Lithium ion battery and preparation method and application thereof

Abstract

The application provides a lithium ion battery and a preparation method and application thereof.The lithium ion battery comprises a positive electrode sheet, the positive electrode sheet comprises a lithium supplementing agent, the lithium supplementing agent comprises elemental boron, a negative electrode sheet, a diaphragm arranged between the positive electrode sheet and the negative electrode sheet, and an electrolyte filled between the positive electrode sheet, the negative electrode sheet and the diaphragm.The lithium ion battery and the preparation method and application thereof can play a high positive electrode lithium supplementing role in various battery systems under the condition of realizing non-deterioration gas production and improve the cycle performance of the lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a lithium-ion battery, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries are the core components driving the electrification transformation of the automotive industry; however, their range and cycle life are insufficient to meet demands. Therefore, improving the energy density and cycle life of lithium-ion batteries for electric vehicles has been a key development direction for some time, while remaining cost-effective. Among these, the lithium iron phosphate system, which is inexpensive and has excellent cycle life, has relatively low energy density, while high-energy-density positive and negative electrode chemistry systems, such as high-nickel or high-silicon systems, face the problem of poor cycle life.

[0003] During the first cycle, a solid electrolyte interphase (SEI) film forms on the negative electrode surface of a lithium-ion battery, leading to irreversible lithium loss and reducing the battery's energy density. Lithium replenishment technology, which introduces lithium-containing compound additives into the positive electrode, addresses this by causing the additive to irreversibly decompose during charging, releasing active lithium and thus replenishing the battery's energy. However, commonly used lithium-rich nickel oxide (Li₂NiO₂, LNO) and lithium-rich lithium iron oxide (Li₅FeO₄, LFO) positive electrode lithium replenishing agents exhibit significant oxygen release during the first charge, resulting in increased gas production and poorer cycle performance. Therefore, the doping concentration of LNO or LFO commonly used in the industry is less than 1 wt%, offering limited gains. Summary of the Invention

[0004] This invention proposes a lithium-ion battery, its preparation method, and its application. It can achieve high positive electrode lithium replenishment in various battery systems without deteriorating gas production, thereby improving the cycle performance of lithium-ion batteries. Furthermore, the products of the lithium replenishment agent oxidation can improve the film quality of the positive electrode electrolyte interface film and reduce DC resistance.

[0005] To address the aforementioned technical problems, this invention proposes a lithium-ion battery, comprising at least:

[0006] A positive electrode sheet, wherein the positive electrode sheet includes a lithium replenishing agent, wherein the lithium replenishing agent includes elemental boron;

[0007] Negative electrode plate;

[0008] A diaphragm is disposed between the positive electrode and the negative electrode; and

[0009] An electrolyte is filled between the positive electrode, the negative electrode, and the separator.

[0010] In one embodiment of the present invention, the positive electrode sheet includes a positive current collector and a positive active material layer disposed at least on one side of the positive current collector, wherein the content of the lithium supplement agent in the positive active material layer is 0.08wt% to 2wt%.

[0011] In one embodiment of the present invention, the positive electrode active material layer includes a positive electrode active material, wherein the positive electrode active material is selected from at least one of lithium iron phosphate or lithium manganese iron phosphate.

[0012] In one embodiment of the present invention, the positive electrode active material layer includes a positive electrode active material, wherein the positive electrode active material is selected from LiNi. x Co y Mn 1-x-y O2, where 0.65≤x<1.0, 0≤y<0.5.

[0013] In one embodiment of the present invention, the negative electrode sheet includes a negative current collector and a negative active material layer disposed at least on one side of the negative current collector. The negative active material layer includes a negative active material selected from at least one of graphite, silicon-oxygen materials or silicon-carbon materials.

[0014] This invention also provides a method for preparing a lithium-ion battery, comprising at least the following steps:

[0015] A lithium supplement agent is mixed into the positive electrode active material to obtain a blended active powder.

[0016] The blended active powder is formulated into a positive electrode slurry;

[0017] The positive electrode slurry is coated onto the positive electrode current collector, and then dried and cold-pressed to obtain the positive electrode sheet.

[0018] The negative electrode active material is formulated into a negative electrode slurry;

[0019] The negative electrode slurry is coated onto the surface of the negative electrode current collector, dried, and cold-pressed to obtain the negative electrode sheet; and

[0020] The lithium-ion battery is obtained by assembling the positive electrode, the negative electrode, the electrolyte, and the separator.

[0021] In one embodiment of the present invention, the lithium supplement and the positive electrode active material are mixed uniformly by ball milling.

[0022] In one embodiment of the present invention, the particle size of the lithium replenishing agent is 10 nm to 500 nm.

[0023] In one embodiment of the present invention, the blended active powder is obtained by the following method:

[0024] Add the positive electrode active material to ice water or ice N,N-dimethylacetamide solvent containing ammonium fluoride. According to the amount of lithium supplementer added, first dissolve boric acid, stir and mix evenly, and then gradually add dimethylamine borane or lithium borohydride.

[0025] After the addition is complete, the reaction is carried out for the first preset time, then filtered and washed to obtain the intermediate product;

[0026] The intermediate product is calcined at a preset temperature and in an oxygen environment for a second preset time.

[0027] The present invention also provides an electronic device comprising the lithium-ion battery described above.

[0028] In summary, this invention proposes a lithium-ion battery, its preparation method, and its application. By selecting elemental boron as the positive electrode lithium replenisher, it undergoes an oxidation reaction during charging, contributing a significant amount of charge. After oxidation, it becomes positively charged, forming a charge balance with the lithium ions embedded in the negative electrode. This prevents the imbalance of ion charge in the solution due to boron's own lack of lithium ion contribution, thus achieving lithium replenishment. Simultaneously, elemental boron has a high specific capacity and a strong ability to fill the irreversible capacity of the negative electrode, resulting in a high positive electrode lithium replenishment effect. The products of the lithium replenisher oxidation can improve the film quality of the positive electrode electrolyte interface film and reduce DC resistance. Through reduction, elemental boron is generated in situ on the surface of the positive electrode active material, resulting in a tighter contact with the positive electrode active material. Compared to ball milling, it is easier to realize its capacity, leading to superior performance improvement for the lithium-ion battery. As a positive electrode lithium replenisher, elemental boron can be applied to various battery systems, improving the cycle performance of lithium-ion batteries without worsening gas production. Detailed Implementation

[0029] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0030] It should be understood that the present invention can be implemented in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Unless otherwise specified, “%” and “parts” as shown in the following embodiments refer to “% by mass” and “parts by mass”, respectively.

[0031] The technical solution of the present invention will be further described in detail below in conjunction with several embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention under the condition of not making creative efforts belong to the scope protected by the present invention.

[0032] The present invention provides a lithium-ion battery, which includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The separator is located between the positive electrode sheet and the negative electrode sheet, and the electrolyte is filled between the positive electrode sheet, the negative electrode sheet, and the separator. Among them, the positive electrode sheet includes a lithium supplement agent, and the lithium supplement agent includes elemental boron. The present invention does not limit the type and shape of the lithium-ion battery. In one embodiment of the present invention, the lithium-ion battery is, for example, a secondary battery, and the secondary battery is, for example, a soft-pack battery, a hard-shell battery, or a cylindrical battery, etc. In this embodiment, for example, a soft-pack secondary battery is taken as an example for elaboration.

[0033] In one embodiment of the present invention, the positive electrode sheet includes a positive electrode current collector and at least one positive electrode active material layer provided on one side of the positive electrode current collector. The positive electrode current collector is, for example, a foil material formed after surface treatment of nickel, titanium, aluminum, nickel, silver, stainless steel, or carbon, etc. The surface of the positive electrode current collector is smooth, and fine纹路 can also be formed on the surface of the positive electrode current collector to improve the adhesion between the positive electrode active material and the positive electrode current collector. In addition to the foil material, the positive electrode current collector can also be used in any one or a combination of multiple forms such as film-like, mesh-like, porous, foam, or non-woven fabric.

[0034] In one embodiment of the present invention, the positive electrode active material layer includes a positive electrode active material, a lithium supplement agent, a binder, and a conductive agent, etc. The positive electrode active material is, for example, selected from at least one of lithium iron phosphate (LiFePO4, LFP) or lithium manganese iron phosphate (LiFe a Mn 1-a PO4, 0.1 < a ≤ 0.5, LMFP), etc., to improve the energy density of the long-cycle lithium-ion battery. The positive electrode active material can also be a ternary high-nickel material (NCM), and the general formula of the ternary high-nickel material is, for example, LiNi x Co y Mn 1-x-y O2, where 0.65 ≤ x < 1.0, 0 ≤ y < 0.5, to extend the cycle life of the high-energy-density lithium-ion battery.

[0035] In one embodiment of the present invention, during charging, the positive electrode active material releases lithium and electrons simultaneously. These electrons undergo a reduction reaction at the negative electrode via an external circuit. If an equal amount of lithium is inserted into the negative electrode, this portion of lithium (lithium carbide) can reversibly release lithium ions and electrons again during discharge, contributing to reversible capacity. In this state, there is no loss of active lithium. The loss of active lithium at the negative electrode arises from the oxidation reaction at the positive electrode. The released charge is not completely converted into lithium ion insertion at the negative electrode; instead, a side reaction of electrolyte decomposition occurs. Therefore, this portion of capacity becomes irreversible, resulting in active lithium loss—that is, the lithium equivalent extracted from the positive electrode is not converted into reversibly dischargeable capacity at the negative electrode. Therefore, considering the existence of active lithium loss, the lithium ion insertion-extraction equivalent at the positive and negative electrodes does not necessarily need to be equal during charging. The negative electrode does not require lithium ions to migrate from the positive electrode to undergo an insertion reaction. All lithium ion exchange occurs with the electrolyte near the positive and negative electrodes. In this process, what is truly conserved is the amount of charge reacting at the positive and negative electrodes. Therefore, during the charging process, substances in the positive electrode that can undergo oxidation and contribute charge can fill the capacity of the negative electrode where lithium ions are not intercalated.

[0036] In one embodiment of the present invention, the lithium replenishing agent includes, for example, elemental boron (B). Experiments have shown that elemental boron can achieve a charging capacity of 1500 mAh / g, with negligible reversible capacity and a charging voltage of 4.5V. Furthermore, elemental boron has a relative atomic mass of 10.81 g / mol, which improves the battery's energy density and cycle performance. Its highest oxidation number is III, thus its theoretical capacity is an impressive 7.44 Ah / g. When elemental boron is chosen as the positive electrode lithium replenishing agent, it can undergo oxidation during charging, contributing a large amount of charge. After oxidation, elemental boron becomes positively charged, thus forming a charge balance with the lithium ions embedded in the negative electrode. This prevents the imbalance of ionic charge in the solution due to its own lack of lithium ion contribution, thereby achieving lithium replenishment. Simultaneously, elemental boron has a high specific capacity, resulting in a strong ability to fill the irreversible capacity of the negative electrode, thus playing a significant role in positive electrode lithium replenishment. In addition, in lithium-ion batteries, the oxidation product of elemental boron may be LiBF4, which basically does not have the ability to reversibly react back to boron. At the same time, LiBF4 is also an additive that can improve the film quality of the cathode electrolyte interface (CEI) and reduce the direct current resistance (DCR).

[0037] In one embodiment of the present invention, the content of the lithium replenishing agent in the positive electrode active material layer is, for example, 0.08 wt% to 2 wt%. As the content of the lithium replenishing agent increases, the battery cycle life can be improved without deteriorating the gas generation performance. When the amount of elemental boron added is low, the lithium replenishing effect is not significant, and the improvement on lithium-ion battery performance is not obvious. When the amount of elemental boron added is high, the conductivity of elemental boron is poor, leading to a decrease in lithium-ion battery performance.

[0038] In one embodiment of the present invention, the adhesive is selected from one or more of the following: polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), polyhexanefluoropropylene (PPD), or polymerized styrene-butadiene rubber (SBR). The conductive agent is selected from one or more of the following: conductive carbon black (Super P, SP), acetylene black, carbon nanotubes, and graphene.

[0039] In one embodiment of the present invention, during the preparation of the positive electrode sheet, a lithium supplement agent is first mixed into the positive electrode active material to obtain a blended active powder. The blended active powder is obtained, for example, by ball milling. The positive electrode active material and nano-elemental boron are weighed and blended according to the ratio set by the lithium supplement agent, and ball milling is performed under inert gas protection. In this embodiment, the size of the grinding balls is, for example, 20 mm and 15 mm, and the number of 20 mm and 15 mm grinding balls is equal. The particle size of the elemental boron powder is, for example, 10 nm to 500 nm. The ball-to-material ratio is, for example, 1:1. The ball milling speed is, for example, 400 rpm / min to 600 rpm / min. The ball milling time is, for example, 10 h to 15 h. The inert gas is, for example, argon, to ensure that the positive electrode active material and nano-elemental boron are mixed uniformly.

[0040] In another embodiment of the present invention, the blended active powder is obtained, for example, by a reduction method. Specifically, the positive electrode active material is added to ice water or ice N,N-dimethylacetamide solvent containing ammonium fluoride. Depending on the amount of lithium supplementer added, boric acid (H3BO3) is first dissolved as an oxidant. After stirring and mixing evenly, dimethylamine borane (DMAB) or lithium borohydride (LiBH4) is gradually added dropwise as a reducing agent. After the addition is complete, the reaction is carried out for a first preset time, then filtered and washed to obtain an intermediate product. The intermediate product is then calcined for a second preset time under a preset temperature and oxygen environment. The intermediate product is washed, for example, with deionized water. The first preset time is, for example, 3h to 3.5h, the preset temperature is, for example, 730℃ to 780℃, and the second preset time is, for example, 1h to 2h. When the blended active powder is obtained by the reduction method, elemental boron is generated in situ on the surface of the positive electrode active material, resulting in a closer contact with the positive electrode active material and easier capacity utilization.

[0041] In one embodiment of the present invention, the positive electrode current collector is, for example, selected from aluminum foil, with a thickness of, for example, 8 μm to 16 μm. Active powder, binder, and conductive agent are mixed, for example, at a mass ratio of 95–98:1–2:1–3, and then an organic solvent is added and stirred until the system is homogeneous to obtain a positive electrode slurry. The organic solvent is, for example, selected from N-methylpyrrolidone (NMP). The positive electrode slurry is uniformly coated onto the aluminum foil, dried at room temperature, and then the aluminum foil is, for example, placed in a vacuum drying oven and dried at 120°C for 1 to 10 hours. The dried aluminum foil is then cold-pressed and slit to form a positive electrode sheet.

[0042] In one embodiment of the present invention, the negative electrode sheet includes, for example, a negative electrode current collector and a negative electrode active material layer disposed at least on one side of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, a binder, a conductive agent, and a thickener. The negative electrode current collector is selected from, for example, one of copper foil current collectors, composite copper foil current collectors, carbon current collectors, foamed copper current collectors, or stainless steel current collectors. The negative electrode active material is selected from, for example, at least one of graphite, silicon oxide materials, or silicon carbon materials. The binder is selected from, for example, any one or more of polyvinylidene fluoride, polyamide, polypropylene, polyacrylate, polyethylene ether, polymethyl methacrylate, polyacrylic acid (PAA), polyhexafluoropropylene, or styrene-butadiene rubber. The conductive agent is selected from, for example, any one or more of conductive carbon black, acetylene black, carbon nanotubes, and graphene. The thickener is selected from, for example, sodium carboxymethyl cellulose.

[0043] In one embodiment of the present invention, the negative electrode current collector is selected, for example, from copper foil, with a thickness of, for example, 8 μm to 16 μm. The negative electrode active material, conductive agent, thickener, and binder are mixed, for example, at a mass ratio of 95–98.9:0.1–1:1–2:0–2, and deionized water is added. The mixture is stirred thoroughly to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated onto the copper foil, dried at room temperature, and then subjected to vacuum drying, cold pressing, and slitting to obtain the negative electrode sheet.

[0044] In one embodiment of the present invention, the electrolyte includes, for example, a non-aqueous solvent, a lithium salt, and additives. The non-aqueous solvent is selected from one or more of ethylene carbonate (EC), ethylene methyl carbonate (EMC), propylene carbonate (PC), ethyl acetate (EA), dimethyl carbonate (DMC), or diethyl carbonate (DEC). The lithium salt is selected from one or more of lithium bis(fluorosulfonyl)imide (LiFSi), lithium difluorophosphate (LiPO2F2), lithium hexafluorophosphate (LiPF6), or lithium tetrafluoroborate (LiBF4). The additive is selected from one or more of vinylene carbonate (VC), 1,3,2-dioxathiolane 2,2-dioxide (DTD), fluoroethylene carbonate (FEC), or 1,3-propane sultone (PS). In one embodiment of the invention, the lithium salt is selected from lithium hexafluorophosphate, and the non-aqueous solvent is selected from a mixture of ethylene carbonate and methyl ethyl carbonate. Ethyl carbonate and methyl ethyl carbonate are mixed at a mass ratio of 3:7. In an argon atmosphere glove box with a water content of less than 10 ppm, thoroughly dried LiPF6 and the additive are dissolved in the mixed non-aqueous solvent and mixed evenly to obtain an electrolyte. The content of LiPF6 in the electrolyte is, for example, 6 wt% to 15 wt%, and the content of the additive in the electrolyte is, for example, 1 wt% to 11 wt%.

[0045] In one embodiment of the present invention, the separator is, for example, a polyethylene (PE) membrane, a polypropylene (PP) membrane, a glass fiber membrane, or a polyethylene membrane. The thickness of the separator is, for example, 9 μm to 15 μm. In one embodiment of the present invention, the above-mentioned positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrode to act as a separator. Then, an aluminum-plastic film is wrapped around the separator, and it is transferred to a vacuum oven to dry at 120°C. After injecting 3.0 g / Ah of the prepared electrolyte, the separator is sealed, and electrolyte liquefaction is performed to finally obtain a 1 Ah soft-pack lithium-ion battery.

[0046] The present invention will be explained in more detail below by referring to embodiments, which should not be construed as limiting. Appropriate modifications can be made within the scope of the present invention, and all such modifications fall within the technical scope of the present invention.

[0047] Example 1

[0048] Preparation of the positive electrode sheet: The positive electrode active material LiFePO4 and elemental boron were mixed by ball milling under an argon atmosphere using equal amounts of 20mm and 15mm grinding balls at a ball-to-material ratio of 1:1 for 12 hours at a milling speed of 500 rpm / min to obtain a mixed active powder. The mixed active powder, binder polyvinylidene fluoride, and conductive agent conductive carbon black were mixed at a mass ratio of 97:1:2. After the mixed active powder, binder, and conductive agent were thoroughly mixed, N-methylpyrrolidone solvent was added, and the mixture was stirred in a vacuum mixer until homogeneous and transparent, obtaining a positive electrode slurry. The positive electrode slurry was uniformly coated onto a 9μm aluminum foil current collector. After drying the current collector at room temperature, it was transferred to a vacuum oven and dried at 120℃ for 10 hours. The resulting material was then cold-pressed and slit to obtain the positive electrode sheet. The elemental boron content in the positive electrode active material layer was 0.08 wt%.

[0049] Preparation of the negative electrode sheet: Artificial graphite (negative electrode active material), conductive carbon black (conductive agent), sodium carboxymethyl cellulose (thickener), and styrene-butadiene rubber (binder) were mixed in a mass ratio of 96:1:1:2. Deionized water was added, and the mixture was stirred in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto a 9μm copper foil current collector. After the copper foil was dried at room temperature, it was transferred to a vacuum oven for further drying. The resulting negative electrode sheet was then cold-pressed and slit to obtain the negative electrode sheet.

[0050] Preparation of electrolyte: Battery-grade ethylene carbonate and ethyl methyl carbonate are mixed at a mass ratio of 3:7 to form a mixed solvent. In an argon atmosphere glove box with a water content of less than 10 ppm, fully dried LiPF6 is dissolved in the mixed solvent. Then, vinylene carbonate and vinyl sulfate are added and mixed evenly to obtain the electrolyte. The content of LiPF6 in the electrolyte is 12 wt%, the content of vinylene carbonate in the electrolyte is 2.5 wt%, and the content of vinyl sulfate in the electrolyte is 0.5 wt%.

[0051] Selection of diaphragm: Use a 12μm thick polypropylene diaphragm.

[0052] Battery fabrication: The positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to provide insulation. Then, an aluminum-plastic film is wrapped around the separator, and the battery is dried in a vacuum oven at 120°C. After injecting 3.0 g / Ah of the prepared electrolyte, the battery is sealed and liquefied to form a 1 Ah soft-pack lithium-ion battery.

[0053] Example 2

[0054] In the positive electrode active material layer, the content of elemental boron is 1.5 wt%, and other operations are consistent with those in Example 1.

[0055] Example 3

[0056] In the positive electrode active material layer, the content of elemental boron is 2 wt%, and other operations are consistent with those in Example 1.

[0057] Example 4

[0058] In the positive electrode active material layer, the content of elemental boron is 0.5 wt%, and other operations are consistent with those in Example 1.

[0059] Example 5

[0060] The positive electrode active material LiFePO4 is mixed with elemental boron through reduction. The specific reduction steps include: adding LiFePO4 to ice water containing ammonium fluoride; calculating equal amounts of H3BO3 and LiBH4 according to the equivalent amount of elemental boron; first dissolving H3BO3 and stirring until homogeneous; then gradually adding LiBH4 dropwise. After the addition is complete, the reaction is carried out for 3 hours, filtered, washed with deionized water, and then calcined at 750℃ for 1.5 hours in an oxygen environment.

[0061] In the positive electrode active material layer, the content of elemental boron is 0.08 wt%, and other operations are consistent with those in Example 1.

[0062] Example 6

[0063] The positive electrode active material LiFePO4 and elemental boron were mixed by reduction. The content of elemental boron in the positive electrode active material layer was 0.5 wt%. Other operations were the same as in Example 1.

[0064] Example 7

[0065] The positive electrode active material LiFePO4 and elemental boron were mixed by reduction. The content of elemental boron in the positive electrode active material layer was 1.5 wt%. Other operations were the same as in Example 1.

[0066] Example 8

[0067] The positive electrode active material LiFePO4 and elemental boron were mixed by reduction. The content of elemental boron in the positive electrode active material layer was 2 wt%, and other operations were consistent with those in Example 1.

[0068] Example 9

[0069] Preparation of the positive electrode: The positive electrode active material LiFe... 0.4 Mn 0.6 PO4 and elemental boron were mixed by ball milling under an argon atmosphere using equal amounts of 20mm and 15mm grinding balls at a ball-to-particle ratio of 1:1 for 12 hours at a speed of 500 rpm / min to obtain a mixed active powder. The mixed active powder, polyvinylidene fluoride binder, and acetylene black conductive agent were mixed at a mass ratio of 96:2:2. After the mixed active powder, binder, and conductive agent were thoroughly mixed, N-methylpyrrolidone solvent was added, and the mixture was stirred in a vacuum mixer until homogeneous and transparent to obtain a positive electrode slurry. The positive electrode slurry was then mixed at a rate of 0.3 g / 1540.25 mm. 2 The coating is applied to both sides of a 9μm thick aluminum foil current collector and then dried. After cold pressing and slitting, the positive electrode sheet is obtained. The elemental boron content in the positive electrode active material layer is 0.08 wt%.

[0070] Preparation of the negative electrode sheet: Artificial graphite (negative electrode active material), conductive carbon black (conductive agent), sodium carboxymethyl cellulose (thickener), and styrene-butadiene rubber (binder) were mixed in a mass ratio of 96:1:1:2. Deionized water was added, and the mixture was stirred in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto a 9μm copper foil current collector. After the copper foil was dried at room temperature, it was transferred to a vacuum oven for further drying. The resulting negative electrode sheet was then cold-pressed and slit to obtain the negative electrode sheet.

[0071] Preparation of electrolyte: Battery-grade ethylene carbonate and ethyl methyl carbonate are mixed at a mass ratio of 3:7 to form a mixed solvent. In an argon atmosphere glove box with a water content of less than 10 ppm, fully dried LiPF6 is dissolved in the mixed solvent. Then, vinylene carbonate and vinyl sulfate are added and mixed evenly to obtain the electrolyte. The content of LiPF6 in the electrolyte is 12 wt%, the content of vinylene carbonate in the electrolyte is 2.5 wt%, and the content of vinyl sulfate in the electrolyte is 0.5 wt%.

[0072] Selection of diaphragm: Use a 12μm thick polypropylene diaphragm.

[0073] Battery fabrication: The positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to provide insulation. Then, an aluminum-plastic film is wrapped around the separator, and the battery is dried in a vacuum oven at 120°C. After injecting 3.0 g / Ah of the prepared electrolyte, the battery is sealed and liquefied to form a 1 Ah soft-pack lithium-ion battery.

[0074] Example 10

[0075] In the positive electrode active material layer, the content of elemental boron is 0.5 wt%, and other operations are consistent with those in Example 9.

[0076] Example 11

[0077] In the positive electrode active material layer, the content of elemental boron is 1.5 wt%, and other operations are consistent with those in Example 9.

[0078] Example 12

[0079] In the positive electrode active material layer, the content of elemental boron is 2 wt%, and other operations are consistent with those in Example 9.

[0080] Example 13

[0081] Preparation of the positive electrode: The positive electrode active material LiNi... 0.93 Co 0.06 Mn 0.01O2 and elemental boron were mixed by ball milling under an argon atmosphere using equal amounts of 20mm and 15mm grinding balls at a ball-to-material ratio of 1:1 for 12 hours at a speed of 500 rpm / min to obtain a mixed active powder. The mixed active powder, polyvinylidene fluoride (PVDF) binder, and conductive carbon black conductive agent were mixed at a mass ratio of 98:1:1. After the mixture was homogeneous, N-methylpyrrolidone (NMP) solvent was added, and the mixture was stirred in a vacuum mixer until homogeneous and transparent to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto a 9μm aluminum foil current collector. After drying the current collector at room temperature, it was transferred to a vacuum oven and dried at 120℃ for 10 hours. The resulting material was then cold-pressed and slit to obtain the positive electrode sheet. The elemental boron content in the positive electrode active material layer was 0.5 wt%.

[0082] Preparation of negative electrode sheet: SiO x (x=0.9-1.1) was mixed with artificial graphite at a mass ratio of 3:7 to form the negative electrode active material. The negative electrode active material, conductive agent carbon nanotubes, and binder polyacrylic acid were mixed at a mass ratio of 96:0.2:3.8, and deionized water was added. The mixture was stirred in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto a 9μm copper foil current collector. After the copper foil was dried at room temperature, it was transferred to a vacuum oven for drying. Then, it was cold-pressed and slit to obtain the negative electrode sheet.

[0083] Preparation of electrolyte: Battery-grade ethylene carbonate and ethyl methyl carbonate were mixed at a mass ratio of 3:7 to form a mixed solvent. In an argon-atmosphere glove box with a water content of less than 10 ppm, thoroughly dried LiPF6 was dissolved in the mixed solvent. Then, fluoroethylene carbonate and 1,3-propanesulfonic acid lactone were added and mixed evenly to obtain the electrolyte. The concentration of LiPF6 in the electrolyte was 6.25 wt%, the content of fluoroethylene carbonate in the electrolyte was 10 wt%, and the content of ethylene sulfate in the electrolyte was 0.5 wt%.

[0084] Battery fabrication: The positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to provide insulation. Then, an aluminum-plastic film is wrapped around the separator, and the battery is dried in a vacuum oven at 120°C. After injecting 3.0 g / Ah of the prepared electrolyte, the battery is sealed and liquefied to form a 1 Ah soft-pack lithium-ion battery.

[0085] Comparative Example 1

[0086] The positive electrode active material was LiFePO4, without the addition of elemental boron. The same ball milling process was performed on LiFePO4 as in Example 1 to obtain the same batch of comparative samples. Other operations were consistent with those in Example 1.

[0087] Comparative Example 2

[0088] The positive electrode active material is LiFePO4, without the addition of elemental boron. The LiFePO4 is subjected to the same reduction operation as in Example 5, but without the addition of oxidant and reducing agent, to obtain the same batch of comparative samples. Other operations are consistent with those in Example 5.

[0089] Comparative Example 3

[0090] The positive electrode active material is LiFe 0.4 Mn 0.6 PO4, without the addition of elemental boron, for LiFe 0.4 Mn 0.6 PO4 was used for ball milling, and other operations were consistent with those in Example 9.

[0091] Comparative Example 4

[0092] The positive electrode active material is LiNi 0.93 Co 0.06 Mn 0.01 O2, without the addition of elemental boron, and other operations are consistent with Example 13.

[0093] In this invention, lithium-ion batteries were prepared using different positive electrode active materials in Examples 1-13 and Comparative Examples 1-4, and the rate performance of the lithium-ion batteries was tested. The test results are shown in Tables 1 to 3.

[0094] In one embodiment of the present invention, in order to achieve the lithium replenishment effect of elemental boron, the lithium-ion batteries obtained in Examples 1-13 and Comparative Examples 1-4 are subjected to an activation charging step, in which the lithium-ion batteries are charged at a constant current of 1C to 4.5V, then charged at a constant voltage until the current is less than 0.05C, left to stand for 30 minutes, and then discharged at 1C to the low voltage.

[0095] In one embodiment of the present invention, the high-temperature cycling test is conducted in an oven at 45°C. The lithium-ion battery, having completed the activation charging step, is cycled with a 1C current within a specified potential range, and the discharge capacity of each cycle is recorded. The test ends when the battery capacity reaches 80% of the first cycle capacity. Specifically, the potential range for the lithium-ion battery with LiFePO4 as the positive electrode active material is 2.0V to 3.8V. 0.4 Mn 0.6 The potential range of PO4 lithium-ion batteries is 2.5V to 4.2V, and the positive electrode active material is LiNi. 0.93 Co 0.06 Mn 0.01 The potential range of O2 lithium-ion batteries is 2.8V to 4.2V.

[0096] In one embodiment of the present invention, the gas production volume change rate test is performed by charging the lithium-ion battery cell to 100% State of Charge (SOC) before the start of high-temperature cycling, and then measuring the cell volume V1 using the water displacement method. After the high-temperature cycling ends, the cell is fully charged again, and the cell volume V2 is measured again using the water displacement method. The cycle gas production is obtained by: (V2-V1) / V1×100%.

[0097] In one embodiment of the present invention, for the high-nickel system, the 250-cycle capacity recovery test is performed by charging with an upper limit voltage of 4.5V every 250 cycles.

[0098] This invention selects some examples and comparative examples to study the effect of using the positive electrode active material LFP and the lithium supplement element boron in combination on the performance of lithium-ion batteries. The results are shown in Table 1.

[0099] Table 1. Performance test results of lithium-ion batteries in Examples 1-8 and Comparative Examples 1-2

[0100]

[0101] Please refer to Table 1. In conjunction with Examples 1-8 and Comparative Examples 1-2, adding elemental boron as a lithium supplement to the positive electrode active material can increase the cycle number of lithium-ion batteries. Furthermore, as the content of elemental boron increases, the cycle number significantly improves, while slightly alleviating the gas generation problem of lithium-ion batteries without worsening it. Due to the poor conductivity of elemental boron, it is doped to a maximum of 2 wt% in the positive electrode active material layer according to process requirements to ensure the energy density of the lithium-ion battery. In conjunction with Examples 1-8, among the methods of incorporating elemental boron into the positive electrode active material, the ball milling method and the reduction method show similar trends. In the same chemical system, with the same amount of elemental boron added, the lithium-ion battery prepared by the reduction method with elemental boron exhibits better cycle performance. This is because elemental boron has extremely poor conductivity; therefore, the contact between the introduced elemental boron and the conductive material in the positive electrode sheet determines the capacity utilization of the elemental boron. The better the contact effect, the greater the capacity utilization. In the reduction method, elemental boron is generated in situ on the surface of the positive electrode active material, and its contact with the positive electrode active material is closer. Therefore, it is easier to bring out the capacity compared to the ball milling method, thus resulting in better performance improvement of lithium-ion batteries.

[0102] This invention selects some examples and comparative examples to study the effect of using the positive electrode active material LMFP and the lithium supplement element boron in combination on the performance of lithium-ion batteries. The results are shown in Table 2.

[0103] Table 2. Performance test results of lithium-ion batteries in Examples 9-12 and Comparative Example 3

[0104]

[0105] Please refer to Table 2. In conjunction with Examples 9-12 and Comparative Example 3, adding elemental boron as a lithium supplement in an LMFP system with elemental boron as the positive electrode active material can increase the cycle number of lithium-ion batteries. Furthermore, the cycle number increases significantly with increasing elemental boron content, without worsening gas production in the lithium-ion battery. This solves the problem that conventional lithium supplement materials in LMFP systems worsen LMFP gas production, achieving improved cycle performance without deteriorating LMFP gas production.

[0106] This invention selects some examples and comparative examples to study the effect of using the positive electrode active material NCM and the lithium supplement element boron in combination on the performance of lithium-ion batteries. The results are shown in Table 3.

[0107] Table 3. Performance test results of lithium-ion batteries in Example 13 and Comparative Example 4

[0108]

[0109] Please refer to Table 3. In conjunction with Example 13 and Comparative Example 4, for a high-nickel, high-silicon system, the conventional cycling step is charging to 4.25V. At this voltage, elemental boron is not oxidized and therefore does not contribute to capacity; the positive electrode capacity is entirely contributed by the delithiation of the positive electrode active material. During the cycling process of a high-nickel, high-silicon battery, the negative electrode experiences severe active lithium loss, meaning that lithium ions embedded in the negative electrode cannot return to the system during discharge. Simultaneously, the negative electrode retains a reserve capacity for further lithium intercalation. In Example 13 and Comparative Example 4, the lithium-ion battery is charged at 4.5V every 250 cycles, oxidizing the elemental boron in the positive electrode and forcing the negative electrode to intercalate lithium to replenish capacity, thus achieving lithium replenishment. This effectively restores capacity and achieves an ultra-long cycling time compared to Comparative Example 4.

[0110] This invention also provides an electronic device comprising at least one of the aforementioned lithium-ion batteries, which provides electrical energy. The electronic device can be a vehicle, mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, or power tool, etc. In one embodiment of this invention, the vehicle is, for example, a new energy vehicle, which can be a pure electric vehicle, a hybrid electric vehicle, or a range-extended electric vehicle, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. The electronic device includes the aforementioned lithium-ion battery, and therefore the advantages of including the aforementioned lithium-ion battery are not elaborated here.

[0111] In summary, this invention proposes a lithium-ion battery, its preparation method, and its application. By selecting elemental boron as the positive electrode lithium replenisher, it undergoes an oxidation reaction during charging, contributing a significant amount of charge. After oxidation, it becomes positively charged, forming a charge balance with the lithium ions embedded in the negative electrode. This prevents the imbalance of ion charge in the solution due to boron's own lack of lithium ion contribution, thus achieving lithium replenishment. Simultaneously, elemental boron has a high specific capacity and a strong ability to fill the irreversible capacity of the negative electrode, resulting in a high positive electrode lithium replenishment effect. The products of the lithium replenisher oxidation can improve the film quality of the positive electrode electrolyte interface film and reduce DC resistance. Through reduction, elemental boron is generated in situ on the surface of the positive electrode active material, resulting in a tighter contact with the positive electrode active material. Compared to ball milling, it is easier to realize its capacity, leading to superior performance improvement for the lithium-ion battery. As a positive electrode lithium replenisher, elemental boron can be applied to various battery systems, improving the cycle performance of lithium-ion batteries without worsening gas production.

[0112] The above description is merely a preferred embodiment of this application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept. For example, technical solutions formed by replacing the above-mentioned features with technical features with similar functions disclosed in this application (but not limited to) each other.

[0113] Apart from the technical features described in the specification, the other technical features are known to those skilled in the art. To highlight the innovative features of this invention, the other technical features will not be described in detail here.

Claims

1. A lithium-ion battery, characterized in that, At least including: The positive electrode includes a lithium replenishing agent, which includes elemental boron. During activation charging of the lithium-ion battery, the lithium-ion battery is charged to 4.5V to achieve the lithium replenishment effect of elemental boron. The positive electrode includes a positive current collector and a positive active material layer disposed at least on one side of the positive current collector. The content of the lithium replenishing agent in the positive active material layer is 0.08wt%~2wt%. Negative electrode plate; A diaphragm is disposed between the positive electrode and the negative electrode; and An electrolyte is filled between the positive electrode, the negative electrode, and the separator.

2. The lithium-ion battery according to claim 1, characterized in that, The positive electrode active material layer includes a positive electrode active material, which is selected from at least one of lithium iron phosphate or lithium manganese iron phosphate.

3. The lithium-ion battery according to claim 1, characterized in that, The positive electrode active material layer includes a positive electrode active material, which is selected from LiNi. x Co y Mn 1-x-y O2, where 0.65≤x<1.0, 0≤y<0.

5.

4. The lithium-ion battery according to claim 1, characterized in that, The negative electrode sheet includes a negative current collector and a negative active material layer disposed at least on one side of the negative current collector. The negative active material layer includes a negative active material selected from at least one of graphite, silicon-oxygen materials, or silicon-carbon materials.

5. A method for preparing a lithium-ion battery, used to prepare the lithium-ion battery as described in any one of claims 1-4, characterized in that, At least the following steps are included: A lithium supplement agent is mixed into the positive electrode active material to obtain a blended active powder. The blended active powder is formulated into a positive electrode slurry; The positive electrode slurry is coated onto the positive electrode current collector, and then dried and cold-pressed to obtain the positive electrode sheet. The negative electrode active material is formulated into a negative electrode slurry; The negative electrode slurry is coated onto the surface of the negative electrode current collector, dried, and cold-pressed to obtain the negative electrode sheet; and The lithium-ion battery is obtained by assembling the positive electrode, the negative electrode, the electrolyte, and the separator.

6. The method for preparing a lithium-ion battery according to claim 5, characterized in that, The lithium supplement and the positive electrode active material are mixed evenly by ball milling.

7. The method for preparing a lithium-ion battery according to claim 6, characterized in that, The lithium replenishing agent has a powder particle size of 10nm~500nm.

8. An electronic device, characterized in that, Includes the lithium-ion battery as described in any one of claims 1-4.

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