A lithium-ion battery

Abstract

This invention discloses a lithium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode active material layer, which comprises a positive electrode active material and a lithium-replenishing material, the lithium-replenishing material comprising a lithium-rich oxide. The negative electrode includes a negative electrode active material layer. The ratio of the molar amount of Li in the positive and negative electrode active material layers to the molar amount of other metal elements in the positive electrode active material layer is R. The electrolyte comprises a non-aqueous solvent and an additive. The non-aqueous solvent includes dimethyl carbonate, and the mass percentage of dimethyl carbonate in the electrolyte is E%. The additive includes the additive shown in structural formula I, and the mass percentage of the additive shown in structural formula I in the electrolyte is A%. In the lithium-ion battery, E, A, and R satisfy: 0.03 ≤ E*A / R ≤ 35. The lithium-ion battery with lithium-rich oxide lithium replenishment of this invention exhibits good initial impedance characteristics, low high-temperature gas generation rate, and low impedance growth characteristics.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and more specifically, to a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are widely used due to their advantages such as high energy density, high operating voltage, long cycle life, low self-discharge rate, no memory effect, and environmental friendliness. Commercial lithium-ion batteries primarily use liquid electrolytes. During the first charge, the liquid electrolyte, along with lithium salts, undergoes electrochemical reduction at the graphite anode, potentially generating products such as Li₂CO₃, LiF, and alkyl lithium carbonate, thus forming a solid electrolyte membrane. This process consumes approximately 5%-15% of the active lithium ions in the cathode and electrolyte, which is detrimental to improving the battery's energy density. Therefore, lithium replenishment technology has emerged to compensate for the lithium ion loss during the first charge.

[0003] Current lithium replenishment technologies can be categorized into chemical lithium replenishment, physical hybrid lithium replenishment, and electrochemical lithium replenishment. Among these, chemical lithium replenishment is complex and environmentally unfriendly, and therefore rarely used. Physical hybrid lithium replenishment involves pre-mixing lithium powder in the positive electrode, separator, and negative electrode before assembling the battery, primarily using the negative electrode. However, lithium powder has poor stability with water and oxygen, requiring sophisticated processes and equipment, making commercialization difficult. Currently, electrochemical lithium replenishment has the greatest commercial potential, especially the addition of positive electrode lithium replenishment materials to the positive electrode.

[0004] Commonly used cathode lithium replenishment materials include binary lithium replenishment materials, ternary lithium-rich oxides, and organic lithium replenishment materials. Binary lithium replenishment materials, such as various binary lithides like Li₂O, Li₂S, and Li₃N, typically have high specific capacity for lithium replenishment. However, their poor water and oxygen stability can easily affect the cathode slurry process, causing the slurry to become jelly-like and unsuitable for coating. Furthermore, they are prone to gas generation in the battery, affecting battery performance. Organic lithium replenishment materials, such as organic lithium-containing compounds like Li₂C₂O₄ and Li₂DHBN, have low lithium release potentials and good environmental stability, but their irreversible capacity is low, limiting their lithium replenishment capability. Ternary lithium-rich oxides, such as Li₅FeO₄ and Li₆CoO₄, offer a more balanced performance. These compounds possess certain water and oxygen stability, can be directly adapted to existing processes, do not significantly affect the cathode slurry process, and have a high theoretical specific capacity for lithium replenishment, making them the most promising cathode lithium replenishment materials for large-scale commercialization.

[0005] However, lithium-rich oxide-based lithium replenishment materials also have significant drawbacks. For example, since the lithium replenishment mechanism of lithium-rich oxides mostly relies on oxygen anion redox for charge balance, oxygen is generated during the release of lithium ions. These reactive oxygen species released from the crystal lattice readily react with the electrolyte, leading to severe gas generation problems. Furthermore, lithium-rich oxides themselves and the lithium release products have extremely low conductivity; for example, Li5FeO4 has a conductivity of only 9-10 S / cm, almost equivalent to an insulator. Introducing such poor electronic conductors into the positive electrode affects electron transport in the positive electrode active material, increasing battery impedance and polarization. Therefore, there is a need for a lithium-ion battery that can eliminate the reactive oxygen species generated by lithium-rich oxide-based lithium replenishment agents and reduce polarization at the positive electrode, thus suppressing gas generation and impedance growth. Summary of the Invention

[0006] This invention is based on the inventor's discovery and understanding of the following facts and problems: lithium-ion batteries using lithium-rich oxides for lithium replenishment suffer from gas generation, impedance, and polarization growth during use.

[0007] Related technologies involve coating and modifying lithium-rich oxides, but this cannot solve the oxygen release and gas generation problems caused by the introduction of lithium-rich oxides, nor can it completely eliminate the effects of increased positive electrode impedance and polarization caused by the introduction of lithium-rich oxides. Related technologies address polarization at the positive electrode from the electrolyte end, for example, by using electrolytes containing ether compounds; however, this does not solve the oxygen release problem, and the introduction of ether compounds may even lead to increased gas generation, thus limiting its applicability.

[0008] The present invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of the present invention provide a lithium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte; the positive electrode comprises a positive electrode active material layer, the positive electrode active material layer comprising a positive electrode active material and a lithium-replenishing material, the lithium-replenishing material comprising a lithium-rich oxide; the negative electrode comprises a negative electrode active material layer;

[0009] The ratio of the molar amount of Li element in the positive electrode active material layer and the negative electrode active material layer to the molar amount of metal elements other than Li element in the positive electrode active material layer is R.

[0010] The electrolyte includes a non-aqueous solvent and additives; the non-aqueous solvent includes dimethyl carbonate, and the mass percentage of dimethyl carbonate in the electrolyte is E%.

[0011] The additive includes the additive shown in structural formula I:

[0012]

[0013] Where X is selected from B or P;

[0014] n is an integer from 0 to 3; R1 and R2 are each independently selected from C1-C6 substituted or unsubstituted hydrocarbon groups, alkyl groups, siloxane groups or halogen atoms, and R3 is selected from C1-C6 substituted or unsubstituted hydrocarbon groups, siloxane groups or OXR1(R2).

[0015] The mass percentage of the additive shown in structural formula I in the electrolyte is A%.

[0016] In the lithium-ion battery, E, A, and R satisfy: 0.03≤E*A / R≤35.

[0017] Optional, 0.1≤E*A / R≤15.

[0018] Optionally, R is 1.1-1.5; and / or, E% is 1%-35%; and / or, A% is 0.01%-2%.

[0019] Optionally, R is 1.2-1.4; and / or, E% is 5%-30%; and / or, A% is 0.05%-1%.

[0020] Optionally, the hydrocarbon group in the C1-C6 substituted or unsubstituted hydrocarbon group is selected from saturated hydrocarbon groups or unsaturated hydrocarbon groups, wherein the unsaturated hydrocarbon group includes alkenyl or aryl.

[0021] Optionally, the additive represented by structural formula I includes at least one of the following compounds:

[0022]

[0023] Optionally, the metal elements in the positive electrode active material layer, other than Li, include at least one of Fe, Ni, Co, Mn, Zn, Cr, Zr, Ti, Mo, and Sn.

[0024] Optionally, the lithium-rich oxide includes at least one of Li5FeO4, Li2NiO2, and Li6CoO4.

[0025] Optionally, the positive electrode active material includes at least one of lithium iron phosphate, lithium iron manganese phosphate, lithium nickel manganese oxide, ternary lithium nickel cobalt manganese oxide, or lithium cobalt oxide.

[0026] Optionally, the negative electrode active material layer includes a negative electrode active material, which includes at least one of graphite, hard carbon, and silicon.

[0027] Optionally, the non-aqueous solvent may further include at least one of the following: chain carbonates, cyclic carbonates, carboxylic acid esters, or ether compounds having more than 3 carbon atoms.

[0028] Optionally, the electrolyte further includes a lithium salt, which includes at least one of LiPF6 and LiFSI; the molar concentration of the lithium salt in the electrolyte is 0.8-1.5M.

[0029] According to the lithium-ion battery provided by the present invention, when the content of the additive shown in structural formula I in the electrolyte, the content of dimethyl carbonate, E% and the proportion of Li element in the electrode active material layer, R, satisfy the relationship 0.03≤E*A / R≤35, the lithium-ion battery with lithium-rich oxide supplementation in the present invention has good initial impedance characteristics, low high-temperature storage gas generation rate and impedance growth characteristics.

[0030] The ratio R of the molar amount of Li in the positive and negative electrode active material layers to the molar amount of other metal elements in the positive electrode active material layer reflects the degree of lithium replenishment in a lithium-ion battery, i.e., the amount of lithium ions added to the replenishing material. Lithium-ion batteries using lithium-rich oxides for replenishment release active oxygen and generate intermediate oxides during use, leading to gas generation, impedance, and polarization increases. The additive shown in Structural Formula I, centered on B atoms and / or trivalent P atoms, can scavenge active oxygen and intermediate oxides, preventing active oxygen from attacking solvent molecules. Furthermore, the additive shown in Structural Formula I migrates more easily to the positive electrode under an electrostatic field, either by combining with lithium salt anions or by doing so. The low bond energy of the PO or BO bonds allows for easy breakage at the positive electrode, forming a relatively dense CEI film. This effectively isolates the positive electrode from the electrolyte, reducing gas generation and impedance increases caused by electrolyte decomposition. Dimethyl carbonate can optimize the solvation structure of lithium ions, improve the kinetic characteristics of lithium ions at the positive electrode, reduce polarization and initial internal resistance, and mitigate the impact of using lithium-rich oxide lithium supplementation materials and additives shown in Formula I on internal resistance.

[0031] In the lithium-ion battery of this invention, the higher the R value, the higher the required content (A%) of the additive shown in Structural Formula I. The additive shown in Structural Formula I causes severe initial impedance growth and requires the use of dimethyl carbonate solvent. When the R value is high but E% and / or A% are too low (i.e., E*A / R < 0.03), the lithium replenishment is excessive, exceeding the lithium-ion loading of the negative electrode, causing lithium plating and capacity decay. It also fails to effectively remove active oxygen in the electrolyte, resulting in minimal improvement in impedance and polarization. Conversely, when the R value is low but E% and / or A% are too high (i.e., E*A / R > 35), the lithium replenishment is too low, leading to minimal performance improvement. Excessive amounts of the additive shown in Structural Formula I cause severe initial impedance growth, and excessive dimethyl carbonate leads to severe gas generation. The lithium-ion battery of this invention, by adjusting E, A, and R to satisfy the relationship 0.03 ≤ E*A / R ≤ 35, enables lithium-ion batteries with lithium-rich oxide replenishment to possess good initial impedance characteristics, low high-temperature gas generation rate, and low impedance growth characteristics. Detailed Implementation

[0032] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0033] An embodiment of the present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte; the positive electrode comprises a positive electrode active material layer, the positive electrode active material layer comprising a positive electrode active material and a lithium supplementation material, the lithium supplementation material comprising a lithium-rich oxide; the negative electrode comprises a negative electrode active material layer;

[0034] The ratio of the molar amount of Li element in the positive electrode active material layer and the negative electrode active material layer to the molar amount of metal elements other than Li element in the positive electrode active material layer is R.

[0035] The electrolyte includes a non-aqueous solvent and additives; the non-aqueous solvent includes dimethyl carbonate, and the mass percentage of dimethyl carbonate in the electrolyte is E%.

[0036] The additive includes the additive shown in structural formula I:

[0037]

[0038] Where X is selected from B or P;

[0039] n is an integer from 0 to 3; R1 and R2 are each independently selected from C1-C6 substituted or unsubstituted hydrocarbon groups, substituted or unsubstituted alkyl groups, substituted or unsubstituted siloxane groups or halogen atoms, and R3 is selected from C1-C6 substituted or unsubstituted hydrocarbon groups, substituted or unsubstituted siloxane groups or OXR1(R2) (i.e. compounds that directly form symmetrical structures with O and the structure to the right of O in structural formula I);

[0040] Optionally, n can be 0, 1, 2, or 3; Optionally, the hydrocarbon group in the C1-C6 substituted or unsubstituted hydrocarbon group is selected from saturated hydrocarbon groups or unsaturated hydrocarbon groups, wherein the unsaturated hydrocarbon group includes alkenyl or aryl; Optionally, the hydrocarbon oxygen group includes alkoxy or olefin oxygen; Optionally, the substitution includes halogen substitution, wherein the halogen substitution is selected from F, Cl, Br, or I; Optionally, the siloxane is selected from trimethylsiloxy; Optionally, the silane is selected from trimethylsilyl; Optionally, the halogen atom is selected from F, Cl, Br, or I.

[0041] The mass percentage of the additive shown in structural formula I in the electrolyte is A%.

[0042] In the lithium-ion battery, E, A, and R satisfy: 0.03≤E*A / R≤35.

[0043] In the lithium-ion battery of this invention, when the content of the additive shown in structural formula I in the electrolyte, the content of dimethyl carbonate, E% and the proportion of Li element in the electrode active material layer, R, satisfy the relationship 0.03≤E*A / R≤35, the lithium-ion battery with lithium-rich oxide supplementation in this invention has good initial impedance characteristics, low high-temperature storage gas generation rate and impedance growth characteristics.

[0044] The ratio R of the molar amount of Li in the positive and negative electrode active material layers to the molar amount of other metal elements in the positive electrode active material layer reflects the degree of lithium replenishment in a lithium-ion battery, i.e., the amount of lithium ions added to the replenishing material. During charging, a large number of lithium ions are released from the crystal lattice in lithium-rich oxide replenishing materials. To achieve charge balance, lattice oxygen begins to escape from the crystal and enter the electrolyte. Most of this active oxygen combines to form elemental oxygen, while a small portion attacks solvent molecules, generating intermediate oxides. These intermediate oxides migrate to the negative electrode under the influence of an electric field and are reduced, producing a large amount of gas. This causes a large amount of gas to be generated even during the initial storage of the battery, posing a serious safety hazard. Therefore, for lithium-rich oxide replenishing materials, it is necessary to combine or remove the active oxygen deposited in the crystal lattice or the intermediate oxides in the solvent, and to strengthen the isolation protection of the positive electrode and reduce the contact between the positive electrode and the electrolyte to effectively suppress the serious gas generation problem caused by lithium-rich oxide replenishing materials.

[0045] The additive shown in Structural Formula I is centered around a B atom and / or a trivalent P atom. Since the B atom has four valence electron orbitals but only three valence electrons, even when bonded to other atoms, its valence electron orbitals are not fully filled, resulting in an overall electron-withdrawing tendency. Such electron-withdrawing compounds can more easily capture reactive oxygen species in the electrolyte than the solvent, thus preventing reactive oxygen species from attacking solvent molecules. The trivalent P atom has two unpaired electrons, which can act as electron donors to combine with intermediate oxides in the solvent, indirectly removing reactive oxygen species deposited in the crystal lattice. Furthermore, the additive shown in Structural Formula I is more likely to migrate to the positive electrode under an electrostatic field, either by combining with lithium salt anions or by doing so. The low bond energy of the PO or BO bonds makes them easier to break at the positive electrode, forming a relatively dense CEI film. This effectively isolates the positive electrode from the electrolyte, reducing gas production and impedance growth caused by electrolyte decomposition.

[0046] After lithium-rich oxide lithium-replenishing materials release lithium ions, they leave behind inactive substances within the normal charge / discharge voltage range. These substances typically have very low electronic conductivity. Although lithium-rich oxide lithium-replenishing materials are usually coated with a carbon layer to reduce impedance, the near-insulating nature of the residue exposes significant polarization in the later stages of battery use. Furthermore, the use of the additive shown in Formula I introduces a noticeable increase in initial impedance. To improve the battery's impedance characteristics, the electrolyte composition needs to be designed accordingly. Dimethyl carbonate, with its low viscosity and low melting point, can optimize the solvation structure of lithium ions and improve their kinetics at the positive electrode, thereby reducing polarization and initial internal resistance, mitigating the impact of using lithium-rich oxide lithium-replenishing materials and the additive shown in Formula I on internal resistance.

[0047] In the lithium-ion battery of this invention, a higher R value requires a higher content of additive A% as shown in Structural Formula I, which leads to severe initial impedance growth and necessitates the use of dimethyl carbonate solvent. When the R value is high but E% and / or A% is too low (i.e., E*A / R < 0.03), the lithium replenishment is excessive, exceeding the lithium-ion loading of the negative electrode, causing lithium plating and capacity decay, and failing to effectively remove active oxygen in the electrolyte, resulting in insignificant improvement in impedance and polarization. When the R value is low but E% and / or A% is too high (i.e., E*A / R > 35), the lithium replenishment is too low, resulting in insignificant performance improvement. Excessive additives as shown in Structural Formula I lead to severe initial impedance growth, and excessive dimethyl carbonate leads to severe gas generation. The lithium-ion battery of this invention, by adjusting E, A, and R to satisfy the relationship 0.03 ≤ E*A / R ≤ 35, enables lithium-ion batteries with lithium-rich oxide replenishment to possess good initial impedance characteristics, low high-temperature storage gas generation rate, and impedance growth characteristics.

[0048] In specific embodiments, E*A / R can be 0.03, 0.05, 0.08, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 15, 18, 20, 25, 30, 35.

[0049] In a preferred embodiment, 0.1 ≤ E*A / R ≤ 15.

[0050] In this embodiment of the invention, by preferably having 0.1≤E*A / R≤15, it is beneficial to further reduce gas production and impedance.

[0051] In some embodiments, the ratio of the molar amount of Li element in the positive electrode active material layer and the negative electrode active material layer to the molar amount of metal elements other than Li element in the positive electrode active material layer is R; R is 1.1-1.5.

[0052] In specific embodiments, R can be 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, or 1.5.

[0053] In a preferred embodiment, R is 1.2-1.4.

[0054] In this embodiment of the invention, R is 1.1-1.5, which can effectively compensate for the consumption of lithium ions during the first charge. If R is too small, the performance improvement is not significant; if R is too large, it may exceed the lithium ion loading capacity of the negative electrode, causing lithium plating and capacity decay.

[0055] In some embodiments, the ratio of the molar amount of Li element in the positive electrode active material layer and the negative electrode active material layer to the molar amount of metal elements other than Li element in the positive electrode active material layer is R.

[0056] The metal elements in the positive electrode active material layer other than Li are all the metal elements in the positive electrode active material layer other than Li; the metal elements other than Li can also be referred to as the main metal elements other than Li.

[0057] Optionally, the metal elements other than Li in the positive electrode active material layer may include at least one of Fe, Ni, Co, Mn, Zn, Cr, Zr, Ti, Mo, and Sn;

[0058] Optionally, the positive electrode active material layer or the negative electrode active material layer is the positive electrode active material layer or the negative electrode active material layer after formation;

[0059] Optionally, R can be obtained by inductively coupled plasma optical emission spectrometry (ICP-OES). Specifically, for example, after removing the leads and tabs, the positive and negative electrode sheets are placed in a digestion solution for digestion. After complete digestion, the mass fraction of Li and other metal elements in the positive and negative electrode active material layers is tested using ICP-OES, and the R value is calculated. Optionally, the digestion solution is aqua regia:pure water = 2:1 mass ratio; the mass ratio of electrode sheet to digestion solution is 1:30-1:50; the metal elements tested using ICP-OES do not include copper and aluminum, i.e., copper and aluminum in aluminum foil and copper foil are not tested. Specifically, R value = (mass fraction of Li / 6.94) / (mass fraction of metal element 1 / relative atomic mass of metal element 1 + mass fraction of metal element 2 / relative atomic mass of metal element 2 + ... + mass fraction of metal element n / relative atomic mass of metal element n).

[0060] In some embodiments, the mass percentage of dimethyl carbonate in the electrolyte is E%; E% is 1%-35%.

[0061] In specific embodiments, E% can be 1%, 3%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 25%, 30%, 32%, or 35%.

[0062] In a preferred embodiment, E% is 5%-30%.

[0063] In this embodiment of the invention, E% is 1%-35%, which can optimize the solvation structure of lithium ions and improve the kinetic characteristics of lithium ions at the positive electrode, thereby reducing polarization and initial internal resistance, and mitigating the impact of using lithium replenishment materials and additives shown in Structural Formula I on internal resistance. When E% is too low, the improvement effect is not significant; when E% is excessive, it will lead to severe gas generation.

[0064] In some embodiments, the additive represented by structural formula I is A% by mass in the electrolyte; A% is 0.01%-2%.

[0065] In specific embodiments, A% is 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.08%, 0.1%, 0.5%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, and 2%.

[0066] In a preferred embodiment, A% is 0.05%-1%.

[0067] In this embodiment of the invention, A% is 0.01%-2%, which can remove active oxygen and intermediate oxides, forming a relatively dense CEI film and reducing gas production and impedance growth caused by electrolyte decomposition. If A% is too low, it cannot effectively remove active oxygen in the electrolyte, and if A% is too high, it will cause serious initial impedance growth.

[0068] In some embodiments, the additive represented by structural formula I includes at least one of the following compounds:

[0069]

[0070] In this embodiment of the invention, the additives represented by structural formula I of compounds 1-10 are beneficial for further reducing gas production and impedance growth. In particular, compounds 5 and 9 have better synergistic effects with lithium-rich oxides and dimethyl carbonate, resulting in superior performance. The compounds substituted with halogen atoms, due to the strong electronegativity of halogens, attract electrons, which strengthens the electron-deficient tendency of B-containing compounds, enhancing their binding ability with reactive oxygen species in the electrolyte. It also exposes the lone electrons of trivalent P more, enhancing their binding ability with intermediate oxides, thereby achieving a better effect in suppressing gas production.

[0071] In some embodiments, the lithium supplement material comprises a lithium-rich oxide, wherein the lithium-rich oxide comprises Lix M m y O z , wherein, M is selected from at least one of Cu, Co, Ni, Mn, Mo, Ru, Al, Fe, Si, m is the valence state of M, 1 < x ≤ 6, 0 < y ≤ 2, 2 ≤ z ≤ 4, x + my - 2z = 0, and x / y ≥ 2. Optionally, the surface of the lithium-rich oxide is coated with a carbon layer.

[0072] In a specific embodiment, x can be 2, 3, 4, 5, 6; y can be 1, 2; z can be 2, 3, 4.

[0073] In a preferred embodiment, the lithium-rich oxide includes at least one of Li5FeO4, Li2NiO2, Li6CoO4.

[0074] In an embodiment of the present invention, when the lithium-ion battery with lithium supplementation by the lithium-rich oxide satisfies the relationship 0.03 ≤ E*A / R ≤ 35, it has good initial impedance characteristics, low gas generation rate during high-temperature storage, and impedance growth characteristics.

[0075] In some embodiments, the positive electrode active material includes at least one of lithium iron phosphate, lithium iron manganese phosphate, lithium nickel manganate, ternary nickel cobalt manganese oxide, or lithium cobalt oxide; optionally, the ternary nickel cobalt manganese oxide includes LiNi 0.8 Co 0.1 Mn 0.1 O2; optionally, the mass percentage of the positive electrode active material in the positive electrode active material layer is 85% - 97%, specifically, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 95%, 97%.

[0076] In some embodiments, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes at least one of graphite, hard carbon, and silicon material; optionally, the mass percentage of the negative electrode active material in the negative electrode active material layer is 85% - 97%, specifically, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 95%, 97%.

[0077] In some embodiments, the non-aqueous solvent further includes at least one of a chain carbonate having more than 3 carbon atoms (i.e., a chain carbonate other than dimethyl carbonate), a cyclic carbonate, a carboxylic acid ester, or an ether compound;

[0078] Optionally, the chain carbonate with more than 3 carbon atoms includes at least one of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC); optionally, the cyclic carbonate includes at least one of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0079] Optionally, the carboxylic ester includes cyclic carboxylic esters and / or chain carboxylic esters; optionally, the cyclic carboxylic ester includes at least one of γ-butyrolactone, γ-valerolactone, and δ-valerolactone; the chain carboxylic ester includes at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.

[0080] Optionally, the ether compound includes cyclic ethers and / or chain ethers; optionally, the cyclic ether is a cyclic ether with 3 to 6 carbon atoms; the chain ether is a chain ether with 3 to 10 carbon atoms; the cyclic ether includes at least one of 1,3-dioxolane (DOL), 1,4-dioxolane (DX), crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF); the chain ether includes at least one of dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether.

[0081] In some embodiments, the non-aqueous solvent accounts for 70%-90% by mass in the electrolyte, specifically, for example, 70%, 75%, 80%, 85%, 90%.

[0082] In some embodiments, the electrolyte further includes a lithium salt, which includes at least one of LiPF6 and LiFSI; optionally, the molar concentration of the lithium salt in the electrolyte is 0.8-1.5M, specifically, for example, 0.8M, 0.9M, 1.0M, 1.1M, 1.2M, 1.3M, 1.4M, 1.5M, preferably 0.8-1.2M.

[0083] In some embodiments, the additive further includes other additives, including at least one of vinylene carbonate, vinyl sulfate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, and 1,3-propanesulfonic acid lactone; optionally, the other additives are present in the electrolyte at a mass percentage of 0.1%-10%, specifically, for example, 0.1%, 0.5%, 1%, 3%, 5%, 7%, 9%, 10%.

[0084] In some embodiments, the positive electrode active material layer further includes a conductive material and / or a binder; optionally, the conductive material includes at least one of conductive carbon black and carbon nanotubes; the conductive carbon black includes Super-P; optionally, the binder includes polyvinylidene fluoride; optionally, the conductive material in the positive electrode active material layer has a mass percentage of 0-10%, specifically, for example, 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%; the binder in the positive electrode active material layer has a mass percentage of 0-10%, specifically, for example, 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%.

[0085] In some embodiments, the positive electrode includes a positive electrode active material layer and an aluminum foil, wherein the positive electrode active material layer is disposed on the aluminum foil.

[0086] In some embodiments, the negative electrode active material layer further includes a conductive material and / or a binder; optionally, the conductive material includes conductive carbon black; the conductive carbon black includes Super-P; optionally, the binder includes at least one of styrene-butadiene rubber and carboxymethyl cellulose; optionally, the conductive material in the negative electrode active material layer has a mass percentage of 0-10%, specifically, for example, 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%; the binder in the negative electrode active material layer has a mass percentage of 0-10%, specifically, for example, 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%.

[0087] In some embodiments, the negative electrode includes a negative electrode active material layer and a copper foil, wherein the negative electrode active material layer is disposed on the copper foil.

[0088] In some embodiments, the lithium-ion battery further includes a separator. Optionally, the separator includes at least one of a polymer separator and a nonwoven fabric. Preferably, the separator includes at least one of a single-layer PP (polypropylene), a single-layer PE (polyethylene), a double-layer PP / PE, a double-layer PP / PP, or a triple-layer PP / PE / PP separator. Optionally, the thickness of the separator is 5-80 micrometers, specifically, for example, 5 micrometers, 10 micrometers, 20 micrometers, 50 micrometers, or 80 micrometers. Optionally, the separator is a separator with ceramic particles coated on the surface of a base film to form a ceramic particle layer. The ceramic particles include at least one of alumina, silicon oxide, titanium oxide, zirconium oxide, barium oxide, magnesium oxide, magnesium hydroxide, or boehmite. The single-layer thickness of the ceramic particle layer is 1-5 micrometers, specifically, for example, 1 micrometer, 2 micrometers, 3 micrometers, 4 micrometers, or 5 micrometers.

[0089] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0090] Example 1

[0091] A method for preparing a lithium-ion battery, comprising:

[0092] (1) The preparation of the positive electrode includes: dispersing positive electrode active material LiFePO4, lithium-rich oxide Li5FeO4, 2.5wt.% conductive carbon black, 1.7wt.% carbon nanotube conductive agent and 0.3wt.% binder polyvinylidene fluoride in N-methyl-2-pyrrolidone to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on both sides of aluminum foil, and after drying, rolling and vacuum drying, aluminum leads are welded on using an ultrasonic welding machine to obtain a positive electrode plate.

[0093] (2) The preparation of the negative electrode includes: mixing graphite, conductive carbon black, styrene-butadiene rubber and carboxymethyl cellulose in a mass ratio of 95.2:1:2.4:1.4, dispersing them in deionized water to obtain a negative electrode slurry, coating the negative electrode slurry on both sides of a copper foil, drying, rolling and vacuum drying, and welding nickel leads on it with an ultrasonic welding machine to obtain a negative electrode plate.

[0094] (3) The preparation of the electrolyte includes: mixing 25 wt.% ethylene carbonate, 4 wt.% propylene carbonate, 12.5 wt.% lithium hexafluorophosphate (1.0M), 3 wt.% vinylene carbonate, 0.5 wt.% ethylene sulfate, 25.3 wt.% dimethyl carbonate and 0.5 wt.% additive compound 5 shown in structural formula I, and then adding methyl ethyl carbonate to make up the mass ratio of 100 wt.% to obtain the electrolyte.

[0095] (4) The preparation of the diaphragm includes: a diaphragm with a base membrane of 18 micrometers made of polypropylene, polyethylene and polypropylene and ceramic particles coated on the base membrane.

[0096] (5) Battery assembly: Three layers of ceramic separator are placed between the positive and negative plates. Then, the sandwich structure composed of the positive plate, negative plate and separator is wound up. The wound body is flattened and placed in a prefabricated aluminum-plastic shell. Nickel tabs and aluminum tabs are welded to the positive and negative leads respectively. The shell is sealed and vacuumed to obtain the cell to be injected with electrolyte. The electrolyte prepared above is injected into the cell through the injection hole. The amount of electrolyte should be enough to fill the gaps in the cell.

[0097] Then, perform the first charging routine formation as follows: charge at a constant current of 0.05C for 2 hours, charge at a constant current of 0.2C to 4.25V, then discharge at a constant current of 0.2C to 2.5V, vent the gas, shape and seal, then charge at a constant current of 0.2C to 3.65V, let stand for 0.5 hours, and then discharge at a constant current of 0.2C to 3.0V.

[0098] In lithium-ion batteries, the ratio R of the molar amount of Li in the positive electrode active material layer and the negative electrode active material layer to the molar amount of metal elements other than Li in the positive electrode active material layer is 1.30.

[0099] Example 2-25

[0100] Examples 2-25 illustrate the lithium-ion battery disclosed in this invention, including most of the operating steps in Example 1, with the following differences:

[0101] The lithium supplementation materials used in Examples 2-25, as well as the R value, the types and mass percentages of additives shown in Structural Formula I, and the mass percentage of dimethyl carbonate are shown in Table 1.

[0102] Example 26

[0103] A method for preparing a lithium-ion battery, comprising:

[0104] (1) The preparation of the positive electrode includes: preparing the positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, lithium-rich oxide Li2NiO2, 1.5 wt.% conductive carbon black, 0.5 wt.% carbon nanotube conductive agent and 1.8 wt.% binder polyvinylidene fluoride are dispersed in N-methyl-2-pyrrolidone to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on both sides of an aluminum foil, and after drying, rolling and vacuum drying, aluminum leads are welded on using an ultrasonic welding machine to obtain a positive electrode plate.

[0105] (2) The preparation of the negative electrode includes: mixing graphite, conductive carbon black, styrene-butadiene rubber and carboxymethyl cellulose in a mass ratio of 95.2:1:2.4:1.4, dispersing them in deionized water to obtain a negative electrode slurry, coating the negative electrode slurry on both sides of a copper foil, drying, rolling and vacuum drying, and welding nickel leads on it with an ultrasonic welding machine to obtain a negative electrode plate.

[0106] (3) The preparation of the electrolyte includes: mixing 25 wt.% ethylene carbonate, 15 wt.% diethyl carbonate, 13 wt.% lithium hexafluorophosphate, 0.5 wt.% vinylene carbonate, 2 wt.% ethylene sulfate, 1 wt.% lithium difluorophosphate, 0.5 wt.% tris(trimethylsilyl) phosphate, 0.3 wt.% 1,3-propanesulfonic acid lactone, 25.3 wt.% dimethyl carbonate and 0.5 wt.% additive compound 5 shown in structural formula I, and then adding methyl ethyl carbonate to make up 100% by mass to obtain the electrolyte.

[0107] (4) The preparation of the diaphragm includes: a diaphragm with a base membrane of 18 micrometers made of polypropylene, polyethylene and polypropylene and ceramic particles coated on the base membrane.

[0108] (5) Battery assembly: Place three layers of ceramic separator between the positive and negative plates, then wind the sandwich structure composed of the positive plate, negative plate and separator, flatten the winding body and put it into a square aluminum-plastic shell, weld the lead wires of the positive and negative electrodes to nickel tabs and aluminum tabs respectively, seal the opening and evacuate to obtain the cell to be injected with electrolyte; inject the electrolyte prepared above into the cell through the injection hole, and the amount of electrolyte should be enough to fill the gaps in the cell.

[0109] Then, perform the initial charging process as follows: charge at a constant current of 0.05C for 3 hours, charge at a constant current of 0.1C for 2 hours, charge at a constant current of 0.2C to 4.25V, let it rest for 0.5 hours, then discharge at a constant current of 0.2C to 3.0V. After venting, shape and seal the container, then charge it again at a constant current of 0.2C to 4.25V, let it rest for 0.5 hours, and then discharge it at a constant current of 0.2C to 3.0V.

[0110] Example 27

[0111] Example 27 illustrates the lithium-ion battery disclosed in this invention, including most of the operating steps in Example 26, except that:

[0112] The lithium supplementation materials used in Example 27, as well as the R value, the types and mass percentages of additives shown in structural formula I, and the mass percentage of dimethyl carbonate are shown in Table 1.

[0113] Examples 28-36

[0114] Examples 28-36 illustrate the lithium-ion battery disclosed in this invention, including most of the operating steps in Example 1, with the following differences:

[0115] The lithium supplementation materials used in Examples 28-36, as well as the R value, the types and mass percentages of additives shown in Structural Formula I, and the mass percentage of dimethyl carbonate are shown in Table 1.

[0116] Comparative Examples 1, 3-8

[0117] Comparative Examples 1, 3-8 are used to illustrate the lithium-ion battery disclosed in this invention, including most of the operating steps in Example 1, with the following differences:

[0118] Table 1 shows the lithium supplementation materials used in Comparative Examples 1, 3-8, as well as the R value, the type and mass percentage of additives shown in structural formula I, and the mass percentage of dimethyl carbonate.

[0119] Comparative Example 2

[0120] Comparative Example 2 is used to illustrate the lithium-ion battery disclosed in this invention, including most of the operating steps in Example 26, except that:

[0121] The lithium supplementation materials used in Comparative Example 2, as well as the R value, the types and mass percentages of additives shown in Structural Formula I, and the mass percentage of dimethyl carbonate are shown in Table 1.

[0122] Performance testing:

[0123] (1) Initial DCIR

[0124] The battery was placed in a 25°C constant temperature test chamber and left to stand for 4 hours. Then, it was run at a constant temperature, charged at 0.5C to the upper limit voltage, with a cutoff current of 0.05C. After standing for 10 minutes, it was discharged at a constant current of 0.5C, with a cutoff capacity of 0.5C. After standing for 30 minutes, it was discharged at a constant current of 2C I for 10 seconds. The discharge start voltage U1 and discharge cutoff voltage U2 were recorded.

[0125] Initial DCIR = (U1-U2) / I*1000, in milliohms.

[0126] (2) Gas production rate during high-temperature storage

[0127] The battery was charged at 0.5C to the upper limit voltage and cutoff voltage at 0.05C. The initial volume V was then measured. 初始 Then, it is placed in a 60℃ constant temperature test chamber. After n days, the test volume V is taken out. n .

[0128] High-temperature storage gas production rate over n days = (V n -V 初始 ) / V 初始 *100%.

[0129] (3) DCIR growth rate under high temperature storage

[0130] Charge the battery at 0.5C to the upper limit voltage, with a cutoff current of 0.05C. Then, place it in a 60℃ constant temperature test chamber for n days. After n days, test the DCIR. Place the battery in a 25℃ constant temperature test chamber for 4 hours, then run it at a constant temperature. Discharge at 0.5C to the lower limit voltage, charge at 0.5C to the upper limit voltage, with a cutoff current of 0.05C. After 10 minutes, discharge at a constant current of 0.5C until the cutoff capacity is 0.5C. After 30 minutes, discharge at a constant current of 2C I for 10 seconds, recording the discharge start voltage U3 and discharge cutoff voltage U4. The DCIR on day n is calculated as (U3-U4) / I*1000, in milliohms.

[0131] The DCIR growth rate during the n-day high-temperature suspension period = (DCIR on day n - initial DCIR) / initial DCIR * 100%.

[0132] (4) R-value test (Li / Me molar ratio)

[0133] Testing method: Disassemble the battery in an inert atmosphere glove box, remove the positive and negative electrode sheets, remove the leads and tabs, clean the positive and negative electrode sheets three times with flowing DMC, and dry them under vacuum at -0.1 MPa for 48 hours. Slowly place the positive and negative electrode sheets into the digestion solution (aqua regia: pure water = 2:1 mass ratio), with the mass ratio of electrode sheet to digestion solution between 1:30 and 1:50. After complete digestion, use ICP-OES to test the mass fraction of Li and other metal elements in the positive and negative active material layers of the sample. It is not necessary to measure the copper and aluminum elements in the aluminum foil and copper foil.

[0134] R value = (mass fraction of Li / 6.94) / (mass fraction of metal element 1 / relative atomic mass of metal element 1 + mass fraction of metal element 2 / relative atomic mass of metal element 2 + ... + mass fraction of metal element n / relative atomic mass of metal element n).

[0135] Table 1

[0136]

[0137]

[0138] As can be seen from Table 1, in Examples 1-36, when the content of the additive shown in Structural Formula I in the electrolyte (A%), the content of dimethyl carbonate (E%), and the proportion of Li element in the electrode active material layer (R) satisfy the relationship 0.03≤E*A / R≤35, the lithium-ion battery with lithium-rich oxide supplementation has good initial impedance characteristics, low high-temperature storage gas generation rate, and impedance growth characteristics.

[0139] Comparing Examples 1-16 and Examples 28-36, Examples 1-16, when satisfying 0.03≤E*A / R≤35 and R being 1.1-1.5, E% being 1%-35%, and A% being 0.01%-2%, can further improve the initial impedance, high-temperature storage gas generation, and impedance growth of lithium-ion batteries. The initial DCIR of the lithium-ion batteries with lithium-rich oxide supplementation in Examples 1-16 is less than 61.5mΩ, the high-temperature storage gas generation rate is less than 17%, and the high-temperature storage DCIR growth rate is less than 40%.

[0140] In Example 29, R > 1.5, which may exceed the lithium-ion loading of the negative electrode, causing lithium plating and capacity decay. The gas generation rate during high-temperature storage is 34.6%, and the DCIR growth rate during high-temperature storage is as high as 56.8%.

[0141] In Example 30, the dimethyl carbonate content was less than 1%, and the DCIR growth rate after high-temperature storage was 48.7%.

[0142] In Example 31, the content of dimethyl carbonate was higher than 35%. A higher content of dimethyl carbonate would lead to serious gas production. The gas production rate during high-temperature storage was 45.8%, and the DCIR growth rate during high-temperature storage was 51.2%.

[0143] In Example 32, the content of the additive shown in Structural Formula I is higher than 2%. The higher content of the additive shown in Structural Formula I leads to an initial impedance increase, with an initial DCIR of 68.9 mΩ and a DCIR increase rate of 37.6% after high-temperature storage.

[0144] In Example 33, the content of the additive shown in Structural Formula I was less than 0.01%. The low content of the additive shown in Structural Formula I could not effectively remove active oxygen in the electrolyte, and the gas generation rate at high temperature was 32.1%.

[0145] As can be seen from the test results of Examples 1 and 17-24, for the different additives shown in Structural Formula I in this invention, when the relationship 0.03≤E*A / R≤35 is satisfied, the resulting lithium-ion batteries all have good initial impedance characteristics, low high-temperature storage gas generation rate and impedance growth characteristics.

[0146] As can be seen from the test results of Examples 1 and 25-27, for different lithium replenishment materials and positive electrode active materials in this invention, when the relationship 0.03≤E*A / R≤35 is satisfied, they play similar roles, and the resulting lithium-ion battery has good initial impedance characteristics, low high-temperature storage gas generation rate and impedance growth characteristics.

[0147] Comparing Examples 1-11 with Examples 12-16, Examples 1-11, under the condition of 0.03≤E*A / R≤35, further satisfy 0.1≤E*A / R≤15, which can further improve the initial impedance, high-temperature storage gas generation, and impedance growth of lithium-ion batteries. The initial DCIR of the lithium-ion batteries with lithium-rich oxide lithium replenishment in Examples 1-11 is less than 58mΩ, the high-temperature storage gas generation rate is less than 16%, and the high-temperature storage DCIR growth rate is less than 30%.

[0148] In Comparative Examples 1 and 2, no lithium replenishment material was added, so the lithium ion consumption during the first charge could not be replenished.

[0149] In Comparative Example 3, without the additive shown in Structural Formula I, the high-temperature gas production rate was 36.1%, and the high-temperature DCIR growth rate was 47.3%.

[0150] In Comparative Example 4, without the addition of dimethyl carbonate, the initial DCIR was 59.7 mΩ. Dimethyl carbonate can optimize the solvation structure of lithium ions, improve the kinetic characteristics of lithium ions at the positive electrode, reduce polarization and initial internal resistance, and mitigate the impact of using lithium-rich oxide lithium supplementation materials and additives shown in Structural Formula I on internal resistance.

[0151] In Comparative Example 5, E*A / R > 35, indicating a small degree of lithium replenishment and insignificant performance improvement. The additive shown in Structural Formula I leads to an initial increase in impedance.

[0152] In Comparative Examples 6 and 7, E*A / R < 0.03, indicating excessive lithium replenishment. The content of the additive shown in Structural Formula I is insufficient, which cannot effectively remove active oxygen in the electrolyte, resulting in severe gas generation.

[0153] In Comparative Example 8, E*A / R > 35, the initial DCIR was 76.5 mΩ, the high-temperature storage gas production rate was 15.3%, and the high-temperature storage DCIR growth rate was 34.5%.

[0154] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0155] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, and an electrolyte; the positive electrode includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material and a lithium supplementation material, the lithium supplementation material includes a lithium-rich oxide; the negative electrode includes a negative electrode active material layer; The ratio of the molar amount of Li element in the positive electrode active material layer and the negative electrode active material layer to the molar amount of metal elements other than Li element in the positive electrode active material layer is R. The electrolyte includes a non-aqueous solvent and additives; the non-aqueous solvent includes dimethyl carbonate, and the mass percentage of dimethyl carbonate in the electrolyte is E%. The additive includes the additive shown in structural formula I: Where X is selected from B or P; n is an integer from 0 to 3; R1 and R2 are each independently selected from C1-C6 substituted or unsubstituted hydrocarbon groups, alkyl groups, siloxane groups or halogen atoms, and R3 is selected from C1-C6 substituted or unsubstituted hydrocarbon groups, siloxane groups or OXR1(R2). The mass percentage of the additive shown in structural formula I in the electrolyte is A%. In the lithium-ion battery, E, A, and R satisfy: 0.03≤E*A / R≤35.

2. The lithium-ion battery according to claim 1, characterized in that, 0.1≤E*A / R≤15.

3. The lithium-ion battery according to claim 1 or 2, characterized in that, R is 1.1-1.5; and / or, E% is 1%-35%; and / or, A% is 0.01%-2%.

4. The lithium-ion battery according to claim 3, characterized in that, R is 1.2-1.4; and / or, E% is 5%-30%; and / or, A% is 0.05%-1%.

5. The lithium-ion battery according to claim 1, characterized in that, The hydrocarbon groups in the C1-C6 substituted or unsubstituted hydrocarbon groups are selected from saturated hydrocarbon groups or unsaturated hydrocarbon groups, and the unsaturated hydrocarbon groups include alkenyl or aryl groups.

6. The lithium-ion battery according to claim 1 or 5, characterized in that, The additive represented by structural formula I includes at least one of the following compounds:

7. The lithium-ion battery according to claim 1, characterized in that, The metal elements in the positive electrode active material layer, excluding Li, include at least one of Fe, Ni, Co, Mn, Zn, Cr, Zr, Ti, Mo, and Sn.

8. The lithium-ion battery according to claim 1, characterized in that, The lithium-rich oxide includes at least one of Li5FeO4, Li2NiO2, and Li6CoO4.

9. The lithium-ion battery according to claim 1, characterized in that, The positive electrode active material includes at least one of lithium iron phosphate, lithium iron manganese phosphate, lithium nickel manganese oxide, ternary lithium nickel cobalt manganese oxide, or lithium cobalt oxide.

10. The lithium-ion battery according to claim 1, characterized in that, The negative electrode active material layer includes a negative electrode active material, which includes at least one of graphite, hard carbon, and silicon. And / or, the non-aqueous solvent further includes at least one of the following: chain carbonates, cyclic carbonates, carboxylic acid esters or ether compounds having more than 3 carbon atoms; And / or, the electrolyte further includes a lithium salt, the lithium salt including at least one of LiPF6 and LiFSI; the molar concentration of the lithium salt in the electrolyte is 0.8-1.5M.

Images