Secondary battery and electrical device

Abstract

A secondary battery and an electrical device, the secondary battery comprising a negative electrode sheet and an electrolyte solution. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material. The electrolyte solution comprises an additive. The secondary battery satisfies the condition: 0.81≤y≤ 3.41, where [Formula (1)], which can enable the secondary battery to have good cycling performance, low impedance, and a low gas production rate.

Description

Secondary battery and electrical equipment

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 5, 2023, with application number 202311667572.0 and application name “A Secondary Battery and Electrical Equipment”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application belongs to the field of battery technology, and specifically relates to a secondary battery and electrical equipment. Background Art

[0003] Secondary batteries are mainly composed of positive electrodes, negative electrodes, electrolytes and isolation membranes. The materials, composition and battery settings of the positive electrodes, negative electrodes, electrolytes and isolation membranes have a significant impact on the electrochemical performance of the battery. Existing secondary batteries are difficult to reasonably balance the cycle performance, rate performance and expansion performance.

[0004] Application Contents

[0005] An embodiment of the present application provides a secondary battery, aiming to achieve excellent cycle performance, rate performance, and expansion performance; another object of the embodiment of the present application is to provide an electrical device.

[0006] In a first aspect, a secondary battery according to an embodiment of the present application comprises: a negative electrode plate and an electrolyte; the negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material; the electrolyte comprises an additive;

[0007] The secondary battery satisfies: 0.81≤y≤3.41,

[0008] M is the filling coefficient of the secondary battery, in g / Ah;

[0009] C is the mass percentage of the additive in the electrolyte, in %;

[0010] W is the surface density of the negative electrode active material layer in the secondary battery, and the unit is g / 1540.25 mm 2 ;

[0011] S BET is the specific surface area of ​​the negative electrode active material, in m 2 / g;

[0012] P is the compaction density of the negative electrode sheet, in g / cm 3 .

[0013] T is the peeling force of the negative electrode active material layer, and the unit is N / m.

[0014] In some embodiments, 2.4≤M≤6.3.

[0015] In some embodiments, 0.18≤W≤0.49.

[0016] In some embodiments, 1≤S BET ≤2.6.

[0017] In some embodiments, 1≤P≤2.5.

[0018] In some embodiments, the electrolyte includes a lithium salt, satisfying: 0.5≤C / D≤2.0, where D is the molar concentration of the lithium salt in the electrolyte, expressed in mol / L.

[0019] In some embodiments, 1.5≤C≤4.

[0020] In some embodiments, 0.1≤D≤4.

[0021] In some embodiments, 9<T<25.

[0022] In some embodiments, the additive comprises a cyclic carbonate additive.

[0023] In some embodiments, the cyclic carbonate additive includes at least one of vinylene carbonate, fluoroethylene carbonate, bisfluoroethylene carbonate, or vinylethylene carbonate.

[0024] In some embodiments, the lithium salt comprises at least one of LiPF6, LiBF4, LiFSI, LiPO2F2, LiTFSI, LiDFOB, and LiBOB.

[0025] In some embodiments, the negative electrode active material includes at least one of artificial graphite or natural graphite.

[0026] In some embodiments, a secondary battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode collector and a positive electrode active material layer disposed on the positive electrode collector, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a lithium transition metal phosphide.

[0027] In a second aspect, an electric device described in an embodiment of the present application includes the secondary battery, and the secondary battery serves as a power supply for the electric device. Beneficial effects

[0028] The secondary battery described in the embodiment of the present application includes a negative electrode plate and an electrolyte; the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, the negative electrode active material layer includes a negative electrode active material; the electrolyte includes an additive; the secondary battery satisfies: 0.81≤y≤3.41, wherein, In the embodiments of the present application, the secondary battery can have excellent cycle performance, rate performance, and low expansion rate.

[0029] The electrical equipment in the embodiment of the present application may include all the technical features and beneficial effects of the above-mentioned secondary battery, which will not be described in detail here.

[0030] Implementation Methods of the Application

[0031] The following will provide a clear and complete description of the technical solutions in the embodiments of the present application, in conjunction with the embodiments of the present application. It should be noted that the embodiments described are only a portion of the embodiments of the present application, and are not intended to be exhaustive. All other embodiments derived by persons skilled in the art based on the embodiments of the present application without inventive effort are intended to fall within the scope of protection of the present application. Furthermore, in the description of the present application, the term "including" means "including but not limited to." The terms "first," "second," and "third," etc., are used merely as designations and do not impose numerical requirements or establish an order. Various embodiments of the present application may be presented in the form of a range. It should be understood that describing in a range format is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the present application. Therefore, the range description should be considered to specifically disclose all possible subranges and individual numerical values ​​within the range. For example, a range description of 1 to 6 should be considered to specifically disclose subranges, such as 1 to 3, 1 to 4, 1 to 5, 2 to 4, 2 to 6, 3 to 6, etc., as well as individual numerical values ​​within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range.

[0032] Additives in secondary battery electrolytes can form a structurally complete SEI film on the surface of the negative electrode material, improving battery performance such as cycling and gas production. The use of specific additives in combination with specific battery negative electrode materials is crucial to battery performance. The embodiments of the present application provide a secondary battery comprising: a negative electrode plate and an electrolyte; the negative electrode plate comprising a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material; and the electrolyte comprising an additive.

[0033] In this application, the secondary battery satisfies: 0.81≤y≤3.41, wherein,

[0034] Where M is the filling coefficient of the secondary battery, in g / Ah; C is the mass percentage of the additive in the electrolyte, in %; W is the surface density of the negative electrode active material layer in the secondary battery, in g / 1540.25mm 2 ;S BET is the specific surface area of ​​the negative electrode active material, in m 2 / g; P is the compaction density of the negative electrode sheet, in g / cm 3 ; T is the peeling force of the negative electrode active material layer, in N / m. The applicant has found that by controlling the specific surface area of ​​the negative electrode active material of the secondary battery, the surface density of the negative electrode active material layer, the compaction density of the negative electrode sheet, the injection coefficient of the electrolyte, and the peeling force of the negative electrode active material layer to meet the range defined in this application, a dense protective film can be formed on the surface of the negative electrode by adding an additive in an amount that matches the specific surface area of ​​the negative electrode active material and the surface density of the negative electrode active material layer, thereby reducing the consumption of electrolyte during the battery cycle. At the same time, a protective film with a suitable thickness and a better composition is formed, which can enable ions to have a better transmission rate, thereby improving the cycle performance and rate performance of the secondary battery, and making the battery have a lower expansion rate. In addition, the present application further limits the peeling force of the negative electrode active material layer to ensure that the negative electrode will not fall off, thereby avoiding the impact of the battery capacity due to the peeling force of the negative electrode active material layer.

[0035] In some embodiments, the value of y is any value of 0.81, 1.25, 1.35, 1.45, 1.55, 1.7, 1.9, 2.2, 2.4, 2.6, 2.8, 3.0, 3.2, 3.4, 3.41, or a range consisting of any two values.

[0036] In some embodiments, the filling coefficient M of the secondary battery satisfies the following: 2.4 ≤ M ≤ 6.3, for example, M is any value selected from 2.4, 2.5, 2.6, 3, 3.2, 3.5, 4, 4.2, 4.5, 4.7, 5.1, and 6.3, or a range consisting of any two values. The filling coefficient M of the secondary battery of the present application within this range can help reduce battery side reactions, lower battery impedance, reduce battery gas production, inhibit battery expansion, and improve battery cycle performance and rate performance.

[0037] In some embodiments, 0.18≤W≤0.49, such as W(g / 1540.25mm 2 ) is any value selected from 0.18, 0.185, 0.2, 0.25, 0.30, 0.35, 0.40, 0.45, and 0.49, or a range consisting of any two values. An area density W of the negative electrode active material layer within the above range is beneficial for reducing the internal resistance of the battery, increasing the battery discharge capacity, and improving the cycle performance.

[0038] In some embodiments, the surface density W of the negative electrode active material layer of the present application is obtained by the following method: cutting the negative electrode sheet into pieces with an area of ​​1540.25 mm 2 The negative electrode active material layer on both sides of the negative electrode sheet is scraped off and the weight of the negative electrode current collector is weighed as m2g. The surface density of the negative electrode active material layer is W = (m1-m2) g / 1540.25 mm 2 .

[0039] In some embodiments, the specific surface area (m 2 / g) satisfies: 1≤S BET ≤2.6, such as S BET The value of is any value selected from 1.0, 1.1, 1.2, 1.24, 1.3, 1.4, 1.45, 1.82, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, and 2.6, or a range consisting of any two values. The specific surface area of ​​the negative electrode active material of the present application within this range can improve battery performance and reduce the occurrence of side reactions. The specific surface area of ​​the negative electrode material can be obtained by the BET test method.

[0040] In some embodiments, the compaction density P (g / cm 3 ) satisfies: 1≤P≤2.5, such as P is any value of 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.55, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, or a range consisting of any two values. The compaction density of the present application is within this range, which can improve the tightness of the electrode sheet and ensure that the electrode sheet has appropriate porosity, thereby ensuring the wettability of the negative electrode sheet and helping to improve battery performance.

[0041] In some embodiments, the compaction density of the negative electrode sheet of the present application is obtained by the following method: compaction density of the negative electrode sheet = surface density of the negative electrode sheet / (thickness of the negative electrode sheet after rolling - thickness of the negative electrode current collector), unit is g / cm 3 Alternatively, the compaction density is tested using a compaction density meter. The test process can refer to the national standard GB / T24533-2019.

[0042] In some embodiments, the electrolyte includes a lithium salt, an organic solvent, and an additive.

[0043] In some embodiments, 0.1≤C / D≤5.5, wherein D is the molar concentration of the lithium salt in the electrolyte, in mol / L.

[0044] In some embodiments, 0.5≤C / D≤3.5, wherein D is the molar concentration of the lithium salt in the electrolyte, in mol / L.

[0045] In some embodiments, 0.5≤C / D≤2.0, wherein D is the molar concentration of the lithium salt in the electrolyte, in mol / L.

[0046] For example, the C / D ratio can be any value selected from 0.1, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 3.0, or 5.0, or a range consisting of any two values. The C / D ratio of the present application is within the range of 0.5 to 2.0, so that the electrolyte has better kinetic properties.

[0047] In some embodiments, the mass percentage C (%) of the additive in the electrolyte satisfies the following: 1.0 ≤ C ≤ 4, for example, C is any value selected from 1.0, 1.2, 1.5, 2.0, 2.5, 3.0, 3.5, and 4.0, or a range consisting of any two values. Within this range, the additive mass percentage of the present invention enables the formation of a structurally intact SEI film at the negative electrode of the battery, effectively preventing side reactions of the electrolyte on the negative electrode surface, thereby improving battery performance, such as cycle life and gas production.

[0048] In some embodiments, the mass percentage C (%) of the additive in the electrolyte satisfies the following: 1.5 ≤ C ≤ 4. Within this range, the additive mass percentage of the present application enables the formation of a more structurally complete SEI film at the negative electrode of the battery, which can further effectively prevent side reactions of the electrolyte on the negative electrode surface, thereby improving battery performance such as cycle life and gas production.

[0049] In some embodiments, the content of the additive in the electrolyte is tested by GC-MS (gas chromatography-mass spectrometry).

[0050] In some embodiments, 0.1≤D≤4, such as D is any value selected from 0.1, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, or a range consisting of any two values. This can result in the electrolyte having a better ion transport rate.

[0051] In some embodiments, the peel force T (N / m) of the negative electrode active material layer satisfies the following: 9 < T < 25, for example, T is any value selected from 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, and 25, or a range consisting of any two values. Within this range, T in the present application can avoid the defect of battery capacity decay caused by peel force. The peel force limit of the present application ensures that the negative electrode active material layer improves the effectiveness of the battery under the premise of a reasonable formulation design.

[0052] In some embodiments, the peeling force of the negative electrode sheet of the present application can be obtained by a tensile test analyzer, and the test method can be: use double-sided tape to fix the test surface of the negative electrode sheet to be tested on a rigid bracket, and stick the other side on a stainless steel plate, and then fix the stainless steel plate and the current collector on the two clamps of the equipment. Before the test starts, the load and stroke are adjusted to zero, and the test is started. The maximum load value of the force when the current collector is completely peeled off is the peeling force. Repeat the test 5 times and take the average value of the test results.

[0053] In some embodiments, the additive includes a cyclic carbonate additive.

[0054] In some embodiments, the cyclic carbonate additive includes at least one of vinylene carbonate, fluoroethylene carbonate, bisfluoroethylene carbonate, or vinylethylene carbonate.

[0055] In some embodiments, the lithium salt comprises at least one of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiFSI (lithium bis(fluorosulfonyl)imide), LiPO2F2 (lithium difluorophosphate), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiDFOB (lithium difluorooxalatoborate), and LiBOB (lithium bis(oxalatoborate)).

[0056] In some embodiments, the lithium salt includes LiPF6 (lithium hexafluorophosphate), and at least one of LiBF4 (lithium tetrafluoroborate), LiFSI (lithium bis(fluorosulfonyl)imide), LiPO2F2 (lithium difluorophosphate), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiDFOB (lithium difluorooxalatoborate), and LiBOB (lithium bis(oxalatoborate)).

[0057] In some embodiments, the lithium salt comprises LiPF6 (lithium hexafluorophosphate), LiFSI (lithium bis(fluorosulfonyl)imide), or LiTFSI (lithium bis(trifluoromethanesulfonyl)imide).

[0058] In some embodiments, the content of LiPF6 accounts for 20% to 80% of the total amount of lithium salt.

[0059] In some embodiments, the content of LiPF6 accounts for 20% to 50% of the total amount of lithium salt.

[0060] In some embodiments, the content of LiPF6 accounts for 20% to 48% of the total amount of lithium salt.

[0061] In some embodiments, the organic solvent in the electrolyte may include one or more of cyclic carbonates, chain carbonates, and chain carboxylates; cyclic carbonates may be selected from one or more of propylene carbonate (PC) and ethylene carbonate (EC); chain carbonates may be selected from one or more of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC); chain carboxylates may be selected from one or more of methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), and propyl propionate (PP).

[0062] In some embodiments, the negative electrode active material includes at least one of artificial graphite or natural graphite. The negative electrode active material of the present application is selected from one or a mixture of two of the above materials, which can help reduce battery costs, improve battery safety and stability, and enhance battery kinetic performance.

[0063] Positive electrode

[0064] In some embodiments, the secondary battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a lithium transition metal phosphide. In some embodiments, the lithium transition metal phosphide includes Li a Mn x Fe 1-x PO4, wherein 0.9≤a≤1.1, 0≤x<1, specifically, the positive electrode active material may be lithium iron phosphate or lithium manganese iron phosphate.

[0065] In some embodiments, the positive electrode plate further includes a conductive agent and a binder. The types and amounts of the conductive agent and binder are not specifically limited and can be selected based on actual needs. In some embodiments, the conductive agent may include conductive carbon black, carbon nanotubes, graphene, etc., and the binder may include polyvinylidene fluoride.

[0066] In some embodiments, the preparation of the positive electrode sheet includes: dispersing the above-mentioned positive electrode active material, conductive agent, and binder in N-methylpyrrolidone (NMP) in a certain proportion, coating the resulting slurry on aluminum foil, drying, and then cold pressing and slitting to obtain the positive electrode sheet.

[0067] Isolation film

[0068] In some embodiments, the type of the isolation membrane is not particularly limited and can be selected according to actual needs. The isolation membrane can be a polypropylene film, a polyethylene film, a polyvinylidene fluoride film, a spandex film, an aramid film, or a multi-layer composite film modified by a coating.

[0069] In some embodiments, the preparation of a secondary battery includes: stacking the positive electrode sheet, the isolation membrane, and the negative electrode sheet in order, so that the isolation membrane is located between the positive and negative electrode sheets to play an isolating role, and then winding them into a square bare battery cell, placing them in a battery shell, and then baking them at 65-95°C to remove water, injecting electrolyte, sealing, and obtaining a secondary battery after standing, hot and cold pressing, formation, clamping, and capacity separation.

[0070] In some embodiments, the secondary battery includes a lithium-ion battery. The above only takes the soft-pack lithium-ion battery as an example. This application is not limited to the application of soft-pack batteries, but also includes the application of common lithium-ion battery forms such as aluminum shell batteries and cylindrical batteries.

[0071] Electrical equipment

[0072] In some embodiments, the present application provides an electrical device, which includes the above-mentioned secondary battery. The electrical device can be used for but is not limited to backup power supplies, motors, electric vehicles, electric motorcycles, power-assisted bicycles, bicycles, power tools, large household batteries, etc.

[0073] The present invention has been tested many times, and some of the test results are now cited as reference to further describe the invention in detail, and the following is a detailed description of the invention in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0074] Example 1:

[0075] The positive electrode active material LiFePO4, conductive agent SP, and binder PVDF were mixed in a mass ratio of 96:2:2, and NMP was added and stirred under vacuum until the system became uniform to obtain the positive electrode slurry; the positive electrode slurry was then evenly coated on one side of the positive electrode current collector aluminum foil, dried in an oven, and then cold pressed to obtain the positive electrode sheet. The compacted density of the positive electrode sheet is 2.45g / cm 3 .

[0076] The negative electrode active material graphite, conductive agent SP, thickener CMC, and binder SBR were mixed in a mass ratio of 96.2:1.2:1.2:1.4, and deionized water was added as a solvent. The mixture was then stirred under vacuum until the system became uniform, thereby obtaining a negative electrode slurry. The negative electrode slurry was evenly coated on one side of a copper foil current collector, dried in an oven, and then cold pressed to obtain a negative electrode sheet. The compaction density of the negative electrode sheet was P g / cm 3 1.55g / cm 3 ; S of negative electrode active material BET m 2 / g is 1.60m 2 / g; the surface density W of the negative electrode active material layer is 0.3g / 1540.25mm 2The peeling force of the negative electrode active material layer is 15.00 N / m. The compaction density and areal density of the negative electrode sheet can be controlled by controlling the coating weight of the negative electrode sheet, the roller pressure during the cold pressing process, and the rolling time. The specific surface area of ​​the negative electrode active material can be regulated by the particle size distribution, morphology, or type of the negative electrode active material. The peeling force of the negative electrode active material layer can be controlled by controlling the proportion of the binder in the slurry, the morphology of the negative electrode active material, and the rolling pressure during the cold pressing process.

[0077] Electrolyte: Ethyl methyl carbonate and dimethyl carbonate are mixed in a mass ratio of 1:1, and then lithium hexafluorophosphate is added. After mixing evenly, vinylene carbonate as an additive is added. Based on the mass of the electrolyte, the concentration of lithium hexafluorophosphate is 2 mol / L, and the mass percentage of the vinylene carbonate additive is 1.6%.

[0078] The above-mentioned positive electrode sheet, separator (16-micron thick PP separator), and 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 wound to obtain a bare battery cell.

[0079] The bare battery cell is encapsulated in an aluminum-plastic film, dried, and injected with the prepared electrolyte. The injection coefficient of the electrolyte is controlled to be 3.8g / Ah (injection coefficient = injection amount of electrolyte / designed capacity of the battery). Then, after vacuum packaging, standing, formation, hot pressing and other processes, a lithium-ion secondary battery with a design capacity of 3Ah is obtained.

[0080] Examples 2 to 4: The preparation method is the same as that of Example 1, except that the mass percentage of the additive in the electrolyte is adjusted by adjusting the content of the additive, as shown in Table 1.

[0081] Example 5 to Example 9: The preparation method is the same as that of Example 2, except that the injection rate of the electrolyte is adjusted, thereby adjusting the injection coefficient of the secondary battery. See Table 1 for details.

[0082] Examples 10 to 14: The preparation method is the same as that of Example 2, except that the specific surface area of ​​the negative electrode material is adjusted by using negative electrode active materials of different shapes, and the concentration of lithium hexafluorophosphate in the electrolyte is adjusted, as shown in Table 1 for details.

[0083] Examples 15 to 18: The preparation method is the same as that of Example 2, except that the compaction density of the negative electrode active material is adjusted by adjusting the rolling pressure of the negative electrode sheet and the mass ratio of the binder to the negative electrode active material in the negative electrode slurry, as shown in Table 1.

[0084] Examples 19 to 22: The preparation method is the same as that of Example 2, except that the surface density of the negative electrode active material layer is adjusted by adjusting the coating weight of the negative electrode slurry and the roller pressing pressure, as shown in Table 1.

[0085] Examples 23-24: The preparation method is the same as that of Example 2, except that the peeling force of the negative electrode active material layer is adjusted by adjusting the mass ratio of the binder to the negative electrode active material in the negative electrode slurry, as shown in Table 1.

[0086] Examples 25 to 28: The preparation method is the same as that of Example 2, except that the lithium hexafluorophosphate in the electrolyte is adjusted to a mixed lithium salt of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide LiFSI (wherein the mass ratios of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide LiFSI in the mixed lithium salts of Examples 25 to 28 are: 8:2, 5:5, 2:8, 1:9, respectively).

[0087] Comparative Examples 1-2: The preparation method is the same as that of Example 1, except that the content of the additives and the amount of electrolyte injected are adjusted, as shown in Table 1 for details.

[0088] Performance testing method:

[0089] Volume expansion rate test: The battery is stored at 60℃ and 100% SOC. The volume is measured every 6 days. After the measurement is completed, the battery is charged at 0.1C to 3.65V and then stored. The above steps are repeated for 30 days and the battery expansion rate is tested. Battery expansion rate = (Vn-V0) / V0*100%, where V0 is the volume of the battery before the test, in cm 3 , Vn is the volume of the battery after 30 days of storage, in cm 3 .

[0090] Battery DC resistance (DCR): At 25°C, place a lithium-ion secondary battery on hold for 5 minutes, charge it at a constant current rate of 1C to 3.65V, then charge it at a constant voltage until the current is less than or equal to 0.05C, at which point the battery's state of charge (SOC) is 100%. Next, place it on hold for 5 minutes, then discharge it at a constant current rate of 1C to adjust the battery's state of charge (SOC) to 50%. Place the lithium-ion secondary battery at 50% SOC on hold for another 10 minutes, then discharge it at a constant current rate of 4C for 30 seconds. Record the voltage U1 during the last second of the hold, the voltage U2 during the last second of the 4C constant current discharge, and the current I during the 4C constant current discharge. Battery DC resistance = (U2 - U1) / I, expressed in mΩ.

[0091] Cycle performance: Cycle capacity retention rate: Under 25±5℃ environment, the battery is subjected to room temperature cycle test: 0.5C constant current charging to 3.65V, 3.65V constant voltage charging to cutoff current 0.05C, and then constant current 1C discharge to 2.8V. The number of cycles at the end point is recorded as 500 cycles, and the 500-cycle battery cycle capacity retention rate is calculated.

[0092] Table 1 Battery parameters of Examples 1 to 24 and Comparative Examples 1 to 2 of the present application

[0093] Table 2 Battery performance test results of Examples 1 to 28 and Comparative Examples 1 to 2

[0094] As can be seen from the results in Table 2, when the present application comprehensively considers the specific surface area of ​​the negative electrode material of the secondary battery, the surface density of the negative electrode material, the compacted density of the negative electrode sheet, the injection coefficient of the electrolyte, and the peeling force of the negative electrode active material layer, it is found that it meets the range defined by the present application and can improve the cycle performance of the secondary battery. Furthermore, when the specific surface area of ​​the negative electrode material, the surface density of the negative electrode material, the compacted density of the negative electrode sheet, the injection coefficient of the electrolyte, and the peeling force of the negative electrode active material layer of the present application meet the range defined by the present application, it can improve the cycle performance, impedance, and gas production performance of the secondary battery.

[0095] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0096] The above is a detailed introduction to a secondary battery and electrical equipment provided in the embodiments of the present application, and specific examples are used to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the technical solutions and core ideas of the present application; ordinary technicians in this field should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some of the technical features therein with equivalents; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A secondary battery, wherein, comprising: a negative electrode plate and an electrolyte; the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, the negative electrode active material layer includes a negative electrode active material; the electrolyte includes an additive; The secondary battery satisfies: 0.81 ≤ y ≤ 3.41, M is the liquid injection coefficient of the secondary battery, with the unit of g / Ah; C is the mass percentage of the additive in the electrolyte, with the unit of %; W is the areal density of the negative electrode active material layer in the secondary battery, with the unit of g / 1540.25mm 2 ; S BET is the specific surface area of the negative electrode active material, with the unit of m 2 / g; P is the compaction density of the negative electrode sheet, with the unit of g / cm 3 ; T is the peeling force of the negative electrode active material layer, with the unit of N / m.

2. The secondary battery according to claim 1, wherein, 2.4≤M≤6.3。 3. The secondary battery according to claim 1, wherein, 0.18≤W≤0.49。 4. The secondary battery according to claim 1, wherein, 1≤S BET ≤2.6。 5. The secondary battery according to claim 1 or 4, wherein, 1≤P≤2.5。 6. The secondary battery according to claim 1, wherein, the electrolyte includes a lithium salt, satisfying: 0.5 ≤ C / D ≤ 2.0, where D is the molar concentration of the lithium salt in the electrolyte, with the unit of mol / L.

7. The secondary battery according to claim 6, wherein, 1.5≤C≤4。 8. The secondary battery according to claim 6 or 7, wherein, 0.1≤D≤4。 9. The secondary battery according to claim 1, wherein, 9＜T＜25。 10. The secondary battery according to claim 1, wherein, the additive includes a cyclic carbonate additive; and / or, the cyclic carbonate additive includes at least one of vinylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate or vinyl ethylene carbonate.

11. The secondary battery according to claim 6, wherein, The lithium salt includes LiPF 6 , LiBF 4 , LiFSI, LiPO 2 F 2 , LiTFSI, LiDFOB, LiBOB, or at least one of them.

12. The secondary battery according to claim 1, wherein, including a positive electrode plate, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a lithium transition metal phosphide.

13. An electrical device, wherein, including the secondary battery according to any one of claims 1 to 12.

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