤1, 0≤y≤0.5, x+y≤1, and preferably, the lithium nickel transition metal oxide includes one or more of NCA, NCM333, NCM523, NCM622, NCM811, Ni90, Ni92, and Ni95. The stable and highly conductive interface layer formed by the additives of the present application is able to slow down the structural degradation of the above-mentioned cathode materials during charging and discharging, thereby further prolonging the cycle life of the battery.

[0113] In a preferred embodiment, the cathode active material further includes a phosphate-based compound, the phosphate-based compound having a chemical formula of LiMn k E (1-k) PO4, where 0≤k≤1, and E includes one or more of iron, cobalt, magnesium, calcium, zinc, chromium, and lead, and preferably, the phosphate-based compound includes one or more of lithium iron phosphate, LiMn 0.6 Fe 0.4 PO4, or LiMn 0.8 Fe 0.2at least one of P04. Typically but not limited to, k is 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1 or any range between two values. The above positive active material can synergize with the additive of the present application, optimize the SEI film structure, further enhance the lithium ion diffusion, and more favorably improve the fast charging performance, cycle stability and safety of the battery, especially under high rate charging and discharging conditions, more effectively inhibit the structural change of the positive active material, and prolong the service life of the battery.

[0114] In a preferred embodiment, the negative active material in the negative active material layer comprises a silicon-based material, the silicon-based material comprises one or more of silicon, silicon alloy, silicon oxide and silicon carbide; preferably, the weight percentage content of the silicon-based material in the negative active material is 10-100%. The additive of the present application can interact with the above-mentioned negative active material to form a more stable SEI film, protect the negative active material from the corrosion of the electrolyte, more effectively buffer the volume change of the silicon-based material during charging and discharging, and improve the conductivity of the negative electrode, thereby more favorably improving the charging and discharging efficiency, cycle stability and safety of the battery.

[0115] The inventors further optimize the type and composition of the negative active material. In a preferred embodiment, the negative electrode further comprises one or more of a carbon-based material, a metal material and a conductive polymer. Preferably, the carbon-based material comprises one or more of natural graphite, artificial graphite, silicon-carbon composite material (silicon-carbon or silicon-oxygen), lithium titanate, carbon black, acetylene black, ketjen black and carbon fiber; and / or, the metal material comprises one or more of copper, nickel, aluminum and silver, in the form of particles or fibers; and / or, the conductive polymer comprises polyphenylene derivative. The above-mentioned types of carbon-based materials are more favorable for the stable existence of nitrogen and oxygen elements in the SEI film, thereby further enhancing the lithium ion conduction and inhibiting side reactions; the high conductivity of the above-mentioned types of metal materials in combination with the nitrogen-containing lithium salt can further accelerate the migration of lithium ions and improve the fast charging efficiency; the above-mentioned types of conductive polymers can synergize with the additive to optimize the SEI film structure, further increase the film toughness and reduce the interfacial impedance during the cycle, thereby further improving the cycle stability and energy density of the battery.

[0116] In a preferred embodiment, the positive electrode and / or the negative electrode further includes a binder and / or a conductive agent. In a preferred embodiment, the binder includes one or more of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethylene oxide-containing polymer, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, and nylon. The above-mentioned kinds of binder can further improve the binding force between the active material particles and each other, and also contribute to improving the binding between the active material and the current collector.

[0117] In a preferred embodiment, the positive electrode further includes a positive electrode current collector, and the positive electrode current collector includes an aluminum foil and / or a composite current collector. Preferably, the aluminum foil includes an aluminum foil; and / or, the composite current collector is prepared by a process of forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate. In a preferred embodiment, the negative electrode further includes a negative electrode current collector, and the negative electrode current collector includes one or more of a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a foamed nickel, a foamed copper, and a polymer substrate coated with a conductive metal.

[0118] In a preferred embodiment, a separator film is provided between the positive electrode and the negative electrode to prevent short circuit. The material and shape of the separator film that can be used in the embodiments of the present application are not particularly limited, and can be any of the techniques disclosed in the prior art. In some embodiments, the separator film includes a polymer or an inorganic substance formed of a material stable to the electrolyte of the present application, etc. The inorganic substance layer including an inorganic substance includes one or more of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate; and / or, the binder includes one or more of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer including a polymer includes one or more of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0119] In a preferred embodiment, the separator film can include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, a film or a composite film having a porous structure, and the material of the substrate layer includes one or more of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric or a polypropylene-polyethylene-polypropylene porous composite film can be used. The surface treatment layer is provided on at least one surface of the substrate layer, and can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

[0120] Typically, but not exclusively, in the lithium nickel transition metal oxide, x is 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1 or a range between any two of these values, and y is 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5 or a range between any two of these values.

[0121] In a preferred embodiment, the method for preparing a secondary battery includes providing an electrode assembly, injecting electrolyte, packaging and formation. In some embodiments, the temperature for formation is 40-50°C, for example 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C or 49°C. In a preferred embodiment, the pressure for formation is 150-250 kgf, for example 160 kgf, 170 kgf, 180 kgf, 190 kgf, 200 kgf, 210 kgf, 220 kgf, 230 kgf or 240 kgf. In a preferred embodiment, the charge current for formation is 0.05-0.1 C and the discharge current is 0.1-0.3 C. In a preferred embodiment, the formation includes charging at 0.05 C to 4.2 V, standing for 60 min, then charging at 0.1 C to 4.2 V, and then discharging at 0.2 C to 3.0 V, at a temperature of 40-50°C, preferably 45°C, and a pressure of 150-250 kgf, preferably 200 kgf.

[0122] If the charging current or the discharging current is too large, the temperature inside the battery can rapidly increase, increasing the risk of overheating, which can damage the performance and life of the battery, and can also cause the internal chemical reaction to be unstable, affecting the charging and discharging efficiency and energy density of the battery. If the charging current or the discharging current is too small, the production efficiency is low, and the electrochemical performance, cycle life and safety performance of the battery are reduced. If the pressure is too large, the electrode structure of the battery can be deformed or damaged, the internal chemical reaction is not sufficient, and the electrochemical performance of the battery is reduced, and even there are safety problems. If the pressure is too small, the positive and negative electrodes can not be in good contact, the battery can be locally overheated, the resistance can be increased, and the performance, life and safety of the battery can be affected.

[0123] In a preferred embodiment, the secondary battery is a lithium secondary battery or a sodium secondary battery. In a preferred embodiment, the lithium secondary battery includes one or more of a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, and a lithium ion polymer secondary battery.

[0124] In a preferred embodiment, the secondary battery includes an outer package, which can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc., and / or the outer package can be a soft package, such as a bag-type soft package, and the material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS). In a preferred embodiment, the shape of the secondary battery is not particularly limited, and it can be cylindrical, square or any other shape.

[0125] In a preferred embodiment, the application also provides a battery module including the above-mentioned secondary battery. The battery module of the application uses the above-mentioned secondary battery, and therefore at least has the same advantages as the secondary battery. The number of secondary batteries contained in the battery module of the application can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0126] In a preferred embodiment, the application also provides a battery pack including the above-mentioned battery module. The number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0127] In another typical embodiment of the present application, a power consuming device is also provided, which comprises the above secondary battery. The power consuming device includes, but is not limited to, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, a power storage system, etc. The power consuming device using the secondary battery of the present application can enhance the fast charging and cycle performance of the power consuming device through the optimized SEI film, significantly improve the overall energy density, power output and durability, and is suitable for application scenarios requiring high energy, fast charging and long-term stable operation. In order to meet the high power and high energy density requirements of the device for the secondary battery, a battery pack or a battery module can be used. The power consuming device can also be a mobile phone, a tablet computer, a notebook computer, etc. The power consuming device can be thinned, and the secondary battery can be used as a power source.

[0128] The present application will be further described in detail below in conjunction with specific examples, which should not be construed as limiting the scope of the present application.

[0129] Example 1

[0130] The positive electrode tab preparation step is as follows: according to the weight ratio of positive active material: conductive agent: binder = 95:3:2, the mixture of positive active material LiNi 0.9 Co 0.05 Mn 0.05 O2, conductive agent carbon nanotube and acetylene black (weight ratio of the two is 2:1), binder polyvinylidene fluoride PVDF, after being fully homogenized in N-methyl pyrrolidone NMP solvent system, coated on a 12 μm thick aluminum-coated current collector, dried and rolled to obtain a positive electrode tab.

[0131] The negative electrode tab preparation step is as follows: according to the weight ratio of negative active material: conductive agent: binder: thickening agent: polyacrylic acid = 95:2:1.5:1:0.5, the negative active material silicon-oxygen (SiO x x = 1) - graphite composite (the weight ratio of silicon-oxygen to graphite in the composite is 14:86), conductive agent acetylene black, binder styrene-butadiene rubber SBR, thickening agent sodium carboxymethyl cellulose CMCNa, and polyacrylic acid PAA are fully homogenized in deionized water, coated on the surface of an 8 μm thick copper current collector, dried, rolled, and then slitted to obtain a negative electrode tab, wherein the negative electrode rolling line load is 470 N / mm, the secondary rolling method is used, the rolling temperature is 120°C, and the rolling speed is 2 min / m, and the obtained negative electrode tab has a tortuosity of 6.2.

[0132] Separator: a PP / PE / PP three-layer composite separator is used.

[0133] Preparation of electrolyte: In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), LiPF6 and solvent EC / DMC / EMC = 25 / 20 / 55 were mixed uniformly to form a 1M solution, and then ethoxylated compound additive (EOEA, 1wt% in electrolyte) and nitrogen-containing compound additive (LiFSI, 3.5wt% in electrolyte) were added, and the electrolyte was obtained after stirring.

[0134] Preparation of lithium ion battery: The prepared positive electrode sheet, separator, and negative electrode sheet were stacked in order with the separator between the positive and negative electrode sheets to obtain a bare battery cell; the bare battery cell was placed in an aluminum plastic film outer package, and after being fully dried, the prepared lithium ion battery electrolyte was injected, and the battery was subjected to 45℃ standing for 48h, high-temperature clamp formation (formation conditions: temperature 45℃, pressure 200kgf, 0.05C current charging to 4.2V standing for 60min, then 0.1C charging to 4.2V, and then 0.2C discharging to 3.0V, and so on, repeated twice), and secondary sealing, and then conventional capacity distribution to obtain a secondary battery-lithium ion battery.

[0135] Examples 2 to 11

[0136] The difference between Example 1 and Examples 2 to 11 is only that:

[0137] The components of the electrolyte are different, as shown in Table 1.

[0138] Examples 12 to 18

[0139] The difference between Example 1 and Examples 12 to 18 is only that:

[0140] The components of the electrolyte and the preparation process parameters of the battery are different, as shown in Table 1.

[0141] Comparative Example 1

[0142] The difference between Example 8 and Comparative Example 1 is only that: no ethoxylated additive is included.

[0143] Comparative Example 2

[0144] The difference between Example 8 and Comparative Example 2 is only that: no nitrogen-containing additive is included.

[0145] Comparative Example 3

[0146] The difference between Example 8 and Comparative Example 3 is only that: the content of the nitrogen-containing additive is too high, as shown in Table 1.

[0147] Comparative Example 4

[0148] The difference between Example 8 and Comparative Example 4 is only that: the content of the ethoxylated additive is too high, as shown in Table 1.

[0149] Comparative Examples 5 to 6

[0150] The difference between Example 8 and the comparative example is that the rolling linear load of the negative electrode sheet is different in the preparation step of the negative electrode sheet. The tortuosity of the negative electrode sheet is different, as shown in Table 1.

[0151] Comparative Examples 7 to 13

[0152] The difference between Example 8 and the comparative example is that the rolling linear load of the negative electrode sheet is different in the preparation step of the negative electrode sheet. The tortuosity of the negative electrode sheet is different, as shown in Table 1.

[0153] The part components and parameters of the secondary batteries prepared in the above examples and comparative examples, the preparation process parameters are shown in Table 1, and the performance parameter test results of the secondary batteries are shown in Table 2.

[0154] Test method:

[0155] 1. Determination of the tortuosity of the electrode sheet:

[0156] The tortuosity of the electrode sheet can be obtained by image recognition analysis, specifically: first, the morphology picture of the electrode surface is taken by scanning electron microscope SEM, and then it is imported into Wolfram Mathmatica software, the tortuosity index estimation code file CDF is run, the active material particle outline in the surface picture is calibrated, the Fit button is clicked, the a, b, c three-axis characteristics and the particle orientation angle of the calibrated particles are calculated, the Calculate button is clicked, and the tortuosity indexes aX, aY, aZ in XYZ three directions are calculated, wherein the aZ value is the tortuosity index of the electrode sheet, and the tortuosity τ = ε -aZ .

[0157] Wherein, ε is the porosity of the electrode sheet, which is measured by a mercury porosimeter, specifically: the dried electrode sheet sample is cut into an elongated strip of a certain size, the apparent volume of the electrode sheet coating is measured by a micrometer, the apparent volume = sample coating thickness x sample length x sample width. Then the electrode sheet is vacuum degassed, wound and placed in the sample cell, and the sample volume is ensured to be 40-70% of the effective volume of the sample tube to ensure the measurement accuracy. Then the pore volume of the sample is measured by using the mercury porosimeter, that is, the volume of the mercury pressed into the sample, and then the porosity ε = pore volume / apparent volume.

[0158] 2. Battery internal resistance test:

[0159] The lithium ion battery is discharged at 1C constant current to the cut-off voltage 3.0V, after 1h storage at 20±2℃, charged at 1C current for 18min, adjust SOC to 30%, storage for 1h, then charged at 3C current for 1.5min, storage for 1h, then discharged at 9C current for 0.5min, storage for 1h, then charged at 1C constant current for 6min, adjust SOC to 40%, storage for 1h. Such cycle until the test to SOC is 70%, the battery direct current resistance DCR value is calculated by the formula R=ΔU / ΔI.

[0160] 3. Battery cycle capacity retention rate test:

[0161] At 25℃, the lithium ion battery is charged at 2C constant current to 4.25V, then charged at constant voltage to 0.05C at 4.25V, and then discharged at 2C constant current to 2.5V. After 500 cycles of charging and discharging, the capacity retention rate after the 500th cycle at 25℃ is calculated according to the following formula: discharge capacity after the 500th cycle / first cycle discharge capacity x 100%.

[0162] At 45℃, the lithium ion battery is charged at 2C constant current to 4.25V, then charged at constant voltage to 0.05C at 4.25V, and then discharged at 2C constant current to 2.5V. After 400 cycles of charging and discharging, the capacity retention rate after the 400th cycle at 45℃ is calculated according to the following formula: discharge capacity after the 400th cycle / first cycle discharge capacity x 100%.

[0163] 4. Battery 45℃ storage thickness change rate test:

[0164] The battery is discharged at 0.5C constant current to 3.0V at 25℃, then charged at 0.5C constant current to 4.45V, then charged at constant voltage to 0.05C at 4.45V, and the thickness of the battery at this time is measured using a PPG soft pack battery thickness gauge and recorded as a. The battery is placed in an oven and stored at 45℃ under constant voltage 4.45V for 15 days, and the thickness after 15 days is recorded as b. The formula for calculating the thickness expansion rate is: (b-a) / a x 100%.

[0165] 5. Test of oxygen and nitrogen element content in SEI film:

[0166] The lithium ion battery is discharged at 0.1C current to 2.5V, and the lithium ion battery is disassembled in an argon-filled glove box to obtain electrode sheets. The obtained positive electrode sheets are cut into test samples of 8mm x 8mm size, and soaked and cleaned with low-boiling dimethyl carbonate (DMC) solvent for half an hour. After complete drying, the positive electrode active material layer is pasted on the sample stage of XPS, with the surface away from the current collector facing up, and the measurement is carried out without exposure to the atmosphere.

[0167] The specific test conditions and steps are as follows: using single crystal spectrum AlKα ray, as for the X-ray point, using an ellipse form of 1000x1750 μm with an output of 10 KV and 22 mA, selecting data with a sputtering etching time of 0 seconds, using 284.8 eV for neutral carbon C1s, and as for data processing such as peak differentiation, using 3-point smoothing, peak area measurement, background subtraction and peak synthesis to calculate the weight percentage of oxygen elements in the ethoxylated compounds contained in the SEI film and the nitrogen elements in the lithium nitride contained in the SEI film.

[0168] Table 1

[0169]

[0170]

[0171]

[0172]

[0173] Table 2

[0174]

[0175]

[0176] As can be seen from the above, compared with the comparative examples, the examples of the application control the type of electrolyte in the secondary battery, and control the content of nitrogen elements and oxygen elements in the solid electrolyte interface film (SEI film) formed on the surface of the negative active material layer to be within a certain range, so that the SEI film has a fast lithium ion transmission speed, while maintaining compactness and stability, effectively inhibiting the continuous side reaction of the electrolyte and the negative active material, the consumption of the electrolyte, and prolonging the cycle life of the secondary battery.

[0177] Specifically, the nitrogen-containing compounds and ethoxylated compounds from the electrolyte in the SEI can quickly transport lithium ions, reduce impedance, thereby improving the fast charging performance and low temperature performance of the battery; in addition, the nitrogen-containing compounds and ethoxylated compounds also have good synergistic effect in structure, further improving the compactness and flexibility of the SEI film, thereby effectively inhibiting the rupture of the SEI film during high temperature cycling, and reducing the negative effects such as continuous side reaction of electrolyte and negative electrode, prolonging the cycle performance of the secondary battery, especially the cycle life and storage performance at high temperature. Based on the above improvements, the secondary battery of the application has excellent fast charging performance, and at the same time, has good cycle performance, storage performance and safety performance at high temperature and low temperature.

[0178] In addition, it can be seen that when each process parameter is within the preferred range of the present application, the overall performance of the secondary battery is better.

[0179] The preferred embodiments of the present application have been described above with the preferred embodiments, but the present application is not limited to them and can be variously changed and modified by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A secondary battery characterized by comprising: The secondary battery includes a positive electrode, a negative electrode, and an electrolyte, The electrolyte includes an ethoxy-containing additive and a nitrogen-containing additive; The negative electrode includes a negative electrode active material layer, and a solid electrolyte interface film on a surface of the negative electrode active material layer, the solid electrolyte interface film containing an ethoxy compound and lithium nitride, the ethoxy compound being derived from the ethoxy-containing additive, and the lithium nitride being derived from the nitrogen-containing additive; The weight percentage of oxygen from the ethoxy compound in the solid electrolyte interface film, as determined by X-ray photoelectron spectroscopy, is defined as W. O The weight percentage of nitrogen element from the lithium nitride in the solid electrolyte interface film is defined as W. N The tortuosity of the negative electrode is defined as τ, where 3 ≤ 2W. O +W N ≤10, 0.05<W O <5, 1 <W N <10, 0<2 (W) N ×W O )-τ<1.

2. The secondary battery according to claim 1, characterized by 1 < W O ≤ 3; and / or, 2 < W N ≤ 8.

3. The secondary battery according to claim 1, characterized by 2.5 < τ < 9.

4. The secondary battery according to claim 1 or 2, characterized by The ethoxy-containing additive includes one or more of an ethoxy acrylate, an ethoxy vinylene carbonate, and an ethoxy vinylene sulfite.

5. The secondary battery according to claim 4, characterized by The ethoxy acrylate has a structure represented by general formula (I-1): Formula (I-1); In the general formula (I-1), n is an integer of 1 to 4, R 11 is selected from hydrogen, C1-C3 alkyl, vinyl carboxylate group, or propenyl carboxylate group, R 12 is selected from hydrogen, C1-C3 alkyl.

6. The secondary battery according to claim 4, characterized by The ethoxy vinylene carbonate has a structure represented by general formula (I-2): Formula (I-2); In the general formula (I-2), m is an integer of 1 to 4, R 13 is selected from hydrogen, C1-C3alkyl, vinyl carboxylate or propenyl carboxylate.

7. The secondary battery according to claim 4, characterized by The ethoxy vinylene sulfite has a structure represented by general formula (I-3): Formula (I-3); In the general formula (I-3), p is an integer of 1 to 4, R 14 is selected from hydrogen, C1-C3alkyl, vinyl carboxylate or propenyl carboxylate.

8. The secondary battery according to claim 1 or 2, characterized by The nitrogen-containing additive includes one or more of a nitrile compound, a phosphazene, an amide, an organic nitrogen-containing lithium salt, an inorganic nitrogen-containing alkali metal salt, a nitrate ester, and a nitro ester.

9. The secondary battery according to claim 8, characterized by The nitrile compound has a structure represented by general formula (II-1): Formula (II-1); In the general formula (II-1), R 21 is selected from C2-C10alkylene or nitrile-substituted C2-C10alkylene, R 22 is selected from hydrogen, nitrile, C1-C6alkyl or carboxylate.

10. The secondary battery according to claim 8, characterized by The phosphazene has a structure represented by general formula (II-2): Formula (II-2); in the general formula (II-2), R 23 is selected from the group consisting of C1-C6 alkyl or fluoro C1-C6 alkyl, R 24 , R 25 , R 26 , R 27 and R 28 are each independently selected from the group consisting of hydrogen, fluorine, C1-C6 alkyl or fluoro C1-C6 alkyl, and R 24 , R 25 , R 26 , R 27 and R 28 at least one of R, R, R, R, R and R is fluorine or fluoro C1-C6 alkyl.

11. The secondary battery according to claim 8, characterized by The amide has a structure represented by general formula (II-3): Formula (II-3); In the general formula (II-3), R 29 , R 210 , R 211 are each independently selected from hydrogen, C1-C6 alkyl or fluorinated C1-C6 alkyl, and R 29 , R 210 , R 211 at least one of which is fluorinated C1-C6 alkyl.

12. The secondary battery according to claim 8, characterized by The organic nitrogen-containing lithium salt has a structure represented by general formula (II-4) or general formula (II-5): Formula (II-4); In the general formula (II-4), R 212 , R 213 , R 214 are each independently selected from hydrogen, fluorine, C1-C6 alkyl, fluorinated C1-C6 alkyl or nitrile group, and R 212 , R 213 , R 214 at least one of which is selected from fluorine, fluorinated C1-C6 alkyl or nitrile group; Formula (II-5); In the general formula (II-5), R 215 , R 216 are each independently selected from the group consisting of fluorine, C1-C6 alkyl, or fluorinated C1-C6 alkyl, and at least one of R 215 and R 216 is selected from the group consisting of fluorine or fluorinated C1-C6 alkyl.

13. The secondary battery according to claim 8, characterized by The inorganic nitrogen-containing alkali metal salt has a structure represented by general formula (II-6): R 217 NO t Formula (II-6); In the general formula (II-6), t is selected from 2 or 3; R 217 is selected from lithium, sodium or potassium.

14. The secondary battery according to claim 8, characterized by The nitrate ester has a structure represented by general formula (II-7): R 218 NO r Formula (II-7); In the general formula (II-7), r is 3; R 218 is selected from C1-C4 alkyl.

15. The secondary battery according to claim 8, characterized by The nitro ester has a structure represented by general formula (II-8): R 219 NO s Formula (II-8); In the general formula (II-8), s is 2; R 219 is selected from C1-C4 alkyl.

16. The secondary battery according to claim 4, wherein The ethoxy acrylate includes one or more of ethoxy ethoxy ethyl acrylate, 2-methoxyethyl 2-propenoate, and triethylene glycol diacrylate; and / or, The ethoxy vinylene carbonate includes methylethoxy vinylene carbonate and / or methoxyethoxymethyl vinylene carbonate; and / or, The ethoxy vinylene sulfite includes ethoxymethyl vinylene sulfite.

17. The secondary battery according to claim 8, wherein The nitrile compound includes one or more of butanedinitrile, hexanedinitrile, pentanedinitrile, hexanetristitnitrile, ethyleneglycol (bis) propionitrile ether, methoxypropionitrile, 2,3-dimethoxypropionitrile, and methyl cyanoacetate; and / or, The phosphazene includes one or more of methoxypentafluorocyclotriphosphazene, trifluoromethoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, and trifluoroethoxypentafluorocyclotriphosphazene; and / or, The amide includes trifluoroformamide or trifluoroacetamide; and / or, The organic nitrogen-containing lithium salt includes one or more of lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate, lithium (fluorosulfonyl)(perfluorobutylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(pentafluoroethylsulfonate)imide; and / or, The inorganic nitrogen-containing alkali metal salt includes one or more of lithium nitrate, lithium nitrite, sodium nitrate, and sodium nitrite; and / or, The nitrate ester includes ethyl nitrate and / or propyl nitrate; and / or, The nitro ester includes nitromethane and / or nitroethane.

18. The secondary battery according to claim 1 or 2, wherein The weight percentage of the ethoxy-containing additive in the electrolyte is 0.05-4%; and / or, The weight percentage of the nitrogen-containing additive in the electrolyte is 0.5-10%.

19. The secondary battery according to claim 1 or 2, characterized by The weight ratio of the ethoxy-containing additive to the nitrogen-containing additive is (0.05-4):

1.

20. The secondary battery of claim 1 or 2, wherein The electrolyte comprises a mixture of ethoxyethoxyethyl acrylate and lithium bis(fluorosulfonyl)imide at a weight ratio of (0.05-4):1; or The electrolyte comprises a mixture of ethoxyethoxyethyl acrylate and ethoxy pentafluorocyclotriphosphazene at a weight ratio of (2-4):1; or The electrolyte comprises a mixture of ethoxyethoxyethyl acrylate and ethyl nitrate at a weight ratio of (1-4):

1.

21. The secondary battery of claim 1 or 2, wherein The electrolyte further comprises other additives, the other additives comprising one or more of vinylene carbonate, vinyl ethylene carbonate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, fluoroethylene carbonate, difluoroethylene carbonate, trifluoroacrylate carbonate, 2,2,2-trifluoroethyl methyl carbonate, 2,2,2-trifluoroethyl diethyl carbonate, tris(trifluoroethyl)phosphate, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether; the weight percentage of the other additives in the electrolyte is 0.1-10%; and / or The positive electrode includes a positive electrode active material including a lithium nickel transition metal oxide having a chemical formula of: LiNi x Co y A (1-x-y) O2, wherein A includes one or more of manganese, aluminum, magnesium, chromium, calcium, zirconium, molybdenum, silver, and niobium, 0.5 < x < 1, 0 < y < 0.5, x + y < 1; and / or, The negative electrode active material in the negative electrode active material layer comprises a silicon-based material, the silicon-based material comprising one or more of silicon, silicon alloy, silicon oxide compound, and silicon carbon compound.

22. The secondary battery according to claim 21, characterized by The weight percentage of the silicon-based material in the negative electrode active material is 10-100%.

23. An electrical device, comprising: The secondary battery of any one of claims 1-22.

Images