A lithium metal battery

Abstract

The application relates to the field of battery materials and discloses a lithium metal battery. The lithium metal battery provided by the application comprises an electrolyte, a diaphragm, a positive electrode sheet and a negative electrode sheet, the electrolyte comprises a compound A and a compound B, the mass proportion of the compound A in the electrolyte is a%, a satisfies 5<=a<=50, the mass proportion of the compound B in the electrolyte is b%, b satisfies 5<=b<=50, and the liquid retention coefficient of the lithium metal battery is z g / Ah, z satisfies 1.5<=z<=2.2. The application can control the liquid retention coefficient in a small value range, comprehensively control the contents of the compound A and the compound B, guarantee high safety performance, and have excellent cycle life. Especially, by controlling (a+b) / z in the range of 13-40, more excellent cycle life, especially low-temperature cycle life, can be obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of battery materials, in particular to a lithium metal battery. BACKGROUND

[0002] Lithium metal battery is considered as an important candidate for the next generation of high energy density batteries due to its extremely high theoretical energy density (far exceeding the current mainstream lithium ion battery). However, the current development of lithium metal battery still faces many challenges. Metal lithium has high reactivity and is prone to react with components in electrolyte, resulting in a large amount of heat and gas generated inside the battery. At the same time, during the charging and discharging process, the uneven deposition of lithium will form lithium dendrites, which may penetrate the separator, causing internal short circuit of the battery, and also may cause serious consequences such as overheating, fire and explosion.

[0003] For the above safety problems, related technical reports disclose that electrolyte systems with better compatibility with lithium metal can be developed to improve the cycle life and safety of the battery. However, the currently disclosed electrolyte systems do not have ideal cycle stability, especially low-temperature cycle stability, under the premise of ensuring safety. Therefore, the existing lithium metal battery cannot simultaneously consider safety and low-temperature cycle performance. SUMMARY

[0004] The present application provides a lithium metal battery, which aims to improve the low-temperature and room-temperature cycle performance on the basis of ensuring the safety performance of the lithium metal battery.

[0005] The lithium metal battery provided by the present application comprises an electrolyte, a separator, a positive electrode sheet and a negative electrode sheet, wherein the electrolyte comprises compound A and compound B;

[0006] The mass fraction of the compound A in the electrolyte is a%, and a satisfies: 5≤a≤50;

[0007] The mass fraction of the compound B in the electrolyte is b%, and b satisfies: 5≤b≤50;

[0008] The liquid retention coefficient of the lithium metal battery is z g / Ah, and z satisfies: 1.5≤z≤2.2;

[0009] The compound A comprises at least one of the structures shown in formula 1,

[0010] Formula 1: wherein R1 and R2 are independently selected from H, halogen, halogen-substituted or unsubstituted hydrocarbon group with carbon atom number of 1-6, and hydroxyl group;

[0011] The compound B comprises at least one of the structures shown in formula 2,

[0012] Formula 2: R3, R4 are independently selected from H, F-substituted or unsubstituted hydrocarbon group with 1-10 carbon atoms, hydrocarbon-oxy group, at least one of R3, R4 containing F.

[0013] The compound A comprises at least one of the following structural formulas of formula 1-1 to formula 1-8:

[0014]

[0015] The compound B comprises at least one of the following structural formulas of formula 2-1 to formula 2-8:

[0016]

[0017] As a preferred setting, the lithium metal battery satisfies: 13≤(a+b) / z≤40.

[0018] As one of the settings, the electrolyte further comprises a compound F, the compound F comprises at least one of the structures shown in formula 3,

[0019] Formula 3: R5, R6 are independently selected from hydrocarbon group with 1-10 carbon atoms, hydrocarbon-oxy group;

[0020] Preferably, the compound F accounts for f% of the total mass of the electrolyte, f satisfies: 10≤f≤20;

[0021] Preferably, the compound F comprises at least one of the following structural formulas of formula 3-1 to formula 3-8:

[0022]

[0023]

[0024] As one of the settings, the separator comprises a base layer and a glue layer arranged on the surface of the base layer; the thickness of the glue layer is dμm, d satisfies: 0.5≤d≤8.

[0025] The base layer comprises a base material layer and a ceramic layer arranged on one side or both sides of the base material layer; preferably, the thickness of the ceramic layer is eμm, e satisfies: 0

[0026] The ceramic layer comprises inorganic particles, the particle size of the inorganic particles is gμm, g satisfies: 0.1≤g≤1.5;

[0027] And / or, the porosity of the separator is h%, h satisfies: 30≤h≤50.

[0028] As one of the settings, the electrolyte further contains a phosphorus-containing compound;

[0029] Preferably, the phosphorus-containing compound accounts for i% of the total mass of the electrolyte, i satisfies: 0.1≤i≤20;

[0030] More preferably, the phosphorus-containing compound is selected from at least one of LiPO2F2, tris(2,2,2-trifluoroethyl) phosphate, triphenyl phosphate, ethoxy pentafluoro-cyclotriphosphazene, triphenyl phosphine oxide, triphenyl phosphine, p-toluoyl phosphate, and cresyl diphenyl phosphate.

[0031] As one of the setting modes, the electrolyte further comprises a nitrogen-containing compound;

[0032] Preferably, the nitrogen-containing compound accounts for j% of the total mass of the electrolyte, j satisfies: 0.1≤j≤5;

[0033] Preferably, the nitrogen-containing compound is selected from one or more of lithium nitrate, 2-fluoropyridine, pentafluoropyridine, 3-fluoropyridine, 2-trimethylsilylethynylpyridine, 1,2-bis(di-2-pyridylphosphino)ethane, 1-methylbenzotriazole, isopropyl nitrate, and 4-ethylpyridine.

[0034] As one of the setting modes, the positive electrode sheet comprises a positive electrode active material, and the positive electrode active material comprises a ternary material.

[0035] Preferably, the lithium metal battery is a laminated battery.

[0036] The technical scheme of the present application has the following advantages:

[0037] The lithium metal battery provided by the present application comprises compound A with low density and viscosity in the electrolyte, and compound B for reducing the flammability of the electrolyte, which can ensure the safety of the battery. At the same time, compound A does not participate in the solvation structure and promotes the formation of a negative electrode film, reducing the continuous consumption of solvents and lithium salts. Therefore, by controlling the liquid retention coefficient in a small value range and comprehensively adjusting the contents of compound A and compound B, the lithium metal battery can have excellent cycle life while ensuring high safety performance. Especially by controlling (a+b) / z in the range of 13-40, more excellent cycle life, especially low-temperature cycle life, can be obtained.

[0038] Additional aspects and advantages of the embodiments of the present application will be described and shown in part in the following description, or will be understood and explained by the practice of the embodiments of the present application. DETAILED DESCRIPTION

[0039] The following examples are provided to better further understand the present application and are not limited to the best mode contemplated, do not limit the scope of the application, and are not intended to suggest that the application must be practiced within the constraints of this combination of features. Any person skilled in the art, based on the teachings provided herein, or otherwise, can arrive at the same or similar results, utilizing any number of alternative compositions and techniques, and still be within the scope of the application.

[0040] Unless otherwise indicated, conventional methods of chemistry, molecular biology, recombinant technology, and the like, are employed in the examples. Unless otherwise indicated, conventional methods of chemistry, molecular biology, recombinant technology, and the like, are employed in the examples. Unless otherwise indicated, the reagents or instruments used in the examples are commercially available products.

[0041] In addition, the technical features involved in the different embodiments of the application described below can be combined with each other as long as there is no conflict.

[0042] The application provides a lithium metal battery, comprising electrolyte, diaphragm, positive electrode sheet and negative electrode sheet, characterized in that the electrolyte comprises compound A and compound B.

[0043] The mass percentage of the compound A in the electrolyte is a%, and a satisfies 5≤a≤50.

[0044] The mass percentage of the compound B in the electrolyte is b%, and b satisfies 5≤b≤50.

[0045] The liquid retention coefficient of the lithium metal battery is z g / Ah, and z satisfies 1.5≤z≤2.2.

[0046] The compound A comprises at least one of the structures shown in formula 1,

[0047] Formula 1: Wherein, R1 and R2 are independently selected from H, halogen, halogen-substituted or unsubstituted hydrocarbon group with carbon atom number of 1-6, and hydroxyl group.

[0048] The compound B comprises at least one of the structures shown in formula 2,

[0049] Formula 2: Wherein, R3 and R4 are independently selected from H, F-substituted or unsubstituted hydrocarbon group with carbon atom number of 1-10, and hydroxyl group, and at least one of R3 and R4 contains F.

[0050] The test method of the liquid retention coefficient in the present application is as follows: first, test the battery capacity D (which can be tested by a conventional method), then, after the battery to be disassembled is disassembled, pour out the free electrolyte and weigh M1, then extract the shell with M mass of dimethyl carbonate (DMC) for 3 times, pour out the residual DMC and weigh M2; weigh the weight of the electrode assembly and the shell M3, then put it into an oven for baking, weigh the mass of the electrode assembly and the shell after drying M4, then M1+M2+M3-M4-M is the amount of electrolyte in the battery m, and then m / D is the liquid retention coefficient of the battery.

[0051] The conventional lithium metal battery needs to control the initial liquid retention coefficient of the lithium metal battery to a high degree to ensure the cycle performance because the electrolyte is denser than the ordinary lithium ion electrolyte, and the electrolyte will continuously participate in film formation during the cycle, thereby causing rapid electrolyte consumption. The liquid retention coefficient of the conventional lithium metal battery needs to be controlled to 4.3-5.0 g / Ah. In the electrolyte of the present application, the compound A can significantly reduce the overall viscosity of the electrolyte. At low temperature, the low viscosity of the electrolyte helps the migration of lithium ions in the electrolyte, improves the conductivity of the electrolyte, and thus improves the low-temperature cycle performance of the battery. At the same time, the compound A also has a small maximum electrostatic potential, is not easy to destroy the ion-solvent interaction in the solvation layer, and does not participate in the solvation structure of lithium ions, which promotes the film formation of the negative electrode and effectively reduces the continuous consumption of solvents, lithium salts and anions during the charge and discharge process. Therefore, the compound A can reduce the consumption of solvents participating in the solvation structure during the cycle. The present application only needs to control a small liquid retention coefficient z in cooperation with the compound A, which can have excellent cycle life, especially low-temperature cycle life. Moreover, it can also prevent the electrolyte from easily reacting and producing gas when the liquid retention coefficient is high, which can cause the internal pressure of the battery to rise, and can cause the battery to swell, leak or even explode during charging and discharging, thereby improving the safety performance of the battery. However, the compound A has high flammability, which can cause serious safety problems when the lithium metal battery causes micro-short circuit due to dendrite growth. In order to reduce the flammability of the electrolyte, the electrolyte of the present application also contains compound B, which has larger viscosity and density than compound A. Although compound B does not improve the cycle performance of the battery as well as compound A, compound B itself is not flammable. Through the cooperation of compound A and compound B in the electrolyte, the flammability of the electrolyte can be reduced, the fire and explosion of the battery can be inhibited when the battery is micro-short-circuited, and the safety performance of the battery can be improved.

[0052] In summary, by comprehensively controlling the relationship among the compound A, the compound B and the liquid retention coefficient z, the battery of the present application can maintain good cycle stability and good safety performance within the range of the liquid retention coefficient, especially can effectively improve the low temperature and normal temperature cycle performance under the condition of ensuring safety, when the conditions of 5≤a≤50, 5≤b≤50, 1.5≤z≤2.2 in the present application are met.

[0053] For example, the mass percentage a% of the compound A in the electrolyte can be 5%, 10%, 20%, 30%, 40%, 50% or within the range composed of any two of the above values; the mass percentage b% of the compound B in the electrolyte can be 5%, 10%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or within the range composed of any two of the above values; and the liquid retention coefficient zg / Ah of the lithium metal battery can be 1.5g / Ah, 1.6g / Ah, 1.7g / Ah, 1.8g / Ah, 1.9g / Ah, 2.0g / Ah, 2.1g / Ah, 2.2g / Ah or within the range composed of any two of the above values.

[0054] In an alternative embodiment, the compound A comprises at least one of the following structural formulas of formula 1-1 to formula 1-8:

[0055]

[0056] Preferably, the compound A of the present application is a para-substituted structure, the interaction between the two substituents is weak, the influence on the electron cloud density of the benzene ring is small, which is conducive to maintaining the stability of the benzene ring, and the benzene ring is not easy to decompose and open in the electrolyte, so that the compound A can form a more stable protective film rich in LiF on the electrode surface, which not only prevents further reaction of the electrolyte with the electrode material, but also reduces the battery interface impedance and improves the cycle performance of the battery.

[0057] The number of F atoms in the compound B is ≥4;

[0058] Preferably, the compound B comprises at least one of the following structural formulas of formula 2-1 to formula 2-8:

[0059]

[0060] In an alternative embodiment, 13≤(a+b) / z≤40 is controlled, under which better safety performance and cycle stability can be achieved.

[0061] For example, (a+b) / z can be 13, 15, 17, 19, 20, 25, 30, 35, 40 or within the range composed of any two of the above values.

[0062] In an alternative embodiment, the electrolyte further comprises a compound F, the compound F accounts for f% of the total mass of the electrolyte, f satisfies: 10≤f≤20; the number of fluorine atoms in the compound F is less than 4, preferably ≤2; since fluorine ethers with ≥4 fluorine atoms do not dissolve lithium salts, in order to improve the solubility of lithium salts and increase the content of lithium salts in the electrolyte, the compound F of the ether type with less than 4 fluorine atoms is added in the present application to solvate the lithium salt, thereby improving the cycle performance.

[0063] The compound F of the present application comprises at least one of the structures shown in formula 3,

[0064] Formula 3: Wherein, R5, R6 are independently selected from hydrocarbon groups with carbon atom number of 1-10, hydrocarbon oxy groups.

[0065] The compound F in the electrolyte of the present application is a non-fluorine ether compound, which not only has good compatibility with lithium metal and is not prone to side reactions, but also has better and superior infiltration ability than ordinary carbonate solvents, can fully infiltrate into the interior of the electrode material, improve the utilization rate of active materials, and further improve the cycle performance and safety performance.

[0066] Preferably, the compound F accounts for f% of the total mass of the electrolyte, f satisfies: 10≤f≤20; as an example, the mass percentage f% of the compound F in the electrolyte can be 10%, 12%, 14%, 16%, 18%, 20% or within the range formed by any two of the above values;

[0067] Preferably, the compound F comprises at least one of the following formulae 3-1 to 3-8:

[0068]

[0069] In an alternative embodiment, the separator comprises a base layer and a glue layer provided on the surface of the base layer; the thickness of the glue layer is dμm, d satisfies: 0.5≤d≤8.

[0070] The separator of the present application has a glue layer with a thickness of dμm, which enables the positive and negative electrodes and the separator to be tightly bonded together, reduces the transmission distance of lithium ions, improves the ion transmission efficiency, and further improves the low-temperature cycle performance of the lithium ion battery; moreover, due to the close bonding relationship between the positive and negative electrodes and the separator, the lithium ions will directly embed into the negative electrode after passing through the microporous structure of the separator, and the pore size and pore channel of the separator are uniformly distributed, therefore, through the optimized setting of the separator, the lithium ions can be uniformly deposited, reducing the lithium precipitation, and further improving the safety performance of the lithium ion battery.

[0071] As an example, the adhesive layer thickness dμm can be 0.5μm, 0.8μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm or within a range between any two of the above values.

[0072] In an alternative embodiment, the base layer comprises a substrate layer and a ceramic layer on one or both sides of the substrate layer; preferably, the ceramic layer has a thickness eμm, e satisfying: 0

[0073] The ceramic layer in the diaphragm of the present application can enhance the mechanical strength of the diaphragm, improve its tensile strength, puncture resistance and other capabilities, prevent the diaphragm from being easily punctured to cause battery short circuit, and further improve the safety performance of the battery.

[0074] As an example, the ceramic layer thickness eμm can be 0.1μm, 0.5μm, 0.8μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm or within a range between any two of the above values.

[0075] In an alternative embodiment, reducing the ceramic particle size can enhance the mechanical strength of the diaphragm and improve the situation of electrolyte flushing and destroying the diaphragm structure. The particle size of the ceramic layer is gμm, g satisfying: 0.1≤g≤1; the particle size range of the ceramic layer in the diaphragm of the present application is small, which not only can provide more intensive ion transmission channels, improve the transmission efficiency of ions and reduce the internal resistance of the battery, but also can increase the contact area of the diaphragm and the electrolyte and improve the diffusion rate of lithium ions, thereby improving the cycle performance of the battery, especially the low-temperature cycle performance. In addition, under high temperature conditions, the nano-sized ceramic particles can also inhibit the thermal shrinkage and deformation of the diaphragm, maintain the integrity of the battery structure, prevent the occurrence of safety problems such as thermal runaway, and further improve the safety.

[0076] As an example, the particle size of the ceramic layer gμm can be 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.0μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm or within a range between any two of the above values.

[0077] In an alternative embodiment, the diaphragm of the present application has a large porosity, which can provide more ion transmission channels, reduce the internal resistance of the battery, thereby improving the ion conductivity of the battery and improving the cycle performance of the battery. However, high porosity may cause the positive and negative electrodes to be in direct contact or the lithium dendrites to penetrate the diaphragm; the porosity of the diaphragm of the present application is h%, h satisfying: 30≤h≤50.

[0078] As an example, the porosity h% of the separator can be 30%, 35%, 40%, 45%, 50% or within a range between any two of the above values.

[0079] In an alternative embodiment, the electrolyte further comprises a phosphorus-containing compound, the phosphorus-containing compound accounts for i% of the total mass of the electrolyte, i satisfies: 0.1≤i≤20.

[0080] The phosphorus-containing additive in the electrolyte described in the present application can form a complex with metal elements in the positive electrode material, further maintaining the structural stability of the electrode material during the cycle process, and improving the cycle life; at the same time, the phosphorus-containing compound can further reduce the flammability of the electrolyte, improve the thermal stability of the electrolyte, and make the battery less likely to heat runaway when short-circuiting.

[0081] As an example, the phosphorus-containing compound can account for i% of the total mass of the electrolyte, which can be 0.1%, 0.5%, 1%, 3%, 5%, 7%, 10%, 12%, 15%, 18%, 20% or within a range between any two of the above values.

[0082] More preferably, the phosphorus-containing compound is selected from at least one of LiPO2F2, tris(2,2,2-trifluoroethyl) phosphate, triphenyl phosphate, ethoxy pentafluoro cyclo-triphosphazene, triphenyl phosphine oxide, triphenyl phosphine, p-toluoyl phosphate, toluene diphenyl phosphate;

[0083] In an alternative embodiment, the electrolyte further comprises a nitrogen-containing compound, the nitrogen-containing compound accounts for j% of the total mass of the electrolyte, j satisfies: 0.1≤j≤5.

[0084] The nitrogen-containing compound in the present application can promote the formation of a SEI film containing Li3N on the negative electrode, not only improving the elasticity and mechanical strength of the SEI film, but also forming a conductive channel, so that lithium ions can more easily migrate through the SEI film. This high conductivity helps to reduce the transmission resistance of lithium ions in the SEI film, thereby increasing the conduction of lithium ions, allowing lithium ions to pass through the SEI film more quickly, reducing the accumulation and blockage of lithium ions in the SEI film, thereby improving the charge-discharge efficiency and cycle stability of the battery.

[0085] As an example, the nitrogen-containing compound can account for j% of the total mass of the electrolyte, which can be 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or within a range between any two of the above values.

[0086] Preferably, the nitrogen-containing compound is selected from one or more of lithium nitrate, 2-fluoropyridine, pentafluoropyridine, 3-fluoropyridine, 2-trimethylsilylethynylpyridine, 1,2-bis(di-2-pyridylphosphino)ethane, 1-methylbenzotriazole, isopropyl nitrate, 4-ethylpyridine.

[0087] In an alternative embodiment, the lithium salt in the electrolyte of the present application can include at least one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluoro oxalato borate (LiDFOB), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethylsulfonylimide (LiTFSI), lithium difluorobisoxalate phosphate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(pentafluoroethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methide, and lithium bis(trifluoromethylsulfonyl)imide.

[0088] In an alternative embodiment, the positive electrode sheet includes a current collector and a positive electrode active material layer disposed on the surface of the current collector, and the positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder.

[0089] Preferably, the positive electrode active material in the positive electrode sheet is a ternary material.

[0090] In an alternative embodiment, the chemical formula of the ternary material is preferably LiNi x Co y Mn z O2, wherein x+y+z = 1, and further includes one or more of the following doping coating elements: Al, Zr, Mg, Y, Ti, B, Sr, W, Si, La, Nb, etc., wherein the total amount of Al+Mg+Zr is 1000-16000 ppm, and wherein the particle size Dv50 of the single crystal particles in the ternary material is 1-6 μm.

[0091] As an example, the total amount of Al+Mg+Zr can be in a range consisting of 1000 ppm, 3000 ppm, 5000 ppm, 8000 ppm, 10000 ppm, 13000 ppm, 16000 ppm, or any two of the above values.

[0092] As an example, the particle size Dv50 of the single crystal particles in the ternary material can be in a range consisting of 1 μm, 1.5 μm, 1 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 5 μm, 6 μm, or any two of the above values.

[0093] The ternary material has better thermal stability than other positive electrode active materials (such as lithium cobaltate), can maintain the stability of the structure under high temperature conditions, and reduces the risk of thermal runaway; therefore, the positive electrode material in the present application is selected as a ternary material. At the same time, the ternary material has good cycle life and can withstand long-term cycle charging and discharging process without easy capacity attenuation. The use of ternary materials in the present application can further improve the cycle performance and safety performance.

[0094] The type of conductive agent used in the positive electrode sheet in the present application is not particularly limited, which can be selected from the conductive agents commonly used in the art, including but not limited to one or more of acetylene black, conductive carbon black, ketjen black, conductive graphite, carbon nanotubes, conductive carbon fibers, graphene;

[0095] The type of binder used in the positive electrode sheet in the present application is also not particularly limited, which can be selected from the binders commonly used in the art, including but not limited to one or more of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, butadiene rubber, polyethylene oxide.

[0096] The negative electrode sheet of the present application includes a current collector and a negative electrode active material layer disposed on the surface of the current collector. The active material of the negative electrode active material layer can be selected from lithium metal, and the current collector of the negative electrode sheet can be selected from copper foil in the art. The negative electrode active material layer also includes a conductive agent and a binder. The type of conductive agent and binder used in the negative electrode sheet is not particularly limited in the present application, and the selection range can refer to the type of conductive agent and binder used in the positive electrode sheet, which will not be described here.

[0097] The negative electrode sheet of the present application can be prepared by the following method: selecting a lithium alloy and a copper foil with a certain thickness, rolling under a certain pressure, and then cutting the sheet to obtain a lithium metal negative electrode sheet. After drying, the negative electrode sheet is obtained.

[0098] In an alternative embodiment, the lithium metal battery is a battery with a stacked structure. The design of the stacked structure enables the lithium metal battery to better dissipate heat and reduces the problem of stress concentration, has higher mechanical stability, and compared with the winding structure, the design can avoid the risk of battery short circuit. And the problem of thermal runaway and overheating of the stacked battery is less, so the safety is higher.

[0099] The preparation method of the lithium ion battery in the present application is not particularly limited, and the lithium ion battery can be prepared by the conventional preparation method in the art. For example, the positive electrode sheet, the separator and the negative electrode sheet are sequentially stacked and placed, the separator is located between the positive electrode sheet and the negative electrode sheet, the cell is obtained by the stacking process, and then the lithium ion battery of the present application is obtained by the processes of baking, liquid injection, formation, packaging and the like.

[0100] In an alternative embodiment, based on the design of the battery volume, the number of negative electrode sheets x in the same volume of the sheet structure is further optimized to fully exploit the high energy density advantage of the lithium metal battery. Specifically, in order to fully exploit the high energy density advantage of the lithium metal battery, the number of positive and negative electrode sheets should be increased as much as possible during the design and preparation of the battery. However, as the number of negative electrode sheets increases, the contact area between the negative electrode sheets and the electrolyte also increases, and the side reactions also increase, which can exacerbate the growth of lithium dendrites and affect the safety performance. During the charging and discharging process of the battery, the volume of the lithium metal negative electrode changes greatly, and when the number of negative electrode sheets increases, the volume change rate of the battery also increases significantly, which can easily cause the battery shell to rupture, leading to problems such as electrolyte leakage, which can further affect the safety performance. Therefore, the number of negative electrode sheets x can be increased without significantly affecting the safety performance. For the design requirements of the sheet battery listed in the following examples, the number of negative electrode sheets x can satisfy 10 < x ≤ 25. As an example, the number of negative electrode sheets x can be 10, 12, 14, 16, 18, 20, 22, 24, 25, or within the range formed by any two of the above values.

[0101] The application will be further described in detail below in conjunction with specific examples, which should not be construed as limiting the scope of the application. In all examples and comparative examples of the application, the unit wt% represents the mass percentage.

[0102] Example 1

[0103] A lithium metal battery is prepared as follows:

[0104] (1) Preparation of positive electrode sheet

[0105] The positive electrode active material (NCM811), polyvinylidene fluoride, conductive carbon black and carbon nanotubes are mixed in a mass ratio of 96:2:1.5:0.5, N-methyl pyrrolidone (NMP) is added, and the mixture is stirred under the action of a vacuum stirrer until the mixture becomes a homogeneous and flowable positive electrode active paste. The positive electrode active paste is uniformly coated on both surfaces of an aluminum foil. The coated aluminum foil is dried, rolled, and cut to obtain the desired positive electrode sheet, wherein the areal density of the positive electrode sheet is 3.5 mAh / cm 2 .

[0106] (2) Preparation of negative electrode sheet

[0107] Lithium metal is compounded onto copper foil by physical rolling method, the pressure of the roller is adjusted to make the thickness of the lithium alloy on the copper foil on both sides be controlled to be about 30 mu m (i.e. the single-sided thickness of the negative electrode active material layer is about 30 mu m), and then the negative electrode sheet is obtained through cutting and slitting, and is placed in a dry argon atmosphere glove box for storage, the area density of the negative electrode sheet is 5 mAh / cm 2 .

[0108] (3) Preparation of electrolyte

[0109] In an argon-filled glove box (H2O<0.1ppm, O2<0.1ppm), f% of compound F based on the total mass of the electrolyte is added to 30% of lithium salt (LiFSI) based on the total mass of the electrolyte, and is dissolved and stirred uniformly, a% of compound A and b% of compound B based on the total weight of the electrolyte are added, and then 5% of phosphorus-containing compound (ethoxy pentafluoro cyclo-triphosphazene) based on the total mass of the electrolyte is added, and finally 1% of nitrogen-containing compound (lithium nitrate) based on the total mass of the electrolyte is added to obtain the electrolyte, and the specific addition amount and addition type are shown in Table 1.

[0110] (4) Obtaining of the separator

[0111] A layer of glue is coated on the ceramic separator to obtain a polyethylene film with a glue layer thickness of 1 mu m, a ceramic layer thickness of 2 mu m, a ceramic layer particle size of 0.5 mu m, and a porosity of 40%, and the specific parameter settings are shown in Table 1 below;

[0112] Table 1

[0113]

[0114]

[0115] The compounds shown in the above table are all existing commercially available products.

[0116] (5) Preparation of the battery

[0117] The positive electrode sheet prepared in step (1), the negative electrode sheet prepared in step (2) and the separator prepared in step (4) are stacked in the order of positive electrode sheet, separator, negative electrode sheet and separator, and the number of stacked negative electrode sheets is 20 to obtain an electric core; the electric core is placed in an outer packaging aluminum foil, the electrolyte prepared in step (3) is injected into the outer packaging aluminum foil, and then the lithium metal battery is obtained through processes such as vacuum packaging, standing, formation, shaping, sorting and the like.

[0118] The battery prepared by the above process has a charge and discharge range of 3.0-4.25V.

[0119] Example 2

[0120] A lithium metal battery, which is different from Example 1 in that the content a% of compound A, the content b% of compound B, the content f% of compound F, the content c% and type of lithium salt, the content i% and type of phosphorus-containing compound, the content j% and type of nitrogen-containing compound are different, and other unshown parameters are exactly the same as Example 1-1, and the specific settings are shown in the following Table 2:

[0121] Table 2

[0122]

[0123]

[0124] Other unshown parameters are exactly the same as Example 1-1, and the compounds shown in the above table are all existing commercial products.

[0125] Example 3

[0126] A lithium metal battery, which is different from Example 1 in that the parameter settings in the separator are different, and the specific parameter settings are shown in the following Table 3:

[0127] Table 3

[0128]

[0129] Other unshown parameters are exactly the same as Example 1-1.

[0130] Experimental Example

[0131] The lithium ion batteries obtained in the examples and comparative examples were respectively subjected to cycle performance test and short circuit safety test.

[0132] 1. 0℃ 0.2C / 1C cycle performance test

[0133] The batteries obtained in the examples and comparative examples were discharged at 0℃ to 3.0V at a current of 1C, then charged to a voltage of 4.25V at a constant current of 0.2C, then charged at a constant voltage of 4.25V to a current of 0.05C, and then discharged at a constant current of 1C to a voltage of 3.0V, which was one charge-discharge cycle. The thickness of the battery was recorded, the discharge capacity of the first week was counted as x mAh, and the discharge capacity of the Nth week was counted as y mAh; the capacity of the Nth week was divided by the capacity of the first week to obtain the cycle capacity retention rate R of the Nth week = y / x, and the cycle number when the battery capacity retention rate was 80% was recorded.

[0134] 2. 25℃ 0.2C / 1C cycle performance test

[0135] The batteries obtained in the examples and comparative examples were discharged at 25°C to 3.0V at a current of 1C, then charged at 0.2C to a voltage of 4.25V, then charged at 4.25V to a current of 0.05C, rested for 5min, then discharged at 1C to a voltage of 3.0V, which was one charge-discharge cycle. The thickness of the battery was recorded, the discharge capacity in the first week was recorded as xmAh, the discharge capacity in the Nth week was recorded as y mAh; the capacity in the Nth week was divided by the capacity in the first week to obtain the cycle capacity retention rate R = y / x in the Nth week, and the cycle number when the battery capacity retention rate was 80% was recorded.

[0136] 3. 25°C 0.5C / 3C cycle test

[0137] The batteries obtained in the examples and comparative examples were discharged at 25°C to 3.0V at a current of 3C. Then charged at 0.5C to a voltage of 4.25V, then charged at 4.25V to a current of 0.05C, rested for 5min, then discharged at 3C to a voltage of 3.0V, which was one charge-discharge cycle. The discharge capacity in the first week was recorded as xmAh, the discharge capacity in the Nth week was recorded as y mAh; the capacity in the Nth week was divided by the capacity in the first week to obtain the cycle capacity retention rate R = y / x in the Nth week, and the cycle number when the battery capacity retention rate was 80% was recorded.

[0138] 4. Battery short circuit safety test

[0139] The batteries obtained in the examples and comparative examples were discharged at 25°C to 3.0V at a current of 5C. Then charged at 1C to a voltage of 4.25V, then charged at 4.25V to a current of 0.05C, rested for 5min, then discharged at 5C to a voltage of 3.0V, which was one charge-discharge cycle. If the voltage value suddenly dropped, especially from the normal value to near zero level, indicating that a short circuit occurred inside the battery, whether the battery had thermal runaway, fire or explosion when the battery short-circuited was recorded.

[0140] The effects detected in the above examples 1-3 are shown in Tables 4-6.

[0141] Table 4

[0142]

[0143]

[0144] Table 5

[0145] 0°C 0.2C / 1C cycle / T 25°C 0.2C / 1C cycle / T 25°C 0.5C / 3C cycle / T Short circuit safety pass rate Example 2-1 389 578 520 10 / 10 Example 2-2 391 581 523 10 / 10 Example 2-3 390 580 521 10 / 10 Example 2-4 393 583 525 10 / 10 Example 2-5 389 571 523 9 / 10 Example 2-6 382 565 514 10 / 10 Example 2-7 371 556 502 10 / 10 Example 2-8 392 581 523 10 / 10 Example 2-9 387 577 518 10 / 10 Example 2-10 374 562 503 10 / 10 Example 2-11 379 568 505 8 / 10 Example 2-12 370 561 496 9 / 10 Example 2-13 363 555 490 10 / 10 Example 2-14 388 573 515 10 / 10 Example 2-15 391 578 520 10 / 10 Example 2-16 390 575 526 10 / 10 Example 2-17 386 570 513 10 / 10 Example 2-18 386 577 520 10 / 10 Example 2-19 385 575 518 10 / 10 Comparative Example 2-1 335 499 453 6 / 10 Comparative Example 2-2 328 491 445 5 / 10

[0146] Table 6

[0147]

[0148]

[0149] It is apparent that the above-described embodiments are merely illustrative for the sake of clarity and are not intended to limit the scope of the application. Other variations and modifications can be made by those skilled in the art based on the above description. All of the embodiments are not required to be exhaustive, and obvious changes or modifications are intended to be within the scope of the present application.

Claims

1. A lithium metal battery comprising an electrolyte, a separator, a positive electrode sheet, a negative electrode sheet, characterized by, The electrolyte comprises compound A and compound B; The mass percentage of the compound A in the electrolyte is a%, and a satisfies: 5≤a≤50; The mass percentage of the compound B in the electrolyte is b%, and b satisfies: 5≤b≤50; The liquid retention coefficient of the lithium metal battery is z g / Ah, and z satisfies: 1.5≤z≤2.2; The compound A comprises at least one of the structures shown in formula 1, Formula 1: wherein R1, R2 are independently selected from H, halogen, halogen substituted or unsubstituted hydrocarbyl of 1-6 carbon atoms, hydrocarboxy; The compound B comprises at least one of the structures shown in formula 2, Formula 2: wherein R3, R4 are independently selected from H, F-substituted or unsubstituted hydrocarbon group having 1 to 10 carbon atoms, hydrocarbonoxy group, at least one of R3, R4 containing F; The electrolyte further comprises compound F, and the compound F comprises at least one of the structures shown in formula 3, Formula 3: wherein R5, R6 are independently selected from hydrocarbon groups having 1-10 carbon atoms, hydrocarbonoxy groups; compound F accounts for f% of the total mass of the electrolyte, f satisfying: 10≤f≤20.

2. The lithium metal battery of claim 1, wherein, The compound A comprises at least one of the following formulae 1-1 to 1-8: Formula 1-1 Formula 1-2 Formula 1-3 Formula 1-4 Formula 1-5 Formula 1-6 Formula 1-7 Formula 1-8. And / or, the compound B comprises at least one of the following formulae 2-1 to 2-8: Formula 2-1 Formula 2-2 Formula 2-3 Formula 2-4 Formula 2-5 Formula 2-6 Formula 2-7 Formula 2-8.

3. The lithium metal battery of claim 1, wherein, The lithium metal battery satisfies: 13≤(a+b) / z≤40.

4. The lithium metal battery of any one of claims 1-3, wherein, The compound F comprises at least one of the following formulae 3-1 to 3-8: Formula 3-1 Formula 3-2 Formula 3-3 Formula 3-4 Formula 3-5 Formula 3-6 Formula 3-7 Formula 3-8.

5. The lithium metal battery of claim 4, wherein, The separator comprises a base layer and a glue layer arranged on the surface of the base layer; the thickness of the glue layer is d μm, and 0.5≤d≤8.

6. The lithium metal battery of claim 5, wherein, The base layer comprises a base material layer and a ceramic layer arranged on one side or both sides of the base material layer.

7. The lithium metal battery of claim 6, wherein, The thickness of the ceramic layer is e μm, and e satisfies: 0 8. The lithium metal battery of claim 6, wherein, The ceramic layer comprises inorganic particles, and the particle size of the inorganic particles is g μm, and g satisfies: 0.1≤g≤1.

5. And / or, the porosity of the separator is h%, and h satisfies: 30≤h≤50.

9. The lithium metal battery of any one of claims 1-3, wherein, The electrolyte further comprises a phosphorus-containing compound.

10. The lithium metal battery of claim 9, wherein, The mass percentage of the phosphorus-containing compound in the total mass of the electrolyte is i%, and i satisfies: 0.1≤i≤20.

11. The lithium metal battery of claim 9, wherein, The phosphorus-containing compound is selected from at least one of LiPO2F2, tris(2,2,2-trifluoroethyl) phosphate, triphenyl phosphate, ethoxy pentafluoro cyclo-triphosphazene, triphenyl phosphine oxide, triphenyl phosphine, p-toluoyl phosphate, and methylphenyl diphenyl phosphate.

12. The lithium metal battery of any one of claims 1-3, wherein, The electrolyte further comprises a nitrogen-containing compound.

13. The lithium metal battery of claim 12, wherein, The mass percentage of the nitrogen-containing compound in the total mass of the electrolyte is j%, and j satisfies: 0.1≤j≤5.

14. The lithium metal battery of claim 12, wherein, The nitrogen-containing compound is selected from one or more of lithium nitrate, 2-fluoropyridine, pentafluoropyridine, 3-fluoropyridine, 2-trimethylsilylethynylpyridine, 1,2-bis(di-2-pyridylphosphino)ethane, 1-methylbenzotriazole, isopropyl nitrate, and 4-ethylpyridine.

15. The lithium metal battery of any one of claims 1-3, wherein, The positive electrode sheet comprises a positive electrode active material, and the positive electrode active material comprises a ternary material.

16. The lithium metal battery of claim 15, wherein, The lithium metal battery is a laminated battery.

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