Lithium ion battery

Abstract

The lithium ion battery comprises a positive plate and an electrolyte, the positive plate comprises a positive current collector, a positive active material layer located on one side or two sides of the positive current collector and a bottom coating located between the positive current collector and the positive active material layer, the weight loss ratio of the bottom coating at 25-800 DEG C is X%, the electrolyte comprises propylene carbonate and propyl propionate, based on the total weight of the electrolyte, the weight content of the propylene carbonate is Bwt%, the weight content of the propyl propionate is Cwt%, and the lithium ion battery meets the condition that (B + C) / X is larger than or equal to 5 and smaller than or equal to 30. The lithium ion battery has the advantages of high safety performance and good cycle performance.

Description

A lithium-ion battery Technical Field

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

[0002] Background of the Invention

[0003] Current lithium-ion batteries are prone to thermal runaway risks when used in extreme environments such as sustained high temperatures. The reasons may be: the electrolyte is prone to redox decomposition reactions with the positive electrode under high temperature and high pressure (for example, temperatures above 85°C and voltage above 4.5V), destroying the CEI film on its surface, causing the lithium-ion battery impedance to continue to increase, causing local deformation, warping or short circuiting of the lithium-ion battery.

[0004] As the demand for secondary batteries increases, the requirements for their safety and cycle performance also increase. Therefore, it is very important to invent a battery that has both high safety performance and good cycle performance.

[0005] Summary of the Invention

[0006] In order to solve the problems of low safety performance and poor cycle performance of batteries in the prior art, the present disclosure provides a battery. The lithium-ion battery disclosed in the present disclosure has the advantages of high safety performance and good cycle performance.

[0007] To achieve the above objectives, the present disclosure provides a lithium-ion battery, comprising a positive electrode sheet and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector, a positive electrode active material layer located on one side or both sides of the positive electrode current collector, and a primer layer located between the positive electrode current collector and the positive electrode active material layer, wherein the primer layer has a weight loss rate of X% at 25°C-800°C; the electrolyte comprises propylene carbonate and propyl propionate, and based on the total weight of the electrolyte, the weight content of the propylene carbonate is Bwt%, and the weight content of the propyl propionate is Cwt%, then the lithium-ion battery satisfies the following: 5≤(B+C) / X≤30.

[0008] The inventors of the present disclosure have discovered that traditional carbonate solvents will cause a certain amount of swelling of the primer layer, resulting in poor adhesion between the primer layer and the positive electrode current collector, and the electrolyte has poor wettability on the corners of the battery casing, which may cause the battery casing to rupture and create a safety hazard. Therefore, by increasing the wettability of the electrolyte in the battery and reducing the swelling effect of the electrolyte on the primer layer, the safety performance and cycle performance of the battery can be improved.

[0009] The inventors of the present disclosure conducted further in-depth research and found that in order to improve the wettability of the electrolyte in the battery and reduce the swelling effect of the electrolyte on the binder in the positive electrode sheet, the specific relationship between the propylene carbonate and propyl propionate in the electrolyte and the base coating in the positive electrode sheet can be regulated: 5≤(B+C) / X≤30, thereby reducing the swelling effect of the electrolyte on the positive electrode sheet, improving the adhesion between the protective coating in the positive electrode sheet and the positive electrode current collector, and at the same time improving the wettability of the battery cell in the electrolyte.

[0010] In one example, along the winding direction of the positive electrode sheet, at the tail of the positive electrode sheet, a projected length of the primer layer on the positive electrode current collector is greater than a projected length of the positive electrode active material layer on the positive electrode current collector.

[0011] In one example, the undercoat layer includes a first binder, and the weight content of the first binder is Ewt% based on the total weight of the undercoat layer; the positive electrode active material layer includes a second binder, and the weight content of the second binder is Fwt% based on the total weight of the positive electrode active material layer, then E>F.

[0012] In one example, the first binder includes sodium element, and the weight content of the sodium element is Gwt% based on the total weight of the primer layer; the electrolyte includes a nitrile compound, and the weight content of the nitrile compound is Dwt% based on the total weight of the electrolyte, then the battery satisfies: 300≤(C+D) / G≤6000.

[0013] Through the above technical solution, the present disclosure has at least the following advantages compared with the prior art:

[0014] When the lithium-ion battery satisfies: 5≤(B+C) / X≤30, the swelling of the bottom coating by the electrolyte can be reduced, preventing the bottom coating from falling off due to the reduced viscosity of the binder in the bottom coating, thereby improving the safety performance of the battery. At the same time, the wettability of the battery by the electrolyte can be improved, reducing the safety hazard of battery shell rupture caused by poor electrolyte wettability, and improving the cycle performance and safety performance of the battery.

[0015] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG1 is a schematic structural diagram of the positive electrode sheet disclosed in the present invention. DETAILED DESCRIPTION

[0017] The following is a detailed description of the specific embodiments of the present disclosure. 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. In this article, unless otherwise specified, data ranges include endpoints.

[0018] The present disclosure provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode sheet and an electrolyte, the positive electrode sheet comprising a positive electrode current collector, a positive electrode active material layer located on one side or both sides of the positive electrode current collector, and a primer layer located between the positive electrode current collector and the positive electrode active material layer, wherein the primer layer has a weight loss rate of X% at 25°C-800°C; the electrolyte comprises propylene carbonate and propyl propionate, and based on the total weight of the electrolyte, the weight content of the propylene carbonate is Bwt%, and the weight content of the propyl propionate is Cwt%, then the lithium-ion battery satisfies the following condition: 5≤(B+C) / X≤30.

[0019] As shown in FIG1 , the positive electrode sheet includes a positive electrode current collector 1 , a positive electrode active material layer 2 located on one side or both sides of the positive electrode current collector, and an undercoat layer 3 located between the positive electrode current collector 1 and the positive electrode active material layer 2 .

[0020] The undercoat layer is located between the positive electrode current collector and the positive electrode active material layer, which can prevent the burrs generated in the positive electrode active material layer of the positive electrode sheet from piercing the separator during the slitting process, thereby improving the safety performance of the positive electrode sheet and the battery. At the same time, it can also improve the adhesion and conductivity between the positive electrode active material layer and the positive electrode current collector, forming a good and stable interface, preventing the reaction or mutual penetration between the positive electrode active material and the current collector, helping to extend the service life of the battery and improve the cycle stability of the battery.

[0021] When (B+C) / X is less than 5, the content of propylene carbonate and propyl propionate in the electrolyte is too low, which easily leads to insufficient wettability of the electrolyte to the primer layer, affecting the safety of the battery. At the same time, the conductivity of lithium ions is poor, which reduces the cycle performance of the battery. When (B+C) / X is greater than 30, the content of propylene carbonate and propyl propionate in the electrolyte is too high, which makes the swelling effect of the electrolyte on the primer layer too large, easily causing the primer layer to fall off, and reducing the safety performance of the battery. The present disclosure adjusts the lithium-ion battery to satisfy the following conditions: 5≤(B+C) / X≤30, which can reduce the swelling effect of the electrolyte on the primer layer, thereby improving the safety performance of the battery. This is because the propylene carbonate and propyl propionate in the electrolyte contain ester groups, and the binder in the primer layer has a certain intermolecular attraction with the ester groups, thereby allowing the battery to be fully immersed in the electrolyte. This is particularly beneficial for improving the electrolyte infiltration of the battery at the corners of the battery shell, alleviating the safety hazard caused by excessive stress at the corners of the battery shell causing the battery shell to rupture, thereby improving the safety performance and cycle performance of the battery.

[0022] By regulating lithium-ion batteries to meet the following conditions: 5≤(B+C) / X≤30, it is possible to achieve higher safety and better cycle performance than existing technologies. To further improve the effect, one or more of the technical features can be further optimized.

[0023] In one embodiment, the weight loss rate X% of the primer layer at 25°C-800°C is 1.5%-10% (e.g., 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%). The weight loss rate is measured by heating the temperature from room temperature (25°C) to 800°C at a rate of 10°C / min under nitrogen conditions. The weight of the primer layer at room temperature is w1. The weight of the primer layer at 800°C is w2 when the temperature is increased at a rate of 10°C / min. The weight loss rate is (w1-w2) / w1*100%.

[0024] In one example, the weight loss rate X% of the primer layer at 25° C.-800° C. is 3%-8%.

[0025] In one embodiment, Bwt% is 35wt%-55wt% (for example, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%). When Bwt% is lower than 35wt%, the content of propylene carbonate in the electrolyte is too low, which will have a certain impact on the fluidity of the electrolyte, thereby reducing the wettability of the electrolyte to the bottom coating, affecting the safety and cycle performance of the battery; when Bwt% is higher than 55wt%, the content of propylene carbonate in the electrolyte is too high, the swelling effect of the electrolyte on the bottom coating is too large, the safety performance of the battery is reduced, and at the same time, the impedance of the electrolyte increases, and the impedance of the battery increases. Regulating Bwt% within the above range can not only ensure that the electrolyte has good fluidity, so that the battery is fully immersed in the electrolyte and improves the safety performance of the battery, but also reduce the swelling effect of the electrolyte on the bottom coating while maintaining a low impedance.

[0026] In one embodiment, Bwt% is 40wt%-50wt%. Adjusting Bwt% within the above range can further improve the wettability of the electrolyte to the undercoat layer, reduce the swelling of the electrolyte to the undercoat layer, further improve the safety of the battery, and reduce the impedance of the battery.

[0027] In one embodiment, Cwt% is 5wt%-25wt% (for example, 20wt%, 25wt%, 30wt%, 35wt%). When Cwt% is lower than 5wt%, the content of propyl propionate in the electrolyte is too low, which will have a certain impact on the fluidity of the electrolyte, thereby reducing the wettability of the electrolyte to the bottom coating, affecting the safety and cycle performance of the battery; when Cwt% is higher than 25wt%, the content of propyl propionate in the electrolyte is too high, the swelling effect of the electrolyte on the bottom coating is too large, the safety performance of the battery is reduced, and at the same time, the impedance of the electrolyte increases, and the impedance of the battery increases. Regulating Cwt% within the above range can not only ensure that the electrolyte has good fluidity, so that the battery is fully immersed in the electrolyte and improves the safety performance of the battery, but also reduce the swelling effect of the electrolyte on the bottom coating while maintaining a low impedance.

[0028] In one embodiment, Cwt% is 10wt%-20wt%. Adjusting Cwt% within the above range can further improve the wettability of the electrolyte to the undercoat layer, reduce the swelling of the electrolyte to the undercoat layer, further improve the safety of the battery, and reduce the impedance of the battery.

[0029] In one example, the weight loss rate X% of the primer layer at 25° C.-800° C. is 1.5%-10%, and / or Bwt% is 35wt%-55wt%, and / or Cwt% is 5wt%-25wt%.

[0030] In one example, the weight loss rate X% of the primer layer at 25° C.-800° C. is 3%-8%, and / or Bwt% is 40wt%-50wt%, and / or Cwt% is 10wt%-20wt%.

[0031] In one embodiment, at the tail of the positive electrode sheet, the projected length of the primer layer 3 on the positive electrode current collector is greater than the projected length of the positive electrode active material layer 2 on the positive electrode current collector. The projection is a positive projection and can be aligned in the vertical direction. The tail length of the primer layer can exceed the tail length of the positive electrode active material layer, which can avoid contact between the positive electrode current collector and the negative electrode sheet at the tail of the positive electrode sheet, reduce the probability of short circuit, and at the same time help to improve the overall hardness and tensile strength of the positive electrode sheet, improve the mechanical properties of the positive electrode sheet, prevent deformation during winding, and cause fracture and breakage. It also increases the contact area between the primer layer and the electrolyte, improves the lithium ion conductivity, improves the lithium ion transmission capacity between the active layer and the current collector, and reduces the loss of energy density.

[0032] In one embodiment, the lithium-ion battery includes a negative electrode and a separator. The positive electrode sheet, the negative electrode sheet, and the separator are stacked in the order of positive electrode sheet, separator, and negative electrode sheet, and then wound to form a winding core. The tail of the positive electrode sheet is the end of the positive electrode sheet along the winding direction A of the winding core. In the winding core, the tail of the positive electrode sheet is located at the end of the winding core.

[0033] In one embodiment, the undercoat layer includes a first binder, and the positive electrode active material layer includes a second binder, wherein the content of the first binder in the undercoat layer is greater than the content of the second binder in the positive electrode active layer. This can improve the bonding between the positive electrode current collector and the undercoat layer, prevent the positive electrode active layer and the current collector or the undercoat layer from falling off during the charge and discharge process, inhibit the expansion of the positive electrode during the charge and discharge process, improve safety performance, and at the same time help reduce the swelling and corrosion of the electrolyte on the positive electrode sheet, prevent the positive electrode sheet and the electrolyte from having side reactions (such as gas production) during the charge and discharge process, effectively reduce the gap between the undercoat layer and the active material layer, improve the adhesion between the undercoat layer and the active material layer, thereby increasing the compaction density of the positive electrode sheet, and thus increasing the energy density of the lithium-ion battery.

[0034] According to one specific embodiment, at the rear end of the positive electrode sheet, the projected length of the undercoat layer 3 on the positive electrode current collector is greater than the projected length of the positive electrode active material layer 2 on the positive electrode current collector, and the content of the first binder in the undercoat layer is greater than the content of the second binder in the positive electrode active layer. In this case, not only can the swelling effect of the electrolyte on the undercoat layer be reduced, but in the event of thermal runaway, the heat and gas generated by the thermal runaway can be easily transferred out of the battery to avoid explosion.

[0035] In one embodiment, the first binder includes one or more of sodium polyacrylate, potassium polyacrylate, magnesium polyacrylate, lithium polyacrylate, polyacrylate, sodium carboxymethyl cellulose, and CMC-Li. These binders have polar functional groups (e.g., hydroxyl groups), large specific surface areas, and high electrolyte absorption capabilities, which can effectively enhance the adhesion between the undercoat layer and the positive electrode current collector and between the undercoat layer and the positive electrode active material layer, while improving the shuttle efficiency of lithium ions and solving the problem of lithium plating.

[0036] In one embodiment, the first binder includes one or more of sodium polyacrylate, potassium polyacrylate, magnesium polyacrylate, and lithium polyacrylate. The first binder has a relatively high carboxyl content, which can form strong ester bonds with active materials containing hydroxyl groups on the surface, thereby promoting more uniform coverage of the primer layer on the surface of the positive electrode current collector.

[0037] In one example, the second binder includes one or more of polyvinylidene fluoride, polyacrylate, and polyacrylic acid.

[0038] In one example, the primer layer includes sodium element, and the weight content of the sodium element is Gwt% based on the total weight of the primer layer; the electrolyte includes nitrile compounds, and the weight content of the nitrile compounds is Dwt% based on the total weight of the electrolyte, then the lithium-ion battery satisfies: 300≤(C+D) / G≤6000. By regulating the lithium-ion battery to meet the following conditions: 300≤(C+D) / G≤6000, the side reaction between the electrolyte on the surface of the positive electrode active layer and the positive electrode active layer can be reduced, and the nitrile compound can coordinate with the positive electrode active material to slow down the volume expansion and particle breakage of the positive electrode active material due to phase change. At the same time, the sodium element contained in the undercoat layer can improve the structural stability of the positive electrode active material and the tensile strength of the electrode sheet, thereby avoiding repeated breakage of the electrode sheet during the winding process, and having good toughness. At the same time, it increases the contact between the positive electrode active material and the positive electrode collector, and alleviates the risk of powder falling off of the positive electrode sheet due to deformation of the positive electrode collector. At the same time, the sodium ions contained in the binder and the ethyl propionate in the electrolyte are beneficial to improving the electron transport performance and ion transport performance of the positive electrode sheet. Therefore, the battery that meets the above specific relationship can improve the battery's kinetic performance, thereby improving the battery's cycle performance.

[0039] In one embodiment, G wt % is 0.005 wt %-0.1 wt % (e.g., 0.005 wt %, 0.01 wt %, 0.03 wt %, 0.05 wt %, 0.07 wt %, 0.1 wt %). When the sodium element in the undercoat layer is controlled within the above-mentioned specific range, it is beneficial to improve the structural stability of the undercoat layer and reduce the phenomenon of shedding between the positive electrode current collector, the undercoat layer, and the positive electrode active material layer during the charge and discharge process of the positive electrode sheet.

[0040] In one embodiment, G wt % is 0.01 wt % to 0.05 wt %.

[0041] In one example, G wt % is 0.005 wt % to 0.1 wt %, and / or D wt % is 0.5 wt % to 8 wt %.

[0042] In one example, G wt % is 0.01 wt % to 0.05 wt %, and / or D wt % is 1 wt % to 6 wt %.

[0043] In one example, the nitrile compound includes one or more of formula (I), formula (II) and formula (III),

[0044] Wherein, R1, R2 and R3 may be the same or different and are each independently selected from a substituted or unsubstituted C1-C10 alkyl group, a substituted or unsubstituted C2-C10 unsaturated hydrocarbon group, a substituted or unsubstituted C4-C10 heterocycloalkyl group, a substituted or unsubstituted C1-C10 alkoxy group, a phenyl group, a substituted or unsubstituted C6-C10 phenylalkyl group, a substituted or unsubstituted C4-C10 heteroaryl group, a substituted or unsubstituted C4-C10 heteroatom-containing carbonyl group, or a substituted or unsubstituted C2-C10 ether group.

[0045] In the present disclosure, the expression "substituted or unsubstituted" means, for example, "substituted or unsubstituted C1-C10 alkyl", which means that the alkyl group may be substituted by halogen or may not be substituted by any substituent. When the alkyl group is substituted by halogen, one H in the alkyl group may be substituted by halogen, multiple H groups may be substituted by halogen, or all H groups may be substituted by halogen.

[0046] The substituted substituent may be selected from one or more of F and a C4-C10 alkyl group containing a heteroatom.

[0047] The nitrile compound having the above-mentioned specific structure can form a better film on the positive electrode sheet, protect the positive electrode sheet, reduce the side reaction between the positive electrode sheet and the electrolyte, and improve the safety of the battery.

[0048] In one example, the nitrile compound includes one or more of succinonitrile (SN), adiponitrile (ADN), 1,2-bis(cyanoethoxy)ethane (DENE), and 1,3,6-hexanetricarbonitrile (HTCN).

[0049] In one example, the primer layer includes inorganic particles and a first conductive agent.

[0050] In one example, based on the total weight of the base coating, the weight content of the inorganic particles is 75wt%-90wt% (for example, 75wt%, 80wt%, 85wt%, 90wt%), the weight content of the first conductive agent is 3wt%-20wt% (for example, 3wt%, 5wt%, 10wt%, 15wt%, 20wt%), and the weight content of the first binder is 4wt%-10wt% (for example, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%).

[0051] In one example, based on the total weight of the primer layer, the weight content of the inorganic particles is 80wt%-85wt%, the weight content of the first conductive agent is 4wt%-12wt%, and the weight content of the first binder is 6wt%-8wt%.

[0052] In one example, the inorganic particles include ceramic and / or boehmite.

[0053] In one embodiment, the inorganic particles include one or more of titanium dioxide, magnesium oxide, zirconium oxide, zinc oxide, and aluminum oxide. These inorganic particles are non-conductive and can improve the safety of the electrode while also having a certain impact on the impedance of the electrode. However, combined with propylene carbonate and propyl propionate in the electrolyte, the electrolyte has high fluidity, thereby maintaining high battery safety while also improving the impedance of the battery.

[0054] In one example, the first conductive agent includes one or more of carbon black, carbon nanotubes, carbon nanofibers, acetylene black, and graphene.

[0055] In one example, the positive electrode active material layer includes an active material and a second conductive agent.

[0056] In one example, the second conductive agent includes one or more of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, metal powder, and carbon fiber.

[0057] In one example, based on the total weight of the positive electrode active material layer, the content of the positive electrode active material is 80wt%-99.8wt% (for example, 80wt%, 85wt%, 90wt%, 95wt%, 99wt%, 99.8wt%), the content of the second conductive agent is 0.1wt%-10wt% (for example, 0.1wt%, 0.5wt%, 1wt%, 3wt%, 5wt%, 7wt%, 10wt%) and the content of the second binder is 0.1wt%-10wt% (for example, 0.1wt%, 0.5wt%, 1wt%, 3wt%, 5wt%, 7wt%, 10wt%).

[0058] In one example, based on the total weight of the positive electrode active material layer, the content of the positive electrode active material is 90 wt %-99.6 wt %, the content of the second conductive agent is 0.2 wt %-5 wt %, and the content of the second binder is 0.2 wt %-5 wt %.

[0059] In one embodiment, the positive electrode active material layer includes a positive electrode active material. The positive electrode active material may include at least one of the following materials: lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel oxide, lithium iron phosphate, lithium iron manganese phosphate, lithium vanadium phosphate, ternary materials (such as NCM), and lithium-rich manganese.

[0060] There is residual alkali on the surface of the ternary material, and the hydroxyl groups of the residual alkali can form ester bonds with the carboxyl groups in the first binder, thereby promoting the primer layer to cover the surface of the positive electrode current collector more evenly.

[0061] In the present invention, the positive electrode active material may be a positive electrode active material that has been subjected to a doping and / or coating modification treatment, or may be a positive electrode active material that has not been subjected to a doping and coating modification treatment.

[0062] In one embodiment, the positive electrode active material includes lithium cobalt oxide, which may be doped and / or coated lithium cobalt oxide, or undoped and uncoated lithium cobalt oxide.

[0063] In one embodiment, the doped lithium cobalt oxide includes a doping element A, which includes one or more of Al, Mg, Ti, Zr, Y, La, and B. Doping is mainly for stabilizing the bulk structure. Al and high-valent metal elements (e.g., Ti, Zr) doped at the Co position mainly stabilize the structure of the Co-O layer, inhibit phase change and cracking, and improve floating charge and cycling. Doping with high-valent metal elements can increase the metal-oxygen bond energy and reduce metal dissolution and lattice oxygen release after particle cracking. One or more elements of Al, Mg, Ti, Zr, Y, La, and B act at the Li / Co position, mainly inhibiting layer slip generated during the delithiation process and inhibiting cracking.

[0064] In one example, based on the total weight of the doped lithium cobalt oxide, the weight content of the doping element A is 2000 ppm-10000 ppm (eg, 2000 ppm, 4000 ppm, 5000 ppm, 7000 ppm, 9000 ppm, 10000 ppm).

[0065] In one embodiment, the coated lithium cobalt oxide has a core-shell structure, wherein the core is doped or undoped lithium cobalt oxide, and the shell comprises a metal oxide or a fast ion conductor. The metal oxide can improve the surface structure stability and inhibit the dissolution of Co, and the fast ion conductor coating mainly improves the surface structure stability and improves the Li + Diffusion rate, reduced polarization, and improved DCR.

[0066] In one example, the metal oxide includes one or more of aluminum oxide and / or magnesium oxide.

[0067] In one example, the fast ion conductor includes one or more of Ag, Cu, Li, Na, F, and O.

[0068] The positive electrode sheet includes lithium cobalt oxide, which can be doped and / or coated lithium cobalt oxide, or undoped and uncoated lithium cobalt oxide, which can further improve the safety and electrochemical performance of the battery, so that the battery has both higher safety and better cycle performance.

[0069] In one example, the primer layer has a thickness of 1 μm to 10 μm (eg, 1 μm, 3 μm, 5 μm, 7 μm, 10 μm).

[0070] In one example, the thickness of the positive electrode active material layer is 30 μm-150 μm (eg, 30 μm, 50 μm, 70 μm, 100 μm, 120 μm, 150 μm).

[0071] In one example, the electrolyte includes a lithium salt, an organic solvent, and an additive.

[0072] In one embodiment, the organic solvent includes one or more of dimethyl carbonate, diethyl carbonate (DEC), ethyl methyl carbonate, EC and EP. The organic solvent is used as a medium in the electrolyte and can be Li + Provide a transmission environment.

[0073] In one embodiment, the additive includes at least one of 1,3-propane sultone and fluoroethylene carbonate. The additive can form a film on the negative electrode sheet, participate in the construction of the SEI film, and further improve the overall safety performance of the battery based on the base coating of the positive electrode sheet.

[0074] In one example, the lithium salt includes one or more of LiPF6 and LiBF4, and / or one or more of formula (1-1), formula (1-2), formula (1-3) and formula (1-4).

[0075] In one example, based on the total weight of the electrolyte, the weight content of the lithium salt is 10wt%-15wt% (for example, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%), the weight content of the organic solvent is 5wt%-30wt% (for example, 5wt%, 10wt%, 20wt%, 30wt%, 40wt%, 50wt%, 60wt%), and the weight content of the additive is 0.5wt%-20wt% (for example, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%).

[0076] In one example, based on the total weight of the electrolyte, the weight content of the lithium salt is 12 wt%-14 wt%, the weight content of the organic solvent is 10 wt%-20 wt%, and the weight content of the additive is 5 wt%-15 wt%.

[0077] In one example, the battery includes a negative electrode sheet and a separator.

[0078] The negative electrode sheet can be a conventional negative electrode sheet in the art. For example, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on one side or both sides of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, a third conductive agent and a third binder.

[0079] In one example, the negative electrode active material includes a carbon-based active material and / or a silicon-based active material.

[0080] In one example, the carbon-based active material includes one or more of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon, and soft carbon.

[0081] In one embodiment, the silicon-based active material includes silicon particles, silicon-oxygen particles, and silicon-carbon particles.

[0082] In one example, the third conductive agent is selected from one or more of conductive carbon black (SP), acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, metal powder, and carbon fiber.

[0083] In one example, the third binder is selected from one or more of sodium carboxymethyl cellulose, styrene-butadiene latex, polytetrafluoroethylene, and polyethylene oxide.

[0084] In one example, based on the total weight of the negative electrode active material layer, the content of the negative electrode active material is 80wt%-99.8wt% (for example, 80wt%, 85wt%, 90wt%, 95wt%, 99wt%, 99.8wt%), the content of the third conductive agent is 0.1wt%-10wt% (for example, 0.1wt%, 0.5wt%, 1wt%, 3wt%, 5wt%, 7wt%, 10wt%) and the content of the third binder is 0.1wt%-10wt% (for example, 0.1wt%, 0.5wt%, 1wt%, 3wt%, 5wt%, 7wt%, 10wt%).

[0085] In one example, based on the total weight of the negative electrode active material layer, the content of the negative electrode active material is 90 wt %-99.6 wt %, the content of the third conductive agent is 0.2 wt %-5 wt %, and the content of the third binder is 0.2 wt %-5 wt %.

[0086] The separator may be a conventional separator in the art. For example, the separator includes one or more of a single-layer PE (polyethylene), a single-layer PP (polypropylene), a PP / PE / PP composite film, and a composite ceramic separator.

[0087] The charge and discharge range of the battery disclosed herein is 3.0V-4.53V.

[0088] 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.

[0089] The following examples are used to illustrate the electrolyte and positive electrode sheet of the present disclosure.

[0090] Example 1 Group

[0091] Example I-1

[0092] (1) Preparation of ingredients

[0093] Positive electrode sheet: positive electrode current collector (aluminum foil);

[0094] Primer: 92 parts by weight of inorganic particles (aluminum oxide), 5 parts by weight of the first binder (sodium polyacrylate), and 3 parts by weight of the first conductive agent (carbon nanotubes).

[0095] Positive electrode active material layer: 98 parts by weight of active material (lithium cobalt oxide), 1 part by weight of second binder (polyvinylidene fluoride), and 1 part by weight of second conductive agent (carbon nanotubes).

[0096] Electrolyte: 13 parts by weight of lithium salt (LiPF6), 15 parts by weight of PC, 45 parts by weight of PP, 13 parts by weight of organic solvent (the weight ratio of EC:EP is 15:10), and 14 parts by weight of additives (4 parts by weight of PS, 10 parts by weight of FEC).

[0097] (2) Preparation of electrolyte

[0098] In a glove box filled with argon (H2O < 0.1ppm, O2 < 0.1ppm), mix the organic solvents evenly, then quickly add fully dried lithium salts, add additives after dissolution, and then add polynitrile compounds and mix evenly to obtain the desired electrolyte.

[0099] (3) Preparation of positive electrode

[0100] Mixing inorganic particles, a first conductive agent, and a first binder, and adding an appropriate amount of solvent NMP to obtain a primer slurry; coating the primer slurry on the surface of one side of the positive electrode current collector, drying, and rolling to form a primer with a thickness of 2.5 μm;

[0101] The positive electrode active material, the second binder, and the second conductive agent are mixed, and an appropriate amount of solvent NMP is added. The positive electrode slurry is obtained by the action of a vacuum mixer to obtain a positive electrode slurry with a solid content of 72wt%. The positive electrode slurry is evenly coated on the surface of the primer layer to obtain a positive electrode active material layer. The positive electrode slurry is then dried in a 125°C oven, cold pressed, and cut, and then baked under vacuum conditions at 80°C for 12h. The desired positive electrode sheet is obtained by roller pressing and cutting, wherein the thickness of the positive electrode active material layer is 45μm.

[0102] Example I-2 group

[0103] This example group was carried out with reference to Example I-1, except that Cwt% was changed. For details, see Tables I-1 and I-2.

[0104] Example 1-3 group

[0105] This example group was carried out with reference to Example I-1, except that B wt % was changed. Please refer to Tables I-1 and I-2 for details.

[0106] Example 1-4 group

[0107] This embodiment group was carried out with reference to embodiment I-1, except that X% was changed by adjusting the contents of the first binder and the first conductive agent. For details, see Tables I-1 and I-2.

[0108] Example 1-5 group

[0109] This example group was carried out with reference to Example I-1, except that the content of the additive in the electrolyte was changed. For details, see Tables I-1 and I-2.

[0110] Example I-6 group

[0111] This example group was carried out with reference to Example I-1, except that L 底 With L 活 For details, see Tables I-1 and I-2.

[0112] Example I-7 group

[0113] This embodiment group was carried out with reference to embodiment I-1, except that the specific selection of the first binder was changed. For details, see Tables I-1 and I-2.

[0114] Example I-8 group

[0115] This example group was carried out with reference to Example I-1, except that Ewt% was changed. For details, see Tables I-1 and I-2.

[0116] Example I-9 Group

[0117] This example group was carried out with reference to Example I-1, except that the Fwt% was changed. For details, see Tables I-1 and I-2.

[0118] Example I-10 group

[0119] This example group was carried out with reference to Example I-1, except that the weight content of A in the doped lithium cobalt oxide was changed. For details, see Tables I-1 and I-2.

[0120] Example I-11 Group

[0121] This example group was carried out with reference to Example I-1, except that the thickness of the primer layer was changed. For details, see Tables I-1 and I-2.

[0122] Example I-12 Group

[0123] This example group was carried out with reference to Example I-1, except that the thickness of the positive electrode active material layer was changed. For details, see Tables I-1 and I-2.

[0124] Comparative Example I-1

[0125] The same process was carried out as in Example I-1, except that there was no primer layer. For details, see Tables I-1 and I-2.

[0126] Comparative Example I-2

[0127] The same process was carried out as in Example I-1, except that propylene carbonate and propyl propionate were not added to the electrolyte. For details, see Tables I-1 and I-2.

[0128] Comparative Example I-3

[0129] The same procedure is carried out as in Example I-1, except that one or more of Bwt%, Cwt% and X% are adjusted to change (B+C) / X. For details, see Tables 1-1 and I-2.

[0130] Comparative Example I-4

[0131] The same procedure is carried out as in Example I-1, except that one or more of Bwt%, Cwt% and X% are adjusted to change (B+C) / X. For details, see Tables 1-1 and I-2.

[0132] Table I-1

[0133] Table I-2 * indicates the same as Example 1;

[0134] L 底Represents the projected length of the primer layer on the positive electrode current collector;

[0135] L 活 It represents the projected length of the positive electrode active material layer on the positive electrode current collector.

[0136] Example II Group

[0137] Example II-1

[0138] The process was carried out in accordance with Example I-1, except that a nitrile additive was added to the electrolyte, specifically as follows: electrolyte: 5 parts by weight of nitrile compounds (1.5 parts by weight of SN, 1 part by weight of ADN, 0.5 parts by weight of DENE, 2 parts by weight of HTCN), 13 parts by weight of lithium salt (LiPF6), 15 parts by weight of PC, 45 parts by weight of PP, 8 parts by weight of organic solvent (the weight ratio of EC:EP is 15:10), and 14 parts by weight of additives (4 parts by weight of PS, 10 parts by weight of FEC).

[0139] Example II-2 Group

[0140] This example group was carried out with reference to Example II-1, except that Cwt% was changed. For details, see Table II-1.

[0141] Example II-3 Group

[0142] This example group was carried out with reference to Example II-1, except that Dwt% was changed. Please refer to Table II-1 for details.

[0143] Example II-4 Group

[0144] This example group was carried out with reference to Example II-1, except that the specific selection of the nitrile compound was changed. For details, see Table II-1.

[0145] Example II-5 Group

[0146] This example group was carried out with reference to Example II-1, except that G wt % was changed. For details, see Table II-1.

[0147] Table II-1 *Same as Example II-1.

[0148] Preparation Example

[0149] The electrolytes and positive plates obtained in the examples and comparative examples were used to prepare batteries in the following manner:

[0150] (1) Positive electrode

[0151] The positive electrode sheets obtained in the above embodiments and comparative examples were used respectively.

[0152] (2) Negative electrode

[0153] The negative electrode active material (artificial graphite), sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber, conductive carbon black (SP) and single-walled carbon nanotubes (SWCNTs) were mixed in a mass ratio of 94.5:2.5:1.5:1:0.5, and deionized water was added to obtain a negative electrode active slurry under the action of a vacuum mixer; the negative electrode active slurry was evenly coated on both surfaces of the 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 the negative electrode sheet.

[0154] (3) Electrolyte

[0155] The electrolytes obtained in the above-mentioned embodiments and comparative examples were used respectively.

[0156] (4) Diaphragm

[0157] The diaphragm is a PP / PE / PP composite film.

[0158] (5) Preparation of lithium-ion batteries

[0159] The positive electrode sheet of step (1), the negative electrode sheet of step (2) and the separator of step (4) 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, the electrolyte of step (3) is injected into the outer packaging, and a lithium ion battery is obtained through vacuum packaging, standing, forming, shaping, sorting and other processes.

[0160] Test Case

[0161] 1. Thermogravimetric testing

[0162] The primer slurry obtained in the embodiment and the comparative example was applied to one side of the positive electrode current collector to prepare a sample, and the prepared sample was subjected to thermogravimetric analysis by thermogravimetric analysis to test the mass change during the thermogravimetric analysis. The test range was 25°C to 800°C, the heating rate was 10°C / min, and the test atmosphere was an inert atmosphere.

[0163] 2. The batteries obtained in the examples and comparative examples were tested as follows:

[0164] (1) Overcharge test

[0165] 1) Under a 25°C ± 5°C environment, test the incoming voltage, internal resistance, and thickness, and take a pre-test photo. 2) Discharge at 0.5C to the lower voltage limit (3V). 3) Allow to rest for 10 minutes. 4) Charge at a constant current of 0.8C to 10V, then charge at a constant voltage of 10V for 1 hour, followed by another 1-hour rest. 5) Monitor the temperature changes of the battery cells during this process. Test three batteries in a group. If the battery does not catch fire or remain intact, it passes. If the battery catches fire and / or explodes, it fails. Record the number of batteries that passed the test. 6) After overcharging is complete, remove the tester and test the voltage and internal resistance. Take a post-test photo. The battery surface temperature should be monitored. The test result is expressed as "number of batteries that passed the test / number of batteries tested." For example, "3 / 3" means all three batteries passed the test; "0 / 3" means all three batteries failed the test.

[0166] (2) Short circuit test

[0167] All samples were discharged according to the ERS standard, then fully charged at 25°C (voltage to standard voltage), cycled for 25T, and allowed to rest for 2 hours before testing. 1) Initial voltage, internal resistance, and thickness were measured, and the batteries were photographed. 2) The batteries were placed in a 55±5°C oven and connected to two temperature-sensing wires: one near the negative electrode of the cell body and the other measuring the ambient temperature. During the test, the surface and ambient temperatures of the cell were measured and recorded. After the cell temperature stabilized, an 80±20mΩ resistor was connected to the positive and negative terminals of the cell until the voltage dropped below 0.1V, the cell surface temperature returned to within ±20°C of the oven temperature, or a fire or explosion occurred, terminating the test. 3) After the batteries were removed from the oven and allowed to rest for 2 hours, the final voltage and internal resistance were measured. Three batteries were tested in a group. If no fire or guarantee occurred, the battery passed. If the battery caught fire and / or exploded, it failed. The number of batteries that passed the test was recorded. The test result is expressed as "number of batteries that passed the test / number of batteries tested". For example, "3 / 3" means that all 3 batteries tested passed the test; "0 / 3" means that all 3 batteries tested failed the test.

[0168] (3) Furnace temperature test

[0169] 1) Discharge at 0.2C at 25°C, then charge to the specified voltage as specified in the specification. 2) Measure the fully charged voltage, internal resistance, and thickness at 25°C. 3) Hang the fully charged battery in a gravity convection or circulating air oven at 25°C (heat transfer is not permitted for non-integrated battery modules). Ensure the voltage and temperature leads are properly insulated to prevent short circuits. Start at room temperature and increase the temperature at 5±2°C / min to 132°C. Hold at 132°C for 60 minutes. The test results are expressed as "number of cells tested / number of cells tested." For example, "3 / 3" means all three cells tested passed the test; "0 / 3" means all three cells tested failed the test.

[0170] (4) Capacity retention after 800 cycles at 45°C

[0171] Place the battery at an ambient temperature of (45±3)℃, charge it at a constant current of 1C to 4.5V with a cutoff current of 0.05C. After the battery is fully charged, let it sit for 5 minutes, and then discharge it at a constant current of 0.5C to a cutoff voltage of 3.0V. Record the highest discharge capacity of the first three cycles as the initial capacity Q. When the cycle reaches 800 weeks, record the last discharge capacity Q1 of the battery.

[0172] The calculation formula is as follows: Capacity retention rate (%) = Q1 / Q×100%.

[0173] (5) Capacity loss

[0174] The test method is based on 800 cycles at 45°C, and the calculation formula is as follows: Capacity loss (%) = (Q-Q1) / Q×100%.

[0175] The results obtained in Example 1 are recorded in Table 1-3.

[0176] Table I-3

[0177] As can be seen from Table I-3, the comparative examples and the examples show that the overcharge failure, short circuit failure, and furnace temperature failure of the lithium-ion batteries of the examples are significantly reduced, the capacity retention rate after 800 cycles at 45°C is significantly improved, and the capacity loss is significantly reduced, indicating that by making the lithium-ion battery meet the condition of 5≤(B+C) / X≤30, the cycle performance and safety performance of the lithium-ion battery are improved.

[0178] The results obtained in Example II are shown in Table II-2.

[0179] Table II-2

[0180] It can be seen from Table II-2 that by adding nitrile compounds to the electrolyte and making the lithium-ion battery meet the following conditions: 300≤(C+D) / G≤6000, the cycle performance of the battery is further improved.

[0181] 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 collector, a positive electrode active material layer located on one side or both sides of the positive electrode collector, and a primer layer located between the positive electrode collector and the positive electrode active material layer, and the primer layer has a weight loss rate of X% at 25°C-800°C; the electrolyte includes propylene carbonate and propyl propionate, and based on the total weight of the electrolyte, the weight content of the propylene carbonate is Bwt%, and the weight content of the propyl propionate is Cwt%, then the lithium-ion battery satisfies: 5≤(B+C) / X≤30.

2. The lithium-ion battery according to claim 1, wherein X% is 1.5% to 10%, and / or Bwt% is 35wt% to 55wt%, and / or Cwt% is 5wt% to 25wt%.

3. The lithium ion battery according to claim 1 or 2, wherein At the tail of the positive electrode sheet, a projected length of the primer layer on the positive electrode current collector is greater than a projected length of the positive electrode active material layer on the positive electrode current collector; And / or, the undercoat layer includes a first binder, the positive electrode active material layer includes a second binder, and the content of the first binder in the undercoat layer is greater than the content of the second binder in the positive electrode active layer.

4. The lithium ion battery according to any one of claims 1 to 3, wherein The first binder comprises one or more of sodium polyacrylate, potassium polyacrylate, magnesium polyacrylate, lithium polyacrylate, polyacrylate, sodium carboxymethyl cellulose and CMC-Li; And / or, the second binder includes one or more of polyvinylidene fluoride, polyacrylate and polyacrylic acid.

5. The lithium ion battery according to any one of claims 1 to 4, wherein The primer layer includes sodium element.

6. The lithium ion battery according to claim 5, wherein Based on the total weight of the primer layer, the weight content of the sodium element is Gwt%; the electrolyte includes a nitrile compound, and based on the total weight of the electrolyte, the weight content of the nitrile compound is Dwt%, then the lithium-ion battery satisfies: 300≤(C+D) / G≤6000.

7. The lithium ion battery according to claim 6, wherein Gwt% is 0.005wt%-0.1wt%, and / or, Dwt% is 0.5wt%-8wt%.

8. The lithium ion battery according to claim 6 or 7, wherein The nitrile compound includes one or more of formula (I), formula (II) and formula (III), wherein R1, R2 and R3 are each independently selected from a substituted or unsubstituted C1-C10 alkyl group, a substituted or unsubstituted C2-C10 unsaturated hydrocarbon group, a substituted or unsubstituted C4-C10 heterocycloalkyl group, a substituted or unsubstituted C1-C10 alkoxy group, a phenyl group, a substituted or unsubstituted C6-C10 phenylalkyl group, a substituted or unsubstituted C4-C10 heteroaryl group, a substituted or unsubstituted C4-C10 carbonyl group containing a heteroatom, or a substituted or unsubstituted C2-C10 ether group; and the substituted substituent is selected from one or more of F and a C4-C10 alkyl group containing a heteroatom; And / or, the nitrile compound includes one or more of succinonitrile, adiponitrile, 1,2-bis(cyanoethoxy)ethane and 1,3,6-hexanetrinitrile.

9. The lithium ion battery according to any one of claims 1 to 8, wherein The electrolyte includes an additive, and the additive includes at least one of 1,3-propane sultone and fluoroethylene carbonate.

10. The lithium ion battery according to any one of claims 1 to 9, wherein The primer layer includes inorganic particles and a first conductive agent. Based on the total weight of the primer layer, the weight content of the inorganic particles is 75wt%-90wt%, the weight content of the first conductive agent is 3wt%-20wt%, and the weight content of the first binder is 4wt%-10wt%.

11. The lithium ion battery according to claim 10, wherein The inorganic particles include ceramics and / or boehmite; and / or, the inorganic particles include one or more of titanium dioxide, magnesium oxide, zirconium oxide, zinc oxide and aluminum oxide; And / or, the first conductive agent includes one or more of carbon black, carbon nanotubes, carbon nanofibers, acetylene black and graphene.

12. The lithium ion battery according to any one of claims 1 to 11, wherein The positive electrode active material includes at least one of the following materials: lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, ternary material and lithium-rich manganese; And / or, the positive electrode active material is a positive electrode active material that has been subjected to doping and / or coating modification treatment, and / or, is a positive electrode active material that has not been subjected to doping and coating modification treatment.

13. The lithium ion battery according to claim 12, wherein The positive electrode active material includes lithium cobaltate, and the lithium cobaltate is doped and / or coated lithium cobaltate, and / or is undoped and uncoated lithium cobaltate.

14. The lithium ion battery according to claim 13, wherein The doped lithium cobalt oxide includes a doping element A, wherein the doping element A includes one or more of Al, Mg, Ti, Zr, Y, La and B; and / or, based on the total weight of the doped lithium cobaltate, the weight content of the doping element A is 2000ppm-10000ppm; And / or, the coated lithium cobalt oxide has a core-shell structure, wherein the core is doped or undoped lithium cobalt oxide, and the shell comprises a metal oxide or a fast ion conductor, the metal oxide comprises one or more of aluminum oxide and / or magnesium oxide, and the fast ion conductor comprises one or more of Ag, Cu, Li, Na, F and O.

15. The lithium ion battery according to any one of claims 1 to 14, wherein The thickness of the primer layer is 1 μm-10 μm; And / or, the thickness of the positive electrode active material layer is 30 μm-150 μm.

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