A positive electrode lithium supplementing additive and a lithium ion battery

Abstract

The application provides a cyano-containing phosphite salt additive, characterized in that the additive has a structure as shown in formula (I) and / or formula (II). The cyano-containing phosphite salt additive with a specific structure and composition designed by the application is used as a lithium ion battery lithium supplement agent, is used for supplementing active lithium lost in the first cycle of lithium ion battery self-sacrifice charging and discharging, improves the first cycle coulomb efficiency, and after the end of delithiation, the phosphorous acid and -CN functional groups of the cyano-containing phosphite salt additive are dissolved in electrolyte, participate in the formation of an SEI film, inhibit the decomposition of electrolyte, and improve the high-temperature cycle performance of the battery. In addition, the phosphite salt organic lithium supplement agent has high water oxygen stability, and solves the problem of harsh use and storage conditions of traditional positive electrode lithium supplement agents.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode lithium replenishment technology, and relates to a cyanophosphite-containing additive and a lithium-ion battery, particularly to a cathode lithium replenishment additive and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are favored by many countries due to their advantages such as high energy density, low self-discharge rate, long cycle life, and cleanliness. Electronic mobile devices such as laptops, mobile phones, handheld game consoles, and tablets are enabling increasingly diverse functions, and their application technologies in electric vehicles and smart grids are maturing. At the same time, consumers are placing higher demands on a balance between battery energy density, cycle life, and environmental suitability.

[0003] To improve the energy density of lithium-ion batteries, the industry needs to develop higher-performance electrode materials to enhance battery performance. However, during the first charge-discharge cycle, an SEI film forms at the electrode-electrolyte interface, consuming active lithium and causing irreversible capacity loss. Therefore, pre-lithiation of the battery can effectively improve its initial capacity. Existing lithium replenishment technologies are mainly divided into positive electrode lithium replenishment and negative electrode lithium replenishment. Negative electrode lithium replenishment technology mainly uses inert lithium powder and lithium foil, which has the advantages of high replenishment efficiency and no residue after reaction. However, lithium metal has high reactivity, requiring strict environmental control, high cost, and significant safety risks. Positive electrode lithium replenishment technology mainly uses lithium compounds, offering significant safety and convenience. It does not require changes to existing processes; only the addition of high-capacity lithium compounds, i.e., positive electrode lithium replenishing agents, to the positive electrode slurry is necessary. These positive electrode lithium replenishing additives act as sacrificial lithium salts, releasing a large number of lithium ions during charging to replenish the lithium ions consumed in the formation of the SEI film at the negative electrode. The key to cathode lithium replenishment technology lies in the selection of cathode lithium replenishing agents. Cathode lithium replenishing agents can be divided into binary lithium-containing compounds represented by Li2O, Li2O2, and Li2S, ternary lithium-containing compounds represented by Li6CoO4 and Li5FeO4, and organic lithium-containing compounds represented by Li2DHBN and Li2C2O4, depending on the type of compound.

[0004] However, traditional lithium replenishing agents have some problems. For example, materials such as Li3N and Li2O have low decomposition potentials but poor stability and are prone to gas generation, affecting battery performance and posing safety hazards. Materials such as Li5FeO4 and Li6CoO4 have high irreversible capacity and good environmental stability, but their decomposition products increase electrode mass and have high decomposition voltages, making them incompatible with most cathode materials. Newer inorganic lithium replenishing agents, such as lithium vanadate, leave inorganic residues in the cathode after lithium replenishment, increasing cathode mass, leading to increased cell impedance and gas generation, which is detrimental to high-temperature battery cycling. Moreover, their optimal addition amount is 5% of the cathode mass; adding too much affects the proportion of active material in the cathode. Organic lithium replenishing agents, on the other hand, do not leave organic residues in the cathode after lithium replenishment, thus not adversely affecting battery performance. However, existing organic lithium replenishing agents have high activity but poor stability.

[0005] Therefore, finding a more suitable positive electrode lithium supplementation additive to solve the above-mentioned technical problems of existing lithium-ion batteries has become one of the urgent problems to be solved by many leading researchers and scientific research companies in this field. Summary of the Invention

[0006] In view of this, the present invention provides a cyanophosphite-containing additive and a lithium-ion battery, particularly a lithium replenishing additive for the positive electrode. The cyanophosphite-containing additive provided by the present invention, as a positive electrode lithium replenisher, is used in lithium-ion batteries to self-sacrifice and replenish the active lithium lost during the first charge-discharge cycle, improving the first-cycle coulombic efficiency. Simultaneously, its phosphorous acid and -CN functional groups dissolve in the electrolyte after delithiation, participating in the formation of the SEI film, inhibiting electrolyte decomposition, and improving the battery's high-temperature cycle performance.

[0007] This invention provides a cyanophosphite-containing additive, characterized in that the additive has a structure as shown in formula (I) and / or formula (II):

[0008]

[0009] In formulas (I) and (II), R1 is independently selected from cyano, cyanoethyl, substituted or substituted C1-C1 groups. 12 Alkyl groups, substituted or unsubstituted C6-C26 aryl groups, and substituted or unsubstituted C6-C22 aromatic heterogroups.

[0010] Preferably, the substituents include halogens;

[0011] The cyanophosphite-containing additive is a positive electrode additive;

[0012] The positive electrode includes a lithium-ion battery positive electrode.

[0013] Preferably, the additive has a structure as shown in any one of formulas (1) to (5):

[0014]

[0015] Preferably, the additive is a positive electrode lithium supplementation additive;

[0016] The additive has a mass content of 0.5% to 2% in the cathode material;

[0017] The preparation method of the additive includes the following steps:

[0018] An additive is obtained by reacting lithium hydroxide with phosphite through a substitution reaction;

[0019] The phosphite has the structure shown in formula (III) or formula (IV);

[0020]

[0021] Preferably, the temperature of the substitution reaction is 20–30°C;

[0022] The substitution reaction takes 0.5 to 1 hour;

[0023] The molar ratio of lithium hydroxide to phosphite is (0.9–1.1):(0.9–1.1).

[0024] This invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte;

[0025] The positive electrode includes any of the cyanophosphite additives described in the above technical solutions.

[0026] Preferably, the positive electrode further includes a positive electrode active material, a conductive agent, and a binder;

[0027] The positive electrode, comprising a cyanophosphite additive, a positive electrode active material, a conductive agent, and a binder, has a mass content of 0.5% to 2%.

[0028] Preferably, the positive electrode active material includes one or more of NCM, NCA, LiFePO4, LiCoO2 and LiMnO2;

[0029] The positive electrode comprises a cyanophosphite additive, a positive electrode active material, a conductive agent, and a binder as a whole, and the mass content of the positive electrode active material is 90% to 97%.

[0030] Preferably, the conductive agent includes one or more of SP, acetylene black, graphene, carbon nanotubes, and VGCF;

[0031] The positive electrode comprises a cyanophosphite additive, a positive electrode active material, a conductive agent, and a binder as a whole, wherein the mass content of the conductive agent is 1% to 5%.

[0032] Preferably, the adhesive comprises one or more of polypropylene, polyethylene, polyvinylidene fluoride, vinylidene fluoride, hexafluoropropylene, polytetrafluoroethylene, and polyhexafluoropropylene;

[0033] The positive electrode comprises a cyanophosphite additive, a positive electrode active material, a conductive agent, and a binder as a whole, wherein the mass content of the binder is 1% to 5%.

[0034] This invention provides a cyanophosphite-containing additive, characterized in that the additive has a structure as shown in formula (I) and / or formula (II). Compared with the prior art, this invention specifically designs a cyanophosphite-containing additive with a specific structure and composition as a lithium replenishing agent for lithium-ion batteries. After delithiation, the organic portion of this phosphite dissolves in the electrolyte. The phosphorous acid and -CN groups themselves have certain positive electrode film-forming functions, inhibiting the decomposition of other components in the electrolyte, thus improving the high-temperature cycle performance of the battery. Moreover, -CN complexes with high-valence metal ions in the positive electrode active material, also playing a role in inhibiting the dissolution of transition metals.

[0035] The novel phosphite organic lithium replenishment additive provided by this invention replenishes active lithium loss and improves initial efficiency during the first cycle. Its unique functional group structure, with phosphite and -CN functional groups dissolving in the electrolyte after delithiation, leaves no residue on the positive electrode and does not adversely affect the battery. Furthermore, the organic portion participates in the formation of the electrode / electrolyte interface film, improving its stability and inhibiting oxidative decomposition of the electrolyte at high temperatures, thus enhancing high-temperature cycle performance. Simultaneously, the -CN functional group complexes with high-valence metal ions in the positive electrode active material, playing a role in inhibiting the dissolution of transition metals. In addition, the phosphite organic lithium replenishment additive of this invention exhibits high water and oxygen stability, solving the problem of harsh usage and storage conditions associated with traditional positive electrode lithium replenishment additives.

[0036] This invention utilizes a novel cathode lithium replenisher containing cyanophosphite for self-sacrifice lithium replenishment in lithium-ion batteries. It effectively compensates for the loss of active lithium caused by the formation of the electrode / electrolyte interface film during the first charge-discharge cycle, thereby increasing the first-cycle discharge capacity and coulombic efficiency. Simultaneously, its phosphorous acid and -CN functional groups dissolve in the electrolyte after delithiation, participating in the formation of the SEI film, inhibiting electrolyte decomposition, and improving the battery's high-temperature cycle performance.

[0037] Furthermore, the organic lithium salt supplementary agent provided by this invention solves the problems of traditional inorganic lithium supplementation, including gas generation during the process, residues on the positive electrode after the reaction, and poor water and oxygen stability. This organic lithium supplementary agent exhibits high water and oxygen stability, requiring no stringent storage or usage conditions, thus reducing the application difficulty of traditional lithium supplementary agents. When using this organic lithium supplementary agent for lithium supplementation, the remaining organic portion after delithiation dissolves in the electrolyte, leaving no residue on the positive electrode and preventing gas generation.

[0038] Experimental results show that the organic lithium salt lithium replenisher provided by this invention effectively improves the first-cycle coulombic efficiency of the battery, reduces the loss of active lithium in the first cycle, and increases the discharge capacity. At the same time, it forms a stable SEI film, which improves the battery's high-temperature cycle capacity retention rate. Attached Figure Description

[0039] Figure 1 The XRD diffraction pattern of the organic lithium supplement (1) prepared in this invention. Detailed Implementation

[0040] To further understand the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] There are no particular restrictions on the source of any raw materials used in this invention; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0042] There are no particular restrictions on the purity of any raw materials used in this invention. However, it is preferred to use analytical grade or conventional purity materials used in the field of lithium-ion battery cathode lithium replenishment agents.

[0043] This invention provides a cyanophosphite-containing additive having a structure as shown in formula (I) and / or formula (II):

[0044]

[0045]

[0046] In formulas (I) and (II), R1 is independently selected from cyano, cyanoethyl, substituted or substituted C1-C1 groups. 12 Alkyl, substituted or unsubstituted C6-C 26 aryl, substituted or unsubstituted C6-C 22 Aromatic compounds.

[0047] In this invention, C1 to C 12Alkyl groups can also be C3 to C4. 10 Alkyl groups, or C5-C8 alkyl groups. The C6-C8 alkyl groups... 26 The aryl group can also be C 10 ~C 22 aryl, or C 14 ~C 18 The aryl group. The C6-C6 group... 22 The aromatic heteroyl group can also be C9~C 19 aryl groups, or C 12 ~C 16 Aryl groups.

[0048] In this invention, the substituents preferably include halogens.

[0049] In this invention, the cyanophosphite-containing additive is preferably a positive electrode additive.

[0050] In this invention, the positive electrode preferably includes a lithium-ion battery positive electrode.

[0051] In this invention, the additive preferably has a structure as shown in any one of formulas (1) to (5):

[0052]

[0053] In this invention, the additive is preferably a positive electrode lithium supplement additive.

[0054] In this invention, the mass content of the additive in the cathode material is preferably 0.5% to 2%, more preferably 0.8% to 1.7%, and even more preferably 1.1% to 1.4%.

[0055] In this invention, the method for preparing the additive preferably includes the following steps:

[0056] An additive is obtained by reacting lithium hydroxide with phosphite through a substitution reaction;

[0057] The phosphite has the structure shown in formula (III) or formula (IV);

[0058]

[0059] In this invention, the temperature of the substitution reaction is preferably 20-30°C, more preferably 22-28°C, and even more preferably 24-26°C.

[0060] In this invention, the substitution reaction time is preferably 0.5 to 1 h, more preferably 0.6 to 0.9 h, and even more preferably 0.7 to 0.8 h.

[0061] In this invention, the molar ratio of lithium hydroxide to phosphite is preferably (0.9-1.1):(0.9-1.1), more preferably (0.95-1.05):(0.9-1.1), and even more preferably (0.9-1.1):(0.95-1.05).

[0062] This invention aims to complete and refine the overall technical solution, thereby improving the lithium replenishment effect of the cathode containing cyanophosphite additives. Specifically, the aforementioned cyanophosphite additives may include the following structures:

[0063] An organic lithium supplement for positive electrodes, wherein the organic lithium supplement is a phosphite containing a cyano group.

[0064] The cyanophosphite is selected from at least one of compounds having the chemical structural formulas shown in Formula I and Formula II:

[0065]

[0066] R1 is selected from cyano, cyanoethyl, substituted or substituted C1 to C1 groups. 12 Alkyl, substituted or unsubstituted C6-C 26 aryl group, substituted or unsubstituted C6-C 22 The aromatic heteroyl group has halogen substituents.

[0067] Specifically, the structural formula of the additive is shown below, and the positive electrode lithium supplementation additive of the present invention is selected from at least one of the following compounds.

[0068]

[0069] The present invention also provides a method for preparing an additive, the method comprising at least reacting lithium hydroxide with phosphites of formulas III and IV via a substitution reaction to prepare compounds of formulas (1) to (2).

[0070]

[0071] R1 is selected from cyano, cyanoethyl, substituted or substituted C1 to C1 groups. 12 Alkyl, substituted or unsubstituted C6-C 26 aryl group, substituted or unsubstituted C6-C 22 The aromatic heteroyl group has halogen substituents.

[0072] Specifically, the reaction temperature is 20–30°C, and the reaction time is 0.5–1 h.

[0073] Specifically, the molar ratio of lithium hydroxide to phosphite is 0.9–1.1:0.9–1.1.

[0074] The present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode and an electrolyte.

[0075] In this invention, the positive electrode preferably includes the cyanophosphite additive described in the above-described technical solution.

[0076] In this invention, the positive electrode preferably includes a positive electrode active material, a conductive agent, and a binder.

[0077] In this invention, the positive electrode, taking the cyanophosphite additive, positive electrode active material, conductive agent and binder as a whole, preferably has a mass content of 0.5% to 2%, more preferably 0.3% to 1.7%, more preferably 0.6% to 1.4%, and even more preferably 0.9% to 1.1%.

[0078] In this invention, the positive electrode active material preferably includes one or more of NCM, NCA, LiFePO4, LiCoO2 and LiMnO2, and more preferably NCM, NCA, LiFePO4, LiCoO2 or LiMnO2.

[0079] In this invention, the positive electrode, taking the cyanophosphite additive, positive electrode active material, conductive agent and binder as a whole, preferably has a mass content of 90% to 97%, more preferably 91% to 96%, and even more preferably 94% to 96%.

[0080] In this invention, the conductive agent preferably includes one or more of SP, acetylene black, graphene, carbon nanotubes and VGCF, and more preferably SP, acetylene black, graphene, carbon nanotubes or VGCF.

[0081] In this invention, the positive electrode is a whole comprising a cyanophosphite additive, a positive electrode active material, a conductive agent, and a binder, and the mass content of the conductive agent is preferably 1% to 5%, more preferably 2% to 3%.

[0082] In this invention, the adhesive preferably includes one or more of polypropylene, polyethylene, polyvinylidene fluoride, vinylidene fluoride, hexafluoropropylene, polytetrafluoroethylene, and polyhexafluoropropylene, more preferably polypropylene, polyethylene, polyvinylidene fluoride, vinylidene fluoride, hexafluoropropylene, polytetrafluoroethylene, or polyhexafluoropropylene.

[0083] In this invention, the positive electrode is a whole comprising a cyanophosphite additive, a positive electrode active material, a conductive agent, and a binder, and the mass content of the binder is preferably 1% to 5%, more preferably 2% to 3%.

[0084] The present invention also provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery comprises a positive electrode active material, a conductive agent, a binder, and the aforementioned organic lithium supplement agent.

[0085] Specifically, the cathode material is selected from one or more of NCM, NCA, LiFePO4, LiCoO2 and LiMnO2.

[0086] Specifically, the conductive agent is one or more of SP, acetylene black, graphene, carbon nanotubes, and VGCF.

[0087] Specifically, the adhesive is one or more of polypropylene, polyethylene, polyvinylidene fluoride, vinylidene fluoride, hexafluoropropylene, polytetrafluoroethylene, or polyhexafluoropropylene.

[0088] Specifically, the organic lithium supplement agent has a mass percentage of 0.5% to 2% in the electrode material. Studies have found that controlling it within this preferred range helps to maximize the effect of the lithium supplement agent.

[0089] Specifically, the lithium-ion battery comprises a positive electrode, a separator located between the positive and negative electrodes, a negative electrode, an electrolyte, tabs, and a casing as described in any of the above technical solutions.

[0090] The present invention provides a lithium-replenishing additive for the positive electrode and a lithium-ion battery. The present invention specifically designs a cyanophosphite additive with a specific structure and composition as a lithium-ion battery replenishing agent. After delithiation, the organic portion of this phosphite dissolves in the electrolyte. The phosphorous acid and -CN groups themselves possess certain positive electrode film-forming functions, inhibiting the decomposition of other components in the electrolyte, thus improving the high-temperature cycle performance of the battery. Furthermore, -CN complexes with high-valence metal ions in the positive electrode active material, also playing a role in inhibiting the dissolution of transition metals.

[0091] The novel phosphite organic lithium replenishment additive provided by this invention replenishes active lithium loss and improves initial efficiency during the first cycle. Its unique functional group structure, with phosphite and -CN functional groups dissolving in the electrolyte after delithiation, leaves no residue on the positive electrode and does not adversely affect the battery. Furthermore, the organic portion participates in the formation of the electrode / electrolyte interface film, improving its stability and inhibiting oxidative decomposition of the electrolyte at high temperatures, thus enhancing high-temperature cycle performance. Simultaneously, the -CN functional group complexes with high-valence metal ions in the positive electrode active material, playing a role in inhibiting the dissolution of transition metals. In addition, the phosphite organic lithium replenishment additive of this invention exhibits high water and oxygen stability, solving the problem of harsh usage and storage conditions associated with traditional positive electrode lithium replenishment additives.

[0092] This invention utilizes a novel cathode lithium replenisher containing cyanophosphite for self-sacrifice lithium replenishment in lithium-ion batteries. It effectively compensates for the loss of active lithium caused by the formation of the electrode / electrolyte interface film during the first charge-discharge cycle, thereby increasing the first-cycle discharge capacity and coulombic efficiency. Simultaneously, its phosphorous acid and -CN functional groups dissolve in the electrolyte after delithiation, participating in the formation of the SEI film, inhibiting electrolyte decomposition, and improving the battery's high-temperature cycle performance.

[0093] Furthermore, the organic lithium salt supplementary agent provided by this invention solves the problems of traditional inorganic lithium supplementation, including gas generation during the process, residues on the positive electrode after the reaction, and poor water and oxygen stability. This organic lithium supplementary agent exhibits high water and oxygen stability, requiring no stringent storage or usage conditions, thus reducing the application difficulty of traditional lithium supplementary agents. When using this organic lithium supplementary agent for lithium supplementation, the remaining organic portion after delithiation dissolves in the electrolyte, leaving no residue on the positive electrode and preventing gas generation.

[0094] Experimental results show that the organic lithium salt lithium replenisher provided by this invention effectively improves the first-cycle coulombic efficiency of the battery, reduces the loss of active lithium in the first cycle, and increases the discharge capacity. At the same time, it forms a stable SEI film, which improves the battery's high-temperature cycle capacity retention rate.

[0095] To further illustrate the present invention, the following detailed description of a cyanophosphite-containing additive and a lithium-ion battery provided by the present invention is provided in conjunction with embodiments. However, it should be understood that these embodiments are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given only to further illustrate the features and advantages of the present invention, and are not intended to limit the scope of the claims of the present invention. The scope of protection of the present invention is not limited to the following embodiments.

[0096] All reagents used in the following embodiments of the present invention are commercially available products.

[0097] Comparative Example

[0098] The positive electrode active material LiCoO2, conductive agent, and binder PVDF are dissolved in NMP in a ratio of 96:2:2. After homogenization, the mixture is coated onto aluminum foil, dried, rolled, and cut into sheets to prepare the positive electrode sheet.

[0099] Example 1

[0100] Add 0.1 mol of an aqueous solution of phosphite (formula 1-1) and 0.1 mol of lithium hydroxide to a three-necked flask, stir magnetically, control the reaction temperature at 25°C, and react for 0.5 hours. After the reaction is complete, remove the solvent by vacuum distillation of the reaction product, then wash repeatedly with methanol, centrifuge, and dry to obtain the organic lithium supplement (1). The reaction equation is as follows:

[0101]

[0102] See Figure 1 , Figure 1 The XRD diffraction pattern of the organic lithium supplement (1) prepared in this invention.

[0103] Other organic lithium supplements of the present invention are also prepared by the above method using different raw materials.

[0104] The positive electrode active material LiCoO2, organic lithium supplement (1), conductive agent SP, and binder PVDF were dissolved in NMP in a ratio of 94:2:2:2. After homogenization, the mixture was coated onto aluminum foil and then dried, rolled, and cut into sheets to prepare the positive electrode sheet.

[0105] Example 2

[0106] The positive electrode active material LiCoO2, organic lithium supplement (1), conductive agent SP, and binder PVDF were dissolved in NMP in a ratio of 95:1:2:2. After homogenization, the mixture was coated onto aluminum foil and then dried, rolled, and cut into sheets to prepare the positive electrode sheet.

[0107] Example 3

[0108] The positive electrode active material LiCoO2, organic lithium supplement (1), conductive agent SP, and binder PVDF were dissolved in NMP in a ratio of 95.5:0.5:2:2. After homogenization, the mixture was coated on aluminum foil and then dried, rolled, and cut into sheets to prepare the positive electrode sheet.

[0109] Example 4

[0110] The positive electrode active material LiCoO2, organic lithium supplement (2), conductive agent SP, and binder PVDF were dissolved in NMP in a ratio of 95.5:0.5:2:2. After homogenization, the mixture was coated on aluminum foil and then dried, rolled, and cut into sheets to prepare the positive electrode sheet.

[0111] Example 5

[0112] The positive electrode active material LiCoO2, organic lithium supplement (3), conductive agent SP, and binder PVDF are dissolved in NMP in a ratio of 95.5:0.5:2:2. After homogenization, the mixture is coated on aluminum foil and then dried, rolled, and cut into sheets to prepare the positive electrode sheet.

[0113] Example 6

[0114] LiNi, the positive electrode active material 0.8 Co 0.1 5Mn 0.1 O2, organic lithium supplement (1), conductive agent SP, and binder PVDF are dissolved in NMP in a ratio of 95.5:0.5:2:2. After homogenization, the mixture is coated on aluminum foil and then dried, rolled, and cut into sheets to prepare positive electrode sheets.

[0115] It should be noted that the positive electrode active materials and proportions are different in the above comparative examples and embodiments. In the embodiments, lithium supplementation additives are added to the positive electrode. Apart from this, the conductive agent, binder, current collector foil are the same, the coating amount per unit area of ​​the positive electrode sheet is the same, the coating length and width of the positive and negative electrode sheets are the same, and the negative electrode sheet and the electrolyte used are the same.

[0116] Preparation of negative electrode sheet: The negative electrode active material artificial graphite, conductive agent SP, binder SBR and CMC are dissolved in deionized water in a ratio of 95:2:1.5:1.5, homogenized and coated on copper foil, and then dried, rolled and cut into sheets to prepare negative electrode sheet.

[0117] Electrolyte preparation: 1M lithium hexafluorophosphate was selected as the lithium salt, and ethylene carbonate (EC): ethyl methyl carbonate (EMC) in a weight ratio of 3:7 was used as the solvent. Other conventional additives to ensure performance were also included.

[0118] The positive and negative electrode sheets prepared in the comparative examples and embodiments above were used to fabricate pouch batteries for testing. Using the Xinwei Battery Testing System, the batteries were charged at a constant current of 1C to 4.5V in a 45°C constant temperature chamber, followed by constant voltage charging until the charging current reached 0.05C. Charging was then stopped, and the batteries were discharged at a constant current of 1C until the cutoff voltage of 3V. This cyclic charge-discharge test was repeated.

[0119] See Table 1, which shows the test data of the embodiments and comparative examples of the present invention under high temperature cycling test at 45°C.

[0120] Table 1

[0121] First lap Coulomb efficiency % 100-cycle capacity retention % Comparative Example 88.7 88.8 Example 1 89.5 89.6 Example 2 90.1 90.8 Example 3 92.3 94.4 Example 4 93.0 95.1 Example 5 88.1 91.3 Example 6 90.2 92.1

[0122] The foregoing has provided a detailed description of a lithium-ion battery and a positive electrode additive provided by the present invention. Specific examples have been used to illustrate the principles and implementation methods of the invention. The descriptions of these embodiments are merely for the purpose of helping to understand the method and core ideas of the present invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that for those skilled in the art, several improvements and modifications can be made to the invention without departing from the principles of the invention, and these improvements and modifications also fall within the protection scope of the claims. The scope of protection of this patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements similar to those expressed in the claims, or if they include equivalent structural elements that are not substantially different from those expressed in the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A lithium-ion battery, characterized in that, Including the positive electrode; The positive electrode includes a cyanophosphite additive; The cyanophosphite-containing additive has a structure as shown in formula (I) and / or formula (II): (I) (II); In formula (I), R1 is selected from cyano, cyanoethyl, substituted or substituted C1~C1 groups. 12 Alkyl, substituted or unsubstituted C6~C 26 aryl, substituted or unsubstituted C6~C 22 Aromatic compounds; R1 in formula (II) is selected from cyano or cyanoethyl.

2. The lithium-ion battery according to claim 1, characterized in that, The substituents mentioned include halogens.

3. The lithium-ion battery according to claim 1, characterized in that, The cyanophosphite-containing additive has a structure as shown in any one of formulas (1) to (5): （1） （2） （3）； （4） （5）。 4. The lithium-ion battery according to claim 1, characterized in that, The cyanophosphite-containing additive is a positive electrode lithium supplementation additive; The cyanophosphite additive has a mass content of 0.5% to 2% in the cathode material; The preparation method of the cyanophosphite-containing additive includes the following steps: An additive is obtained by reacting lithium hydroxide with phosphite through a substitution reaction; The phosphite has the structure shown in formula (III) or formula (IV); (III) (IV); In formula (III), R1 is selected from cyano, cyanoethyl, substituted or substituted C1~C1 groups. 12 Alkyl, substituted or unsubstituted C6~C 26 aryl, substituted or unsubstituted C6~C 22 Aromatic compounds; R1 in formula (IV) is selected from cyano or cyanoethyl.

5. The lithium-ion battery according to claim 4, characterized in that, The temperature for the substitution reaction is 20~30℃; The substitution reaction takes 0.5 to 1 hour; The molar ratio of lithium hydroxide to phosphite is (0.9~1.1):(0.9~1.1).

6. The lithium-ion battery according to claim 1, characterized in that, It also includes the negative electrode and the electrolyte.

7. The lithium-ion battery according to claim 1, characterized in that, The positive electrode also includes a positive electrode active material, a conductive agent, and a binder; The positive electrode comprises a cyanophosphite additive, a positive electrode active material, a conductive agent, and a binder as a whole, and the mass content of the cyanophosphite additive is 0.5% to 2%.

8. The lithium-ion battery according to claim 7, characterized in that, The positive electrode active material includes one or more of NCM, NCA, LiFePO4, LiCoO2, and LiMnO2; The positive electrode comprises a cyanophosphite additive, a positive electrode active material, a conductive agent, and a binder as a whole, and the mass content of the positive electrode active material is 90% to 97%.

9. The lithium-ion battery according to claim 7, characterized in that, The conductive agent includes one or more of SP, acetylene black, graphene, carbon nanotubes, and VGCF. The positive electrode comprises a cyanophosphite additive, a positive electrode active material, a conductive agent, and a binder as a whole, and the mass content of the conductive agent is 1% to 5%.

10. The lithium-ion battery according to claim 7, characterized in that, The adhesive includes one or more of polypropylene, polyethylene, polyvinylidene fluoride, vinylidene fluoride, hexafluoropropylene, polytetrafluoroethylene, and polyhexafluoropropylene; The positive electrode comprises a cyanophosphite additive, a positive electrode active material, a conductive agent, and a binder as a whole, and the binder has a mass content of 1% to 5%.

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