Battery

Abstract

The present invention relates to the technical field of batteries, and specifically relates to a battery. The battery comprises a positive electrode sheet and an electrolyte, wherein the electrolyte comprises a lithium salt and a nitrile compound, and based on the total weight of the electrolyte, the weight content of the lithium salt is Y wt% and the weight content of the nitrile compound is X wt%; the positive electrode sheet comprises a positive electrode current collector, the positive electrode current collector comprises Si and / or Fe, and based on the total weight of the positive electrode current collector, the weight content of Si and / or Fe is Z wt%; and the battery satisfies the condition: 8.4≤Y-(X×Z)≤17.98. The battery has high cycling stability, a low thickness swelling rate during a cycling process, and a low thickness swelling rate during high-temperature storage.

Description

A battery Technical Field

[0001] The present disclosure relates to the technical field of batteries, and in particular to a battery.

[0002] Background of the Invention

[0003] Since their commercialization, lithium-ion batteries have been widely used in digital, energy storage, power, military, aerospace, and communications equipment due to their lightweight, high specific energy, lack of memory effect, and excellent cycle performance. With the widespread use of lithium-ion batteries, consumers have placed higher demands on their energy density, cycle life, high-temperature performance, and safety.

[0004] With the increasing demand for energy density, efforts to improve energy density can be made, on the one hand, by increasing the positive electrode's charging voltage or using a silicon negative electrode with better capacity. On the other hand, efforts are underway to improve battery design, achieve higher compaction and higher surface density, and thus allow more active material to be loaded onto the current collector per unit volume. Furthermore, efforts are underway to reduce the thickness of copper foil, aluminum foil, and separators. As aluminum foil current collectors become thinner, interfacial side reactions increase, leading to rapid capacity decay, excessive thickness expansion, or even bloating during battery cycling.

[0005] Therefore, it is very important to invent a battery with high cycle stability and low thickness expansion rate.

[0006] Summary of the Invention

[0007] The present disclosure provides a battery that can solve the problems of rapid capacity decay and high-temperature storage during battery cycling.

[0008] When the lithium salt in the electrolyte encounters trace water, it will hydrolyze to produce HF. HF will also destroy the protective film on the surface of the positive electrode, causing the transition metal ions (such as Ni ions, Co ions and Mn ions) in the positive electrode to dissolve. The transition metal ions dissolved in the positive electrode will catalyze the decomposition of the lithium salt or solvent in the electrolyte, thereby further accelerating the dissolution of the transition metal ions. In addition, if the Si and / or Fe content in the aluminum foil exceeds a certain content, the HF produced by the hydrolysis of the lithium salt or the LiFSI or LiTFSI contained in the electrolyte will cause certain corrosion to the blank area of ​​the aluminum foil (the aluminum foil in the area not coated with active material), causing an increase in interfacial side reactions, resulting in rapid capacity decay, excessive thickness expansion and even bulging during the battery cycle.

[0009] To address the technical issues of increased interfacial side reactions caused by thinning the current collector, resulting in rapid capacity decay during battery cycling, excessive thickness expansion during cycling, and gas generation during high-temperature storage, the present disclosure provides a battery. The battery of the present disclosure exhibits high cycling stability, low thickness expansion during cycling, and low thickness expansion during high-temperature storage.

[0010] The inventors of the present disclosure have discovered that by reducing the interfacial side reactions between the electrolyte and the positive electrode sheet, the capacity decay during battery cycling can be slowed down, the thickness expansion rate can be reduced, and the thickness expansion rate during high-temperature storage can be reduced.

[0011] The inventors of the present disclosure conducted further in-depth research and found that in order to reduce the interfacial side reactions between the electrolyte and the positive electrode sheet, a compound with a specific structure can be added to the electrolyte, and the content of lithium salt and the compound with a specific structure in the electrolyte and the content of Si element and / or Fe element in the positive electrode current collector can be limited. This can reduce the corrosion of HF produced by the hydrolysis of lithium salt or LiFSI or LiTFSI contained in the electrolyte on the blank area of ​​aluminum foil (aluminum foil in the area not coated with active material), thereby reducing the interfacial side reactions between the electrolyte and the positive electrode sheet.

[0012] To achieve the above objectives, the present disclosure provides a battery, comprising a positive electrode sheet and an electrolyte, wherein the electrolyte comprises a lithium salt and a nitrile compound, and based on the total weight of the electrolyte, the weight content of the lithium salt is Ywt%, and the weight content of the nitrile compound is Xwt%; the positive electrode sheet comprises a positive electrode current collector, and the positive electrode current collector comprises Si element and / or Fe element, and based on the total weight of the positive electrode current collector, the weight content of the Si element and / or Fe element is Zwt%, then the battery satisfies: 8.4≤Y-(X×Z)≤17.98.

[0013] In one embodiment, the nitrile compound includes a phosphorus-containing trinitrile having a structure represented by formula (I),

[0014] Wherein, R1, R2, and R3 are each independently selected from a C1-C10 alkyl group.

[0015] In one embodiment, R1, R2, and R3 are each independently selected from a C1-C5 alkyl group.

[0016] In one embodiment, the phosphorus-containing trinitrile is selected from one or more of the following structures:

[0017] In one embodiment, the nitrile compound includes an ether nitrile compound having a structure represented by formula (II), NC-R4-O-R5-O-R6-CN (II), wherein R4, R5, and R6 are each independently selected from a C1-C10 alkyl group.

[0018] In one embodiment, R4, R5, and R6 are each independently selected from C1-C5 alkyl groups.

[0019] In one example, the ether nitrile compound is selected from one or more of the following structures:

[0020] In one example, the nitrile compound includes a phosphorus-containing trinitrile having a structure represented by formula (I) and an ether nitrile compound having a structure represented by formula (II), and the weight ratio of the phosphorus-containing trinitrile to the weight of the ether nitrile compound is (0-30):1, preferably (0-10):1.

[0021] In one embodiment, the phosphorus-containing trinitrile comprises a structure represented by formula (I-1), and / or the ether nitrile comprises a structure represented by formula (II-1).

[0022] In one example, based on the total weight of the positive electrode current collector, the weight content of the Si element and the Fe element ranges from 0.1 wt % to 1.5 wt %.

[0023] Through the above technical solution, the present disclosure has at least the following advantages compared with the prior art:

[0024] The present disclosure reduces or inhibits the interfacial side reactions between the electrolyte and the positive electrode sheet by adding a compound with a specific structure to the electrolyte and limiting the relationship between the content of the lithium salt and the compound with a specific structure in the electrolyte and the content of the Si element and / or Fe element in the positive electrode current collector through a specific relationship formula, thereby solving the problems of battery cycle capacity or energy attenuation, thickness expansion during the cycle, and gas production during high-temperature storage, thereby improving the cycle stability of the battery, reducing the thickness expansion rate during the battery cycle, and reducing the thickness expansion rate during high-temperature storage. DETAILED DESCRIPTION

[0025] The following describes the specific embodiments of the present disclosure in detail. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure and are not intended to limit the present disclosure.

[0026] The present disclosure provides a battery, which includes a positive electrode sheet and an electrolyte, wherein the electrolyte includes a lithium salt and a nitrile compound, and the weight content of the lithium salt is Ywt% and the weight content of the nitrile compound is Xwt% based on the total weight of the electrolyte; the positive electrode sheet includes a positive electrode current collector, and the positive electrode current collector includes Si element and / or Fe element, and the weight content of the Si element and / or Fe element is Zwt% based on the total weight of the positive electrode current collector. Then, the battery satisfies: 8.4≤Y-(X×Z)≤17.98.

[0027] A nitrile compound is added to the electrolyte. The nitrile compound can effectively complex transition metal ions (such as Ni, Co, and Mn ions) on the surface of the positive electrode, reducing the dissolution of transition metal ions or damage to the positive electrode surface by HF. The nitrile compound can also form a protective layer with a certain bonding effect on the surface of the positive electrode current collector, providing a certain degree of protection for the positive electrode current collector, thereby reducing interfacial side reactions between the electrolyte and the positive electrode. At the same time, the battery can satisfy 8.4≤Y-(X×Z)≤17.98 (for example, 8.4, 8.5, 9, 10, 11, 12, 13, 14, 15, 16, 17, 17.5, 17.98). When a nitrile compound is added to the electrolyte and the lithium salt content in the electrolyte, the content of the nitrile compound in the electrolyte and the content of the Si element and / or Fe element in the positive electrode current collector satisfy the above-mentioned specific relationship, the nitrile compound in the electrolyte can form a better protective effect on the positive electrode sheet, reducing the dissolution of transition metal ions (such as Ni ions, Co ions and Mn ions) in the active material layer of the positive electrode sheet, thereby reducing the hydrolysis of the lithium salt by the transition metal ions, and further reducing the amount of HF generated by the hydrolysis of the lithium salt, reducing the damage of HF to the positive electrode, and reducing the damage of HF to the positive electrode and the damage of HF or lithium salt LiFSI or LiTFSI in the electrolyte to the positive electrode sheet when the content of Si element and / or Fe element in the positive electrode current collector is excessive.

[0028] By adding the aforementioned nitrile compound with a specific structure to the electrolyte, and simultaneously specifying the relationship between the lithium salt and nitrile compound content in the electrolyte and the Si and / or Fe content in the positive electrode current collector, the battery has achieved higher cycle stability, lower expansion rate, and lower thickness expansion rate during high-temperature storage than the existing technology. To further improve the effect, one or more of these technical features can be further optimized.

[0029] Based on the total weight of the positive electrode current collector, the weight content of the Si element and / or the Fe element may be Zwt%. It will be understood that when the positive electrode current collector includes the Si element but does not include the Fe element, Zwt% represents the weight content of the Si element in the positive electrode current collector; when the positive electrode current collector includes the Fe element but does not include the Si element, Zwt% represents the weight content of the Fe element in the positive electrode current collector; when the positive electrode current collector includes the Si element and the Fe element, Zwt% represents the sum of the weight contents of the Si element and the Fe element in the positive electrode current collector.

[0030] For example, when the weight content of the lithium salt in the electrolyte is 15 wt%, the weight content of the nitrile compound is 1.5 wt%, and the weight content of the Si element and / or Fe element in the positive electrode current collector is 0.5 wt%, Y-(X×Z)=15-(1.5×0.5)=14.25.

[0031] In one example, the battery satisfies: 10.8≤Y-(X×Z)≤15.9.

[0032] In one embodiment, the nitrile compound includes a phosphorus-containing trinitrile having a structure represented by formula (I),

[0033] A phosphorus-containing trinitrile with a specific structure is added to the electrolyte. The -OR-CN group (where R represents an alkyl group) in the structure can well complex the transition metal ions on the surface of the positive electrode sheet, reducing the dissolution of transition metal ions or the damage to the surface of the positive electrode sheet caused by HF. In addition, the nitrile compound can also form a protective layer with a certain bonding effect on the surface of the positive electrode collector, which plays a certain protective role on the positive electrode collector, thereby reducing the interfacial side reactions between the electrolyte and the positive electrode sheet.

[0034] R1, R2, and R3 may be the same or different and are each independently selected from a C1-C10 alkyl group.

[0035] The C1-C10 alkyl group is, for example, selected from methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, tert-pentyl, neopentyl, cyclopentyl, 2,2-dimethylpropyl, 1-ethylpropyl, 1-methylbutyl, 2-methylbutyl, n-hexyl, isohexyl, 2-hexyl, 3-hexyl, cyclohexyl, 2-methylpentyl, 3-methylpentyl, 1,1,2-trimethylpropyl, 3,3-dimethylbutyl, n-heptyl, 2-heptyl, 3-heptyl, 2-methylhexyl, 3-methylhexyl, 4-methylhexyl, isoheptyl, cycloheptyl, n-octyl, cyclooctyl, nonyl, and decyl.

[0036] The structural formula of the phosphorus-containing trinitrile is shown in formula (I). It can be seen that both sides of R1, R2, and R3 are connected to the oxy group (-O) and the cyano group (-CN). Therefore, the alkyl groups selected from R1, R2, and R3 can all satisfy the structure of formula (I). For example, if R1 is a methyl group, the structure of the methyl group is -CH2-.

[0037] In one embodiment, R1, R2, and R3 are each independently selected from a C1-C5 alkyl group.

[0038] In one embodiment, R1, R2, and R3 are the same.

[0039] In one embodiment, the phosphorus-containing trinitrile is selected from one or more of the following structures:

[0040] In one embodiment, the nitrile compound includes an ether nitrile compound having a structure represented by formula (II): NC-R4-O-R5-O-R6-CN (II). When an ether nitrile compound having a specific structure is added to the electrolyte, the -OR-CN group (wherein R represents an alkyl group) in the structure can effectively complex transition metal ions on the surface of the positive electrode sheet, reducing the dissolution of transition metal ions in the positive electrode current collector or damage to the positive electrode sheet surface by HF. In addition, the nitrile compound can also form a protective layer with a certain bonding effect on the surface of the positive electrode current collector, providing a certain degree of protection for the positive electrode current collector, thereby reducing interfacial side reactions between the electrolyte and the positive electrode sheet.

[0041] Wherein, R4, R5, and R6 may be the same or different and are independently selected from C1-C10 alkyl groups;

[0042] In one example, R4, R5, and R6 may be the same or different, and are each independently selected from a C1-C5 alkyl group.

[0043] In one embodiment, R4, R5, and R6 are the same.

[0044] The nitrile compound includes an ether nitrile having a structure shown in formula (II). The structural formula of the ether nitrile is shown in formula (II). It can be seen that both sides of R4, R5, and R6 are connected to an oxy group (-O) and a cyano group (-CN). Therefore, the alkyl groups selected from R4, R5, and R6 can all satisfy the structure of formula (II). For example, if R4 is a methyl group, the structure of the methyl group is -CH2-.

[0045] In one example, the ether nitrile is selected from one or more of the following structures:

[0046] In one example, the nitrile compound includes a phosphorus-containing trinitrile having a structure represented by formula (I) and an ether nitrile compound having a structure represented by formula (II), and the weight ratio of the phosphorus-containing trinitrile to the weight of the ether nitrile compound is (0-30):1 (for example, 0, 0.1:1, 0.5:1, 1:1, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1).

[0047] In one example, the weight ratio of the phosphorus-containing trinitrile to the ether nitrile is (0-10):1.

[0048] It can be seen from the structures shown in formula (I) and formula (II) that although the phosphorus-containing trinitrile and ether nitrile have certain structural differences, the phosphorus-containing trinitrile and ether nitrile both include an -OR-CN group, wherein R represents an alkyl group, which can well complex the transition metal ions on the surface of the positive electrode. Therefore, the phosphorus-containing trinitrile and ether nitrile can both protect the positive electrode current collector and reduce the interfacial side reactions between the electrolyte and the positive electrode sheet. In particular, when the weight ratio of the phosphorus-containing trinitrile to the weight of the ether nitrile is within the above-mentioned specific range, the nitrile compound can better complex the transition metal ions on the positive electrode surface, reduce the oxidative decomposition of the electrolyte by the high-valent transition metal ions, and reduce its own dissolution, thereby having a better protection effect on the positive electrode sheet, thereby further improving the high-temperature cycle stability and high-temperature storage performance of the battery.

[0049] According to a specific embodiment, based on the total weight of the electrolyte, the weight content of the phosphorus-containing trinitrile is 0 wt%-3 wt% (e.g., 0 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%), and the weight content of the ether nitrile is 0.1 wt%-2 wt% (e.g., 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%). When the weight content of the phosphorus-containing trinitrile in the electrolyte is 0 wt%, it means that no phosphorus-containing trinitrile is present in the electrolyte.

[0050] According to a specific embodiment, based on the total weight of the electrolyte, the weight content of the phosphorus-containing trinitrile is 0 wt%-2 wt%, and the weight content of the ether nitrile is 0.2 wt%-1.5 wt%.

[0051] In one embodiment, the phosphorus-containing trinitrile is a structure represented by formula (I-1), and / or the ether nitrile is a structure represented by formula (II-1). The ether nitrile of the structure represented by formula (II-1) is ethylene glycol bis(propionitrile) ether (DENE).

[0052] The phosphorus-containing trinitrile and the ether nitrile can be purchased commercially or prepared through conventional preparation processes.

[0053] According to a specific embodiment, based on the total weight of the electrolyte, the weight content Xwt% of the nitrile compound is 0.1wt%-5wt% (for example, 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%).

[0054] In one example, based on the total weight of the electrolyte, the weight content X wt % of the nitrile compound is 0.2 wt %-3.5 wt %.

[0055] In one example, the lithium salt includes one or more of LiPF6, LiFSI, and LiTFSI.

[0056] According to a specific embodiment, based on the total weight of the electrolyte, the weight content Ywt% of the lithium salt is 12wt%-18wt% (for example, 12wt%, 12.5wt%, 13wt%, 13.5wt%, 14wt%, 14.5wt%, 15wt%, 15.5wt%, 16wt%, 16.5wt%, 17wt%, 17.5wt%, 18wt%). When the weight content of the lithium salt in the electrolyte is higher than 18wt%, the transition metal ions (such as Ni ions, Co ions and Mn ions) dissolved in the positive electrode sheet catalyze the decomposition of the lithium salt in the electrolyte to a large extent, and the amount of HF generated by the hydrolysis of the lithium salt is large. HF corrodes the positive electrode sheet more, affecting the cycle stability and thickness expansion rate of the battery, causing the battery cycle stability to deteriorate and the thickness expansion rate to be larger. At the same time, an excessively high content of lithium salt will also increase the viscosity of the electrolyte, resulting in poor room temperature cycle performance of the battery. When the weight content of the lithium salt in the electrolyte is lower than 12wt%, the impedance of the battery is too large and the room temperature cycle performance of the battery is poor.

[0057] In one example, based on the total weight of the electrolyte, the weight content Y wt % of the lithium salt is 13 wt %-16 wt %.

[0058] In one example, the electrolyte includes an organic solvent.

[0059] In one example, the organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, propyl propionate, ethyl propionate, fluoroethylene carbonate, and ethyl difluoroacetate.

[0060] The organic solvent can be adjusted within a wide range. For example, when the content of each of the above components in the electrolyte is less than 100%, the portion less than 100% can be supplemented with an organic solvent.

[0061] In one example, the Si element and the Fe element exist in the positive electrode current collector in the form of an alloy.

[0062] In one example, the positive electrode current collector includes aluminum foil.

[0063] According to a specific embodiment, the weight content Zwt% of the Si and / or Fe elements is 0.1wt%-1.5wt% (e.g., 0.1wt%, 0.3wt%, 0.5wt%, 0.8wt%, 1wt%, 1.3wt%, 1.5wt%) based on the total weight of the positive electrode current collector. The Si and Fe elements in the positive electrode current collector can be determined by ICP testing. When the weight content of the Si element is too low, it is not conducive to the formation of Al-Fe compounds and is not conducive to the processing of the positive electrode current collector material. When the weight content of the Si element is too high, it will strongly increase the strength of the positive electrode current collector material and significantly harden the work, which is not conducive to the processing and mechanical properties of the positive electrode current collector material. An appropriate amount of Si element can reduce the diffusion activation energy of Fe in the Al alloy, which is conducive to the formation of Al-Fe compounds. When the weight content of the Fe element is too low, it will not fully form the α-phase Al-Fe alloy. When the weight content of the Fe element is too high, it will easily lead to coarse Al-Fe compounds and reduced corrosion resistance.

[0064] In one example, based on the total weight of the positive electrode current collector, the weight content Zwt% of the Si element and / or the Fe element is 0.3wt%-0.7wt%.

[0065] In one example, the positive electrode sheet includes a positive electrode active material layer, and the positive electrode active material layer is located on one side or both sides of the positive electrode current collector.

[0066] In one example, the positive electrode active material layer includes a positive electrode material, a conductive agent, and a binder.

[0067] In one example, the positive electrode material is selected from one or more layered oxides containing metal ions and / or transition metal ions.

[0068] In one example, the metal ions include Al and / or Mg.

[0069] In one example, the transition metal ions include one or more of Ni, Co, Mn, Ti, Nb, Fe, Zr, and Ta.

[0070] In one embodiment, the layered oxide is a lithium cobalt oxide material. The lithium cobalt oxide material is either doped or undoped. The doped and coated lithium cobalt oxide material, when combined with a nitrile compound in the electrolyte, can better protect the positive electrode sheet, reduce the dissolution of transition metals (e.g., Ni ions, Co ions, and Mn ions) in the positive electrode active material layer in the positive electrode sheet, and also reduce side reactions between the positive electrode sheet and the electrolyte, thereby improving the cycle stability of the battery.

[0071] In one embodiment, the chemical formula of the lithium cobalt oxide material is Li x Co1-y1-y2-y3-y4A y1 B y2 C y3 D y4 O2. Chemical formula Li x Co1-y1-y2-y3-y4A y1 B y2 C y3 D y4 O2 satisfies the principle that the algebraic sum of the positive and negative valences of each element is zero.

[0072] Among them, 0.95≤x≤1.05 (for example, 0.95, 0.96, 0.97, 0.98, 0.98, 1, 1.01, 1.02, 1.03, 1.04, 1.05), 0≤y1≤0.1 (for example, 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1), 0≤y2≤0.1 (for example, 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1), 0≤y3≤0.1 (for example, 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1), 0≤y4≤0.1 (for example, 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1). When y1, y2, y3 and y4 are all 0, the lithium cobalt oxide material is lithium cobalt oxide that has not been doped or coated. When y1, y2, y3 and y4 are not all 0, the lithium cobalt oxide material is lithium cobalt oxide that has been doped and coated.

[0073] In one embodiment, A, B, C, and D are doping elements, and A, B, C, and D are selected from one or more of Al, Mg, Mn, Ni, Nb, Ta, Cr, Ti, Zr, Y, La, and Ce.

[0074] In one example, the conductive agent is selected from one or more of single-walled carbon tubes, multi-walled carbon tubes, SP, Ketjen black, acetylene black, conductive graphite, VCGF, and graphene.

[0075] In one example, the binder is selected from one or more of styrene-butadiene rubber, styrene-propylene rubber, polyacrylate, polyacrylic acid, polyacrylamide, polyvinyl alcohol, polyacrylic acid-acrylamide copolymer, polyacrylic acid-acrylonitrile copolymer, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose and PVDF.

[0076] In one example, the battery is a lithium-ion battery.

[0077] In one embodiment, the upper limit voltage of the battery is ≥4.4V (for example, 4.41V, 4.42V, 4.43V, 4.44V, 4.45V, 4.46V, 4.47V, 4.48V, 4.5V, 4.51V, 4.52V, 4.53V, 4.54V, 4.55V, 4.56V, 4.57V, 4.58V, 4.59V, 4.6V). By limiting the content of the nitrile compound in the electrolyte to a specific range, the battery can achieve better electrical performance at an upper limit voltage of ≥4.4V, and at a higher voltage, the battery cycle can stably maintain higher performance.

[0078] The present disclosure will be described in detail below through examples. The examples described in this disclosure are only a portion of the examples of the present disclosure, not all of the examples. Based on the examples in this disclosure, all other examples obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this disclosure.

[0079] The following examples are used to illustrate the electrolyte and positive electrode sheet of the present disclosure.

[0080] Example 1

[0081] (1) Preparation of ingredients

[0082] Electrolyte: 15 parts by weight of lithium salt (lithium hexafluorophosphate (LiPF6)), 1.5 parts by weight of polynitrile compound (1 part by weight of phosphorus-containing trinitrile having formula (I-1), 0.5 parts by weight of DENE), 82.5 parts by weight of organic solvent (wherein the weight ratio EC:PC:PP=15:15:70);

[0083] Positive electrode sheet: positive electrode current collector (aluminum foil, wherein the weight content of Si element and Fe element in the aluminum foil is 0.5wt%).

[0084] (2) Preparation of electrolyte

[0085] In a glove box filled with argon (H2O < 0.1ppm, O2 < 0.1ppm), EC, PC, and PP are mixed evenly, and then fully dried lithium salt is added thereto. After dissolution, polynitrile compound is added and stirred evenly. After passing the moisture and free acid tests, the electrolyte is obtained.

[0086] (3) Preparation of positive electrode

[0087] The positive electrode active material (lithium cobalt oxide (LCO)), binder (polyvinylidene fluoride (PVDF),) and conductive agent (acetylene black) are mixed in a weight ratio of 98:1.5:0.5, N-methylpyrrolidone (NMP) is added, and the mixture is stirred under the action of a vacuum mixer until the mixed system becomes a positive electrode slurry with uniform fluidity; the positive electrode slurry is evenly coated on both sides of an aluminum foil with a thickness of 12 μm; the coated aluminum foil is baked in an oven with 5 different temperature gradients, and then dried in an oven at 120°C for 8 hours, and then rolled and slit to obtain a positive electrode sheet.

[0088] Example 2

[0089] The same method was used as in Example 1, except that the specific selection and weight proportions of the phosphorus-containing trinitrile and ether nitrile, the specific selection of the lithium salt, and the content of the Si element and / or Fe element were changed. For details, see Table 1.

[0090] Example 3

[0091] The same method was used as in Example 1, except that the specific selection and weight proportions of the phosphorus-containing trinitrile and ether nitrile, the specific selection of the lithium salt, and the content of the Si element and / or Fe element were changed. For details, see Table 1.

[0092] Example 4 Group

[0093] This set of examples is used to illustrate the effects of changing the content of nitrile compounds in the electrolyte by X wt %.

[0094] This group of examples was carried out with reference to Example 1, except that the content of the nitrile compound in the electrolyte was changed to Xwt%. See Table 1 for details.

[0095] Example 5 Group

[0096] This group of examples is used to illustrate the effects of changing the lithium salt content (Y wt %) in the electrolyte.

[0097] This group of examples was carried out with reference to Example 1, except that the content of lithium salt in the electrolyte was changed to Ywt%. See Table 1 for details.

[0098] Example 6

[0099] This group of examples is used to illustrate the effects produced when the weight content Zwt% of Si element and / or Fe element in the positive electrode current collector is changed.

[0100] This group of examples was carried out with reference to Example 1, except that the content of transition metal elements in the positive electrode current collector was changed to Zwt%. See Table 1 for details.

[0101] Example 7 Group

[0102] This set of examples is used to illustrate the effects of varying the specific selection of nitrile compounds.

[0103] This group of examples was carried out with reference to Example 1, except that the specific selection of the nitrile compound was changed. For details, see Table 1.

[0104] Example 8 Group

[0105] This set of examples is used to illustrate the effects of varying the weight ratio of phosphorus-containing trinitriles to ether nitrile.

[0106] This group of examples was carried out with reference to Example 1, except that the weight ratio of the phosphorus-containing trinitriles to the weight of the ether nitrile was changed, as shown in Table 1.

[0107] Comparative Example 1

[0108] The process was carried out in accordance with Example 1, except that no phosphorus-containing trinitrile and ether nitrile were added to the electrolyte. For details, see Table 1.

[0109] Comparative Example 2

[0110] The same method was used as in Example 1, except that the phosphorus-containing trinitrile and ether nitrile were adjusted to 1,3,6-hexanetrinitrile (HTCN) in equal parts by weight.

[0111] Comparative Example 3

[0112] The same procedure was followed as in Example 1, except that the weight content of the nitrile compound in the electrolyte was adjusted to Xwt% and the weight content of the Si element and / or Fe element in the positive electrode current collector was adjusted to Zwt%. For details, see Table 1.

[0113] Comparative Example 4

[0114] The same procedure was carried out as in Example 1, except that the weight content of the nitrile compound in the electrolyte was adjusted to Y wt %. For details, see Table 1.

[0115] Table 1 * indicates the same as Example 1; - indicates absence.

[0116] Preparation Example

[0117] Batteries were prepared using the electrolytes and positive electrodes obtained in the examples and comparative examples in the following manners.

[0118] (1) Positive electrode

[0119] The positive electrode sheets obtained in the above embodiments and comparative examples were used respectively.

[0120] (2) Negative electrode

[0121] The negative electrode active material (graphite), thickener (sodium carboxymethyl cellulose (CMC-Na)), binder (styrene-butadiene rubber), and conductive agent (acetylene black) were mixed in a weight ratio of 97:1:1:1, deionized water was added, and a negative electrode slurry was obtained under the action of a vacuum mixer; the negative electrode slurry was evenly coated on a negative electrode current collector (copper foil) with a thickness of 8 μm; the copper foil was dried at room temperature and transferred to an 80°C oven for drying for 10 hours, and then cold pressed and slit to obtain the negative electrode sheet.

[0122] (3) Electrolyte

[0123] The electrolytes obtained in the above-mentioned embodiments and comparative examples were used respectively.

[0124] (4) Preparation of lithium-ion batteries

[0125] The positive electrode sheet of step (1), the negative electrode sheet of step (2) and the diaphragm are stacked in order so that the diaphragm is located between the positive electrode and the negative electrode, and then the tabs are welded and wound to obtain a roll core, which is then placed in an aluminum-plastic film packaging bag. Finally, the electrolyte of step (3) is injected and the lithium-ion battery is prepared through vacuum sealing, standing, forming, shaping and other processes.

[0126] Test Case

[0127] The batteries obtained in the examples and comparative examples were tested as follows:

[0128] (1) 25℃ normal temperature cycle test

[0129] Before testing, the thickness D0 of the fully charged battery was measured. The battery was placed in a (25±3)°C environment and allowed to stand for 3 hours. When the battery reached (25±3)°C, the battery was charged at 1C to 4.2V, then at 0.7C to 4.48V, then at 4.48V constant voltage charge to a cutoff current of 0.05C, and then discharged at 0.5C to 3V. The initial discharge capacity Q0 was recorded. When the cycle reached 300 cycles, the discharge capacity was used as the battery capacity Q2, and the capacity retention rate (%) was calculated. The battery was then fully charged, the cell removed, and allowed to stand at room temperature for 3 hours. The fully charged thickness D2 was measured, and the thickness change rate (%) was calculated. The results are recorded in Table 2. The calculation formulas used are as follows: Thickness change rate (%) = (D2-D0) / D0×100%; Capacity retention rate (%) = Q2 / Q0×100%.

[0130] (2) 45℃ high temperature cycle test

[0131] Before testing, the thickness D0 of the fully charged battery was measured. The battery was placed in a (45±3)°C environment and allowed to stand for 3 hours. When the battery reached (45±3)°C, the battery was charged at a constant current of 0.7C to 4.48V. It was then charged at a constant voltage of 4.48V to a cutoff current of 0.05C. It was then discharged at 0.5C. The initial discharge capacity Q0 was recorded. This cycle was repeated. When the cycle reached 100 cycles, the discharge capacity was used as the battery capacity Q3. The capacity retention rate (%) was calculated. The fully charged battery was then removed and allowed to stand at room temperature for 3 hours. The fully charged thickness D3 at this time was measured and the thickness change rate (%) was calculated. The results are recorded in Table 2. The calculation formulas used are as follows: Thickness change rate (%) = (D3 - D0) / D0 × 100%; Capacity retention rate (%) = Q3 / Q0 × 100%.

[0132] (3) 45℃ interval cycle test

[0133] Before testing, the thickness D0 of the fully charged battery was measured. The battery was placed in a (45±3)°C environment and allowed to stand for 3 hours. When the battery reached (45±3)°C, the battery was charged at a constant current of 0.7C to 4.48V. Then, it was charged at a constant voltage of 4.48V to a cutoff current of 0.05C. The battery was allowed to stand at 45°C for a period of time, ensuring that the constant current and constant voltage charging time plus the standing time was 24 hours. The battery was then discharged at 0.5C, and the initial discharge energy E0 was recorded. This cycle was repeated for 30 cycles. The discharge energy was used as the battery energy E1, and the energy retention rate (%) was calculated. The fully charged battery was then removed and allowed to stand at room temperature for 3 hours. The fully charged thickness D4 at this time was measured, and the thickness change rate (%) was calculated. The results are recorded in Table 2. The calculation formulas used are as follows: Thickness change rate (%) = (D4 - D0) / D0 × 100%; Capacity retention rate (%) = E1 / E0 × 100%.

[0134] (4) 60℃ high temperature storage test

[0135] At 25°C, the thickness D0 of a fully charged battery was measured. The sorted battery was charged to 4.48V at 0.7C, then charged at a constant voltage of 4.48V to a cutoff current of 0.05C. It was then discharged at a constant current of 0.5C to 3.0V. The battery was then charged to 4.48V at 0.7C, and then charged at a constant voltage of 4.48V to a cutoff current of 0.05C. After being placed in a 60°C environment for 14 days, the fully charged thickness D5 was measured and the thickness change rate (%) was calculated. The results are recorded in Table 2. The calculation formula used is as follows: Thickness change rate (%) = (D5 - D0) / D0 × 100%.

[0136] The obtained results are recorded in Table 2.

[0137] Table 2

[0138] As can be seen from Table 2, it can be seen from the comparative examples and the embodiments that the capacity retention rate of the battery of the embodiment after 300 cycles at 25°C is improved, and the thickness change rate is reduced, the capacity retention rate after 100 cycles at 45°C is improved, and the thickness change rate is reduced, the capacity retention rate after 30 cycles at 45°C is improved, and the thickness change rate is reduced, and the thickness change rate after 14 days of storage at 60°C is reduced, indicating that the battery of the present invention limits the content of lithium salt and nitrile compound in the electrolyte and the content of Si element and / or Fe element in the positive electrode current collector to a specific relationship, thereby improving the cycle stability of the battery, reducing the cycle expansion rate, and reducing the thickness expansion rate of high-temperature storage, so that the battery has both good room temperature cycle performance and good high-temperature cycle performance.

[0139] The preferred embodiments of the present disclosure are described in detail above, but the present disclosure is not limited thereto. Within the technical concept of the present disclosure, various simple variations of the technical solution of the present disclosure may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed by the present disclosure and fall within the scope of protection of the present disclosure.

Claims

1. A battery, characterized in that: The battery includes a positive electrode sheet and an electrolyte, the electrolyte includes a lithium salt and a nitrile compound, and based on the total weight of the electrolyte, the weight content of the lithium salt is Ywt%, and the weight content of the nitrile compound is Xwt%; the positive electrode sheet includes a positive electrode collector, and the positive electrode collector includes Si element and / or Fe element, and based on the total weight of the positive electrode collector, the weight content of the Si element and / or Fe element is Zwt%, then the battery satisfies: 8.4≤Y-(X×Z)≤17.

98.

2. The battery according to claim 1, characterized in that The nitrile compound comprises a phosphorus-containing trinitrile having a structure shown in formula (I), Wherein, R1, R2, and R3 are each independently selected from a C1-C10 alkyl group; Preferably, R1, R2, and R3 are each independently selected from a C1-C5 alkyl group.

3. The battery according to claim 2, characterized in that The phosphorus-containing trinitrile is selected from one or more of the following structures:

4. The battery according to any one of claims 1 to 3, characterized in that The nitrile compound includes an ether nitrile having a structure shown in formula (II), NC-R4-O-R5-O-R6-CN (II), wherein R4, R5, and R6 are each independently selected from a C1-C10 alkyl group; Preferably, R4, R5, and R6 are each independently selected from C1-C5 alkyl groups.

5. The battery according to any one of claims 4, characterized in that The ether nitrile is selected from one or more of the following structures:

6. The battery according to claim 1, characterized in that The nitrile compound comprises a phosphorus-containing trinitrile having a structure represented by formula (I) and an ether nitrile compound having a structure represented by formula (II), wherein the weight ratio of the phosphorus-containing trinitrile to the ether nitrile compound is (0-30):1, preferably (0-10):1; Preferably, the phosphorus-containing trinitrile comprises the structure shown in formula (I-1), and / or the ether nitrile comprises the structure shown in formula (II-1).

7. The battery according to any one of claims 1 to 5, characterized in that Based on the total weight of the electrolyte, the weight content of the phosphorus-containing trinitrile is 0wt%-3wt%, preferably 0wt%-2wt%; And / or, based on the total weight of the electrolyte, the weight content of the ether nitrile is 0.1wt-2wt%, preferably 0.2wt-1.5wt%.

8. The battery according to any one of claims 1 to 7, characterized in that Xwt% is 0.1wt%-5wt%, preferably 0.2wt%-3.5wt%.

9. The battery according to any one of claims 1 to 8, characterized in that The lithium salt includes one or more of LiPF6, LiFSI and LiTFSI.

10. The battery according to any one of claims 1 to 9, characterized in that Ywt% is 12wt%-18wt%, preferably 13wt%-16wt%.

11. The battery according to any one of claims 1 to 10, characterized in that The Si element and the Fe element are present in the positive electrode current collector; And / or, the positive electrode current collector is aluminum foil.

12. The battery according to any one of claims 1 to 11, characterized in that Zwt% is 0.1wt%-1.5wt%, preferably 0.3wt%-0.7wt%.

13. The battery according to any one of claims 1 to 12, characterized in that The battery satisfies: 10.8≤Y-(X×Z)≤15.

9.

14. The battery according to any one of claims 1 to 13, characterized in that The battery is a lithium-ion battery.

15. The battery according to any one of claims 1 to 14, characterized in that The upper limit voltage of the battery is ≥4.4V.

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