Secondary battery and electric device

Abstract

The invention discloses a secondary battery and an electric device, and belongs to the technical field of batteries. According to the secondary battery provided by the invention, a specific type of substance is selected as the organic solvent, and meanwhile, a proper type of electrolyte additive is selected; according to the present invention, the relationship among the mass percentages of the compound A, the ethylenediamine tetraacetic acid dilithium salt, the lithium hydroxide and the lithium ferrite in the positive electrode active material layer in the electrolyte is established so as to make the secondary battery meet the relational expressions (1)-(3); the obtained secondary battery has excellent high-temperature cycle and storage stability, and the obtained secondary battery has excellent thermal shock resistance.

Description

Technical Field

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

[0002] In order to improve the energy density of lithium-ion batteries, major lithium-ion battery manufacturers use a mixture of graphite and silicon as the negative electrode active material. The introduction of silicon materials can significantly increase the negative electrode capacity and improve the overall energy density of lithium-ion batteries, but it also brings problems such as large volume expansion and low initial efficiency. In order to solve the problem of low initial efficiency, lithium replenishment additives can be introduced into lithium-ion batteries. Lithium replenishment technology is divided into positive electrode lithium replenishment, negative electrode lithium replenishment, and electrolyte lithium replenishment. Taking into account the current process of the lithium-ion battery manufacturing industry, the most suitable technology for the current situation is positive electrode lithium replenishment technology. There is no need to make major changes to the manufacturing process, which can minimize costs. Among the positive electrode lithium replenishment materials, lithium ferrite Li5FeO4 (LFO) has the best performance, high lithium replenishment capacity, low reversible capacity, and moderate price. However, this also presents the problem of high-temperature gas production. LFO releases a large amount of highly reactive singlet oxygen at high temperatures. Under high voltage, solvents with poor oxidation resistance are more susceptible to oxidation, producing more CO2. CO2 reacts with the highly reactive LFO, causing the lithium replenishment efficiency of the LFO to decrease, and the energy density (ED) yield to decrease, or even become negative. Furthermore, LFO is more prone to metal ion dissolution than LiCoO2. After dissolution, the metal ions will deposit on the surface of the negative electrode material, continuously damaging the solid electrolyte interface (SEI) and causing the negative electrode SEI to grow rapidly.

[0003] Therefore, there is an urgent need to develop an electrolyte that is suitable for high-voltage lithium cobalt oxide + lithium supplement-graphite / silicon mixed negative electrode system, which can inhibit the gas production of lithium-ion batteries under high temperature environment, increase the thermal shock failure temperature, and improve its safety performance. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and an electrical device to solve the problem that the existing technology cannot solve the problem of silicon-containing system batteries using lithium cobalt oxide as the positive electrode active material and lithium ferrite (Li5FeO4) as the lithium supplement during high-temperature storage and circulation gas production and thermal shock failure temperature being too low.

[0005] To achieve the above objectives, in a first aspect of the present application, a secondary battery is provided, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, wherein the electrolyte comprises an organic solvent, a first additive, a second additive, and a lithium salt, and the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector;

[0006] The organic solvent includes compound A, the first additive includes dilithium ethylenediaminetetraacetic acid, and the second additive includes lithium hydroxide;

[0007] The positive electrode active material layer includes lithium cobaltate, lithium ferrite, a positive electrode conductor and a positive electrode binder;

[0008] The structural formula of the compound A is shown in Formula I:

[0009]

[0010] wherein R1 to R6 are independently selected from fluorine, C1 to C10 alkyl, C2 to C10 alkenyl or alkynyl, or C5 to C10 aromatic group, and at least two of R1 to R6 are fluorine;

[0011] The secondary battery satisfies

[0012] (1)4.4≤A≤16.4, where A=α+β+γ;

[0013] (2)2.1≤B≤30.2, where B=α / x+α / y;

[0014] (3)4.5≤C≤74.0, where C=2*(α+β+γ) / x;

[0015] α% is the mass percentage of compound A based on the total mass of the electrolyte;

[0016] β% is the mass percentage of dilithium ethylenediaminetetraacetic acid based on the total mass of the electrolyte;

[0017] γ% is the mass percentage of lithium hydroxide based on the total mass of the electrolyte;

[0018] x% is the mass percentage of lithium ferrite based on the total mass of the positive electrode active material layer;

[0019] y% is the mass percentage of the fluorine-containing compound capable of forming a film based on the total mass of the electrolyte.

[0020] As an embodiment of the present application, the electrolyte of the secondary battery has a liquid retention coefficient z of 0.9 g / Ah-1.8 g / Ah.

[0021] As an embodiment of the present application, based on the total mass of the electrolyte, the mass percentage α% of compound A is 3% to 15%.

[0022] As an embodiment of the present application, based on the total mass of the electrolyte, the mass percentage β% of dilithium salt of ethylenediaminetetraacetic acid is 0.2% to 3%.

[0023] As an embodiment of the present application, the mass percentage γ% of lithium hydroxide is 0.1% to 1% based on the total mass of the electrolyte.

[0024] As an embodiment of the present application, the mass percentage w% of lithium ferrite is 0.2% to 3% based on the total mass of the positive electrode active material layer.

[0025] As an embodiment of the present application, based on the total mass of the electrolyte, the mass percentage y% of the fluorine-containing compound capable of forming a film is 13% to 40%.

[0026] As an embodiment of the present application, the compound A includes at least one of hexafluorobenzene, 1,2,4,5-tetrafluorobenzene, and 5-(1,1-difluoropropyl)-1,2,3-trifluorobenzene.

[0027] As an embodiment of the present application, the electrolyte further includes a third additive, and the third additive includes at least one of 1,3-propane sultone, vinyl sulfate, tris(trimethylsilyl)borate, and tris(trimethylsilyl)phosphate.

[0028] As an embodiment of the present application, the mass percentage of the third additive is 0.1% to 20% based on the total mass of the electrolyte.

[0029] As an embodiment of the present application, the mass percentage of the lithium salt is 8% to 25% based on the total mass of the electrolyte.

[0030] As an embodiment of the present application, the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tetrafluoroborate, bistrifluoromethanesulfonyl imide lithium salt, and lithium bisfluorosulfonyl imide.

[0031] As an embodiment of the present application, the negative electrode active material layer includes a silicon-based material, graphite, a negative electrode conductor, a thickener, and a negative electrode binder.

[0032] As an embodiment of the present application, the silicon-based material includes at least one of silicon carbon and silicon oxygen.

[0033] As an embodiment of the present application, the organic solvent further includes at least one of propylene carbonate, dimethyl carbonate, ethylene carbonate, fluoroethylene carbonate, bisfluoroethylene carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0034] In a second aspect of the present application, the present application provides an electrical device, which includes the secondary battery described in the present application.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] The present application provides a secondary battery which selects a specific type of substance as an organic solvent and a suitable type of electrolyte additive. Furthermore, the present application establishes a relationship between the mass percentages of compound A, dilithium ethylenediaminetetraacetic acid, lithium hydroxide, and lithium ferrite in the positive electrode active material layer so that the secondary battery satisfies the relationship equations (1) to (3). The obtained secondary battery can effectively solve the problem of serious gas generation during storage or circulation at high temperatures in silicon-containing system batteries which use lithium cobalt oxide as the positive electrode active material and add lithium ferrite as a lithium supplement. That is, the obtained secondary battery has excellent room temperature cycle performance, high temperature cycle and storage stability, and the obtained secondary battery has excellent thermal shock resistance. DETAILED DESCRIPTION

[0037] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0038] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0039] In this application, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0040] The reagents and instruments used in this application without manufacturer indication are all conventional products that can be purchased commercially.

[0041] In one embodiment of the present application, the present application proposes to provide a secondary battery, the secondary battery comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, the electrolyte comprising an organic solvent, a first additive, a second additive and a lithium salt, the positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector;

[0042] The organic solvent includes compound A, the first additive includes dilithium ethylenediaminetetraacetic acid, and the second additive includes lithium hydroxide;

[0043] The positive electrode active material layer includes lithium cobaltate, lithium ferrite, a positive electrode conductor and a positive electrode binder;

[0044] The structural formula of the compound A is shown in Formula I:

[0045]

[0046] wherein R1 to R6 are independently selected from fluorine, C1 to C10 alkyl, C2 to C10 alkenyl or alkynyl, or C5 to C10 aromatic group, and at least two of R1 to R6 are fluorine;

[0047] The secondary battery satisfies

[0048] (1)4.4≤A≤16.4, where A=α+β+γ;

[0049] (2)2.1≤B≤30.2, where B=α / x+α / y;

[0050] (3)4.5≤C≤74.0, where C=2*(α+β+γ) / x;

[0051] α% is the mass percentage of compound A based on the total mass of the electrolyte;

[0052] β% is the mass percentage of dilithium ethylenediaminetetraacetic acid based on the total mass of the electrolyte;

[0053] γ% is the mass percentage of lithium hydroxide based on the total mass of the electrolyte;

[0054] x% is the mass percentage of lithium ferrite based on the total mass of the positive electrode active material layer;

[0055] y% is the mass percentage of the fluorine-containing compound capable of forming a film based on the total mass of the electrolyte.

[0056] The present application has found that a secondary battery provided by the present application selects a specific type of substance as an organic solvent and selects a suitable type of electrolyte additive. Furthermore, the present application establishes a relationship between the mass percentage of compound A, dilithium ethylenediaminetetraacetic acid salt and lithium hydroxide, and lithium ferrite in the positive electrode active material layer in the electrolyte so that the secondary battery satisfies the relationship formulas (1) to (3); the obtained secondary battery can effectively solve the problem of serious gas generation when silicon-containing system batteries using lithium cobalt oxide as the positive electrode active material and adding lithium ferrite are stored or cycled at high temperatures; that is, the obtained secondary battery has excellent room temperature cycle performance, high temperature cycle and storage stability, and the obtained secondary battery has excellent thermal shock resistance.

[0057] Specifically, by limiting the value of A=α+β+γ within the above range, that is, controlling the addition amount of compound A, dilithium ethylenediaminetetraacetic acid and lithium hydroxide in the electrolyte within the above range, the stability of the electrolyte can be effectively improved, and the gas production of the secondary battery at high temperature and high pressure can be reduced. At the same time, it can also better complex the metal ions dissolved from the positive electrode, thereby improving the high-temperature storage and cycle performance of the secondary battery, and also improving the thermal shock resistance and room temperature cycle performance of the secondary battery. By limiting the value of B=α / x+α / y within the above range, the ion conductivity and redox resistance of the electrolyte can be balanced, while ensuring the stability of the electrolyte, the ion conductivity of the electrolyte is improved; at the same time, LiF and LiPO in the SEI film are reduced. x F y Achieving a balance between the content of organic alkyl lithium carbonate also helps balance the cycle performance and storage stability of the secondary battery. By limiting C = 2*(α+β+γ) / x to the above range, it is possible to effectively balance the gassing problem caused by the additive to LFO while maximizing the additive's ability to dissolve transition metal ions.

[0058] Specifically, the additive A selected in this application is a fluorobenzene compound, which has a higher HOMO energy and a lower LUMO energy, and can simultaneously take precedence over other components in the electrolyte to undergo oxidation and reduction reactions on the positive and negative electrode surfaces, respectively, thereby contributing to increasing the content of LiF compounds in SEI and improving stability. At the same time, due to the strong electronegativity of the fluorine atom, the fluorobenzene compound reduces the electron cloud density of the benzene ring, causing the fluorobenzene compound to present a low dipole moment state as a whole, thereby reducing the surface tension of the electrolyte, improving the wettability of the electrolyte to the electrode sheet, and contributing to improving the overall performance uniformity of the lithium ion battery. The first additive selected in the present invention includes dilithium ethylenediaminetetraacetic acid, which has more complexing active sites and can more effectively complex with transition metal ions such as Co and Fe relative to nitrile compounds, more efficiently suppressing the dissolution of transition metal ions of the positive electrode, and at the same time occupying the outermost empty orbital of the transition metal ion, thereby suppressing its catalytic decomposition of the electrolyte, which has an effect far exceeding that of conventional nitrile additives. The second additive selected in this application includes LiOH, which is a lithium-containing alkaline compound. After being introduced into the electrolyte system, it can effectively absorb the lithium supplement agent LFO and the electrolyte at high temperature and high voltage to produce CO2, thereby inhibiting the negative effects of the gas on the secondary battery and reducing the gas production during high-temperature storage of the secondary battery.

[0059] Illustratively, A can be any point value or any two point range values ​​between 4.4 and 16.4, such as 4.4, 4.8, 5.2, 5.6, 6, 6.4, 6.8, 7.2, 7.6, 8, 8.4, 8.8, 9.2, 9.6, 10, 10.4, 10.8, 11.2, 11.6, 12, 12.4, 12.8, 13.2, 13.6, 14, 14.4, 14.8, 15.2, 15.6, 16, 16.4, etc.

[0060] Exemplarily, B can be any point value or any two point range values ​​between 2.1 and 30.2, such as 2.1, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 30.2, etc.

[0061] Exemplarily, C can be any point value or any two point range values ​​between 4.5 and 74.0, such as 4.5, 5.0, 6.0, 7.0, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 35, 40, 45, 50, 55, 60, 65, 70, 74, etc.

[0062] In one embodiment, the secondary battery satisfies 5.4≤A≤11.4. For example, A can be 5.4, 5.6, 5.8, 6, 6.2, 6.4, 6.6, 6.8, 7, 7.2, 7.4, 7.6, 7.8, 8, 8.2, 8.4, 8.6, 8.8, 9, 9.2, 9.4, 9.6, 9.8, 10, 10.2, 10.4, 10.6, 10.8, 11, 11.2, 11.4, etc.

[0063] In one embodiment, the secondary battery satisfies 2.8≤B≤7.1. For example, B can be 2.8, 3, 3.2, 3.4, 3.6, 3.8, 4, 4.2, 4.4, 4.6, 4.8, 5, 5.2, 5.4, 5.6, 5.8, 6, 6.2, 6.4, 6.6, 6.8, 7, 7.1, etc.

[0064] In one embodiment, the secondary battery satisfies 7.2≤C≤15.3. For example, C can be 7.2, 7.4, 7.6, 7.8, 8.0, 8.2, 8.4, 8.6, 8.8, 9.0, 9.2, 9.4, 9.6, 9.8, 10.8, 11.8, 12.8, 13.8, 14.8, 15.3, etc.

[0065] The present application study found that when A, B, and C are further selected within the above-mentioned preferred range, the resulting secondary battery has better stability at high temperatures, better high-temperature storage and cycle performance, stronger resistance to thermal shock, and better room-temperature cycle performance.

[0066] In one embodiment, the electrolyte of the secondary battery has a liquid retention coefficient z of 0.9 g / Ah to 1.8 g / Ah.

[0067] Exemplarily, the electrolyte retention coefficient z of the secondary battery can be any point value or any two point range values ​​between 0.9g / Ah and 1.8g / Ah, such as 0.9g / Ah, 1g / Ah, 1.2g / Ah, 1.4g / Ah, 1.6g / Ah, 1.8g / Ah, etc.

[0068] The present study found that the electrolyte retention coefficient will affect the electrolyte's wetting effect on the positive and negative electrodes, thereby affecting the performance of the secondary battery. When the electrolyte retention coefficient σ is further selected to be within the above range, the overall performance of the secondary battery obtained is better.

[0069] In one embodiment, based on the total mass of the electrolyte, the mass percentage α% of compound A is 3% to 15%.

[0070] It should be noted that, based on the total mass of the electrolyte, the mass percentage α of compound A is obtained by gas chromatography (GC) testing.

[0071] Exemplarily, α% can be any point value between 3% and 15% or any two point range values, such as 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc.

[0072] In one embodiment, based on the total mass of the electrolyte, the mass percentage α% of compound A is 4% to 10%.

[0073] The research of this application found that selecting a suitable mass percentage of a specific type of compound of this application as part of the organic solvent in the electrolyte can effectively improve the stability of the electrolyte, reduce the gas production of the battery at high temperature and high pressure, thereby improving the high-temperature storage and cycle performance of the secondary battery, and also improving the thermal shock resistance and room temperature cycle performance of the secondary battery.

[0074] In one embodiment, based on the total mass of the electrolyte, the mass percentage β% of dilithium ethylenediaminetetraacetic acid is 0.2% to 3%.

[0075] It should be noted that the mass percentage β of dilithium ethylenediaminetetraacetic acid based on the total mass of the electrolyte is obtained through ion chromatography (IC) testing.

[0076] Exemplarily, β% can be any point value between 0.2% and 3% or any two point range values, such as 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, etc.

[0077] In one embodiment, based on the total mass of the electrolyte, the mass percentage β% of dilithium ethylenediaminetetraacetic acid is 0.3% to 2%.

[0078] The present study found that selecting a suitable mass percentage of dilithium ethylenediaminetetraacetic acid as one of the additives in the electrolyte can significantly enhance the complexation effect of the electrolyte on the metal ions dissolved from the positive electrode, greatly reducing the negative impact of the metal ions dissolved from the positive electrode on the performance of the secondary battery, thereby improving the overall performance of the secondary battery.

[0079] In one embodiment, based on the total mass of the electrolyte, the mass percentage γ% of lithium hydroxide is 0.1% to 1%.

[0080] It should be noted that the mass percentage γ of lithium hydroxide based on the total mass of the electrolyte is obtained through ion chromatography (IC) testing.

[0081] Exemplarily, γ% can be any point value between 0.1% and 1% or any two point range values, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc.

[0082] In one embodiment, based on the total mass of the electrolyte, the mass percentage γ% of lithium hydroxide is 0.2% to 0.6%.

[0083] In one embodiment, based on the total mass of the positive electrode active material layer, the mass percentage x% of lithium ferrite is 0.2% to 3%.

[0084] It should be noted that the mass percentage x of lithium ferrite based on the total mass of the positive electrode active material layer is obtained by inductively coupled plasma-optical emission spectroscopy (ICP-OES) testing.

[0085] Exemplarily, x% can be any point value between 0.2% and 3% or any two point range values, such as 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, etc.

[0086] In one embodiment, based on the total mass of the positive electrode active material layer, the mass percentage x% of lithium ferrite is 0.5% to 1.5%.

[0087] The present application has found that further selecting the mass percentage of lithium ferrite in the positive electrode active material layer to be within the above range can not only supplement sufficient lithium ions but also have good cycle performance and thermal shock resistance.

[0088] In one embodiment, based on the total mass of the electrolyte, the mass percentage y% of the film-forming fluorine-containing compound is 13% to 40%.

[0089] It should be noted that the mass percentage of the film-forming fluorine-containing compound is obtained through ion chromatography (IC) testing.

[0090] Exemplarily, y% can be any point value between 13% and 40% or any two point range values, such as 13%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, etc.

[0091] In one embodiment, based on the total mass of the electrolyte, the mass percentage y% of the film-forming fluorine-containing compound is 21% to 32%.

[0092] The present application has found that by further selecting the mass percentage of the film-forming fluorine-containing compound to be within the above range, the secondary battery can have better overall performance.

[0093] In one embodiment, the compound A includes at least one of hexafluorobenzene (CAS: 392-56-3), 1,2,4,5-tetrafluorobenzene (CAS: 327-54-8), and 5-(1,1-difluoropropyl)-1,2,3-trifluorobenzene (CAS: 1138445-53-0).

[0094] The present application study found that when compound A is further selected as the above substance, the gas production of the secondary battery under high temperature and high pressure can be better reduced, and the thermal shock resistance, storage and cycle performance of the secondary battery under high temperature can be improved.

[0095] In one embodiment, the electrolyte further includes a third additive, and the third additive includes at least one of 1,3-propane sultone (PS), dithiothreitol (DTD), tris(trimethylsilyl)borate (TMSB), and tris(trimethylsilyl)phosphate (TMSP).

[0096] The third additive provided in the present application is a film-forming additive. The selection of the above-mentioned type of film-forming additive can better cooperate with compound A, the first additive and the second additive to improve the overall performance of the secondary battery.

[0097] In one embodiment, the mass percentage of the third additive is 0.1% to 20% based on the total mass of the electrolyte.

[0098] It should be noted that the mass percentage of the third additive based on the total mass of the electrolyte is obtained through gas chromatography (GC) testing.

[0099] Illustratively, based on the total mass of the electrolyte, the mass percentage of the third additive can be any point value between 0.1% and 20% or any two point range values, such as 0.1%, 1%, 3%, 5%, 7%, 9%, 10%, 12%, 14%, 16%, 18%, 20%, etc.

[0100] In one embodiment, the mass percentage of the lithium salt is 8% to 25% based on the total mass of the electrolyte.

[0101] It should be noted that the mass percentage of the lithium salt based on the total mass of the electrolyte is obtained through ion chromatography (IC) testing.

[0102] Illustratively, based on the total mass of the electrolyte, the mass percentage of the lithium salt can be any point value between 8% and 25% or any two points in the range, such as 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 25%, etc.

[0103] In one embodiment, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiDFP), lithium difluorobis(oxalatophosphate) (LiODFP), lithium tetrafluorooxalatophosphate (LiOTFP), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI) and lithium bis(fluorosulfonyl imide) (LiFSI).

[0104] In one embodiment, the negative electrode active material layer includes a silicon-based material, graphite, a negative electrode conductor, a thickener, and a negative electrode binder.

[0105] In one embodiment, the silicon-based material includes at least one of silicon carbon and silicon oxygen.

[0106] In one embodiment, the Dv50 particle size of the silicon-based material is 2.3 μm to 7 μm.

[0107] It should be noted that the Dv50 particle size of the silicon-based material is obtained by testing with a laser particle size analyzer.

[0108] Exemplarily, the Dv50 particle size of the silicon-based material can be any point value or any two point range values ​​between 2.3μm and 7μm, such as 2.3μm, 2.5μm, 2.8μm, 3μm, 3.3μm, 3.5μm, 3.8μm, 4μm, 4.3μm, 4.5μm, 4.8μm, 5μm, 5.3μm, 5.5μm, 5.8μm, 6μm, 6.3μm, 63.5μm, 6.8μm, 7μm, etc.

[0109] The research in this application found that the Dv50 particle size of the silicon-based material will affect its distribution in the negative electrode active material layer, and thus affect the stability of the negative electrode plate. When the Dv50 particle size of the silicon-based material is further selected to be within the above range, the comprehensive performance of the secondary battery obtained is even better.

[0110] In one embodiment, based on the total mass of the negative electrode active material layer, the mass percentage v of the silicon-based material is 3% to 20%.

[0111] It should be noted that the mass percentage v of the silicon-based material, based on the total mass of the negative electrode active material layer, is obtained through inductively coupled plasma spectrometry (ICP) testing.

[0112] For example, based on the total mass of the negative electrode active material layer, the mass percentage v of the silicon-based material can be any point value between 3% and 20% or any two points in the range, such as 3%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, etc.

[0113] The research in this application found that the mass percentage of silicon-based materials in the negative electrode active material layer not only affects the stability of the negative electrode plate, but also affects the cycle performance and thermal shock resistance of the secondary battery at high temperature. When the mass percentage of silicon-based materials in the negative electrode active material layer is further selected within the range given in this application, the comprehensive performance of the secondary battery obtained is even better.

[0114] In one embodiment, the silicon-based material includes silicon carbon (SiC), silicon oxide (SiO x ) at least one of .

[0115] In one embodiment, the organic solvent further comprises at least one of propylene carbonate, dimethyl carbonate, ethylene carbonate, fluoroethylene carbonate, bisfluoroethylene carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0116] The present application has no restrictions on the selection of the positive electrode conductive agent, and the positive electrode conductive agent conventionally used in the art can be selected, such as at least one of SuperP, carbon nanotubes, and graphene.

[0117] The present application has no restrictions on the selection of positive electrode binders, and positive electrode binders commonly used in the art can be selected, such as at least one of PVDF, PTFE, PAANa, CMC, SBR, and sodium alginate.

[0118] The present application has no restrictions on the selection of the negative electrode conductive agent, and the negative electrode conductive agent conventionally used in the art can be selected, such as at least one of CNT, acetylene black, and Ketjen black.

[0119] The present application has no restrictions on the selection of thickeners, and thickeners commonly used in the art, such as sodium carboxymethyl cellulose, can be selected.

[0120] The present application has no restrictions on the selection of negative electrode binders, and negative electrode binders commonly used in the art can be selected, such as at least one of PVDF, PTFE, PAANa, CMC, SBR, and sodium alginate.

[0121] The present application has no limitation on the diaphragm, and the diaphragm conventionally used in the art can be selected; for example, the material of the diaphragm can be polypropylene, polyethylene, or a composite of polypropylene and polyethylene, etc.

[0122] In a second aspect of the present application, the present application provides an electrical device comprising the secondary battery described in the present application.

[0123] Example 1

[0124] An embodiment of the present application provides a secondary battery, wherein a method for preparing the secondary battery comprises the following steps:

[0125] (1) Preparation of negative electrode sheet

[0126] Graphite, silicon-based material (SiC, Dv50 is 4.8 μm), conductive agent (carbon nanotubes CNT), thickener (sodium carboxymethyl cellulose), and negative electrode binder (polyacrylic acid PAA) are mixed in a mass ratio of 97:0.8:1.2:1 of silicon-based material (SiC), conductive agent (carbon nanotubes CNT), thickener (sodium carboxymethyl cellulose), and negative electrode binder (polyacrylic acid PAA), and a mass ratio of graphite to silicon-based material is 80:20. The mixture is then added to deionized water, stirred thoroughly, and coated on a copper foil. The mixture is dried, rolled, and slit to obtain a negative electrode sheet.

[0127] (2) Preparation of positive electrode sheet

[0128] The positive electrode material lithium cobalt oxide, lithium supplement agent (Li5FeO4), positive electrode conductive agent (Super P), and positive electrode binder (polyvinylidene fluoride PVDF) are thoroughly stirred and mixed in N-methylpyrrolidone at a mass ratio of 97:1.5:0.5:1, and then coated on aluminum foil. After drying, rolling, and slitting, the positive electrode sheet is obtained;

[0129] (3) Preparation of electrolyte

[0130] In an argon-filled glove box, ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DEC), propyl propionate (PP), and compound A (hexafluorobenzene) were mixed in a mass ratio of 10:10:40:30:10; then, 18 wt% of lithium hexafluorophosphate (LiPF6) based on the total weight of the electrolyte was slowly added to the mixed solution, and finally 1 wt% of dilithium ethylenediaminetetraacetic acid salt, 0.4 wt% of lithium hydroxide, 15 wt% of fluoroethylene carbonate (FEC), and 4 wt% of 1,3-propane sultone (PS) based on the total weight of the electrolyte were added and stirred uniformly to obtain an electrolyte;

[0131] (5) Preparation of secondary batteries

[0132] The prepared positive electrode sheet, negative electrode sheet, separator (polypropylene porous polymer film) and other battery components are assembled, and a secondary battery is obtained through processes such as shaping, baking, packaging, liquid injection, formation, and capacity division.

[0133] Examples 2 to 5

[0134] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the mass percentage of compound A is changed by adjusting the addition amount of compound A.

[0135] Examples 6 to 9

[0136] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the mass percentage of the dilithium salt of ethylenediaminetetraacetic acid is changed by adjusting the addition amount of the dilithium salt of ethylenediaminetetraacetic acid.

[0137] Examples 10 to 13

[0138] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the mass percentage of lithium hydroxide is changed by adjusting the amount of lithium hydroxide added.

[0139] Examples 14 to 17

[0140] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the mass percentage of lithium ferrite is changed by adjusting the amount of lithium ferrite compound added.

[0141] Examples 18 to 20

[0142] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the mass percentage of the fluorine-containing compound capable of forming a film is changed by adjusting the amount of the fluorine-containing substance added to the electrolyte.

[0143] Example 21

[0144] This embodiment of the present application provides a secondary battery. The difference between the secondary battery and Example 1 lies in that the type of compound A is adjusted.

[0145] Example 22

[0146] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 lies in that the type and amount of the third additive are adjusted.

[0147] Example 23

[0148] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the type and addition amount of the lithium salt are adjusted.

[0149] Comparative Examples 1 to 4

[0150] The comparative example of the present application provides a secondary battery. The difference between the secondary battery and Example 1 lies in adjusting the amount of substances added in the electrolyte and the amount of lithium ferrite added to achieve the parameters in Tables 1 and 2.

[0151] Comparative Example 5

[0152] The comparative example of the present application provides a secondary battery. The difference between the secondary battery and Example 1 is that compound A is not added.

[0153] Comparative Example 6

[0154] The comparative example of the present application provides a secondary battery, which differs from Example 1 in that lithium ethylenediaminetetraacetic acid salt is not added.

[0155] Comparative Example 7

[0156] The comparative example of the present application provides a secondary battery, which differs from Example 1 in that lithium hydroxide is not added.

[0157] The values ​​of α / %, β / %, γ / %, x / %, y / %, σ / g / Ah, A, B, C, the selection of compound A, the selection of the third additive and its mass percentage m / %, and the selection of the lithium salt and its mass percentage n / % in the secondary batteries in the embodiments and comparative examples are shown in Tables 1 to 2.

[0158] Table 1

[0159]

[0160]

[0161] Table 2

[0162]

[0163]

[0164] The high temperature storage performance, cycle performance and thermal shock resistance of the secondary batteries prepared in the examples and comparative examples are shown in Table 3. The test method includes the following steps:

[0165] (1) Normal temperature cycle performance test: In a 25°C environment, the divided battery is charged to 4.55V at a constant current and constant voltage of 0.7C, with a cut-off current of 0.05C, and then discharged to 3.0V at a constant current of 0.5C. After 400 cycles of charge and discharge, the capacity retention rate at the 400th week is calculated. The calculation formula is as follows:

[0166] 400th cycle capacity retention rate (%) = (400th cycle discharge capacity / first cycle discharge capacity) × 100%;

[0167] Thickness growth rate at the 400th cycle = (thickness at the 400th cycle at full charge / thickness at the first cycle at full charge) × 100%;

[0168] (2) High temperature cycle performance test: In a 45°C environment, the divided battery is charged to 4.55V at a constant current and constant voltage of 0.7C, with a cut-off current of 0.05C, and then discharged to 3.0V at a constant current of 0.5C. After 300 cycles of charge and discharge, the capacity retention rate at the 300th week is calculated. The calculation formula is as follows:

[0169] 300th cycle capacity retention rate (%) = (300th cycle discharge capacity / first cycle discharge capacity) × 100%;

[0170] Thickness growth rate at the 300th cycle (%) = (thickness at the 300th cycle in full charge state / thickness at the first cycle in full charge state) × 100%;

[0171] (3) 85℃ / 24h high temperature storage test: The battery was placed at room temperature and charged and discharged once at 0.5C (3.0V-4.55V), and the discharge capacity C0 of the battery before storage was recorded. The battery was then charged to 4.55V at a constant current and constant voltage (100% SOC). A PPG battery thickness gauge (600g) was used to test the thickness d1 of the battery before high temperature storage. The battery was placed in an 85℃ constant temperature box and stored for 24h. After the storage was completed, the battery was taken out and the thermal thickness d2 of the battery after storage was tested. The thickness expansion rate of the battery after storage at 85℃ for 24h was calculated. After the battery was cooled at room temperature for 24h, the battery was again discharged at a constant current of 0.5C to 3.0V, and then charged to 4.55V at a constant current and constant voltage of 0.5C. The discharge capacity C1 and charge capacity C2 of the battery after storage were recorded. The capacity remaining rate and recovery rate of the battery after storage at 85℃ for 24h were calculated as follows:

[0172] Thickness expansion ratio after storage at 85℃ for 24h = (d2-d1) / d1*100%;

[0173] After storage at 85℃ for 24h, the remaining capacity is C1 / C0*100%.

[0174] After storage at 85°C for 24 hours, the capacity recovery rate = C2 / C0*100%.

[0175] (4) Thermal shock performance: Under 25°C ambient conditions, discharge the battery to 3.0V at a given current of 0.2C; place it aside for 5 minutes; charge it to 4.55V at a charging current of 0.2C. When the battery cell voltage reaches 4.55V, change to 4.55V constant voltage charging until the charging current ≤ the cut-off current of 0.05C; place the battery cell in an oven after 1 hour, and increase the oven temperature to 135±2°C at a rate of 5±2°C / min and keep it there for 60 minutes before stopping. The judgment standard is that the battery cell does not catch fire or explode.

[0176] Table 3

[0177]

[0178]

[0179] As can be seen from Table 3, the secondary battery prepared by the method provided in the present application has excellent high-temperature cycling and storage performance, and excellent thermal shock resistance. Specifically, the capacity retention rate of the secondary battery obtained after 400 cycles at room temperature is above 80.1%, and the thickness growth rate is below 18.0%; the capacity retention rate of the high-temperature cycle for 300 cycles is above 77.1%, and the thickness growth rate is above 22.5%. The thickness expansion rate after storage at 85°C for 24 hours is below 15.5%, the capacity retention rate after storage at 85°C for 24 hours is above 84.3%, and the capacity recovery rate after storage at 85°C for 24 hours is above 87.5%. The 135°C thermal shock pass rate is 6 / 6, that is, all passed.

[0180] It can be seen from Examples 1 to 23 and Comparative Examples 1 to 4 that when the secondary battery does not satisfy the relationship equations (1) to (3), the comprehensive performance of the obtained secondary battery is significantly reduced, and the effect of the present application cannot be achieved. It can be seen from Examples 1 to 23 and Comparative Examples 5 to 7 that when any substance specified in the present application is not added to the secondary battery, the comprehensive performance of the obtained secondary battery also shows a significant downward trend.

[0181] Finally, it should be noted that the above embodiments are intended to illustrate the technical solutions of the present application rather than to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, wherein the electrolyte comprises an organic solvent, a first additive, a second additive, and a lithium salt, and the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector; It is characterized by: The organic solvent includes compound A, the first additive includes dilithium ethylenediaminetetraacetic acid, and the second additive includes lithium hydroxide; The positive electrode active material layer includes lithium cobaltate, lithium ferrite, a positive electrode conductor and a positive electrode binder; The structural formula of the compound A is shown in Formula I: wherein R1 to R6 are independently selected from fluorine, C1 to C10 alkyl, C2 to C10 alkenyl or alkynyl, or C5 to C10 aromatic group, and at least two of R1 to R6 are fluorine; The secondary battery satisfies (1)4.4≤A≤16.4, where A=α+β+γ; (2)2.1≤B≤30.2, where B=α / x+α / y; (3)4.5≤C≤74.0, where C=2*(α+β+γ) / x; α% is the mass percentage of compound A based on the total mass of the electrolyte; β% is the mass percentage of dilithium ethylenediaminetetraacetic acid based on the total mass of the electrolyte; γ% is the mass percentage of lithium hydroxide based on the total mass of the electrolyte; x% is the mass percentage of lithium ferrite based on the total mass of the positive electrode active material layer; y% is the mass percentage of the fluorine-containing compound capable of forming a film based on the total mass of the electrolyte.

2. The secondary battery according to claim 1, wherein The electrolyte of the secondary battery has a liquid retention coefficient z of 0.9 g / Ah to 1.8 g / Ah.

3. The secondary battery according to claim 1, wherein Meet at least one of the following: 1) Based on the total mass of the electrolyte, the mass percentage α% of compound A is 3% to 15%; 2) Based on the total mass of the electrolyte, the mass percentage β% of dilithium salt of ethylenediaminetetraacetic acid is 0.2% to 3%; 3) Based on the total mass of the electrolyte, the mass percentage γ% of lithium hydroxide is 0.1% to 1%; 4) Based on the total mass of the positive electrode active material layer, the mass percentage x% of lithium ferrite is 0.2% to 3%; 5) Based on the total mass of the electrolyte, the mass percentage y% of the film-forming fluorine-containing compound is 13% to 40%.

4. The secondary battery according to claim 1, wherein The compound A includes at least one of hexafluorobenzene, 1,2,4,5-tetrafluorobenzene, and 5-(1,1-difluoropropyl)-1,2,3-trifluorobenzene.

5. The secondary battery according to claim 1, wherein The electrolyte further includes a third additive, which includes at least one of 1,3-propane sultone, vinyl sulfate, tris(trimethylsilyl)borate, and tris(trimethylsilyl)phosphate.

6. The secondary battery according to claim 5, characterized in that Based on the total mass of the electrolyte, the mass percentage of the third additive is 0.1% to 20%.

7. The secondary battery according to claim 1, wherein The mass percentage of the lithium salt is 8% to 25% based on the total mass of the electrolyte; And / or, the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tetrafluoroborate, bistrifluoromethanesulfonyl imide lithium salt, and lithium bisfluorosulfonyl imide.

8. The secondary battery according to claim 1, wherein The negative electrode active material layer includes a silicon-based material, graphite, a negative electrode conductor, a thickener and a negative electrode binder; And / or, the silicon-based material includes at least one of silicon carbon and silicon oxygen.

9. The secondary battery according to claim 1, wherein The organic solvent further comprises at least one of propylene carbonate, dimethyl carbonate, ethylene carbonate, fluoroethylene carbonate, bisfluoroethylene carbonate, diethyl carbonate, and ethyl methyl carbonate.

10. An electrical device, characterized in that: The electric device includes the secondary battery according to any one of claims 1 to 9.

Images