Secondary battery, battery module, battery pack and power consuming device

Abstract

The present application provides a secondary battery, a battery module, a battery pack, and a power consumption device. The secondary battery includes a positive electrode sheet, a negative electrode sheet, and an electrolyte, the negative electrode sheet includes a negative electrode active material, the electrolyte includes a first additive and a carbonate ester solvent, the first additive includes a boron-containing lithium salt and an ester-based additive, and is arranged to form a solid electrolyte interfacial film on the surface of the negative electrode active material, where the discharge capacity of the secondary battery is B1 Ah, the gas generation change amount of the secondary battery is B2 mL, the mass of the electrolyte is C g, and the reduction potential of the first additive to metallic lithium is D (V, vs Li + |Li), the secondary battery is 0.5≦B2 / B1≦5, 0.1≦C / B1≦100, 0.8≦D≦2, 10 -4 ≦A1+A2≦10. The present application can improve the safety performance, cycle performance and electrolyte utilization rate of the secondary battery.

Description

[Technical field]

[0001] The present application relates to the field of batteries, and in particular to secondary batteries, battery modules, battery packs and power consuming devices. [Background technology]

[0002] Due to their characteristics of high capacity and long life, secondary batteries are widely used in electronic devices, such as mobile phones, notebook computers, battery cars, electric cars, electric airplanes, electric ships, electric toy cars, electric toy vehicles, electric toy airplanes, electric tools, etc. As the range of applications of batteries becomes wider and wider, the requirements for the performance of secondary batteries become more and more stringent.

[0003] However, when improving the performance of a secondary battery, it is difficult to simultaneously provide the safety performance, cycle performance, and electrolyte utilization rate of the secondary battery. Summary of the Invention

[0004] The present application has been made in view of the above-mentioned problems, and has an object to provide a secondary battery, a battery module, a battery pack, and a power consuming device.

[0005] A first aspect of the present application is a secondary battery including a positive electrode sheet, a negative electrode sheet, and an electrolyte solution, The negative electrode sheet contains a negative electrode active material, The electrolyte includes a first additive and a carbonate ester solvent, the first additive includes a boron-containing lithium salt and an ester-based additive, and is disposed on a surface of the negative electrode active material so as to form a solid electrolyte interfacial film; Here, the discharge capacity of the secondary battery is B1 Ah, the gas generation change amount of the secondary battery is B2 mL, the mass of the electrolyte is C g, and the reduction potential of the first additive with respect to metallic lithium is D (V, vs Li + |Li), the mass percentage of the boron-containing lithium salt with respect to the total mass of the electrolyte is A1%, and the mass percentage of the ester additive with respect to the total mass of the electrolyte is A2%, 0.5≦B2 / B1≦5, 0.1≦C / B1≦100, 0.8≦D≦2, 10 -4 To provide a secondary battery that satisfies ≦A1+A2≦10.

[0006] Thus, the present application satisfies the above formula by jointly adjusting the discharge capacity, gas generation amount, injection amount, reduction potential of the boron-containing lithium salt, and the content of the boron-containing lithium salt and the ester additive of the secondary battery, thereby ensuring that the components in the electrolyte form a stable SEI film on the surface of the negative electrode active material, and that the degree of decomposition of the carbonate ester solvent in the electrolyte is small and the amount of gas generation is within a controllable range, thereby ensuring the safety performance of the secondary battery, and ensuring the smooth movement of metal ions and the cycle performance of the secondary battery. In addition, the electrolyte has a low risk of causing side reactions, so that the utilization rate of the electrolyte is relatively high.

[0007] In any embodiment, the secondary battery satisfies at least one of the following conditions (1) to (4). (1) 1≦B2 / B1≦5, (2) 1≦C / B1≦5, (3) 0.85≦D≦2; (4) 3≦A1+A2≦10.

[0008] By controlling the ratio of the change in gas generation of the electrolyte to the discharge capacity of the secondary battery to satisfy 1≦B2 / B1≦5, it is possible to ensure that the secondary battery can fully demonstrate its capacity when a relatively safe internal pressure is ensured within the secondary battery.

[0009] By controlling the ratio of the mass of the electrolyte to the discharge capacity of the secondary battery to satisfy 1≦C / B1≦5, it is possible to ensure that the utilization rate of the electrolyte is ensured and that the secondary battery is able to fully demonstrate its capacity.

[0010] By adjusting the reduction potential of the first additive with respect to metallic lithium to satisfy 0.85≦D≦2, it is possible to adjust the film formation speed of the first additive on the negative electrode active material and the structural stability of the SEI film formed thereby.

[0011] By adjusting the total amount of the boron-containing lithium salt and the ester-based additive to satisfy 3≦A1+A2≦10, the structural stability of the SEI film formed on the surface of the negative electrode active material can be adjusted, and the low resistance of the SEI film can be ensured, which is advantageous for improving the low-temperature performance of the secondary battery.

[0012] In any embodiment, the reduction potential of the boron-containing lithium salt with respect to metallic lithium is D1 (V, vs Li + |Li), 0.85≦D1≦2, optionally 0.85≦D1≦1.8, and / or the reduction potential of the ester additive with respect to metallic lithium is D2 (V, vs Li + |Li), where 0.85≦D2≦2, and optionally 0.85≦D2≦1.2.

[0013] When D1 is within the above range, the reduction potential of the boron-containing lithium salt is relatively high, which is advantageous in that the boron-containing lithium salt can be rapidly formed into a film on the surface of the negative electrode active material, thereby further reducing the risk of the carbonate ester solvent decomposing.

[0014] When D2 is within the above range, the reduction potential of the ester additive is relatively low, and it can be mixed with a boron-containing lithium salt to form a film on the surface of the negative electrode active material, which is advantageous for improving the structural stability of the SEI film.

[0015] In any embodiment, the boron-containing lithium salt has the molecular formula LiBF a O b C c P d and in the molecular formula, 0≦a≦4, 0≦b≦8, 0≦c≦4, and 0≦d≦4.

[0016] The B atom can bond with an oxygen-containing oxalic acid ligand, and the resulting bonded product has excellent thermal stability and is easy to form a high-performance SEI film on the surface of the negative electrode active material, thereby ensuring the structural stability of the negative electrode active material and ultimately improving the cycle performance of the secondary battery.

[0017] In any embodiment, the boron-containing lithium salt includes one or more of lithium tetrafluoroborate LiBF4, lithium disoxalate borate LiBOB, and lithium difluorooxalate borate LiDFOB.

[0018] When the secondary battery of the present application contains the above-mentioned boron-containing lithium salt, a SEI film having a stable structure and a relatively low resistance value can be formed on the surface of the negative electrode active material, thereby improving the high-temperature performance and low-temperature performance of the secondary battery. In addition, the above-mentioned boron-containing lithium salt has a high reduction potential with respect to metallic lithium, which is advantageous for preferentially forming a film on the surface of the negative electrode active material, and can reduce the decomposition of the carbonate ester solvent.

[0019] In any embodiment, the electrolyte further comprises an ion-conducting lithium salt, which comprises one or more of lithium hexafluorophosphate LiPF6, lithium difluorophosphate LiPO2F2, lithium difluorodioxalyl phosphate LiDODFP, lithium tetrafluorooxalyl phosphate LiDFBP, lithium bisfluorosulfonyl imide LiFSI, lithium bistrifluoromethanesulfonyl imide LiTFSI, lithium fluorosulfonate LiFSO3, lithium bistrifluoromethanesulfonyl imide LiTFSI, lithium nitrate LiNO3, lithium perchlorate LiClO4, lithium hexafluoroantimonate LiSbF6, and lithium hexafluoroarsenate LiAsF6. The ion-conducting lithium salt has a high degree of dissociation and a high electrical conductivity, which is favorable for the movement of lithium ions.

[0020] In any embodiment, the mass percentage of the ion-conductive lithium salt is A3%, based on the total mass of the electrolyte, and the secondary battery satisfies 5≦A3≦25, optionally 10≦A3≦20.

[0021] When the mass percentage of the ion-conductive lithium salt is within the above range, the conductivity of the electrolyte can be ensured, which is advantageous for providing good protection to the negative electrode active material when used in combination with the boron-containing lithium salt and the ester-based additive, and can also ensure the stability of the electrolyte and improve the utilization rate of the electrolyte.

[0022] In any embodiment, the carbonate ester solvent includes a cyclic carbonate ester solvent having a mass percentage A4% relative to the total mass of the electrolyte, and a chain carbonate ester solvent having a mass percentage A5% relative to the total mass of the electrolyte, and the secondary battery satisfies 1≦A5 / A4≦10, optionally 5≦A4≦50, and / or 50≦A5≦70.

[0023] The cyclic carbonate ester solvent has a higher dielectric constant, can dissolve the lithium salt to a greater extent, and the lithium salt can more easily dissociate lithium ions, improving the conductivity of the electrolyte. The chain carbonate ester has a low viscosity, and can improve the migration speed of the lithium ions. In the present application, the cyclic carbonate ester solvent and the chain carbonate ester solvent are adjusted so as to satisfy the above-mentioned ratio range, thereby achieving both the conductivity of the electrolyte and the migration speed of the lithium ions, and further improving the cycle performance of the secondary battery.

[0024] In any embodiment, the cyclic carbonate ester solvent comprises one or more of vinylene carbonate VC, fluoroethylene carbonate FEC, difluoroethylene carbonate DFEC, vinyl ethylene carbonate VEC, and dioctyl carbonate CC, and / or the linear carbonate ester solvent comprises one or more of ethyl allyl carbonate AEC, diphenyl carbonate DPC, methyl allyl carbonate MAC, polycarbonate VA, diethyl carbonate DEC, ethyl methyl carbonate EMC, methyl propyl carbonate MPC, ethyl propyl carbonate EPC, methyl butyl carbonate MBC, methyl acetate MA, ethyl acetate EA, methyl propionate MP, and ethyl propionate EP.

[0025] In an optional embodiment, the positive electrode sheet includes a positive electrode active material, and the molecular formula of the positive electrode active material is LiNi x Co y Mn z M 1-x-y-z O2 or LiNi a Co b Al c N 1-a-b-c O2, in which M and N are each independently any one selected from Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, and Ti, and 0≦y≦1, 0≦x<1, 0≦z≦1, x+y+z≦1, 0≦a≦1, 0≦b≦1, 0≦c≦1, a+b+c≦1.

[0026] A second aspect of the present application further provides a battery module including a secondary battery according to any one of the embodiments of the first aspect of the present application.

[0027] A third aspect of the present application further provides a battery pack including a battery module according to an embodiment of the second aspect of the present application.

[0028] A fourth aspect of the present application further provides a power consuming device including a secondary battery according to any of the embodiments of the first aspect of the present application, a battery module according to an embodiment of the second aspect of the present application, or a battery pack according to an embodiment of the third aspect of the present application. [Brief description of the drawings]

[0029] In order to more clearly describe the technical solutions of the embodiments of the present application, the drawings necessary for the embodiments of the present application are briefly described below. It is clear that the drawings described below are only some embodiments of the present application. Those skilled in the art can further obtain other drawings based on the drawings even without creative labor.

[0030] [Figure 1] FIG. 1 is a schematic diagram of an embodiment of a secondary battery of the present application. [Diagram 2] FIG. 2 is an exploded schematic view of the embodiment of the secondary battery of FIG. 1. [Diagram 3] FIG. 1 is a schematic diagram of one embodiment of a battery module of the present application. [Figure 4] FIG. 1 is a schematic diagram of one embodiment of a battery pack of the present application. [Diagram 5] 5 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 4. [Figure 6] FIG. 1 is a schematic diagram of one embodiment of an electrical device that includes the secondary battery of the present application as a power source.

[0031] The drawings are not necessarily drawn to scale.

[0032] The explanation is as follows.

[0033] 1 battery pack, 2 upper case, 3 lower case, 4 battery module, 5 secondary battery, 51 housing, 52 electrode assembly, 53 Cover plate, 6 Power consumption equipment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] Hereinafter, the embodiments specifically disclosing the secondary battery, battery module, battery pack, and power consumption device of the present application will be described in detail. However, unnecessary detailed description may be omitted. For example, detailed description of known matters or duplicate description of substantially the same configuration may be omitted. This is to avoid the following description from becoming unnecessarily redundant and to facilitate understanding by those skilled in the art. Note that the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

[0035] The "ranges" disclosed in this application are defined in the form of lower and upper limits, where a given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of the particular range. Such defined ranges may be inclusive or exclusive of the end values, and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are recited for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Also, if minimum range values ​​1 and 2 and maximum range values ​​3, 4 and 5 are recited, the ranges of 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5 may all be contemplated. In this application, unless otherwise stated, the numerical range "a-b" is a shorthand notation representing any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed herein, with "0-5" being an abbreviation for combinations of these numerical values. Also, expressing a parameter as an integer greater than or equal to 2 (≧2) is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0036] Unless otherwise specified, all embodiments and optional embodiments of the present application may be combined with each other to form a new technical solution.Unless otherwise specified, all technical features and optional technical features of the present application may be combined with each other to form a new technical solution.

[0037] Unless otherwise stated, all steps in this application may be performed in sequence or randomly, but are preferably performed in sequence. For example, the method includes steps (a) and (b) and may include steps (a) and (b) performed in sequence, or may include steps (b) and (a) performed in sequence. For example, when it is stated that the method may further include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), may include steps (a), (c) and (b), may include steps (c), (a) and (b), etc.

[0038] Unless otherwise specified, the terms "comprise" and "include" used in this application mean open-ended and may also be closed-ended. For example, the terms "comprise" and "include" can mean "comprise" or "include" other components not listed, or "comprise" or "include" only the listed components.

[0039] Unless otherwise stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following conditions are met: A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), or both A and B are true (or exist).

[0040] In this application, the terms "plurality" and "plurality" mean two or more than two.

[0041] Secondary batteries are widely used due to their characteristics such as high capacity and long life. With the expansion of the range of applications of secondary batteries, the requirements for the performance of secondary batteries are gradually increasing. An electrolyte is an important component of a secondary battery, and plays a role in conducting metal ions between a positive electrode sheet and a negative electrode sheet. An electrolyte usually contains a lithium salt and an organic additive. In order to improve the solubility of the lithium salt, the dielectric constant of the organic additive is usually required to be relatively high. In order to facilitate the movement of lithium ions, the viscosity of the organic additive is usually required to be relatively low. A carbonate ester solvent is usually used as an additive for an electrolyte because it can meet the requirements for a high dielectric constant and a low viscosity. However, at high voltages, the carbonate ester solvent in the electrolyte is easily reduced and decomposed, generating gas, and the water remaining in the electrolyte is decomposed during the charging process to generate hydrogen gas and the like. The decomposition of the electrolyte will cause the secondary battery to generate gas during the cycle process, which will not only cause the secondary battery to swell due to the gas generation, posing a safety risk, but will also cause the positive and negative electrode sheets in the secondary battery to become less tightly attached, which may result in a decrease in the performance of the secondary battery. In addition, as the electrolyte decomposition progresses, the utilization rate of the electrolyte will also decrease.

[0042] Therefore, the inventors have intensively studied the secondary battery and found that when the discharge capacity of the secondary battery, the amount of gas generated, the mass of the electrolyte, and the components in the electrolyte satisfy a specific relationship, the safety performance and cycle performance of the secondary battery can be achieved and the utilization rate of the electrolyte can be ensured. Next, the technical proposal of the present application will be described in detail.

[0043] secondary battery

[0044] According to a first aspect, the present application provides a method for producing a method for a method of manufacturing a semiconductor device comprising: A secondary battery including a negative electrode sheet, a positive electrode sheet, and an electrolyte solution, The negative electrode sheet contains a negative electrode active material, The electrolyte includes a first additive and a carbonate ester solvent, the first additive includes a boron-containing lithium salt and an ester-based additive, and is disposed on a surface of the negative electrode active material so as to form a solid electrolyte interfacial film; Here, the discharge capacity of the secondary battery is B1 Ah, the gas generation change amount of the secondary battery is B2 mL, the mass of the electrolyte is C g, and the reduction potential of the first additive with respect to metallic lithium is D (V, vs Li + |Li), the mass percentage of the boron-containing lithium salt with respect to the total mass of the electrolyte is A1%, and the mass percentage of the ester additive with respect to the total mass of the electrolyte is A2%, 0.5≦B2 / B1≦5, 0.1≦C / B1≦100, 0.8≦D≦2, 10 -4 To provide a secondary battery that satisfies ≦A1+A2≦10.

[0045] Although the mechanism is not clear, the secondary battery of the present application can simultaneously achieve both safety performance and cycle performance of the secondary battery, and ensure the utilization rate of the electrolyte.

[0046] The inventors speculate that the mechanism of action of the present application is that the boron-containing lithium salt and the ester-based additive, as negative electrode film-forming additives, both form a film on the surface of the negative electrode active material, thereby exerting a certain passivation effect on the surface of the negative electrode active material and protecting the structural stability of the negative electrode active material.

[0047] The boron-containing lithium salt and the ester additive together constitute the first additive, and the reduction potential of the first additive relative to metallic lithium is relatively high. In the chemical formation process of the secondary battery, the first additive preferentially forms a solid electrolyte interphase (SEI film) on the surface of the negative electrode active material over the carbonate ester solvent, reducing the risk that the carbonate ester solvent continues to decompose and form a film on the surface of the negative electrode active material, inhibiting further decomposition of the solvent, and ensuring the stability of the carbonate ester solvent in the electrolyte while maintaining the interface stability of the negative electrode active material, thereby improving the utilization rate of the electrolyte. In addition, the decomposition degree of the electrolyte is reduced, so that the risk of gas generation in the electrolyte is reduced, and the internal pressure of the secondary battery is within the range of safe pressure, thereby improving the safety performance of the secondary battery. In addition, the reduction in the decomposition degree of the electrolyte can ensure smooth movement of metal ions, such as lithium ions, and therefore the cycle performance of the secondary battery can be ensured.

[0048] The boron-containing lithium salt and the ester additive together form an SEI film, which has many components and a more stable structure. The resistance of the SEI film is also low, which is favorable for the movement of lithium ions.

[0049] The organic solvent in the electrolyte generally includes a cyclic carbonate ester solvent and a chain carbonate ester solvent. The cyclic carbonate ester solvent provides a high dielectric constant to the electrolyte, which is advantageous for promoting dissociation of metal ions, such as lithium ions, and improving the ionic conductivity of the electrolyte. The chain carbonate ester solvent can provide a low viscosity, which is advantageous for the migration of metal ions, such as lithium ions.

[0050] By controlling the ratio of the mass of the electrolyte to the discharge capacity of the secondary battery within the above range, it is possible to ensure that the secondary battery can fully demonstrate its capacity while ensuring the utilization rate of the electrolyte.

[0051] In the present application, the discharge capacity, gas generation amount, injection amount, reduction potential of the boron-containing lithium salt, and the contents of the boron-containing lithium salt and ester additive of the secondary battery are controlled to satisfy the above formula, thereby ensuring that the components in the electrolyte form a stable SEI film on the surface of the negative electrode active material, and that the degree of decomposition of the carbonate ester solvent in the electrolyte is small and the amount of gas generated is within a controllable range, ensuring the safety performance of the secondary battery, ensuring smooth movement of metal ions, and ensuring the cycle performance of the secondary battery. In addition, the electrolyte has a low risk of causing side reactions, so that the utilization rate of the electrolyte is high.

[0052] In some embodiments, 0.5≦B2 / B1≦5, and optionally, 1≦B2 / B1≦5.

[0053] By controlling the ratio of the gas generation change rate of the electrolyte to the discharge capacity of the secondary battery within a certain range, it is possible to ensure that the secondary battery can fully exert its capacity when a relatively safe internal pressure is ensured in the secondary battery. Exemplarily, B2 / B1 may be 0.5, 1, 1.2, 1.5, 1.8, 2, 2.5, 3, 3.5, 4, 4.2, 4.5, or 5, or may be a range consisting of any two of the above values.

[0054] In some embodiments, 0.01≦B1≦500. When the discharge capacity of the secondary battery is in the above range, it can meet the application in different scenes. Optionally, 2≦B1≦300, and for example, the discharge capacity B1 Ah of the secondary battery can be 0.01 Ah, 0.1 Ah, 0.2 Ah, 0.5 Ah, 1 Ah, 2 Ah, 5 Ah, 10 Ah, 15 Ah, 20 Ah, 50 Ah, 80 Ah, 100 Ah, 200 Ah, 300 Ah or 500 Ah, or can be a range consisting of any two of the above values, or can be a range consisting of any two of the above values.

[0055] In this application, the discharge capacity B1 Ah of the secondary battery refers to the capacity value of the secondary battery measured by setting the corresponding current and voltage with a constant current charge / discharge tester at room temperature, and can be measured by using methods and equipment well known in the art. Taking a ternary material as an example, the test method of the discharge capacity of the secondary battery is to place the secondary battery in a constant current charge / discharge tester at a test temperature of 25°C, first charge the product battery to the upper limit voltage (the upper limit voltage of the ternary material is generally 4.2-4.5V) at a constant rate of 0.05C (0.05C is the current value when all the electricity of the secondary battery is discharged in 20h), leave it for 30 minutes, and discharge it to the lower limit voltage (the lower limit voltage of the ternary material is generally 2.5V) at a rate of 0.05C, and the measured discharge capacity is the discharge capacity B1 Ah of the secondary battery.

[0056] In some embodiments, 0.1≦B2≦2000. When the gas generation change rate of the secondary battery is within the above range, the air pressure change in the secondary battery is not too large, and the secondary battery does not expand excessively, so that the safety performance of the secondary battery can be ensured. Optionally, 1≦B2≦1000, and illustratively, the gas generation change rate of the secondary battery may be 0.1, 1, 2, 5, 10, 15, 20, 25, 30, 35, 50, 80, 100, 200, 300, 400, 500, 600, 700, 800, 1000, 1200, 1500, 1600, 1700, 1800, or 2000.

[0057] In this application, the gas generation change amount of the secondary battery has a meaning well known in the art, and can be measured using a method and device well known in the art. If the secondary battery is a prismatic battery, a CDK oil gauge (brand CCDK, model number: PPX-R10NH-6m-KA) is inserted into the liquid injection hole of the secondary battery, and the display value of the device is the pressure parameter and the gas generation amount of the secondary battery, and the display value is pressure MPa (according to the ideal gas state equation PV=nRT, the gas generation amount and the pressure are positively correlated). If the secondary battery to be tested is a soft package battery, a balance is used to test the gas change amount in the soft package battery. Specifically, first, fill a 2L beaker with deionized water up to 1.8L, place the water-filled beaker on a balance to return it to zero, clamp the negative terminal of the soft-packaged battery with an iron stand tool, and completely immerse the secondary battery in water (drainage method), recording the balance reading at this time as the initial secondary battery volume mL of the product, then charge the soft-packaged battery at 25°C and 0.33C to 100% SOC, fully discharge it, and measure the actual capacity Ah. Finally, place the fully charged soft-packaged battery in a high-temperature furnace at 70°C for 5 days (5D), and measure the secondary battery volume mL again using the drainage method, and the volume change mL / Ah of the secondary battery stored at a high temperature of 70°C = (volume of secondary battery stored for 5D - initial secondary battery volume of the product) / actual capacity.

[0058] In some embodiments, 0.1≦C / B1≦100, and optionally, 1≦C / B1≦5.

[0059] By controlling the ratio of the mass of the electrolyte to the discharge capacity of the secondary battery within a certain range, the secondary battery can fully exert its capacity while ensuring the utilization rate of the electrolyte. For example, C / B1 may be 1, 1.2, 1.5, 1.8, 2, 2.5, 3, 3.5, 4, 4.5, or 5, or may be a range consisting of any two of the above values.

[0060] In some embodiments, 0.01≦C≦2000. When the mass of the electrolyte is in the above range, the capacity of the secondary battery can be fully exerted. Optionally, 1≦C≦1000, and for example, the mass C g of the electrolyte may be 0.01g, 0.05g, 0.1g, 0.2g, 0.5g, 0.6g, 0.8g, 1g, 2g, 5g, 8g, 10g, 15g, 20g, 30g, 50g, 80g, 100g, 200g, 300g, 500g, 700g, 800g, 1000g, 1500g or 2000g, or may be a range consisting of any two of the above values.

[0061] In this application, the mass C of the electrolyte is the mass of the electrolyte in the product secondary battery, and the method of measuring the mass C g of the electrolyte is an exemplary method of obtaining the electrolyte from a secondary battery, which is to discharge the secondary battery to the discharge end voltage (for safety reasons, the battery is generally in a fully discharged state) and perform a centrifugation process, first pour out and collect the liberated electrolyte from the injection hole, and then centrifuge the remaining bare cell parts such as the electrode sheet and separator, and repeat the centrifugation to collect the electrolyte until the centrifugal rotation speed becomes greater than 10,000 rpm and no obvious liquid is present after centrifugation, and the total amount of collected electrolyte is the mass C g of the electrolyte in the product cell.

[0062] In some embodiments, 0.8≦D≦2, optionally 0.85≦D≦2, and further optionally 0.85≦D≦1.8. D indicates the reduction potential of the first additive, and when the first additive includes multiple materials, D may be a range value because the reduction potentials of different materials may be different.

[0063] By adjusting the reduction potential of the first additive with respect to metallic lithium, it is possible to adjust the film-forming speed of the first additive on the negative electrode active material and the structural stability of the SEI film formed thereby.

[0064] In this application, the reduction potential of the first additive to metallic lithium is a well-known meaning in the art, and can be measured by using methods and equipment common in the art. For example, the test method is to add 1% of the first additive to a blank electrolyte containing only a non-aqueous solvent and a main lithium salt LiPF6, mix it uniformly, use a lithium sheet as the negative electrode, and use a graphite sheet as the positive electrode to assemble it into a coin cell. Activate it by placing it on a constant current charge-discharge tester at 45°C for 2 hours, first discharge it to 5mV at 200uA, then discharge it to 5mV at 50uA, leave it for 5min, and charge it to 2V at a constant current of 0.1C. The measurement results are shown as a graph of dQ / dV-V, where Q represents the discharge capacity of the battery, V represents the voltage, and dQ / dV represents the differential of the discharge capacity of the battery with respect to the voltage. The reduction potential of the first additive is obtained by identifying the peak position corresponding to the boron-containing lithium salt from the graph.

[0065] In some embodiments, the reduction potential of the boron-containing lithium salt with respect to metallic lithium is D1 (V, vs Li + |Li), where 0.8≦D1≦2, and optionally 0.85≦D1≦1.8.

[0066] When D1 is in the above range, the reduction potential of the boron-containing lithium salt is relatively high, and the boron-containing lithium salt is advantageously rapidly formed on the surface of the negative electrode active material, thereby further reducing the risk of the carbonate ester solvent decomposing.Optionally, 0.85≦D1≦2, and for example, D1 may be 0.8, 0.85, 1, 1.2, 1.5, 1.6, 1.7, 1.8, 1.9, or 2, or may be a range consisting of any two of the above values.

[0067] In some embodiments, the reduction potential of the ester additive relative to metallic lithium is D2 (V, vs Li + |Li), where 0.8≦D2≦2.

[0068] When D2 is in the above range, the reduction potential of the ester additive is relatively low, and it can be mixed with the boron-containing lithium salt to form a film on the surface of the negative electrode active material, which is advantageous for improving the structural stability of the SEI film.Optionally, 0.8≦D2≦1.8, and further optionally, 0.8≦D2≦1.2. For example, D2 may be 0.8, 0.85, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, or 1.8, or may be a range consisting of any two of the above values.

[0069] In some embodiments, 10 -4 ≦A1+A2≦10, and optionally 3≦A1+A2≦10.

[0070] By adjusting the total amount of the boron-containing lithium salt and the ester additive, the structural stability of the SEI film formed on the surface of the negative electrode active material can be adjusted, and the low resistance of the SEI film can be ensured, which is advantageous for improving the low temperature performance of the secondary battery. -4 , 10 -3 , 10 -2 , 0.1, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.5, 4, 4.5, 5, 5.5, 5.8, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5 or 10, or may be a range consisting of any two of the above numbers.

[0071] In the present application, the mass percentage A1% of the boron-containing lithium salt and the mass percentage A2% of the ester additive can be measured according to a method known in the art, for example, gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), etc.

[0072] In some embodiments, 10 -4When the mass percentage of the boron-containing lithium salt is within the above range, a stable SEI film can be formed on the surface of the negative electrode active material, which is also advantageous in ensuring the conductivity of the electrolyte. For example, the mass percentage A1% of the boron-containing lithium salt is 1×10 -4 %, 1.5×10 -4 %, 2×10 -4 %, 5×10 -4 %, 1×10 -3 %, 1.5×10 -3 %, 2×10 -3 %, 5×10 -3 %, 1×10 -2 %, 5×10 -2 %, 0.1%, 0.5%, 0.8%, 1%, 1.5%, 2%, 3%, 4% or 5%, or may be a range consisting of any two of the foregoing values.

[0073] In some embodiments, 10 -4 ≦A2≦5. When the mass percentage of the ester additive is in the above range, the SEI film component is more abundant, which is favorable for improving the cycle and storage performance of the secondary battery. For example, the mass percentage A2% of the ester additive is 1×10 -4 %, 1.5×10 -4 %, 2×10 -4 %, 5×10 -4 %, 1×10 -3 %, 1.5×10 -3 %, 2×10 -3 %, 5×10 -3 %, 1×10 -2 %, 5×10 -2 %, 0.1%, 0.5%, 0.8%, 1%, 1.5%, 2%, 3%, 4% or 5%, or may be a range consisting of any two of these values.

[0074] [Electrolyte]

[0075] The electrolyte serves to conduct metal ions between the positive electrode sheet and the negative electrode sheet, and the electrolyte of the present application may be any electrolyte used in secondary batteries known in the art. The electrolyte includes a lithium salt and an organic solvent.

[0076] In some embodiments, the lithium salt comprises a boron-containing lithium salt, the molecular formula of the boron-containing lithium salt being LiBF a O b C c P d and in the molecular formula, 0≦a≦4, 0≦b≦8, 0≦c≦4, and 0≦d≦4.

[0077] B atom can be bonded with oxygen-containing oxalic acid ligand, and the product after bonding has excellent thermal stability and is easy to form a high-performance SEI film on the surface of the negative electrode active material, so that the structural stability of the negative electrode active material can be ensured and the cycle performance of the secondary battery can be improved. Of course, B atom can be bonded with halogen atom, especially fluorine atom, which has a strong electron-attracting induction effect, high thermal stability and chemical stability, and is favorable for improving the number of lithium ions moving in the electrolyte, improving the rate performance of the secondary battery, and reducing the polarization phenomenon.

[0078] As an example, the boron-containing lithium salt includes one or more of lithium tetrafluoroborate (LiBF4), lithium disoxalate borate (LiB(C2O4)2, abbreviated as LiBOB), and lithium difluorooxalate borate (LiBC2O4F2, abbreviated as LiDFOB). Further, the boron-containing lithium salt includes a composition of lithium tetrafluoroborate LiBF4, lithium disoxalate borate (LiB(C2O4)2, abbreviated as LiBOB), and lithium difluorooxalate borate (LiBC2O4F2, abbreviated as LiDFOB).

[0079] When lithium tetrafluoroborate LiBF4 is used in combination with a carbonate ester solvent or additive in the electrolyte, the viscosity of the system made of lithium tetrafluoroborate LiBF4 is relatively low, which is favorable for the release of lithium ions, thereby improving the conductivity of the electrolyte. The SEI film formed from lithium tetrafluoroborate LiBF4 has a uniform thickness, good kinetic activity, and small charge transfer resistance in the secondary battery, which can significantly improve the low-temperature performance of the secondary battery. In addition, the SEI film is not easily thermally decomposed, and its performance at high temperatures is stable, which can significantly improve the high-temperature performance of the secondary battery.

[0080] Either one of the lithium disoxalate borate LiBOB and the lithium difluorooxalate borate LiDFOB has a passivation effect on the positive electrode current collector in the positive electrode sheet, and can reduce the risk of corroding the positive electrode current collector by a side reaction with the positive electrode current collector, and can improve the structural stability of the positive electrode sheet. In addition, an electrolyte containing either one of the lithium disoxalate borate LiBOB and the lithium difluorooxalate borate LiDFOB is less likely to produce acidic substances, so that the risk of corroding the positive electrode current collector can be further reduced. The lithium disoxalate borate LiBOB and the lithium difluorooxalate LiDFOB have good compatibility with the positive electrode active material, which is advantageous for the movement of lithium ions, and can also form an effective SEI film on the surface of the negative electrode active material to improve the protective performance for the negative electrode active material.

[0081] By using a combination of lithium tetrafluoroborate LiBF4, lithium disoxalate borate LiBOB, and lithium difluorooxalate LiDFOB, the SEI film formed by the three components contains many components, the structure of the SEI film is more stable, and the stability of the structure is ensured. In addition, the resistance of the SEI film is relatively small, and the low-temperature performance of the secondary battery can be ensured.

[0082] When the secondary battery of the present application contains the above-mentioned boron-containing lithium salt, a SEI film having a stable structure and a relatively small resistance value can be formed on the surface of the negative electrode active material, thereby improving the high low-temperature performance of the secondary battery. In addition, the above-mentioned boron-containing lithium salt has a high reduction potential with respect to metallic lithium, which is advantageous for preferentially forming a film on the surface of the negative electrode active material, thereby reducing the decomposition of the carbonate ester solvent.

[0083] In some embodiments, the lithium salt may further comprise an ion-conducting lithium salt, which comprises one or more of lithium hexafluorophosphate LiPF6, lithium difluorophosphate LiPO2F2, lithium difluorodioxalyl phosphate LiDODFP, lithium tetrafluorooxalyl phosphate LiDFBP, lithium bisfluorosulfonyl imide LiFSI, lithium bistrifluoromethanesulfonyl imide LiTFSI, lithium fluorosulfonate LiFSO3, lithium nitrate LiNO3, lithium perchlorate LiClO4, lithium hexafluoroantimonate LiSbF6, and lithium hexafluoroarsenate LiAsF6. The dissociation degree of the ion-conducting lithium salt is relatively high, and its electrical conductivity is high, which is favorable for the movement of lithium ions.

[0084] In some embodiments, the weight percentage of the ion-conducting lithium salt, based on the total weight of the electrolyte, is A3%, where 5≦A3≦25, and optionally 10≦A3≦20.

[0085] When the mass percentage of the ion-conductive lithium salt is in the above range, the conductivity of the electrolyte can be ensured. It is advantageous to perform a good protective effect on the negative electrode active material when used in combination with the boron-containing lithium salt and the ester additive, and can ensure the stability of the electrolyte and improve the utilization rate of the electrolyte. Alternatively, 10≦A3≦20, and for example, the mass percentage A3% of the ion-conductive lithium salt can be 5%, 6%, 8%, 10%, 12%, 15%, 16%, 18%, 20%, 21%, 23% or 25%, or can be a range consisting of any two of the above values.

[0086] In some embodiments, the ester additive may include one or more of ethylene carbonate EC, propylene carbonate PC, vinylene carbonate VC, fluoroethylene carbonate FEC, difluoroethylene carbonate DFEC, vinylethylene carbonate VEC, and dioctyl carbonate CC. Of course, the ester additive may include linear carbonate ester additives, etc. The mass percentage of the ester additive is usually 1% or less.

[0087] In some embodiments, the carbonate ester solvent includes a cyclic carbonate ester solvent and a chain carbonate ester solvent, the mass percentage of the cyclic carbonate ester solvent relative to the total mass of the electrolyte is A4%, and the mass percentage of the chain carbonate ester solvent relative to the total mass of the electrolyte is A5%, and the secondary battery satisfies 1≦A5 / A4≦10.

[0088] The cyclic carbonate ester solvent has a high dielectric constant, and can dissolve the lithium salt to a greater extent, so that the lithium salt is more likely to dissociate lithium ions, thereby improving the conductivity of the electrolyte. The chain carbonate ester has a relatively low viscosity, and can improve the migration speed of the lithium ions. In the present application, the cyclic carbonate ester solvent and the chain carbonate ester solvent are adjusted to satisfy the above ratio range, thereby achieving both the conductivity of the electrolyte and the migration speed of the lithium ions, and further improving the cycle performance of the secondary battery. Alternatively, 2≦A5 / A4≦8, and for example, A5 / A4 may be 2, 3, 4, 5, 6, 7, 8, 9, or 10, or may be a range consisting of any two of the above values.

[0089] In some embodiments, 5≦A4≦50.

[0090] When the mass percentage of the cyclic carbonate ester solvent is within the above range, the conductivity of the electrolyte can be further improved. Exemplarily, the mass percentage A4% of the cyclic carbonate ester solvent is 5%, 6%, 7%, 8%, 9%, 10%, 12%, 15%, 16%, 18%, 20%, 30%, 40%, or 50%, or is within a range consisting of any two of the above numerical values.

[0091] In some embodiments, 50≦A5≦70.

[0092] When the mass percentage of the chain carbonate ester solvent is within the above range, the viscosity of the electrolyte can be further improved, and the migration speed of lithium ions can be improved. Exemplarily, the mass percentage A5% of the chain carbonate ester solvent is 50%, 52%, 55%, 56%, 58%, 60%, 62%, 65%, 66%, 68%, or 70%, or a range consisting of any two of the above values.

[0093] In some embodiments, the cyclic carbonate solvent comprises one or more of ethylene carbonate EC, propylene carbonate PC, vinylene carbonate VC, fluoroethylene carbonate FEC, difluoroethylene carbonate DFEC, vinylethylene carbonate VEC, and dioctyl carbonate CC, which have a higher dielectric constant and are more favorable for dissociation of lithium salts.

[0094] In some embodiments, the chain carbonate ester solvent comprises one or more of ethyl allyl carbonate AEC, diphenyl carbonate DPC, methyl allyl carbonate MAC, polycarbonate VA, diethyl carbonate DEC, ethyl methyl carbonate EMC, methyl propyl carbonate MPC, ethyl propyl carbonate EPC, methyl butyl carbonate MBC, methyl acetate MA, ethyl acetate EA, methyl propionate MP, and ethyl propionate EP. The carbonate ester solvent has a relatively small viscosity and can further improve the migration speed of lithium ions.

[0095] In some embodiments, the electrolyte may further include a film-forming additive, for example, a negative electrode film-forming additive, and the negative electrode film-forming additive may include one or more of a sulfate ester-based additive and a sulfite ester-based additive. The negative electrode film-forming additive may form an SEI film on the surface of the negative electrode active material, and a plurality of components may be formed on the surface of the SEI film to enrich the film layer structure of the SEI film, and the structural stability of the SEI film may be improved. Furthermore, the negative electrode film-forming additive may include a sulfate ester-based additive and a sulfite ester-based additive, and the SEI film formed by the additive may have a rich composition, a higher structural stability, and improve the storage performance of the negative electrode active material. Of course, a positive electrode film-forming additive may be added to the electrolyte, which may form a film on the surface of the positive electrode active material and play a protective role on the positive electrode active material.

[0096] The sulfate additive includes a cyclic sulfonate additive and / or a hydrocarbyl sulfate additive. The cyclic sulfonate additive includes one or more of 1,3-propane sultone PS, propene sultone PES, and 3-fluoro-1,3-propane sultone FPS. The hydrocarbyl sulfate additive includes one or more of vinyl sulfate DTD, diethyl sulfate DES, and dimethyl sulfate DMS.

[0097] Sulfite additives include ethylene sulfite ES and / or vinyl ethylene sulfite VES.

[0098] The electrolyte of the present application can be manufactured according to a conventional method in the art. For example, the additive, the solvent, the electrolyte salt, etc. can be mixed uniformly to obtain the electrolyte. The order of addition of each material is not particularly limited. For example, the additive, the electrolyte salt, etc. can be added to the non-aqueous solvent and mixed uniformly to obtain the non-aqueous electrolyte.

[0099] In the present application, each component and its content in the electrolyte solution can be measured according to a method known in the art, for example, gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), etc.

[0100] In the electrolyte test of the present application, a freshly prepared electrolyte may be taken out directly, or the electrolyte may be taken out from a secondary battery. One exemplary method for taking out the electrolyte from a secondary battery is to discharge the secondary battery to the discharge end voltage (for safety reasons, the battery is generally placed in a fully discharged state), and then to perform a centrifugation process, and then to take out an appropriate amount of the liquid obtained by the centrifugation process as the nonaqueous electrolyte. The nonaqueous electrolyte may be taken out directly from the electrolyte inlet of the secondary battery.

[0101] [Positive electrode sheet]

[0102] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector. For example, the positive electrode current collector has two surfaces facing each other in a thickness direction of the positive electrode current collector, and the positive electrode film layer is provided on one or both of the two facing surfaces of the positive electrode current collector.

[0103] The positive electrode film layer includes a positive electrode active material, and the positive electrode active material can be a positive electrode active material used in a secondary battery known in the art. For example, the positive electrode active material may include at least one of a lithium transition metal oxide, a lithium-containing phosphate having an olivine structure, and a modified compound thereof. Examples of the lithium transition metal oxide may include at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and a modified compound thereof. Examples of the lithium-containing phosphate having an olivine structure may include at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and a modified compound thereof. The present application is not limited to these materials, and other materials known in the art that are used as a secondary battery positive electrode active material may be used. These positive electrode active materials may be used alone or in combination of two or more.

[0104] In some embodiments, the positive electrode active material is LiNi x Co y Mn z M 1-x-y-z O2 or LiNi a Co b Al c N 1-a-b-cO2, where M and N are each independently one of Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, and Ti, and 0≦y≦1, 0≦x<1, 0≦z≦1, x+y+z≦1, 0≦a≦1, 0≦b≦1, 0≦c≦1, a+b+c≦1. When the secondary battery is subjected to a charge-discharge cycle under high pressure conditions, the structure of the positive electrode active material is relatively stable. In addition, when the positive electrode active material is used in combination with a boron-containing lithium salt, the B atom in the boron-containing lithium salt is easily bonded to the O atom in the positive electrode active material, so that the charge transfer resistance of the positive electrode active material is reduced, and the diffusion resistance of lithium ions in the bulk of the positive electrode active material is reduced. Therefore, when the non-aqueous electrolyte contains an appropriate content of lithium tetrafluoroborate and lithium difluoroborate, the low-cobalt or cobalt-free positive electrode active material can have a significantly improved lithium ion diffusion rate, and the lithium ions in the bulk of the low-cobalt or cobalt-free positive electrode active material can be timely replenished to the surface, and excessive lithium desorption from the surface of the low-cobalt or cobalt-free positive electrode active material can be avoided, thereby stabilizing the crystal structure of the low-cobalt or cobalt-free positive electrode active material. Since the crystal structure of the low-cobalt or cobalt-free positive electrode active material is more stable, the probability of problems such as excessive lithium desorption from the surface of the low-cobalt or cobalt-free positive electrode active material causing instability in the structural, chemical or electrochemical properties of the positive electrode active material, for example, the probability of irreversible distortion or increased lattice defects in the positive electrode active material occurring can be greatly reduced.

[0105] LiNi x Co y Mn z M 1-x-y-z O2 or LiNi a Co b Al c N 1-a-b-cO2 can be produced according to a conventional method in the art. An exemplary production method is to mix a lithium source, a nickel source, a cobalt source, a manganese source, an aluminum source, an M element precursor, and an N element precursor, followed by sintering. The sintering atmosphere can be an oxygen-containing atmosphere, for example, an air atmosphere or an oxygen gas atmosphere. The O2 concentration in the sintering atmosphere is, for example, 70% to 100%. The sintering temperature and sintering time can be adjusted according to the actual situation.

[0106] Exemplary lithium sources include, but are not limited to, at least one of lithium oxide (Li2O), lithium phosphate (Li3PO4), lithium dihydrogen phosphate (LiH2PO4), lithium acetate (CH3COOLi), lithium hydroxide (LiOH), lithium carbonate (Li2CO3), and lithium nitrate (LiNO3). Exemplary nickel sources include, but are not limited to, at least one of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate. Exemplary cobalt sources include, but are not limited to, at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate. Exemplary manganese sources include, but are not limited to, at least one of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate. Exemplary aluminum sources include, but are not limited to, at least one of aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum oxalate, and aluminum acetate. By way of example, the M element precursor includes at least one of the following: an oxide, a nitrate compound, a carbonate compound, a hydroxide compound, and an acetate compound of the M element. By way of example, the N element precursor includes at least one of the following: ammonium fluoride, lithium fluoride, hydrogen fluoride, ammonium chloride, lithium chloride, hydrogen chloride, ammonium nitrate, ammonium nitrite, ammonium carbonate, ammonium hydrogen carbonate, ammonium phosphate, phosphoric acid, ammonium sulfate, ammonium hydrogen sulfate, ammonium hydrogen sulfite, ammonium sulfite, ammonium hydrogen sulfide, hydrogen sulfide, lithium sulfide, ammonium sulfide, and elemental sulfur.

[0107] In some embodiments, the molecular formula is LiNi x Co y Mn z M 1-x-y-z O2 or LiNi a Co b Al c N 1-a-b-c The mass percentage of the layered material that is O2 is 80% to 99%. For example, the molecular formula is LiNix Co y Mn z M 1-x-y-z O2 or LiNi a Co b Al c N 1-a-b-c The mass percentage of the layered material that is O2 may be in the range of any of the following values: 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more. Optionally, the molecular formula is LiNi x Co y Mn z M 1-x-y-z O2 or LiNi a Co b Al c N 1-a-b-c The mass percentage of the O2 layered material is 85%-99%, 90%-99%, 95%-99%, 80%-98%, 85%-98%, 90%-98%, 95%-98%, 80%-97%, 85%-97%, 90%-97% or 95%-97%.

[0108] In some embodiments, the positive electrode film layer may further include a selective positive electrode conductive agent. In the present application, the type of the positive electrode conductive agent is not particularly limited, but for example, the positive electrode conductive agent may include one or more combinations selected from superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the positive electrode conductive agent is 5% or less based on the total mass of the positive electrode film layer.

[0109] In some embodiments, the positive electrode membrane layer may further include a selective positive electrode binder. In the present application, the type of the positive electrode binder is not particularly limited, but for example, the positive electrode binder may include one or more combinations selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene ternary copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene ternary copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin. In some embodiments, the mass percentage of the positive electrode binder is 5% or less based on the total mass of the positive electrode membrane layer.

[0110] In some embodiments, the positive electrode current collector may be a metal foil piece or a composite current collector. Examples of the metal foil piece include aluminum foil or aluminum alloy foil. The composite current collector may include a polymeric material base layer and a metal material layer formed on at least one surface of the polymeric material base layer. For example, the metal material may include one or more combinations selected from aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, and the polymeric material base layer may include one or more combinations selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0111] The positive electrode membrane layer is typically formed by applying a positive electrode slurry to a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent, and stirring the mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP).

[0112] [Negative electrode sheet]

[0113] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0114] For example, the negative electrode current collector has two surfaces opposing each other in the thickness direction of the negative electrode current collector, and the negative electrode film layer is provided on either one or both of the two opposing surfaces of the negative electrode current collector.

[0115] In some embodiments, the negative electrode active material may be a negative electrode active material used in batteries known in the art. For example, the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, lithium titanate, and lithium aluminum alloy. The silicon-based material may be at least one selected from elemental silicon, silicon oxide, silicon carbon composite, silicon nitrogen composite, and silicon alloy. The tin-based material may be at least one selected from elemental tin, tin oxide, and tin alloy. However, the present application is not limited to these materials, and other conventional materials used as negative electrode active materials in batteries may be used. These negative electrode active materials may be used alone or in combination of two or more.

[0116] In some embodiments, the negative electrode membrane layer may further include a selective negative electrode binder. In the present application, the type of the negative electrode binder is not particularly limited, but as an example, the negative electrode binder may include one or more combinations selected from styrene butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-soluble acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMMA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage of the negative electrode binder is 5% or less based on the total mass of the negative electrode membrane layer.

[0117] In some embodiments, the negative electrode film layer may further include a selective negative electrode conductive agent. In the present application, the type of the negative electrode conductive agent is not particularly limited, but for example, the negative electrode conductive agent may include one or more combinations selected from superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the negative electrode conductive agent is 5% or less based on the total mass of the negative electrode film layer.

[0118] In some embodiments, the negative electrode membrane layer may further include other optional auxiliary agents. For example, the other auxiliary agents may include thickeners such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, the mass percentage of the other auxiliary agents is 2% or less based on the total mass of the negative electrode membrane layer.

[0119] In some embodiments, the negative electrode current collector may be a metal foil piece or a composite current collector. Examples of the metal foil piece include copper foil and copper alloy foil. The composite current collector may include a polymeric material base layer and a metal material layer formed on at least one surface of the polymeric material base layer. For example, the metal material may include one or more combinations selected from copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, and the polymeric material base layer may include one or more combinations selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0120] The negative electrode membrane layer is typically formed by applying a negative electrode slurry to a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional auxiliary agents in a solvent and stirring uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0121] The negative electrode sheet does not exclude additional functional layers other than the negative electrode film layer. For example, in some embodiments, the negative electrode sheet further includes a protective layer coated on the surface of the negative electrode film layer.

[0122] [Separator]

[0123] In some embodiments, the secondary battery further includes a separator. The type of the separator in the present application is not particularly limited, and any well-known separator with a porous structure having good chemical stability and mechanical stability can be selected.

[0124] In some embodiments, the separator is made of at least one material selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, but is not particularly limited thereto. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, but is not particularly limited thereto.

[0125] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly by a winding process or a stacking process.

[0126] In some embodiments, the secondary battery can include an exterior packaging, which can be used to seal the electrode assembly and electrolyte.

[0127] In some embodiments, the exterior of the secondary battery may be a hard package such as a hard plastic case, an aluminum case, a steel case, etc. The exterior of the sodium ion battery may be a soft package such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0128] The shape of the secondary battery of the present application is not particularly limited, and may be cylindrical, rectangular, or any other shape. For example, FIG. 1 shows an exemplary secondary battery 5 with a rectangular structure.

[0129] In some embodiments, as shown in FIG. 1 and FIG. 2, the exterior may include a housing 51 and a cover plate 53. The housing 51 includes a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are surrounded to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 covers the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator may form an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is sealed in the receiving cavity. The electrode assembly 52 is impregnated with an electrolyte. The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and may be adjusted as needed.

[0130] The method for manufacturing the secondary battery of the present application is well known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte solution can be assembled to form a secondary battery. For example, a positive electrode sheet, a separator, and a negative electrode sheet can be wound or stacked to form an electrode assembly, and the electrode assembly can be placed in a case, dried, and then injected with an electrolyte solution, followed by vacuum sealing, standing, chemical formation, shaping, and other processes to obtain a secondary battery.

[0131] In some embodiments of the present application, the secondary battery of the present application may be assembled into a battery module, and the number of secondary batteries included in the battery module may be multiple, and the specific number may be adjusted according to the application and capacity of the battery module.

[0132] Fig. 3 is a schematic diagram of an example battery module 4. As shown in Fig. 3, in the battery module 4, the multiple secondary batteries 5 may be arranged in sequence along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the multiple secondary batteries 5 may be fixed by fasteners.

[0133] Optionally, the battery module 4 further includes an external housing having an accommodating space in which a plurality of secondary batteries 5 are accommodated.

[0134] In some embodiments, the battery modules may be assembled into a battery pack, and the number of battery modules included in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0135] 4 and 5 are schematic diagrams of an example battery pack 1. As shown in Fig. 4 and 5, the battery pack 1 may include a battery case and a plurality of battery modules 4 provided in a battery box. The battery case includes an upper case 2 and a lower case 3, and the upper case 2 covers the lower case 3 to form an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery case in any manner.

[0136] power consumption equipment

[0137] In a second aspect, the present application provides a power consuming device including at least one of the secondary batteries, battery modules, and battery packs of the present application. The secondary batteries, battery modules, and battery packs may be used as power sources for the power consuming devices, or may be used as energy storage units for the power consuming devices. The power consuming devices may be, but are not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0138] A power consuming device can select a secondary battery, a battery module or a battery pack according to its usage needs.

[0139] 6 is a schematic diagram of an example power consuming device 6, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. A battery pack 1 or a battery module can be employed to meet the high power and high energy density demands of the power consuming device.

[0140] Other examples of power consuming devices may be mobile phones, tablet computers, notebook computers, etc. Such power consuming devices are usually required to be thin and may employ secondary batteries as their power source.

[0141] Working Example

[0142] The following examples are provided to more specifically describe the contents of the present application, but these examples are merely illustrative, and it is obvious to those skilled in the art that various modifications and changes may be made within the scope of the disclosure of the present application. All quantities, percentages, and ratios described in the following examples are based on mass unless otherwise specified. In addition, all reagents used in the examples are commercially available or may be synthesized according to conventional methods, and can be used as is without further treatment. In addition, all devices used in the examples are commercially available.

[0143] Example 1

[0144] 1. Manufacturing of positive electrode sheet

[0145] As the positive electrode current collector, an aluminum foil having a thickness of 12 μm is used.

[0146] Positive electrode active material LiNi 0.6 Co 0.2Mn2O2, carbon black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder are mixed in a weight ratio of 97.5:1.4:1.1 in an appropriate amount of NMP as a solvent by thorough stirring to form a uniform positive electrode slurry. The positive electrode slurry is then evenly applied to the surface of aluminum foil as a positive electrode current collector, and after drying and cold pressing, a positive electrode sheet is obtained.

[0147] 2. Manufacturing of negative electrode sheet

[0148] A copper foil with a thickness of 8 μm is used as the negative electrode current collector.

[0149] The negative electrode active material graphite, the binder styrene butadiene rubber (SBR), the thickener sodium carboxymethylcellulose (CMC-Na), and the conductive agent carbon black (Super P) are mixed in a weight ratio of 96.2:1.8:1.2:0.8 in an appropriate amount of deionized water as a solvent and stirred thoroughly to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly applied to the surface of copper foil, the negative electrode current collector, and dried and cold pressed to obtain a negative electrode sheet.

[0150] 3. Separator

[0151] A porous polyethylene (PE) film is used as the separator.

[0152] 4. Electrolyte production

[0153] In an environment with a water content of less than 10 ppm, the non-aqueous organic solvents EC and DEC are mixed in a volume ratio of 1:1 to obtain a solvent for the electrolyte, and then the organic solvent is mixed with the first additive to obtain an electrolyte with a lithium salt concentration of 1 mol / L, with LiPF6 as the main lithium salt. The reduction potential of EC against the metallic lithium sheet is 0.7 (V, Li+|Li), and the reduction potential of DEC against the metallic lithium sheet is 0.8 (V, Li+|Li).

[0154] 5. Secondary battery manufacturing

[0155] The positive electrode sheet, separator, and negative electrode sheet are stacked in this order, and a separator is interposed between the positive electrode sheet and the negative electrode sheet to perform an isolating function. The stack is then wound to obtain an electrode assembly. The electrode assembly is placed in an exterior housing, dried, and then an electrolyte is injected. The lithium ion battery is obtained through processes such as vacuum sealing, standing, chemical formation, and shaping.

[0156] Example 2

[0157] The secondary batteries of Examples 2-1 and 2-2 were manufactured in a manner similar to that of Example 1, and differed from Example 1 in that the type of boron-containing lithium salt was adjusted in Examples 2-1 and 2-2.

[0158] The secondary batteries of Examples 2-3 and 2-4 were manufactured in a manner similar to that of Example 1, and differed from Example 1 in that the type of ester-based additive was adjusted in Examples 2-3 and 2-4.

[0159] Example 3

[0160] The secondary batteries of Examples 3-1 to 3-5 were manufactured in a manner similar to that of Example 1, and differed from Example 1 in that the amount of boron-containing lithium salt added was adjusted in Examples 3-1 to 3-5.

[0161] Example 4

[0162] The secondary batteries of Examples 4-1 to 4-4 were manufactured in a manner similar to that of Example 1, and differed from Example 1 in that the amount of the ester-based additive added was adjusted in Examples 4-1 to 4-4.

[0163] Example 5

[0164] The secondary batteries of Examples 5-1 to 5-4 were manufactured in a manner similar to that of Example 1, and differed from Example 1 in that the amount of ion-conductive lithium salt added was adjusted in Examples 5-1 to 5-4.

[0165] Example 6

[0166] The secondary batteries of Examples 6-1 and 6-2 were manufactured in a manner similar to that of Example 1, and differed from Example 1 in that the type of ion-conductive lithium salt was adjusted in Examples 6-1 and 6-2.

[0167] The data for Examples 1 to 6 and the Comparative Example are shown in Tables 1 and 2.

[0168] [Table 1]

[0169] [Table 2]

[0170] Testing Part

[0171] (1) Testing the cycle performance of secondary batteries at room temperature

[0172] At 25°C, the secondary battery was charged to 4.4V at a constant current of 1C, and continued charging at a constant voltage until the current became 0.05C. At this time, the secondary battery was in a 100% state of charge (100% SOC), and the charge capacity at this time was recorded as the first charge capacity. After leaving the secondary battery to stand for 5 minutes, it was discharged to 2.8V at a constant current of 1C, which was one cycle charge / discharge process, and the discharge capacity at this time was recorded as the first discharge capacity. The secondary battery was subjected to a cycle charge / discharge test according to the above method, and the discharge capacity after each cycle was recorded. Capacity retention rate (%) of the secondary battery after 600 cycles at 25°C = discharge capacity after 600 cycles / first discharge capacity x 100%.

[0173] (2) Testing gas generation performance of secondary batteries after storage at 70°C

[0174] The safety performance of a secondary battery can be characterized by testing the secondary battery's gas generation performance after storage at high temperature.

[0175] Test method for gas generation performance after storage: The cell volume of the soft package product was tested by the drainage method at room temperature of 25°C, and the cell volume at this time was recorded as the initial volume mL. Then, the capacity was tested, and the battery was left at 70°C for 6 hours, and the secondary battery was charged to 4.4V at a constant current of 1C, and charging was continued at a constant voltage until the current became 0.05C, and the discharge capacity at this time was recorded as the actual capacity Ah of the secondary battery. Then, the soft package secondary battery was charged to 4.4V at 0.33C, and the secondary battery was placed in a thermostat at 60°C and stored for 5 days, after which it was taken out, and at this time, the secondary battery was tested by the drainage method, and the volume of the secondary battery was recorded as the volume mL after 5D storage. The volume change of the secondary battery after 5 days of storage at 70°C (mL / Ah) = (volume after 5D storage - initial volume) / actual capacity of the secondary battery.

[0176] (3) Testing the utilization rate of electrolyte The method for measuring the mass of the electrolyte in the secondary battery after cycling at 25°C is to charge and discharge the secondary battery product at 25°C for 10 cycles at a constant current of 0.33C rate and leave it for 5 minutes. The secondary battery is discharged to the discharge end voltage (for safety reasons, the secondary battery is generally in a fully discharged state), and then centrifuged. First, the liberated electrolyte is poured out from the injection hole and collected, and then the bare cell parts such as the remaining electrode sheet and separator are centrifuged. The centrifugation is repeated until the rotation speed of the centrifuge is greater than 10,000 rpm and there is no obvious liquid after centrifugation to collect the electrolyte. The total amount of electrolyte collected is the mass g of the excess electrolyte in the cell, and the utilization rate g of the electrolyte amount is the mass of the excess electrolyte in the cell / mass of the product cell x 100%.

[0177] Test results

[0178] The effect of the present application on improving the performance of secondary batteries is shown in Table 3.

[0179] [Table 3]

[0180] As can be seen from Table 3, the comparative example does not contain boron-containing lithium salt and ester-based additive, and the overall performance of the secondary battery, especially its cycle performance and safety performance, is relatively poor.

[0181] In the examples of the present application, the type and content of the boron-containing lithium salt or the type and content of the ester additive are within the range of the formula: 0.5≦B2 / B1≦5, 0.1≦C / B1≦100, 0.8≦D≦2, 10 -4 The cycle performance and gas generation amount of the secondary battery can be significantly improved by controlling the ratio A1 to A2 so as to satisfy ≦A1+A2≦10. In addition, the performance of the secondary battery can be further improved by adding an ion-conductive lithium salt to the electrolyte.

[0182] Although the present application has been described with reference to the preferred embodiments, various improvements may be made without departing from the scope of the present application, or some of the components may be replaced with equivalents. In particular, as long as there is no structural contradiction, the technical features mentioned in each embodiment may be arbitrarily combined. The present application is not limited to the specific embodiments disclosed above, but includes all aspects included in the scope of the claims.

Claims

1. A secondary battery, A positive electrode sheet; a negative electrode sheet including a negative electrode active material; an electrolyte solution including a first additive and a carbonate ester solvent, the first additive including a boron-containing lithium salt and an ester-based additive, and the electrolyte solution being disposed so as to form a solid electrolyte interfacial film on a surface of the negative electrode active material; The discharge capacity of the secondary battery is B1 Ah, The amount of gas generation change of the secondary battery is B2 mL, The mass of the electrolyte is C g, The reduction potential of the first additive with respect to metallic lithium is D (V, vs Li ＋ |Li), The mass percentage of the boron-containing lithium salt with respect to the total mass of the electrolyte solution is A1%, and the mass percentage of the ester-based additive with respect to the total mass of the electrolyte solution is A2%, The secondary battery has a structure in which 0.5≦B2 / B1≦5, 0.1≦C / B1≦100, 0.8≦D≦2, 10 －４ ≦A1+A2≦10 is satisfied; Secondary battery.

2. The secondary battery satisfies at least one of the following conditions (1) to (4): (1) 1≦B2 / B1≦5, (2) 1≦C / B1≦5, (3) 0.85≦D≦2; (4) 3≦A1+A2≦10; The secondary battery according to claim 1 .

3. The reduction potential of the boron-containing lithium salt with respect to metallic lithium is defined as D1 (V, vs Li ＋ |Li), where 0.85≦D1≦2, and optionally 0.85≦D1≦1.8; and / or The reduction potential of the ester additive with respect to metallic lithium is D2 (V, vs Li ＋ |Li), where 0.85≦D2≦2, and optionally 0.85≦D2≦1.2; The secondary battery according to claim 1 or 2.

4. The molecular formula of the boron-containing lithium salt is LiBF ａ O ｂ C ｃ P ｄ and in the molecular formula, 0≦a≦4, 0≦b≦8, 0≦c≦4, and 0≦d≦4. The secondary battery according to claim 1 .

5. The boron-containing lithium salt is lithium tetrafluoroborate LiBF ４ , Lithium borodioxalate LiBOB and Lithium difluoroborate LiDFOB; The secondary battery according to claim 4 .

6. The electrolyte further comprises an ionically conductive lithium salt; The ionically conductive lithium salt is lithium hexafluorophosphate LiPF ６ , lithium difluorophosphate LiPO ２ F ２ , lithium difluorooxalyl phosphate LiDODFP, lithium tetrafluorooxalyl phosphate LiDFBP, lithium bisfluorosulfonylimide LiFSI, lithium bistrifluoromethanesulfonylimide LiTFSI, lithium fluorosulfonate LiFSO ３ , lithium bistrifluoromethanesulfonylimide LiTFSI, lithium nitrate LiNO ３ , Lithium perchlorate LiClO ４ , lithium hexafluoroantimonate LiSbF ６ and lithium hexafluoroarsenate LiAsF ６ One or more of the following may be included: The secondary battery according to claim 1 .

7. The mass percentage of the ion-conductive lithium salt is A3%, calculated based on the total mass of the electrolyte solution; The secondary battery satisfies 5≦A3≦25, optionally 10≦A3≦20; The secondary battery according to claim 6.

8. The carbonate ester solvent is A cyclic carbonate solvent having a mass percentage of A4% relative to the total mass of the electrolyte; A chain carbonate ester solvent having a mass percentage of A5% relative to the total mass of the electrolyte solution; The secondary battery satisfies 1≦A5 / A4≦10, Optionally, 5≦A4≦50 and / or 50≦A5≦70; The secondary battery according to claim 1 .

9. The cyclic carbonate solvent comprises one or more of ethylene carbonate EC, propylene carbonate PC, vinylene carbonate VC, fluoroethylene carbonate FEC, difluoroethylene carbonate DFEC, vinylethylene carbonate VEC, and dioctyl carbonate CC; and / or The chain carbonate ester solvent includes one or more of ethyl allyl carbonate AEC, diphenyl carbonate DPC, methyl allyl carbonate MAC, polycarbonate VA, diethyl carbonate DEC, ethyl methyl carbonate EMC, methyl propyl carbonate MPC, ethyl propyl carbonate EPC, methyl butyl carbonate MBC, methyl acetate MA, ethyl acetate EA, methyl propionate MP, and ethyl propionate EP. The secondary battery according to claim 8.

10. The positive electrode sheet contains a positive electrode active material, The molecular formula of the positive electrode active material is LiNi ｘ Co ｙ Mn ｚ M １－ｘ－ｙ－ｚ O ２ Or LiNi ａ Co ｂ A ｃ N １－ａ－ｂ－ｃ O ２ In the molecular formula, M and N are each independently any one selected from Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, and Ti, and 0≦y≦1, 0≦x<1, 0≦z≦1, x+y+z≦1, 0≦a≦1, 0≦b≦1, 0≦c≦1, a+b+c≦1. The secondary battery according to claim 1 .

11. A secondary battery comprising the secondary battery according to any one of claims 1 to 10. Battery module.

12. The battery module according to claim 11, Battery pack.

13. A battery pack comprising the secondary battery according to any one of claims 1 to 10, the battery module according to claim 11, or the battery pack according to claim 12. Power consumption equipment.

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