Lithium ion secondary battery and electric equipment

Abstract

The invention belongs to the technical field of secondary batteries, and particularly relates to a lithium ion secondary battery and electric equipment. The lithium ion secondary battery comprises a positive electrode, a negative electrode and an electrolyte, a specific amount of a lithium cobalt oxide material and a nickel cobalt lithium manganate ternary material are cooperatively used, and a compound A, a compound B and a compound C are added into the electrolyte for cooperative use, so that the cost can be reduced, the energy density can be improved, and meanwhile, the cycle performance and the safety performance can be improved.

Description

Technical Field

[0001] This application belongs to the technical field of secondary batteries, and specifically relates to a lithium-ion secondary battery and an electrical device. Background Art

[0002] With the rapid development of technology and the continuous improvement of living standards, consumers' demand for batteries with higher energy density and faster charging speed is increasing. Lithium cobalt oxide material is a commonly used cathode material for lithium-ion batteries with high energy density at present. However, although the lithium cobalt oxide cathode material has a relatively high capacity and a long cycle life, cobalt resources are scarce and the price is expensive. The ternary material is a cathode material prepared from nickel salt, cobalt salt, and manganese salt. As a cathode material with low cost, high safety, and relatively superior comprehensive performance, the ternary material is gradually popularized.

[0003] Using lithium cobalt oxide material and ternary material in combination can reduce costs while ensuring energy density. However, due to the difference in the voltage platforms of the two substances, there is a large potential difference during charge and discharge, which may cause electrochemical mismatch between different materials. During the battery cycle, transition metal elements in the cathode material will dissolve out. These metal ions migrate in the electrolyte and are reduced on the surface of the negative electrode, damaging the SEI film and causing side reactions, deteriorating the cycle performance and safety performance of the battery. Summary of the Invention

[0004] Therefore, the technical problem to be solved by this application is to overcome the defects such as the deterioration of the cycle performance and safety performance of the battery after using lithium cobalt oxide material and ternary material in combination in the prior art, so as to provide a lithium-ion secondary battery and an electrical device.

[0005] For this reason, this application provides the following technical solutions:

[0006] According to one aspect of this application, a lithium-ion secondary battery is provided, including a positive electrode, a negative electrode, and an electrolyte.

[0007] Wherein, the positive electrode includes a positive electrode current collector and an active layer coated on at least one surface of the positive electrode current collector. The active layer includes a positive electrode active material. The positive electrode active material includes a lithium cobalt oxide material and a nickel cobalt manganese lithium ternary material. Based on the total mass of the positive electrode active material, the mass percentage content of the nickel cobalt manganese lithium ternary material is d%, and 1 ≤ d ≤ 50.

[0008] The electrolyte includes compound A, compound B, and compound C. Compound B includes a polyether nitrile compound, and compound C includes 1,3,6-hexane trinitrile; Compound A has the structure shown in the following general formula:

[0009]

[0010] Among them, L is O or a linking group; R is selected from unsubstituted or Ra-substituted C2-C6 alkyl, unsubstituted or Ra-substituted C2-C6 alkenyl, unsubstituted or Ra-substituted C2-C6 alkynyl, unsubstituted or Ra-substituted C2-C6 nitrogen-containing heteroaryl, unsubstituted or Ra-substituted C6-C 12 aryl, and the substituents Ra of each group are independently selected from fluorine or C1-C6 fluoroalkyl; R1 is selected from one of fluorine or C1-C6 fluoroalkyl;

[0011] Based on the total mass of the electrolyte, the mass percentage of compound A is a%, 0.1 ≤ a ≤ 15; the mass percentage of compound B is b%, 0.1 ≤ b ≤ 5; the mass percentage of compound C is 0.1 ≤ c ≤ 5; and it satisfies: 0.3 ≤ d / (b + c) ≤ 20, 0.02 < a / (b + c) ≤ 2.

[0012] In some alternative embodiments, compound A has any of the following structures:

[0013]

[0014]

[0015] In some alternative embodiments, compound B includes at least one of 1,2,3,4,5-penta(2-cyanoethoxy)pentane (CAS: 55726-81-3), ethylene glycol bis(2-cyanoethyl) ether (CAS: 59086-77-0), diethylene glycol bis(2-cyanoethyl) ether triethylene glycol bis(2-cyanoethyl) ether tetraethylene glycol bis(2-cyanoethyl) ether ethylene glycol bis(4-cyanobutyl) ether and ethylene glycol (bis) propionitrile ether (DENE, CAS: 3386-87-6), 1,2,3-tris(2-cyanoxy)propane (TCEP, CAS: 2465-93-2).

[0016] In some alternative embodiments, compound C further includes at least one of benzonitrile, p-tolunitrile, 3,5-difluorobenzonitrile, adiponitrile (AND), succinonitrile (SN), 1,2,6-hexanetricarbonitrile, 3,5-bis(trifluoromethyl)benzonitrile, ethoxypentafluorocyclotriphosphazene, and hexafluorocyclotriphosphazene.

[0017] In some alternative embodiments, the electrolyte further includes a lithium salt. Based on the total mass of the electrolyte, the mass percentage of the lithium salt in the electrolyte is 10-30%;

[0018] Optionally, the lithium salt includes lithium hexafluorophosphate and lithium bis(trifluoromethanesulfonyl)imide. Based on the total mass of the electrolyte, the mass percentage of lithium hexafluorophosphate is e%, and the mass percentage of lithium bis(trifluoromethanesulfonyl)imide is f%, and 8 ≤ e ≤ 20, 0.5 ≤ f ≤ 10, 1 ≤ e / f ≤ 5 are satisfied.

[0019] In some alternative embodiments, the electrolyte further includes ethylene carbonate. Based on the total mass of the electrolyte, the mass percentage of ethylene carbonate is g%, and 0.1 < g ≤ 20, 0.1 < a / g ≤ 0.8 are satisfied.

[0020] In some alternative embodiments, the electrolyte further includes a sulfur-containing additive. Based on the total mass of the electrolyte, the mass percentage of the sulfur-containing additive is h%, and 0.1 < h < 6, 0.3 ≤ h / a ≤ 3 are satisfied.

[0021] Optionally, the sulfur-containing additive has any of the following structures:

[0022]

[0023] In some alternative embodiments, the positive electrode active material further contains aluminum. Based on the total mass of the positive electrode active material, the mass percentage of aluminum is i%, and 0.3 ≤ i ≤ 1.2.

[0024] In some alternative embodiments, the negative electrode includes a negative electrode active material, and the negative electrode active material includes graphite and a silicon-carbon composite material. The mass percentage of silicon in the silicon-carbon composite material in the negative electrode active material is j%, and 0.5 ≤ j ≤ 35.

[0025] Optionally, 0.1 ≤ j / a ≤ 10 is satisfied.

[0026] According to another aspect of the present application, there is provided an electrical device including the above lithium ion secondary battery.

[0027] The technical solution of the present application has the following advantages:

[0028] The lithium-ion secondary battery provided by the present application includes a positive electrode, a negative electrode, and an electrolyte. Among them, the positive electrode includes a positive electrode current collector and an active layer coated on at least one surface of the positive electrode current collector. The active layer includes a positive electrode active material, and the positive electrode active material includes a lithium cobaltate material and a lithium nickel cobalt manganese oxide ternary material. Based on the total mass of the positive electrode active material, the mass percentage content of the lithium nickel cobalt manganese oxide ternary material is d%, where 1 ≤ d ≤ 50; the electrolyte includes a compound A, a compound B, and a compound C with a specific structure. The compound B includes a polyether nitrile compound, and the compound C includes 1,3,6-hexanetricarbonitrile; based on the total mass of the electrolyte, the mass percentage content of the compound A is a%, where 0.1 ≤ a ≤ 15; the mass percentage content of the compound B is b%, where 0.1 ≤ b ≤ 5; the mass percentage content of the compound C is 0.1 ≤ c ≤ 5; and it satisfies: 0.3 ≤ d / (b + c) ≤ 20, 0 < a / (b + c) ≤ 2. By using a specific amount of the lithium cobaltate material and the lithium nickel cobalt manganese oxide ternary material in combination, and by using the compound A, the compound B, and the compound C in the electrolyte in combination, the present application can improve the cycle performance and safety performance while reducing costs and increasing the energy density. Specifically, when the lithium cobaltate material and the lithium nickel cobalt manganese oxide ternary material are used in combination, although the cost can be reduced and the energy density can be increased, when using this blended positive electrode active material, during the battery cycle, due to the voltage platform difference between the two, the transition metal elements in the positive electrode active material will be more likely to dissolve. These metal ions migrate in the electrolyte and are reduced on the surface of the negative electrode, damaging the SEI film and causing more side reactions to occur, deteriorating the battery performance; in the present application, by adding the compound B and the compound C to the electrolyte, and using the compound B and the compound C in synergy, they act on the positive electrode. Through the interaction between the ether bond and the cyano group within and between molecules, the polarity of the molecule can be enhanced, providing a strong electron-withdrawing effect, forming a stable chemical bond on the surface of the positive electrode, inhibiting the dissolution of the positive electrode transition metal ions, and at the same time improving the stability and conductivity of the positive electrode interface film, improving the cycle performance of the battery; the use of the compound A can not only improve the thermal stability of the positive electrode, but also inhibit the co-insertion of the compound B and the compound C into the negative electrode, alleviating the volume expansion of the negative electrode; in addition, the compound A can also participate in the formation of an SEI film with good mechanical properties on the negative electrode. When subjected to the expansion stress of the negative electrode, the SEI film is not easily deformed, so it can also inhibit the cyclic expansion of the battery.

[0029] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present application. Detailed Embodiments

[0030] The following embodiments are provided to better further understand the present application, which are not limited to the described best mode, and do not limit the content and protection scope of the present application. Any product identical or similar to the present application obtained by anyone under the inspiration of the present application or by combining the features of the present application with other prior art features falls within the protection scope of the present application.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the text of this application are intended to cover non-exclusive inclusion.

[0032] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in connection with the embodiments can be included in at least one embodiment of this application. The phrase does not necessarily refer to the same embodiment at every occurrence in the specification, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0033] The "range" disclosed in this application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The ranges defined in this way can include or exclude the end values and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. In this application, unless otherwise stated, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" have been fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when it is stated that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter can be, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0034] In the description of the embodiments of this application, the term "and / or" is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone.

[0035] In the description of the embodiments of this application, the term "at least one" refers to one or more than two (including two).

[0036] For those embodiments where specific experimental procedures or conditions are not specified, the operations or conditions of the conventional experimental procedures described in the literature in this field can be followed. For reagents or instruments whose manufacturers are not specified, they are all conventional reagent products that can be obtained commercially.

[0037] As described in the background art, to solve the technical problem that the cycle performance and safety performance of the battery will deteriorate when lithium cobaltate material and ternary material are used in combination, the present application provides the following technical solutions.

[0038] According to one aspect of the present application, a lithium ion secondary battery is provided, including a positive electrode, a negative electrode and an electrolyte,

[0039] Wherein, the positive electrode includes a positive electrode current collector and an active layer coated on at least one surface of the positive electrode current collector. The active layer includes positive electrode active materials. The positive electrode active materials include lithium cobaltate material and nickel cobalt manganese oxide ternary material. Based on the total mass of the positive electrode active materials, the mass percentage content of the nickel cobalt manganese oxide ternary material is d%, 1≤d≤50;

[0040] The electrolyte includes compound A, compound B and compound C. Compound B includes polyether nitrile compounds. Compound C includes 1,3,6-hexanetricarbonitrile. Compound A has the structure shown by the following general formula:

[0041]

[0042] Wherein, L is O or a linking bond; R is selected from one of unsubstituted or Ra-substituted C2-C6 alkyl, unsubstituted or Ra-substituted C2-C6 alkenyl, unsubstituted or Ra-substituted C2-C6 alkynyl, unsubstituted or Ra-substituted C2-C6 nitrogen-containing heteroaryl, unsubstituted or Ra-substituted C6-C 12 aryl. The substituents Ra of each group are independently selected from fluorine or C1-C6 fluoroalkyl; R1 is selected from one of fluorine or C1-C6 fluoroalkyl;

[0043] Based on the total mass of the electrolyte, the mass percentage content of compound A is a%, 0.1≤a≤15; the mass percentage content of compound B is b%, 0.1≤b≤5; the mass percentage content of compound C is 0.1≤c≤5; and it satisfies: 0.3≤d / (b + c)≤20, 0.02<a / (b + c)≤2.

[0044] As an example, based on the total mass of the positive electrode active material, the mass percentage of the lithium nickel cobalt manganese oxide ternary material can be 1%, 3%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or within the range composed of any of the above values; based on the total mass of the electrolyte, the mass percentage of Compound A can be 0.1%, 3%, 5%, 7%, 9%, 10%, 12%, 13%, 15%, or within the range composed of any of the above values; the mass percentage of Compound B can be 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.7%, 2%, 2.3%, 2.5%, 2.8%, 3%, 3.5%, 4%, 4.5%, 5%, or within the range composed of any of the above values; the mass percentage of Compound C can be 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.7%, 2%, 2.3%, 2.5%, 2.8%, 3%, 3.5%, 4%, 4.5%, 5%, or within the range composed of any of the above values; the value of d / (b + c) can be 0.3, 0.5, 1, 3, 5, 7, 9, 10, 12, 15, 17, 19, 20, or within the range composed of any of the above values; the value of a / (b + c) can be 0.02, 0.1, 0.3, 0.5, 0.7, 0.9, 1, 1.3, 1.5, 1.8, 2, or within the range composed of any of the above values.

[0045] The lithium ion secondary battery provided by this application can improve the cycle performance and safety performance while reducing costs and increasing the energy density by using a specific amount of lithium cobalt oxide material and lithium nickel cobalt manganese oxide ternary material in combination, and by using Compound A, Compound B, and Compound C added to the electrolyte. Specifically:

[0046] In this application, a specific amount of lithium cobaltate material and lithium nickel cobalt manganese oxide ternary material are used in combination, which can improve the energy density and reduce the cost. However, when using this blended cathode active material, since the voltage plateau of the lithium cobaltate material is higher than that of the lithium nickel cobalt manganese oxide ternary material, during the battery cycling process, due to the voltage plateau difference between the two, the transition metal elements in the cathode material are more likely to dissolve out. These metal ions migrate in the electrolyte and are reduced on the surface of the negative electrode, damaging the SEI film, resulting in more side reactions and deteriorating the battery performance. Therefore, it is necessary to add compound B and compound C to the electrolyte. 1,3,6-Hexanetricarbonitrile in compound C has higher chemical stability and reactivity compared to other alkyl nitrile compounds. The three cyano groups of 1,3,6-hexanetricarbonitrile are asymmetrically distributed on the hexane chain, and its molecular configuration is more flexible, which can cover different sites on the electrode surface simultaneously and form a denser adsorption layer. Compound B and compound C act synergistically on the positive electrode. Through the interaction between the intramolecular and intermolecular ether bonds and cyano groups, the polarity of the molecule can be enhanced, providing a strong electron-withdrawing effect, and it is easier to form stable chemical bonds on the positive electrode surface, inhibiting the dissolution of the positive electrode transition metal ions, and also improving the stability and conductivity of the positive electrode interface film, thereby improving the cycling performance of the battery. However, compound B and compound C will co-embed with lithium ions into the negative electrode, damaging the structural stability of the negative electrode; since compound A has a relatively high reduction potential and can preferentially form a film on the negative electrode of the battery, the SEI film has good ionic conductivity and electron insulation. The ionic conductivity ensures the intercalation and deintercalation of lithium ions in the SEI film, while the electron insulation helps to stabilize the potential on the surface of the negative electrode, avoiding the generation of local overpotential, reducing the possibility of reduction decomposition of solvent molecules and co-intercalation of solvent molecules. Therefore, after adding compound A, the co-embedding of compound B and compound C into the negative electrode can be inhibited; and compound A can also participate in the formation of an SEI film with good mechanical properties on the negative electrode, and it is not easy to deform when subjected to the expansion stress of the negative electrode. Therefore, it can also inhibit the cyclic swelling of the battery.

[0047] In this application, if the content of the ternary material of lithium nickel cobalt manganate in the positive electrode active material is too small, the cost reduction is not obvious; when the content is too high, more metal ions will dissolve out at high voltages, and Li and Ni mixing is more likely to occur, resulting in the destruction of the positive electrode structure and further deterioration of performance such as cycling. Compound A has relatively poor oxidation resistance and is prone to oxidation decomposition at high voltages, generating harmful substances such as HF, corroding the electrode, and further deteriorating the battery cycling performance; when the content in the electrolyte is too small, the improvement of battery performance is not significant. When the contents of Compound B and Compound C are too small, sufficient protection cannot be provided to the positive electrode to inhibit problems such as the dissolution of positive electrode metal ions, etc., but when the content is too high, there will be a large amount of free compounds that do not form protection on the positive electrode, causing co-insertion of solvents at the negative electrode, affecting the structural stability of the negative electrode, and leading to the deterioration of cycling performance and safety performance. When the ratio d / (b + c) of the ternary material of lithium nickel cobalt manganate to Compound B and Compound C in the positive electrode material reaches a certain proportional relationship, sufficient protection can be provided to the positive electrode, and the risk of co-insertion of solvents occurring at the negative electrode can be reduced. When the ratio a / (b + c) of Compound A to Compound B and Compound C satisfies a certain proportional relationship, sufficient protection can be provided to the negative electrode to inhibit the co-insertion of solvent molecules.

[0048] In some optional embodiments, Compound A has any of the following structures:

[0049]

[0050]

[0051] In some optional embodiments, Compound B includes at least one of 1,2,3,4,5-penta(2-cyanoethoxy)pentane (CAS: 55726-81-3), ethylene glycol bis(2-cyanoethyl) ether (CAS: 59086-77-0), diethylene glycol bis(2-cyanoethyl) ether triethylene glycol bis(2-cyanoethyl) ether tetraethylene glycol bis(2-cyanoethyl) ether ethylene glycol bis(4-cyanobutyl) ether and ethylene glycol (bis) propionitrile ether (DENE, CAS: 3386-87-6), 1,2,3-tris(2-cyanooxy)propane (TCEP, CAS: 2465-93-2).

[0052] In some optional embodiments, Compound C further includes at least one of benzonitrile, p-tolunitrile, 3,5-difluorobenzonitrile, adiponitrile (AND), succinonitrile (SN), 1,2,6-hexanetricarbonitrile, 3,5-bis(trifluoromethyl)benzonitrile, ethoxypentafluorocyclotriphosphazene, and hexafluorocyclotriphosphazene.

[0053] In some optional embodiments, the electrolyte further includes a lithium salt. Based on the total mass of the electrolyte, the mass percentage of the lithium salt in the electrolyte is 10-30%; the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorobis(oxalato)phosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methyl, or lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethanesulfonate, lithium hexafluorozirconate (Li2ZrF6);

[0054] Optionally, the lithium salt includes lithium hexafluorophosphate (LiPF6) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Based on the total mass of the electrolyte, the mass percentage of lithium hexafluorophosphate is e%, and the mass percentage of lithium bis(trifluoromethanesulfonyl)imide is f%, and 8 ≤ e ≤ 20, 0.5 ≤ f ≤ 10, 1 ≤ e / f ≤ 5 are satisfied. As an example, based on the total mass of the electrolyte, the mass percentage of lithium hexafluorophosphate can be 8%, 10%, 12%, 15%, 17%, 19%, 20%, or within the range composed of any of the above values; the mass percentage of lithium bis(trifluoromethanesulfonyl)imide can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 8%, 10%, or within the range composed of any of the above values; the value of e / f can be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or within the range composed of any of the above values.

[0055] In this application, by using lithium salts LiPF6 and LiTFSI in combination and regulating the ratio of LiPF6 and LiTFSI, the solvation structure of the electrolyte can be optimized. This is because the anion (TFSI - ) of LiTFSI binds to Li+ more easily than the anion (PF6 - ) of LiPF6, thus providing a more stable solvation structure. The optimization of this structure can enhance the oxidation stability of the electrolyte, reduce the oxidation of compound A, further improve the anode and cathode stability, and further optimize the cycling performance of the battery.

[0056] In some optional embodiments, the electrolyte further includes ethylene carbonate (EC). Based on the total mass of the electrolyte, the mass percentage of ethylene carbonate is g%, and it satisfies: 0.1 < g ≤ 20, 0.1 < a / g ≤ 0.8. As an example, based on the total mass of the electrolyte, the mass percentage of ethylene carbonate can be 0.1%, 1%, 3%, 5%, 7%, 9%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, or within the range composed of any of the above values; the value of a / g can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or within the range composed of any of the above values.

[0057] In this application, ethylene carbonate and compound A cooperate to form a SEI film with intertwined organic and inorganic components on the surface of the negative electrode. This SEI film not only has good flexibility and elasticity but also sufficient mechanical strength and hardness, enabling the SEI film to better adapt to the volume change of the battery during charge and discharge, improving the cyclic swelling of the battery, and further enhancing the battery cycle life. As the main solvent for dissolving lithium salts, if the content of ethylene carbonate is too low, the solubility of lithium salts will be reduced; while if the content is too high, there will be a risk of decomposition and gas generation, and it may also form an excessive amount of SEI film with organic components on the negative electrode, reducing the mechanical strength and hardness of the SEI film, resulting in poor electron insulation of the SEI film, and further affecting the further improvement of the battery cycle performance. That g / a satisfies a certain proportional relationship can adjust the proportion of organic and inorganic components in the SEI film, enabling both the mechanical strength and elasticity of the SEI film to meet the battery performance requirements. When the proportion exceeds the range, the content of the SEI film with a single component will be relatively high, causing insufficient elasticity of the SEI film to adapt to the expansion of the negative electrode or poor electron insulation leading to co-insertion of solvents, etc., and further affecting the further improvement of the battery cycle performance.

[0058] In some optional embodiments, the electrolyte further includes a sulfur-containing additive. Based on the total mass of the electrolyte, the mass percentage of the sulfur-containing additive is h%, and it satisfies: 0.1 < h < 6, 0.3 ≤ h / a ≤ 3; As an example, based on the total mass of the electrolyte, the mass percentage of the sulfur-containing additive can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, or within the range composed of any of the above values; the value of h / a can be 0.3, 0.5, 0.8, 1, 1.2, 1.5, 1.7, 2, 2.2, 2.5, 2.8, 3, or within the range composed of any of the above values.

[0059] In this application, the sulfur-containing compound has a lower reduction potential than Compound A and Compound G, and can form a stable sulfur-containing compound film layer outside the SEI layer formed by Compound A and / or Compound G. Since film formation inhibits side reactions occurring due to direct contact between the electrode and the electrolyte, avoids decomposition of the electrolyte, and the formed film has good ionic conductivity and electronic insulation, reducing the damage to the negative electrode structure caused by co-insertion of the solvent, thereby further improving the cycle and thermal box safety performance of the battery. If the amount of the sulfur-containing compound is too small, the effect of further improving the battery performance is not obvious. However, if it is too much, although the thermal box safety performance of the battery is improved more, the impedance of the SEI film formed by it will further increase, which will affect the cycle performance. By controlling the ratio of h / a, the negative electrode SEI film can not only improve the thermal box safety performance of the battery, but also have a smaller interfacial impedance, improving the cycle performance.

[0060] Optionally, the sulfur-containing additive has any one of the following structures:

[0061]

[0062]

[0063] In some alternative embodiments, the positive electrode active material further contains aluminum element, and based on the total mass of the positive electrode active material, the mass percentage of the aluminum element is i%, where 0.3 ≤ i ≤ 1.2. As an example, based on the total mass of the positive electrode active material, the mass percentage of the aluminum element can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, or within the range composed of any of the above values.

[0064] In this application, aluminum can be doped into the lithium cobalt oxide material, or into the ternary lithium nickel cobalt manganese oxide material, or doped into both simultaneously, as long as the content of aluminum in the cathode active material is within the above range. The radius of aluminum is similar to that of cobalt and it shows electrochemical inertness, which can stabilize the structure of the ternary material. Especially at high voltages, aluminum forms stable bonds with oxygen, showing good structural stability and lattice strain, and improving the cycle stability of the battery. In addition, since the Al element has higher chemical activity compared with other doping elements in the cathode material, during the synthesis of the cathode material, some aluminum elements are likely to accumulate on the surface of the cathode active material. Since the conductivity of aluminum itself can provide good interfacial contact for the internal particles of the cathode active material, the rate performance of the material is improved. In addition, the aluminum element enriched on the surface of the cathode active material is easily oxidized to form Al2O3, forming a protective layer on the electrode surface, inhibiting the side reaction between the electrode and the electrolyte and effectively inhibiting the oxidation activity of the surface cations of the material at high voltages. Together with Compound B and Compound C, it slows down the side reaction between the material and the organic electrolyte at high voltages, stabilizes the surface of the material, and further improves the cycle life of the battery. If the aluminum content is too low, the effect of further stabilizing the structure of the cathode material is not obvious, while if the content is too high, it will affect the energy density of the material, and the Al2O3 layer formed on the electrode surface will also greatly increase the interfacial impedance, affecting the further improvement of the cycle performance and rate performance.

[0065] In some alternative embodiments, the negative electrode includes a negative electrode active material, and the negative electrode active material includes graphite and a silicon-carbon composite material. The percentage content of silicon in the silicon-carbon composite material in the negative electrode active material is j%, where 0.5 ≤ j ≤ 35; as an example, the percentage content of silicon in the silicon-carbon composite material in the negative electrode active material can be 0.5%, 1%, 3%, 5%, 7%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, or within the range composed of any of the above values. In this application, the use of the silicon-carbon composite material can store more lithium ions compared with the carbon-based negative electrode material, improving the energy density of the battery. If the silicon content is too low, it cannot play the role of improving the energy density of the battery, while if the content is too high, the negative electrode will expand greatly, consuming the electrolyte to repair the damaged SEI film during the cycle process, resulting in a decline in the cycle performance.

[0066] Optionally, it satisfies: 0.1 ≤ j / a ≤ 10. As an example, the value of j / a can be 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 7, 8, 9, 10, or within the range composed of any of the above values. When the content of the compound A and the silicon content of the negative electrode satisfy the above relationship, the SEI film formed on the surface of the battery negative electrode has sufficient strength and elasticity. When the negative electrode expands and contracts during the cycling process, the SEI film can adapt to the volume change of the negative electrode and is not easily broken, thereby further improving the cycling performance of the battery.

[0067] According to another aspect of the present application, there is provided an electrical device including the above-mentioned lithium-ion secondary battery.

[0068] Those skilled in the art can understand that the lithium-ion secondary battery provided by the present application further includes structural components such as a separator and a housing. During the charge and discharge process of the battery, lithium ions are embedded and extracted back and forth between the positive electrode and the negative electrode, and the electrolyte plays a role in conducting ions between the positive electrode and the negative electrode. The separator is arranged between the positive electrode and the negative electrode, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows lithium ions to pass through.

[0069] As an example, the materials, compositions, and manufacturing methods of the positive electrode used in the lithium-ion battery of the present application may further include any technologies disclosed in the prior art.

[0070] As an example, the negative electrode includes a negative electrode current collector and a negative electrode active material layer. The negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active material layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector. The materials, compositions, and manufacturing methods of the negative electrode used in the lithium-ion battery of the present application may include any technologies disclosed in the prior art.

[0071] There are no particular limitations on the materials and shapes of the separator used in the lithium-ion secondary battery of the present application, and it may include any technologies disclosed in the prior art.

[0072] The electrolyte used in the lithium-ion secondary battery of the present application may also include any technologies disclosed in the prior art.

[0073] The present application does not specifically limit the preparation method of the lithium-ion secondary battery, and the lithium-ion secondary battery can be prepared by using conventional preparation methods in the art. For example, the positive electrode, the separator, and the negative electrode are stacked in sequence, with the separator located between the positive electrode and the negative electrode, and the battery cell is obtained through a stacking or winding process, and then through processes such as baking, liquid injection, formation, and encapsulation, the lithium-ion secondary battery of the present application can be obtained.

[0074] It can be understood that in the electrical device provided by the present application, the lithium-ion secondary battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0075] The electrical device has the same advantages as the above lithium-ion secondary battery compared with the prior art, which will not be elaborated here.

[0076] Next, the present application will be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present application in any way.

[0077] Embodiment 1

[0078] This embodiment provides a lithium-ion secondary battery, and its specific composition and preparation method are as follows:

[0079] 1) Preparation of the positive electrode

[0080] Mix the positive electrode active materials lithium cobalt oxide (LiCoO2), nickel cobalt manganese ternary material (NCM811), polyvinylidene fluoride (PVDF), SP (super P), and carbon nanotubes (CNT) according to a mass ratio of 57.6:38.4:2:1.5:0.5, add N-methylpyrrolidone (NMP), and stir under a vacuum mixer until the mixed system becomes a homogeneous and flowing positive electrode active paste; uniformly coat the positive electrode active paste on both surfaces of the aluminum foil; dry the coated aluminum foil, and then obtain the required positive electrode through rolling and slitting. The areal density of the positive electrode can be 0.010 - 0.018 g / cm2, and the tap density can be 3.8 - 4.5 g / cm 3 , in this embodiment, the areal density of the positive electrode is 0.016 g / cm2, and the tap density is 4.2 g / cm 3 .

[0081] 2) Preparation of the negative electrode

[0082] Mix artificial graphite as the negative electrode active material, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber, conductive carbon black (SP), and single-walled carbon nanotubes (SWCNTs) in a mass ratio of 94.5:2.5:1.5:1:0.5, add deionized water, and obtain the negative electrode active paste under the action of a vacuum mixer; uniformly coat the negative electrode active paste on both surfaces of the copper foil; dry the coated copper foil at room temperature, then transfer it to an 80°C oven and dry for 10 h, and then obtain the negative electrode through cold pressing and slitting. The areal density of the negative electrode can be 0.004 - 0.007 g / cm 2 , and the tap density is 1.65 - 1.78 g / cm 3 . In this example, the areal density of the negative electrode is 0.0055 g / cm2, and the tap density is 1.7 g / cm 3 .

[0083] 3) Preparation of the electrolyte

[0084] In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), mix propylene carbonate (PC) / propyl propionate (PP) / ethyl propionate (EP) evenly in a mass ratio of 20:20:50. Then quickly add lithium hexafluorophosphate (LiPF6) that is fully dried based on e% of the total mass of the electrolyte, and after dissolution, add compound A, compound B, and compound C based on a%, b%, and c% of the total mass of the electrolyte. The specific addition amounts and compound selections are shown in Table 1. After stirring evenly and passing the moisture and free acid tests, the required electrolyte is obtained.

[0085] 4) Assembly of the battery

[0086] Stack the positive electrode in step 1), the negative electrode in step 2), and the separator in the order of positive electrode, separator (a polypropylene separator with a thickness of 8 μm), and negative electrode, and then wind them to obtain an electrode core; place the electrode core in an outer packaging aluminum foil, inject the electrolyte in step 3) into the outer packaging, and obtain a lithium-ion secondary battery with a capacity of 6 Ah through processes such as vacuum packaging, standing, formation, shaping, and sorting. In this application, the charge and discharge range of the battery is 3.0 - 4.55 V.

[0087] Example 2

[0088] This example provides a lithium-ion secondary battery. Compared with Example 1, the difference is that the electrolyte also includes g% of ethylene carbonate, as shown in Table 1 specifically.

[0089] Example 3

[0090] This example provides a lithium-ion secondary battery. Compared with Example 1, the difference is that the electrolyte also includes h% of a sulfur-containing additive, as shown in Table 1 specifically.

[0091] Example 4

[0092] This example provides a lithium-ion secondary battery. Compared with Example 1, the difference is that the lithium salt in the electrolyte is a mixture of lithium hexafluorophosphate and lithium bis(trifluoromethanesulfonyl)imide. Based on the total mass of the electrolyte, their mass percentages are e% and f% respectively, as shown in Table 1 for details.

[0093] Example 5

[0094] This example provides a lithium-ion secondary battery. Compared with Example 1, the difference is that the positive electrode active material is doped with i% of aluminum element. In this example, both lithium cobaltate and NCM811 contain i% of aluminum element, as shown in Table 1 for details.

[0095] Example 6

[0096] This example provides a lithium-ion secondary battery. Compared with Example 1, the difference is that the composition of the negative electrode active paste is different. In this example, the negative electrode active paste includes artificial graphite, silicon-carbon material, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber, conductive carbon black (SP), and single-walled carbon nanotubes (SWCNTs) with a mass ratio of 54.5:40:2.5:1.5:1:0.5.

[0097] Example 7

[0098] This example provides a lithium-ion secondary battery, and its specific composition and preparation method are as follows:

[0099] 1) Preparation of the positive electrode

[0100] Mix the positive electrode active materials lithium cobaltate (LiCoO2), nickel-cobalt-manganese ternary material (NCM811), polyvinylidene fluoride (PVDF), SP (super P), and carbon nanotubes (CNT) according to a mass ratio of 57.6:38.4:2:1.5:0.5. In this example, both lithium cobaltate and NCM811 contain i% of aluminum element. Add N-methylpyrrolidone (NMP) and stir under a vacuum mixer until the mixed system becomes a homogeneous and fluid positive electrode active paste; uniformly coat the positive electrode active paste on both surfaces of the aluminum foil; dry the coated aluminum foil, and then obtain the required positive electrode through rolling and slitting. In this example, the surface density and compaction density of the positive electrode are the same as those in Example 1.

[0101] 2) Preparation of the negative electrode

[0102] Mix artificial graphite, silicon-carbon material, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber, conductive carbon black (SP), and single-walled carbon nanotubes (SWCNTs) as the negative electrode active materials in a mass ratio of 54.5:40:2.5:1.5:1:0.5, add deionized water, and obtain the negative electrode active paste under the action of a vacuum mixer; uniformly coat the negative electrode active paste on both surfaces of the copper foil; air-dry the coated copper foil at room temperature, then transfer it to an 80°C oven for drying for 10 h, and then obtain the negative electrode through cold pressing and slitting. In this example, the surface density and tap density of the negative electrode are the same as those in Example 1.

[0103] 3) Preparation of the electrolyte

[0104] In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), mix propylene carbonate (PC) / propyl propionate (PP) / ethyl propionate (EP) evenly in a mass ratio of 20:20:50. Then quickly add lithium hexafluorophosphate (LiPF6) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) that are fully dried based on e% and f% of the total mass of the electrolyte, and after dissolution, add compound A, compound B, compound C, ethylene carbonate (EC), and sulfur-containing additive based on a%, b%, c%, g%, h% of the total mass of the electrolyte. The specific addition amounts and compound selections are shown in Table 1. After stirring evenly and passing the moisture and free acid tests, the required electrolyte is obtained.

[0105] 4) Assembly of the battery

[0106] Stack the positive electrode in step 1), the negative electrode in step 2), and the separator in the order of positive electrode, separator (a polypropylene separator with a thickness of 8 μm), and negative electrode, and then wind them to obtain an electrode core; place the electrode core in an outer packaging aluminum foil, inject the electrolyte in step 3) into the outer packaging, and obtain a lithium-ion secondary battery with a capacity of 6 Ah through processes such as vacuum packaging, standing, formation, shaping, and sorting. In this application, the charge and discharge range of the battery is 3.0 - 4.55 V.

[0107] Examples 8 - 38

[0108] This example provides a lithium-ion secondary battery. Compared with Example 7, the difference lies in the composition of the electrolyte, the positive electrode active material, and the negative electrode active material, as detailed in Table 1.

[0109] Example 39

[0110] This example provides a lithium-ion secondary battery. Compared with Example 1, the difference is that the electrolyte also includes 1% of succinonitrile based on the total mass of the electrolyte.

[0111] Comparative Examples 1 - 7

[0112] Comparative Examples 1 - 7 are different from Example 7 in that the compositions of the electrolytes, the cathode active materials, and the anode active materials are different. In Comparative Example 4, adiponitrile is used instead of HTCN. Comparative Examples 5 - 7 do not satisfy the two relationships of d / (b + c) and / or a / (b + c). See Table 1 for details.

[0113] Table 1

[0114]

[0115]

[0116] Performance Test

[0117] 1. 25°C Cycling Test

[0118] The batteries obtained from each example and comparative example are charged at a constant current of 3C to a voltage of 4.55V at 25°C, then charged at a constant voltage of 4.55V until the current is 0.05C, left standing for 5 minutes, and then discharged at a constant current of 3C to a voltage of 3.0V. This is one charge - discharge cycle. The discharge capacity in the first week is recorded as x mAh, and the discharge capacity in the Nth week is recorded as y mAh; the capacity in the Nth week is divided by the capacity in the first week to obtain the cycle capacity retention rate R = y / x×100%. Record the number of cycles of the battery when the cycle capacity retention rate is 80%.

[0119] 2. Cycle Expansion Test

[0120] The thickness value d1 of the batteries obtained from each example and comparative example is measured at 25°C, then charged at a constant current of 3C to a voltage of 4.55V, then charged at a constant voltage of 4.55V until the current is 0.05C, left standing for 5 minutes, and then discharged at a constant current of 3C to a voltage of 3.0V. This is one charge - discharge cycle. Record the thickness d2 of the battery after 500 cycles. The battery thickness change rate D=(d2 - d1) / d1×100%.

[0121] 3. Thermal Box Performance Test

[0122] At room temperature, the batteries obtained from each example and comparative example are charged at a constant current of 1C to 4.55V, left standing for 60 minutes, the appearance is inspected and photographed. Then the temperature is raised to 132°C ± 2°C at a rate of 3°C / min ± 2°C / min and maintained for 60 minutes. If the sample does not leak liquid, does not emit smoke, does not catch fire, and does not explode, it is recorded as passing the test. 10 samples of each example or comparative example are tested, and the number of samples n passing the thermal box performance test is recorded, and it is calculated as n / 10.

[0123] The specific test results are shown in the following table:

[0124] Table 2

[0125]

[0126]

[0127] As can be seen from the data in the above table, in the embodiments provided by the present application, by using a specific amount of lithium cobaltate material and ternary lithium nickel cobalt manganate material in combination, and by using compounds A, B, and C in combination in the electrolyte, and regulating the amounts of each component within the scope defined in the present application, it is possible to improve the cycle performance and safety performance while reducing costs and increasing the energy density.

[0128] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. A lithium ion secondary battery, characterized in that: Including positive electrode, negative electrode and electrolyte, The positive electrode comprises a positive electrode current collector and an active layer coated on at least one side of the positive electrode current collector, the active layer comprises a positive electrode active material, the positive electrode active material comprises a lithium cobalt oxide material and a nickel cobalt lithium manganese oxide ternary material, and the mass percentage of the nickel cobalt lithium manganese oxide ternary material is d%, 1≤d≤50, based on the total mass of the positive electrode active material; The electrolyte includes compound A, compound B and compound C, wherein compound B includes a polyether nitrile compound, and compound C includes 1,3,6-hexane trinitrile; and compound A has a structure shown in the following general formula: Wherein, L is O or a connecting bond; R is selected from C2-C6 alkyl which is unsubstituted or substituted by Ra, C2-C6 alkenyl which is unsubstituted or substituted by Ra, C2-C6 alkynyl which is unsubstituted or substituted by Ra, C2-C6 nitrogen-containing heteroaryl which is unsubstituted or substituted by Ra, C6-C 12 One of the aryl groups, the substituents Ra of each group are independently selected from fluorine or C1-C6 fluoroalkyl; R1 is selected from one of fluorine or C1-C6 fluoroalkyl; Based on the total mass of the electrolyte, the mass percentage of the compound A is a%, 0.1≤a≤15; the mass percentage of the compound B is b%, 0.1≤b≤5; the mass percentage of the compound C is 0.1≤c≤5; and satisfies: 0.3≤d / (b+c)≤20, 0.02<a / (b+c)≤2.

2. The lithium ion secondary battery according to claim 1, characterized in that: The compound A has any of the following structures:

3. The lithium ion secondary battery according to claim 1, characterized in that: The compound B includes at least one of 1,2,3,4,5-penta(2-cyanoethoxy)pentane, ethylene glycol di(2-cyanoethyl) ether, diethylene glycol di(2-cyanoethyl) ether, triethylene glycol di(2-cyanoethyl) ether, tetraethylene glycol di(2-cyanoethyl) ether, ethylene glycol di(4-cyanobutyl) ether, ethylene glycol (bis) propionitrile ether and 1,2,3-tri(2-cyanoxy)propane.

4. The lithium-ion secondary battery according to claim 1, characterized in that: The compound C also includes at least one of benzonitrile, p-toluene nitrile, 3,5-difluorobenzonitrile, adiponitrile, succinonitrile, 1,2,6-hexanetrinitrile, 3,5-bistrifluoromethylbenzonitrile, ethoxypentafluorocyclotriphosphazene and hexafluorocyclotriphosphazene.

5. The lithium ion secondary battery according to claim 1, characterized in that: The electrolyte also includes a lithium salt, and the mass percentage of the lithium salt in the electrolyte is 10-30% based on the total mass of the electrolyte; Optionally, the lithium salt includes lithium hexafluorophosphate and lithium bis(trifluoromethanesulfonyl imide), and based on the total mass of the electrolyte, the mass percentage of the lithium hexafluorophosphate is e%, the mass percentage of the lithium bis(trifluoromethanesulfonyl imide is f%, and 8≤e≤20, 0.5≤f≤10, 1≤e / f≤5 are satisfied.

6. The lithium ion secondary battery according to claim 1, characterized in that: The electrolyte also includes ethylene carbonate. The mass percentage of the ethylene carbonate is g% based on the total mass of the electrolyte, and satisfies the following conditions: 0.1<g≤20, 0.1<a / g≤0.

8.

7. The lithium ion secondary battery according to claim 1, characterized in that: The electrolyte further includes a sulfur-containing additive, and the mass percentage of the sulfur-containing additive is h% based on the total mass of the electrolyte, and satisfies: 0.1<h<6, 0.3≤h / a≤3; Optionally, the sulfur-containing additive has a structure as shown in any of the following:

8. The lithium ion secondary battery according to claim 1, characterized in that: The positive electrode active material further contains aluminum element. Based on the total mass of the positive electrode active material, the mass percentage of the aluminum element is i%, and 0.3≤i≤1.

2.

9. The lithium ion secondary battery according to any one of claims 1 to 8, characterized in that: The negative electrode includes a negative electrode active material, the negative electrode active material includes graphite and a silicon-carbon composite material, the mass percentage of silicon element in the silicon-carbon composite material in the negative electrode active material is j%, and 0.5≤j≤35; Optionally, it satisfies: 0.1≤j / a≤10.

10. An electrical device, characterized in that: A lithium ion secondary battery comprising any one of claims 1 to 9.

Images