Secondary battery and device

Abstract

The invention provides a secondary battery, a battery module and a device wherein the secondary battery comprises a positive pole piece, a negative pole piece and an electrolyte; the negative pole piece comprises a negative active material, the negative active material comprises a silicon material, and based on the mass of the negative active material, the mass fraction of the silicon material is X wt%; the electrolyte comprises an isocyanate additive, and based on the mass of the electrolyte, the mass fraction of the isocyanate additive is Y wt%; wherein-0.55 < = Y-0. 1X < = 0.25, 5 < = X < = 50, and 0.5 < = Y < = 5. According to the secondary battery, the stability of the SEI film can be improved, side reactions are reduced, and the cycle performance and the safety performance of the battery are improved.

Description

Technical Field

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

[0002] Among commercial rechargeable batteries, lithium-ion batteries have higher energy density and wider operating voltage, and are widely used in electric vehicles, digital 3C, and energy storage. The cost, life, and safety of lithium-ion batteries have always been the focus of researchers. Safety performance, cycle performance, and calendar life are the key to whether lithium-ion batteries can be used in electric vehicles.

[0003] Silicon-based negative electrode is a negative electrode material for lithium-ion batteries with a relatively high specific capacity. The theoretical specific capacity is 4200mAh / g, which is a very promising negative electrode material. However, there are some bottlenecks in the application of silicon-based negative electrodes. The first is that silicon will expand and shrink during the reaction, and the volume change can reach 400%. The drastic volume change will cause the solid electrolyte interface film (SEI film) on the surface of the negative electrode to fall off, exposing silicon to the electrolyte and triggering a series of side reactions. This cycle will consume active lithium in the electrolyte and affect the battery's cycle performance and safety performance. Secondly, the SEI film on the silicon surface is relatively thick and uneven. In response to the above problems, it is necessary to develop electrolyte additives suitable for silicon-based negative electrodes to improve the stability of the SEI film and enhance the battery's cycle performance. Summary of the invention

[0004] In view of the above problems existing in the prior art, the present application provides a secondary battery, a battery module and a device.

[0005] A first aspect of the present application provides a secondary battery, comprising a positive electrode plate, a negative electrode plate and an electrolyte; the negative electrode plate comprises a negative electrode active material, the negative electrode active material comprises a silicon material, and the mass fraction of the silicon material is X wt% based on the mass of the negative electrode active material; the electrolyte comprises an isocyanate additive, and the mass fraction of the isocyanate additive is Y wt% based on the mass of the electrolyte; wherein -0.55≤Y-0.1X≤0.25, 5≤X≤50, 0.5≤Y≤5.

[0006] The present application introduces an isocyanate additive into the electrolyte, which can form a dense SEI film on the surface of the negative electrode plate, protect the negative electrode and the electrolyte, and improve the cycle performance of the battery. In addition, it can also effectively remove free acid and trace moisture in the electrolyte, stabilize lithium salts, inhibit the occurrence of electrolyte side reactions, and improve the safety performance of lithium-ion batteries. In addition, the mass fraction X wt% of silicon material in the negative electrode plate and the mass fraction Y wt% of isocyanate additive in the electrolyte are controlled to satisfy: -0.55≤Y-0.1X≤0.25. On the one hand, it can ensure that the isocyanate additive forms a dense SEI film on the surface of the negative electrode plate; on the other hand, it can ensure that during the cycle, there is a sufficient amount of unfilmed isocyanate additive in the electrolyte, which can repair the SEI film and maintain cycle stability.

[0007] A second aspect of the present application provides a device including the aforementioned secondary battery. DETAILED DESCRIPTION

[0008] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The relevant embodiments described herein are illustrative and are used to provide a basic understanding of the present application. The embodiments of the present application should not be interpreted as limiting the present application.

[0009] For simplicity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and any upper limit can be combined with any other upper limit to form an unspecified range. In addition, each separately disclosed point or single value can itself be combined as a lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an unspecified range.

[0010] In the description herein, unless otherwise specified, “above” and “below” include the number.

[0011] Unless otherwise specified, the terms used in this application have the commonly known meanings generally understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0012] A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0013] The term "C1-C6 alkyl" may be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl or n-hexyl.

[0014] The term "C1-C6 alkoxy" may be methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, tert-butoxy, n-pentoxy, isopentyloxy or n-hexyloxy.

[0015] The present application is further described below in conjunction with specific implementations. It should be understood that these specific implementations are only used to illustrate the present application and are not used to limit the scope of the present application.

[0016] Primary and secondary batteries

[0017] One or more embodiments of the present application provide a secondary battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte; the negative electrode sheet comprises a negative electrode active material, the negative electrode active material comprises a silicon material, and the mass fraction of the silicon material is X wt% based on the mass of the negative electrode active material; the electrolyte comprises an isocyanate additive, and the mass fraction of the isocyanate additive is Y wt% based on the mass of the electrolyte; wherein -0.55≤Y-0.1X≤0.25, and exemplarily, Y-0.1X is -0.55, -0.5, -0.4, -0.3, -0.2, -0.1, -0.05, 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.12, 0.14, 0.15, 0.16, 0.18, 0.2, 0.25 or a range consisting of any two of the above values; 5≤X≤50, exemplarily, X is 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 or a range consisting of any two of the above values; 0.5≤Y≤5, exemplarily, Y is 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or a range consisting of any two of the above values.

[0018] In the above implementation, the introduction of isocyanate additives into the electrolyte can form a dense SEI film on the surface of the negative electrode plate, protect the negative electrode and the electrolyte, and improve the cycle performance of the battery. In addition, it can also effectively remove free acid and trace water in the electrolyte, stabilize lithium salts, inhibit the occurrence of electrolyte side reactions, and improve the safety performance of lithium. In addition, the mass fraction X wt% of silicon material in the negative electrode plate and the mass fraction Y wt% of isocyanate additives in the electrolyte are controlled to meet: -0.55≤Y-0.1X≤0.25. On the one hand, it can ensure that the isocyanate additive forms a dense SEI film on the surface of the negative electrode plate; on the other hand, during the cycle, if the negative electrode plate expands and contracts, causing the SEI film to break continuously, causing fresh silicon particles to be exposed to contact with the electrolyte, there can be a sufficient amount of unfilmed isocyanate additives in the electrolyte to repair the SEI film and maintain cycle stability.

[0019] Specifically, the isocyanate additive provided by the present invention can be preferentially used over conventional carbonate solvents to undergo a reduction reaction on the negative electrode surface, undergo electrochemical polymerization, and form an SEI film, thereby preventing further decomposition of the electrolyte. The specific reaction mechanism is shown in Reaction Formula 1, where the isocyanate monomer gains electrons on the negative electrode side and is converted into an intermediate. The intermediate formed can react with another isocyanate monomer to form a product similar to polyamide.

[0020]

[0021] In some preferred embodiments, -0.2≤Y-0.1X≤0.2. Exemplarily, Y-0.1X is -0.2, -0.18, -0.15, -0.12, -0.1, -0.08, -0.06, -0.05, -0.04, -0.02, 0.02, 0.04, 0.05, 0.06, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2, or a range consisting of any two of the above values.

[0022] In some preferred embodiments, 10≤X≤35. Exemplarily, X is 10, 10.5, 12, 14, 16, 18, 19.5, 20, 22, 24, 26, 28, 30, 32, 34, 34.5, 35, or a range consisting of any two of the above values.

[0023] In some preferred embodiments, 0.5≤Y≤2. Exemplarily, Y is 0.5, 0.55, 0.6, 0.7, 0.8, 0.9, 1.1, 1.2, 1.3, 1.4, 1.6, 1.7, 1.8, 1.9, 1.95, 2 or a range consisting of any two of the above values.

[0024] In some embodiments, the isocyanate additive comprises a structure shown in Formula 1:

[0025]

[0026] Among them, R 1 , R 2 , R 3 , R 4 , R 5 Each is independently selected from one of a hydrogen atom, a fluorine atom, a substituted or unsubstituted C1-C6 alkyl group, a substituted or unsubstituted C1-C6 alkoxy group, an isocyanate group and a phenyl group. It is understood that various isomers of the groups satisfying the above carbon number are all included in the scope of the present application.

[0027] In the above implementation, the isocyanate group of the isocyanate additive provided by the present invention is connected to the benzene ring, and the SEI film formed at the negative electrode is more compact, which can effectively inhibit the occurrence of electrolyte side reactions and improve the cycle performance. The benzene ring structure can also form a conjugated effect with the double bond in the isocyanate to stabilize the structure. Different substituent groups can also be connected to the benzene ring to adjust the electron affinity of the molecule and thus control the polymerization potential. On the other hand, it is well known that the presence of trace amounts of water in the electrolyte will accelerate the polymerization of LiPF 6 The hydrolysis of 3 and acidic substances such as HF. These substances will catalyze the decomposition of the SEI film, and the specific reaction is shown in reaction formula 2-7. At the same time, HF will also corrode the positive electrode material, causing the transition metal ions of the positive electrode to dissolve, causing a micro short circuit, and causing the capacity of the lithium-ion battery to decay rapidly. The isocyanate additive provided by the present invention can also effectively remove trace amounts of moisture and HF impurities in the electrolyte, thereby minimizing the harm to the battery. The specific reaction mechanism is shown in reaction formula 8.

[0028] LiPF 6 (s)+H 2 O(I)→LiF(s)+POF 3 (g)+2HF(g) Reaction 2

[0029]

[0030] PF 5 (g)+H 2 O(I)→POF 3 (g)+2HF(g) Reaction 4

[0031] LiCO 3 (s)+2HF(g)→2LiF(s)+H 2 O(I)+CO 2 (g) Reaction 5

[0032] LiO(s)+2HF(g)→2LiF(s)+H 2 O(I) Reaction 6

[0033] LiOCO 2 R(s)+HF(g)→LiF(s)+ROH(I)+CO 2 (g) Reaction 7

[0034]

[0035] In some embodiments, in Formula 1, R 1 , R 2 , R 4 , R 5 is a hydrogen atom, R 3 One selected from a fluorine atom, a substituted or unsubstituted C1-C4 alkyl group, a substituted or unsubstituted C1-C4 alkoxy group, an isocyanate group and a phenyl group.

[0036] In some embodiments, the isocyanate additive includes at least one of the following compounds:

[0037]

[0038] In some embodiments, in Formula 1, R 1 , R 3 , R 5 is a hydrogen atom, R 2 , R 4 One selected from a fluorine atom, a substituted or unsubstituted C1-C3 alkyl group, a substituted or unsubstituted C1-C3 alkoxy group, an isocyanate group and a phenyl group.

[0039] In some embodiments, the isocyanate additive includes at least one of the following compounds:

[0040]

[0041] In some embodiments, the isocyanate additive further comprises at least one of the following compounds:

[0042] In some embodiments, the isocyanate additive includes at least one of the following compounds:

[0043]

[0044] In some embodiments, the electrolyte further includes a lithium salt and an organic solvent.

[0045] In some embodiments, the lithium salt includes lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium (trifluoromethylsulfonyl)(perfluorobutylsulfonyl)imide (LiFNFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(oxalatoborate) (LiBOB), lithium bis(fluoromalonate)borate (LiBFMB), lithium 4,5-dicyano-2-(trifluoromethyl)imidazolium (LiTDI) and at least one of lithium difluorooxalatoborate (LiDFOB).

[0046] In some embodiments, the concentration of the lithium salt is 0.5 mol / L to 1.5 mol / L. Exemplarily, the concentration of the lithium salt is 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L or a range consisting of any two of the above values.

[0047] In some embodiments, the organic solvent includes at least one of a linear carbonate, a cyclic carbonate, and a carboxylic acid ester.

[0048] In some embodiments, the linear carbonate includes, but is not limited to, at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate.

[0049] In some embodiments, the cyclic carbonate includes, but is not limited to, at least one of ethylene carbonate, propylene carbonate, and butylene carbonate.

[0050] In some embodiments, the carboxylic acid ester includes, but is not limited to, at least one of methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and butyl propionate.

[0051] In some embodiments, the mass fraction of the organic solvent is 50% to 90% based on the mass of the electrolyte. In some embodiments, the mass fraction of the organic solvent is 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or a range consisting of any two of the above values ​​based on the mass of the electrolyte.

[0052] In some embodiments, the positive electrode sheet includes a positive electrode active material, the positive electrode active material includes a lithium nickel transition metal oxide, and the lithium nickel transition metal oxide includes a formula LiNi m Co n A (1-m-n) O2 At least one of the compounds shown, wherein A is selected from at least one of manganese, aluminum, magnesium, zirconium, strontium, yttrium, lanthanum, molybdenum, silver, niobium, iron, titanium, copper, zinc, chromium, calcium, barium and tungsten, 0.5≤m≤1, 0≤n≤0.5, m+n≤1; exemplarily, m is 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95 or a range consisting of any two of these values, and / or, n is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 or a range consisting of any two of these values. In some embodiments, 0.8≤m≤1, 0≤n≤0.2, m+n≤1; exemplarily, 0.86≤m≤1, 0≤n≤0.14, m+n≤1.

[0053] In some embodiments, the lithium nickel transition metal oxide includes at least one of NCM523, NCM622, NCM811, Ni90 (ie, NCM90), Ni92 (ie, NCM92), or Ni95 (ie, NCM900).

[0054] In some embodiments, the lithium nickel transition metal oxide includes at least one of NCM811, Ni90, Ni92, or Ni95.

[0055] In some embodiments, the lithium nickel transition metal oxide may further include a coating layer, wherein the coating layer may be composed of one or more of lithium metaaluminate, aluminum oxide, lithium borate or lithium boride.

[0056] In some embodiments, the positive electrode active material may also include at least one of the phosphate compounds, the phosphate compounds including LiMn k B (1-k) PO 4 , wherein 0≤k≤1, and B is selected from at least one of iron, cobalt, magnesium, calcium, zinc, chromium, and lead. In some embodiments, k is 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or a range consisting of any two of these values.

[0057] In some embodiments, the phosphate compound includes lithium iron phosphate, LiMn 0.6 Fe 0.4 PO 4 or LiMn 0.8 Fe 0.2 PO 4 At least one of .

[0058] In some embodiments, the positive electrode active material includes, but is not limited to, at least one of lithium nickel oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium nickel manganese cobalt magnesium oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium iron phosphate, or lithium iron manganese phosphate.

[0059] In some embodiments, the positive electrode sheet further includes a positive electrode current collector, a conductive agent and a binder. The positive electrode active material, the conductive agent and the binder are fully stirred and mixed in a solvent system (for example, N-methylpyrrolidone) in a certain proportion, and then coated on an aluminum current collector, dried and rolled to obtain a positive electrode sheet.

[0060] In some embodiments, the silicon material includes at least one of silicon, silicon alloy, silicon oxide and silicon carbon compound. In some embodiments, the silicon material includes silicon oxide and / or silicon carbon compound. Exemplarily, the silicon oxide has the general formula SiOx, where 0.5≤x≤1.5, and the silicon oxide can be a single substance or a mixture, as long as its average composition conforms to the general formula.

[0061] In some embodiments, the negative electrode active material further includes at least one of a carbon material, a tin material, a phosphorus material, and metallic lithium.

[0062] In some embodiments, the carbon material includes, but is not limited to at least one of graphite, soft carbon, hard carbon, carbon nanotubes and graphene. In some embodiments, the carbon material includes natural graphite and / or artificial graphite.

[0063] In some embodiments, the tin material includes, but is not limited to, at least one of tin, tin oxide, and tin alloy.

[0064] In some embodiments, the phosphorus material includes, but is not limited to, phosphorus and / or phosphorus complexes.

[0065] In some embodiments, the secondary battery may further include a separator, which is polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyimide film, or a multilayer composite film thereof, or a composite film modified by a ceramic material coating.

[0066] In some embodiments, the secondary battery may be a lithium secondary battery or a sodium secondary battery. In some embodiments, the lithium secondary battery includes, but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0067] 2. Battery Module

[0068] One or more embodiments of the present application further provide a battery module, the battery module comprising the aforementioned secondary battery.

[0069] The battery module of the present application uses the above-mentioned secondary battery, and therefore has at least the same advantages as the secondary battery. The number of secondary batteries contained in the battery module of the present application can be one or more, and the specific number can be adjusted according to the application and capacity of the battery module.

[0070] 3. Battery Pack

[0071] One or more embodiments of the present application further provide a battery pack, which includes the aforementioned battery module.

[0072] The number of battery modules contained in a battery pack may be one or more, and the specific number may be adjusted according to the application and capacity of the battery pack.

[0073] 4. Device

[0074] One or more embodiments of the present application also provide a device, which includes at least one of the aforementioned secondary battery, battery module and battery pack.

[0075] In some embodiments, the device includes, but is not limited to: electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, power storage systems, etc. In order to meet the device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0076] In other embodiments, the device may be a mobile phone, a tablet computer, a laptop computer, etc. The device is usually required to be thin and light, and a secondary battery may be used as a power source. The technical solution of the present application will be further described below in conjunction with specific embodiments and comparative examples. In the present application, unless otherwise specified, the materials or reagents used are commercially available, and the methods used are conventional methods in the art.

[0077] Examples and Comparative Examples

[0078] Comparative Example 1

[0079] 1. Preparation of positive electrode sheet of lithium-ion battery: LiNi 0.9 Co 0.05 Mn 0.05 O 2 , conductive agent carbon nanotubes, conductive agent acetylene black, binder polyvinylidene fluoride PVDF, by weight proportion LiNi 0.9 Co 0.05 Mn 0.05 O 2 ∶CNT∶Super-P∶PVDF=95∶2.0∶1.0∶2 was fully slurried in N-methylpyrrolidone solvent (NMP) system, coated on 12μm thick aluminum-coated current collector, dried and roll-pressed to obtain positive electrode sheet.

[0080] 2. Preparation of negative electrode sheets for lithium-ion batteries: artificial graphite as a negative electrode active material, silicon oxide as a negative electrode active material, acetylene black as a conductive agent, styrene-butadiene rubber as a binder, sodium carboxymethyl cellulose as a thickener, and polyacrylic acid as a binder are fully slurried in a deionized water solvent at a weight ratio of 85:10:2:1.5:1:0.5, and then applied on a 8 μm thick copper current collector, dried, and rolled to obtain a negative electrode sheet.

[0081] 3. Preparation of non-aqueous electrolyte for lithium-ion batteries: Fluorinated ethylene carbonate (FEC), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a weight ratio of FEC:EC:EMC=8:30:62, and LiPF was added thereto. 6 , prepared into a non-aqueous electrolyte with a lithium salt concentration of 1.2 mol / L, the electrolyte does not contain an isocyanate additive.

[0082] 4. Lithium-ion battery separator: polyethylene separator is selected;

[0083] 5. Preparation of lithium-ion batteries: The positive electrode sheets, separators, and negative electrode sheets are stacked in a Z-shaped stack in order, and the obtained bare cells are placed in punched aluminum-plastic film soft-package shells. After drying, non-aqueous electrolyte is injected, and after standing, forming, aging, degassing, shaping and other processes, a lithium-ion battery is finally obtained.

[0084] Comparative Examples 2-6 and Examples 1-36

[0085] Comparative Examples 2-6 and Examples 1-36 are achieved by adjusting the mass fraction of silicon material (average composition formula of silicon oxide compound SiOx, 0.5≤x≤1.5) in the negative electrode active material to X wt%, the type and mass fraction of isocyanate additive to Y wt%, and the rest of the preparation method is the same as that of Comparative Example 1, see Table 1 for details.

[0086] Table 1

[0087]

[0088]

[0089]

[0090]

[0091]

[0092]

[0093]

[0094]

[0095]

[0096]

[0097]

[0098] The lithium-ion batteries prepared in the comparative example and the embodiment were subjected to cycle performance tests, and the test method was as follows:

[0099] 1. First cycle charge and discharge coulomb efficiency (ICE)

[0100] Battery formation process: Place the soft-pack battery in an environment of 25°C, charge it to 3.0V at 0.05C constant current, charge it to 3.4V at 0.1C constant current, and charge it to 3.75V at 0.2C constant current.

[0101] Battery capacity division process: Place the soft-pack battery in an environment of 25°C, charge it to 4.25V at 0.33C constant current and constant voltage, discharge it to 3.0V at 0.33C constant current, and cycle it twice.

[0102] The calculation formula of ICE is as follows:

[0103] ICE = first discharge capacity of capacity division / (formation charge capacity + first charge capacity of capacity division) × 100%

[0104] 2. Normal temperature cycle capacity retention rate

[0105] Place the soft pack battery in an environment of 25°C, charge it to 4.25V with constant current and constant voltage, with a cut-off current of 0.01C, and then discharge it to 3V with constant current. Calculate the capacity retention rate after 300 cycles. The calculation formula is as follows:

[0106] Capacity retention rate (%) = discharge capacity after N cycles / initial discharge capacity × 100%

[0107] The test results of Comparative Example 1 and Examples 1-36 show that the battery containing isocyanate additive has a higher first charge and discharge coulomb efficiency and a better cycle capacity maintenance rate. This is because isocyanate can decompose before the electrolyte solvent at a lower potential to form an SEI film on the surface of the silicon-based negative electrode. The benzene ring structure in the molecule will make the formed SEI more compact and more effective in protecting the negative electrode. At the same time, isocyanate can remove trace moisture and free acid in the electrolyte, stabilize lithium salts, and inhibit the occurrence of electrolyte side reactions, thereby effectively improving the cycle life of the battery. In addition, by replacing the substituents on the benzene ring, the effect of the additive molecules on the battery performance will also be affected. Groups with higher electron affinity, such as F-containing groups, contribute more to the first charge and discharge coulomb efficiency and cycle capacity maintenance rate of the battery. Furthermore, combined with the test results of Comparative Examples 2-6, it can be seen that if the negative electrode silicon content and the amount of isocyanate additive added do not satisfy the inequality -0.55≤Y-0.1X≤0.25, even if the negative electrode silicon content and the amount of isocyanate additive added are within the appropriate range, the performance of the battery will still be reduced. It can be seen that the synergistic effect between the negative electrode silicon content and the amount of isocyanate additive added is obvious.

[0108] Although some exemplary embodiments of the present application have been illustrated and described, the present application is not limited to the disclosed embodiments. On the contrary, those skilled in the art will recognize that some modifications and changes may be made to the described embodiments without departing from the spirit and scope of the present application as described in the appended claims.

Claims

1. A secondary battery, characterized in that: Including positive electrode sheet, negative electrode sheet and electrolyte; The negative electrode plate includes a negative electrode active material, the negative electrode active material includes a silicon material, and based on the mass of the negative electrode active material, the mass fraction of the silicon material is X wt%; The electrolyte includes an isocyanate additive, and the mass fraction of the isocyanate additive is Y wt % based on the mass of the electrolyte; Among them, -0.55≤Y-0.1X≤0.25, 5≤X≤50, 0.5≤Y≤5.

2. The secondary battery according to claim 1, characterized in that: -0.2≤Y-0.1X≤0.

2.

3. The secondary battery according to claim 1, characterized in that: At least one of the following conditions is met: (a) 10≤X≤35; (b)0.5≤Y≤2.

4. The secondary battery according to claim 1, characterized in that: The isocyanate additive comprises a structure shown in Formula 1: Wherein, R1, R2, R3, R4, and R5 are each independently selected from one of a hydrogen atom, a fluorine atom, a substituted or unsubstituted C1-C6 alkyl group, a substituted or unsubstituted C1-C6 alkoxy group, an isocyanate group, and a phenyl group, and the substituted substituent includes fluorine.

5. The secondary battery according to claim 4, characterized in that: The isocyanate additive satisfies any one of the following conditions: (c) In Formula 1, R1, R2, R4, and R5 are hydrogen atoms, and R3 is selected from a fluorine atom, a substituted or unsubstituted C1-C4 alkyl group, a substituted or unsubstituted C1-C4 alkoxy group, an isocyanate group, and a phenyl group; (d) In Formula 1, R1, R3, and R5 are hydrogen atoms, and R2 and R4 are selected from one of a fluorine atom, a substituted or unsubstituted C1-C3 alkyl group, a substituted or unsubstituted C1-C3 alkoxy group, an isocyanate group, and a phenyl group.

6. The secondary battery according to claim 4, characterized in that: The isocyanate additive comprises at least one of the following compounds:

7. The secondary battery according to claim 6, characterized in that: The isocyanate additive comprises at least one of the following compounds:

8. The secondary battery according to any one of claims 1 to 7, characterized in that: The electrolyte further comprises a lithium salt and an organic solvent, and the electrolyte further satisfies at least one of the following conditions: (f) the lithium salt comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium (trifluoromethylsulfonyl)(perfluorobutylsulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(oxalatoborate), lithium bis(fluoromalonate)borate, lithium 4,5-dicyano-2-(trifluoromethyl)imidazole and lithium difluorooxalatoborate; (g) the concentration of the lithium salt is 0.5 mol / L to 1.5 mol / L; (h) the organic solvent comprises at least one of a linear carbonate, a cyclic carbonate and a carboxylic acid ester; the linear carbonate comprises at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate and ethyl propyl carbonate; the cyclic carbonate comprises at least one of ethylene carbonate, propylene carbonate and butylene carbonate; the carboxylic acid ester comprises at least one of methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate and butyl propionate; (i) Based on the mass of the electrolyte, the mass fraction of the organic solvent is 50% to 90%.

9. The secondary battery according to any one of claims 1 to 7, characterized in that: The positive electrode sheet includes a positive electrode active material, the positive electrode active material includes a lithium nickel transition metal oxide, and the lithium nickel transition metal oxide includes a formula LiNi m Co n A (1-m-n) O2, wherein A comprises at least one of manganese, aluminum, magnesium, zirconium, strontium, yttrium, lanthanum, molybdenum, silver, niobium, iron, titanium, copper, zinc, chromium, calcium, barium and tungsten, 0.5≤m≤1, 0≤n≤0.5, m+n≤1; and / or, The silicon material includes at least one of a silicon-oxygen compound and a silicon-carbon compound; and / or, The negative electrode active material further includes a carbon material, and the carbon material includes at least one of natural graphite, artificial graphite, soft carbon, hard carbon, carbon nanotubes and graphene.

10. A device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 9.

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