Secondary batteries and devices

Abstract

The present application relates to secondary batteries and devices. The secondary battery of the present application includes a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte includes a sulfur-containing additive and a nitrogen-containing additive; the positive electrode includes a positive electrode active material layer and a solid electrolyte interface membrane located on the surface of the positive electrode active material layer. The solid electrolyte interface membrane is tested using an X-ray photoelectron spectrometer. The mass percentage of sulfur element in the solid electrolyte interface membrane is S%, and the mass percentage of nitrogen element is N%, wherein 0<2S‑N≤1.5. The secondary battery of the present application improves its cycle performance, storage performance and safety performance at high temperature while taking into account the low impedance of the secondary battery by controlling the content of sulfur and nitrogen elements in the solid electrolyte interface membrane formed on the surface of the positive electrode active material layer.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and in particular to a secondary battery and a device. Background Art

[0002] Lithium-ion batteries, with their numerous advantages, have rapidly taken over the 3C market, including mobile phones and laptops, and have even become a key component of various electric vehicles. To further meet the demand for higher battery performance, many researchers are pursuing the development of lithium-ion batteries that offer low cost, high energy density, high safety, and a long lifespan.

[0003] However, during battery cycling, side reactions between the positive and negative electrodes and the electrolyte can lead to capacity degradation and a significant reduction in cycle life. Furthermore, these reactions can cause gas generation and battery volume expansion, compromising battery safety. These side reactions become more intense as the battery's operating temperature increases, exacerbating the gassing problem. Summary of the Invention

[0004] To address the challenges currently faced by lithium-ion batteries, this application provides a secondary battery and related devices. By controlling the sulfur and nitrogen content of the solid electrolyte interface (CEI) film formed on the surface of the positive electrode active material layer, this secondary battery achieves low impedance while improving its high-temperature cycling performance, storage performance, and safety.

[0005] A first aspect of the present application provides a secondary battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte comprises a sulfur-containing additive and a nitrogen-containing additive; the positive electrode comprises a positive electrode active material layer and a solid electrolyte interface membrane located on the surface of the positive electrode active material layer, and an X-ray photoelectron spectrometer is used for testing. The mass percentage of sulfur element in the solid electrolyte interface membrane is S%, and the mass percentage of nitrogen element is N%, wherein 0<2S-N≤1.5.

[0006] A second aspect of the present application provides a device, comprising the secondary battery according to the first aspect.

[0007] The beneficial effects of this application are:

[0008] The secondary battery of the present application controls the content of sulfur and nitrogen elements in the solid electrolyte interface film (CEI film) formed on the surface of the positive electrode active material layer, making the CEI film denser and more stable, which can effectively inhibit the continuous decomposition of the electrolyte due to contact with the positive electrode active material, inhibit gas production, and thus improve the cycle performance and safety performance of the secondary battery, especially the cycle performance and storage performance at high temperatures. At the same time, the CEI film with a specific content of sulfur and nitrogen elements has high lithium ion conductivity, which can reduce the interface impedance and thus reduce the impedance of the secondary battery. DETAILED DESCRIPTION

[0009] For the sake of clarity, this application only specifically discloses certain numerical ranges. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0010] Unless otherwise specified, the terms used in this application have the commonly understood meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0011] A list of items linked by the term "at least one of" or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one 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 contain a single component or multiple components. Item B can contain a single component or multiple components. Item C can contain a single component or multiple components.

[0012] The present application will be further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0013] Primary and secondary batteries

[0014] The secondary battery provided herein includes a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte includes a sulfur-containing additive and a nitrogen-containing additive; the positive electrode includes a positive electrode active material layer and a solid electrolyte interface membrane located on the surface of the positive electrode active material layer. Using X-ray photoelectron spectroscopy, the mass percentage of sulfur in the solid electrolyte interface membrane is S%, and the mass percentage of nitrogen is N%, where 0 < 2S - N ≤ 1.5. The sulfur element in the positive electrode solid electrolyte interface membrane (CEI) from the sulfur-containing additive can improve the high-temperature stability of the CEI membrane, thereby improving the high-temperature storage performance and high-temperature cycling performance of the positive electrode; however, since sulfur is a poor conductor of lithium ions and electrons, a high content of sulfur can affect the kinetic performance of the electrode, thereby affecting the electrochemical performance of the battery. The nitrogen element in the CEI membrane from the nitrogen-containing additive can improve the conductivity of lithium ions and electrons, but the CEI membrane formed on the surface of the positive electrode active material layer is not dense and stable enough, thereby affecting the cycling performance and storage performance of the battery. Through research, the inventors of this application have discovered that by controlling the content of sulfur and nitrogen elements within the above-mentioned range, on the one hand, the CEI membrane will be denser and more stable, which can effectively inhibit the continuous decomposition of the electrolyte and the positive electrode active material due to contact, inhibit gas production, and thus improve the cycle performance and safety performance of the secondary battery, especially the cycle performance and storage performance at high temperatures. On the other hand, the sulfur and nitrogen elements in the CEI membrane have a good synergistic effect, which can improve the kinetic characteristics of lithium ion transmission at the interface, thereby achieving a significant improvement in the performance of the secondary battery.

[0015] In some embodiments, 2S-N is 0.05, 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, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, or a range consisting of any two of these values. In some embodiments, 0<2S-N≤1.

[0016] In some embodiments, 0.2≤S≤10. In some embodiments, S is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 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, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or a range consisting of any two of these values. In some embodiments, 0.5≤S≤5. In some embodiments, 1≤S≤3.

[0017] In some embodiments, 1 ≤ N ≤ 12. In some embodiments, N is 1, 1.3, 1.5, 1.7, 2, 2.3, 2.5, 2.7, 3, 3.3, 3.5, 3.7, 4, 4.3, 4.5, 4.8, 5, 5.3, 5.5, 5.8, 6, 6.3, 6.5, 6.8, 7, 7.3, 7.5, 7.8, 8, 8.3, 8.5, 8.8, 9, 9.3, 9.5, 9.8, 10, 10.3, 10.5, 10.8, 11, 11.3, 11.5, 11.8, 12 or a range formed by any two of these values. In some embodiments, 2 ≤ N ≤ 10. In some embodiments, 2 ≤ N ≤ 6.

[0018] In this application, the tortuosity of the positive electrode sheet is τ. Tortuosity is a parameter reflecting the degree of meandering of the pore channels from one end to the other end in a porous medium, that is, the ratio of the actual flow path length to the straight-line distance between the ends of the flow path. In an electrode structure, the electrolyte fully infiltrates into the pores, and the transport of lithium ions needs to migrate along the pore channels through the electrolyte. Therefore, the electrode tortuosity has an important impact on the lithium-ion conductivity and electrolyte diffusion in the electrode. At the same time, it is of great significance for constructing the relationship among the performance of the battery, the interface composition of the electrode, and the electrode structure characteristics. In this application, the tortuosity can be adjusted by conventional technical means in the art according to the characteristics of the selected active material, such as controlling the roller pressing pressure, roller pressing temperature, roller pressing speed, and roller pressing times of the electrode sheet.

[0019] In some embodiments, 0 < NS - 2τ < 8. When the value of NS - 2τ is too large, correspondingly, the content of nitrogen and sulfur elements in the CEI film is too high, or the tortuosity of the positive electrode sheet is too small, which will lead to an increase in the reaction between the electrolyte and the electrode, consume the electrolyte, reduce the cycle life, and at the same time increase the gas generation of the battery. When the value of NS - 2τ is too small, correspondingly, the content of nitrogen and sulfur elements in the CEI film is too low, or the tortuosity of the positive electrode sheet is relatively large, the wettability of the positive electrode electrolyte is reduced, the polarization of the secondary battery will increase during the cycling process, the capacity will decrease, and thus its cycling performance will be affected.

[0020] In some embodiments, NS - 2τ is 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.4, 5.6, 5.8, 6, 6.5, 7, 7.5 or a range formed by any two of these values. In some embodiments, 0 < NS - 2τ < 6. In some embodiments, 0 < NS - 2τ ≤ 5. In some other embodiments, 1 ≤ NS - 2τ ≤ 5.

[0021] In some embodiments, 0.5 < τ < 5. In some embodiments, τ is 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.4, 3.6, 3.8, 4, 4.2, 4.4, 4.6, 4.8, or a range consisting of any two of these values. In some embodiments, 1 < τ < 3. In other embodiments, 1.5 < τ < 2.5.

[0022] In some embodiments, the sulfur-containing additive comprises at least one selected from sulfonates, sulfates, and sulfites. The sulfur-containing additive can improve the composition and structure of the interface film, allowing it to more effectively exert the above-mentioned effects, thereby further improving the cycle performance and storage performance of the secondary battery.

[0023] In some embodiments, the sulfonate comprises at least one compound of Formula I-1,

[0024] Formula I-1

[0025] In formula I-1, Q1 and Q2 are independently selected from C1-C6 alkylene groups.

[0026] In some embodiments, Q1 and Q2 are independently selected from C1-C4 alkylene, such as methylene, ethylene or propylene. In some embodiments, the sulfonate comprises at least one of methylene methyl disulfonate (MMDS), ethylene ethyl disulfonate and propylene methyl disulfonate.

[0027] In some embodiments, the sulfonate comprises at least one of the compounds shown in Formula I-2,

[0028] Formula I-2

[0029] In formula I-2, R1 and R2 are independently selected from a hydrogen atom or a C1-C6 alkyl group, and Q3 is selected from a C1-C6 alkylene group and a C2-C6 alkenylene group.

[0030] In some embodiments, in formula I-2, R1 and R2 are independently selected from a hydrogen atom or a C1-C4 alkyl group, and Q3 is selected from a C1-C4 alkylene group and a C2-C4 alkenylene group.

[0031] In some embodiments, the sulfonate ester includes at least one of 1,3-propane sultone (PS), 1-propylene-1,3-sultone (PST), and 1,4-butane sultone (BS).

[0032] In some embodiments, the sulfate ester comprises at least one of the compounds shown in Formula I-3,

[0033] Formula I-3

[0034] In formula I-3, R3, R4, R5, and R6 are independently selected from a hydrogen atom or a C1-C6 alkyl group, and Q4 is absent or selected from a C1-C6 alkylene group.

[0035] In some embodiments, in formula I-3, R3, R4, R5, and R6 are independently selected from a hydrogen atom or a C1-C4 alkyl group, and Q4 is absent or selected from a C1-C4 alkylene group.

[0036] In some embodiments, in formula I-3, R3, R4, R5, and R6 are independently selected from hydrogen atom, methyl, ethyl, n-propyl, or isopropyl, and Q4 is absent.

[0037] In some embodiments, the sulfate ester includes at least one of diethyl thiosulfate (DTD), 4-methylethylene sulfate (PCS), 4-ethylethylene sulfate (PES), 4-propylethylene sulfate (PEGLST), and propylene sulfate (TS).

[0038] In some embodiments, the sulfite comprises at least one of the compounds shown in Formula I-4,

[0039] Formula I-4

[0040] In formula I-4, R7, R8, R9, R 10 Q5 is independently selected from a hydrogen atom or a C1-C6 alkyl group, Q5 is absent or Q5 is selected from a C1-C6 alkylene group.

[0041] In some embodiments, in Formula I-4, R7, R8, R9, R 10 Q5 is independently selected from a hydrogen atom or a C1-C4 alkyl group, Q5 is absent or Q5 is selected from a C1-C4 alkylene group.

[0042] In some embodiments, the sulfite comprises ethylene sulfite (DTO).

[0043] In some embodiments, the sulfite comprises at least one of the compounds shown in Formula I-5,

[0044] Formula I-5

[0045] In formula I-5, R 11 and R 12 Independently selected from C1-C6 alkyl.

[0046] In some embodiments, in Formula I-5, R 11 and R 12are independently selected from C1-C4 alkyl. In some embodiments, the sulfite comprises at least one of dimethyl sulfite (DMS) and diethyl sulfite (DES).

[0047] In some embodiments, the nitrogen-containing additive includes at least one selected from a nitrile compound, a phosphazene, a nitrogen-containing lithium salt, and an amide. The nitrogen-containing additive can increase the ionic conductivity of the electrolyte and improve the composition and structure of the interfacial film, thereby more effectively exerting the above effects and further improving the cycling performance and storage performance of the secondary battery.

[0048] In some embodiments, the nitrile compound includes at least one compound represented by Formula II-1,

[0049] Formula II-1

[0050] In formula II-1, R 13 It is selected from C2-C10 alkylene, oxygen-containing C2-C10 alkylene or nitrile-substituted C2-C10 alkylene.

[0051] In some embodiments, in Formula II-1, R 13 The nitrile compound is selected from C2-C6 alkylene, oxygen-containing C2-C6 alkylene, or nitrile-substituted C2-C6 alkylene, such as ethylene, propylene, butylene, pentylene, hexylene, ethylene, propylene, butylene, pentylene, hexylene containing 1 or 2 oxygen atoms, or nitrile-substituted ethylene, propylene, butylene, pentylene, hexylene. In some embodiments, the nitrile compound includes at least one of succinonitrile (SN), adiponitrile (ADN), glutaronitrile (GLN), hexanetrinitrile (HTN), and ethylene glycol (bis)propionitrile ether (DENE).

[0052] In some embodiments, the phosphazene comprises at least one compound of formula II-2,

[0053] Formula II-2

[0054] In formula II-2, R 19 is selected from C1-C6 alkyl or fluorinated C1-C6 alkyl, R 14 、R 15 、R 16 、R 17 and R 18 are independently selected from a hydrogen atom, a fluorine atom, a C1-C6 alkyl group or a fluorinated C1-C6 alkyl group, and R 14 、R 15 、R 16 、R 17 and R 18At least one of them is a fluorine atom or a fluorinated C1-C6 alkyl group.

[0055] In some embodiments, in Formula II-2, R 19 is selected from C1-C4 alkyl or fluorinated C1-C4 alkyl, R 14 、R 15 、R 16 、R 17 and R 18 are independently selected from fluorine atoms, C1-C4 alkyl groups or fluorinated C1-C4 alkyl groups, and R 14 、R 15 、R 16 、R 17 and R 18 At least one of them is a fluorine atom or a fluorinated C1-C6 alkyl group.

[0056] In some embodiments, in Formula II-2, R 19 is selected from methyl, ethyl, n-propyl, isopropyl, trifluoromethyl or 2,2,2-trifluoroethyl, R 14 、R 15 、R 16 、R 17 、R 18 are independently selected from fluorine atoms or fluorinated C1-C4 alkyl groups, and R 14 、R 15 、R 16 、R 17 and R 18 At least one of them is a fluorine atom.

[0057] In some embodiments, the phosphazene includes at least one of methoxypentafluorocyclotriphosphazene, trifluoromethoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene (PFPN), and trifluoroethoxypentafluorocyclotriphosphazene (TFPN).

[0058] In some embodiments, the nitrogen-containing lithium salt includes at least one compound represented by Formula II-3,

[0059] Formula II-3

[0060] In formula II-3, R 20 、R 21 are each independently selected from a fluorine atom, a C1-C6 alkyl group or a fluorinated C1-C6 alkyl group, and R 20 and R 21 At least one of them is a fluorine atom or a fluorinated C1-C6 alkyl group.

[0061] In some embodiments, in Formula II-3, R 20 、R 21are each independently selected from a fluorine atom, a C1-C4 alkyl group or a fluorinated C1-C4 alkyl group, and R 20 and R 21 At least one of them is a fluorine atom or a fluorinated C1-C4 alkyl group.

[0062] In some embodiments, the nitrogen-containing lithium salt includes at least one of lithium bis(fluorosulfonyl)imide (LiFSi), lithium bis(trifluoromethylsulfonyl)imide (LiTFSi), lithium bis(pentafluoroethylsulfonic acid)imide (LiBETI), and lithium (trifluoromethylsulfonyl)(perfluorobutylsulfonyl)imide (LiFNFSI).

[0063] In some embodiments, the nitrogen-containing lithium salt includes at least one compound represented by Formula II-4,

[0064] Formula II-4

[0065] In formula II-4, R 22 、R 23 、R 24 are each independently selected from a hydrogen atom, a fluorine atom, a C1-C6 alkyl group, a fluorinated C1-C6 alkyl group or a nitrile group, and R 22 、R 23 and R 24 At least one of them is a fluorine atom, a fluorinated C1-C6 alkyl group or a nitrile group.

[0066] In some embodiments, in Formula II-4, R 22 is a fluorine atom or a fluorinated C1-C4 alkyl group, R 23 and R 24 In some embodiments, the nitrogen-containing lithium salt includes lithium 4,5-dicyano-2-(trifluoromethyl)imidazolium (LiTDI).

[0067] In some embodiments, the amide comprises at least one compound of formula II-5,

[0068] Formula II-5

[0069] In formula II-5, R 25 、R 26 、R 27 are each independently selected from a hydrogen atom, a C1-C6 alkyl group or a fluorinated C1-C6 alkyl group, and R 25 、R 26 and R 27 At least one of them is a fluorinated C1-C6 alkyl group.

[0070] In some embodiments, in Formula II-5, R 25 、R 26 、R27 are each independently selected from a hydrogen atom, a C1-C4 alkyl group or a fluorinated C1-C4 alkyl group, and R 25 、R 26 and R 27 At least one of the amides is a fluorinated C1-C4 alkyl. In some embodiments, the amide comprises trifluoroacetamide.

[0071] In some embodiments, the mass content of the sulfur-containing additive is 0.05%-4% based on the mass of the electrolyte. In some embodiments, the mass content of the sulfur-containing additive is 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 consisting of any two of these values. In some embodiments, the mass content of the sulfur-containing additive is 0.2%-3%.

[0072] In some embodiments, the mass content of the nitrogen-containing additive is 0.1%-15%. In some embodiments, the mass content of the nitrogen-containing additive is 0.2%, 0.4%, 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%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 11%, 12%, 13%, 14%, 15%, or a range consisting of any two of these values. In some embodiments, the mass content of the nitrogen-containing additive is 0.2%-10%.

[0073] In some embodiments, the electrolyte further includes other additives, and the other additives include at least one selected from vinylene carbonate (VC), vinyl ethylene carbonate (VEC), lithium difluorophosphate (LiDFP), tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, fluoroethylene carbonate, difluoroethylene carbonate, trifluoropropylene 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. In some embodiments, the other additives include at least one selected from vinylene carbonate, vinyl ethylene carbonate, and lithium difluorophosphate.

[0074] Based on the mass of the electrolyte, the mass content of the other additives is 0.1%-10%. In some embodiments, the mass content of the other additives is 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, or a range consisting of any two of these values. In some embodiments, the mass content of the other additives is 0.1%-5%.

[0075] In some embodiments, the electrolyte further includes an electrolyte lithium salt, wherein the lithium salt includes at least one selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium trifluoromethylsulfonyl (LiOTf), lithium bis(oxalatoborate) (LiBOB), lithium bis(fluoromalonate)borate (LiBFMB), and lithium difluorooxalatoborate (LiDFOB).

[0076] In some embodiments, the lithium salt may further include at least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(pentafluoroethylsulfonic acid)imide (LiBETI), lithium (trifluoromethylsulfonyl)(perfluorobutylsulfonyl)imide (LiFNFSI), and lithium 4,5-dicyano-2-(trifluoromethyl)imidazolium (LiTDI).

[0077] In some embodiments, the electrolyte further comprises a solvent. In some embodiments, the solvent comprises at least one of a linear carbonate, a cyclic carbonate, and a carboxylate.

[0078] In some embodiments, the linear carbonate is selected from at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, ethylpropyl carbonate and fluorinated linear carbonate. In some embodiments, the cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate and butylene carbonate. In some embodiments, the carboxylate is selected from at least one of methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, gamma-butyrolactone and fluorinated carboxylate.

[0079] In some embodiments, the solvent includes linear carbonate and / or cyclic carbonate, and based on the mass of the solvent, the mass content of the linear carbonate and / or cyclic carbonate is more than 90%, for example more than 95%, more than 98%. In some embodiments, the solvent does not include carboxylate. In some embodiments, the solvent does not include ether.

[0080] In some embodiments, the positive electrode includes a positive electrode active material layer, and the positive electrode active material includes at least one selected from lithium nickel transition metal oxides. In some embodiments, the chemical formula of the lithium nickel transition metal oxide is as follows: LiNim Co n A (1-m-n) O2, wherein A is selected from at least one of manganese, aluminum, magnesium, chromium, calcium, zirconium, molybdenum, silver or niobium, 0.5≤m≤1, 0≤n≤0.5, and m+n≤1.

[0081] In some embodiments, m is 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or a range consisting of any two of these values. In some embodiments, n is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, or a range consisting of any two of these values.

[0082] In some embodiments, the lithium nickel transition metal oxide includes at least one of NCA, NCM111, NCM523, NCM622, NCM811, Ni90, Ni92, or Ni95.

[0083] In some embodiments, the positive electrode active material may also include at least one phosphate compound, the chemical formula of which is LiMn k B (1-k) PO4, wherein 0≤k≤1, and the B element is selected from at least one of iron, cobalt, magnesium, calcium, zinc, chromium, or lead. In some embodiments, k is 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, or a range consisting of any two of these values. In some embodiments, the phosphate compound includes lithium iron phosphate, LiMn 0.6 Fe 0.4 PO4 or LiMn 0.8 Fe 0.2 At least one of PO4.

[0084] In some embodiments, the positive electrode active material layer further includes a binder, and optionally a conductive agent. The binder improves the bonding between the positive electrode active material particles and also improves the bonding between the positive electrode active material and the current collector.

[0085] In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon, etc.

[0086] In some embodiments, the conductive agent includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0087] In some embodiments, the positive electrode further includes a positive electrode current collector, which can be a metal foil or a composite current collector. For example, aluminum foil can be used. The composite current collector can be produced by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate.

[0088] In some embodiments, the negative electrode includes a negative electrode active material layer, wherein the negative electrode active material includes a silicon-based material. The silicon-based material includes at least one of silicon, a silicon alloy, a silicon oxide, and a silicon-carbon compound. In some embodiments, the silicon-based material includes a silicon oxide and / or a silicon-carbon compound.

[0089] In some embodiments, the negative electrode active material further comprises a mixture of at least one of a carbon-based material, a tin-based material, a phosphorus-based material, and metallic lithium. The carbon-based material comprises at least one of graphite, soft carbon, hard carbon, carbon nanotubes, and graphene. The tin-based material comprises at least one of tin, tin oxide, and a tin alloy. The phosphorus-based material comprises phosphorus and / or a phosphorus complex.

[0090] In some embodiments, the mass content g% of the silicon-based material, based on the mass of the negative electrode active material, satisfies the following: 10 ≤ g ≤ 100. In some embodiments, g is 11, 13, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or a range consisting of any two of these values. In some embodiments, 10 ≤ g ≤ 50. In other embodiments, 12 ≤ g ≤ 35.

[0091] In some embodiments, the negative electrode active material layer further includes a binder and a conductive agent. In some embodiments, the binder includes, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0092] In some embodiments, the conductive agent includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0093] In some embodiments, the negative electrode further includes a negative electrode current collector, and the negative electrode current collector includes: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.

[0094] In some embodiments, a separator is provided between the positive and negative electrodes to prevent short circuits. The material and shape of the separator that can be used in the embodiments of the present application are not particularly limited and can be any material disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material that is stable to the electrolyte of the present application.

[0095] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, film, or composite film having a porous structure, and the material of the substrate layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Specifically, polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric, or polypropylene-polyethylene-polypropylene porous composite film can be used.

[0096] A surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic layer.

[0097] The inorganic layer includes inorganic particles and a binder, wherein the inorganic particles include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene.

[0098] The polymer layer includes a polymer, and the polymer material includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0099] In some embodiments, the preparation method of the secondary battery includes providing an electrode assembly, injecting, packaging and forming. In some embodiments, the temperature of the formation is 40°C to 50°C, for example, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C or 49°C. In some embodiments, the pressure of the formation is 150kgf to 250kgf, for example, 160kgf, 170kgf, 180kgf, 190kgf, 200kgf, 210kgf, 220kgf, 230kgf or 240kgf. In some embodiments, the charging current of the formation is 0.05C-0.1C, and the discharge current of the formation is 0.1C-0.3C.

[0100] In some embodiments, the formation comprises: charging to 4.2V at 0.05C current and standing for 60 minutes, then charging to 4.2V at 0.1C current, and then discharging to 3.0V at 0.2C current, at a temperature of 40°C-50°C, such as 45°C, and a pressure of 150kgf-250kgf, such as 200kgf.

[0101] In some embodiments, the secondary battery is a lithium secondary battery or a sodium secondary battery. In some embodiments, the lithium secondary battery includes, but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0102] In some embodiments, the secondary battery may include an outer packaging, which may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging may also be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0103] In some embodiments, the shape of the secondary battery is not particularly limited, and can be cylindrical, square, or any other shape.

[0104] In some embodiments, the present application also provides a battery module. The battery module includes the aforementioned secondary battery. The battery module of the present application utilizes the aforementioned secondary battery and therefore has at least the same advantages as the aforementioned secondary battery. The battery module of the present application may include multiple secondary batteries, the specific number of which can be adjusted based on the application and capacity of the battery module.

[0105] In some embodiments, the present application further provides a battery pack comprising 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.

[0106] 2. Device

[0107] The present application also provides a device comprising at least one of the above-mentioned secondary battery, battery module or battery pack.

[0108] In some embodiments, the device includes, but is not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, power storage systems, etc. To meet the device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0109] In other embodiments, the device may be a mobile phone, a tablet computer, a laptop computer, etc. The device is usually required to be lightweight and thin, and may use a secondary battery as a power source. Example

[0110] Test Method

[0111] 1. Determination of electrode tortuosity

[0112] The tortuosity of the electrode can be obtained by image recognition and analysis. Specifically, the following steps are taken: first, a morphological image of the electrode surface is taken with a scanning electron microscope (SEM), and then the image is imported into the Wolfram Mathematica software. The tortuosity index estimation code file CDF is run to calibrate the contours of the active material particles in the surface photo. Click the Fit button to calculate the a, b, and c three-axis characteristics and particle orientation angles of the calibrated particles. Click the Calculate button to calculate the tortuosity indices aX, aY, and aZ in the XYZ directions. The aZ value is the tortuosity index of the electrode, and the tortuosity τ = ε -aZ .

[0113] Where ε is the porosity of the electrode, which is measured using a mercury intrusion porosimeter. Specifically, the dried electrode sample is cut into thin strips of a certain size and the apparent volume of the electrode coating is measured using a micrometer. Apparent volume = sample coating thickness × sample length × sample width. The electrode is then vacuum degassed, rolled, and placed in a sample cell. The sample volume must be 40-70% of the effective volume of the sample tube to ensure measurement accuracy. The pore volume of the sample is then measured using a mercury intrusion porosimeter, that is, the volume of mercury pressed into the sample. Porosity ε = pore volume / apparent volume.

[0114] 2. Battery internal resistance test

[0115] The lithium-ion battery is discharged at a constant current of 1C to a cut-off voltage of 3.0V. After being placed at 20±2℃ for 1h, it is charged at a current of 1C for 18min, the SOC is adjusted to 30%, and it is placed for 1h. The voltage U1 after the rest period is recorded. Then, it is charged at a current of 3C for 1.5min, placed for 1h, and then discharged at a current of 9C for 0.5min, placed for 1h, and then charged at a constant current of 1C for 6min, the SOC is adjusted to 40%, and placed for 1h. This cycle is repeated until the SOC is 70%. The voltage U2 after the rest period is recorded, the current of 1C is recorded as I, and the DCR value is calculated by the formula R=U2-U1 / I.

[0116] 3. Battery cycle capacity retention test

[0117] At 25°C, the lithium-ion battery was charged at a constant current of 1C to 4.25V, then charged at a constant voltage of 0.05C at 4.25V, and then discharged at a constant current of 1C to 2.5V. After 500 charge and discharge cycles, the capacity retention rate after the 500th cycle at 25°C was calculated according to the following formula: discharge capacity after the 500th cycle / discharge capacity in the first cycle × 100%.

[0118] At 45°C, the lithium-ion battery was charged at a constant current of 1C to 4.25V, then charged at a constant voltage of 0.05C at 4.25V, and then discharged at a constant current of 1C to 2.5V. After 400 charge and discharge cycles, the capacity retention rate after the 400th cycle at 45°C was calculated according to the following formula: discharge capacity after the 400th cycle / discharge capacity in the first cycle × 100%.

[0119] 4. Battery thickness change rate test at 45°C storage

[0120] The battery was discharged at a constant current of 0.5C to 3.0V at 25°C, then charged at a constant current of 0.5C to 4.45V. Then, it was charged at a constant voltage of 0.05C at 4.45V. The thickness of the battery at this point was measured using a PPG soft-pack battery thickness gauge, and recorded as a. The battery was placed in an oven and stored at a constant voltage of 4.45V at 45°C for 15 days. The thickness after 15 days was recorded as b. The thickness expansion ratio was calculated as: (b a) / a × 100%.

[0121] 5. Testing of sulfur and nitrogen content in CEI membranes

[0122] The lithium-ion battery was discharged at a current of 0.1C to 2.5V. The battery was then disassembled in an argon-filled glove box to obtain the electrode sheets. The resulting positive electrode sheets were cut into 8mm x 8mm test specimens and soaked and cleaned in a low-boiling-point dimethyl carbonate (DMC) solvent for half an hour. After complete drying, they were attached to the XPS sample stage with the surface of the positive electrode active material layer facing away from the current collector facing upward. Measurements were performed without exposure to the atmosphere. The specific test conditions and steps are as follows:

[0123] Single crystal spectroscopy AlKα rays were used, and as for the X-ray point, an elliptical form of 1000×1750 μm with an output of 10 KV and 22 mA was used, data when the sputtering etching time was 0 seconds was selected, 284.8 eV was used for neutral carbon C1s, and as for data processing such as peak differentiation, 3-point smoothing, peak area measurement, background subtraction and peak synthesis were used to calculate the mass percentage content of sulfur and nitrogen elements.

[0124] Example 1

[0125] The positive electrode preparation steps are: LiNi 0.9 Co 0.05 Mn 0.05 O2, conductive agent carbon nanotube / acetylene black, binder polyvinylidene fluoride PVDF, by weight proportion LiNi 0.9 Co 0.05 Mn 0.05 After being fully homogenized in an N-methylpyrrolidone (NMP) solvent system, O2﹕CNT / Super-P﹕PVDF=95﹕2.0 / 1.0﹕2 was coated on a 12μm thick aluminum-coated current collector, dried, and roller-pressed to obtain a positive electrode sheet, wherein the tortuosity of the positive electrode sheet was 1.98.

[0126] The steps for preparing the negative electrode are: x , 0.5≤x≤1.5)-graphite composite (the mass ratio of silicon oxide to graphite in the composite is 14:86), conductive agent acetylene black, binder styrene-butadiene rubber SBR, thickener sodium carboxymethyl cellulose CMCNa, and polyacrylic acid PAA are fully homogenized in deionized water in a weight ratio of 96:2:1.5:1:0.5, and then coated on the surface of an 8μm thick copper current collector. After drying, rolling, and slitting, the negative electrode sheet is obtained.

[0127] Diaphragm: PP / PE / PP three-layer composite diaphragm.

[0128] Preparation of the electrolyte: In an argon-filled glove box (H2O <0.1ppm, O2 <0.1ppm), the lithium salt LiPF6 and the solvent EC / DEC / EMC = 25 / 20 / 55 were mixed uniformly in a certain proportion to prepare a 1M solution. Finally, the sulfur-containing compound additive (0.6% by weight of the total electrolyte) and the nitrogen-containing compound additive (1% by weight of the total electrolyte) listed in Table 1 were added and stirred uniformly to obtain the lithium-ion battery electrolyte of Example 1.

[0129] Preparation of lithium-ion batteries: The prepared positive electrode sheets, separators, and negative electrode sheets are stacked in order with the separator placed between the positive and negative electrode sheets, and then wound to obtain a bare cell; the bare cell is placed in an aluminum-plastic film outer packaging, and after being fully dried, the prepared lithium-ion battery electrolyte is injected. The battery is left at 45°C for 48 hours, formed in a high-temperature fixture (the formation conditions are: temperature 45°C, pressure 200kgf, 0.05C current charging to 4.2V and standing for 60 minutes, then 0.1C charging to 4.2V, and then 0.2C discharge to 3.0V, and this is repeated twice) and secondary sealing, and then conventional capacity division is carried out.

[0130] Examples 2 to 11 and Comparative Examples 1 to 11

[0131] Examples 2 to 11 and Comparative Examples 1 to 11 are achieved on the basis of Example 1 by adjusting the type and content of the additives in the electrolyte, the tortuosity of the positive electrode sheet (wherein the tortuosity is achieved by adjusting the positive electrode roller line load during the preparation process, etc.), and the formation conditions. Specific adjustment measures and detailed data are shown in Table 1.

[0132] Table 1

[0133]

[0134] The battery performance test results of Examples 1-11 and Comparative Examples 1-11 are shown in Table 2.

[0135] Table 2

[0136]

[0137] Although some exemplary embodiments of the present application have been illustrated and described, the present application is not limited to the disclosed embodiments. On the contrary, those skilled in the art will recognize that some modifications and changes may be made to the described embodiments without departing from the spirit and scope of the present application as described in the appended claims.

Claims

1. A secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte, wherein, the electrolyte includes a sulfur-containing additive and a nitrogen-containing additive; the positive electrode includes a positive electrode active material layer and a solid electrolyte interface film on the surface of the positive electrode active material layer, the solid electrolyte interface film is obtained by formation, and is tested by an X-ray photoelectron spectrometer at a sputtering etching time of 0 seconds. The mass percentage content of sulfur element in the solid electrolyte interface film is S%, and the mass percentage content of nitrogen element is N%, wherein, 0 < 2S - N ≤ 1.5, 0.2 ≤ S ≤ 10, and 1 ≤ N ≤ 12; the tortuosity of the positive electrode sheet is τ, wherein, 0 < NS - 2τ < 8 and 0.5 < τ < 5; the sulfur-containing additive includes at least one selected from sulfonates, sulfates, and sulfites; the nitrogen-containing additive includes at least one selected from nitrile compounds, phosphonitriles, nitrogen-containing lithium salts, and amides.

2. The secondary battery according to claim 1, wherein 0.5 ≤ S ≤ 5, and / or, 2 ≤ N ≤ 10.

3. The secondary battery according to claim 1 or claim 2, wherein, the sulfonate includes at least one of the compounds shown in Formula I-1 and Formula I-2, Formula I-1, Formula I-2 in Formula I-1, Q1 and Q2 independently selected from C1-C6 alkylene groups, in Formula I-2, R1 and R2 independently selected from a hydrogen atom or a C1-C6 alkyl group, and Q3 selected from C1-C6 alkylene groups, C2-C6 alkenylene groups; the sulfate includes at least one of the compounds shown in Formula I-3, Formula I-3 in Formula I-3, R3, R4, R5, and R6 independently selected from a hydrogen atom or a C1-C6 alkyl group, and Q4 is absent or Q4 selected from C1-C6 alkylene groups; the sulfite includes at least one of the compounds shown in Formula I-4 and Formula I-5, Formula I-4, Formula I-5 In formula I-4, R7, R8, R9, R 10 independently selected from hydrogen atom or C1-C6 alkyl, Q5 is absent or Q5 is selected from C1-C6 alkylene, in formula I-5, R 11 and R 12 Independently selected from C1-C6 alkyl; the nitrile compound includes at least one of the compounds shown in Formula II-1, Formula II-1 In formula II-1, R 13 Selected from C2-C10 alkylene, oxygen-containing C2-C10 alkylene or nitrile-substituted C2-C10 alkylene; the phosphonitrile includes at least one of the compounds shown in Formula II-2, Formula II-2 In formula II-2, R 19 is selected from C1-C6 alkyl or fluorinated C1-C6 alkyl, R 14 、R 15 、R 16 、R 17 、R 18 are independently selected from a hydrogen atom, a fluorine atom, a C1-C6 alkyl group or a fluorinated C1-C6 alkyl group, and R 14 、R 15 、R 16 、R 17 、R 18 At least one of them is a fluorine atom or a fluorinated C1-C6 alkyl group; the nitrogen-containing lithium salt includes at least one of the compounds shown in Formula II-3 and Formula II-4, Formula II-3, Formula II-4 In formula II-3, R 20 、R 21 are each independently selected from a fluorine atom, a C1-C6 alkyl group or a fluorinated C1-C6 alkyl group, and R 20 and R 21 At least one of them is a fluorine atom or a fluorinated C1-C6 alkyl group. In formula II-4, R 22 、R 23 、R 24 are each independently selected from a hydrogen atom, a fluorine atom, a C1-C6 alkyl group, a fluorinated C1-C6 alkyl group or a nitrile group, and R 22 、R 23 and R 24 At least one of them is a fluorine atom, a fluorinated C1-C6 alkyl group or a nitrile group; the amide includes at least one of the compounds shown in Formula II-5, Formula II-5 In formula II-5, R 25 、R 26 、R 27 are each independently selected from a hydrogen atom, a C1-C6 alkyl group or a fluorinated C1-C6 alkyl group, and R 25 、R 26 and R 27 At least one of them is a fluorinated C1-C6 alkyl group.

4. The secondary battery according to claim 3, wherein the sulfonate includes at least one of methylene bis(methanesulfonate), ethylene bis(ethanesulfonate), propylene bis(methanesulfonate), 1,3-propane sultone, 1-propene-1,3-sultone, and 1,4-butane sultone, and / or, the sulfate includes at least one of ethylene sulfate, 4-methyl ethylene sulfate, 4-ethyl ethylene sulfate, 4-propyl ethylene sulfate, and allyl sulfate, and / or, the sulfite includes at least one of ethylene sulfite, dimethyl sulfite, and diethyl sulfite, and / or, the nitrile compound includes at least one of succinonitrile, adiponitrile, glutaronitrile, hexane trinitrile, and ethylene glycol bis(propionitrile ether), and / or, the phosphonitrile includes at least one of methoxy pentafluorocyclotriphosphazene, trifluoromethoxy pentafluorocyclotriphosphazene, ethoxy pentafluorocyclotriphosphazene, and trifluoroethoxy pentafluorocyclotriphosphazene, and / or, The nitrogen-containing lithium salt includes at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonic acid)imide, lithium (trifluoromethylsulfonyl)(perfluorobutylsulfonyl)imide and lithium 4,5-dicyano-2-(trifluoromethyl)imidazole, and / or, The amides include trifluoroacetamide.

5. The secondary battery according to claim 1 or 2, characterized in that Based on the mass of the electrolyte, the mass content of the sulfur-containing additive is 0.05%-4%; and / or, Based on the mass of the electrolyte, the mass content of the nitrogen-containing additive is 0.1%-15%; and / or, The electrolyte further comprises other additives, wherein the other additives include at least one of vinylene carbonate, vinyl ethylene carbonate and lithium difluorophosphate, and the mass content of the other additives is 0.1%-10% based on the mass of the electrolyte; and / or, The electrolyte includes a solvent, and the solvent includes a linear carbonate and / or a cyclic carbonate. Based on the mass of the solvent, the mass content of the linear carbonate and / or the cyclic carbonate is greater than 90%.

6. The secondary battery according to claim 1 or 2, characterized in that The positive electrode comprises an active material selected from lithium nickel transition metal oxides, the chemical formula of which is LiNi m Co n A (1-m-n) O2, wherein A is selected from at least one of manganese, aluminum, magnesium, chromium, calcium, zirconium, molybdenum, silver or niobium, 0.5≤m≤1, 0≤n≤0.5, m+n≤1; and / or, The negative electrode includes an active material selected from silicon-based materials, wherein the silicon-based material includes at least one of silicon, silicon alloys, silicon oxides and silicon carbon compounds. Based on the mass of the negative electrode active material, the mass content g% of the silicon-based material satisfies: 10≤g≤100.

7. A device comprising the secondary battery according to any one of claims 1 to 6.

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