Electrolyte, secondary battery and electric device

Abstract

The invention discloses an electrolyte, a secondary battery and an electric device, and belongs to the technical field of batteries. The electrolyte provided by the invention comprises the additive, the additive comprises the component A and the component B, and the component A and the component B cooperate with each other, so that when the electrolyte containing the additive is applied to the secondary battery, the SEI film repairing effect of the secondary battery can be effectively improved, the compactness and uniformity of the SEI film can be improved, and the side reaction between a negative electrode and the electrolyte can be reduced; therefore, the cycle life of the secondary battery is prolonged; meanwhile, the side reaction of the negative electrode and the electrolyte can be reduced, the growth of lithium dendrites is effectively inhibited, and the short circuit risk is reduced, so that the safety of the secondary battery is improved; in addition, the performance stability of the repaired SEI membrane can be improved, the internal resistance fluctuation is reduced, and the ion conduction stability is maintained, so that the impedance increase of the secondary battery is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to an electrolyte, a secondary battery, and an electrical device. Background Art

[0002] Lithium-ion batteries are widely used. The SEI film on the negative electrode is crucial for performance, which can prevent excessive reaction between the negative electrode and the electrolyte and ensure lithium-ion transmission. However, in actual use, situations such as high-rate charge and discharge, long-term cycling, and extreme temperatures are likely to cause the SEI film to rupture. After the SEI film ruptures, the negative electrode reacts with the electrolyte, resulting in battery capacity attenuation, increased internal resistance, reduced Coulomb efficiency, and is also prone to generating lithium dendrites, leading to problems such as short circuit and thermal runaway. Existing SEI film protection and repair technologies have problems such as insignificant repair effects and poor compatibility between additives and battery systems, which limit the improvement of battery performance and the expansion of applications. Summary of the Invention

[0003] The purpose of the present invention is to solve the technical problems in the prior art that the repair effect of the SEI film is poor, the stability after repair is not high, and the compatibility with the battery system is poor, and to provide an electrolyte, a secondary battery, and an electrical device that can effectively improve the repair efficiency of the SEI film and the performance stability of the SEI film after repair, and at the same time have excellent versatility and applicability.

[0004] To achieve the above purpose, in the first aspect of the present invention, an electrolyte is provided. The electrolyte includes an organic solvent, a lithium salt, and an additive, and the additive includes component A and component B;

[0005] Component A includes a compound represented by formula I,

[0006]

[0007] R is selected from C6-C10 alkyl, fluorine-substituted C2-C5 alkyl, or -(OCH2CH2) n OH; wherein, in -(OCH2CH2) n OH, n is a positive integer between 2 and 8;

[0008] Component B includes nitrogen-doped nanoparticles;

[0009] The nanoparticles include metal oxides and / or metal nitrides;

[0010] The nanoparticles include at least one of carboxyl group, pyridyl group, and phenanthroline group.

[0011] As an embodiment of the present invention, R is selected from octyl, trifluoroethyl, or -(OCH2CH2)4OH.

[0012] As an embodiment of the present invention, the component A includes at least one of lithium N-octylbis(trifluoromethylsulfonyl)imide, lithium N-trifluoroethylbis(trifluoromethylsulfonyl)imide, and lithium N-PEG4bis(trifluoromethylsulfonyl)imide.

[0013] As an embodiment of the present invention, the Dv50 particle size of the nitrogen-doped nanoparticles is 50 nm to 300 nm.

[0014] As an embodiment of the present invention, the mass ratio of the component A to the component B is (3 to 5):1.

[0015] As an embodiment of the present invention, based on the total mass of the electrolyte, the sum of the mass percentages of the component A and the component B is 0.3% to 3%.

[0016] As an embodiment of the present invention, the metal element in the metal oxide includes at least one of zinc, cobalt, and manganese; and / or

[0017] the metal element in the metal nitride includes at least one of zinc, cobalt, and manganese.

[0018] As an embodiment of the present invention, the preparation method of the nitrogen-doped nanoparticles includes the following steps: calcining a nitrogen-containing metal-organic framework material in an inert gas environment, followed by grinding and sieving to obtain the nitrogen-doped nanoparticles;

[0019] the temperature of the calcination is 450 °C to 550 °C, and the time of the calcination is 1.5 h to 3.5 h.

[0020] In the second aspect of the present invention, a secondary battery is provided, which includes a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte according to the present invention.

[0021] In the third aspect of the present invention, an electrical device is provided, which includes the secondary battery according to the present invention.

[0022] The beneficial effects of the present invention are:

[0023] The electrolyte provided by the present invention includes additives. Among them, the additives include component A and component B, which cooperate with each other. Therefore, when the electrolyte containing the additives of the present invention is applied to a secondary battery, it can effectively improve the SEI film repair effect of the secondary battery, enhance the denseness and uniformity of the SEI film, reduce the side reaction between the negative electrode and the electrolyte, thereby prolonging the cycle life of the secondary battery; at the same time, it can reduce the side reaction between the negative electrode and the electrolyte, effectively inhibit the growth of lithium dendrites, reduce the short-circuit risk, thereby improving the safety of the secondary battery; in addition, it can improve the performance stability after the SEI film is repaired, reduce the internal resistance fluctuation, maintain the ion conduction stability, thereby reducing the impedance growth of the secondary battery. Description of the Drawings

[0024] Figure 1 Raman spectra of lithium bis(trifluoromethanesulfonyl)imide and components A-1 to A-3. Detailed implementation manners

[0025] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely below. Apparently, the described embodiments are only a part rather than all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0026] In the present invention, among the technically characterized described in an open-ended manner, a closed technical solution composed of the listed features is included, and an open technical solution including the listed features is also included.

[0027] In the present invention, regarding numerical ranges, unless otherwise specified, the above numerical ranges are considered continuous and include the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when the range refers to integers, each integer between the minimum and maximum values of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, these ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0028] In one embodiment of the present invention, an electrolyte is provided. The electrolyte includes an organic solvent, a lithium salt, and an additive. The additive includes component A and component B;

[0029] Component A includes a compound represented by Formula I,

[0030]

[0031] R is selected from C6-C10 alkyl, fluorine-substituted C2-C5 alkyl, or -(OCH2CH2) n OH; wherein, in -(OCH2CH2) n OH, n is a positive integer between 2 and 8;

[0032] Component B includes nitrogen-doped nanoparticles;

[0033] The nanoparticles include metal oxides and / or metal nitrides;

[0034] The nanoparticles include at least one of carboxyl group, pyridyl group, and phenanthroline group.

[0035] The electrolyte provided by the present invention includes the additive described in the present invention. Among them, the additive includes component A and component B, which cooperate with each other. When the electrolyte containing the additive of the present invention is applied to a secondary battery, the repair effect of the SEI film of the secondary battery can be effectively improved, the compactness and uniformity of the SEI film can be enhanced, the side reaction between the negative electrode and the electrolyte can be reduced, and thus the cycle life of the secondary battery can be extended. Specifically, on the one hand, by reducing the side reaction between the negative electrode and the electrolyte, it is avoided that the products generated by the side reaction between the negative electrode and the electrolyte are unevenly deposited to provide nucleation points for the subsequent formation of lithium dendrites, thereby effectively inhibiting the growth of lithium dendrites, reducing the short-circuit risk, further enhancing the safety of the secondary battery, and extending the cycle life of the secondary battery; on the other hand, by improving the compactness and uniformity of the SEI film, the performance stability of the SEI is improved, the internal resistance fluctuation is reduced, and the ion conduction stability is maintained, thereby reducing the impedance growth of the secondary battery, and further extending the cycle life of the secondary battery.

[0036] Specifically, when the electrolyte containing the additive of the present invention is applied to a secondary battery, on the first hand, the decomposition of component A can provide film-forming substances, further cooperate with component B to catalyze and stabilize free radicals, promote the formation of a uniform and dense SEI film, complete the rapid and good repair of the SEI film, reduce the side reaction between the negative electrode and the electrolyte, slow down the capacity decay, and extend the cycle life of the secondary battery; on the second hand, component B can regulate the decomposition process of component A, reduce the heat generation and gas generation of side reactions during the decomposition process, and further improve the safety of the secondary battery during high-temperature and high-rate charge and discharge on the basis of effectively reducing the growth of lithium dendrites; on the third hand, the SEI film jointly constructed by component A and component B has high stability, can reduce the internal resistance fluctuation, maintain the ion conduction stability, reduce the impedance growth of the secondary battery, and improve the stability of the output voltage and capacity performance parameters of the secondary battery.

[0037] More specifically, the principle speculation of the cooperation between component A and component B to achieve the effects described in the present invention includes the following steps:

[0038] 1. Potential activation

[0039] When the working negative electrode potential of the secondary battery decreases, taking the potential when Li is converted to Li + as the reference potential, when it is between 0.2V and 0.5V, component B is reduced and activated, the electron of the nitrogen atom in component B changes the electron cloud density, and the metal atom site is activated, preparing to act with component A;

[0040] 2. Decomposition and preliminary reaction of component A

[0041] Taking Li converted to Li +The potential at this time is used as the reference potential. When the potential of the negative electrode is 0.5V - 0.8V, component A decomposes into free radicals and reactive intermediates (the free radicals and reactive intermediates of component A vary depending on the selection of R. Exemplarily, the free radicals can be alkyl radicals, fluoroalkyl radicals, alkoxy radicals, etc.; the reactive intermediates can be hexafluorosulfonimide anions, Li + - polyether complexes, hydroxyl groups, Li + - alkyl complexes, etc.); the nitrogen atom in the activated component B stabilizes the free radicals through the action of Lewis acid-base pairs, delays the termination of free radicals, and directs the transport of free radicals to the active sites of the negative electrode, that is, helps the free radicals react with the negative electrode active material and enables the components that can participate in the formation of the SEI film to form a film through a series of physical and electrochemical effects; at the same time, the electron conductivity of component B accelerates the electron transfer of the decomposition of component A, and component B can also serve as a nanoparticle adsorption site to guide the uniform distribution of products and ions, so that the SEI film grows uniformly and is dense and stable, thereby improving the comprehensive performance of the secondary battery.

[0042] It should be noted that components A and B in the electrolyte are obtained through combined tests of Raman, mass spectrometry, nuclear magnetic resonance, and elemental analysis.

[0043] Specifically, component B can be characterized by the following methods:

[0044] Through XPS characterization, determine the presence of nitrogen (N) in the sample and its chemical state, as well as the chemical environments of metal elements (such as: Zn), carbon (C), and oxygen (O). N 1s peak: The characteristic peaks of pyridine nitrogen, pyrrole nitrogen, or graphitic nitrogen appear, proving successful nitrogen doping; metal 2p peak: Present in the positive oxidation state, indicating that the metal exists in the form of oxides or nitrides; C 1s peak: The main peak reflects the characteristics of graphitic carbon. In addition, small peaks representing C-N bonds or C-O bonds appear, indicating that the carbon element in the sample mainly exists in the form of graphitic carbon, and there is also a small amount of carbon bonded to nitrogen and oxygen. Thus, it can be determined that the sample is nitrogen-doped and includes metal oxides and / or metal nitrides in the sample.

[0045] Through TEM, characterize the sample morphology and particle size. Particle morphology: The diameter of the nanoparticles is 50 - 300nm, and the surface is uniformly coated with a nitrogen-doped carbon layer; Lattice fringes: High-resolution TEM shows the lattice fringes of metal oxides or metal nitrides (such as the lattice fringes of ZnO or Zn), and the carbon layer shows a disordered or partially graphitized structure. Combining energy spectrum (EDS) Mapping shows the distribution of metal elements, N, and C elements. This further determines that the sample includes metal oxides and / or metal nitrides and the sample is nitrogen-doped, which is consistent with the XPS characterization conclusion.

[0046] Auxiliary FTIR characterization is used to detect functional groups and further confirm whether the sample contains at least one of carboxyl group, pyridyl group, and phenanthroline group. By comparing with the standard spectrum, the functional group information in the sample is determined. Auxiliary elemental analysis characterization is used to measure the element content.

[0047] In summary, combining XPS characterization, TEM characterization, and FTIR characterization, the sample is characterized.

[0048] In one embodiment, R is selected from octyl, trifluoroethyl, or -(OCH2CH2)4OH.

[0049] In one embodiment, the component A includes at least one of lithium N-octyl-bis(trifluoromethylsulfonyl)imide, lithium N-trifluoroethyl-bis(trifluoromethylsulfonyl)imide, and lithium N-PEG4-bis(trifluoromethylsulfonyl)imide.

[0050] The research of the present invention finds that there are differences in the decomposition efficiency of different substances as component A, and there are also differences in the action intensity of the decomposed free radicals, active intermediates and component B. When further selecting component A to include the above substances, under the synergistic effect of component B, the decomposed free radicals and active intermediates can better react with the negative electrode active material to construct a more uniform and dense SEI film basic unit, thereby improving the cycle performance and safety performance of the secondary battery and reducing the impedance growth of the secondary battery.

[0051] Specifically, when component A is lithium N-trifluoroethyl-bis(trifluoromethylsulfonyl)imide, its R is selected from trifluoroethyl. The strong electron-withdrawing effect of the fluoroalkyl group can change the polarity and bond energy of the relevant chemical bonds in component A, thereby affecting its decomposition potential and decomposition products, and can introduce more fluorine-containing components during the construction of the SEI film, thereby further improving the chemical stability and ionic conductivity of the SEI film, and then improving the comprehensive performance of the subsequent prepared secondary battery, especially the cycle performance is improved significantly. When component A is lithium N-PEG4-bis(trifluoromethylsulfonyl)imide, its R is selected from -(OCH2CH2)4OH. This relatively long-chain structure can regulate its decomposition potential window, so that it preferentially decomposes to generate a lithium salt intermediate containing polyetheroxy groups in a specific voltage range. These products form a low-barrier ion conduction channel in the SEI film through the coordination of ether oxygen atoms with Li + ions; at the same time, the relatively long-chain structure can also affect the decomposition potential and provide a flexible structure in the SEI film to relieve the volume change of the subsequent prepared secondary battery during charge and discharge, and improve the safety of the secondary battery.

[0052] It should be noted that lithium N-octylbis(trifluoromethylsulfonyl)imide, lithium N-trifluoroethylbis(trifluoromethylsulfonyl)imide, and lithium N-PEG4-bis(trifluoromethylsulfonyl)imide in the present invention can be prepared by conventional preparation methods; for example, they can be prepared by a substitution reaction using lithium bis(trifluoromethylsulfonyl)imide as a raw material.

[0053] Exemplarily, the preparation method of the lithium N-octylbis(trifluoromethylsulfonyl)imide (LiN(SO2CF3)2-C8H 17 ) comprises the following steps: Dissolve lithium bis(trifluoromethylsulfonyl)imide and potassium carbonate in an organic solvent, then dropwise add octyl bromide for a substitution reaction under an inert gas atmosphere. After the substitution reaction is completed, filter, collect the filtrate and concentrate, wash, and dry to obtain lithium N-octylbis(trifluoromethylsulfonyl)imide.

[0054] In some embodiments, during the preparation of lithium N-octylbis(trifluoromethylsulfonyl)imide, the organic solvent includes acetonitrile, and the temperature of the substitution reaction is 50°C to 70°C, and the time is 16 h to 20 h.

[0055] In some embodiments, during the preparation of lithium N-octylbis(trifluoromethylsulfonyl)imide, the molar ratio of lithium bis(trifluoromethylsulfonyl)imide, potassium carbonate, and octyl bromide is 1:(1 to 1.5):(1.2 to 1.8).

[0056] Exemplarily, the preparation method of the lithium N-trifluoroethylbis(trifluoromethylsulfonyl)imide (LiN(SO2CF3)2-C2F5) comprises the following steps: Dissolve lithium bis(trifluoromethylsulfonyl)imide and sodium hydride in an organic solvent, then dropwise add trifluoroethyl iodide for a substitution reaction under an inert gas atmosphere. After the substitution reaction is completed, cool and quench the reaction with water, then extract with ethyl acetate, collect the extract and concentrate, and dry to obtain lithium N-trifluoroethylbis(trifluoromethylsulfonyl)imide.

[0057] In some embodiments, during the preparation of lithium N-trifluoroethylbis(trifluoromethylsulfonyl)imide, the organic solvent includes N,N-dimethylformamide, and the temperature of the substitution reaction is 60°C to 80°C, and the time is 10 h to 14 h.

[0058] In some embodiments, during the preparation of lithium N-trifluoroethylbis(trifluoromethylsulfonyl)imide, the molar ratio of lithium bis(trifluoromethylsulfonyl)imide, sodium hydride, and trifluoroethyl iodide is 1:(1 to 1.5):(1.2 to 1.8).

[0059] Exemplarily, the preparation method of the N-PEG4-lithium bis(trifluoromethanesulfonyl)imide comprises the following steps: adding lithium bis(trifluoromethanesulfonyl)imide, polyethylene glycol-4 (PEG4) and a catalyst into an organic solvent, heating under reflux, cooling to room temperature after the reaction, then washing, collecting the organic phase, concentrating and drying to obtain N-PEG4-lithium bis(trifluoromethanesulfonyl)imide.

[0060] In some embodiments, in the preparation process of the N-PEG4-lithium bis(trifluoromethanesulfonyl)imide, the organic solvent includes toluene, the catalyst includes p-toluenesulfonic acid, and the reflux reaction time is 22 h to 26 h.

[0061] In some embodiments, the molar ratio of lithium bis(trifluoromethanesulfonyl)imide, monomethyl polyethylene glycol and p-toluenesulfonic acid is 1:(1.2 - 1.8):(45 - 55).

[0062] In one embodiment, the Dv50 particle size of the nitrogen-doped nanoparticles is 50 nm to 300 nm.

[0063] It should be noted that the Dv50 particle size of the nitrogen-doped nanoparticles is obtained by testing with a particle size distribution analyzer.

[0064] Exemplarily, the Dv50 particle size of the nitrogen-doped nanoparticles can be any point value or any two-point range value between 50 nm and 300 nm, such as 50 nm, 80 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, 200 nm, 220 nm, 240 nm, 260 nm, 280 nm, 300 nm, etc.

[0065] In one embodiment, the Dv50 particle size of the nitrogen-doped nanoparticles is 140 nm to 220 nm. Such as 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, 210 nm, 220 nm, etc.

[0066] The present invention has found through research that in the later stage of the synergistic interaction between component A and component B, the nanoparticle form of component B can guide the uniform distribution of the product and ions, thereby improving the uniformity and compactness of the SEI film, and further improving the comprehensive performance of the secondary battery; especially when the average particle size of component B is further selected within the above range, the comprehensive performance of the obtained secondary battery is better.

[0067] In one embodiment, the mass ratio of component A to component B is (3 - 5):1.

[0068] Exemplarily, the mass ratio of component A to component B can be any point value or any two-point range value between (3 to 5):1, such as 3:1, 3.5:1, 4:1, 4.5:1, 5:1, etc.

[0069] The research of the present invention finds that when the mass ratio of component A to component B is within the above range, on the one hand, it can not only accelerate the formation rate of the initial SEI film, but also have good SEI film repair ability to ensure the capacity retention rate of the secondary battery during the cycling process; on the other hand, based on the SEI film repair ability, it can avoid the slowdown of capacity utilization caused by the complexity of the decomposition and reaction process of component A in the early stage. That is, when further selecting the mass ratio of component A to component B within the above range, the nitrogen atoms in the pre-activated component B can act on the free radicals decomposed from component A with higher efficiency by Lewis acid-base pairs, thereby effectively promoting the reaction of the free radicals decomposed from component A with the reactive intermediates, the nitrogen atoms in component B and the negative electrode active material, thus more quickly constructing the basic units of the SEI film, improving the repair efficiency of the SEI film, and further helping to reduce the impedance growth of the secondary battery and improve the cycle life of the secondary battery.

[0070] In one embodiment, based on the total mass of the electrolyte, the sum of the mass percentages of component A and component B is 0.3% to 3%.

[0071] Exemplarily, based on the total mass of the electrolyte, the sum of the mass percentages of component A and component B can be any point value or any two-point range value between 0.3% and 3%, such as 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, etc.

[0072] In one embodiment, based on the total mass of the electrolyte, the sum of the mass percentages of component A and component B is 1% to 2%.

[0073] It should be noted that during the preparation of the electrolyte, based on the total mass of the electrolyte, the sum of the mass percentages of component A and component B is 1% to 5%; after the formation stage in the preparation of the secondary battery, based on the total mass of the electrolyte, the sum of the mass percentages of component A and component B is 0.3% to 3%.

[0074] In one embodiment, during the preparation of the electrolyte, based on the total mass of the electrolyte, the sum of the mass percentages of component A and component B is 2 to 3%.

[0075] The research of the present invention finds that components A and B within an appropriate addition amount range can enable the SEI film to be repaired and formed sufficiently, thereby effectively improving the capacity retention rate of the secondary battery; and avoid significantly affecting the viscosity of the electrolyte and the ion migration rate, and avoid the problem of significant impedance increase caused by difficult ion conduction; that is, when the sum of the mass percentages of components A and B is further selected within the above range, the comprehensive performance of the obtained secondary battery is better.

[0076] In one embodiment, the metal element in the metal oxide includes at least one of zinc, cobalt, and manganese; and / or

[0077] The metal element in the metal nitride includes at least one of zinc, cobalt, and manganese.

[0078] In one embodiment, the preparation method of the nitrogen-doped nanoparticles includes the following steps: calcining the nitrogen-containing metal-organic framework material in an inert gas environment and then grinding and sieving to obtain the nitrogen-doped nanoparticles;

[0079] The temperature of the calcination is 450°C to 550°C, and the time of the calcination is 1.5 h to 3.5 h.

[0080] The research of this application finds that by calcining the nitrogen-containing metal-organic framework material (MOF) in an inert gas environment within the above temperature range for a certain time, some of the organic ligands (such as trimesic acid, bipyridine, phenanthroline, etc.) in the metal-organic framework material can be decomposed into a carbon-based structure, and the nitrogen in the organic ligand is retained and doped into the carbon-based structure in the form of non-free elements such as pyridine nitrogen, pyrrole nitrogen, or graphitic nitrogen to form a nitrogen-doped carbon-based structure; at the same time, the metal in the metal-organic framework material combines with the oxygen element and / or nitrogen element in the organic ligand to form metal oxides and / or metal nitrides through ionic bonds or covalent bonds, etc. The formed metal oxides and / or metal nitrides provide stable and reliable catalytic active sites for the SEI film formation reaction, and cooperate with the decomposed nitrogen-doped carbon-based structure to accelerate the electrochemistry reaction kinetics and help to efficiently construct the SEI film unit.

[0081] Exemplarily, the temperature of the calcination can be maintained at any point value or any two-point range value between 450°C and 550°C, such as 450°C, 480°C, 500°C, 530°C, 550°C, etc. The time of the calcination can be maintained at any point value or any two-point range value between 1.5 h and 3.5 h, such as 1.5 h, 2.0 h, 2.5 h, 3.0 h, 3.5 h, etc.

[0082] In one embodiment, the nitrogen-containing metal-organic framework material includes at least one of zinc-trimesic acid metal-organic framework material, cobalt-bipyridine metal-organic framework material, and manganese-phenanthroline metal-organic framework material.

[0083] It has been found in the research of the present invention that the selection of metals and groups in Component B will affect its catalytic activity for the decomposition reaction of Component A and the subsequent coordination with the active intermediates generated by the decomposition of Component A, thereby affecting the construction process of the SEI film and the uniformity and compactness of the SEI film; when further selecting the metals and groups in Component B to be of the above types; specifically, when the metal in Component B is cobalt and the group is pyridyl (i.e., the MOF material in the corresponding preparation process is cobalt-bipyridine metal-organic framework material), its catalytic effect on Component A is more conducive to the formation of a uniform and stable SEI film, improving the cycling performance of the secondary battery; when the metal in Component B is manganese and the group is phenanthroline (i.e., the MOF material in the corresponding preparation process is manganese-phenanthroline metal-organic framework material), it can endow Component B with good antioxidant performance, effectively protecting the SEI film from being oxidized and damaged during cycling, thereby improving the cycling performance of the secondary battery.

[0084] In some embodiments, the inert gas environment includes a nitrogen environment and a noble gas environment.

[0085] In some embodiments, the nitrogen-containing metal-organic framework material is heated to the calcination temperature at a heating rate of 4 °C / min to 10 °C / min in an inert gas environment.

[0086] It should be noted that different average particle size products of Component B can be obtained by grinding and sieving.

[0087] It should be noted that there is no particular limitation on the preparation method of the metal-organic framework material in the present invention, and any method that can be implemented by those skilled in the art for the preparation of the metal-organic framework material is feasible.

[0088] Exemplarily, the preparation method of the metal-organic framework material includes the following steps: adding metal nitrides and organic ligands to a solvent and dissolving them, then performing a thermal reaction, centrifuging after the thermal reaction is completed, collecting the precipitate and washing and drying it to obtain the metal-organic framework material.

[0089] In some embodiments, the molar ratio of the metal nitrides to the organic ligands is 1:(1 - 3).

[0090] In some embodiments, the temperature of the thermal reaction is 110 °C to 150 °C, and the time of the thermal reaction is 28 h to 50 h.

[0091] In some embodiments, the solvent includes DMF or an aqueous solution of DMF.

[0092] In one embodiment, in the nitrogen-doped nanoparticles, the mass percentage of nitrogen element is 5% to 15%.

[0093] In one embodiment, in the nitrogen-doped nanoparticles, the mass percentage of the metal element is 30% to 50%.

[0094] In one embodiment, the organic solvent includes at least one of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0095] In one embodiment, the lithium salt includes at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide.

[0096] In a second aspect of the present invention, the present invention provides a secondary battery, including a positive electrode plate, a negative electrode plate, a separator, and the electrolyte of the present invention.

[0097] The secondary battery provided by the present invention contains the electrolyte of the present invention. During the electrochemical reaction process of the secondary battery, component A and component B in the electrolyte cooperate with each other, which can effectively improve the repair efficiency of the SEI film of the secondary battery, improve the compactness and uniformity of the SEI film, reduce the side reaction between the negative electrode and the electrolyte, thereby prolonging the cycle life of the secondary battery; at the same time, reduce the side reaction between the negative electrode and the electrolyte, effectively inhibit the growth of lithium dendrites, reduce the short-circuit risk, thereby improving the safety of the secondary battery; in addition, it can improve the performance stability after the SEI film is repaired, reduce the internal resistance fluctuation, and maintain the ion conduction stability, thereby reducing the impedance growth of the secondary battery.

[0098] In one embodiment, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector; the positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder. The present invention places no restrictions on the positive electrode active material, the conductive agent, and the binder, and any known positive electrode active material, conductive agent, and binder can be used.

[0099] Exemplarily, the positive electrode active material may be at least one of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based material, lithium manganate, lithium manganese iron phosphate, lithium titanate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, or lithium manganese silicate. The conductive agent may be at least one of SuperP, carbon nanotubes, and graphene. The binder may be at least one of PVDF, PTFE, PAANa, CMC, SBR, and sodium alginate.

[0100] In one embodiment, the positive electrode active material includes the following components in mass percentages: 70% to 95% positive electrode active substance, 3% to 20% conductive agent, and 2% to 10% binder.

[0101] In one embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector; the negative electrode active material layer includes a negative electrode active material. The present invention places no restrictions on the negative electrode active material, and any known negative electrode active material can be used.

[0102] Exemplarily, the negative electrode active material may be at least one of lithium metal, carbon-based material, silicon-based material, and metal oxide material.

[0103] The present invention places no restrictions on the separator, and a separator commonly used in the art can be selected; exemplarily, the material of the separator may be polypropylene, polyethylene, or a composite of polypropylene and polyethylene, etc.

[0104] In the third aspect of the present invention, the present invention provides an electrical device including the secondary battery of the present invention.

[0105] Exemplarily, the above electrical device may include 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, satellites, energy storage systems, etc., but is not limited thereto.

[0106] The components A and B used in the examples and comparative examples of the present invention are as follows:

[0107] Component A-1: Lithium N-octylbis(trifluoromethylsulfonyl)imide, self-made, and the preparation method includes the following steps:

[0108] In a three-necked flask under an argon atmosphere, add 0.1 mol of lithium bis(trifluoromethylsulfonyl)imide, 0.12 mol of potassium carbonate, and 100 mL of acetonitrile, then heat to 60 °C and stir to dissolve lithium bis(trifluoromethylsulfonyl)imide and potassium carbonate; then slowly dropwise add 0.15 mol of octyl bromide, and stir and react at 60 °C for 18 h; after the reaction is completed, filter to remove solid impurities, collect the filtrate and distill it under reduced pressure to obtain a crude product, wash the crude product with ether and then vacuum dry it at 80 °C for 24 h to obtain lithium N-octylbis(trifluoromethylsulfonyl)imide.

[0109] Component A-2: Lithium N-trifluoroethylbis(trifluoromethylsulfonyl)imide, self-made, and the preparation method includes the following steps:

[0110] In a three-necked flask under an argon atmosphere, 0.1 mol of lithium bis(trifluoromethylsulfonyl)imide, 0.12 mol of sodium hydride and 100 mL of N,N-dimethylformamide were added, and then stirred at 25 °C for 30 min; then 0.15 mol of trifluoroethyl iodide was slowly added dropwise. After the addition was completed, the temperature was raised to 70 °C and stirred for 12 h; after the reaction was completed, it was cooled to 25 °C, 100 mL of water was added to quench the reaction, then ethyl acetate was added for extraction, the extract was collected and dried over anhydrous sodium sulfate. After drying, the filtrate was collected by filtration and concentrated, and then vacuum dried at 80 °C for 24 h to obtain lithium N-trifluoroethyl-bis(trifluoromethylsulfonyl)imide.

[0111] Component A-3: Lithium N-PEG4-bis(trifluoromethylsulfonyl)imide, self-made, the preparation method includes the following steps:

[0112] In a three-necked flask under an argon atmosphere, 0.1 mol of lithium bis(trifluoromethylsulfonyl)imide, 0.15 mol of methoxypolyethylene glycol, 50 mol of p-toluenesulfonic acid and 50 mL of toluene were added, and then heated to reflux for 24 h; after the reaction was completed, it was cooled to 25 °C, washed with saturated sodium bicarbonate solution, dried over anhydrous sodium sulfate, the filtrate was collected by filtration and concentrated after drying, and then vacuum dried at 80 °C for 24 h to obtain lithium N-PEG4-bis(trifluoromethylsulfonyl)imide.

[0113] Among them, the Raman spectra of lithium bis(trifluoromethylsulfonyl)imide and Components A-1 to A-3 are as Figure 1 shown.

[0114] Component B-1: The metal element in Component B-1 is zinc, the group includes carboxyl groups, and the average particle size is 140 nm, self-made, the preparation method includes the following steps:

[0115] Zinc nitrate and 2-aminobenzene-1,3,5-tricarboxylic acid were dissolved in 100 mL of DMF aqueous solution (the volume ratio of DMF to water is 9:1) according to a molar ratio of 1:1, and then reacted in a reaction kettle at 130 °C for 36 h; after the reaction was completed, it was naturally cooled, and then the precipitate was collected by centrifugation, washed alternately with DMF and ethanol, and vacuum dried at 80 °C for 12 h after washing to obtain zinc-trimesic acid MOF; finally, the zinc-trimesic acid MOF was placed in a tube furnace, under an argon atmosphere, heated to 500 °C at a heating rate of 8 °C / min and held for 3 h, and then ground and sieved to obtain Component B-1.

[0116] The metal oxide in the said Component B-1 includes zinc metal oxide; and / or

[0117] The metal nitride in the said Component B-1 includes zinc metal nitride.

[0118] Component B-2: The metal element in Component B-2 is cobalt, the group includes pyridyl, the average particle size is 140 nm, self-made, and the preparation method includes the following steps:

[0119] Dissolve cobalt nitrate and bipyridine in 100 mL of DMF at a molar ratio of 1:2, and then react in a reaction kettle at 140 °C for 48 h; after the reaction is completed, cool naturally, then centrifuge to collect the precipitate, wash it alternately with DMF and ethanol, and dry it in vacuo at 80 °C for 12 h to obtain cobalt-bipyridine MOF; finally, place the cobalt-bipyridine MOF in a tube furnace, under an argon atmosphere, heat it to 450 °C at a heating rate of 5 °C / min and hold for 2.5 h, and then grind and sieve to obtain Component B-2.

[0120] The metal oxide in the Component B-2 includes cobalt metal oxide; and / or

[0121] The metal nitride in the Component B-2 includes cobalt metal nitride.

[0122] Component B-3: The metal element in Component B-3 is manganese, the group includes phenanthroline group, the average particle size is 140 nm, self-made, and the preparation method includes the following steps:

[0123] Dissolve manganese nitrate and phenanthroline in 100 mL of DMF at a molar ratio of 1:1, and then react in a reaction kettle at 120 °C for 30 h; after the reaction is completed, cool naturally, then centrifuge to collect the precipitate, wash it alternately with DMF and ethanol, and dry it in vacuo at 80 °C for 12 h to obtain manganese-phenanthroline MOF; finally, place the manganese-phenanthroline MOF in a tube furnace, under an argon atmosphere, heat it to 550 °C at a heating rate of 6 °C / min and hold for 2 h, and then grind and sieve to obtain Component B-3.

[0124] The metal oxide in the Component B-3 includes manganese metal oxide; and / or

[0125] The metal nitride in the Component B-3 includes manganese metal nitride.

[0126] Component B-4: The metal element in Component B-1 is zinc, the group includes carboxyl group, the average particle size is 220 nm, self-made, and the difference in the preparation method from Component B-1 lies in grinding and sieving.

[0127] Component B-5: The metal element in Component B-1 is zinc, the group includes carboxyl group, the average particle size is 50 nm, self-made, and the difference in the preparation method from Component B-1 lies in grinding and sieving.

[0128] Component B-6: The metal element in Component B-1 is zinc, the group includes carboxyl group, the average particle size is 300 nm, self-made, and the difference in the preparation method from Component B-1 lies in grinding and sieving.

[0129] Component B-7: The metal element in Component B-1 is zinc, the group includes carboxyl group, the average particle size is 30 nm, self-made, and the preparation method is different from that of Component B-1 in grinding and sieving.

[0130] Component B-8: The metal element in Component B-1 is zinc, the group includes carboxyl group, the average particle size is 350 nm, self-made, and the preparation method is different from that of Component B-1 in grinding and sieving.

[0131] Example 1

[0132] The embodiments of the present invention provide an electrolyte and a secondary battery. The preparation methods of the electrolyte and the secondary battery include the following steps:

[0133] (1) Preparation of the electrolyte

[0134] In a glove box protected by argon, a lithium salt (lithium bis(trifluoromethanesulfonyl)imide, LiTFSI) is added to an organic solvent (ethylene carbonate and dimethyl carbonate with a volume ratio of 3:2) and mixed evenly. Subsequently, an additive (the mass ratio of Component A-1 to Component B-1 is 4:1) is added and mixed evenly to obtain the electrolyte;

[0135] Among them, based on the electrolyte, the molar concentration of the lithium salt is 1 mol / L, and the mass percentages of Component A-1 and Component B-1 are 3%;

[0136] (2) Preparation of the secondary battery

[0137] The positive electrode active material (NCM535), the positive electrode binder (PVDF), and the positive electrode conductive agent (Super P) are mixed in a mass ratio of 90:5:5. N-methylpyrrolidone (NMP) is added dropwise and ground until uniform. Subsequently, the obtained slurry is coated on a copper foil and dried in a vacuum oven at 80 °C for 12 h to obtain the positive electrode plate. A secondary battery is assembled with graphite as the negative electrode and polyolefin as the separator.

[0138] Examples 2 to 3

[0139] The embodiments of the present invention provide an electrolyte and a secondary battery. The preparation methods of the electrolyte and the secondary battery are different from those of Example 1 in that the type of Component A is replaced.

[0140] Examples 4 to 10

[0141] The embodiments of the present invention provide an electrolyte and a secondary battery. The preparation methods of the electrolyte and the secondary battery are different from those of Example 1 in that the type of Component B is replaced.

[0142] Examples 11 to 14

[0143] An embodiment of the present invention provides an electrolyte and a secondary battery. The preparation methods of the electrolyte and the secondary battery are different from those of Example 1 in that the addition amounts of Component A and Component B are changed to change the mass ratio of Component A to Component B.

[0144] Examples 15 to 18

[0145] An embodiment of the present invention provides an electrolyte and a secondary battery. The preparation methods of the electrolyte and the secondary battery are different from those of Example 1 in that the addition amounts of Component A and Component B are changed to change the sum of the mass percentages of Component A and Component B in the electrolyte.

[0146] Comparative Example 1

[0147] The comparative example of the present invention provides an electrolyte and a secondary battery. The preparation methods of the electrolyte and the secondary battery are different from those of Example 1 in that Component A is not added.

[0148] Comparative Example 2

[0149] The comparative example of the present invention provides an electrolyte and a secondary battery. The preparation methods of the electrolyte and the secondary battery are different from those of Example 1 in that Component B is not added.

[0150] Comparative Example 3

[0151] The comparative example of the present invention provides an electrolyte and a secondary battery. The preparation methods of the electrolyte and the secondary battery are different from those of Example 1 in that neither Component A nor Component B is added.

[0152] The types of Component A and Component B, the average particle size d of Component B, Component A: Component B (i.e., the mass ratio of Component A to Component B), and the sum w of the mass percentages of Component A and Component B in the electrolytes of the examples and comparative examples are shown in Table 1;

[0153] Table 1 Selection results of substances and parameters in the electrolytes of examples and comparative examples

[0154]

[0155]

[0156] The secondary batteries prepared in the examples and comparative examples were subjected to a constant current charge-discharge cycle test at a rate of 1C at room temperature for 1000 cycles, and the capacity retention rate and impedance change of the secondary batteries were recorded. The results obtained are shown in Table 2;

[0157] Among them, the test method for impedance is as follows: The impedance of the battery is tested using an electrochemical workstation, with a perturbation voltage of 10Mv and a test frequency of 50mHZ to 10000HZ.

[0158] Table 2 Performance test results of secondary batteries prepared in examples and comparative examples

[0159]

[0160] As can be seen from Table 2, when the electrolyte of the present invention is applied to the preparation of secondary batteries, the obtained secondary batteries have excellent cycling performance and excellent stability; specifically, the capacity retention rate of the obtained secondary batteries after 1000 cycles is above 68%, and the impedance growth rate is below 52%.

[0161] The results of Examples 1-18 and Comparative Examples 1-3 of the present invention also show that when any one or both of Component A and Component B are not introduced, the obtained secondary batteries cannot achieve the effects of the present invention.

[0162] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An electrolyte, the electrolyte comprising an organic solvent, a lithium salt, and an additive, characterized in that, The additive includes component A and component B; Component A includes a compound represented by Formula I, R is selected from C6-C10 alkyl, fluorine-substituted C2-C5 alkyl or -(OCH2CH2) n OH; wherein, -(OCH2CH2) n OH, n is a positive integer between 2 and 8; Component B includes nitrogen-doped nanoparticles; The nanoparticles include metal oxides and / or metal nitrides; The nanoparticles include at least one of carboxyl group, pyridyl group, and phenanthroline group.

2. The electrolyte according to claim 1, characterized in that, R is selected from octyl, trifluoroethyl, or -(OCH2CH2)4OH.

3. The electrolyte according to claim 1, wherein Component A includes at least one of lithium N-octylbis(trifluoromethanesulfonyl)imide, lithium N-trifluoroethylbis(trifluoromethanesulfonyl)imide, and lithium N-PEG4bis(trifluoromethanesulfonyl)imide.

4. The electrolyte according to claim 1, wherein, The Dv50 particle size of the nitrogen-doped nanoparticles is 50 nm to 300 nm.

5. The electrolyte according to claim 1, characterized in that, The mass ratio of component A to component B is (3 to 5):

1.

6. The electrolyte according to claim 1, characterized in that, Based on the total mass of the electrolyte, the sum of the mass percentages of component A and component B is 0.3% to 3%.

7. The electrolyte according to claim 1, characterized in that, The metal element in the metal oxide includes at least one of zinc, cobalt, and manganese; and / or The metal element in the metal nitride includes at least one of zinc, cobalt, and manganese.

8. The electrolyte according to claim 1, wherein The preparation method of the nitrogen-doped nanoparticles includes the following steps: calcining a nitrogen-containing metal-organic framework material in an inert gas environment, followed by grinding and sieving to obtain the nitrogen-doped nanoparticles; The temperature of the calcination is 450 °C to 550 °C, and the time of the calcination is 1.5 h to 3.5 h.

9. A secondary battery, characterized in that, It includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte according to any one of claims 1 to 8.

10. An electrical device, characterized in that, It includes a secondary battery according to claim 9.

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