Lithium ion battery and electric device using the same

Abstract

The application provides a lithium ion battery and an electric device, and belongs to the technical field of lithium ion batteries.The lithium ion battery comprises a positive electrode sheet and a negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, and the content of manganese in the negative electrode sheet is less than or equal to 331 ppm; and the negative electrode active material layer has an absorption peak within a specific range in an infrared spectrum. 2+ The application adds a negative electrode additive in the negative electrode sheet, which helps the negative electrode to maintain structural integrity at high temperature and in the charging and discharging process, prevents the SEI film of the negative electrode from being destroyed by Mn 2+ , and further improves the cycle life and storage performance of the battery and reduces the gas production problem of the secondary battery in the charging and discharging cycle.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a lithium-ion battery and an electrical device thereof. Background Technology

[0002] Lithium manganese iron phosphate (MFP), as a cathode active material, has the advantage of higher operating voltage compared to lithium iron phosphate (LFP), thus exhibiting higher energy density and great commercial potential. However, MFP suffers from manganese (Mn) leaching. Specifically, trivalent manganese ions (Mn) leach out. 3+ Exhibiting the John-Teller effect, it spontaneously generates Mn 2+ and Mn 4+ During charging, they migrate towards the negative electrode, among which divalent manganese ions (Mn) are... 2+ It will deposit on the surface of the negative electrode and continuously damage the formation of the negative electrode SEI film, causing irreversible capacity loss, and ultimately leading to a sharp deterioration in various battery performance indicators (such as cycle life and storage performance). Summary of the Invention

[0003] The purpose of this invention is to overcome the defect of Mn leaching leading to the deterioration of the electrochemical performance of lithium-ion batteries, and to provide a lithium-ion battery and electrical device. The negative electrode of the lithium-ion battery contains a negative electrode additive with a specific chemical structure. This negative electrode additive helps the negative electrode maintain its structural integrity at high temperatures and during charge and discharge processes, and the negative electrode additive can also form Mn. 2+ An insulating layer is used to prevent the negative electrode from direct contact with the dissolved manganese, thereby preventing the SEI film on the negative electrode from being damaged by Mn. 2+ This process can improve battery cycle life and storage performance, extend electrode life, and further reduce gas generation issues in secondary batteries during charge-discharge cycles.

[0004] To achieve the above objectives, in a first aspect of the present invention, the present invention provides a lithium-ion battery, comprising a positive electrode and a negative electrode, wherein the negative electrode comprises a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector.

[0005] The manganese content in the negative electrode sheet is ≤331ppm;

[0006] In the infrared spectrum of the negative electrode active material layer, the range is 1000–1050 cm⁻¹. -1 It has an absorption peak within the range, and has an absorption peak in at least one of the following ranges: 530–620 cm⁻¹ -1 1068~1190cm -1 650~900cm -1 1590~1650cm -1 3400~3500cm -11720~1770cm -1 2995~3030cm -1 3072~3100cm -1 3150~3300cm -1 .

[0007] In a preferred embodiment of the present invention, the manganese content in the negative electrode sheet is ≤299ppm.

[0008] In a preferred embodiment of the present invention, the manganese content in the negative electrode sheet is 157-234 ppm.

[0009] In a preferred embodiment of the present invention, the negative electrode active material layer comprises a negative electrode active substance and a negative electrode additive, wherein the negative electrode additive has a structure as shown in formula (1):

[0010]

[0011] Wherein, n is an integer from 10 to 10000, and at least one of the groups R1, R2, and R3 is selected from a first polar functional group, which includes one or more of -OH, -COOH, -CH2COOH, -SO3H, and -NH2.

[0012] In a preferred embodiment of the present invention, in the negative electrode additive, the groups in R1, R2, and R3 that are not first polar functional groups are each independently selected from second polar functional groups, including -CHO, -NHR, and -[-O-]-. m At least one of -COOX and -SO3X; wherein X in -COOX and -SO3X is independently selected from alkali metal elements, and R in -NHR is selected from C1 to C6 alkyl groups, wherein -[-O-]- m In this case, m is a positive integer between 2 and 20.

[0013] As a preferred embodiment of the present invention, the negative electrode additive has a structure as shown in formula (2), formula (3) or formula (4):

[0014]

[0015] In a preferred embodiment of the present invention, n in the negative electrode additive is an integer from 100 to 1000.

[0016] In a preferred embodiment of the present invention, the negative electrode active material layer further includes a conductive agent and a thickener.

[0017] As a preferred embodiment of the present invention, the mass ratio of negative electrode active material, conductive agent, thickener and negative electrode additive in the negative electrode active material layer is (93-98):(0.5-2):(0.5-5):(1-2).

[0018] As a preferred embodiment of the present invention, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes lithium iron manganese oxide.

[0019] As a preferred embodiment of the present invention, the lithium iron manganese oxide comprises a compound with the molecular formula Li a Mn x Fe 1-x Me 1-a Compounds of PO4, wherein Me includes at least one of In, La, Zr, Ce, W, Al, Ti, Sr, Mg, Sb, V, Zn, Cu, and Cr, with 0.95 ≤ a ≤ 1 and 0.4 ≤ x ≤ 0.8.

[0020] In a second aspect, the present invention provides an electrical device comprising the aforementioned lithium-ion battery.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] This invention provides a lithium-ion battery and an electrical device thereof. The negative electrode of the lithium-ion battery of this invention contains a negative electrode additive with a specific chemical structure. This negative electrode additive helps the negative electrode maintain its structural integrity at high temperatures and during charge and discharge processes. Furthermore, the negative electrode additive can also form Mn. 2+ An insulating layer is used to prevent the negative electrode from direct contact with the dissolved manganese, thereby preventing the SEI film on the negative electrode from being damaged by Mn. 2+ This process can improve battery cycle life and storage performance, extend electrode life, and further reduce gas generation issues in secondary batteries during charge-discharge cycles. Attached Figure Description

[0023] Figure 1 This is a preparation route diagram for the negative electrode additive of this application.

[0024] Figure 2 The image shows the infrared spectrum of the negative electrode additive prepared in Example 1.

[0025] Figure 3 The image shows the infrared spectrum of the negative electrode additive prepared in Example 2.

[0026] Figure 4 The image shows the infrared spectrum of the negative electrode additive prepared in Example 3. Detailed Implementation

[0027] To better illustrate the objectives, technical solutions, and advantages of this invention, the technical solutions in the embodiments of this invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this invention, not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0028] In this invention, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0029] In this invention, numerical ranges are involved. Unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe features or characteristics, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0030] In this invention, there are no particular limitations on the specific dispersion and stirring methods.

[0031] Unless otherwise specified, all reagents or instruments used in this invention are commercially available products.

[0032] To address the problem of Mn leaching leading to deterioration of the electrochemical performance of lithium-ion batteries in existing technologies.

[0033] This invention provides a lithium-ion battery, including a positive electrode and a negative electrode. The negative electrode includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector.

[0034] The manganese content in the negative electrode sheet is ≤331ppm;

[0035] In the infrared spectrum of the negative electrode active material layer, the range is 1000–1050 cm⁻¹. -1 It has an absorption peak within the range, and has an absorption peak in at least one of the following ranges: 530–620 cm⁻¹ -1 1068~1190cm -1 650~900cm -1 1590~1650cm -1 3400~3500cm -1 1720~1770cm -1 2995~3030cm -1 3072~3100cm-1 3150~3300cm -1 .

[0036] In this invention, the manganese content deposited on the negative electrode of the lithium-ion battery is low, thereby reducing the damage to the formation of the SEI film on the negative electrode and enabling the lithium-ion battery to have a high cycle life and storage performance.

[0037] The inventors discovered that when the infrared absorption peak of the negative electrode active material layer is within the range given above, the battery can have a higher cycle life and storage performance, and further reduce the gas generation problem of the secondary battery during charge and discharge cycles.

[0038] In one embodiment, the manganese content in the negative electrode is ≤299ppm.

[0039] In one embodiment, the manganese content in the negative electrode sheet is 157–234 ppm.

[0040] In one embodiment, the negative electrode active material layer includes a negative electrode active substance and a negative electrode additive, the negative electrode additive having a structure as shown in formula (1):

[0041]

[0042] Wherein, n is an integer from 10 to 10000, and at least one of the groups R1, R2, and R3 is selected from a first polar functional group, which includes one or more of -OH, -COOH, -CH2COOH, -SO3H, and -NH2.

[0043] In one embodiment, in the negative electrode additive, the groups in R1, R2, and R3 that are not first polar functional groups are each independently selected from second polar functional groups, including -CHO, -NHR, and -[-O-]-. m At least one of -COOX and -SO3X; wherein X in -COOX and -SO3X is independently selected from alkali metal elements, and R in -NHR is selected from C1 to C6 alkyl groups, wherein -[-O-]- m In this case, m is a positive integer between 2 and 20.

[0044] The negative electrode additive of this invention is a water-soluble compound with a cyclic structure and containing polar functional groups. In the negative electrode active material layer, the negative electrode additive can form a network structure through the interaction of chemical bonds and hydrogen bonds, thereby encapsulating the negative electrode active material. The network structure of the negative electrode additive serves both as a binder, ensuring the structural integrity of the negative electrode at high temperatures and during charge-discharge processes, and as a barrier against Mn. 2+ Its function is to prevent the negative electrode from reacting with dissolved Mn.2+ Direct contact. Through the combined effect of bonding and insulating properties, the lithium-ion battery of the present invention exhibits excellent cycle life and storage performance, and the gas generation problem of the secondary battery during charge-discharge cycles is also improved.

[0045] The hydrogen bonding in the negative electrode additive primarily originates from the polar functional groups R1, R2, and R3. Higher polarity of R1, R2, and R3 results in stronger hydrogen bonding forces and a more compact and robust network structure formed by the negative electrode additive, leading to stronger adhesion and better barrier properties for the negative electrode active material. Simultaneously, the polarity of R1, R2, and R3 also affects the water solubility of the negative electrode additive. A negative electrode additive with better water solubility can be more uniformly dispersed in the negative electrode active material layer of this invention, further enhancing the adhesion and barrier properties provided by the negative electrode additive.

[0046] Hydroxyl (-OH), carboxyl (-COOH), sulfonic acid (-SO3H), and amino (-NH2) groups, as polar functional groups, possess relatively higher polarity, resulting in stronger hydrogen bonds in the network structure formed by the negative electrode additive. Therefore, when the negative electrode additives R1, R2, and R3 contain -OH, -COOH, -CH2COOH, -SO3H, or -NH2, the electrochemical performance of the lithium-ion battery is better.

[0047] In one embodiment, X in -COOX and -SO3X is independently selected from Li, Na, or K.

[0048] In one embodiment, the negative electrode additive has a structure as shown in formula (2), formula (3) or formula (4):

[0049]

[0050] In one embodiment, n in the negative electrode additive is an integer between 100 and 5000.

[0051] In one embodiment, n in the negative electrode additive is an integer from 100 to 1000.

[0052] The value of n in negative electrode additives affects their dispersion. Higher n values ​​result in larger molecular weights, higher polymerization degrees, higher viscosity, relatively lower water solubility, and slightly poorer dispersion performance. Lower n values ​​lead to slightly poorer stability. The inventors have found that when n is in the range of 100–1000, the overall water solubility, dispersibility, and stability are optimal.

[0053] In one embodiment, the method for preparing the negative electrode additive includes the following steps:

[0054] Using α-glucan oligosaccharides as raw materials, an intermediate product containing R1, R2, and R3 groups was obtained through a functional group substitution reaction.

[0055] The intermediate product was subjected to an aldol condensation reaction to obtain the negative electrode additive.

[0056] The preparation route of the negative electrode additive is as follows: Figure 1 As shown.

[0057] The functional group substitution reaction can be either adding a polar functional group to the carbon ring of the α-glucan oligosaccharide, or replacing the existing hydroxyl group in the α-glucan oligosaccharide with a polar functional group. The functional group substitution reaction includes, but is not limited to, one or more of the following: halogenation reaction (RH→RX, X = Cl, Br, I, etc., heating or light irradiation); hydrolysis of haloalkanes to generate hydroxyl groups (R-X+NaOH→R-OH+NaX, X = Cl, Br, I, etc., heating); substitution reaction of haloalkanes to generate cyano groups (R-X+NaCN→R-CN+NaX, X = Cl, Br, I, etc., heating), followed by reduction to generate amino groups (R-CN→R-NH2, hydrogen environment, catalyst); direct substitution reaction of haloalkanes to generate amino groups (R-X+NH3→R-NH2+HX, X = Cl, Br, I, etc., heating and pressurization); oxidation reaction of hydroxyl groups to generate carboxyl groups (R-OH+O2→R-COOH, heating, catalyst).

[0058] In one embodiment, the aldol condensation reaction is carried out under the catalysis of a catalyst, which is at least one of niobic acid, zeolite, oxides of alkali metals or alkaline earth metals, hydroxides, bicarbonates, carbonates, and carboxylates.

[0059] In one embodiment, the negative electrode active material layer further includes a conductive agent and a thickener.

[0060] In one embodiment, the mass ratio of negative electrode active material, conductive agent, thickener and negative electrode additive in the negative electrode active material layer is (93-98):(0.5-2):(0.5-5):(1-2).

[0061] In one embodiment, the mass ratio of negative electrode active material, conductive agent, thickener and negative electrode additive in the negative electrode active material layer is (95-97):(0.8-1):(0.8-1.2):(1.5-1.8).

[0062] In one embodiment, the negative electrode active material comprises a carbon material.

[0063] The carbon material can be at least one of artificial graphite, natural graphite, and mesophase carbon microspheres.

[0064] The conductive agent can be any type of conductive agent commonly used in the art.

[0065] In one embodiment, the conductive agent includes at least one of spherical conductive agents, tubular conductive agents, and sheet-like conductive agents.

[0066] In one embodiment, the spherical conductive agent includes at least one of Super P, Ketjen Black, and acetylene black; the tubular conductive agent includes at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, and conductive carbon fibers; and the sheet-like conductive agent includes at least one of graphene, flake graphite, and KS-6.

[0067] The thickener may be a conventional type of thickener in the art.

[0068] In one embodiment, the thickener includes at least one of carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), and ethylene-vinyl acetate copolymer (EVA).

[0069] In one embodiment, the method for preparing the negative electrode sheet includes the following steps:

[0070] A negative electrode slurry is coated onto at least one surface of a negative electrode current collector, and after drying and cold pressing, a negative electrode sheet is obtained; the negative electrode slurry includes a negative electrode active material, a negative electrode additive, a conductive agent, a thickener, and a solvent.

[0071] In one embodiment, the negative current collector is a copper foil with a purity of ≥99%.

[0072] In one embodiment, the negative current collector is a copper foil with a purity of ≥99.99%.

[0073] In one embodiment, the thickness of the negative electrode current collector is 4–12 μm and the width is 100–1000 mm.

[0074] In one embodiment, the weight of the coated negative electrode slurry is 50 mg to 300 mg per unit area, where the unit area is 1540.25 mm². 2 .

[0075] In one embodiment, the coating speed is 5-35 m / min, the indoor temperature during the coating process is controlled at 25±5℃, and the indoor humidity during the coating process is controlled at ≤70%.

[0076] In one embodiment, the drying temperature is 80–120°C and the drying time is 5–60 min.

[0077] In one embodiment, the cold pressing speed is 5-60 m / min, the pressure is 5-50 T, and the cold pressing thickness is 50 μm-500 μm.

[0078] In one embodiment, the method for preparing the negative electrode slurry includes the following steps:

[0079] The negative electrode active material, conductive agent, thickener and negative electrode additive are mixed, and then a solvent is added and mixed evenly to obtain the negative electrode slurry.

[0080] In one embodiment, the solvent is deionized water, and the conductivity of the deionized water is ≤20 μS / cm.

[0081] In one embodiment, the negative electrode slurry has a solid content of 25-65% and a viscosity of 1000-10000 mPa·s.

[0082] In one embodiment, the positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer including lithium iron manganese oxide.

[0083] In one embodiment, the lithium iron manganese oxide comprises a compound with the molecular formula Li. a Mn x Fe 1-x Me 1-a Compounds of PO4, wherein Me includes at least one of In, La, Zr, Ce, W, Al, Ti, Sr, Mg, Sb, V, Zn, Cu, and Cr, with 0.95 ≤ a ≤ 1 and 0.4 ≤ x ≤ 0.8.

[0084] In one embodiment, the lithium-ion battery further includes an electrolyte comprising a lithium salt solute and an electrolyte solvent.

[0085] In one embodiment, the solute lithium salt comprises at least one selected from lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorooxalate borate (LiDFOB), and lithium tetrafluoroborate (LiBF4). The molar concentration of the solute lithium salt in the electrolyte is 0.5–2 mol / L.

[0086] In one embodiment, the electrolyte solvent includes at least one of butenyl carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and methyl propyl carbonate (MPC).

[0087] To ensure the reversibility of lithium ion insertion / extraction on the negative electrode and improve the first charge / discharge efficiency of the electrode, an appropriate amount of propylene carbonate (PC) and / or ethylene carbonate (EC) may be added to the electrolyte.

[0088] One embodiment of the present invention provides an electrical device including the above-mentioned lithium-ion battery.

[0089] The electrical devices of this invention can be vehicles, portable devices, laptops, ships, spacecraft, electric toys, and power tools, etc. Vehicles can be gasoline-powered cars, natural gas-powered cars, or new energy vehicles; new energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, 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.

[0090] The present invention is further illustrated below with specific embodiments:

[0091] Example 1

[0092] This embodiment provides a negative electrode additive, the preparation method of which is as follows:

[0093] S1. Using α-glucan oligosaccharides as raw materials, an intermediate product containing R1, R2, and R3 groups is obtained through a substitution reaction; wherein R1 is -OH, R2 is -OH, and R3 is -NH2.

[0094] S2. The intermediate product was subjected to aldol condensation in a 10% NaOH solution and reacted at 25°C for 12 hours to obtain a negative electrode additive with the structure shown in formula (2), where n is 1000.

[0095]

[0096] Infrared spectroscopy analysis revealed the following infrared spectrum of the negative electrode additive prepared in this embodiment: Figure 2 As shown, it can be seen that a compound with the structure shown in formula (2) was successfully prepared.

[0097] Example 2

[0098] This embodiment provides a negative electrode additive, the preparation method of which is as follows:

[0099] S1. Using α-glucan oligosaccharides as raw materials, through Friedel-Crafts alkylation, oxidation, and sulfonation reactions, an intermediate product containing R1, R2, and R3 groups is obtained; wherein R1 is -CH2COOH, R2 is -OH, and R3 is -SO3H;

[0100] S2. The intermediate product was subjected to aldol condensation in a 10% NaOH solution and reacted at 25°C for 12 hours to obtain a negative electrode additive with the structure shown in formula (3), where n is 1000.

[0101]

[0102] Infrared spectroscopy analysis revealed the following infrared spectrum of the negative electrode additive prepared in this embodiment: Figure 3 As shown, it can be seen that a compound with the structure shown in formula (3) was successfully prepared.

[0103] Example 3

[0104] This embodiment provides a negative electrode additive, the preparation method of which is as follows:

[0105] S1. Using α-glucan oligosaccharides as raw materials, an intermediate product containing R1, R2, and R3 groups is obtained through oxidation and substitution reactions; wherein R1 is -OH, R2 is -CHO, and R3 is -NHCH3;

[0106] S2. The intermediate product was subjected to aldol condensation in a 10% NaOH solution and reacted at 25°C for 12 hours to obtain a negative electrode additive with the structure shown in formula (4), where n is 1000.

[0107]

[0108] Infrared spectroscopy analysis revealed the following infrared spectrum of the negative electrode additive prepared in this embodiment: Figure 4 As shown, it can be seen that a compound with the structure shown in formula (4) was successfully prepared.

[0109] Example 4

[0110] This embodiment provides a negative electrode additive, the preparation method of which is as follows:

[0111] S1. Using α-glucan oligosaccharides as raw materials, through Friedel-Crafts alkylation, oxidation, sulfonation, and neutralization reactions, an intermediate product containing R1, R2, and R3 groups is obtained; wherein R1 is -CHO, R2 is -COONa, and R3 is -SO3Na.

[0112] S2. The intermediate product was subjected to aldol condensation in a 10% NaOH solution and reacted at 25°C for 12 hours to obtain a negative electrode additive with the structure shown in formula (1), wherein R1 is -CHO, R2 is -COONa, R3 is -SO3Na, and n is 1000.

[0113] Example 5

[0114] This embodiment provides a negative electrode additive, the preparation method of which differs from that of Example 1 in that:

[0115] In step S2, the reaction time of the aldol condensation reaction is adjusted to 2 hours. The R1, R2, and R3 in the obtained negative electrode additive are the same as those in Example 1, and the n value is 10.

[0116] Example 6

[0117] This embodiment provides a negative electrode additive, the preparation method of which differs from that of Example 1 in that:

[0118] In step S2, the reaction time of the aldol condensation reaction is adjusted to 6 hours. The R1, R2, and R3 in the obtained negative electrode additive are the same as those in Example 1, and the n value is 100.

[0119] Example 7

[0120] This embodiment provides a negative electrode additive, the preparation method of which differs from that of Example 1 in that:

[0121] In step S2, the reaction time of the aldol condensation reaction is adjusted to 18h. The R1, R2, and R3 in the obtained negative electrode additive are the same as those in Example 1, and the n value is 5000.

[0122] Example 8

[0123] This embodiment provides a negative electrode additive, the preparation method of which differs from that of Example 1 in that:

[0124] In step S2, the reaction time of the aldol condensation reaction is adjusted to 24h. The R1, R2, and R3 in the obtained negative electrode additive are the same as those in Example 1, and the n value is 10000.

[0125] Application Example 1

[0126] This application example provides a lithium-ion battery, the preparation method of which is as follows:

[0127] (1) Preparation of negative electrode sheet:

[0128] The negative electrode active material graphite, the conductive agent carbon nanotubes (CNTs), the thickener CMC, and the negative electrode additive prepared in Example 1 were mixed in a mass ratio of 96.5:0.8:1.2:1.5. Deionized water was added to adjust the solid content to 45%–55%, and the mixture was stirred to obtain a uniform negative electrode slurry. The negative electrode slurry was then uniformly coated onto the upper and lower surfaces of the negative electrode current collector copper foil, with a coating weight of 128 mg / unit area. After air-drying at room temperature, the slurry was transferred to a 120°C oven for further drying for 1 hour, finally achieving a compacted density of 1.7 g / cm³. 3 The negative electrode sheet is obtained after cold pressing and slitting under the conditions of cold pressing speed of 20m / min, pressure of 50T, and cold pressing thickness of 110μm.

[0129] (2) Preparation of the positive electrode sheet:

[0130] The positive electrode active material LMFP, conductive agent carbon black, and binder PVDF were mixed in a mass ratio of 96.5:2.3:1.2. N-methylpyrrolidone (NMP) solvent was added to adjust the solid content to 58%–68%, and the mixture was stirred under vacuum until homogeneous to obtain the positive electrode slurry. The chemical formula of the positive electrode active material LMFP is LiMn. 0.6 Fe 0.4 PO4, i.e., a manganese-iron ratio of 6:4, was then uniformly coated onto the upper and lower surfaces of the positive electrode current collector aluminum foil. After air-drying at room temperature, it was transferred to a 120℃ oven for further drying for 1 hour, and finally, the compaction density was 2.3 g / cm³. 3 The positive electrode sheet is obtained by cold pressing and slitting under certain conditions.

[0131] (3) Preparation of electrolyte:

[0132] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent; then, thoroughly dried lithium salt LiPF6 was dissolved in the organic solvent and mixed evenly to obtain an electrolyte, wherein the molar concentration of LiPF6 was 1 mol / L.

[0133] (4) Separating membrane:

[0134] Polyethylene film was chosen as the separator.

[0135] (5) Preparation of lithium batteries:

[0136] The above-mentioned positive electrode sheet, negative electrode sheet and membrane separator are stacked in sequence and wound to obtain a bare cell; the bare cell is then placed in a packaging bag, dried and electrolyte is added, and lithium-ion batteries are obtained through vacuum sealing, standing, formation and capacity testing.

[0137] Application Examples 2-20

[0138] Application Examples 2-20 provide a lithium-ion battery. Except for the differences shown in Table 1, the preparation method steps of the lithium-ion battery in Application Examples 2-20 are the same as those in Application Example 1.

[0139] Table 1

[0140]

[0141] Performance testing

[0142] The electrochemical performance of the lithium-ion batteries prepared in the above application examples was tested, and the specific methods and results are as follows:

[0143] (1) First Coulomb efficiency test

[0144] An uncharged lithium-ion battery is charged at a constant current rate of 0.1C to a voltage of 4.25V under a constant temperature environment of 25℃. It is then charged at a constant voltage of 4.25V until the current is less than or equal to 0.05C. After resting for 5 minutes, the initial charge capacity is recorded as CapC. Next, it is discharged at a constant current rate of 0.1C to a voltage of 2.8V. The initial discharge capacity is recorded as CapD. The initial coulombic efficiency is equal to the initial discharge capacity divided by the initial charge capacity, i.e., η = CapD / CapC × 100%.

[0145] (2) High-temperature storage test

[0146] The lithium-ion battery was charged at a constant current rate of 0.1C to a voltage of 4.25V under a constant temperature environment of 25℃, and then charged at a constant voltage rate of 4.25V until the current was less than or equal to 0.05C. After that, it was left to stand for 5 minutes. At this point, the battery was in a fully charged state, and the thickness of the battery at this time was measured, which is the initial thickness of the battery, denoted as T0. Then, it was discharged at a constant current rate of 0.1C to a voltage of 2.8V. The discharge capacity at this point is the initial discharge capacity, denoted as C0.

[0147] After completing the above steps, the battery is charged at a constant current rate of 0.1C to a voltage of 4.25V in a constant temperature environment of 25℃. Then, it is charged at a constant voltage of 4.25V until the current is less than or equal to 0.05C, and then left to stand for 5 minutes. At this point, the battery is fully charged. The fully charged battery is then placed in a high-temperature oven at 60℃ for high-temperature storage testing for 72 hours. After storage, the battery is removed from the oven and left to stand at room temperature for 2 hours. After it has completely cooled down, the thickness is measured, which is the final thickness, denoted as T1. Then, it is discharged at a constant current rate of 0.1C to a voltage of 2.8V. The discharge capacity at this point is the final discharge capacity, denoted as C1.

[0148] Among them, the battery capacity retention rate is the completed discharge capacity divided by the initial discharge capacity, i.e., η = C1 / C0 × 100%. The battery thickness expansion rate is the difference between the completed thickness and the initial thickness, divided by the initial thickness, i.e., thickness expansion rate (Swelling) = (T1 - T0) / T0 × 100%.

[0149] (3) High-temperature cycling performance test

[0150] The lithium-ion battery underwent high-temperature cycle performance testing at a constant temperature of 45℃. The charge / discharge conditions were as follows: constant current charging at a 1C rate to a voltage of 4.25V, then constant voltage charging at 4.25V until the current is less than or equal to 0.05C, followed by a 10-minute rest period. Then, constant current discharging at a 1C rate to a constant voltage of 2.8V, followed by another 10-minute rest period, constituted one charge / discharge cycle. The capacity of the first discharge was recorded as the initial discharge capacity, denoted as C0. This charge / discharge cycle was repeated thereafter, with the discharge capacity recorded for each cycle, denoted as Cn, and the capacity retention rate at that cycle number n was calculated. The battery's capacity retention rate is the discharge capacity per cycle divided by the initial discharge capacity, i.e., η = Cn / C0 × 100%. When the discharge capacity retention rate drops to 80%, the number of cycles at this point is the cycle life.

[0151] The test results for the application examples are shown in Table 2.

[0152] (4) Manganese dissolution test of negative electrode sheet

[0153] ICP testing was performed on samples of the negative electrode to detect the manganese content in the negative electrode. The lower the detected amount, the better the control over manganese leaching.

[0154] ICP testing method for anode materials: Reference standards: EPA6010D-2018 Inductively Coupled Plasma Atomic Emission Spectrometry and GB / T 24533-2019 Graphite-based anode materials for carp-ion batteries. Sample weight: 0.5g; Digestion reagent: 10mL nitric acid; Digestion method: Microwave digestion (microwave digestion settings: 10min to 400W, hold for 3min, continue for 10min to 700W, hold for 30min, then cool to 70℃); Diluent: Pure water; Volume adjustment: 50mL; Quantitative method: Calibration curve method; Test procedure: Digest the sample using the digestion reagent and microwave digestion method; after digestion, transfer 1mL of solution and dilute with pure water to 50mL; perform calibration curve method test on the diluted solution, see reference standards for details.

[0155] Table 2

[0156]

[0157]

[0158] Based on the test results in Table 2, it can be seen that:

[0159] The initial coulombic efficiency test results show that the initial coulombic efficiency of the lithium-ion battery is significantly improved when the negative electrode additive prepared according to the embodiments of the present invention is added to the negative electrode sheet. The test results of Application Examples 1, 12-15, 19, and 20 show that the additive described in this invention has an improving effect when used with LMFP positive electrode materials of different manganese-iron ratios. The structural formula is LiMn. 0.6 Fe 0.4 The LMFP cathode material of PO4 exhibited the highest initial coulombic efficiency.

[0160] The high-temperature storage test results show that the storage performance of lithium-ion batteries is significantly improved when the negative electrode additive prepared according to the embodiments of the present invention is added to the negative electrode sheet. The improvement in thickness expansion rate indicates that the addition of the negative electrode additive effectively suppresses high-temperature gas generation in the battery. The test results of Application Examples 1, 12-15, 19, and 20 show that the additive described in this invention has an improving effect when used with LMFP positive electrode materials of different manganese-iron ratios. When the manganese-iron ratio is in the range of 4:6 to 6:4, the battery storage performance is not significantly different. As the manganese-iron ratio further increases, the battery storage performance gradually deteriorates, but it is still better than Application Example 19 without the negative electrode additive.

[0161] The high-temperature cycle performance test results show that when the negative electrode additive prepared according to the embodiments of the present invention is added to the negative electrode sheet, the cycle life of the battery is significantly improved. From the test results of Application Examples 1, 12-15, 19, and 20, it can be seen that the additive described in this invention has an improving effect when used with LMFP positive electrode materials of different manganese-iron ratios. When the manganese-iron ratio is in the range of 4:6 to 6:4, the high-temperature cycle performance of the battery is not significantly different. When the manganese-iron ratio is further increased, the battery cycle performance gradually deteriorates, but it is still better than Application Example 19 without the negative electrode additive.

[0162] According to the manganese leaching test results of the negative electrode sheet, when the negative electrode additive prepared in the embodiments of the present invention is added to the negative electrode sheet, the manganese content in the negative electrode sheet is significantly reduced. In application examples 1 to 18, the manganese content in the negative electrode sheet is ≤331ppm, and in some application examples, the manganese content in the negative electrode sheet is ≤299ppm.

[0163] Based on the test results of Application Examples 1 to 8, and in conjunction with Examples 1 to 8, it can be seen that when the negative electrode additive contains hydroxyl (-OH), carboxyl (-COOH), sulfonic acid (-SO3H), and amino (-NH2) as polar functional groups, the resulting lithium-ion battery exhibits better electrochemical performance.

[0164] Based on the test results of Application Examples 1, 9-11, and 17-18, it can be seen that when the mass ratio of negative electrode active material, conductive agent, thickener, and negative electrode additive in the negative electrode active material layer meets the range of (95-97):(0.8-1):(0.8-1.2):(1.5-1.8), the electrochemical performance of the lithium-ion battery is relatively better.

[0165] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A lithium-ion battery, comprising a positive electrode and a negative electrode, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector; The manganese content in the negative electrode sheet is ≤331ppm; In the infrared spectrum of the negative electrode active material layer, the range is 1000~1050 cm⁻¹. -1 It has an absorption peak within the range, and has an absorption peak in at least one of the following ranges: 530~620 cm⁻¹ -1 1068~1190 cm -1 650~900cm -1 1590~1650 cm -1 3400~3500 cm -1 1720~1770cm -1 2995~3030 cm -1 3072~3100 cm -1 3150~3300 cm -1 ; The negative electrode active material layer includes a negative electrode active substance and a negative electrode additive, wherein the negative electrode additive has the structure shown in formula (1): ； Equation (1) Wherein, n is an integer from 10 to 10000, and at least one of the groups R1, R2, and R3 is selected from a first polar functional group, which includes one or more of -OH, -COOH, -CH2COOH, -SO3H, and -NH2.

2. The lithium-ion battery according to claim 1, characterized in that, The manganese content in the negative electrode sheet is ≤299ppm.

3. The lithium-ion battery according to claim 2, characterized in that, The manganese content in the negative electrode sheet is 157~234 ppm.

4. The lithium-ion battery according to claim 3, characterized in that, The groups in R1, R2, and R3 that are not first polar functional groups are each independently selected from second polar functional groups, including -CHO, -NHR, and -[-O-]-. m At least one of -COOX and -SO3X, wherein X in -COOX and -SO3X is independently selected from an alkali metal element; R in -NHR is selected from a C1-C6 alkyl group; and -[-O-]- m In this case, m is a positive integer between 2 and 20.

5. The lithium-ion battery according to claim 3, characterized in that, The negative electrode additive has a structure as shown in formula (2), formula (3) or formula (4): 、 、 。 Equation (2) Equation (3) Equation (4) 6. The lithium-ion battery according to claim 3, characterized in that, In the negative electrode additive, n is an integer between 100 and 1000.

7. The lithium-ion battery according to claim 3, characterized in that, The negative electrode active material layer also includes a conductive agent and a thickener; the mass ratio of the negative electrode active substance, conductive agent, thickener and negative electrode additive in the negative electrode active material layer is (93~98):(0.5~2):(0.5~5):(1~2).

8. The lithium-ion battery according to claim 1, characterized in that, The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes lithium iron manganese oxide.

9. The lithium-ion battery according to claim 8, characterized in that, The lithium iron manganese oxide includes compounds with the molecular formula Li. a Mn x Fe 1-x Me 1-a Compounds of PO4, wherein Me includes at least one of In, La, Zr, Ce, W, Al, Ti, Sr, Mg, Sb, V, Zn, Cu, and Cr, with 0.95 ≤ a ≤ 1 and 0.4 ≤ x ≤ 0.

8.

10. An electrical device, characterized in that, Includes the lithium-ion battery according to any one of claims 1 to 9.

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