Secondary battery and device containing the same

Abstract

The present application provides a secondary battery and a device containing the secondary battery, wherein the secondary battery comprises a negative electrode plate and an electrolyte; the negative electrode plate comprises a negative electrode current collector and a negative electrode film disposed on at least one surface of the negative electrode current collector and comprising a negative electrode active material; the electrolyte comprises an electrolyte salt and an organic solvent; wherein the negative electrode active material comprises a silicon-based material; the organic solvent comprises ethylene carbonate (EC) and ethyl methyl carbonate (EMC), wherein the weight proportion of ethylene carbonate (EC) in the organic solvent is ≤10%, and the weight proportion of ethyl methyl carbonate (EMC) in the organic solvent is 70% to 95%. The secondary battery of the present application and the device containing the secondary battery can have both good high-temperature storage performance and high-temperature cycle performance under the premise of high energy density.

Description

Technical Field

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

[0002] With the increasing exhaustion of fossil energy and the increasing pressure of environmental pollution, the automotive industry urgently needs a new type of energy to drive it. Secondary batteries stand out due to their high energy density, no memory effect, and high operating voltage, making them the preferred solution for the current new energy vehicle power supply. The new energy vehicle industry usually requires its power supply to have high energy density, long cycle life and other performance, but this is a big challenge for traditional secondary batteries.

[0003] At present, using high specific capacity silicon-based materials as negative electrode active materials for secondary batteries can effectively improve the energy density of secondary batteries. However, the volume of silicon-based materials expands severely during the charge and discharge cycle, causing a sharp drop in the electrochemical performance of the secondary battery.

[0004] Therefore, in order to meet the needs of electric vehicles for secondary battery performance, it is necessary to provide a secondary battery with good comprehensive performance. Summary of the invention

[0005] In view of the problems existing in the background technology, the present application provides a secondary battery and a device containing the secondary battery. The secondary battery can have both good high-temperature storage performance and high-temperature cycle performance under the premise of high energy density.

[0006] In order to achieve the above-mentioned purpose, the secondary battery provided in the first aspect of the present application includes: a negative electrode plate and an electrolyte; the negative electrode plate includes a negative electrode collector and a negative electrode film arranged on at least one surface of the negative electrode collector and including a negative electrode active material; the electrolyte includes an electrolyte salt and an organic solvent; wherein the negative electrode active material includes a silicon-based material; the organic solvent includes ethylene carbonate (EC) and ethyl methyl carbonate (EMC), and the weight proportion of ethylene carbonate (EC) in the organic solvent is ≤10%, and the weight proportion of ethyl methyl carbonate (EMC) in the organic solvent is 70% to 95%.

[0007] In a second aspect of the present application, a device is provided, which includes the secondary battery described in the first aspect of the present application.

[0008] This application has at least the following beneficial effects:

[0009] The secondary battery of the present application has a negative electrode including a silicon-based material, and the organic solvent in the electrolyte includes a specific content of ethylene carbonate (EC) and ethyl methyl carbonate (EMC). Under the combined action of the above substances, the secondary battery has good high-temperature storage performance and high-temperature cycle performance. The device of the present application includes the secondary battery, and thus has at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a schematic diagram of one embodiment of a secondary battery.

[0011] Figure 2 is a schematic diagram of an embodiment of a battery module.

[0012] Figure 3 is a schematic diagram of one embodiment of a battery pack.

[0013] Figure 4 yes Figure 3 Exploded diagram of .

[0014] Figure 5 It is a schematic diagram of one embodiment of a device in which a secondary battery is used as a power source.

[0015] The reference numerals are described as follows:

[0016] 1 battery pack

[0017] 2 upper box

[0018] 3 lower cabinets

[0019] 4 battery modules

[0020] 5. Secondary battery DETAILED DESCRIPTION

[0021] The secondary battery according to the present application and a device including the secondary battery are described in detail below.

[0022] The secondary battery described in the present application includes: a negative electrode plate and an electrolyte; the negative electrode plate includes a negative electrode collector and a negative electrode film arranged on at least one surface of the negative electrode collector and including a negative electrode active material; the electrolyte includes an electrolyte salt and an organic solvent; wherein the negative electrode active material includes a silicon-based material; the organic solvent includes ethylene carbonate (EC) and ethyl methyl carbonate (EMC), the weight proportion of ethylene carbonate (EC) in the organic solvent is ≤10%, and the weight proportion of ethyl methyl carbonate (EMC) in the organic solvent is 70% to 95%.

[0023] In order to improve the energy density of secondary batteries, the negative electrode active material of the present application adopts silicon-based materials, but the silicon-based negative electrode active material has a serious volume effect during the battery cycle, which limits its practical application. After a lot of research, the inventors of the present application found that when a specific amount of organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are added to the electrolyte at the same time, the high temperature storage and high temperature cycle performance of the secondary battery using silicon-based materials as negative electrode active materials can be effectively improved. The inventor speculates that it may be because when a specific amount of EC and EMC solvents are added to the electrolyte at the same time, the electrolyte salt can be well dissociated, and at the same time, under their joint action, the gas production of the battery during the cycle can be effectively reduced, so that the secondary battery can improve the energy density while taking into account good high temperature cycle performance and high temperature storage performance.

[0024] In the secondary battery described in the first aspect of the present application, preferably, the weight proportion of the ethylene carbonate (EC) in the organic solvent is ≤5%.

[0025] In the secondary battery described in the first aspect of the present application, preferably, the weight proportion of the ethyl methyl carbonate (EMC) in the organic solvent is 75% to 95%; more preferably, the weight proportion of the ethyl methyl carbonate (EMC) in the organic solvent is 85% to 95%.

[0026] In the secondary battery described in the first aspect of the present application, preferably, the electrolyte salt includes lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonyl imide (LiFSI), and the concentration of the lithium bisfluorosulfonyl imide (LiFSI) is 0.8mol / L to 1.3mol / L. When the electrolyte includes lithium fluorophosphate (LiPF6) and lithium bisfluorosulfonyl imide (LiFSI) at the same time, and the concentration of the lithium bisfluorosulfonyl imide (LiFSI) is within the given range, the high temperature storage and high temperature cycle performance of the secondary battery can be further improved. More preferably, the concentration of the lithium bisfluorosulfonyl imide (LiFSI) is 0.9mol / L to 1.1mol / L.

[0027] In the secondary battery described in the first aspect of the present application, preferably, the organic solvent may also include one or more of dimethyl carbonate (DMC) and diethyl carbonate (DEC); more preferably, the weight proportion of dimethyl carbonate (DMC) and / or diethyl carbonate (DEC) in the organic solvent is ≤10%.

[0028] In the secondary battery described in the first aspect of the present application, preferably, the electrolyte further includes an additive, and the additive includes one or more of fluoroethylene carbonate (FEC), vinyl sulfate (DTD), 1,3-propane sultone (PS), 1,3-propenyl-sultone (PST), succinic anhydride (SA), tris(trimethylsilyl)borate (TMSB), tris(trimethylsilyl)phosphate (TMSP), lithium difluorooxalatoborate (LiDFOB), and lithium difluorobis(oxalatophosphate) (LiDFOP).

[0029] In the secondary battery described in the first aspect of the present application, preferably, the conductivity of the electrolyte at 25° C. is 7 mS / cm to 9.5 mS / cm, and more preferably, the conductivity of the electrolyte at 25° C. is 7.5 mS / cm to 9.0 mS / cm.

[0030] In the secondary battery described in the first aspect of the present application, preferably, the viscosity of the electrolyte at 25° C. is 3.5 mPa.s to 5.5 mPa.s, and more preferably, the viscosity of the electrolyte at 25° C. is 4 mPa.s to 5 mPa.s.

[0031] In the secondary battery described in the first aspect of the present application, preferably, the silicon-based material includes one or more of elemental silicon, silicon-carbon composites, silicon-oxygen compounds, silicon-nitrogen compounds, and silicon alloys; more preferably, the silicon-based material includes silicon-oxygen compounds.

[0032] In the secondary battery described in the first aspect of the present application, preferably, the negative electrode active material also includes a carbon material; more preferably, the carbon material includes one or more of natural graphite, artificial graphite, hard carbon, and soft carbon; further preferably, the carbon material includes one or more of natural graphite and artificial graphite.

[0033] In the secondary battery described in the first aspect of the present application, preferably, the mass proportion of the silicon-based material in the negative electrode active material is ≥15%; more preferably, the mass proportion of the silicon-based material in the negative electrode active material is 20% to 40%.

[0034] In the secondary battery described in the first aspect of the present application, the type of the negative electrode current collector is not specifically limited and can be selected according to actual needs. Specifically, the negative electrode current collector can be selected from metal foil, such as copper foil.

[0035] In the secondary battery described in the first aspect of the present application, the secondary battery further comprises a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode collector and a positive electrode membrane disposed on at least one surface of the positive electrode collector and comprising a positive electrode active material.

[0036] In the secondary battery according to the first aspect of the present application, preferably, the positive electrode active material includes one or more of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide. As positive electrode active materials of secondary batteries, lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide have the advantages of high specific capacity and long cycle life, and are used in combination with negative electrode active materials including silicon-based materials to further improve the electrochemical performance of the battery.

[0037] In the secondary battery according to the first aspect of the present application, preferably, the positive electrode active material includes Li a Ni b Co c M d M' e O f A g or a Li having a coating layer disposed on at least a portion of the surface a Ni b Co c M d M' e O f A g One or more of the following: 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 0≤e≤0.1, 1≤f≤2, 0≤g≤1, M is selected from one or two of Mn and Al, M' is selected from one or more of Zr, Al, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is selected from one or more of N, F, S, and Cl.

[0038] The coating layer of the positive electrode active material can be a carbon layer, an oxide layer, an inorganic salt layer or a conductive polymer layer. The cycle performance of the secondary battery can be further improved by coating and modifying the surface of the positive electrode active material.

[0039] In the secondary battery described in the first aspect of the present application, further, the positive electrode active material may also include one or more of lithium manganese oxide (such as spinel lithium manganese oxide, layered structure lithium manganese oxide, etc.) and its modified compounds, lithium iron phosphate and its modified compounds, lithium cobalt oxide and its modified compounds.

[0040] In the secondary battery described in the first aspect of the present application, the type of the positive electrode current collector is not specifically limited and can be selected according to actual needs. Specifically, the positive electrode current collector can be selected from metal foil, such as aluminum foil.

[0041] In the secondary battery described in the first aspect of the present application, the secondary battery further comprises a separator. The type of the separator is not specifically limited and can be selected according to actual needs. Specifically, the separator can be selected from one or more of a polyethylene film, a polypropylene film, a polyvinylidene fluoride film, and a multilayer composite film thereof.

[0042] In some embodiments, the secondary battery may include an outer package for packaging the positive electrode sheet, the negative electrode sheet and the electrolyte. As an example, the positive electrode sheet, the negative electrode sheet and the separator may be laminated or wound to form an electrode assembly of a laminate structure or an electrode assembly of a wound structure, and the electrode assembly is packaged in the outer package; the electrolyte is infiltrated in the electrode assembly. The number of electrode assemblies in the secondary battery may be one or more, which can be adjusted according to demand.

[0043] In some embodiments, the outer packaging of the secondary battery may be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, such as one or more of polypropylene PP, polybutylene terephthalate PBT, polybutylene succinate PBS, etc. The outer packaging of the secondary battery may also be a hard shell, such as an aluminum shell, etc.

[0044] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 1 The secondary battery 5 is a square structure as an example.

[0045] In some embodiments, secondary batteries may be assembled into a battery module. The battery module may contain multiple secondary batteries, and the specific number may be adjusted according to the application and capacity of the battery module.

[0046] Figure 2 4 is an example of a battery module. Figure 2 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

[0047] Optionally, the battery module 4 may further include a housing having a housing space, and the plurality of secondary batteries 5 are housed in the housing space.

[0048] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0049] Figure 3 and Figure 4 1 is a battery pack 1 as an example. Figure 3 and Figure 4 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0050] The second aspect of the present application provides a device, which includes the secondary battery described in the first aspect of the present application. The secondary battery can be used as a power source for the device, and can also be used as an energy storage unit for the device. The device includes but is not limited to mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as 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.

[0051] The device can select a secondary battery, a battery module or a battery pack according to its usage requirements.

[0052] Figure 5 The device is used as an example. The device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module can be used.

[0053] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be light and thin, and a secondary battery may be used as a power source.

[0054] The present application is further described below in conjunction with the examples. It should be understood that these examples are only used to illustrate the present application and are not used to limit the scope of the present application.

[0055] The secondary batteries of Examples 1-11 and Comparative Examples 1-3 were prepared according to the following method:

[0056] (1) Preparation of positive electrode sheet

[0057] The positive electrode active material NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O2), binder polyvinylidene fluoride, and conductive agent Super P are mixed in a weight ratio of 98:1:1, N-methylpyrrolidone (NMP) is added, and the system is stirred under the action of a vacuum mixer until the system becomes a uniform and transparent state to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on an aluminum foil; after drying at room temperature, it is transferred to an oven for drying, and then cold pressed and cut to obtain a positive electrode sheet.

[0058] (2) Preparation of negative electrode sheet

[0059] The negative electrode active materials silicon oxide and artificial graphite are mixed in a mass ratio of 2:8, and then mixed with a conductive agent Super P, a thickener sodium carboxymethyl cellulose (CMC-Na), and a binder styrene-butadiene rubber (SBR) in a mass ratio of 92:2:2:4, and deionized water is added to obtain a negative electrode slurry under the action of a vacuum mixer; the negative electrode slurry is evenly coated on the negative electrode current collector copper foil; after drying at room temperature, it is transferred to an oven for drying, and then cold pressed and cut to obtain a negative electrode sheet.

[0060] (3) Preparation of electrolyte

[0061] In an argon atmosphere glove box with a water content of less than 10ppm, the organic solvents are mixed according to a weight ratio to obtain a mixed solvent, and then the fully dried electrolyte salt is dissolved in the mixed solvent, and then additives (8% FEC, 0.5% SA, 0.5% TMSP) are added, and the electrolyte is obtained after mixing evenly. The content of each additive is the weight percentage calculated based on the total weight of the electrolyte. Among them, the composition of the organic solvent, the specific type and content of the electrolyte salt are shown in Table 1. In Table 1, the content of each organic solvent is the weight percentage calculated based on the total mass of the organic solvent, and the concentration of each electrolyte salt is the concentration calculated based on the total concentration of the electrolyte.

[0062] (4) Preparation of isolation membrane

[0063] Polyethylene (PE) film is used as the isolation film.

[0064] (5) Preparation of secondary batteries

[0065] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is placed between the positive and negative electrode sheets to play an isolating role, and then they are wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, and the prepared electrolyte is injected into the dried secondary battery. After vacuum packaging, standing, formation, shaping and other processes, a secondary battery is obtained.

[0066] Table 1 Parameters of Examples 1-11 and Comparative Examples 1-3

[0067]

[0068]

[0069] Next, the test process of the secondary battery is described.

[0070] (1) High temperature storage performance test

[0071] At 60°C, the secondary battery was charged at a constant current of 0.5C to 4.25V, and then charged at a constant voltage of 4.25V to a current of 0.05C. The volume of the lithium-ion battery at this time was tested by the drainage method and recorded as V1. The secondary battery was then placed in a constant temperature box at 60°C, taken out after storage for 30 days, and the volume of the secondary battery at this time was tested and recorded as V2.

[0072] Volume expansion ratio of secondary battery after storage at 60°C for 30 days (%) = [(V2-V1) / V1] × 100%

[0073] (2) High temperature cycle performance test

[0074] At 45°C, charge the secondary battery at a constant current of 1C to 4.25V, then charge at a constant voltage of 4.25V to a current of 0.05C, let stand for 5 minutes, and then discharge at a constant current of 1C to 2.5V. This is the first charge / discharge cycle of the secondary battery. The discharge capacity is recorded as the discharge capacity of the first cycle of the secondary battery. Perform 800 charge / discharge cycles of the secondary battery according to the above method, and record the discharge capacity of the secondary battery after 800 cycles.

[0075] Capacity retention rate (%) of the secondary battery after 800 cycles at 45° C.=(discharge capacity of the secondary battery after 800 cycles / discharge capacity of the secondary battery at the first cycle)×100%.

[0076] Table 2 Performance test results of Examples 1-11 and Comparative Examples 1-3

[0077]

[0078]

[0079] From the test results analysis of Table 2, it can be seen that the organic solvent of the secondary battery of Examples 1-11 includes specific contents of ethylene carbonate (EC) and ethyl methyl carbonate (EMC), which can take into account good high-temperature storage performance and high-temperature cycle performance; in particular, when the electrolyte salt of the secondary battery includes lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonyl imide (LiFSI) at the same time, and the lithium bisfluorosulfonyl imide (LiFSI) meets a specific concentration, as shown in Examples 7-11, the high-temperature storage performance and high-temperature cycle performance of the secondary battery are better.

[0080] The content of ethylene carbonate (EC) in the electrolyte in Comparative Example 1 was greater than 10%, and the high-temperature storage performance and high-temperature cycle performance of the obtained secondary battery were both poor.

[0081] In Comparative Examples 2 and 3, the content of ethylene carbonate (EC) in the electrolyte is greater than 10%, and the content of ethyl methyl carbonate (EMC) does not meet 70% to 95%, and the obtained secondary batteries have poor high-temperature storage performance and high-temperature cycle performance.

Claims

1. A secondary battery comprising: A negative electrode sheet and an electrolyte; the negative electrode sheet comprises a negative electrode current collector and a negative electrode membrane disposed on at least one surface of the negative electrode current collector and comprising a negative electrode active material; the electrolyte comprises an electrolyte salt and an organic solvent; characterized in that: The negative electrode active material includes a silicon-based material; The organic solvent comprises ethylene carbonate and ethyl methyl carbonate, wherein the weight proportion of ethylene carbonate in the organic solvent is greater than 0 and ≤ 10%, and the weight proportion of ethyl methyl carbonate in the organic solvent is 75% to 95%; The electrolyte salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, and the concentration of the lithium bis(fluorosulfonyl)imide is 0.8 mol / L to 1.3 mol / L.

2. The secondary battery according to claim 1, characterized in that: The weight proportion of the ethylene carbonate in the organic solvent is greater than 0 and ≤5%.

3. The secondary battery according to claim 1, characterized in that: The weight proportion of the ethyl methyl carbonate in the organic solvent is 85% to 95%.

4. The secondary battery according to claim 1, characterized in that: The concentration of the lithium bis(fluorosulfonyl)imide (LiFSI) is 0.9 mol / L to 1.1 mol / L.

5. The secondary battery according to claim 1, characterized in that: The organic solvent also includes one or more of dimethyl carbonate and diethyl carbonate.

6. The secondary battery according to claim 5, characterized in that: The mass proportion of the dimethyl carbonate and / or diethyl carbonate in the organic solvent is ≤10%.

7. The secondary battery according to claim 1, characterized in that: The electrolyte also includes additives, which include one or more of fluoroethylene carbonate, vinyl sulfate, 1,3-propane sultone, 1,3-propylene-sultone, vinylene carbonate, succinic anhydride, tris(trimethylsilane)borate, tris(trimethylsilane)phosphate, lithium difluorooxalatoborate, and lithium difluorobisoxalatophosphate.

8. The secondary battery according to claim 1, characterized in that: The conductivity of the electrolyte at 25° C. is 7 mS / cm to 9.5 mS / cm; and / or, The viscosity of the electrolyte at 25° C. is 3.5 mPa·s to 5.5 mPa·s.

9. The secondary battery according to claim 8, characterized in that: The conductivity of the electrolyte at 25° C. is 7.5 mS / cm to 9.0 mS / cm; and / or, The viscosity of the electrolyte at 25° C. is 4 mPa·s to 5 mPa·s.

10. The secondary battery according to claim 1, characterized in that: The silicon-based material includes one or more of elemental silicon, silicon-carbon composites, silicon-oxygen compounds, silicon-nitrogen compounds, and silicon alloys.

11. The secondary battery according to claim 10, characterized in that: The silicon-based material includes a silicon-oxygen compound.

12. The secondary battery according to claim 1, characterized in that: The negative electrode active material further includes a carbon material, and the carbon material includes one or more of natural graphite, artificial graphite, soft carbon, and hard carbon.

13. The secondary battery according to claim 12, characterized in that: The carbon material includes one or more of natural graphite and artificial graphite.

14. The secondary battery according to claim 1, characterized in that: The mass proportion of the silicon-based material in the negative electrode active material is ≥15%.

15. The secondary battery according to claim 14, characterized in that: The mass proportion of the silicon-based material in the negative electrode active material is 20% to 40%.

16. The secondary battery according to claim 1, characterized in that: The secondary battery also includes a positive electrode plate, which includes a positive electrode collector and a positive electrode membrane arranged on at least one surface of the positive electrode collector and including a positive electrode active material, wherein the positive electrode active material includes one or more of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.

17. The secondary battery according to claim 16, characterized in that: The positive electrode active material includes a general formula of Li a Ni b Co c M d M' e O f A g or a Li having a coating layer disposed on at least a portion of the surface a Ni b Co c M d M' e O f A g One or more of the following: 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 0≤e≤0.1, 1≤f≤2, 0≤g≤1, M is selected from one or more of Mn and Al, M' is selected from one or more of Zr, Al, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is selected from one or more of N, F, S, and Cl.

18. The secondary battery according to claim 16, characterized in that: The positive electrode active material also includes one or more of lithium nickel oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium cobalt oxide and modified compounds thereof.

19. A device, characterized in that: The device comprises the secondary battery according to any one of claims 1-18.

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