Secondary battery and electrical device

Abstract

The present application provides a secondary battery and an electrical device. According to the present application, a battery negative electrode sheet, a negative electrode active material and an electrolyte are controlled to satisfy formula (I), thereby ensuring good cycle and storage stability of the secondary battery.

Description

Secondary battery and electrical equipment 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 recent years, batteries, such as lithium-ion batteries, have been widely used in consumer electronics due to their high voltage platform, high energy density, lack of memory effect, and long lifespan. At the same time, increasingly severe global environmental challenges and fossil fuel shortages are rapidly driving the development of electric vehicles. As a core component of electric vehicles, lithium-ion batteries are increasingly demanding higher requirements for cycle performance and storage stability.

[0003] Therefore, there is an urgent need to provide a secondary battery with excellent cycle and storage stability.

[0004] Summary of the Invention

[0005] In order to provide a secondary battery with excellent cycle and storage stability, the present application comprehensively designs the design of the battery negative electrode plate, the intrinsic parameters of the negative electrode active material and the amount of electrolyte additive added, so as to quickly determine the reasonable range of the electrolyte additive addition amount to ensure that the secondary battery has good performance requirements.

[0006] To achieve the above objectives, in a first aspect, the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer comprises a negative electrode active material, the electrolyte comprises a phosphate additive, and the secondary battery satisfies the following relationship:

[0007] Wherein, mg / Ah represents the injection coefficient of the electrolyte in the secondary battery;

[0008] C represents the mass percentage concentration of the phosphate additive in the electrolyte of the secondary battery;

[0009] P g / cm 3 represents the compaction density of the negative electrode active material layer;

[0010] D V50 μm represents the particle size corresponding to 50% of the cumulative volume of the negative electrode active material;

[0011] W g / 1540.25mm 2 represents the area density of the negative electrode active material layer.

[0012] In some embodiments, the secondary battery satisfies:

[0013] In some embodiments, the electrolyte has an injection coefficient of 2 to 5 g / Ah in mg / Ah.

[0014] In some embodiments, the concentration C of the phosphate additive in the electrolyte is 0.1-3 wt %.

[0015] In some embodiments, the compaction density of the negative electrode active material layer is P g / cm 3 1.2~1.8g / cm 3 .

[0016] In some embodiments, the D of the negative electrode active material V50 μm is 4 to 18 μm.

[0017] In some embodiments, the surface density of the negative electrode active material layer is W g / 1540.25 mm 2 0.08~0.28g / 1540.25mm 2 .

[0018] In some embodiments, the electrolyte further includes a lithium salt, and the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalatophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalatoborate, and lithium bis(oxalatoborate).

[0019] In some embodiments, the electrolyte further includes an organic solvent, and the organic solvent includes at least one of a cyclic carbonate, a chain carbonate, and a chain carboxylate.

[0020] In some embodiments, the phosphate additive includes at least one of tris(trimethylsilyl)phosphate and tripropargyl phosphate.

[0021] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes lithium nickel cobalt oxide and / or lithium iron oxide.

[0022] In some embodiments, the negative electrode active material includes at least one of graphite and silicon-based materials.

[0023] In a second aspect of the present application, an electrical device is provided, wherein the electrical device includes the secondary battery described above.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] This application controls the design of the battery's negative electrode plate, the intrinsic parameters of the negative electrode active material, and the amount of electrolyte additives added, so as to control the SEI membrane of the prepared battery to have better active ion conductivity, thereby providing a basis for improving the battery's circulation, storage, and gas production. DETAILED DESCRIPTION

[0026] To better illustrate the purpose, technical solutions and advantages of the present application, the present application will be further described below in conjunction with specific examples, but the examples do not limit the present application in any form. Unless otherwise specified, the reagents, methods and equipment used in the present application are conventional reagents, methods and equipment in the art. Unless otherwise specified, the reagents and materials used in the present application are commercially available.

[0027] An embodiment of the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer comprises a negative electrode active material. The electrolyte comprises a phosphate additive. The secondary battery satisfies the following relationship:

[0028] Wherein, mg / Ah represents the injection coefficient of the electrolyte in the secondary battery;

[0029] C represents the mass percentage concentration of the phosphate additive in the electrolyte of the secondary battery;

[0030] P g / cm 3 represents the compaction density of the negative electrode active material layer;

[0031] D V50 μm represents the particle size corresponding to 50% of the cumulative volume of the negative electrode active material;

[0032] W g / 1540.25mm 2 represents the area density of the negative electrode active material layer.

[0033] In secondary batteries, additives, as important components of the electrolyte, can optimize the composition of the battery's SEI film and play a significant role in the battery's cycling performance and storage stability. Electrolyte consumption is primarily due to the negative electrode film formation reaction and side reactions caused by electron tunneling during the cycling process. This application comprehensively designs the design of the battery's negative electrode plate, the intrinsic parameters of the negative electrode active material, and the amount of additives added to the electrolyte, controlling the correlation value within an appropriate range to ensure that the secondary battery has good cycling and storage stability.

[0034] In some embodiments of the present application, the injection coefficient mg / Ah of the electrolyte is 2 to 5 g / Ah. For example, the injection coefficient mg / Ah of the electrolyte can be 2 g / Ah, 3 g / Ah, 4 g / Ah, 5 g / Ah or a range consisting of any two of the above values. In order to ensure the normal circulation of the secondary battery throughout its life cycle, it is necessary to ensure that the battery still has a sufficient amount of electrolyte after formation to ensure the wettability of the electrode, to ensure the formation of a stable SEI film at the negative electrode and to have a small internal resistance. By limiting the injection coefficient of the electrolyte to the above reasonable range, it is possible to prevent black spots from appearing on the interface due to insufficient electrolyte and battery failure due to excessive internal resistance, while avoiding safety hazards caused by excessive electrolyte, and effectively improving the service life of the battery.

[0035] The secondary battery further satisfies:

[0036] In some embodiments of the present application, the concentration C of the phosphate additive in the electrolyte is 0.1 to 3 wt%. For example, the concentration C of the phosphate additive can be 0.1 wt%, 0.5 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.5 wt%, 2.8 wt%, 3 wt% or a range consisting of any two of the above values. Phosphate additives can optimize the composition of the SEI film of the secondary battery and play an important role in the performance of the secondary battery. The addition of additives can improve the conductivity of ions between the positive and negative electrodes, reduce the internal impedance of the battery, and can also form an SEI film at the negative electrode of the battery to improve the cycle stability of the battery. In some embodiments, when the phosphate additive includes more than one, those skilled in the art can determine without a doubt that the mass percentage concentration C of the phosphate additive in the electrolyte refers to the sum of the mass percentage concentrations of all phosphate additives in the electrolyte.

[0037] In some embodiments of the present application, the phosphate additive includes at least one of tris(trimethylsilyl)phosphate (TMSP) and tripropargyl phosphate (TPP).

[0038] In some embodiments of the present application, the compaction density of the negative electrode sheet is P g / cm 3 1.2~1.8g / cm 3 For example, the compaction density of the negative electrode sheet is P g / cm 3 It can be 1.2g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3, 1.7g / cm 3 , 1.8g / cm 3 Or the range formed by any two of the above values. When the compaction density is within the above appropriate range, the prepared battery has both high energy density and good cycle and storage stability.

[0039] In some embodiments of the present application, the D of the negative electrode active material V50 μm is 4~18μm, D V50 The particle size corresponding to the cumulative volume percentage of the negative electrode active material reaches 50%. V50 μm can be 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm or a range consisting of any two of the above values. V50 The value of is within this range, which can ensure that the negative electrode active material and the electrolyte are fully in contact and infiltrated, which is conducive to the rapid diffusion of ions in the negative electrode active material; it has a suitable specific surface area and will not expose too many active sites to consume the electrolyte and induce more side reactions, so that the battery has better cycle and storage stability.

[0040] In some embodiments of the present application, the surface density of the negative electrode active material layer is W g / 1540.25 mm 2 0.08~0.28g / 1540.25mm 2 For example, the surface density of the negative electrode active material layer is W g / 1540.25 mm 2 It can be 0.08g / 1540.25mm 2 , 0.12g / 1540.25mm 2 、0.14g / 1540.25mm 2 、0.16g / 1540.25mm 2 、0.18g / 1540.25mm 2 、0.2g / 1540.25mm 2 、0.22g / 1540.25mm 2 , 0.24g / 1540.25mm 2 、0.26g / 1540.25mm 2 、0.28g / 1540.25mm 2 Or the range formed by any two of the above values. When the surface density of the negative electrode active material layer is within an appropriate range, it can provide more lithium insertion sites for the negative electrode and improve the polarization and lithium precipitation phenomena during the charge and discharge process of the battery.

[0041] It should be noted that in this application, the surface density of the negative electrode active material layer is measured by using a mold to extract a fixed area of ​​the negative electrode active material layer and weighing it, and then calculating it according to "weight / mold area". The area of ​​the negative electrode active material layer extracted by the mold in this application is 1540.25mm 2 .

[0042] Among the components of the secondary battery of the present application, an electrolyte salt is also added to the electrolyte. For example, in a lithium-ion secondary battery, the electrolyte salt is a lithium salt. Common lithium salts for lithium-ion batteries in the art can be used in the present application. For example, the lithium salt includes but is not limited to at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate, lithium difluorooxalatophosphate (LiDFOP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorooxalatoborate (LiDFOB), and lithium bis(oxalatoborate) (LiBOB).

[0043] Among the components of the secondary battery of the present application, the electrolyte further includes an organic solvent, and the organic solvent includes but is not limited to at least one of a cyclic carbonate, a chain carbonate, and a chain carboxylic acid ester. Among them, the cyclic carbonate can be selected from one or a combination of propylene carbonate (PC), ethylene carbonate (EC), γ-butyrolactone (GBL), butylene carbonate (BC), and fluoroethylene carbonate (FEC); the chain carbonate can be selected from one or a combination of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), and methylpropyl carbonate (MPC); the chain carboxylic acid ester can be selected from one or a combination of ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), and ethyl butyrate (EB).

[0044] Among the components of the secondary battery of the present application, the electrolyte may further include other additives, for example, including but not limited to sulfur-based additives.

[0045] In some embodiments of the present application, the positive electrode active material includes lithium nickel cobalt oxide and / or iron lithium oxide. In some embodiments, the lithium nickel cobalt oxide includes a molecular formula of Li x Ni a Co b M c O2 compound, wherein in the molecular formula, M is one or both of Mn and Al, 0.95≤x≤1.2, 0<a<1, 0<b<1, 0<c<1, a+b+c=1.

[0046] In some embodiments of the present application, the negative electrode active material includes at least one of graphite and silicon-based materials.

[0047] In some embodiments of the present application, the secondary battery has a resistance less than or equal to 20 mΩ at 25° C. When the resistance of the battery at 25° C. is within this range, the secondary battery has better overall performance.

[0048] In a second aspect of the present application, an electrical device is provided, wherein the electrical device includes the secondary battery described above.

[0049] The following are specific examples of the present application, and the technical solutions of the present application are further described in conjunction with the examples, but the present application is not limited to these examples. The reagents, methods and equipment used in this application, unless otherwise specified, are conventional reagents, methods and equipment in the art.

[0050] Example 1

[0051] This embodiment provides a secondary battery, and a preparation method thereof includes the following steps:

[0052] Preparation of positive electrode sheet

[0053] The positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 O2 (denoted as NCM622), conductive agent acetylene black, and binder PVDF are mixed in a mass ratio of 96:2:2, and 1-methyl-2-pyrrolidone (NMP) is added and evenly dispersed to prepare a uniform positive electrode slurry. The positive electrode slurry is coated on the positive electrode current collector aluminum foil, and after drying, cold pressing, and cutting, a positive electrode sheet with a positive electrode active material layer is obtained. The compaction density of the positive electrode active material layer is 3.6 g / cm 3 .

[0054] Preparation of negative electrode sheet

[0055] The negative electrode active material graphite, the conductive agent acetylene black, the thickener carboxymethyl cellulose (CMC) and the binder SBR were mixed uniformly in a mass ratio of 96.4:1:1.2:1.4, and uniformly dispersed in deionized water to prepare a uniform negative electrode slurry. The negative electrode slurry was coated on the negative electrode current collector copper foil, dried, cold pressed, and cut to obtain a negative electrode sheet provided with a negative electrode active material layer. The parameters of the negative electrode sheet are:

[0056] Particle size D of negative electrode active material V50 :12μm;

[0057] Negative electrode active material layer compaction density P: 1.6g / cm 3 ;

[0058] Negative electrode active material layer density W: 0.122g / 1540.25mm 2 .

[0059] Preparation of electrolyte

[0060] At room temperature (25±5°C), in a glove box filled with argon (H2O<1ppm, O2<1ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of 30:50:20 and heated to 400°C. The molecular sieve is used to remove water to obtain a mixed solvent, and lithium salts (common lithium salts for lithium ion batteries in the art can be used in this application, for example, the lithium salts include but are not limited to lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bisfluorosulfonyl imide (LiFSI), lithium difluorophosphate, lithium difluorooxalatophosphate (LiDFOP), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium difluorooxalatoborate (LiDFOB), lithium bisoxalatoborate (LiBOB) at least one; this embodiment exemplarily uses LiPF6; the concentration of the lithium salt described in this application can be determined by conventional screening by those skilled in the art) are added gradually to the obtained mixed solvent, and the mixture is stirred continuously and cooled with dry ice to ensure that the electrolyte temperature does not rise by more than 2°C. LiPF6 can be continued to be added to control the mass fraction of the lithium salt LiPF6 in the electrolyte to 12.5%, and finally a colorless transparent liquid is obtained. Then, tris(trimethylsilyl) phosphate, an additive equivalent to 0.5 wt% of the total mass of the electrolyte, is added and stirred evenly to obtain the electrolyte used in this embodiment.

[0061] Secondary battery assembly

[0062] The prepared positive electrode sheet, separator (commercially available polypropylene), and negative electrode sheet are stacked in order with the separator placed between the positive and negative electrode sheets. After winding, hot pressing and shaping, and tab welding, a bare cell is obtained. The bare cell is placed in an outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24h. The configured electrolyte is injected into the dried battery, allowed to stand, formed, and divided to complete the preparation of the lithium-ion battery. The battery injection coefficient m is 2.5g / Ah.

[0063] Referring to the preparation method of Example 1, relevant parameters of the secondary battery during the preparation process were changed (see Table 1 for details) to obtain different secondary batteries.

[0064] Table 1 Relevant parameters of secondary batteries used in the examples and comparative examples of this application

[0065] The performance of the secondary batteries obtained in the above examples and comparative examples was tested. The specific test items, test methods and results are as follows:

[0066] 1. 25℃ Cyclic Test: In a 25℃ constant temperature box, perform cyclic charge and discharge tests at 1C charge and 1C discharge, and record the number of cycles when the discharge capacity retention rate of the secondary battery reaches 85%;

[0067] 2. 45°C cycle test: In a 45°C constant temperature box, perform cyclic charge and discharge tests at 1C charge and 1C discharge, and record the number of cycles at which the capacity retention rate of the secondary battery reaches 85% of the initial discharge capacity;

[0068] 3. 100% SOC (fully charged state), store in a 60°C oven, test capacity recovery every 7 days, and record the longest number of days the capacity can be maintained at 90% or above of the initial capacity;

[0069] 4. 100% SOC (full charge state), 70℃ oven storage, every 5 days using the drainage method to test the volume change rate (%) of the secondary battery, volume change rate = (V t -V0) / V0*100%,V t is the volume on day t, V0 is the volume of the initial secondary battery, and the maximum number of days (d) during which the volume change rate is controlled within 10% is recorded;

[0070] 5. Resistance (DCR) test at 25°C: Discharge (DC) at 1C to 2.5V; charge (CC) at 1C to 4.25V; discharge (DC) at 1C for 30min; discharge (DC) at 5C for 1s; charge (CC) at 5C for 10s. Measure resistance (mΩ) after each cycle.

[0071] Table 2 Performance test results of secondary batteries prepared in Examples and Comparative Examples

[0072] From the above results we can see that:

[0073] When the formula value is within the given range, the overall performance is good, but when the formula value is lower than the given lower limit, the cycle, storage, and gas production performance of the secondary battery are poor; and when the formula value is greater than the given upper limit, the cycle and storage of the battery deteriorate, and the resistance deteriorates significantly.

[0074] In summary, by establishing the relationship between the negative electrode design parameters and the electrolyte additive content, the electrolyte additive content is ensured to be within a reasonable range, thereby ensuring that the secondary battery has good performance.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and are not intended 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 negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer comprises a negative electrode active material, the electrolyte comprises a phosphate additive, and the secondary battery satisfies the following relationship: Wherein, mg / Ah represents the injection coefficient of the electrolyte in the secondary battery; C represents the mass percentage concentration of the phosphate additive in the electrolyte of the secondary battery; P g / cm 3 represents the compaction density of the negative electrode active material layer; D V50 μm represents the particle size corresponding to 50% of the cumulative volume of the negative electrode active material; W g / 1540.25mm 2 represents the surface density of the negative electrode active material layer.

2. The secondary battery according to claim 1, wherein The secondary battery satisfies the following relationship:

3. The secondary battery according to claim 1, wherein The electrolyte injection coefficient mg / Ah is 2 to 5 g / Ah.

4. The secondary battery according to claim 1, wherein The concentration C of the phosphate additive in the electrolyte is 0.1-3 wt %.

5. The secondary battery according to claim 1, wherein The compaction density of the negative electrode active material layer is P g / cm 3 1.2~1.8g / cm 3 .

6. The secondary battery according to claim 1, wherein The negative electrode active material D V50 μm is 4~18μm.

7. The secondary battery according to claim 1, wherein The surface density of the negative electrode active material layer is W g / 1540.25 mm 2 0.08~0.28g / 1540.25mm 2 .

8. The secondary battery according to any one of claims 1 to 7, wherein: The electrolyte further includes a lithium salt and an organic solvent, and the electrolyte satisfies at least one of the following conditions: (1) The lithium salts include lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate At least one of lithium, lithium difluorooxalate phosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalate borate, and lithium bis(oxalate borate); (2) the phosphate additive includes at least one of tris(trimethylsilyl) phosphate and tripropargyl phosphate; (3) The organic solvent includes at least one of cyclic carbonate, chain carbonate, and chain carboxylic acid ester.

9. The secondary battery according to any one of claims 1 to 7, wherein: The positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, the positive electrode active material layer comprises a positive electrode active material, and the positive electrode active material comprises lithium nickel cobalt oxide and / or iron lithium oxide; and / or the negative electrode active material comprises at least one of graphite and silicon-based materials.

10. An electrical device, comprising the secondary battery according to any one of claims 1 to 9.

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