A lithium-ion battery

Abstract

The present application relates to the technical field of battery, and particularly relates to a lithium ion battery. The lithium ion battery comprises an electrolyte, a negative electrode sheet and a positive electrode sheet. The electrolyte comprises a fluorinated solvent, and the weight content of the fluorinated solvent is f wt% based on the total weight of the electrolyte. The ratio of the width of the negative electrode sheet to the width of the positive electrode sheet is g. The lithium ion battery satisfies the following relationship: 2 <= f / g <= 30. The lithium ion battery of the present application controls the relationship between the weight content of the fluorinated solvent in the electrolyte and the ratio of the widths of the positive and negative electrode sheets, so that the fluorinated solvent can form a SEI film rich in LiF on the surfaces of the positive and negative electrodes and the edges of the negative electrode sheet. The SEI film rich in LiF has a relatively thin thickness and high toughness, which can reduce the short circuit risk caused by the burrs on the edges of the negative electrode sheet, improve the diffusion speed of lithium ions in the electrolyte, and improve the lithium precipitation, thereby improving the safety performance and cycle stability of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a lithium ion battery. BACKGROUND

[0002] In recent years, lithium ion batteries have made significant progress in energy density, safety, charging speed, cycle life and other aspects, which provides better support and guarantee for their wide application in various application scenarios. However, the lithium precipitation problem of lithium ion batteries hinders the further development of lithium ion batteries. SUMMARY

[0003] The lithium precipitation problem of lithium ion batteries can be solved by adding a functionalized solvent to the electrolyte, which has a specific functional group and can improve the safety and cycle performance of the battery. For example, by adding a fluorinated solvent to the organic solvent to improve the solubility of the organic solvent to lithium salt and improve the stability of the electrolyte, thereby improving the lithium precipitation of the battery and improving the safety and cycle performance of the battery. However, burrs will be generated at the edge of the negative electrode sheet after slitting, and the burrs at the edge of the negative electrode sheet will increase the risk of short circuit of the battery, affecting the safety and cycle performance of the battery.

[0004] In order to overcome the above technical problems existing in the prior art, the present application provides a lithium ion battery. The lithium ion battery of the present application controls the relationship between the weight content of the fluorinated solvent in the electrolyte and the width ratio of the positive and negative electrode sheets, so that the fluorinated solvent can form a SEI film rich in LiF on the surface of the positive and negative electrodes and the edge of the negative electrode sheet. The thickness of the SEI film rich in LiF is relatively thin and has high toughness, which can reduce the short circuit risk caused by the burrs at the edge of the negative electrode sheet, and at the same time improve the diffusion speed of lithium ions in the electrolyte, improve the lithium precipitation, and improve the safety and cycle stability of the battery.

[0005] The present application provides a lithium ion battery, wherein the lithium ion battery comprises an electrolyte, a negative electrode sheet and a positive electrode sheet, wherein the electrolyte comprises a fluorinated solvent, and the weight content of the fluorinated solvent is f wt% based on the total weight of the electrolyte; the width ratio of the negative electrode sheet to the positive electrode sheet is g, and the lithium ion battery satisfies the following relationship: 2≤f / g≤30.

[0006] Compared with the prior art, the present application has at least the following advantages:

[0007] The lithium ion battery of the present application can improve the stability of the interface between the positive and negative electrode sheets and the electrolyte, reduce the concentration polarization and electrochemical reaction polarization phenomenon of the electrolyte during lithium extraction, especially can form a SEI film with strong toughness around the burr of the negative electrode sheet, make the current of the burr part of the negative electrode sheet more uniform, reduce the short circuit risk caused by the burr of the negative electrode sheet edge, improve the cycle performance and safety performance of the battery, and at the same time in the cycle process, the fluorinated solvent in the electrolyte can repair the SEI film in time, so that the battery maintains high cycle performance, improves the transmission rate of lithium ion in the electrolyte, and improves the lithium precipitation situation.

[0008] Other features and advantages of the present application will be described in detail in the following specific embodiments.

[0009] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as exactly that endpoint. Any values that fall within common interpretations of the endpoints should be considered as if explicitly written herein. For values having an inherent range, such as pH, molecular weight, etc., the endpoints are presented as a range between the lower and upper limits of that range. For numerical values, the endpoints between any lower value and any upper value, between any lower value and a singular value, and between a singular value and any upper value can be combined to create one or more new ranges. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 The schematic diagram of the negative electrode sheet and the positive electrode sheet of the present application is shown.

[0011] Figure 2 The structural schematic diagram of the negative electrode sheet of the present application is shown.

[0012] Figure 3 The structural schematic diagram of the positive electrode current collector of the present application is shown.

[0013] Figure 4 The schematic diagram of the tab in an embodiment of the present application is shown. DETAILED DESCRIPTION

[0014] The specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application. In this paper, the data range includes the end point without special explanation.

[0015] It should be noted that the "first", "second" and the like in the present disclosure are only used to distinguish different substances or use methods, and do not represent the difference in order.

[0016] The present application provides a lithium ion battery, wherein the lithium ion battery comprises an electrolyte, a negative electrode sheet and a positive electrode sheet, wherein the electrolyte comprises a fluorinated solvent, the weight content of the fluorinated solvent is f wt% based on the total weight of the electrolyte; the ratio of the width of the negative electrode sheet to the width of the positive electrode sheet is g, and the lithium ion battery satisfies the following relationship: 2≤f / g≤30.

[0017] Figure 1 The schematic diagram of the negative electrode sheet and the positive electrode sheet stacked is shown, in order to illustrate the relative relationship between the width of the negative electrode sheet and the width of the positive electrode sheet, Figure 1 The separator is omitted in the figure, but the separator exists in the lithium ion battery, which can isolate the positive electrode sheet and the negative electrode sheet. As shown in Figure 1 The width b1 of the negative electrode sheet 1 is greater than the width b2 of the positive electrode sheet 2, and the ratio g of the width of the negative electrode sheet to the width of the positive electrode sheet is b2 / b1. In the present application, the width is the length in the width direction.

[0018] The lithium ion battery of the present application can be a lithium ion battery with a roll core structure or a lithium ion battery with a stacked structure. For the lithium ion battery with a roll core structure, the positive electrode sheet and the negative electrode sheet can be stacked as shown in Figure 1 The positive electrode sheet and the negative electrode sheet can be stacked as shown in Figure 1 The positive electrode sheet and the negative electrode sheet can be stacked as shown in Figure 1 The positive electrode sheet and the negative electrode sheet can be stacked as shown in

[0019] The electrolyte of the present application comprises a fluorinated solvent, which forms a solvation sheath around the lithium ion during the first discharge. In the sheath, the fluorinated solvent has a high anion concentration, which increases the LUMO energy level of the anion, and can promote the SEI film to be rich in LiF. The SEI film rich in LiF has a higher Young's modulus and a more uniform lithium ion flux, which can make the lithium dendrites more tend to grow in a plane, so as to make the interface between the electrolyte and the positive and negative electrode sheets more stable, and reduce the concentration polarization of the electrolyte and the electrochemical polarization phenomenon of the deintercalated lithium.

[0020] By controlling the relationship between the weight content of the fluorinated solvent in the electrolyte and the width ratio of the positive and negative electrode sheets, the fluorinated solvent can form a SEI film rich in LiF at the edge burr of the negative electrode sheet. The SEI film has a thinner thickness, higher toughness and lower impedance, which can promote the diffusion and transmission of ions, improve the lithium precipitation situation of the interface between the negative electrode sheet and the electrolyte, and continuously repair the SEI film during the cycle process to ensure the high stability of the SEI film near the burr of the negative electrode sheet, avoid the local polarization of the surface of the negative electrode sheet caused by the uneven current of the burr part of the negative electrode sheet, reduce the risk of short circuit caused by the edge burr of the negative electrode sheet, and improve the transmission rate of lithium ions in the electrolyte, thereby enabling the battery to maintain long cycle performance and high safety performance.

[0021] The lithium ion battery can satisfy the following relationship: 2≤f / g≤30 (for example, 2, 5, 8, 10, 12, 15, 18, 20, 22, 25, 28 or 30). When f / g<2, the content of the fluorinated solvent is low or the width ratio of the negative electrode sheet to the positive electrode sheet is too high, the content of the fluorinated solvent in the electrolyte is too low, and a SEI film rich in LiF cannot be formed on the surface of the positive and negative electrodes, and the SEI film cannot be repaired in time during the cycle process, so that the polarization and short circuit problems caused by the burr of the negative electrode sheet cannot be effectively improved. The width ratio of the negative electrode sheet to the positive electrode sheet is too high, which can reduce the effective surface area of the electrode and increase the burr of the negative electrode, greatly increasing the micro-short circuit situation during the cycle process. When f / g>30, the content of the fluorinated solvent is high or the width ratio of the negative electrode sheet to the positive electrode sheet is too low, the fluorinated solvent is too high, the viscosity of the electrolyte increases, and the risk of lithium precipitation of the battery increases. The width ratio of the negative electrode sheet to the positive electrode sheet is too low, which can reduce the lithium intercalation capacity of the negative electrode sheet compared to the positive electrode sheet. In addition, a high content of the fluorinated solvent can further slow down the rate of lithium ion intercalation into the negative electrode sheet, making the lithium ion intercalation rate of the negative electrode sheet slower.

[0022] In the present application, by controlling the relationship between the weight content of the fluorinated solvent in the electrolyte and the width ratio of the positive and negative electrode sheets, the battery can achieve higher safety performance and more stable cycle performance compared to the prior art. In order to further improve the effect, one or more technical features can be further optimized.

[0023] In an example, the lithium ion battery satisfies the following relationship: 6≤f / g≤15.

[0024] In an example, 3 wt%≤f wt%≤30 wt% (e.g., 3 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, or 30 wt%). Controlling the weight content of the fluorinated solvent in the electrolyte within the above range can moderate the viscosity of the electrolyte, increase the transport rate of lithium ions in the electrolyte, increase the solubility of lithium salt in the electrolyte, increase the conductivity of the electrolyte, and improve the cycle stability of the battery.

[0025] In an example, 5 wt%≤f wt%≤20 wt%.

[0026] In an example, the fluorinated solvent includes one or more of fluorinated carbonate, fluorinated carboxylate, fluorinated ether, fluorinated benzene, fluorinated phosphate, and fluorinated olefin. The fluorinated solvent has a high dielectric constant, which is conducive to the dissolution and dissociation of lithium salt, thereby improving the cycle performance of the battery, and can also form a protective film on the surface of the positive current collector to inhibit the corrosion of the positive current collector (aluminum foil).

[0027] In an example, the number of fluorine substitutions in the fluorinated solvent is ≤2 (e.g., 1 or 2). When the number of fluorine substitutions in the fluorinated solvent is higher than 2, the viscosity of the electrolyte increases, which leads to easy lithium precipitation of the electrolyte, and the structure of the fluorinated solvent is unstable, and the fluorine element in the fluorinated solvent is prone to breakage to form HF to corrode the positive electrode sheet during the cycle process. Therefore, the number of fluorine substitutions in the fluorinated solvent needs to be controlled to be ≤2.

[0028] In an example, the fluorinated carbonate includes monofluoroethylene carbonate and / or monofluoromethylethylene carbonate.

[0029] In an example, the fluorinated carboxylate includes one or more of monofluoroethyl acetate, dimethyl difluoroacetate, ethyl difluoroacetate (DFEA), and vinyl difluoroacetate.

[0030] In an example, the fluorinated ether includes one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane (DTDL), and octafluoropentyl-tetrafluoroethyl ether.

[0031] In an example, the fluorinated benzene includes one or more of fluorobenzene and 1,2-difluorobenzene.

[0032] In an example, the fluorinated phosphate includes one or more of tris(2,2,2-trifluoroethyl) phosphate and bis(2,2,2-trifluoroethyl)-ethyl phosphate.

[0033] In an example, the fluorinated olefin includes one or more of 1,2-difluoroethylene, monofluoroethylene, and monofluoropropylene.

[0034] In one example, 1.01 ≤ g ≤ 1.08 (e.g., 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08). By controlling the ratio of the width of the negative electrode to the width of the positive electrode, the effective surface area of ​​the electrode can be increased, the available capacity of the electrode active material can be improved, and thus the energy density of the battery can be increased.

[0035] In one instance, 1.03 ≤ g ≤ 1.06.

[0036] In one example, the ratio n of the area of ​​the negative electrode to the area of ​​the positive electrode is (1.01-1.12):1 (e.g., 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, 1.11, or 1.12). By controlling the ratio of the area of ​​the negative electrode to the area of ​​the positive electrode, the effective surface area of ​​the electrode can be increased, the available capacity of the electrode active material can be improved, and thus the energy density of the battery can be increased.

[0037] In one instance, n is (1.03-1.08):1.

[0038] In one example, 1.01 ≤ g ≤ 1.08 and n is (1.01 - 1.12):1. The values ​​of g and n can be the same or different. When the values ​​of g and n are the same, it means that the ratio of the width of the negative electrode to the width of the positive electrode and the ratio of the area of ​​the negative electrode to the area of ​​the positive electrode are the same, and the lengths of the positive and negative electrodes are the same. When the values ​​of g and n are different, it means that the ratio of the width of the negative electrode to the width of the positive electrode and the ratio of the area of ​​the negative electrode to the area of ​​the positive electrode are different, and the lengths of the positive and negative electrodes are different.

[0039] In one instance, 1.03 ≤ g ≤ 1.06 and n is (1.03 - 1.08): 1.

[0040] like Figure 2 As shown, the negative electrode sheet 1 includes a negative electrode current collector 11 and a negative electrode active material layer. The negative electrode current collector 11 includes a single-sided region 111 and a double-sided region 112. The negative electrode active material layer includes a first negative electrode active material layer 121, a second negative electrode active material layer 122 and a third negative electrode active material layer 123. In the single-sided region 111, the third negative electrode active material layer 123 is located on the surface of the negative electrode current collector on one side. In the double-sided region 112, the first negative electrode active material layer 121 and the second negative electrode active material layer 122 are located on the surfaces of the negative electrode current collector 11 on both sides.

[0041] When the lithium ion battery is a lithium ion battery with a winding core structure, the single-sided area is located at the tail of the winding core structure.

[0042] In an example, the thickness of the third negative electrode active material layer in the single-sided area is h, in units of μm, and the lithium ion battery satisfies the following relationship: 0.1≤f / h≤0.7 (for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, or 0.7).

[0043] In the single-sided area of the negative electrode sheet, since the negative electrode active material layer is coated only on one side of the negative electrode current collector, the current density is high, which easily causes local overheating of the negative electrode sheet and exacerbates the lithium precipitation on the surface of the negative electrode sheet. The present inventors have found through research that by controlling the relationship between the weight content of the fluorinated solvent in the electrolyte and the thickness of the third negative electrode active material layer in the single-sided area, a low-impedance SEI film rich in LiF can be formed on the surface of the single-sided area, thereby alleviating the lithium precipitation on the surface of the negative electrode sheet caused by local overheating, and the fluorinated solvent can accelerate the desolvation of lithium ions and the deintercalation of lithium ions, thereby avoiding the deposition of transition metals and the side reactions of electrolyte decomposition.

[0044] In an example, the lithium ion battery satisfies the following relationship: 0.23≤f / h≤0.5.

[0045] In an example, 30 μm≤hμm≤75 μm. Controlling h in the above range can avoid increasing the difficulty of deintercalation of lithium on the surface of the negative electrode sheet due to excessively high thickness, and the moderate thickness can enable the battery to maintain high performance while having high energy density.

[0046] In an example, 40 μm≤hμm≤68 μm.

[0047] In an example, the second negative electrode active material layer and the third negative electrode active material layer are located on the same side of the negative electrode current collector, the thickness of the first negative electrode active material layer is the same as or different from the thickness of the second negative electrode active material layer, and the ratio of the thickness of the first negative electrode active material layer to the thickness of the third negative electrode active material layer is 1:(0.8-0.99). By controlling the ratio of the thickness of the first negative electrode active material layer to the thickness of the third negative electrode active material layer, the overall thickness of the negative electrode active material layer in the negative electrode sheet can be controlled in an appropriate range, and the thickness of the third negative electrode active material layer is relatively thin, thereby helping to reduce the transmission path of electrons and ions, improve the electronic conductivity and ionic conductivity of the battery, and thus reduce the internal resistance of the battery and improve the lithium precipitation, thereby improving the charge-discharge efficiency and cycle performance of the battery.

[0048] In an example, the ratio of the thickness of the first negative electrode active material layer to the thickness of the third negative electrode active material layer is 1:(0.86-0.96).

[0049] In an example, the components and the weight content of each component of the first negative electrode active material layer, the second negative electrode active material layer, and the third negative electrode active material layer can be the same or different.

[0050] In an example, the components and the weight content of each component of the second negative electrode active material layer and the third negative electrode active material layer are the same.

[0051] In an example, the components and the weight content of each component of the first negative electrode active material layer and the second negative electrode active material layer are different.

[0052] In an example, the negative electrode active material layer includes a negative electrode active substance, and the negative electrode active substance includes a carbon-based material and / or a silicon-based material.

[0053] In an example, the carbon-based material includes at least one of natural graphite, artificial graphite, mesocarbon microbeads, soft carbon, and hard carbon.

[0054] In an example, the silicon-based material can include at least one of silicon, silicon-oxygen, silicon-carbon, and silicon alloy.

[0055] In an example, the negative electrode active material layer includes a negative electrode conductive agent and a negative electrode binder.

[0056] In an example, the negative electrode conductive agent includes at least one of conductive carbon black (Super P), acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, and metal powder.

[0057] In an example, the negative electrode binder includes at least one of styrene butadiene rubber, sodium carboxymethyl cellulose, polyacrylic acid, polyvinyl alcohol, and polyvinylidene fluoride.

[0058] In an example, the weight content of the negative electrode active substance is 96wt%-98wt% (for example, 96wt%, 96.5wt%, 97wt%, 97.5wt%, or 98wt%) based on the total weight of the negative electrode active material layer, the weight content of the negative electrode conductive agent is 0.5wt%-2wt% (for example, 0.5wt%, 1wt%, 1.5wt%, or 2wt%), and the weight content of the negative electrode binder is 1wt%-2wt% (for example, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, or 2wt%).

[0059] In an example, the negative electrode current collector includes a polymer layer including PP and / or PE and copper foil layers on both sides of the surface of the polymer layer.

[0060] In order to further improve the safety of the battery, the negative electrode current collector of the present application adopts a composite current collector, such as Figure 3 As shown in the figure, the negative electrode current collector 11 includes a polymer layer 113 and a copper foil layer 114 on both sides of the polymer layer.

[0061] In an example, the composition of the polymer layer includes PP and / or PE.

[0062] Through research, the stronger the polarity of the solvent in the electrolyte, the greater the degree of corrosion of the copper foil. The electrolyte of the present application includes weakly polar fluorinated solvent, which can form a protective film after passivation on the surface of the copper foil. The protective film can improve the stability of the copper foil in the electrolyte environment, further reducing the degree of corrosion of the electrolyte on the negative electrode current collector. Through the synergistic effect of the negative electrode composite current collector and the fluorinated solvent in the electrolyte, the degree of corrosion of the electrolyte on the negative electrode current collector can be further reduced, and the corrosion resistance of the negative electrode current collector can be improved.

[0063] In an example, the copper foil layer is a copper foil.

[0064] In an example, the thickness of the copper foil layer is 0.3-1.5 μm (e.g., 0.3 μm, 0.5 μm, 0.8 μm, 1 μm, 1.3 μm or 1.5 μm). The thickness of the copper foil layer is the thickness of a single side. Both sides of the polymer layer have a copper foil layer, and the thickness of the copper foil layer on both sides is the same. Therefore, the thickness of the copper foil layer is the thickness of the copper foil layer on either side.

[0065] In an example, the thickness of the polymer layer is 4-8 μm (e.g., 4 μm, 5 μm, 6 μm, 7 μm or 8 μm).

[0066] In an example, the thickness of the copper foil layer t1 is 0.3-1.5 μm, and the thickness of the polymer layer is 4-8 μm. Controlling the thickness of the copper foil layer and the polymer layer within the above range can ensure that the thickness of the copper foil layer is thin, thereby accelerating the rate of electron transfer. The thickness of the polymer layer in the middle position is moderate, which can enhance the mechanical strength of the negative electrode current collector and improve the structural stability of the battery. Moreover, the polymer layer has excellent corrosion resistance and high temperature resistance, and can still maintain stable performance under extreme working conditions. Compared with conventional current collectors such as pure copper foil current collectors, the negative electrode current collector of the present application has a thinner thickness, better conductivity, stronger heat dissipation ability, and moderate weight, which can improve the weight energy density of the battery.

[0067] In an example, the lithium ion battery includes a negative tab, and the area of the negative tab is s, with the unit being mm 2then the lithium ion battery satisfies the following relationship: 0.1 ≤ f / s ≤ 3 (e.g., 0.1, 0.5, 1, 1.5, 2, 2.5, or 3).

[0068] The area s of the tab is the area of the overlap of the tab and the tab piece. In the present application, the lithium ion battery includes a negative tab, and the area s of the tab is the area of the positive tab, as shown in Figure 4 As shown, the area of the negative tab 31 of the negative tab piece 1 and the overlap portion 41 of the negative tab piece 1 is the area s of the tab.

[0069] In the case of long-term use, the tab is in the electrolyte environment and is affected by electrochemical corrosion. The corrosion causes the surface of the tab to be rough, thereby increasing the resistance and affecting the performance and efficiency of the battery. Currently, the purpose of corrosion prevention is achieved by covering the tab with adhesive paper. However, due to current overload, the negative tab piece quickly releases lithium, resulting in serious lithium precipitation at the edge of the tab.

[0070] To solve the above technical problems of the tab, the present application simultaneously controls the relationship between the weight content of the fluorinated solvent in the electrolyte and the size of the tab, and the fluorinated solvent forms a protective layer near the negative tab. The protective layer is ion-conducting and electron-non-conducting, thereby reducing the current overload near the tab, accelerating the release of lithium ions, and reducing lithium precipitation.

[0071] When f / s < 0.1, the weight content of the fluorinated solvent in the electrolyte is low, the film at the edge interface of the tab is unstable under high pressure, and the protective layer is repaired in time when it is damaged. When f / s > 3, the weight content of the fluorinated solvent in the electrolyte is too high, and the viscosity of the electrolyte is large, which seriously slows down the transmission rate of lithium ions in the electrolyte during the process of large-rate charging and discharging, and there is a risk of increasing lithium precipitation in the tab; if the current transmission density is too large, the tab size is too small, which will increase the resistance at the tab, cause local overheating, and increase the risk of battery safety.

[0072] In an example, the lithium ion battery satisfies the following relationship: 0.4 ≤ f / s ≤ 1.

[0073] In an example, 10 ≤ s ≤ 30 (e.g., 10, 15, 20, 25, or 30).

[0074] When s>30, the tab area is too large, the space occupation of the tab is increased, which leads to the increase of the size of the battery, especially when the battery is integrated in a limited space. The tab with too large area will increase the weight of the battery, reduce the energy density and power density of the battery, and increase the corresponding cost. However, the area of the tab cannot be too small, when s<10, the current carrying capacity is insufficient: the tab serves as a current conducting channel, if it is too small, it may not be able to carry enough current, resulting in too large current density, increasing the resistance at the tab, affecting the charge and discharge performance of the battery, and the tab with small area will limit the heat dissipation and heat dissipation capacity, which will cause local overheating of the battery, accelerate the aging and damage of the battery.

[0075] In an example, 15≤s≤25.

[0076] In an example, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer on one or both sides of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material, a positive electrode conductive agent and a positive electrode binder.

[0077] In an example, the positive electrode active material comprises at least one of lithium cobaltate, lithium nickel cobalt manganese acid, lithium nickel cobalt aluminum acid, lithium nickel cobalt manganese aluminum acid, lithium manganese acid, lithium nickel manganese acid, lithium nickel acid, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate and lithium-rich manganese.

[0078] In an example, the positive electrode conductive agent comprises at least one of conductive carbon black (Super P), acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube and metal powder.

[0079] In an example, the positive electrode binder comprises at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose, butadiene rubber, polytetrafluoroethylene and polyethylene oxide.

[0080] In an example, based on the total weight of the positive electrode active material layer, the weight content of the positive electrode active material is 96wt%-98.5wt%, the weight content of the positive electrode conductive agent is 0.5wt%-2wt%, and the weight content of the positive electrode binder is 0.5wt%-2wt%.

[0081] In an example, the electrolyte further comprises a lithium salt, ethylene carbonate (EC), propylene carbonate (PC), an organic solvent and an additive.

[0082] In an example, the lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluoro oxalate borate (LiDFOB), lithium bisfluorosulfonylimide (LiTFSI), lithium bis-trifluoromethylsulfonylimide, lithium difluorobisoxalate phosphate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methide, and lithium bis(trifluoromethylsulfonyl)imide. The lithium salt can affect the basic physical and chemical properties of the electrolyte, is an important component in the electrolyte that affects the characteristics of the lithium ion battery, has the effect of conducting lithium ions, and can improve the electrical conductivity of the electrolyte.

[0083] The ethylene carbonate (EC) can form an SEI film on the negative electrode sheet during the first charge and discharge process, improve the efficiency of lithium ion deintercalation in the negative electrode, and reduce the occurrence of side reactions.

[0084] The propylene carbonate (PC) has a high dielectric constant, can promote the dissociation of the lithium salt, and greatly improve the electrical conductivity of the ions in the electrolyte.

[0085] In an example, the organic solvent includes one or more of propyl propionate (PP), ethyl propionate (EP), ethyl butyrate (EB), ethyl acetate (EA), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0086] In an example, the additive includes one or more of 1,3-propane sulfolactone (PS), 1,3-propenenitrile lactone (PST), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), adiponitrile (ADN), succinonitrile (SN), fluoroethylene carbonate (FEC), and 1,3,6-hexane trinitrile (HTCN). Among them, succinonitrile (SN) and 1,3,6-hexane trinitrile (HTCN) mainly complex with cobalt ions in the positive electrode sheet to protect the positive electrode material from dissolving and falling out at high voltage; VC and PS preferentially form a film on the surface of the negative electrode sheet, making the SEI film more robust.

[0087] In an example, the weight content of the lithium salt is 10-21 wt%, the weight content of the EC is 0-15 wt%, the weight content of the PC is 7-15 wt%, the weight content of the organic solvent is 30-60 wt%, and the weight content of the additive is 15-25 wt%, based on the total weight of the electrolyte.

[0088] The present application will be described in detail below by way of examples. The examples described in the present application are only a part of the examples of the present application, but not all the examples. Based on the examples in the present application, all the other examples obtained by those skilled in the art without creative labor shall fall within the scope of protection of the present application.

[0089] The following examples are used to illustrate the lithium ion battery of the present application.

[0090] Example 1

[0091] (1) Preparation of the positive electrode sheet

[0092] The positive electrode active material (lithium cobaltate), the positive electrode conductive agent (Super P), and the positive electrode binder (polyvinylidene fluoride (PVDF)) were dispersed in an appropriate amount of N-methyl pyrrolidone (NMP) at a weight ratio of 98:1.2:0.8, and were fully stirred to form a uniform positive electrode slurry. The positive electrode slurry was coated on both sides of the positive electrode current collector (a conventional aluminum foil), and then was dried, rolled, cut (cutting size of 6.5 cm*120 cm), cleaned (cleaning area of 3*5 mm), and pasted with the positive tab adhesive to obtain the positive electrode sheet, wherein the width of the positive electrode sheet was 118 mm, and the area of the positive electrode sheet was 104481 mm 2 .

[0093] (2) Preparation of the negative electrode sheet

[0094] The negative electrode active material (graphite), the negative electrode conductive agent (Super P), and the negative electrode binder (styrene-butadiene rubber (SBR) 1.5 parts by weight and thickening agent sodium carboxymethyl cellulose (CMC) 0.5 parts by weight) were dispersed in an appropriate amount of deionized water at a weight ratio of 97:1:2, and were fully stirred to form a uniform negative electrode slurry. The negative electrode slurry was coated on the surface of the negative electrode current collector (a conventional copper foil) to form a negative electrode active material layer, wherein a first negative electrode active material layer and a second negative electrode active material layer were coated in the double-sided area of the negative electrode current collector, the thickness of the first negative electrode active material layer was 51.2 μm, and the thickness of the second negative electrode active material layer was 51.2 μm. A third negative electrode active material layer was coated on one side surface (on the same side as the second negative electrode active material layer) of the single-sided area of the negative electrode current collector, and the thickness of the third negative electrode active material layer was 49.1 μm. Then, the negative electrode sheet was obtained by drying, rolling, cutting (cutting size of 6.8 cm*120.5 cm), cleaning, and pasting with the negative tab adhesive.

[0095] The width of the negative electrode sheet was 123 mm, and the area of the negative electrode sheet was 109456 mm 2 , the ratio of the thickness of the first negative electrode active material layer to the third negative electrode active material was 1:0.959, and the area of the negative electrode tab was 15 mm 2 .

[0096] (3) Preparation of electrolyte

[0097] Preparation of components: fluorinated solvent: DFEA (wherein the number of fluorine substitution in the fluorinated solvent is 2), 12 parts by weight; EC, 10 parts by weight; PC, 10 parts by weight; organic solvent: PP, 35 parts by weight; lithium salt: lithium hexafluorophosphate, 15 parts by weight; additives: PS, 3 parts by weight, FEC, 8 parts by weight; SN, 2 parts by weight, HTCN, 3 parts by weight, ADN (2 parts) in total 18 parts by weight.

[0098] The EC / PC / PP / DFEA is mixed uniformly in a glove box (H2O < 0.01 ppm, O2 < 0.01 ppm, Ar atmosphere), and then the fully dried lithium salt is added thereto, and after dissolution, the additives are added, and stirred uniformly, and after passing the moisture and free acid detection, the required electrolyte is obtained.

[0099] (4) Separator

[0100] The separator is composed of a substrate layer and a coating layer located on both sides of the substrate layer, and the components of the substrate layer are PP / PE, the coating layer located on one side of the substrate layer is PVDF, and the coating layer located on the other side of the substrate layer is PMMA.

[0101] (5) Preparation of lithium ion battery

[0102] The positive electrode sheet of step (1), the separator of step (4), and the negative electrode sheet of step (2) are wound to obtain a bare battery without liquid injection, the bare battery is placed in an outer packaging foil, the electrolyte of step (3) is injected into the dried bare battery, and after passing through the processes of vacuum packaging, standing, formation, shaping, sorting, etc., the required lithium ion battery is obtained.

[0103] Wherein, the ratio g of the width of the negative electrode sheet to the width of the positive electrode sheet is 1.04, the ratio n of the area of the negative electrode sheet to the area of the positive electrode sheet is 1.05, f / g = 12 / 1.04 = 11.51, f / h = 0.244, and f / s = 0.8.

[0104] Example 2

[0105] Reference is made to Example 1, except that the negative current collector is a composite current collector, which includes a polymer layer and a copper foil layer located on both sides of the polymer, wherein the polymer layer is PP, and the thickness of the polymer layer is 6 μm, and the thickness of the copper foil layer is 1 μm.

[0106] Example 3 group

[0107] This group of examples is used to illustrate the influence when f / g changes.

[0108] Example 3a

[0109] Example 1 was followed except that the weight content of the fluorinated solvent in the electrolyte was f% = 5%, accordingly f / g = 4.8, f / h = 0.102, f / s = 0.333.

[0110] Example 3b

[0111] Example 1 was followed except that the weight content of the fluorinated solvent in the electrolyte was f% = 18%, accordingly f / g = 17.27, f / h = 0.367, f / s = 1.2.

[0112] Example 3c

[0113] Example 1 was followed except that the weight content of the fluorinated solvent in the electrolyte was f% = 31%, accordingly f / g = 29.81, f / h = 0.631, f / s = 2.067.

[0114] Example 3d

[0115] Example 1 was followed except that the weight content of the fluorinated solvent in the electrolyte was f% = 3%, accordingly f / g = 2.88, f / h = 0.061, f / s = 0.2.

[0116] Example 3e

[0117] Example 1 was followed except that the width of the negative electrode sheet was 126.5 mm, the area of the negative electrode sheet was 112571 mm 2 , the width of the positive electrode sheet was 118.2 mm, the area of the positive electrode sheet was 104658 mm 2 , accordingly g = 1.07, n = 1.08, f / g = 11.21.

[0118] Example 3f

[0119] Example 1 was followed except that the width of the negative electrode sheet was 119.5 mm, the area of the negative electrode sheet was 106341 mm 2 , the width of the positive electrode sheet was 118.3 mm, the area of the positive electrode sheet was 104746 mm 2 , accordingly g = 1.01, n = 1.02, f / g = 11.88.

[0120] Example 3g

[0121] Example 1 was followed except that the width of the negative electrode sheet was 130.1 mm, the area of the negative electrode sheet was 115774 mm 2 , the width of the positive electrode sheet was 118.3 mm, the area of the positive electrode sheet was 104746 mm 2, accordingly, g = 1.1, n = 1.11, f / g = 10.91.

[0122] Example 4 Group

[0123] This group of examples is used to illustrate the effect of changing f / h.

[0124] Example 4a

[0125] Example 1 is followed except that the thickness h of the third negative electrode active material layer is 41.2 μm. In order to keep the ratio of the thickness of the first negative electrode active material layer to the thickness of the third negative electrode active material layer substantially unchanged, the thickness of the first negative electrode active material layer is adjusted to 43 μm, and f / h = 0.291.

[0126] Example 4b

[0127] Example 1 is followed except that the thickness h of the third negative electrode active material layer is 67.4 μm. In order to keep the ratio of the thickness of the first negative electrode active material layer to the thickness of the third negative electrode active material layer substantially unchanged, the thickness of the first negative electrode active material layer is adjusted to 70.3 μm, and f / h = 0.178.

[0128] Example 4c

[0129] Example 1 is followed except that the weight content of the fluorinated solvent in the electrolyte is 25%, the thickness h of the third negative electrode active material layer is 31.3 μm. In order to keep the ratio of the thickness of the first negative electrode active material layer to the thickness of the third negative electrode active material layer substantially unchanged, the thickness of the first negative electrode active material layer is adjusted to 32.6 μm, and f / g = 23.98, f / h = 0.799, f / s = 1.667.

[0130] Example 4d

[0131] Example 1 is followed except that the thickness h of the third negative electrode active material layer is 74.6 μm. In order to keep the ratio of the thickness of the first negative electrode active material layer to the thickness of the third negative electrode active material layer substantially unchanged, the thickness of the first negative electrode active material layer is adjusted to 77.8 μm, and f / h = 0.161.

[0132] Example 4e

[0133] Example 1 is followed except that the thickness h of the third negative electrode active material layer is 28.5 μm. In order to keep the ratio of the thickness of the first negative electrode active material layer to the thickness of the third negative electrode active material layer substantially unchanged, the thickness of the first negative electrode active material layer is adjusted to 29.7 μm, and f / h = 0.421.

[0134] Example 4c

[0135] Example 1 was repeated except that the weight content of the fluorinated solvent in the electrolyte was 3%, the thickness h of the third negative electrode active material layer was 78.8 μm, and the thickness of the first negative electrode active material layer was adjusted to 82.2 μm in order to maintain the ratio of the thickness of the first negative electrode active material layer to the thickness of the third negative electrode active material layer substantially constant, so that f / g = 2.88, f / h = 0.038, and f / s = 0.2.

[0136] Example 5 Group

[0137] This group of examples was intended to show the effects when the ratio of the thickness of the first negative electrode active material layer to the thickness of the third negative electrode active material layer was changed.

[0138] Example 5a

[0139] Example 1 was repeated except that the thickness h of the third negative electrode active material layer was 50.4 μm, so that the ratio of the thickness of the first negative electrode active material layer to the thickness of the third negative electrode active material layer was 1:0.984, and f / h = 0.238.

[0140] Example 5b

[0141] Example 1 was repeated except that the thickness h of the third negative electrode active material layer was 44.3 μm, so that the ratio of the thickness of the first negative electrode active material layer to the thickness of the third negative electrode active material layer was 1:0.865, and f / h = 0.271.

[0142] Example 5c

[0143] Example 1 was repeated except that the thickness h of the third negative electrode active material layer was 41.8 μm, so that the ratio of the thickness of the first negative electrode active material layer to the thickness of the third negative electrode active material layer was 1:0.816, and f / h = 0.287.

[0144] Example 5d

[0145] Example 1 was repeated except that the thickness h of the third negative electrode active material layer was 62.1 μm, so that the ratio of the thickness of the first negative electrode active material layer to the thickness of the third negative electrode active material layer was 1:1.213, and f / h = 0.193.

[0146] Example 5e

[0147] Example 1 was repeated except that the thickness h of the third negative electrode active material layer was 535.7 μm, so that the ratio of the thickness of the first negative electrode active material layer to the thickness of the third negative electrode active material layer was 1:0.697, and f / h = 0.336.

[0148] Example 6 Group

[0149] This group of examples is used to illustrate the effect when f / s changes.

[0150] Example 6a

[0151] Example 2 was followed except that the area s of the tab was 10 mm 2 f / s = 1.2.

[0152] Example 6b

[0153] Example 2 was followed except that the area s of the tab was 8 mm 2 f / s = 1.5.

[0154] Example 6c

[0155] Example 2 was followed except that the area s of the tab was 40 mm 2 f / s = 0.3.

[0156] Example 6d

[0157] Example 2 was followed except that the area s of the tab was 30 mm 2 f / s = 0.4.

[0158] Example 6e

[0159] Example 2 was followed except that the weight content of the fluorinated solvent in the electrolyte was 30%, and the area s of the tab was 10 mm 2 f / g = 28.78, f / h = 0.611, f / s = 3.

[0160] Example 6f

[0161] Example 2 was followed except that the weight content of the fluorinated solvent in the electrolyte was 30%, and the area s of the tab was 8 mm 2 f / g = 28.78, f / h = 0.611, f / s = 3.75.

[0162] Example 6g

[0163] Example 2 was followed except that the area s of the tab was 25 mm 2 f / s = 0.48.

[0164] Example 7 group

[0165] This group of examples is used to illustrate the effect when the fluorinated solvent changes.

[0166] Example 7a

[0167] Example 1 was followed, except that the fluorinated solvent was monofluorobenzene (the number of fluorine substitutions in the fluorinated solvent was 1).

[0168] Example 7b

[0169] Example 1 was followed, except that the fluorinated solvent was octafluoropentyl-tetrafluoroethyl ether (the number of fluorine substitutions in the fluorinated solvent was 12).

[0170] Example 7c

[0171] Example 1 was followed, except that the fluorinated solvent was 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (the number of fluorine substitutions in the fluorinated solvent was 8).

[0172] Comparative Example 1

[0173] Example 1 was followed, except that the weight content of the fluorinated solvent in the electrolyte was 33%, f / g = 31.73, f / h = 0.672, and f / s = 0.367.

[0174] Comparative Example 2

[0175] Example 1 was followed, except that the weight content of the fluorinated solvent in the electrolyte was 1.5%, the thickness h of the third negative electrode active material layer was 12 μm, and the thickness of the first negative electrode active material layer was adjusted to 12.5 μm in order to maintain the ratio of the thickness of the first negative electrode active material layer to the thickness of the third negative electrode active material layer substantially unchanged, f / g = 1.44, f / h = 0.125, and f / s = 0.05.

[0176] Comparative Example 3

[0177] Example 1 was followed, except that no fluorinated solvent was added to the electrolyte.

[0178] Comparative Example 4

[0179] Example 1 was followed, except that the width of the positive electrode sheet was the same as the width of the negative electrode sheet, and the area of the positive electrode sheet was the same as the area of the negative electrode sheet.

[0180] Test Example

[0181] The lithium ion batteries obtained in the examples and comparative examples were tested as follows:

[0182] 1. Cycle performance test

[0183] The lithium ion battery was placed at 25°C, first discharged to 3V at 0.2C, then charged to 4.48V at 0.5C, and the full-charge capacity, thickness, and the like were recorded. The battery was discharged to 3V at 0.2C, then charged to 4.48V at 1C, and then charged to the upper limit voltage (4.53V) at 0.7C, and then charged at 4.53V to 0.05C, and then left for 5 minutes. Then, the battery was discharged at 0.7C to 3V, and then left for 5 minutes. This was one charge-discharge cycle. The battery was charged and discharged for 1000T in this way, and the performance parameters of the lithium ion battery were recorded during the cycle, including the capacity retention rate and the appearance abnormalities. After the cycle, the battery was disassembled to observe the lithium precipitation.

[0184] Capacity retention rate = 1000T capacity / initial capacity * 100%.

[0185] Lithium precipitation: The battery was charged to 4.48V at 0.5C, and then the battery was disassembled, and the top, bottom, surface, and arc of the negative electrode interface were observed to see if there were grayish white spots or sheet-shaped abnormalities. When there were no grayish white spots or sheet-shaped abnormalities, it was not lithium precipitation. When the area of the grayish white spots or sheet-shaped abnormalities accounted for less than 10% of the area of the electrode sheet, it was slight lithium precipitation. When the area of the grayish white spots or sheet-shaped abnormalities accounted for more than or equal to 10% of the area of the electrode sheet, it was lithium precipitation.

[0186] 2. Safety performance test - 25°C external short circuit

[0187] The battery was fully charged (100% SOC) at 0.5C, and then left for 10 minutes. The voltage, internal resistance, and thickness of the battery in the full-charge state (100% SOC) were tested at 25±5°C. The battery was placed in an environment at 25°C±5°C for 30 minutes, and then the positive and negative electrodes were short-circuited, and the resistance of the short circuit was ≤50mΩ. The voltage and the temperature rise of the battery body were monitored, and the test was terminated when the temperature of the battery dropped to less than 20% of the peak temperature or when the test time was greater than 24H. When the battery exploded or caught fire, it was considered to have failed the test. A total of 10 battery samples were tested, and the test results were represented by "pass the test / 10". For example, "8 / 10" means that 8 out of 10 tests passed.

[0188] The results obtained were recorded in Table 1.

[0189] Table 1

[0190]

[0191]

[0192] As can be seen from Table 1, by comparing the examples and the comparative examples, the capacity retention rate of the lithium ion battery of the examples is obviously improved, and the safety pass rate is obviously improved, which indicates that by controlling the weight content of the fluorinated solvent in the electrolyte and the ratio of the width of the positive and negative electrode sheets, the safety performance and the cycle stability performance of the battery are improved.

[0193] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including that various technical features are combined in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application and belong to the protection scope of the present application.

Claims

1. A lithium-ion battery, characterized by, The lithium ion battery comprises an electrolyte, a negative electrode sheet and a positive electrode sheet, wherein the electrolyte comprises a fluorinated solvent, the weight content of the fluorinated solvent is fwt% based on the total weight of the electrolyte; the ratio of the width of the negative electrode sheet to the width of the positive electrode sheet is g, and the lithium ion battery satisfies the following relationship: 2≤f / g≤30, 1.01≤g≤1.08, 3wt%≤f wt%≤30wt%; The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer, the negative electrode current collector comprises a single-sided area and a double-sided area, the negative electrode active material layer comprises a first negative electrode active material layer, a second negative electrode active material layer and a third negative electrode active material layer, in the single-sided area, the third negative electrode active material layer is located on one side of the surface of the negative electrode current collector, in the double-sided area, the first negative electrode active material layer and the second negative electrode active material layer are respectively located on both sides of the surface of the negative electrode current collector, the thickness of the third negative electrode active material layer in the single-sided area is 30μm≤h μm≤75μm, the second negative electrode active material layer and the third negative electrode active material layer are located on the same side of the negative electrode current collector, the ratio of the thickness of the first negative electrode active material layer to the thickness of the third negative electrode active material layer is 1:(0.8-0.99), and when the lithium ion battery is a lithium ion battery in a roll core structure, the single-sided area is located at the tail of the roll core structure.

2. The lithium-ion battery of claim 1, wherein, The lithium ion battery satisfies the following relationship: 6≤f / g≤15; And / or, the fluorinated solvent comprises one or more of fluorinated carboxylic acid ester, fluorinated ether, fluorinated benzene, fluorinated phosphate ester and fluorinated olefin; And / or, 1.03≤g≤1.06; And / or, 5wt%≤f wt%≤20wt%; And / or, the ratio n of the area of the negative electrode sheet to the area of the positive electrode sheet is (1.01-1.12):

1.

3. The lithium-ion battery of claim 2, wherein, n is (1.03-1.08):

1.

4. The lithium-ion battery of claim 1, wherein, The lithium ion battery satisfies the following relationship: 0.04≤f / h≤0.

9.

5. The lithium-ion battery of claim 2 or 3, wherein, The fluorinated carboxylic acid ester comprises one or more of monofluoroacetic acid ethyl ester, difluoroacetic acid dimethyl ester, difluoroacetic acid ethyl ester and difluoroacetic acid vinyl ester; And / or, the fluorinated ether comprises one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane and octafluoropentyl-tetrafluoroethyl ether; And / or, the fluorinated benzene comprises one or more of monofluorobenzene and 1,2-difluorobenzene; And / or, the fluorinated phosphate ester comprises one or more of phosphoric acid tris(2,2,2-trifluoroethyl) ester and phosphoric acid bis(2,2,2-trifluoroethyl)-ethyl ester; And / or, the fluorinated olefin comprises one or more of 1,2-difluoroethylene, monofluoroethylene and monofluoropropylene; And / or, the number of fluorine substitutions in the fluorinated solvent is ≤2.

6. The lithium-ion battery of claim 4, wherein, The lithium ion battery satisfies the following relationship: 0.1≤f / h≤0.7; And / or, 40μm≤h μm≤68μm; And / or, the thickness of the first negative electrode active material layer is the same as or different from the thickness of the second negative electrode active material layer.

7. The lithium-ion battery of claim 4, wherein, The negative electrode current collector comprises a polymer layer and a copper foil layer on both sides of the polymer layer, and the polymer layer comprises PP and / or PE.

8. The lithium-ion battery of claim 7, wherein, The thickness of the copper foil layer is 0.3-1.5 μm. And / or, the thickness of the polymer layer is 4-8 μm.

9. The lithium-ion battery of claim 8, wherein, The lithium ion battery comprises a negative tab, the area of the negative tab is s, unit: mm 2 The area s of the negative tab is the area of the overlapping part of the tab and the tab piece, and the lithium ion battery satisfies the following relationship: 0.1≤f / s≤3.

10. The lithium-ion battery of claim 9, wherein, The lithium ion battery satisfies the following relationship: 0.4≤f / s≤1. And / or, 10≤s≤30.

11. The lithium-ion battery of claim 4, wherein, The negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises at least one of a carbon-based material and / or a silicon-based material; the carbon-based material comprises at least one of natural graphite, artificial graphite, mesocarbon microbeads, soft carbon and hard carbon; and the silicon-based material comprises at least one of silicon, silicon-oxygen, silicon-carbon and silicon alloy.

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