Lithium ion battery

Abstract

A lithium ion battery. The lithium ion battery comprises a positive electrode sheet and an electrolyte; the electrolyte comprises a first additive having a mass content of a%; the first additive comprises a cyano group and a group represented by formula (i) and / or formula (ii); the positive electrode sheet comprises a positive electrode current collector having a tensile strength of L MPa; a and L satisfy 0.05≤100×a / L≤5.The lithium ion battery has good high-temperature cycling stability and a long service life.

Description

lithium-ion batteries Technical Field

[0001] The present disclosure relates to the field of batteries, and in particular to a lithium-ion battery. Background Art

[0002] High-voltage lithium-ion electrolyte technology is an electrolyte technology used in lithium-ion batteries, primarily to improve their energy density and cycle life. Over the past few decades, lithium-ion batteries have been widely used in electric vehicles, smartphones, and other portable electronic devices. However, due to limitations of lithium-ion batteries (such as energy density and capacity fading), researchers have been seeking ways to improve them to meet various application requirements.

[0003] In order to improve the energy density of lithium-ion batteries, increasing the charge cut-off voltage of the positive electrode active material is an effective solution. However, as the charge voltage of the positive electrode active material continues to increase, such as when it reaches 4.5V, the cycle performance of the lithium-ion battery will be significantly reduced.

[0004] Therefore, it is very important to find a lithium-ion battery with excellent cycling performance at high voltage. Summary of the Invention

[0005] The present disclosure aims to overcome the aforementioned problems of the prior art by providing a lithium-ion battery. The lithium-ion battery disclosed herein comprises a positive electrode and an electrolyte, which can reduce the occurrence of side reactions between the positive electrode and the electrolyte, thereby improving the cycling performance of the lithium-ion battery at high voltages (e.g., 4.5V and above), particularly high-temperature cycling stability.

[0006] The present disclosure provides a lithium-ion battery, comprising a positive electrode sheet and an electrolyte; the positive electrode sheet comprises a positive electrode current collector; the electrolyte comprises a first additive, wherein the first additive comprises a cyano group and a group represented by formula i and / or a group represented by formula ii,

[0007] The tensile strength of the positive electrode current collector is 1 MPa. In the electrolyte, the mass content of the first additive is a%, and 0.05≤100×a / L≤5 is satisfied.

[0008] Through the above technical solution, the present disclosure has at least the following advantages compared with the prior art:

[0009] (1) The electrolyte in the lithium-ion battery disclosed herein includes a first additive, the content of which satisfies a specific relationship with the tensile strength of the positive electrode current collector, and can improve the cycle performance of the lithium-ion battery under high temperature conditions.

[0010] (2) The lithium-ion battery disclosed herein includes a first additive having a special group, which is easily oxidized to form a film on the surface of the positive electrode, thereby reducing the risk of side reactions between the positive electrode active material and the electrolyte; and the groups in the first additive can complex with the metal ions in the positive electrode active material, thereby forming a protective layer on the surface of the positive electrode, further reducing the risk of side reactions between the positive electrode active material and the electrolyte.

[0011] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein. DETAILED DESCRIPTION

[0012] The following describes the specific embodiments of the present disclosure in detail. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure and are not intended to limit the present disclosure.

[0013] The present disclosure provides a lithium-ion battery, wherein the lithium-ion battery may include a positive electrode sheet and an electrolyte; the positive electrode sheet may include a positive electrode current collector; the electrolyte may include a first additive, wherein the first additive may include a cyano group and a group represented by formula i and / or a group represented by formula ii.

[0014] The tensile strength of the positive electrode current collector is L (in MPa). In the electrolyte, the mass content of the first additive is a (in %), which satisfies 0.05≤100×a / L≤5. For example, 100×a / L is equal to 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1. 4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, or 5.

[0015] In one example, 0.25≤100×a / L≤2.5.

[0016] In one example, 0.5≤100×a / L≤1.5.

[0017] Under high voltage conditions, the cycle stability and safety of lithium-ion batteries will be significantly reduced. Through extensive research, the inventors of the present disclosure have found that the reasons for the above problems are: under high voltage conditions, the positive electrode active material will expand in volume, resulting in the continuous release of reactive oxygen, which oxidizes the electrolyte. The oxidized electrolyte will intensify the corrosion of the positive electrode collector, thereby reducing the current conductivity of the positive electrode collector and causing the cycle performance of the lithium-ion battery to decline. In addition, due to the corrosion of the electrolyte, the positive electrode collector in a wound state is prone to breakage, which increases the possibility of contact with the negative electrode active material, and ultimately leads to a decline in the safety performance of the lithium-ion battery.

[0018] The inventors of the present disclosure have discovered that by adding a first additive having a specific functional group, the cycle stability and safety performance of a lithium-ion battery can be improved. The reason for this may be that: when the first additive includes a group represented by formula i and / or a group represented by formula ii, it can be preferentially oxidized on the surface of the positive electrode to form a stable CEI film, thereby reducing the corrosion of the positive electrode current collector by oxygen generated by the side reaction between the electrolyte and the positive electrode active material; when the first additive includes a cyano group, the cyano group can undergo a complex reaction with metal ions dissolved in the positive electrode active material to form a protective film on the surface of the positive electrode, thereby further reducing the corrosion of the positive electrode current collector by oxygen generated by the side reaction between the electrolyte and the positive electrode active material; and the cyano group and the group represented by formula i and / or the group represented by formula ii have a synergistic effect, which can further improve the cycle stability and safety performance of the lithium-ion battery. The reason for this may be that the formation mechanism of the "protective film formed by the group represented by formula i and / or the group represented by formula ii" and the "protective film formed by the cyano group" are different, and the protective effects of the two are also different. Therefore, the synergistic use of the two can provide a more excellent protective effect on the positive electrode.

[0019] However, even with a specific first additive, the cycling stability and safety performance of lithium-ion batteries are not significantly improved at higher temperatures. Therefore, after extensive research, the inventors of the present disclosure discovered that limiting the mass content a of the first additive and the tensile strength L of the positive electrode current collector to satisfy 0.05 ≤ 100 × a / L ≤ 5 can significantly improve the cycling performance and safety performance of lithium-ion batteries under high temperature conditions. This may be because: first, at high temperatures, the positive electrode active material is more likely to undergo phase transitions, causing structural collapse, which in turn leads to deformation of the positive electrode current collector, affecting the cycling stability and safety performance of the lithium-ion battery; if the mass content of the additive and the tensile strength of the positive electrode current collector are limited and matched, the effect of the structural collapse of the positive electrode active material on the deformation of the positive electrode current collector can be reduced. Second, the cyano group in the first additive reacts with water to form an acid (i.e., -CN + H2O → -CONH2, CONH2 + H2O → -COOH + NH3), which hinders the conversion of LiPF6 in the electrolyte to HF, further reducing damage to the positive electrode current collector. Again, when 0.05≤100×a / L≤5 is met, the phase change rate of the positive electrode active material under high temperature conditions can be slowed down, delaying its impact on the positive electrode current collector, thereby further improving the cycle stability and safety performance of the lithium-ion battery. When 0.05≤100×a / L≤5 is met, the CEI film formed by the first additive on the positive electrode surface can alleviate the burr puncturing the diaphragm, thereby improving the safety performance of the battery. Finally, when 0.05≤100×a / L≤5 is met, it is not only conducive to the discharge of oxygen generated by the side reaction between the electrolyte and the positive electrode active material, but also can improve the mechanical properties of the positive electrode current collector, avoid breaking during the winding process, and thus improve the safety performance of the battery.

[0020] <Electrolyte>

[0021] In the present disclosure, the cyano group, the group represented by formula i, and the group represented by formula ii can be detected by conventional methods in the art, such as infrared spectroscopy.

[0022] In the present disclosure, in the electrolyte, the mass content a of the first additive can be 0.1%-10%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0023] The inventors of the present disclosure discovered that the first additive has a specific mass content. Within this mass content range, the first additive is more easily oxidized on the surface of the positive electrode sheet, and the cyanide group can undergo a more stable complexation reaction with the metal ions dissolved in the positive electrode active material, which is conducive to the formation of a more stable protective film on the positive electrode surface and will not have a negative impact on the negative electrode.

[0024] In one embodiment, a is 0.5%-5%.

[0025] In one embodiment, a is 1%-3%.

[0026] In the present disclosure, the mass content of the first additive in the electrolyte can be measured by conventional methods in the art, such as gas chromatography.

[0027] In the present disclosure, the mass content of the group represented by formula i and / or the group represented by formula ii in the electrolyte can be 0.003%-1.6% (for example, 0.003%, 0.004%, 0.005%, 0.006%, 0.007%, 0.008%, 0.009%, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% or 1.6%). The mass content of cyano groups in the electrolyte can be 0.008%-4% (for example, 0.008%, 0.009%, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3% or 4%).

[0028] In one embodiment, the mass content of the group represented by formula i and / or the group represented by formula ii in the electrolyte is 0.015%-0.8%, and the mass content of the cyano group in the electrolyte is 0.004%-2%.

[0029] In one embodiment, the mass content of the group represented by formula i and / or the group represented by formula ii in the electrolyte is 0.03%-0.48%, and the mass content of the cyano group in the electrolyte is 0.08%-1.2%.

[0030] In one embodiment, the mass content of the group represented by formula i and / or the group represented by formula ii in the electrolyte is 0.1%-0.4%, and the mass content of the cyano group in the electrolyte is 0.3%-1%.

[0031] In the present disclosure, the mass content of the group represented by formula i and / or the group represented by formula ii in the electrolyte and the mass content of the cyano group in the electrolyte can be obtained by conventional testing methods in the art. For example, the mass content of the group represented by formula i and / or the group represented by formula ii in the electrolyte is obtained by infrared spectroscopy or chromatography-mass spectrometry (GC-MC) testing; the mass content of the cyano group in the electrolyte is obtained by infrared spectroscopy testing.

[0032] The inventors of the present disclosure have found that the mass content of the group shown in formula i and / or the group shown in formula ii in the electrolyte and the mass content of the cyano group in the electrolyte have a specific range, which can further improve the cycle stability of the lithium-ion battery. The reason may be that when the mass content of the cyano group is too small, a structurally stable and complete protective film cannot be formed on the surface of the positive electrode, thereby failing to effectively reduce the side reaction between the electrolyte and the positive electrode active material, resulting in a decrease in the cycle performance of the lithium-ion battery; and when the mass content of the cyano group is too large, the excess cyano group has poor compatibility with the negative electrode, destroying the protective film on the surface of the negative electrode, thereby affecting the cycle performance of the lithium-ion battery. In addition, when the mass content of the group shown in formula i and / or the group shown in formula ii is too small, a structurally stable and complete protective film cannot be formed on the surface of the positive electrode, thereby failing to effectively reduce the side reaction between the electrolyte and the positive electrode active material, resulting in a decrease in the cycle performance of the lithium-ion battery; and when its mass content is too large, the excess of the group cannot play a protective role at the positive electrode, and will affect the content of other components in the electrolyte, thereby affecting the electrochemical performance of the lithium-ion battery.

[0033] In the present disclosure, the first additive may include a substance represented by Formula I and / or a substance represented by Formula II,

[0034] wherein m1, m2, and m3 are each independently selected from an integer greater than or equal to 1 (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30), and n1, n2, and n3 are each independently selected from an integer greater than or equal to 1 (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30).

[0035] In one embodiment, m1, m2, and m3 are each independently selected from an integer of 1 to 20. n1, n2, and n3 are each independently selected from an integer of 1 to 20.

[0036] In one example, m1=m2=m3.

[0037] In one example, n1=n2=n3.

[0038] In the present disclosure, the first additive may include At least one of .

[0039] The inventors of the present disclosure have discovered that the first additive with a specific structure is more likely to lose electrons and is oxidized to form a protective film on the surface of the positive electrode, thereby further improving the cycle stability of the lithium-ion battery.

[0040] In one example, the first additive includes At least one of .

[0041] In the present disclosure, the electrolyte may further include an organic solvent, and the organic solvent may include at least one of a carbonate compound and a carboxylate compound.

[0042] In the present disclosure, the carbonate compound may include at least one of the following fluorine-substituted or unsubstituted solvents and ethylene carbonate (EC): propylene carbonate (PC), dimethyl carbonate, diethyl carbonate (DEC), and ethyl methyl carbonate.

[0043] In the present disclosure, the carboxylate compound may include at least one of the following fluorine-substituted or unsubstituted solvents: propyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, propyl propionate (PP), ethyl propionate (EP), methyl butyrate and ethyl butyrate.

[0044] The inventors of the present disclosure discovered that a specific organic solvent has a synergistic effect with the first additive. The specific organic solvent has a low viscosity, which is conducive to the rapid transmission of ions. While improving the fast charging performance of the lithium-ion battery, it can also form better interface protection for the positive electrode.

[0045] In one example, the organic solvent includes propyl propionate and ethyl propionate.

[0046] In the present disclosure, the mass ratio of propyl propionate to ethyl propionate is (1-2):1, for example, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1 or 2:1.

[0047] In the present disclosure, the ratio of the mass content of the first additive in the electrolyte to the total mass content of propyl propionate and ethyl propionate in the electrolyte is (0.015-0.05):1, for example, 0.015:1, 0.016:1, 0.017:1, 0.018:1, 0.019:1, 0.02:1, 0.025:1, 0.03:1, 0.035:1, 0.04:1, 0.045:1 or 0.05:1.

[0048] In the present disclosure, the electrolyte may further include a lithium salt, and the lithium salt may include at least one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium bis(trifluoromethylsulfonyl)imide, lithium difluorobis(oxalatophosphate), lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(pentafluoroethylsulfonyl)imide, tris(trifluoromethylsulfonyl)methyllithium and lithium bis(trifluoromethylsulfonyl)imide.

[0049] In the present disclosure, based on the total weight of the electrolyte, the sum of the mass contents of propyl propionate and ethyl propionate can be 5%-60%, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55% or 60%.

[0050] The inventors of the present disclosure have discovered that a specific second additive can further enhance the cycling stability of lithium-ion batteries. This may be because the specific second additive not only compensates for the damage to the negative electrode surface protective film caused by the first additive, but also reduces the corrosion of the electrolyte on the current collectors (including the positive and negative electrode current collectors), thereby further improving the cycling stability of the lithium-ion battery.

[0051] In the present disclosure, the electrolyte may further include a second additive, and the second additive may include at least one of fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), and vinylene carbonate (VC).

[0052] <Positive electrode>

[0053] In the present disclosure, L may be 100 MPa to 1000 MPa, for example, 100 MPa, 200 MPa, 300 MPa, 400 MPa, 500 MPa, 600 MPa, 700 MPa, 800 MPa, 900 MPa, or 1000 MPa.

[0054] The inventors of the present disclosure have discovered that when L is within a specific range, lithium-ion batteries have good cycling stability. When L is too small (e.g., less than 100 MPa), the positive electrode current collector is prone to fracture, seriously affecting the safety performance of the lithium-ion battery. When L is too large (e.g., greater than 1000 MPa), the positive electrode current collector surface may have many burrs, also affecting the safety performance of the lithium-ion battery.

[0055] In the present disclosure, the positive electrode current collector may include aluminum, an aluminum alloy, or a composite current collector. The composite current collector may include a substrate layer and a coating on at least one side of the substrate layer. The substrate layer may include elemental Al. The coating may include elemental C.

[0056] The inventors of the present disclosure have discovered that when the positive electrode current collector includes a composite current collector, it is beneficial to improve the safety performance of the battery.

[0057] In one example, L is 133 MPa-400 MPa.

[0058] In one example, L is 600 MPa-800 MPa.

[0059] In the present disclosure, the tensile strength L of the positive electrode current collector can be measured by conventional testing methods in the art, for example, by the following method:

[0060] (1) The cycled lithium-ion battery was discharged, disassembled, the positive electrode was removed, the electrolyte and byproducts on the surface of the positive electrode were removed, and the battery was placed in a fume hood for 12 hours. The dried positive electrode was taken out and immersed in N-methylpyrrolidone (NMP) for 45 minutes;

[0061] (2) Lay the positive electrode sheet treated in step (1) flat on a glass plate, wipe off the positive electrode coating with dust-free paper, rinse with NMP until no black or gray blocky substances with a diameter greater than 500 μm adhere, and dry naturally to obtain a sample to be tested;

[0062] (3) Take the sample to be tested and measure its thickness h (in μm). Use a blade to cut a sample with a width of 20 mm and a length of 100 mm. Fix the two ends of the cut sample on the clamp of the tensile testing machine. Use a high-speed rail tensile testing machine to pull at a speed of 1 mm / min until the sample is broken. The test is completed and the tensile force value F (in N) is obtained. The tensile strength is calculated using the following formula: R = F / (8×h).

[0063] In the present disclosure, the positive electrode sheet may further include a positive electrode coating, the positive electrode coating being located on at least one surface of the positive electrode current collector. The positive electrode coating may include a positive electrode additive.

[0064] In the present disclosure, the positive electrode coating may further include a positive electrode active material, and the positive electrode active material may include elemental cobalt.

[0065] The inventors of the present disclosure have found that when the positive electrode sheet includes a positive electrode additive, the cycle stability and service life of the lithium-ion battery can be improved. The reason may be that: during the later stage of cycling, the positive electrode sheet may undergo irreversible phase transformation due to excessive de-lithiation, thereby destroying the structural stability. A specific positive electrode additive can act as a lithium source supplement, thereby delaying the occurrence of irreversible phase transformation, reducing the deformation effect of the phase transformation of the positive electrode active material on the positive electrode current collector, and further reducing the occurrence of side reactions between the positive electrode and the electrolyte. And the inventors of the present disclosure have further found that the cycle stability and service life of the lithium-ion battery can be further improved by adjusting the mass content of elemental cobalt in the positive electrode active material, the mass content of the positive electrode additive in the positive electrode coating, and the mass content of the first additive in the electrolyte.

[0066] In the present disclosure, the mass content of elemental cobalt in the positive electrode active material is c, and the mass content of the positive electrode additive in the positive electrode coating is b, satisfying 0 < c / (a + b) ≤ 100. For example, c / (a + b) is equal to 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100.

[0067] In one example, 15 ≤ c / (a + b) ≤ 50.

[0068] In the present disclosure, b can be 0.1% - 1%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%.

[0069] In one example, b is 0.2% - 0.6%.

[0070] In the present disclosure, c can be 35% - 80%, for example, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%.

[0071] In the present disclosure, the positive electrode active material may include a transition metal lithium oxide. The chemical formula of the transition metal lithium oxide may be Li 1+e Ni f Co g M 1 hO2, where, -0.1 ≤ e ≤ 1; 0 ≤ f < 1, 0 < g ≤ 1, and 0 < f + g ≤ 1, 0 ≤ h < 1, M 1It may include at least one of Y, La, B, P, Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo and Zr.

[0072] In one example, the positive electrode active material includes lithium cobalt oxide.

[0073] In the present disclosure, the mass content of the element cobalt in the positive electrode active material and the mass content of the positive electrode additive in the positive electrode coating can be obtained by testing using conventional testing methods in the art. For example, the mass content of the element cobalt in the positive electrode active material is obtained by ICP (inductively coupled plasma) testing; the mass content of the positive electrode additive in the positive electrode coating is obtained by ICP testing.

[0074] In the present disclosure, the positive electrode additive may include Li x R y Q z M 2 d The substance shown, wherein 1≤x≤10 (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10), 0≤y≤10 (e.g., 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10), 0≤z≤10 (e.g., 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10), 1≤d≤15 (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15), R may include at least one of P, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, La, and Zr, Q may include at least one of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, La, and Zr, M 2 At least one of O and S may be included.

[0075] The inventors of the present disclosure have discovered that specific cathode additives can further reduce the side reactions between the electrolyte and the cathode active material, and alleviate the phase transition caused by excessive delithiation in the late cycle.

[0076] In one embodiment, the positive electrode additive includes LLZO (Li7La3Zr2O 12 )、Li2O、Li3PS4、Li7P3S 11 , at least one of LiNiO2, LiMnO2 and LiTiO2.

[0077] In the present disclosure, the positive electrode sheet may further include a carbon primer layer, wherein the carbon primer layer is located between the positive electrode current collector and the positive electrode coating layer.

[0078] In the present disclosure, the positive electrode coating layer may further include a positive electrode conductor and a positive electrode binder.

[0079] In the present disclosure, based on the total weight of the positive electrode coating, the content of the positive electrode active material may be 75%-99.7% (e.g., 75%, 80%, 85%, 90%, 95% or 99.7%), the content of the positive electrode additive may be 0.1%-5% (e.g., 5%, 4%, 3%, 2%, 1%, 0.5% or 0.1%), the content of the positive electrode conductor may be 0.1%-10% (e.g., 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5% or 0.1%), and the content of the positive electrode binder may be 0.1%-10% (e.g., 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5% or 0.1%).

[0080] In one example, based on the total weight of the positive electrode coating, the content of the positive electrode active material is 85%-99.4%, the content of the positive electrode additive is 0.2%-5%, the content of the positive electrode conductor is 0.2%-5%, and the content of the positive electrode binder is 0.2%-5%.

[0081] In one example, based on the total weight of the positive electrode coating, the content of the positive electrode active material is 93.4%-97.8%, the content of the positive electrode additive is 0.2%-0.6%, the content of the positive electrode conductor is 1%-3%, and the content of the positive electrode binder is 1%-3%.

[0082] The positive electrode conductive agent may include a conductive agent commonly used in the art, such as at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes (including single-walled carbon nanotubes and multi-walled carbon nanotubes), metal powder, and carbon fiber. The positive electrode binder may be a binder commonly used in the art, such as at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene, and polyethylene oxide.

[0083] <Negative electrode sheet and separator>

[0084] In the present disclosure, the components of the lithium-ion battery other than the electrolyte and the positive electrode (such as the negative electrode and the separator) can be conventionally selected in the art.

[0085] In one example, the lithium-ion battery is a wound battery.

[0086] In one example, the lithium-ion battery further includes a negative electrode sheet and a separator.

[0087] In the present disclosure, the negative electrode sheet may include a negative electrode current collector and a negative electrode coating on at least one side of the negative electrode current collector. The negative electrode coating may include a negative electrode active material.

[0088] In the present disclosure, the negative electrode active material may be a conventional choice in the art. For example, the negative electrode active material includes at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon, and soft carbon.

[0089] In the present disclosure, the negative electrode coating may further include a negative electrode conductive agent and a negative electrode binder. The negative electrode conductive agent may include a conductive agent commonly used in the art, for example, at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes (which may include single-walled carbon nanotubes and multi-walled carbon nanotubes), metal powder, and carbon fiber. The negative electrode binder may be selected from binders commonly used in the art, for example, at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene, and polyethylene oxide.

[0090] In the present disclosure, based on the total weight of the negative electrode coating, the content of the negative electrode active material may be 80%-99.8% (e.g., 80%, 85%, 90%, 95% or 99.8%), the content of the negative electrode conductor may be 0.1%-10% (e.g., 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5% or 0.1%), and the content of the negative electrode binder may be 0.1%-10% (e.g., 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5% or 0.1%).

[0091] In one example, based on the total weight of the negative electrode coating, the content of the negative electrode active material is 90%-99.6%, the content of the negative electrode conductor is 0.2%-5%, and the content of the negative electrode binder is 0.2%-5%.

[0092] In the present disclosure, the separator may include separators commonly used in the art, for example, a polyethylene film.

[0093] The lithium-ion battery can be assembled in accordance with conventional methods in the art.

[0094] It should be noted that the numerical expressions such as "first" and "second" in the present disclosure are only used to distinguish different substances or usage methods, and do not represent a difference in order.

[0095] The present disclosure will be described in detail below through examples. The examples described in this disclosure are only a portion of the examples of the present disclosure, not all of the examples. Based on the examples in this disclosure, all other examples obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this disclosure.

[0096] In the following examples, unless otherwise specified, all materials used were commercially available analytical grade.

[0097] The following examples are used to illustrate the lithium-ion batteries of the present disclosure.

[0098] Example 1

[0099] Follow these steps to prepare a lithium-ion battery:

[0100] (1) Preparation of electrolyte

[0101] In a glove box filled with argon (H2O <0.1ppm, O2 <0.1ppm), EC, PC, DEC, PP and EP were mixed in a mass ratio of 1:1:2:4:2, 1 mol / L lithium hexafluorophosphate (LiPF6) was added, the first additive (II-2) was added, and 9% FEC and 3% PS based on the total mass of the electrolyte were added.

[0102] (2) Preparation of positive electrode sheet

[0103] Lithium cobalt oxide (the mass content of element Co in lithium cobalt oxide is 60%), polyvinylidene fluoride, conductive carbon black (SP) and single-walled carbon nanotubes are mixed in a mass ratio of 96:2:1.5:0.5, a certain mass content of positive electrode additives is added, and N-methylpyrrolidone (NMP) is added with a solid content of 75wt%. The mixture is stirred under the action of a vacuum mixer until the mixed system becomes a positive electrode active slurry with uniform fluidity; the positive electrode active slurry is evenly coated on both surfaces of an aluminum foil; the coated aluminum foil is dried, and then rolled and slit to obtain the desired positive electrode sheet.

[0104] (3) Preparation of negative electrode sheet

[0105] Artificial graphite, sodium carboxymethyl cellulose, styrene-butadiene rubber, conductive carbon black (SP) and single-walled carbon nanotubes were mixed in a mass ratio of 94.5:2.5:1.5:1:0.5, and deionized water was added to obtain a solid content of 65 wt%. A negative electrode active slurry was obtained under the action of a vacuum mixer; the negative electrode active slurry was evenly coated on both surfaces of a copper foil; the coated copper foil was dried at room temperature, then transferred to an 80°C oven for drying for 10 hours, and then cold pressed and slit to obtain a negative electrode sheet.

[0106] (4) Preparation of lithium-ion batteries

[0107] The positive electrode sheet prepared in step (2), the negative electrode sheet prepared in step (3), and a separator (polyethylene film) are stacked in the order of positive electrode sheet, separator, and negative electrode sheet, and then wound to obtain a battery cell; the battery cell is placed in an outer packaging aluminum foil, and the electrolyte prepared in step (1) is injected into the outer packaging. After vacuum packaging, standing, forming, shaping, and sorting, a lithium-ion battery is obtained. The lithium-ion battery disclosed in the present invention has a charge and discharge range of 3.0V to 4.53V.

[0108] Examples 2-11 and Comparative Examples 1-3 were carried out with reference to Example 1 above, except that the composition of the electrolyte was changed (Example 10 removed the second additives FEC and PS), the type and mass content of the positive electrode additives in the positive electrode coating, the tensile strength of the positive electrode collector, the positive electrode collector (Examples 11a-11d used carbon-coated aluminum foil), and the positive electrode active material (the positive electrode active material of Example 7a was lithium cobalt oxide with a mass content of 80% of the Co element, and the positive electrode active material of Example 7b was a mixture of lithium cobalt oxide and lithium nickel cobalt manganese oxide 622 in a mass ratio of 6:4, wherein the mass content of the Co element was 35%), as shown in Table 1.

[0109] Table 1 Note: "X" in Table 1 represents the mass content of the group represented by formula i and / or the group represented by formula ii in the electrolyte.

[0110] Test Case

[0111] (1) 45℃ cycle performance test

[0112] The lithium-ion batteries prepared in the examples and comparative examples were subjected to cycle performance tests at 45°C. The specific test methods are as follows:

[0113] 1. Place at 45℃±2℃ for 10 minutes;

[0114] 2. Discharge at 0.2C to the lower limit voltage of 3.0V; let it stand for 10 minutes;

[0115] 3. Charge at 0.7C to the upper limit voltage of 4.53V, cut off at 0.05C, and let it stand for 10 minutes;

[0116] 4. Discharge at 0.2C to the lower limit voltage of 3.0V (discharge capacity in the first week of testing is x1 mAh);

[0117] 5. Let it stand for 10 minutes;

[0118] 6. 2C charging to the upper limit voltage of 4.53V, 0.05C cut-off;

[0119] 7. Place at 45℃±2℃ for 10 minutes;

[0120] 8. Discharge at 0.7C to the lower limit voltage of 3.0V; let it stand for 10 minutes;

[0121] 9. Charge at 2C to the upper limit voltage of 4.53V, cut off at 0.05C, and let it stand for 10 minutes;

[0122] Steps 8 to 9 were cycled 300 / 500 / 800 times; the discharge capacity of the Nth cycle was calculated as y1 mAh; the capacity of the Nth cycle was divided by the capacity of the first cycle to obtain the cycle capacity retention rate of the Nth cycle R1 = y1 / x1, and the results are recorded in Table 2.

[0123] (2) 85℃ high temperature storage test

[0124] The lithium-ion batteries prepared in the examples and comparative examples were allowed to stand for 10 minutes, then discharged at 0.2C to a lower voltage of 3.0V and allowed to stand for 10 minutes; then fully charged at 0.5C to an upper voltage of 4.53V, cut off at 0.05C, and allowed to stand for 10 minutes; the voltage, internal resistance, and thickness of the fully charged state were tested at 25±5°C. After the fully charged lithium-ion batteries were placed in an 85°C oven for 8 hours, the hot lithium-ion batteries were taken out and tested for voltage, internal resistance, thickness, and capacity retention and recovery tests. The results are recorded in Table 2.

[0125] Table 2

[0126] As can be seen from Table 2, compared with the comparative example, the 45°C cycle capacity retention rate and 85°C high-temperature storage performance of the lithium-ion battery disclosed in the present invention are significantly improved.

[0127] The preferred embodiments of the present disclosure are described in detail above, but the present disclosure is not limited thereto. Within the technical concept of the present disclosure, various simple variations of the technical solution of the present disclosure may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed by the present disclosure and fall within the scope of protection of the present disclosure.

Claims

1. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode sheet and an electrolyte; the positive electrode sheet includes a positive electrode current collector; the electrolyte includes a first additive, and the first additive includes a cyano group and a group represented by Formula I and / or a group represented by Formula II. The tensile strength of the positive current collector is L MPa. In the electrolyte, the mass content of the first additive is a%, satisfying 0.05 ≤ 100×a / L ≤ 5.

2. The lithium ion battery according to claim 1, wherein, 0.25 ≤ 100×a / L ≤ 2.5; preferably, 0.5 ≤ 100×a / L ≤ 1.

5.

3. The lithium ion battery according to claim 1 or 2, wherein, a is 0.1% - 10%; preferably 0.5% - 5%; more preferably 1% - 3%.

4. The lithium-ion battery according to any one of claims 1 to 3, wherein, The positive current collector includes at least one of aluminum, aluminum alloy, and composite current collector; Preferably, L is 100 MPa - 1000 MPa; More preferably, L is 133 MPa - 400 MPa; More preferably, L is 600 MPa - 800 MPa.

5. The lithium-ion battery according to any one of claims 1-4, wherein, The mass content of the group represented by formula (i) and / or the group represented by formula (ii) in the electrolyte is 0.003% - 1.6%, and the mass content of cyano group in the electrolyte is 0.008% - 4%; Preferably, the mass content of the group represented by formula (i) and / or the group represented by formula (ii) in the electrolyte is 0.03% - 0.48%, and the mass content of cyano group in the electrolyte is 0.08% - 1.2%; More preferably, the mass content of the group represented by formula (i) and / or the group represented by formula (ii) in the electrolyte is 0.1% - 0.4%, and the mass content of cyano group in the electrolyte is 0.3% - 1%.

6. The lithium-ion battery according to any one of claims 1-5, wherein, The first additive includes the substance represented by Formula I and / or the substance represented by Formula II, Wherein, m1, m2, and m3 are each independently selected from integers greater than or equal to 1, and n1, n2, and n3 are each independently selected from integers greater than or equal to 1; Preferably, m1, m2, and m3 are each independently selected from integers of 1 - 20, and n1, n2, and n3 are each independently selected from integers of 1 - 20; Preferably, m1 = m2 = m3, n1 = n2 = n3.

7. The lithium-ion battery according to any one of claims 1-6, wherein, The first additive includes at least one of; Preferably, the first additive includes at least one of 8. The lithium ion battery according to any one of claims 1-7, wherein, The electrolyte further includes an organic solvent, and the organic solvent includes at least one of carbonate compounds and carboxylate compounds; Preferably, the carbonate compounds include at least one of the following solvents with or without fluorine substitution and ethylene carbonate: propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; Preferably, the carboxylate compounds include at least one of the following solvents with or without fluorine substitution: propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, propyl propionate, ethyl propionate, methyl butyrate, and n-butyl ethyl acetate.

9. The lithium ion battery according to claim 8, wherein, The organic solvent includes propyl propionate and ethyl propionate; Preferably, the mass content ratio of propyl propionate to ethyl propionate is (1 - 2):1; Preferably, the mass ratio of the first additive to the total mass of propyl propionate and ethyl propionate is (0.015 - 0.05):

1.

10. The electrolyte according to any one of claims 1-9, wherein, The electrolyte further includes a second additive, and the second additive includes at least one of fluoroethylene carbonate, 1,3 - propane sultone, and vinylene carbonate.

11. The lithium-ion battery according to any one of claims 1 to 10, wherein, The positive electrode sheet further includes a positive electrode coating, the positive electrode coating is located on at least one surface of the positive current collector, and the positive electrode coating includes a positive electrode active material, and the positive electrode active material includes cobalt element; Preferably, the positive electrode active material includes a transition metal lithium oxide; the chemical formula of the transition metal lithium oxide is Li 1+e Ni f Co g M 1 hO2, where, -0.1 ≤ e ≤ 1; 0 ≤ f < 1, 0 < g ≤ 1, and 0 < f + g ≤ 1, 0 ≤ h < 1, M 1 includes at least one of Y, La, B, P, Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr.

12. The lithium ion battery according to claim 11, wherein, The positive electrode coating further includes a positive electrode additive; the positive electrode additive includes Li x R y Q z M 2 d The substance shown, where 1 ≤ x ≤ 10, 0 ≤ y ≤ 10, 0 ≤ z ≤ 10, 1 ≤ d ≤ 15, R includes at least one of P, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, La, and Zr, Q includes at least one of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, La, and Zr, and M 2 includes at least one of O and S; Preferably, the positive electrode additive includes at least one of LLZO, Li2O, Li3PS4, Li7P3S 11 , LiNiO2, LiMnO2, and LiTiO2.

13. The lithium ion battery according to claim 12, wherein, The mass content of the cobalt element in the positive electrode active material is c, the mass content of the positive electrode additive in the positive electrode coating is b, and the mass content of the first additive in the electrolyte is a, satisfying 0 < c / (a + b) ≤ 100; preferably, 15 ≤ c / (a + b) ≤ 50.

14. The lithium-ion battery according to claim 13, wherein, b is 0.1% - 1%, preferably 0.2% - 0.6%; and / or, c is 35% - 80%.

15. The lithium-ion battery according to any one of claims 1-14, wherein, The positive electrode sheet further includes a positive electrode coating located on at least one surface of the positive electrode current collector; the positive electrode sheet further includes a bottom carbon layer located between the positive electrode current collector and the positive electrode coating.

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