Lithium ion battery

Abstract

The invention relates to a lithium ion battery. The lithium ion battery comprises a positive pole piece and electrolyte, the positive pole piece comprises a positive active material, the positive active material comprises a doping element, and the electrolyte comprises a nitrile additive; wherein a first mass ratio of the doping element in the positive electrode active material and a second mass ratio of the nitrile additive in the electrolyte meet a set corresponding relation. According to the scheme provided by the invention, the doping element of the positive active material of the lithium ion battery and the nitrile compound of the nitrile additive in the electrolyte can play a positive role and play a positive synergistic role, so that the phenomena of oxygen release and cobalt dissolution of the lithium ion battery in high-temperature circulation can be inhibited, the interface side reaction is relieved, and the service life of the lithium ion battery is prolonged. The capacity of the lithium ion battery can be fully exerted, the electrical performance of the lithium ion battery is improved, and the lithium ion battery is ensured to have high capacity and excellent electrical performance at the same time.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and in particular to a lithium-ion battery. Background Art

[0002] Lithium-ion batteries are widely used in the field of consumer electronics due to their high energy density, fast charging and discharging capabilities, and low self-discharge. However, as the cut-off voltage of lithium-ion batteries continues to increase, the positive electrode material will release oxygen and dissolve transition metal ions during high-temperature cycles, causing the collapse of the positive electrode material structure. In addition, the cobalt ions in the positive electrode material will also catalyze side reactions in the electrolyte, causing further deterioration of the electrical performance of lithium-ion batteries. In addition, during high-temperature cycles, the electrolyte lithium salt (lithium hexafluorophosphate) is easily decomposed to produce HF (hydrogen fluoride), which will corrode the electrode interface film and cause capacity loss.

[0003] In order to solve the above technical problems of lithium-ion batteries, on the one hand, elements are doped into the active substances of the positive electrode materials to stabilize the bulk and surface structures of the active substances of the positive electrode materials and inhibit oxygen release and transition metal dissolution; on the other hand, nitrile compounds are added to the electrolyte. Since the cyanide group in the nitrile compounds has a strong electronegativity, the cyanide group has a strong coordination effect with the transition metal ions, which can inhibit the dissolution of metal ions. In addition, the cyanide group can preferentially capture H ions when an oxidative side reaction occurs in the electrolyte, thereby inhibiting the decomposition of LiPR (inorganic lithium salt) and FEC (fluoroethylene carbonate). However, the more nitrile compounds added to the electrolyte, the better. When too many nitrile compounds are added and the cyanide functional groups are excessive, there are not many active sites in the positive electrode material that can be complexed. Excess cyanide groups will increase the positive electrode impedance and increase the polarization of the positive electrode side, resulting in an increase in the positive electrode potential. The positive electrode material decomposes under high voltage, thereby causing the cycle performance to decay; and when the content of nitrile compounds is high, lithium-ion batteries are more likely to decompose and produce gas under high temperature conditions. The acidic byproducts produced by the decomposition corrode the electrode interface film, thereby deteriorating the high-temperature storage performance of lithium-ion batteries.

[0004] Therefore, how to determine the amount of nitrile compounds added to the lithium-ion battery electrolyte so that the nitrile compounds in the electrolyte can play a positive role is an issue that needs to be solved urgently. Summary of the invention In order to solve or partially solve the problems existing in the related art, the present application provides a lithium ion battery, which can make the doping elements of the positive active material of the lithium ion battery and the nitrile compounds of the nitrile additives in the electrolyte play a positive role and play a positive synergistic role, can inhibit the oxygen release and cobalt dissolution of the lithium ion battery in the high temperature cycle, alleviate the interface side reaction, can make the capacity of the lithium ion battery be fully exerted, improve the electrical performance of the lithium ion battery, and ensure that the lithium ion battery has both high capacity and excellent electrical performance.

[0005] In a first aspect, the present application provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode plate and an electrolyte; the positive electrode plate comprises a positive electrode active material, the positive electrode active material comprises a doping element, and the electrolyte comprises a nitrile additive; wherein, The first mass proportion of the doping element in the positive electrode active material is x, the second mass proportion of the nitrile additive in the electrolyte is y, the value range of x is 0.5%≤x≤1.4%, the value range of y is 3.5%≤y≤5.0%, and x and y satisfy the following relationship: 184.4x-37.7y≤1, 13.2x-432y 2 +38.9y≥1.

[0006] Preferably, the x and y satisfy: 0.12≤184.4x-37.7y≤0.9, 1.0≤13.2x-432y 2 +38.9y≤1.2.

[0007] Preferably, the nitrile additive includes one or more of adiponitrile, succinonitrile, and ethylene glycol bis(propionitrile) ether.

[0008] Preferably, the electrolyte further comprises a solvent; wherein, The solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, and tetrahydrofuran.

[0009] Preferably, the electrolyte further comprises an electrolyte salt; wherein, The electrolyte salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenide, lithium perchlorate, lithium trifluoromethanesulfonate, lithium bis(oxalatoborate), lithium bis(trifluoromethyl)sulfonyl imide, and lithium bis(trifluoromethanesulfonyl imide).

[0010] Preferably, the electrolyte also includes other types of electrolyte additives; wherein, The other types of electrolyte additives include one or more of methyl (2,2,2-trifluoroethyl) carbonate, fluoroethylene carbonate, and 4,5-dicyano-2-(trifluoromethyl) imidazole lithium.

[0011] Preferably, the positive electrode active material is LiCo 1-a M a O2, M represents the doping element; wherein, The doping elements include one or more of aluminum, magnesium, titanium, nickel, manganese, lanthanum, cerium, zirconium, yttrium, and cadmium.

[0012] Preferably, the weight ratio of the positive electrode active material in the positive electrode plate is 97%-99%.

[0013] Preferably, the positive electrode plate further includes a conductive agent; wherein, The conductive agent includes one or more of conductive carbon, porous carbon, carbon nanotubes, and graphene.

[0014] Preferably, the positive electrode plate further includes an adhesive, wherein: The adhesive is polyvinylidene fluoride.

[0015] The technical solution provided by this application may have the following beneficial effects: According to the technical solution of the present application, the positive electrode active material of the positive electrode plate includes a doping element, and the electrolyte includes a nitrile additive; wherein the first mass proportion of the doping element in the positive electrode active material and the second mass proportion of the nitrile additive in the electrolyte satisfy a set corresponding relationship, so that the doping element in the positive electrode active material of the lithium-ion battery and the nitrile compound of the nitrile additive in the electrolyte can both play a positive role and play a positive synergistic role, which can inhibit the oxygen release and cobalt dissolution of the lithium-ion battery in high-temperature cycles, alleviate interfacial side reactions, and enable the capacity of the lithium-ion battery to be fully utilized, thereby improving the electrical performance of the lithium-ion battery and ensuring that the lithium-ion battery has both high capacity and excellent electrical performance.

[0016] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. DETAILED DESCRIPTION

[0017] The terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The singular forms of "a", "said" and "the" used in this application and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0018] It should be understood that although the terms "first", "second", "third", etc. may be used in this application to describe various information, this information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of this application, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0019] The embodiment of the present application provides a lithium-ion battery, which can make the doping elements of the positive active material of the lithium-ion battery and the nitrile compounds of the nitrile additives in the electrolyte play a positive role and play a positive synergistic role, can inhibit the oxygen release and cobalt dissolution of the lithium-ion battery in the high-temperature cycle, alleviate the interface side reaction, can make the capacity of the lithium-ion battery be fully exerted, improve the electrical performance of the lithium-ion battery, and ensure that the lithium-ion battery has both high capacity and excellent electrical performance.

[0020] A lithium-ion battery according to an embodiment of the present application comprises a positive electrode plate and an electrolyte; the positive electrode plate comprises a positive electrode active material, the positive electrode active material comprises a doping element, and the electrolyte comprises a nitrile additive; wherein a first mass proportion of the doping element in the positive electrode active material and a second mass proportion of the nitrile additive in the electrolyte satisfy a set range and a corresponding relationship.

[0021] In the lithium-ion battery of the embodiment of the present application, the positive electrode active material of the positive electrode plate includes a doping element, and the electrolyte includes a nitrile additive; wherein the first mass proportion of the doping element in the positive electrode active material and the second mass proportion of the nitrile additive in the electrolyte are both within an appropriate range, and the two satisfy a set corresponding relationship, so that the doping element of the positive electrode active material of the lithium-ion battery and the nitrile compound of the nitrile additive in the electrolyte can both play a positive role, and play a positive synergistic role, can inhibit the oxygen release and cobalt dissolution of the lithium-ion battery in high-temperature cycles, alleviate interfacial side reactions, and can fully utilize the capacity of the lithium-ion battery, improve the electrical properties of the lithium-ion battery, and ensure that the lithium-ion battery has both high capacity and excellent electrical properties.

[0022] In one embodiment, a lithium-ion battery may include a battery housing, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte. The positive electrode sheet, the separator, and the negative electrode sheet are stacked and wound to obtain a bare cell; the bare cell is placed in a battery aluminum housing after hot pressing and shaping, and the electrolyte is injected into the dried bare cell, and a lithium-ion battery is obtained through processes such as standing, formation, high-temperature aging, and vacuum packaging.

[0023] In one embodiment, the positive electrode plate of the lithium-ion battery may include but is not limited to a positive electrode active material, a conductive agent, and a binder.

[0024] In one embodiment, the positive electrode active material, the conductive agent and the adhesive etc. can be mixed according to a set positive electrode weight ratio, and then N-methylpyrrolidone (NMP) is added to obtain a positive electrode slurry under the action of a vacuum mixer; the positive electrode slurry is evenly coated on the positive electrode collector, and the positive electrode sheet of the lithium-ion battery is obtained after drying and cold pressing and cutting.

[0025] In one embodiment, the positive electrode active material of the positive electrode plate of the lithium-ion battery can be LiCo 1-a Ma O2, wherein Li is lithium, Co is cobalt, O is oxygen, and the doping element is M, wherein M includes but is not limited to one or more of Al (aluminum), Mg (magnesium), Ti (titanium), Ni (nickel), Mn (manganese), La (lanthanum), Ce (cerium), Zr (zirconium), Y (yttrium), and Cd (cadmium).

[0026] In one embodiment, the weight ratio of the positive electrode active material in the positive electrode sheet of the lithium-ion battery is 97%-99%.

[0027] In one embodiment, the conductive agent of the positive electrode plate of the lithium-ion battery includes one or more of conductive carbon, porous carbon, carbon nanotubes, and graphene.

[0028] In one embodiment, the adhesive of the positive electrode plate of the lithium-ion battery may be polyvinylidene fluoride (PVDF).

[0029] In one embodiment, the thickness of the positive electrode plate of the lithium-ion battery is 75um-85um (micrometers).

[0030] In one embodiment, the negative electrode plate of the lithium-ion battery may include but is not limited to a negative electrode active material, a conductive agent, a plasticizer, and a binder. The negative electrode active material may be graphite. The conductive agent may be conductive carbon.

[0031] In one embodiment, graphite, conductive carbon, plasticizer, and adhesive can be mixed according to a set negative electrode mass ratio, deionized water is added, and negative electrode slurry is obtained under the action of a vacuum mixer; the negative electrode slurry is evenly coated on the negative electrode collector, and the negative electrode sheet of the lithium-ion battery is obtained after drying and cold pressing.

[0032] In one embodiment, the electrolyte of the lithium-ion battery may include but is not limited to a solvent, an electrolyte salt, and an electrolyte additive.

[0033] In one embodiment, the solvent of the lithium-ion battery electrolyte may include, but is not limited to, one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, and tetrahydrofuran.

[0034] In one embodiment, the electrolyte salt of the lithium-ion battery electrolyte may include one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenide, lithium perchlorate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethyl)sulfonyl imide, and lithium bis(trifluoromethanesulfonyl imide).

[0035] In one embodiment, the electrolyte additives of the lithium-ion battery electrolyte may include but are not limited to nitrile additives and other types of electrolyte additives.

[0036] In one embodiment, the nitrile additive may include, but is not limited to, one or more of AND (adiponitrile), SN (succinonitrile), and DENE [ethylene glycol bis(propionitrile) ether].

[0037] In one embodiment, other types of electrolyte additives may include, but are not limited to, one or more of methyl (2,2,2-trifluoroethyl) carbonate, fluoroethylene carbonate, and lithium 4,5-dicyano-2-(trifluoromethyl)imidazolium.

[0038] In one embodiment, the first mass proportion of the doping element in the positive electrode active material is x, the second mass proportion of the nitrile additive in the electrolyte is y, the value range of x is 0.5%≤x≤1.4%, the value range of y is 3.5%≤y≤5.0%, and x and y satisfy the following relationship: 184.4x-37.7y≤1, 13.2x-432y 2 +38.9y≥1.

[0039] In one embodiment, the first mass ratio x of the doping element in the positive electrode active material, the value range of x is 0.5%≤x≤1.4%, and the relationship 184.4x-37.7y≤1 and the relationship 13.2x-432y 2 +38.9y≥1, calculate the second mass proportion y of the nitrile additive in the electrolyte, where the value range of y is 3.5%≤y≤5.0%, so that the first mass proportion x of the doping element in the positive electrode active material and the second mass proportion y of the nitrile additive in the electrolyte satisfy the set range and the set corresponding relationship.

[0040] In one embodiment, the second mass proportion y of the nitrile additive in the electrolyte, the value range of y is 3.5%≤y≤5.0%, and the relationship 184.4x-37.7y≤1 and the relationship 13.2x-432y 2 +38.9y≥1, calculate the first mass proportion x of the doping element in the positive electrode active material, where the value range of x is 0.5%≤x≤1.4%, so that the first mass proportion x of the doping element in the positive electrode active material and the second mass proportion y of the nitrile additive in the electrolyte satisfy the set range and the set corresponding relationship.

[0041] In the lithium-ion battery of the embodiment of the present application, the positive electrode active material of the positive electrode plate includes a doping element, and the electrolyte includes a nitrile additive; the first mass proportion of the doping element in the positive electrode active material is x, and the second mass proportion of the nitrile additive in the electrolyte is y, wherein the value range of x is 0.5%≤x≤1.4%, the value range of y is 3.5%≤y≤5.0%, and x and y satisfy the relationship: 184.4x-37.7y≤1 and 13.2x-432y 2 +38.9y≥1, the first mass proportion x of the doping element in the positive electrode active material and the second mass proportion y of the nitrile additive in the electrolyte satisfy the set corresponding relationship, which can make the doping element of the positive electrode active material of the lithium-ion battery and the nitrile compound of the nitrile additive in the electrolyte both play a positive role and play a positive synergistic role, can inhibit the oxygen release and cobalt dissolution of the lithium-ion battery in the high-temperature cycle, alleviate the interface side reaction, can make the capacity of the lithium-ion battery be fully exerted, improve the electrical performance of the lithium-ion battery, and ensure that the lithium-ion battery has both high capacity and excellent electrical performance.

[0042] Further, in the lithium-ion battery of the embodiment of the present application, the first mass proportion x of the doping element in the positive electrode active material and the second mass proportion y of the nitrile additive in the electrolyte satisfy a set corresponding relationship, and the doping amount of the doping element in the positive electrode active material or the amount of the nitrile additive added in the electrolyte can be determined according to the set corresponding relationship satisfied by the first mass proportion x of the doping element in the positive electrode active material and the second mass proportion y of the nitrile additive in the electrolyte, and the doping amount of the doping element in the positive electrode active material and the amount of the nitrile additive added in the electrolyte satisfy the set corresponding relationship, so that the nitrile additive in the electrolyte It can play a positive role and avoid the negative effects caused by excessive nitrile additives in the electrolyte; the doping elements in the positive electrode active material can also play a positive role and avoid the negative effects caused by excessive doping elements in the positive electrode active material; the nitrile additives in the electrolyte and the doping elements in the positive electrode active material can play a positive synergistic role, so that the oxygen release and cobalt dissolution of the lithium-ion battery in the high-temperature cycle are suppressed, the interface side reactions are alleviated, the electrical performance of the lithium-ion battery is improved and the capacity is fully utilized, so that the lithium-ion battery can have both high capacity and excellent electrical performance.

[0043] In order to further enhance the positive synergistic effect between the doping elements in the positive electrode active material and the nitrile additives in the electrolyte, x and y in the lithium-ion battery satisfy: 0.12≤184.4x-37.7y≤0.9, 1.5≤13.2x-432y 2 +38.9y≤2.2.

[0044] The following is further described by specific comparative examples 1-12 and embodiments 1-11.

[0045] Embodiment 1: (1) Preparation of electrolyte Ethylene carbonate (EC), propylene carbonate (PC), and propyl propionate (PP) were mixed in a mass ratio of 1:1:1 to obtain a solvent; then, based on the total mass of the electrolyte, 8wt% of fluoroethylene carbonate (FEC) and an additive adiponitrile in the mass percentage amount shown in Table 1 were added, and after mixing evenly, lithium salt LiPF6 was added, and after mixing evenly, an electrolyte with a lithium salt concentration of 1.1 mol / L was obtained.

[0046] (2) Preparation of positive electrode sheet The positive electrode active material lithium cobalt oxide (doped with aluminum, magnesium, and titanium, the mass percentage of the doped elements is shown in Table 1), the conductive agent carbon nanotube (CNT), and the adhesive polyvinylidene fluoride (PVDF) are mixed at a mass ratio of 95:2.5:2.5, and then N-methylpyrrolidone (NMP) is added as a solvent, and the mixture is stirred and mixed to form a uniform positive electrode slurry. The slurry is coated on the positive electrode current collector aluminum foil, dried, and cold pressed to obtain a positive electrode sheet.

[0047] (3) Preparation of negative electrode sheet The negative electrode active material graphite, the conductive agent acetylene black, the binder styrene butadiene rubber, and the thickener sodium carboxymethyl cellulose are fully stirred and mixed in a deionized water solvent at a mass ratio of 96:1.2:1.5:1.3 to form a uniform negative electrode slurry. The slurry is coated on the negative electrode current collector copper foil, dried, and cold pressed to obtain a negative electrode sheet.

[0048] (4) Preparation of lithium-ion batteries PE porous polymer film is used as the separator.

[0049] The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, so that the separator is in the middle of the positive and negative electrodes to play a role of isolation, and then the stacked electrode sheet and the separator are wound to obtain a roll core. The roll core is placed in the aluminum-plastic film bag formed by punching the shell, and the non-aqueous electrolyte prepared above is injected into the baked and dried battery cells respectively. After vacuum packaging, standing, formation and other processes, a lithium-ion battery is obtained.

[0050] The models and specifications of the lithium-ion batteries of Comparative Examples 1-12 and Examples 1-10 are the same, except that the first mass proportion x of the doping element in the positive electrode active material and the second mass proportion y of the nitrile additive in the electrolyte are different. The specific values ​​of the first mass proportion x and the second mass proportion y of Comparative Examples 1-12 and Examples 1-10 are shown in Tables 1 and 2.

[0051] The models and specifications of the lithium-ion batteries of Examples 11-12 and Example 4 are the same, except that the composition of the nitrile additive in the electrolyte is different, as shown in Table 1. The models and specifications of the lithium-ion batteries of Examples 13-14 and Example 4 are the same, except that the positive electrode active material LiCo 1-a M a The doping elements M in O2 are different, as shown in Table 1.

[0052] The lithium ion batteries of Comparative Examples 1-12 and Examples 1-14 were tested to obtain the first discharge capacity (mAh / g, milliampere-hour per gram) of the lithium ion batteries of Comparative Examples 1-12 and Examples 1-14, and the battery cycle number at 45°C when the cycle capacity retention rate was 80% of the lithium ion batteries of Comparative Examples 1-12 and Examples 1-14, respectively. The specific values ​​of the first discharge capacity of the lithium ion batteries of Comparative Examples 1-12 and Examples 1-14 and the battery cycle number at 45°C when the cycle capacity retention rate was 80% are shown in Tables 1 and 2.

[0053] Table 1:

[0054] Table 2:

[0055] According to the data of Examples 1-14 in Table 1 and Comparative Examples 1-12 in Table 2, the first mass proportion x of the doping element in the positive electrode active material of the positive electrode sheet of the lithium ion battery and the second mass proportion y of the nitrile additive in the electrolyte satisfy the relationship: 184.4x-37.7y≤1 and 13.2x-432y 2 +38.9y≥1, and the value range of x is 0.5%≤x≤1.4%, and the value range of y is 3.5%≤y≤5.0%, so that the nitrile additives in the electrolyte can play a positive role and avoid the negative effects caused by excessive nitrile additives in the electrolyte; the doping elements in the positive electrode active material can also play a positive role and avoid the negative effects caused by excessive doping elements in the positive electrode active material; the nitrile additives in the electrolyte and the doping elements in the positive electrode active material can play a positive synergistic role, so that the oxygen release and cobalt dissolution of the lithium-ion battery in high-temperature cycling are suppressed, the interface side reactions are alleviated, the electrical performance of the lithium-ion battery is improved and the capacity is fully utilized, so that the lithium-ion battery can have both high capacity (first discharge capacity) and excellent electrical performance (cycle performance).

[0056] According to the data of Examples 1-5 in Table 1 and Comparative Examples 1-4 in Table 2, when the second mass proportion y of the nitrile additive in the electrolyte of the lithium-ion battery remains unchanged, as the first mass proportion x of the doping element in the positive electrode active material increases, the doping amount of the doping element in the positive electrode active material continues to increase, the overall structural stability of the positive electrode plate of the lithium-ion battery is enhanced, and the cycle performance (the number of battery cycles when the cycle capacity retention rate of the lithium-ion battery at 45°C is 80%) is improved; however, due to the increase in the doping amount of the doping element, the mass proportion of the electrochemically active positive electrode active material decreases, resulting in a continuous decrease in the gram capacity of the battery cell. Therefore, only when the first mass proportion x of the doping element in the positive electrode active material of the positive electrode plate of the lithium-ion battery and the second mass proportion y of the nitrile additive in the electrolyte satisfy the relationship: 184.4x-37.7y≤1 and 13.2x-432y 2 +38.9y≥1, and the value range of x is 0.5%≤x≤1.4%, and the value range of y is 3.5%≤y≤5.0%. Only then can the nitrile additives in the electrolyte and the doping elements in the positive electrode active material play a positive synergistic role, so that the lithium-ion battery can have both high capacity (first discharge capacity) and excellent electrical properties (cycle performance).

[0057] According to the data of Examples 6-10 in Table 1 and Comparative Examples 5-9 in Table 2, when the first mass proportion x of the doping element in the positive electrode active material of the positive electrode sheet of the lithium ion battery remains unchanged, as the second mass proportion y of the nitrile additive in the electrolyte gradually increases, the first discharge capacity and the number of battery cycles of the lithium ion battery are improved, the oxygen release and cobalt dissolution of the lithium ion battery in the high temperature cycle are suppressed, and the overall performance is improved; but as the second mass proportion y gradually increases, the first mass proportion x of the doping element in the positive electrode active material and the second mass proportion y of the nitrile additive in the electrolyte do not satisfy the relationship: 184.4x-37.7y≤1 and 13.2x-432y 2 +38.9y≥1, the nitrile additive is excessive, there are not too many active sites in the positive electrode material that can be complexed, the positive electrode impedance increases, the positive electrode side polarization increases, the positive electrode potential increases, and the positive electrode material decomposes under high voltage, resulting in the attenuation of the cycle performance (the number of battery cycles when the cycle capacity retention rate of the lithium-ion battery is 80% at 45°C). Therefore, only when the first mass proportion x of the doping element in the positive electrode active material of the positive electrode sheet of the lithium-ion battery and the second mass proportion y of the nitrile additive in the electrolyte meet the relationship: 184.4x-37.7y≤1 and 13.2x-432y 2+38.9y≥1, and the value range of x is 0.5%≤x≤1.4%, and the value range of y is 3.5%≤y≤5.0%. Only then can the nitrile additives in the electrolyte and the doping elements in the positive electrode active material play a positive synergistic role, so that the lithium-ion battery can have both high capacity (first discharge capacity) and excellent electrical properties (cycle performance).

[0058] According to the data of Example 4 and Examples 11-14 in Table 1, the nitrile additive in the electrolyte of the lithium ion battery is selected from any one of adiponitrile, succinonitrile, and ethylene glycol bis(propionitrile) ether, or a combination of two or more compounds; when the doping element of the positive active material in the positive electrode plate of the lithium ion battery is selected from an element or a combination of elements selected from aluminum, magnesium, titanium, nickel, manganese, lanthanum, cerium, zirconium, yttrium, and cadmium, when the first mass proportion x of the doping element of the positive active material of the positive electrode plate of the lithium ion battery in the positive active material and the second mass proportion y of the nitrile additive in the electrolyte satisfy the relationship: 184.4x-37.7y≤1 and 13.2x-432y 2 +38.9y≥1, and the value range of x is 0.5%≤x≤1.4%, and the value range of y is 3.5%≤y≤5.0%. The nitrile additives in the electrolyte and the doping elements in the positive electrode active material can play a positive synergistic role, so that the lithium-ion battery has both high capacity (first discharge capacity) and excellent electrical properties (cycle performance).

[0059] The embodiments of the present application have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or improvements to the technology in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A lithium ion battery, characterized in that: It comprises a positive electrode plate and an electrolyte; the positive electrode plate comprises a positive electrode active material, the positive electrode active material comprises a doping element, and the electrolyte comprises a nitrile additive; wherein, The first mass proportion of the doping element in the positive electrode active material is x, the second mass proportion of the nitrile additive in the electrolyte is y, the value range of x is 0.5%≤x≤1.4%, the value range of y is 3.5%≤y≤5.0%, and x and y satisfy the following relationship: 184.4x-37.7y≤1, 13.2x-432y 2 +38.9y≥1.

2. The lithium-ion battery according to claim 1, characterized in that The x and y satisfy: 0.12≤184.4x-37.7y≤0.9, 1.0≤13.2x-432y 2 +38.9y≤1.

2.

3. The lithium-ion battery according to claim 1, characterized in that: The nitrile additive includes one or more of adiponitrile, succinonitrile, and ethylene glycol bis(propionitrile) ether.

4. The lithium ion battery according to any one of claims 1 to 3, characterized in that: The electrolyte also includes a solvent; wherein, The solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, and tetrahydrofuran.

5. The lithium ion battery according to any one of claims 1 to 3, characterized in that: The electrolyte also includes an electrolyte salt; wherein, The electrolyte salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenide, lithium perchlorate, lithium trifluoromethanesulfonate, lithium bis(oxalatoborate), lithium bis(trifluoromethyl)sulfonyl imide, and lithium bis(trifluoromethanesulfonyl imide).

6. The lithium ion battery according to any one of claims 1 to 3, characterized in that: The electrolyte also includes other types of electrolyte additives; wherein, The other types of electrolyte additives include one or more of methyl (2,2,2-trifluoroethyl) carbonate, fluoroethylene carbonate, and 4,5-dicyano-2-(trifluoromethyl) imidazole lithium.

7. The lithium-ion battery according to claim 1, characterized in that: The positive electrode active material is LiCo 1-a M a O2, M represents the doping element; wherein, The doping elements include one or more of aluminum, magnesium, titanium, nickel, manganese, lanthanum, cerium, zirconium, yttrium, and cadmium.

8. The lithium-ion battery according to claim 1, characterized in that: The weight ratio of the positive electrode active material in the positive electrode sheet is 97%-99%.

9. The lithium-ion battery according to claim 1, characterized in that: The positive electrode sheet also includes a conductive agent; wherein, The conductive agent includes one or more of conductive carbon, porous carbon, carbon nanotubes, and graphene.

10. The lithium-ion battery according to claim 1, characterized in that: The positive electrode sheet also includes an adhesive, wherein: The adhesive is polyvinylidene fluoride.

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