A lithium-ion battery

Abstract

The present application relates to a kind of lithium ion batteries, including positive pole piece, negative pole piece and non-aqueous electrolyte;Negative pole piece includes the negative pole material layer containing negative pole active material;Non-aqueous electrolyte includes lithium salt, organic solvent and additive;Additive includes first additive and second additive;Lithium ion battery satisfies: 2≤[(A+B) / R]×Y≤48, 0.1≤A≤3, 0.5≤B≤5, 0.1≤R≤1, 0.8≤Y≤1.8.In the present application, through the synergistic effect of first additive and second additive, while retaining the improvement of nitrile on high temperature storage performance, the deterioration of negative electrode is inhibited.By controlling the order degree of negative pole active material, a uniform and stable SEI film is formed;At the same time, the ratio range of the mass of suitable electrolyte and the discharge capacity of the battery is limited, the battery cycle diving is delayed, the battery cycle performance is improved, the stability of the battery as a whole is further improved, and the high temperature cycle life of the battery is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a lithium-ion battery that can improve high-temperature cycle performance. Background Technology

[0002] Lithium-ion batteries are widely used in portable electronic products due to their advantages such as high operating voltage, high safety, long lifespan, and no memory effect. With the increasing frequency of daily use of electronic products, the requirements for battery cycle life are also becoming more stringent; while the demand for lightweight and portable electronic products necessitates high energy density in batteries, usually achieved by matching high voltage. However, high voltage often leads to a significant reduction in battery cycle life. This is because in the later stages of cycling, the SEI film is damaged and the electrolyte dries up, triggering widespread side reactions and causing rapid degradation of battery performance.

[0003] To improve the cycle life of batteries for electronic products while adapting to high voltages, some studies have added nitrile compounds as positive electrode protective additives to the electrolyte of lithium-ion batteries. Although this has improved the high-voltage stability of lithium-ion batteries to some extent and significantly improved their high-temperature storage performance, nitrile additives are incompatible with the negative electrode and can easily damage the negative electrode interface, leading to a decline in high-temperature cycle performance. Therefore, finding a way to improve high-voltage stability while also considering high-temperature storage performance and high-temperature cycle performance is a popular research direction in the field of power lithium-ion batteries. Summary of the Invention

[0004] To address the technical problem of decreased high-temperature cycle performance in batteries using non-aqueous electrolytes containing nitrile additives, this invention provides a lithium-ion battery that balances high-temperature storage performance and high-temperature cycle performance.

[0005] The present invention adopts the following technical solution:

[0006] A lithium-ion battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte;

[0007] The negative electrode sheet includes a negative electrode material layer containing a negative electrode active material, wherein the negative electrode active material includes graphite, and the degree of order of the negative electrode active material is R = I. D / I G In the spectrum measured by Raman spectroscopy analysis of the negative electrode using a laser with a wavelength of 532 nm to 785 nm, I D It appeared at 1300cm -1 Up to 1400cm -1 The peak intensity of the inner D peak, I G It appeared at 1530cm -1 Up to 1630cm -1 Peak intensity of the inner D peak;

[0008] The non-aqueous electrolyte includes lithium salts, organic solvents, and additives;

[0009] The additive includes a first additive and a second additive, wherein the first additive includes at least one of the following compounds:

[0010]

[0011] The second additive includes at least one of butadionitrile, adiponitrile, or 1,3,6-hexanetrionitrile;

[0012] The lithium-ion battery meets the following conditions:

[0013] 2≤[(A+B) / R]×Y≤48, 0.1≤A≤3, 0.5≤B≤5, 0.1≤R≤1, 0.8≤Y≤1.8;

[0014] Where A is the mass percentage of the first additive in the non-aqueous electrolyte, in %;

[0015] B represents the mass percentage of the second additive in the non-aqueous electrolyte, in %;

[0016] R represents the degree of order of the negative electrode active material;

[0017] Y is the ratio of the mass of the non-aqueous electrolyte to the battery's discharge capacity, expressed in g / Ah.

[0018] The lithium-ion battery of this invention uses a second additive containing nitrile compounds as a positive electrode protective additive, which can complex high-valence transition metal ions at the positive electrode and inhibit the dissolution of transition metal ions, thereby improving the stability of the positive electrode under high voltage and the battery's high-temperature storage performance. However, nitrile compounds have a degrading effect on the negative electrode. From the perspective of protecting the negative electrode, a first additive with a specific structure is used as a highly efficient negative electrode protective additive in the non-electrolyte. This additive can form a uniform and stable SEI film on the negative electrode surface, retaining the improving effect of nitrile compounds on high-temperature storage while inhibiting the degradation of the negative electrode by nitrile compounds.

[0019] However, the degradation of the negative electrode by the second additive is not only reflected in its impact on film formation. The cyano group of the second additive has strong electronegativity, which promotes the formation of a solvation structure with the solvent EC and lithium ions, affecting the film formation of the negative electrode. This results in poor SEI film quality, further reduction of the solvent at the negative electrode, and a decrease in the orderliness of the negative electrode active material, leading to a rapid decline in battery cycle performance. By limiting the orderliness of the negative electrode active material, the negative impact of the solvation structure formed by the second additive on the reduced orderliness of the negative electrode active material can be offset, thereby extending the battery cycle life.

[0020] The quality of the electrolyte affects the battery's cycle performance. Electrolyte is consumed during battery cycling, especially when the battery is operating at high voltage, which accelerates electrolyte depletion. In the later stages of cycling, the electrolyte level may become too low or even dry up. Therefore, the amount of electrolyte needed needs to match the battery's discharge capacity. Furthermore, the lower the ratio of electrolyte quality to discharge capacity, the more prone the negative electrode surface is to single-point electrolyte depletion, thus amplifying the degradation of the negative electrode by the secondary additive.

[0021] Through extensive research, the inventors discovered that when the mass percentage A of the first additive in the non-aqueous electrolyte, the mass percentage B of the second additive in the non-aqueous electrolyte, the degree of order R of the negative electrode active material, and the ratio Y of the mass of the non-aqueous electrolyte to the battery's discharge capacity satisfy the following relationships: 2≤[(A+B) / R]×Y≤48, 0.1≤A≤3, 0.5≤B≤5, 0.1≤R≤1, 0.8≤Y≤1.8, the non-aqueous electrolyte, positive electrode, and negative electrode of the lithium-ion battery achieve excellent coordination. This not only ensures the stability of the positive and negative electrodes but also significantly improves the battery's high-temperature cycle performance. The second additive, as a positive electrode protective additive, can complex high-valence transition metal ions in the positive electrode, inhibiting the dissolution of positive electrode metal ions, thereby improving the battery's high-temperature storage performance. The first additive, acting as a negative electrode protection additive, forms a uniform, stable, and high-quality SEI film on the negative electrode surface. While retaining the high-temperature storage improvement effect of the second additive, it slows down the process of the second additive forming a solvation structure with the solvent EC and lithium ions under the influence of its strongly electronegative cyano groups, reducing its impact on negative electrode film formation and thus inhibiting the deterioration effect of the second additive on the negative electrode. Simultaneously, the synergistic use of the first and second additives helps to regulate the orderliness R value of the negative electrode active material, improves the electrolyte retention per unit battery capacity, reduces defect sites on the negative electrode, controls the increase in impedance, and compensates for the deterioration loss of the orderliness of the negative electrode active material caused by the solvation structure formed by nitrile-EC-lithium ions. This improves the battery's cycle performance and extends the cycle life of the lithium-ion battery. It ensures that there is still an appropriate amount of electrolyte in the later stages of battery cycling, preventing single-point electrolyte depletion on the negative electrode surface, slowing down battery performance degradation, significantly improving the cycle performance of the lithium-ion battery, and extending its cycle life, ensuring that the battery maintains high-efficiency output throughout its entire life cycle.

[0022] When the relationship between the mass percentage A of the first additive in the lithium-ion battery, the mass percentage B of the second additive in the non-aqueous electrolyte, the degree of order of the negative electrode active material, and the ratio of the mass of the non-aqueous electrolyte to the discharge capacity of the battery [(A+B) / R]×Y<2, the content of positive and negative electrode protective additives in the non-aqueous electrolyte is too low, which cannot effectively inhibit the dissolution of positive electrode transition metal ions and the formation of a stable SEI film on the surface of the negative electrode, thus failing to achieve effective protection of the positive and negative electrodes; or when the battery capacity is constant, the degree of order of the negative electrode active material is too high, affecting the freedom of lithium ion insertion and extraction.

[0023] When the relationship between the mass percentage A of the first additive in the lithium-ion battery, the mass percentage B of the second additive in the non-aqueous electrolyte, the degree of order of the negative electrode active material, and the ratio of the mass of the non-aqueous electrolyte to the discharge capacity of the battery [(A+B) / R]×Y>2, excessive content of positive and negative electrode protective additives in the non-aqueous electrolyte leads to increased impedance of the electrolyte film on the negative electrode surface, hindering the insertion and extraction of lithium ions on the negative electrode surface. Furthermore, excessive solvation structures further damage the degree of order of the negative electrode active material. If the degree of order of the negative electrode is too low, the SEI film formed on the negative electrode surface will be uneven, affecting the cycle performance of the lithium-ion battery.

[0024] Preferably, the relationship between the mass percentage A of the first additive, the mass percentage B of the second additive in the non-aqueous electrolyte, the degree of order R of the negative electrode active material, and the ratio Y of the mass of the non-aqueous electrolyte to the discharge capacity of the battery satisfies 2.8 ≤ [(A+B) / R]×Y ≤ 28. Within this range, the electrolyte content in the battery is at a reasonable level, which can ensure sufficient film formation of the first additive A. The film formation of A can effectively inhibit the damage of the nitrile additive B to the negative electrode. Therefore, the R value can be well controlled, further improving the lithium-ion insertion / extraction efficiency and speed.

[0025] The first additive, acting as a negative electrode protective additive, can lead to excessive impedance of the electrolyte film on the negative electrode surface when its content is too high, hindering the insertion and extraction of lithium ions at the negative electrode interface. Conversely, when its content is too low, the negative electrode becomes unstable due to film rebuilding and consumption of the negative electrode film additive during battery cycling, thus affecting the electrical performance stability of the lithium-ion battery. Specifically, the mass percentage A% of the first additive is 0.1%, 0.2%, 0.5%, 0.6%, 0.8%, 1%, 1.1%, 1.2%, 1.3%, 1.5%, 1.6%, 1.8%, 1.9%, 2%, 2.3%, 2.5%, 2.6%, 2.8%, 3%, or any combination of these values. Preferably, the mass percentage A% of the first additive in the non-aqueous electrolyte is 0.5% to 2%.

[0026] The second additive, acting as a positive electrode protective additive, contains cyano or cyanooxy groups. These groups can form a stable interfacial film on the surface of the positive electrode material, continuously protecting the positive electrode and preventing the electrolyte components from being oxidized on the positive electrode surface, thereby improving the cycle performance of the lithium-ion battery. When its content is too high, the antagonism to the negative electrode additive increases, leading to negative electrode instability and affecting the stability of the lithium-ion battery; when its content is too low, it fails to protect the positive electrode. Specifically, the mass percentage B% of the second additive is 0.5%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.7%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, or any combination of these values. Preferably, the mass percentage B% of the second additive in the non-aqueous electrolyte is 2-4%.

[0027] Preferably, the second additive comprises succinic anionyl nitrile and 1,3,6-hexanetrionitrile; or the second additive comprises adiponitrile and 1,3,6-hexanetrionitrile. When the positive electrode protection additive uses a combination of succinic anionyl nitrile and trionitrile, it can ensure coverage of more active sites of the positive electrode material, inhibit the dissolution of positive electrode metal ions, and thus improve the high-temperature storage performance of the battery.

[0028] The degree of order in the negative electrode active material affects the electrochemical performance of the negative electrode. A suitable degree of order allows for the formation of an ordered microporous structure on the negative electrode surface, providing uniform and efficient transport channels for lithium ions. This facilitates the insertion and extraction of lithium ions on the negative electrode surface and promotes lithium ion transport between the positive and negative electrodes, thereby improving the charge and discharge efficiency and rate of the lithium-ion battery. A suitable degree of order also promotes the formation of a stable and uniform lithium carbonate protective film on the negative electrode surface. During charge and discharge, the movement of lithium ions is more stable, which helps increase the cycle life and lifespan of the lithium-ion battery. This invention controls the degree of order of the negative electrode active material to be within the range of 0.1 to 1, which further helps to form a stable SEI film on the negative electrode surface, improves the lithium-ion conduction rate, and thus improves the cycle performance of the lithium-ion battery. In some embodiments of the invention, the degree of order R of the negative electrode active material is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or any combination of these values. Preferably, the degree of order R of the negative electrode active material is 0.3 to 0.8.

[0029] Specifically, in some embodiments of the present invention, the degree of order of the negative electrode active material is determined by the following method:

[0030] The lithium-ion battery was discharged to 2.75V at 0.1C, and the negative electrode was obtained by disassembling the lithium-ion battery in an argon-filled glove box. The obtained negative electrode was cut into test samples of 100μm×100μm size, and then immersed and cleaned with low-boiling-point dimethyl carbonate (DMC) solvent. After being completely dried, it was pasted onto the sample stage with the surface of the negative electrode material layer facing upwards away from the current collector, and then tested.

[0031] The specific test conditions and steps are as follows: The graphite particles within this area are scanned using a laser confocal Raman spectrometer. The laser wavelength of the Raman spectrometer can be in the range of 532nm to 785nm. A 5μm sample is obtained from the scan. 2 The D and G peaks of graphite particles within the range, with the D peak appearing at 1300 cm⁻¹. -1 Up to 1400cm -1 Within the range, the G peak appears at 1530 cm. -1 Up to 1630cm -1 Internally, LabSpec software was used to process the data to obtain the peak intensities of the D and G peaks for each graphite particle, which are respectively I... D and I G Then calculate I for each graphite particle. D / I G The ratio is taken as the I value of all graphite anode particles measured within this range. D / I G The average value of the ratios is taken as the degree of order R of the negative electrode active material.

[0032] I D / I G The value reflects the lattice defect degree and crystallinity of graphite, I D The value represents the peak intensity of peak D, reflecting the degree of defect in the negative electrode active material. Peak D is the peak intensity measured by Raman spectroscopy analysis of the negative electrode, with a shift range of 1300 cm⁻¹. -1 Up to 1400cm -1 The peak is caused by material defects, I G The value represents the peak intensity of the G peak, reflecting the degree of graphite crystallinity. The G peak, measured by Raman spectroscopy analysis of the negative electrode, has a shift range of 1530 cm⁻¹. -1 Up to 1630cm -1 The peak is caused by the stretching vibration between sp2 carbon atoms, which corresponds to the vibration of the E2g optical phonon (in-plane vibration of carbon atoms) at the center of the Brillouin zone. D / I G A higher I value indicates that graphite has more defects and a higher degree of disorder. D / I G The value depends on the carbon source used to prepare graphite, as well as the preparation method and process conditions.

[0033] The ratio of the mass of the non-aqueous electrolyte to the battery's discharge capacity reflects the amount of electrolyte retained per unit battery capacity. Since the electrolyte is continuously consumed with each battery cycle, controlling this ratio can delay battery degradation and improve cycle performance. Specifically, in some embodiments of the present invention, the ratio Y of the electrolyte mass to the battery's discharge capacity is 0.8 g / Ah, 0.9 g / Ah, 1 g / Ah, 1.1 g / Ah, 1.2 g / Ah, 1.3 g / Ah, 1.4 g / Ah, 1.5 g / Ah, 1.6 g / Ah, 1.7 g / Ah, 1.8 g / Ah, or any combination of these values; preferably, the ratio Y of the non-aqueous electrolyte mass to the battery's discharge capacity is 0.9–1.4 g / Ah.

[0034] Specifically, in some embodiments of the present invention, the mass of the non-aqueous electrolyte in the lithium-ion battery = the mass of the battery after capacity grading - the mass of the battery before electrolyte injection, or the mass of the non-aqueous electrolyte in the lithium-ion battery = the total amount of liquid squeezed out after the capacity-graded cells are centrifuged at 8000 r / min for 20 minutes; the discharge capacity of the battery is the discharge capacity of the battery after being fully charged at 0.2C current at 25°C and then discharged at a constant current of 0.2C to 3.0V.

[0035] In some preferred embodiments, the second additive comprises 1,3,6-hexanetrionitrile and butadionitrile; or the second additive comprises 1,3,6-hexanetrionitrile and adiponitrile. By forming ion complexes at different sites on the positive electrode through the dinitrile + trinitrile combination, the positive electrode is better protected, improving the high-temperature storage performance of the battery without degrading its cycle performance.

[0036] In some more preferred embodiments, the second additive includes 1,3,6-hexanetrionitrile, butadionitrile, and adiponitrile. The simultaneous presence of these three nitrile compounds allows for better protection of the positive electrode through the combination of dinitrile and trinitrile compounds with different molecular chain lengths and steric hindrances, further improving the battery's high-temperature storage performance without degrading its high-temperature cycling performance.

[0037] Specifically, in some embodiments of the present invention, the organic solvent includes one or more of cyclic carbonates, chain carbonates, carboxylic acid esters, and ethers.

[0038] In some preferred embodiments, the cyclic carbonate compound includes one or more of vinylene carbonate, propylene carbonate, ethylene carbonate, and butene carbonate.

[0039] In some preferred embodiments, the chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl trifluoroethyl carbonate, and bis(2,2,2-trifluoroethyl) carbonate.

[0040] In some preferred embodiments, the carboxylic acid ester includes one or more of propyl propionate, ethyl propionate, methyl propionate, ethyl acetate, 2,2-difluoroethyl acetate, ethyl difluoroacetate, and ethyl trifluoroacetate.

[0041] In some preferred embodiments, the ethers include one or more of ethylene glycol dimethyl ether, 1,3-dioxolane, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0042] Specifically, in some embodiments of the present invention, the additive further includes auxiliary additives, which include at least one of cyclic sulfate compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate compounds, and borate compounds.

[0043] In some preferred embodiments, the cyclic sulfate compound includes at least one of 4-methyl vinyl sulfate, vinyl sulfate, and propylene sulfate.

[0044] In some preferred embodiments, the sulfonyl lactone compound includes at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and propenyl-1,3-sulfonyl lactone.

[0045] In some preferred embodiments, the cyclic carbonate compound includes at least one of vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, and a compound represented by structural formula 1 below:

[0046]

[0047] In the structural formula 1 shown, R 21 R 22 R 23 R 24 R 25 R 26 Each is independently selected from one of the following: hydrogen atom, halogen atom, or C1-C5 group;

[0048] In some preferred embodiments, the compound of structural formula 1 includes at least one of the compounds shown in compounds 1-1 to 1-6 below:

[0049]

[0050] The phosphate ester compounds include at least one of the compounds shown in structural formula 2:

[0051]

[0052] In structural formula 2, R 31 R 32 R 33 Each independent group is selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halohydrocarbon groups, and -Si(C m H 2m+1 )3, where m is a natural number from 1 to 3; more preferably, the compound represented by structural formula 2 includes at least one of tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, triargylpropyl phosphate, diargylpropylmethyl phosphate, diargylpropylethyl phosphate, diargylpropylpropyl phosphate, diargylpropyltrifluoromethyl phosphate, diargylpropyl-2,2,2-trifluoroethyl phosphate, diargylpropyl-3,3,3-trifluoropropyl phosphate, diargylpropylhexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, and diallyl hexafluoroisopropyl phosphate.

[0053] In some preferred embodiments, the borate ester compound includes at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate.

[0054] In some embodiments of the present invention, the content of the auxiliary additive is 0.01% to 10% based on 100% by weight of the non-aqueous electrolyte. Specifically, the content of any one optional substance in the auxiliary additive can be 0.01%, 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, etc.

[0055] 4.5%, 5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or a range of any two of these values.

[0056] Specifically, in some embodiments of the present invention, the lithium salt further includes lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), LiPO₂F₂, LiBF₄, LiBOB, LiSbF₆, LiAsF₆, LiCF₃SO₃, LiDFOB, LiDFOP, LiN(SO₂CF₃)₂, LiC(SO₂CF₃)₃, LiN(SO₂C₂F₅)₂, LiCl, LiBr, LiI, LiClO₄, and LiB₂. 10 Cl 10 At least one of the following: LiAlCl4, lithium chloroborane, lithium lower aliphatic carboxylic acids having four or fewer carbon atoms, and lithium tetraphenylborate.

[0057] Specifically, in some embodiments of the present invention, the graphite content is 85% to 100% by mass, based on the total mass of the negative electrode active material as 100%. The graphite includes, but is not limited to, one or more of natural graphite, artificial graphite, amorphous carbon, carbon-coated graphite, graphite-coated graphite, and resin-coated graphite. Controlling the graphite content within the above range allows additive A to more fully form a negative electrode film, thus protecting the negative electrode.

[0058] The negative electrode active material further includes a silicon-based material. Specifically, the silicon-based material is selected from one or more of silicon materials, silicon oxide materials, silicon carbon materials, and silicon alloy materials; preferably, the silicon material is a nano-silicon material; preferably, the silicon oxide material is SiO2. x Materials, wherein 0 ≤ x < 2; preferably, the silicon-carbon material is a silicon-based material containing silicon and carbon materials and / or containing SiO2. y The silicon-based material is a carbon material, wherein 0 ≤ y < 2; preferably, the silicon alloy material is a Mg2Si alloy material and / or an Fe2Si alloy material.

[0059] Specifically, in some embodiments of the present invention, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent.

[0060] Specifically, in some embodiments of the invention, the negative electrode binder includes one or more of the following: polyvinylidene fluoride (PVDF), copolymers of PVDF, polytetrafluoroethylene (PTFE), copolymers of PVDF-hexafluoropropylene, copolymers of tetrafluoroethylene-hexafluoropropylene, copolymers of tetrafluoroethylene-perfluoroalkyl vinyl ethers, copolymers of ethylene-tetrafluoroethylene, copolymers of PVDF-tetrafluoroethylene, copolymers of PVDF-trifluoroethylene, copolymers of PVDF-trichloroethylene, copolymers of PVDF-fluorinated vinylidene, copolymers of PVDF-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene-butadiene rubber.

[0061] The negative electrode conductive agent includes one or more of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene or reduced graphene oxide.

[0062] Specifically, in some embodiments of the present invention, the negative electrode current collector includes a metal material capable of conducting electrons. Preferably, the negative electrode current collector includes one or more of aluminum, nickel, tin, copper, and stainless steel.

[0063] Specifically, in some embodiments of the present invention, the positive electrode includes a positive electrode material layer, the positive electrode material layer includes a positive electrode active material, and the positive electrode active material includes LiNi x Co y Mn z L (1-x-y-z) O2, LiCo x’ L (1-x’) O2, LiNi x” L’ y’ Mn (2-x”-y’) O4, Li z’ MPO4, etc.; where L is one or more of Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, or Fe, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 < x + y + z ≤ 1, 0 < x’ ≤ 1, 0.3 ≤ x” ≤ 0.6, 0.01 ≤ y’ ≤ 0.2, L’ is one or more of Co, Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe; 0.5 ≤ z’ ≤ 1, M is one or more of Fe, Mn, Co. Preferably, the positive electrode active material includes LiCoO2, LiFePO4, LiFe 0.4 Mn 0.6 PO4, LiMn2O4, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.5 Co 0.2 Mn 0.2 Al0.1 O2, LiNi 0.5 Co 0.2 Al 0.3 One or more of O2.

[0064] Specifically, in some embodiments of the present invention, the positive electrode further includes a positive current collector, and the positive electrode material layer is disposed on the surface of the positive current collector. The material of the positive current collector may be the same as that of the negative current collector, and will not be described in detail here.

[0065] Specifically, in some embodiments of the present invention, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductive agent, and the positive electrode active material, the positive electrode binder, and the positive electrode conductive agent are blended to obtain the positive electrode material layer. The positive electrode binder and the positive electrode conductive agent can be the same as the negative electrode binder and the negative electrode conductive agent, respectively, and will not be described in detail here.

[0066] Specifically, in some embodiments of the present invention, the lithium-ion battery further includes a separator located between the positive electrode and the negative electrode.

[0067] The diaphragm can be a conventional diaphragm, such as a ceramic diaphragm, a polymer diaphragm, a non-woven fabric, or an inorganic-organic composite diaphragm, including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP, and triple-layer PP / PE / PP diaphragms.

[0068] The lithium-ion battery of the present invention includes a first additive as a negative electrode protective additive and a second additive as a positive electrode protective additive in the non-aqueous electrolyte. The mass percentage A of the first additive in the non-aqueous electrolyte, the mass percentage B of the second additive in the non-aqueous electrolyte, the degree of order R of the negative electrode active material, and the ratio Y of the mass of the non-aqueous electrolyte to the discharge capacity of the battery are defined such that the relationship satisfies 2≤[(A+B) / R]×Y≤48, 0.1≤A≤3, 0.5≤B≤5, 0.1≤R≤1, and 0.8≤Y≤1.8. This significantly reduces the degradation of the negative electrode by nitriles and forms a stable interface film on the surfaces of the positive and negative electrodes, thus optimizing the high-temperature cycle performance of the lithium-ion battery. Detailed Implementation

[0069] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0070] Example 1

[0071] The method for preparing the lithium-ion battery in this embodiment includes the following steps:

[0072] 1) Preparation of electrolyte

[0073] Ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), propyl propionate (PP), and ethyl propionate (EP) were mixed in a mass ratio of EC:PC:DEC:PP:EP = 10:15:20:40:15. Then, lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1 mol / L. Next, 4% of 1,3-propanesulfonyl lactone and 5% of fluoroethylene carbonate were added based on the total mass of the electrolyte. Then, the first additive (compound 1) and the second additive were added. The content of the first additive and the types and contents of the second additive are shown in Table 1.

[0074] 2) Preparation of positive electrode sheet

[0075] The positive electrode active material, lithium nickel cobalt manganese oxide (LiNiO), was mixed in a mass ratio of 93:4:3. 0.5 Co 0.2 Mn 0.3 O2, conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) are dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The slurry is uniformly coated on both sides of an aluminum foil, dried, calendered, and vacuum dried, and then aluminum leads are welded on using an ultrasonic welder to obtain a positive electrode sheet with a thickness of 120-150 μm.

[0076] 3) Preparation of negative electrode sheet

[0077] Artificial graphite, conductive carbon black Super-P, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 94:1:2.5:2.5, and then dispersed in deionized water to obtain a negative electrode slurry. The slurry was coated on both sides of a copper foil, dried, calendered, and vacuum dried, and then nickel leads were welded on using an ultrasonic welder to obtain a negative electrode sheet with a thickness of 120-150 μm.

[0078] 4) Cell fabrication

[0079] A three-layer separator with a thickness of 20 μm is placed between the positive electrode and the negative electrode. Then, the sandwich structure composed of the positive electrode, the negative electrode and the separator is wound up. The wound body is then flattened and placed in an aluminum foil packaging bag. It is then vacuum baked at 75°C for 48 hours to obtain the battery cell to be injected with electrolyte.

[0080] 5) Electrolyte injection and formation of battery cells

[0081] In a glove box with the dew point controlled below -40°C, the electrolyte prepared above was injected into the battery cell, vacuum sealed, and left to stand for 24 hours. Then, the first charge was carried out at 80°C for hot-pressing formation according to the following steps: 0.1C constant current charging for 4 minutes, pressure 12.51 kg / cc; 0.3C constant current charging for 15 minutes, pressure 12.51 kg / cc; 1C constant current charging for 45 minutes, pressure 12.51 kg / cc; secondary vacuum sealing, and then further constant current charging at 0.2C to the upper limit voltage, left to stand at room temperature for 24 hours, and then constant current discharge at 0.2C to 3.0V.

[0082] Examples 2-42 and Comparative Examples 1-14

[0083] This embodiment and comparative example are used to illustrate the lithium-ion battery disclosed in this invention. They include most of the operating steps in the above embodiment 1. The differences are: the composition and content of additives in the non-aqueous electrolyte, the degree of order of the negative electrode active material, and the ratio of the mass of the non-aqueous electrolyte to the discharge capacity of the battery, as shown in Tables 1-6.

[0084] Table 1

[0085]

[0086]

[0087] The lithium-ion batteries prepared in each embodiment and comparative example were subjected to performance testing according to the following methods:

[0088] I. High-Temperature Cyclic Performance Test

[0089] The lithium-ion battery prepared above was placed in an oven at a constant temperature of 45°C and charged at a constant current of 1C to the upper limit voltage of the battery. Then it was charged at a constant voltage until the current dropped to 0.02C. Then it was discharged at a constant current of 1C to 3.0V. This cycle was repeated, and the discharge capacity of the first discharge and the discharge capacity of the 500th discharge were recorded.

[0090] Calculate the capacity retention during high-temperature cycling using the following formula:

[0091] Capacity retention rate (%) = Discharge capacity at the 500th discharge / Discharge capacity at the 1st discharge × 100%.

[0092] II. High-Temperature Storage Performance Test

[0093] High-temperature storage performance test

[0094] The formed lithium-ion battery was charged to its upper limit voltage at room temperature using a 1C constant current and constant voltage method. The initial discharge capacity and initial battery thickness were measured. Then, after storage at 60℃ for 30 days, the battery was discharged to 3V using a 1C method, and the retention capacity, recovery capacity, and battery thickness after storage were measured. The calculation formula is as follows:

[0095] Battery capacity retention rate (%) = Retained capacity / Initial capacity × 100%;

[0096] Battery capacity recovery rate (%) = Recovered capacity / Initial capacity × 100%;

[0097] Thickness expansion rate (%) = (Battery thickness after storage - Initial battery thickness) / Initial battery thickness × 100%.

[0098] (1) The test results of Examples 1-21 and Comparative Examples 1-14 are shown in Table 2.

[0099] Table 2

[0100]

[0101]

[0102]

[0103] The test results of Examples 1-21 and Comparative Examples 1-14 show that in the lithium-ion battery of the present invention, the additives in the non-aqueous electrolyte are a second additive as a positive electrode protection additive and a first additive as a negative electrode protection additive. Furthermore, when the relationships between the mass percentage A of the first additive in the non-aqueous electrolyte, the mass percentage B of the second additive in the non-aqueous electrolyte, the degree of order R of the negative electrode active material, and the ratio Y of the mass of the non-aqueous electrolyte to the discharge capacity of the lithium-ion battery satisfy 2≤[(A+B) / R]×Y≤48, 0.1≤A≤3, 0.5≤B≤5, 0.1≤R≤1, and 0.8≤Y≤1.8, the degradation of the negative electrode by nitriles can be greatly reduced, and a stable interface film can be formed on the positive and negative electrode surfaces. This reduces the impact of excessive electrolyte consumption on battery performance and further optimizes the high-temperature cycle performance of the lithium-ion battery.

[0104] As can be seen from the test results of Example 1 and Comparative Examples 1-14, when any one or more of the following parameters—A (mass percentage of the first additive in the non-aqueous electrolyte), B (mass percentage of the second additive in the non-aqueous electrolyte), R (order degree of the negative electrode active material), and Y (mass ratio of the non-aqueous electrolyte to the discharge capacity of the lithium-ion battery)—do not meet the specified range, or when the value of the relationship [(A+B) / R]×Y is too large or too small, it is impossible to guarantee that the lithium-ion battery has good cycle performance. This indicates that the mass percentage of the first additive in the non-aqueous electrolyte, B (mass percentage of the second additive in the non-aqueous electrolyte), R (order degree of the negative electrode active material), and Y (mass ratio of the non-aqueous electrolyte to the discharge capacity of the lithium-ion battery) are strongly correlated with improving the high-temperature cycle performance of lithium-ion batteries.

[0105] (3) The test results of Examples 1 and Examples 22-32 are shown in Table 3.

[0106] Table 3

[0107]

[0108]

[0109] As shown in Table 3, the test results of Examples 1 and 22-32 indicate that for the non-aqueous electrolyte of the present invention, when the total content of the second additive in the additive is constant, and three different combinations of nitrile compounds—butaniline, adiponitrile, and 1,3,6-hexanetrionitrile—are used as positive electrode protection additives, as long as the mass percentage A of the first additive in the non-aqueous electrolyte, the mass percentage B of the second additive, the degree of order R of the negative electrode active material, and the ratio Y of the mass of the non-aqueous electrolyte to the discharge capacity of the battery all meet the corresponding conditions, the positive electrode can be protected, thus optimizing the high-temperature cycle performance of the battery. This demonstrates that the battery system of the present invention has universal applicability to the above three second additives as positive electrode protection additives. In particular, when three nitrile compounds are contained simultaneously, the high-temperature storage performance and high-temperature cycle performance of the battery are better than those containing one or two nitrile compounds. This indicates that by combining dinitrile and trinitrile compounds with different molecular chain lengths and steric hindrances, better protection of the positive electrode can be formed, further improving the high-temperature storage performance of the battery without degrading the high-temperature cycle performance.

[0110] (4) The test results of Examples 1 and Examples 33-36 are shown in Table 4. The difference between Examples 33-36 and Example 1 lies in the relevant parameters in Table 4.

[0111] Table 4

[0112]

[0113] As can be seen from the test structures of Examples 1 and 33-36 in Table 4, for the non-aqueous electrolyte of the present invention, when different first additives are used in the additives, when the mass percentage A of the first additive in the non-aqueous electrolyte, the mass percentage B of the second additive, the degree of order R of the negative electrode active material, and the ratio Y of the mass of the non-aqueous electrolyte to the discharge capacity of the battery all meet the corresponding conditions, the goal of optimizing the high-temperature cycle performance of the lithium-ion battery can be achieved. This shows that the battery system of the present invention has universality for different first additives, and can play a role in protecting the negative electrode of the battery within the limited protection range.

[0114] (4) The test results of Examples 1 and Examples 37-38 are shown in Table 5. The difference between Examples 37-38 and Example 1 lies in the relevant parameters in Table 5.

[0115] Table 5

[0116]

[0117] As can be seen from the comparison of the test results of Examples 1 and 37-38 in Table 5, the lithium-ion battery of the present invention, with the addition of additives such as ethylene sulfate (DTD) and vinylene carbonate (VC) to the non-aqueous electrolyte, can further optimize the high-temperature cycle performance of the lithium-ion battery, indicating that there is a complementary effect between the additives and auxiliary additives of the present invention.

[0118] (5) The test results of Examples 1 and Examples 39-42 are shown in Table 6. The difference between Examples 39-42 and Example 1 lies in the relevant parameters in Table 6.

[0119] Table 6

[0120]

[0121] As can be seen from the test results of Examples 1 and 39-42 in Table 6, for the lithium-ion battery of the present invention, when different negative electrode active materials are used, the high-temperature cycle performance of the lithium-ion battery can be optimized when the mass percentage A of the first additive in the non-aqueous electrolyte, the mass percentage B of the second additive in the non-aqueous electrolyte, the degree of order R of the negative electrode active material, and the ratio Y of the mass of the non-aqueous electrolyte of the lithium-ion battery to the discharge capacity meet the corresponding conditions. This shows that the battery system of the present invention has universality for different negative electrode active materials.

[0122] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the nature and scope of the present invention. Various modifications made to the above embodiments by those skilled in the art after reading this specification are all within the scope of protection of the present invention.

Claims

1. A lithium-ion battery, characterized by, The lithium ion battery comprises a positive electrode sheet, a negative electrode sheet and a non-aqueous electrolyte. The negative electrode sheet includes a negative electrode material layer containing a negative electrode active material, the negative electrode active material including graphite, the negative electrode active material having an order degree R = I D / I G In a spectrum determined by performing Raman spectroscopic analysis on the negative electrode using laser light having a wavelength of 532 nm to 785 nm, I D is the peak intensity of a D peak appearing in a range of 1300 cm -1 to 1400 cm -1 , and I G is the peak intensity of a G peak appearing in a range of 1530 cm -1 to 1630 cm -1 . The non-aqueous electrolyte comprises a lithium salt, an organic solvent and an additive. The additive comprises a first additive and a second additive, the first additive comprises at least one of the following compounds: ； The second additive comprises at least one of succinonitrile, adiponitrile or 1,3,6-hexanetricarbonitrile. The lithium ion battery satisfies: 2≤[(A+B) / R]×Y≤48, 0.1≤A≤3, 0.5≤B≤5, 0.1≤R≤1, 0.8≤Y≤1.

8. Wherein, A is the mass percentage content of the first additive in the non-aqueous electrolyte, and the unit is %. B is the mass percentage content of the second additive in the non-aqueous electrolyte, and the unit is %. R is the order degree of the negative electrode active material. Y is the ratio of the mass of the non-aqueous electrolyte to the discharge capacity of the battery, and the unit is g / Ah.

2. The lithium-ion battery of claim 1, wherein, The lithium ion battery satisfies the condition: 2.8≤[(A+B) / R]×Y≤28.

3. The lithium-ion battery of claim 1, wherein, The mass percentage content A% of the first additive in the non-aqueous electrolyte is 0.5% to 2%.

4. The lithium-ion battery of claim 1, wherein, The mass percentage content B% of the second additive in the non-aqueous electrolyte is 2% to 4%.

5. The lithium-ion battery of claim 1, wherein, The order degree R of the negative electrode active material is 0.3 to 0.

8.

6. The lithium-ion battery of claim 1, wherein, The ratio Y of the mass of the non-aqueous electrolyte to the discharge capacity of the battery is 0.9 g / Ah to 1.4 g / Ah.

7. The lithium-ion battery of claim 1, wherein, The second additive comprises 1,3,6-hexanetricarbonitrile and succinonitrile; or, the second additive comprises 1,3,6-hexanetricarbonitrile and adiponitrile.

8. The lithium-ion battery of claim 1, wherein, The non-aqueous electrolyte further comprises an auxiliary additive, the auxiliary additive comprises at least one of a cyclic sulfate compound, a sulfonic acid lactone compound, a cyclic carbonate compound, a phosphate compound, a borate compound; and / or, The mass percentage content of the auxiliary additive is 0.01% to 10% based on 100% of the mass of the non-aqueous electrolyte.

9. The lithium-ion battery of claim 8, wherein, The cyclic sulfate compound comprises at least one of 4-methyl vinyl sulfate, vinyl sulfate, propylene sulfate; and / or, The sulfonic acid lactone compound comprises at least one of 1,3-propane sulfonic acid lactone, 1,4-butane sulfonic acid lactone, propylene-1,3-sulfonic acid lactone; and / or, The cyclic carbonate compound comprises at least one of vinylene carbonate, vinyl ethylene carbonate, methylene vinyl carbonate, fluorinated vinyl carbonate, trifluoromethyl vinyl carbonate, difluorinated vinyl carbonate and a compound represented by the following structural formula 1: ； Structural formula 1 In the structural formula 1 shown, R 21 , R 22 , R 23 , R 24 , R 25 , R 26 each is independently selected from a hydrogen atom, a halogen atom, one of C1-C5 groups; and / or, The phosphate compound comprises at least one of a compound represented by the following structural formula 2: ； Structural formula 2 In the structural formula 2, R 31 , R 32 , R 33 are each independently selected from a C1-C5 saturated hydrocarbon group, an unsaturated hydrocarbon group, a halogenated hydrocarbon group, -Si(C m H 2m+1 )3, and m is a natural number from 1 to 3; and / or, The borate compound comprises at least one of tris(trimethylsilyl) borate and tris(triethylsilyl) borate.

10. The lithium-ion battery of claim 1, wherein, The mass percentage content of the graphite is 85% to 100% based on 100% of the total mass of the negative electrode active material.

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