Lithium battery, its manufacturing method, charging method, and powered vehicle

Abstract

The present application provides a lithium battery, a manufacturing method thereof, a charging method thereof, and a power vehicle, the lithium battery comprising: a positive electrode plate; a negative electrode plate; a separator and an electrolyte solution disposed between the positive electrode plate and the negative electrode plate; a negative electrode material layer of the negative electrode plate contains a lithium silicon composite negative electrode active material; a protective layer is provided on the surface of the negative electrode material layer or a protective layer is provided on the surface of the lithium silicon composite negative electrode active material, the protective layer includes a polymer matrix and a lithium salt; and when the lithium battery is fully charged, the lithium silicon composite negative electrode active material is a lithium elemental material and a lithium silicon alloy Li 4.4 The lithium silicon composite negative electrode active material contains Si, and the molar ratio of lithium in the lithium silicon composite negative electrode active material is 15% to 95%.

Description

[Technical Field]

[0001] (Priority information) This application claims priority to Chinese Patent Application No. 202110730852.6, entitled "Lithium Battery and Its Manufacturing Method, Charging Method, and Powered Vehicle," filed with the State Intellectual Property Office of the People's Republic of China on June 29, 2021, the entire contents of which are incorporated herein by reference.

[0002] This application relates to the technical field of lithium batteries, and more particularly to lithium batteries and methods of manufacturing, charging, and powering vehicles. [Background technology]

[0003] Lithium batteries are widely used in fields such as portable electronic products such as mobile phones and laptops, and new energy vehicles. Currently, commercial lithium batteries generally use graphite as the negative electrode active material. To ensure that lithium ions are effectively released from the positive and negative electrodes during battery cycling, the effective capacity of the graphite-based negative electrode is generally greater than that of the positive electrode (i.e., the N / P ratio of the battery is generally greater than 1), thereby preventing lithium dendrites from precipitating on the negative electrode and affecting cycle performance. However, the volume and weight proportion of the negative electrode active material in the battery is high, limiting the improvement of the energy density of lithium-ion batteries, making it difficult to exceed 350 mAh / g, and therefore unable to meet people's increasing demands for range and standby time.

[0004] Metallic lithium has a high theoretical specific capacity (3861 mAh / g) and the most negative electrochemical potential (-3.04 V, vs. a standard hydrogen electrode), and is considered to be the optimal choice for the negative electrode material of next-generation high-energy density batteries. Currently, some organizations use metallic lithium with a much lower volume fraction than conventional negative electrodes, even lithium-free negative electrodes (such as CN201911075192.1), which can achieve high-energy density lithium batteries. However, the resulting batteries have poor cycling performance, hindering the commercialization of high-energy density lithium metal batteries. Summary of the Invention [Problem to be solved by the invention]

[0005] In view of this, the present application provides a lithium battery, a manufacturing method thereof, a charging method thereof, and a power vehicle thereof, in order to solve the problem of the low cycle performance of current metallic lithium batteries. [Means for solving the problem]

[0006] Specifically, in a first aspect, the lithium battery according to the present invention includes a positive electrode plate, a negative electrode plate, a separator and an electrolyte solution located between the positive electrode plate and the negative electrode plate, the negative electrode material layer of the negative electrode plate contains a lithium silicon composite negative electrode active material, and a protective layer is provided on the surface of the negative electrode material layer or on the surface of the lithium silicon composite negative electrode active material, the protective layer includes a polymer matrix and a lithium salt, and when the lithium battery is fully charged, the lithium silicon composite negative electrode active material contains a mixture of lithium elemental and lithium silicon alloy Li 4.4 The lithium silicon composite negative electrode active material contains Si, and the molar ratio of the lithium element in the lithium silicon composite negative electrode active material is 15% to 95%.

[0007] The lithium battery according to the first aspect of the present application contains the lithium silicon composite negative electrode active material, and therefore has a high energy density, a long cycle life, and high safety performance.

[0008] In a second aspect, a method for producing a lithium battery according to the present application includes: a mixed paste containing a silicon-based material, a conductive agent, and an adhesive is applied to a negative electrode current collector, dried, and roll-pressed to form a silicon-based material layer on the negative electrode current collector; hot pressing the lithium thin film and the silicon-based material layer in a glove box, so that all lithium elements in the lithium thin film are transferred to the silicon-based material layer and react with the silicon-based material in situ to form a negative electrode material layer containing a lithium silicon composite negative electrode active material, thereby obtaining a negative electrode plate; forming a protective layer on the surface of the silicon-based material layer before hot pressing the silicon-based material layer and the lithium thin film, or forming a protective layer on the surface of the negative electrode material layer after forming the negative electrode material layer, the protective layer comprising a polymer matrix and a lithium salt; a step of assembling the negative electrode plates to form a lithium battery, wherein the lithium silicon composite negative electrode active material is a lithium element and a lithium silicon alloy Li when the lithium battery is fully charged; 4.4 and a step of containing Si, and wherein the molar ratio of the lithium element in the lithium silicon composite negative electrode active material is 15% to 95%.

[0009] The production method described in the second embodiment of the present application is a simple process, easy to control, and suitable for large-scale industrial production.

[0010] In a third aspect, the method for charging the lithium battery according to the present application includes: When the lithium battery needs to have a long cycle life, the end-of-charge voltage V s V s =cV b + a × c × K + b × c × (dQ / dV) / (3.6 × CA), and when the lithium battery exhibits long cycle life characteristics, the V s In this case, lithium element is not deposited on the negative electrode of the lithium battery, and V s <V h and where V h is the upper limit charging voltage that the lithium battery can tolerate, CA is the nominal capacity when the lithium battery is discharged at 0.33C, and V b is the reference voltage when elemental lithium does not precipitate on the negative electrode in the real-time charge capacity of the lithium battery, K is the internal resistance increase rate of the real-time DC internal resistance during the charging process of the lithium battery relative to the shipping DC internal resistance, dQ / dV is the real-time differential value of the charged quantity of electricity of the lithium battery with respect to the charging voltage, c is the calibration coefficient of the real-time cell temperature during the charging process of the lithium battery, a is the calibration coefficient of K, and b is the calibration coefficient of (dQ / dV) / CA.

[0011] The charging method according to the third aspect of the present application can ensure the longest possible driving range with a long life of the lithium battery.

[0012] In a fourth aspect, a battery system for a power vehicle according to the present application includes at least one first battery unit, the first battery unit including a plurality of lithium batteries and a first charge control device according to the first aspect of the present application.

[0013] A power vehicle having the first battery unit can control the end-of-charge voltage for charging each lithium battery in the first battery unit according to the actual driving range requirements. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic diagram of a lithium battery according to an embodiment of the present invention; [Figure 2] 1 is a discharge curve of a lithium battery according to an embodiment of the present invention. [Figure 3] 1 is a schematic diagram of a powered vehicle according to an embodiment of the present invention; [Figure 4] FIG. 2 is another schematic diagram of a powered vehicle according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] The following description is an exemplary embodiment of the present application, and it is to be noted that those skilled in the art may make some improvements and modifications without departing from the principles of the present application, and these improvements and modifications are also deemed to be within the protection scope of the present application.

[0016] Hereinafter, technical means in the embodiments of the present application will be described in detail with reference to the drawings in the embodiments of the present application.

[0017] The negative electrode plate of the lithium battery according to the present embodiment contains a lithium silicon composite negative electrode active material. In some embodiments of the present application, as shown in FIG. 1 , a lithium battery 100 includes a negative electrode plate 10, a positive electrode plate 20, a separator 30 between the positive electrode plate 20 and the negative electrode plate 10, and an electrolyte (not shown). Generally, the negative electrode plate 10 includes a negative electrode current collector 11 and a negative electrode material layer 12 disposed on the negative electrode current collector 11. The negative electrode material layer 12 contains the lithium silicon composite negative electrode active material, a suitable conductive agent, an adhesive, and the like. Similarly, the positive electrode plate 20 includes a positive electrode current collector 21 and a positive electrode material layer 22 disposed on the positive electrode current collector 21. The positive electrode material layer 22 contains the positive electrode active material, a suitable conductive agent, an adhesive, and the like.

[0018] The negative electrode layer 12 may further include a protective layer 13 (see FIG. 1 ), or the lithium silicon composite negative electrode active material may include a protective layer, the protective layer comprising a polymer matrix and a lithium salt. The protective layer guides the flow of lithium ions, controls the lithium ions to deposit uniformly on the surface of the negative electrode plate, and effectively inhibits the growth of lithium dendrites on the surface of the negative electrode plate 10, preventing the lithium dendrites from penetrating the separator and causing an internal short circuit in the battery. This also reduces the occurrence of side reactions between the negative electrode and the electrolyte, mitigates volume expansion of the negative electrode during cycling, and improves cycle performance and safety.

[0019] The protective layer can better suppress cycle decay and internal battery short-circuit problems caused by lithium deposition on the negative electrode. The protective layer is substantially insoluble in the battery electrolyte. Specifically, the polymer matrix may include, but is not limited to, one or more of polyethylene oxide (PEO), polysiloxane, polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, and derivatives and copolymers thereof. The lithium salt has ion conductivity and may include one or more of lithium nitrate (LiNO), lithium sulfide (LiS), lithium chloride (LiCl), lithium bromide (LiBr), lithium iodide (LiI), lithium fluoride (LiF), lithium phosphate (LiPO), and the like. In some embodiments, the protective layer may further contain an inorganic filler to increase lithium ion transport pathways, improve mechanical performance, and the like. The inorganic filler may be at least one of an oxide (for example, silicon dioxide, aluminum oxide, titanium dioxide, etc.), a hydroxide (for example, aluminum hydroxide, magnesium hydroxide), and a salt.

[0020] In the present application, the lithium silicon composite negative electrode active material contains lithium and silicon. When the lithium battery 100 is fully charged, the lithium silicon composite negative electrode active material contains lithium and a lithium silicon alloy Li. 4.4 The lithium silicon composite negative electrode active material contains Si, and the molar ratio of the lithium element in the lithium silicon composite negative electrode active material is 15% to 95%.

[0021] "Full charge" means that the positive electrode of the battery is charged to 100% SOC (State of Charge). In this case, the positive electrode capacity of the battery is fully exerted, the energy density of the battery is high, there is "deposited lithium" on the negative electrode, and this "deposited lithium" is active lithium, which can exert its capacity at the negative electrode end. Regarding the negative electrode of the battery according to the present application, in the case of full charge of the battery, in addition to allowing the active lithium ions released from the positive electrode to be stored in the negative electrode in the form of an alloy-type material, it is allowed to be directly deposited on the negative electrode in the form of elemental lithium. Therefore, in the negative electrode material layer manufactured in the present application, the amount of lithium silicon alloy material Li x Si (0 < x ≤ 4.4) is small, and the energy density of the battery can be significantly improved. Further, by providing the protective layer, the side reaction between the "deposited lithium" in the high energy density state of the negative electrode of the battery and the electrolyte can be suppressed, and the risk of lithium dendrites depositing and penetrating the separator can be reduced. Therefore, the lithium battery of the embodiment of the present application has a high energy density and high cycle performance and safety performance, etc.

[0022] In an embodiment of the present application, when the lithium battery 100 is not fully charged, for example, when the SOC value charged to the positive electrode of the battery is lower than the first threshold value, the lithium silicon composite negative electrode active material does not contain elemental lithium. In this case, the lithium silicon alloy in the lithium silicon composite negative electrode active material can be represented by the general chemical formula Li x Si, where 0 < x ≤ 4.4. The "first threshold value" is the SOC critical value charged to the positive electrode when metallic lithium just deposits at the negative electrode end during charging of the battery, that is, when the lithium silicon alloy of the negative electrode of the battery is completely filled with lithium ions (that is, the lithium silicon alloy is specifically Li 4.4 Si, and at this time, it can also be said that the negative electrode of the battery is charged to 100% SOC), and it is the SOC value when not all the lithium ions on the positive electrode side are released.

[0023] When the SOC charged to the positive electrode of the battery is lower than the first threshold, lithium is not deposited in the battery, the energy density of the lithium battery is not fully realized, and the negative electrode terminal is a lithium silicon alloy Li x It only exhibits the capacity of Si, has relatively low allowable volume expansion, and is weak in side reactions with the electrolyte. As such, lithium batteries can undergo multiple charge-discharge cycles at low energy densities (much higher than the energy densities of current batteries that use graphite as the anode), i.e., have a long cycle life. Therefore, the lithium battery of the present application can combine the characteristics of "long cycle life" and the above-mentioned "high energy density," and by combining the lithium battery's battery management system and freely selecting these two characteristics, it can meet the full life cycle requirements of power vehicles.

[0024] In the present application, when the positive electrode of a lithium battery is charged to 100% SOC, the lithium silicon composite negative electrode active material contains an adjustable proportion of metallic lithium, with the molar ratio of metallic lithium being in the range of 15% to 95%. Accordingly, the first threshold value can be controlled according to the molar ratio of metallic lithium. Preferably, the first threshold value is also in the range of 15% to 95%. Referring to the discharge curve of a lithium battery shown in Figure 2, a lithium battery using a lithium silicon composite negative electrode active material exhibits a discharge inflection point at a discharge capacity of 58 mAh. The "discharge inflection point" refers to the minimum value of dV / dQ in the battery discharge curve. Before this inflection point, the energy density of the battery (i.e., the product of the battery voltage and the battery charge) becomes high, and the lithium silicon alloy Li 4.4 The capacity of both Si and lithium alone is demonstrated. After this inflection point, the SOC of the battery is low and the lithium silicon alloy Li is present on the negative electrode side. x Only the capacity of Si is utilized, and the energy density of the battery is low, but the cycle life of the battery is extended.

[0025] Preferably, when the lithium battery 100 is fully charged, the lithium silicon alloy Li in the lithium silicon composite negative electrode active material 4.4In some embodiments, the molar ratio of the lithium silicon alloy Li in the lithium silicon composite negative electrode active material is 5% to 85% when the lithium battery is fully charged. 4.4 The sum of the molar ratios of Si and lithium is 100%. In other words, when the lithium battery is fully charged, the lithium silicon composite negative electrode active material is composed of lithium and lithium silicon alloy Li. 4.4 In this case, the lithium silicon composite negative electrode active material contains only lithium element and silicon element (that is, it may be formed by pressing elemental silicon and metallic lithium in-situ).

[0026] Generally, the N / P ratio of conventional lithium batteries (using graphite or silicon as the negative electrode) is generally greater than 1, thereby preventing the precipitation of lithium dendrites and poor cycle performance that occur when the N / P ratio is less than 1. When the N / P ratio is greater than 1, the volume ratio of the negative electrode active material to the entire battery is large, generally 37% or more. For example, when graphite is used in the negative electrode, the volume ratio of graphite to the entire battery is 44% to 48%, and when the negative electrode active material is silicon, the volume ratio of the battery can reach 37% to 44%. In the lithium battery of the present application, when fully charged as described above, the lithium element and Li 4.4 Because a Si-containing lithium silicon composite negative electrode active material is used, the N / P ratio of the lithium battery is less than 1. Thus, the volume ratio (less than 37%, for example, 20% or less) and mass ratio of the negative electrode active material in the lithium battery can be small, which significantly improves the energy density of the battery and increases its cruising capacity. Furthermore, the presence of the protective layer described above suppresses side reactions between elemental lithium and the electrolyte and penetration of the separator due to disordered growth of elemental lithium when "deposited lithium" is present on the negative electrode, further increasing the cycle capacity of the battery.

[0027] In this application, the N / P ratio of the lithium battery 100 being less than 1 specifically means that the ratio of the capacity of the lithium silicon composite negative electrode active material to the capacity of the positive electrode active material is less than 1. The capacity of the lithium silicon composite negative electrode active material corresponding to the N / P ratio is the capacity at which lithium is just absorbed in the negative electrode and the lithium silicon alloy Li 4.4 This means the negative electrode capacity when the form of Si is formed and elemental lithium is not precipitated (in this case, the lithium ions of the positive electrode have not yet been completely released), i.e., the corresponding negative electrode capacity at the first threshold value.

[0028] Preferably, in the lithium battery 100, the volume ratio of the lithium silicon composite negative electrode active material to the positive electrode active material is 0.1375 to 0.825. The ratio of the thickness of the positive electrode plate 20 to the thickness of the negative electrode plate 10 is 8:1 to 4:3. This can better ensure that the N / P ratio of the lithium battery is less than 1, which is advantageous for improving the energy density of the battery.

[0029] The electrolyte of the lithium battery 100 generally contains a solvent and a second lithium salt. In an embodiment of the present application, the solvent of the electrolyte of the lithium battery 100 is a non-carbonate solvent. Specifically, the solvent of the electrolyte includes an ether solvent, and may include at least one of a non-halogenated ether solvent and a fluorinated ether solvent. Carbonate solvents undergo a rapid side reaction with the metallic lithium negative electrode, forming sharp lithium dendrites at the battery negative electrode and easily penetrating the battery separator, leading to spontaneous combustion of the battery. Ether solvents have good compatibility with metallic lithium and are much less likely to undergo a side reaction with metallic lithium than carbonate solvents. This effectively reduces the consumption of active lithium during cycling, improves the uniformity and density of lithium ion deposition, and prevents the formation of sharp lithium dendrites that penetrate the battery separator, posing a safety risk.

[0030] Preferably, the non-halogenated ether solvent may be one or more selected from ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, tripropylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, etc., but is not limited thereto. Preferably, the fluorinated ether solvent is 1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, hexafluoroisopropyl ether, tetrafluoroethyl-tetrafluoropropyl ether, 2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, difluoromethyl-2,2,3,3-tetrafluoropropyl ether, 2,2,3 ... The fluoroisopropyl ether may be one or more selected from the group consisting of pentafluoropropyl methyl ether, 1,1,2,3,3,3-hexafluoropropyl ethyl ether, 1,1,2,3,3,3-pentafluoropropyl difluoromethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, bis(2,2,2-trifluoroethyl) ether, and the like, but is not limited thereto.

[0031] The second lithium salt in the electrolyte may be one or more selected from the group consisting of lithium bisfluorosulfonimide (LiN(SOF)N), lithium bis(trifluoromethanesulfonyl)imide (Li(CFSON), lithium bis(perfluoroethylsulfonyl)imide (Li(CFSON), lithium dioxaborate (LiB(CO), LiBOB), lithium trifluoromethanesulfonate (LiCFSO), lithium perfluorobutanesulfonate (LiCFSO), tris(trifluoromethanesulfonyl)methyllithium (LiC(CFSO)), and the like, but is not limited thereto.

[0032] Preferably, the lithium silicon composite negative electrode active material is formed by in-situ pressing of a silicon-based material and metallic lithium. The silicon-based material may include, but is not limited to, elemental silicon, silicon oxide, silicon-based non-lithium alloys (e.g., silicon-germanium alloys, silicon-magnesium alloys, silicon-copper alloys, silicon-iron alloys, etc.), or other silicon compounds.

[0033] In some embodiments, the negative electrode material layer 12 containing the lithium silicon composite negative electrode active material is formed by in-situ hot pressing of a lithium thin film (e.g., a lithium thin film attached to a lithium foil or a release film) and an initial negative electrode material layer containing a silicon-based material. In this case, all of the lithium element in the lithium thin film can be transferred to the initial negative electrode material layer and react in situ with the silicon-based material to form the lithium silicon composite negative electrode active material. In other embodiments, the lithium silicon composite negative electrode active material is formed by in-situ pressing of a mixture (which may be a wet paste or dry powder) of metallic lithium powder and a silicon-based material. In this case, for the negative electrode material layer 12, a mixed paste of a silicon-based material and lithium powder can be applied to a negative electrode current collector, dried, and pressed, and then reacted in situ on the negative electrode current collector to form a negative electrode material layer containing a lithium silicon composite negative electrode active material. Alternatively, a mixture of metallic lithium powder and a silicon-based material can be pressed in situ to form a lithium silicon composite negative electrode active material, which can be applied, dried, and pressed to produce a negative electrode plate.

[0034] When it is necessary to form a negative electrode material layer 12 having a protective layer on its surface, a lithium thin film attached to a release film and a silicon-based material layer having a protective layer on its surface (the silicon-based material layer is the initial negative electrode material layer described above, and contains a silicon-based material, a preferred adhesive, and a conductive agent) can be hot-pressed in situ. In another embodiment of the present application, for the negative electrode material layer having a protective layer on its surface, a negative electrode material layer containing a lithium silicon composite negative electrode active material can be formed, and then the protective layer can be formed on the surface.

[0035] In the present application, the negative electrode current collector 11 and the positive electrode current collector 21 are independently selected from a metal foil material or an alloy foil material. For example, the negative electrode current collector 11 may be a copper foil, and the positive electrode current collector 21 may be an aluminum foil. The positive electrode active material may be at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium cobalt oxide, lithium manganate, lithium nickel manganate, lithium nickel cobalt manganate (NCM), and lithium nickel cobalt aluminate (NCA). Conventional materials may be used as adhesives and conductive agents in the negative electrode plate 10 and the positive electrode plate 20. The conductive agent may be one or more of conductive carbon black (e.g., acetylene black, ketjen black), carbon nanotubes, carbon fiber, graphite, furnace black, and the like. The adhesive may independently be one or more of styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyolefin (e.g., polyethylene, polypropylene, etc.), sodium carboxymethylcellulose (CMC), sodium alginate, etc.

[0036] The lithium battery according to the embodiment of the present application contains the lithium silicon composite negative electrode active material and the protective layer. Therefore, the proportion of the lithium silicon composite negative electrode active material in the lithium battery can be low, which is advantageous for improving the energy density of the battery. Furthermore, lithium does not deposit on the negative electrode at low SOC, resulting in excellent cycle life. Furthermore, the energy density of the battery is high at high SOC. Furthermore, the provision of the protective layer alleviates the side effects of lithium deposition. Therefore, the lithium battery according to the embodiment of the present application can combine high energy density, long cycle life, and high safety.

[0037] In a second aspect, the method for manufacturing the lithium battery according to the embodiment of the present application includes: a mixed paste containing a silicon-based material, a conductive agent, and an adhesive is applied to a negative electrode current collector, dried, and roll-pressed to form a silicon-based material layer on the negative electrode current collector; hot pressing the lithium thin film and the silicon-based material layer in a glove box, so that all lithium elements in the lithium thin film migrate to the silicon-based material layer and react with the silicon-based material in situ to form a negative electrode material layer containing a lithium silicon composite negative electrode active material, thereby obtaining a negative electrode plate; forming a protective layer on the surface of the silicon-based material layer before hot pressing the silicon-based material layer and the lithium thin film, or forming a protective layer on the surface of the negative electrode material layer after forming the negative electrode material layer, wherein the protective layer includes a polymer matrix and a lithium salt; a step of assembling the negative electrode plates to form a lithium battery, wherein the lithium silicon composite negative electrode active material is a lithium element and a lithium silicon alloy Li when the lithium battery is fully charged; 4.4 and a step of containing Si, and the molar ratio of the lithium element in the lithium silicon composite negative electrode active material being 15% to 95%.

[0038] The silicon-based material may include, but is not limited to, silicon element, silicon oxide, silicon-based non-lithium alloy (e.g., silicon germanium alloy, silicon magnesium alloy, silicon copper alloy, silicon iron alloy, etc.), or other silicon compounds (e.g., fluorine-containing silicon oxide, lithium hexafluorosilicate, silicon carbide, silicon boride), etc. When the silicon-based material used contains elements other than silicon (e.g., oxygen, fluorine), the lithium silicon composite negative electrode active material also contains these elements accordingly. For example, when the silicon-based material is silicon element, if the SOC of the battery is lower than the first threshold, the lithium silicon composite negative electrode active material may be a lithium silicon alloy Li x When the lithium battery is fully charged, the lithium silicon composite negative electrode active material contains only lithium and Li 4.4For example, when the silicon-based material is silicon oxide, if the SOC of the battery is lower than the first threshold, the lithium silicon composite negative electrode active material is a lithium silicon alloy Li x When the lithium battery is fully charged, the lithium silicon composite negative electrode active material 4.4 Contains Si, elemental lithium, Li2O, Li2SiO3, etc.

[0039] In an embodiment of the present application, when a silicon-based material layer having a protective layer on its surface and a lithium thin film are hot-pressed in-situ, the protective layer and the silicon-based material layer exhibit a porous structure due to the hot-pressing, and the lithium element of the lithium thin film enters the silicon-based material layer and reacts with the silicon-based material in situ to form the lithium silicon composite negative electrode active material, finally forming a negative electrode material layer having a protective layer, which contains the lithium silicon composite negative electrode active material.

[0040] The lithium thin film hot-pressed together with the silicon-based material layer may be a lithium foil or a lithium thin film attached to a release film, with a lithium thin film attached to a release film being preferred in order to avoid loss of lithium element due to direct contact of the lithium thin film with the pressing equipment.

[0041] The protective layer may be formed on the negative electrode material layer by liquid phase coating, vapor phase deposition, electrodeposition, or the like.

[0042] The step of "assembling the negative electrode plate to form a lithium battery" specifically includes the steps of stacking and arranging a positive electrode plate, a separator, and the negative electrode plate in order to manufacture a bare cell, and placing the bare cell in a battery housing, injecting an electrolyte, and sealing the battery housing to obtain a lithium battery.

[0043] The lithium battery manufacturing method according to the embodiment of the present application is a simple process, easy to control, and suitable for large-scale industrial production of lithium batteries that can combine high energy density and long cycle life.

[0044] In a third aspect, the method for charging the lithium battery according to the embodiment of the present application includes: If the lithium battery needs to have a long cycle life, the charge cut-off voltage V s V s =cV b + a × c × K + b × c × (dQ / dV) / (3.6 × CA), and when the lithium battery exhibits long cycle life characteristics, the V s So, the lithium element is not deposited on the negative electrode of the lithium battery, and V s <V h and where V h is the upper limit of charging voltage that the lithium battery can tolerate, CA is the nominal capacity of the lithium battery when it is discharged at 0.33C, and V b is the reference voltage when elemental lithium does not precipitate on the negative electrode in the real-time charge capacity of the lithium battery, K is the internal resistance increase rate of the real-time DC internal resistance during the charging process of the lithium battery relative to the shipping DC internal resistance, dQ / dV is the real-time differential value of the charged quantity of electricity of the lithium battery with respect to the charging voltage, c is the calibration coefficient of the real-time cell temperature during the charging process of the lithium battery, a is the calibration coefficient of K, and b is the calibration coefficient of (dQ / dV) / CA.

[0045] In addition, the above V s The V is also the battery voltage when the negative electrode of the lithium battery is charged until elemental lithium is deposited (i.e., the positive electrode of the battery is charged to the first threshold). his the battery voltage when the lithium battery is fully charged (i.e., the positive electrode is charged to SOC 100%), that is, the end voltage corresponding to the maximum capacity that the positive electrode can exert, also called the rated voltage. Obviously, when the voltage of the lithium battery is V s When the capacitance C s is the voltage of the lithium battery above V h When the capacitance C h Smaller than.

[0046] If the lithium battery needs to have a long cycle life, the end-of-charge voltage must be V s When the negative electrode of the lithium battery is charged to a low SOC, the lithium battery is not fully charged, and the negative electrode terminal has a relatively low tolerance for volume expansion and a low side reaction with the electrolyte. Therefore, the lithium battery can be charged and discharged multiple times, i.e., has a long cycle life. When the lithium battery needs to exhibit high energy density characteristics, the end-of-charge voltage of the lithium battery is set to V. h When V h At this voltage, the negative electrode generally contains a lithium silicon alloy and a certain amount of elemental lithium.

[0047] Therefore, the end-of-charge voltage V h As the number of times a lithium battery is charged (i.e., fully charged) increases, the active lithium element is constantly consumed, and the end-of-charge voltage V s If you continue to charge a lithium battery at 100V, the V s is increased according to the above formula, and V s and V h This reduces the difference between V and V without compromising the battery's long cycle life. s It is possible to ensure that the energy density of the battery is improved when the end-of-charge voltage is V, and furthermore, the power vehicle using the lithium battery can exhibit a long driving range. For example, when the end-of-charge voltage of the lithium battery is V hIf the lithium battery needs to have a long cycle life, the final charge voltage V s should be increased according to the above formula, and the lithium battery should reach the end-of-charge voltage V h If a lithium battery is to exhibit long cycle life characteristics when not charged at V s remains as is.

[0048] For the assembled battery, its CA, V h is a constant value. b , dQ / dV, K, a, b, and c can be known by a lithium battery charging control device such as a Battery Management System (BMS), which can monitor battery status information such as the battery's charging current, real-time charging voltage, temperature, and internal resistance. This information can be collected and acquired by a collection module of the BMS and stored in the BMS control device. dQ / dV represents the amount of electricity charged at a unit voltage and can be calculated and obtained based on the current charging capacity point data (charging current and charging voltage) and the previous charging capacity point data during the same charging process, which are known by the battery's BMS.

[0049] V b is the reference voltage when no elemental lithium is deposited on the negative electrode in the real-time charge capacity of a lithium battery. It can be obtained by standardizing the capacity of the lithium-silicon composite negative electrode active material when no elemental lithium is deposited. Furthermore, by charging a battery that combines a positive electrode with the highest design capacity and a silicon-based negative electrode with a capacity 10% higher than this design capacity (i.e., the aforementioned lithium battery with N / P=1.1), a curve of its charge capacity and real-time battery voltage during the charging process can be obtained. Based on this curve, the real-time battery voltage at any charge capacity (i.e., the voltage reference value), i.e., V b It is possible to obtain V at each charge capacity. b may be pre-stored in the BMS.

[0050] The parameters a, b, and c are empirical values ​​and dimensionless. Preferably, the value range of a is 0.02 to 1.2, the value range of b is -0.008 to -0.15, and the value range of c is 0.8 to 1.5. The parameters a, b, and c can determine the corresponding calibration coefficients from the current battery state information based on the established correspondence between the battery state information and the corresponding calibration coefficients. Note that in the above formulas, a, b, c, and K are all obtained at the same time / time period during the same charging process of the lithium battery.

[0051] For example, a lithium battery generally has a specific operating temperature range, for example, between 10°C and 40°C. When the temperature of the lithium battery is high, for example, above a threshold temperature (for example, 42°C), for example, 45°C, the value of c becomes 0.92, and the adjusted end-of-charge voltage V s This is more effective in limiting the occurrence of lithium precipitation and fully utilizing the capacity before lithium precipitation. For example, the BMS may pre-store a correspondence relationship between the real-time cell temperature of the battery during charging and the temperature calibration factor c, and based on this correspondence, the temperature calibration factor c at the current charging temperature of the lithium battery cell can be determined. Table 1A below shows the correspondence relationship between cell temperature and temperature calibration factor. [Table 1A]

[0052] The internal resistance increase rate K is the increase rate of the collected real-time DC internal resistance of the lithium battery relative to the shipping DC internal resistance (also called the "initial DC internal resistance"). For example, if the shipping DC internal resistance of the lithium battery is R b Let R be the real-time internal resistance collected at a certain point in time. c Then, the internal resistance increase rate K is (R c -R b ) / R b Similarly, the correspondence relationship between the internal resistance increase rate K and the internal resistance calibration factor b may be stored in advance in the mobile terminal. For example, the following Table 1B is a correspondence relationship table between the internal resistance increase rate and the internal resistance calibration factor. [Table 1B]

[0053] Similarly, the correspondence between the differential of the electrical quantity ((dQ / dV) / CA) at unit capacitance and its calibration coefficient b may be stored in advance in the BMS. For example, the following Table 1C is a correspondence table between (dQ / dV) / CA and its calibration coefficient b. [Table 1C]

[0054] The charging method for the lithium battery is as follows: s When the above-mentioned lithium battery needs to exhibit high energy density characteristics, the above-mentioned lithium battery is h and stopping charging the lithium battery when it is no longer necessary for the lithium battery to exhibit high energy density characteristics (i.e., to maintain long cycle life characteristics).

[0055] Whether or not the lithium battery needs to exhibit high energy density characteristics can be determined by a user remotely during the charging process or by mode selection before charging, as will be described in detail below in the description of the powered vehicle.

[0056] In a fourth aspect, a battery system of a power vehicle 300 according to an embodiment of the present application includes at least one first battery unit, and the first battery unit includes a plurality of lithium batteries according to the first aspect of the present application. The battery system of the power vehicle can communicate with a vehicle drive unit 301. For example, the power vehicle 300 may be a pure electric vehicle or a hybrid electric vehicle. The vehicle drive unit 301 may be a motor.

[0057] In some embodiments, as shown in FIG. 3 , the battery system of the power vehicle 300 includes only a first battery unit 1. The first battery unit 1 may be a battery pack without modules or a battery pack with modules. When the first battery unit 1 is a battery pack with modules, multiple lithium batteries 100 may be connected in series, parallel, or a combination thereof to form a modularized battery pack. As shown in FIG. 3 , the first battery unit 1 includes multiple lithium batteries 100 and a first charge controller 110. The first charge controller 110 monitors status information of each lithium battery 100, such as voltage, current, internal resistance, and temperature, and controls the charging status of each lithium battery 100. Specifically, the first charge controller 110 may be a BMS (Battery Management System) for the first battery unit 1, or may be electrically connected to the BMS of the second battery unit as a separate module (in this case, the two may be connected via a CAN bus).

[0058] If the battery system of the power vehicle 300 includes only the first battery unit 1, the lithium battery can be controlled to be fully charged or charged to a low SOC depending on the actual driving range requirements of the power vehicle, thereby satisfying the long driving range requirements when necessary and ensuring a long cycle life when a short driving range is required.

[0059] Specifically, when the power vehicle operates in the first mode, the first charge control device 110 sets the charge end voltage for charging the lithium battery to V s When the power vehicle is operated in the second mode, the first charge control device further controls the charge end voltage for charging the lithium battery to V h and V s <V h and the above V s Therefore, no lithium element is deposited on the negative electrode of the lithium battery, and the lithium battery has a long cycle life characteristic and V his the upper limit charging voltage that the lithium battery can tolerate, and the cruising range provided to the power vehicle by the first battery unit in the first mode is shorter than the cruising range provided to the power vehicle by the first battery unit in the second mode. Here, the first mode can be called a short range mode, and the second mode can be called a long range mode.

[0060] The first mode is a mode frequently used by a power vehicle for, for example, daily short- to medium-distance commuting, while the second mode is less frequently activated and typically only needs to be activated when the vehicle is traveling long distances on holidays. When the power vehicle needs to operate in short-range mode, the first battery unit 1 controls the charging of the power vehicle by charging the lithium battery to a low SOC rather than to the upper charging voltage limit, thereby preventing elemental lithium from being deposited on the battery's negative electrode, which is beneficial to the lithium battery of the first battery unit exhibiting its long cycle life characteristics. When the power vehicle needs to operate in long-range mode, the lithium battery is fully charged, ensuring that the first battery unit exhibits high energy density characteristics. Thus, although the cycle life of the lithium battery in "long range mode" is not longer than its cycle life in "short range mode," because the "long range mode" is used less frequently, the protective layer prevents side reactions with the electrolyte when the lithium battery 100 is in a high energy density state, reducing the risk of lithium precipitation and penetration of the separator. This allows the entire first battery unit of the power vehicle to have multiple low SOC cycles and multiple full charge cycles, providing the vehicle with a long range when needed.

[0061] For example, the range of the powered vehicle in the first mode may be 400-800 km, and the range of the powered vehicle in the second mode may be 800-1200 km. The first mode may also be referred to as "daily mode" and is the mode most frequently used by the powered vehicle. The second mode may also be referred to as "holiday mode" and is the mode occasionally used by the powered vehicle.

[0062] In the process of charging the lithium battery, if the first charge control device 110 does not receive a command to activate the second operating mode of the powered vehicle 300, the first charge control device 110 sets the default charge end voltage for charging the lithium battery 100 to V s During or before charging the lithium battery 100, when the first charge control device 110 receives a command to activate the second operating mode of the powered vehicle 300, the first charge control device 110 sets the end-of-charge voltage for charging the lithium battery to V h Control to.

[0063] The "command to activate the second operating mode of the powered vehicle" may be set by mode selection before charging, or may be remotely activated during the charging process. Specifically, the command may be transmitted by the user of the powered vehicle pressing a mode button on the vehicle operation panel, or may be realized by the user remotely operating a smart device that can communicate with the vehicle (for example, when the charging voltage of the lithium battery is V s If the vehicle is close to the target, the vehicle's intelligent network connection system will push information to the user, such as whether to activate long-range mode.

[0064] In some embodiments of the present application, the end-of-charge voltage for charging the lithium battery for the i-th time is V h If so, the final charge voltage for the (i+1)th charge of the lithium battery is V s Adjust the above V s teeth, V s =cV b +a×c×K+b×c×(dQ / dV) / (3.6×CA), where CA is the nominal capacity of the lithium battery when it is discharged at 0.33C, and V bis the reference voltage when elemental lithium does not precipitate on the negative electrode in the real-time charge capacity of the lithium battery, K is the internal resistance increase rate of the real-time DC internal resistance during the (i+1)th charge process of the lithium battery relative to the shipping DC internal resistance, dQ / dV is the real-time differential value of the charged quantity of electricity with respect to the charge voltage during the (i+1)th charge process of the lithium battery, c is the calibration coefficient of the real-time cell temperature during the (i+1)th charge process of the lithium battery, a is the calibration coefficient of K, and b is the calibration coefficient of (dQ / dV) / CA.

[0065] As previously stated in this application, in this case, V s The main thing to adjust is V s and V h This is to minimize the difference and ensure as long a driving range as possible with the long life of the lithium battery.

[0066] In some other embodiments, as shown in FIG. 4 , the battery system of the power vehicle 300 further includes at least one second battery unit 2, which includes a plurality of second cells 200, and the negative electrode active material of the second cells 200 includes graphite and / or a silicon-based material. The silicon-based material includes one or more of elemental silicon, silicon oxide, silicon-based alloy, and silicon-carbon composite material. The second cells 200 are conventional lithium batteries that do not use metallic lithium (elemental lithium and / or lithium-silicon alloy) as the negative electrode active material, and their energy density is lower than that of the lithium battery 100 according to the first aspect of the present application.

[0067] Similar to the first battery unit 1, the second battery unit 2 may be a "module-less" battery pack or a "module-containing" battery pack, and in addition to a plurality of second cells 200, further includes a second charge control device 210 that monitors the charging of the second cells 200. Similarly, the second charge control device 210 may specifically be the BMS of the second battery unit 2, or may be an independent module electrically connected to the BMS of the second battery unit. Naturally, the second charge control device 210 and the first charge control device 110 may be integrated into the same control device.

[0068] In some embodiments of the present application, the power vehicle 300 operates in a first mode, and power is supplied to the power vehicle 300 only by the second battery unit 2, and the power vehicle 300 operates in a second mode, and power is supplied to the power vehicle 300 by both the first battery unit 1 and the second battery unit 2, or power is supplied to the power vehicle 300 only by the first battery unit 1, and the cruising range of the power vehicle in the first mode is less than the cruising range in the second mode.

[0069] Preferably, when the first charge control device 110 determines that the power vehicle is operating in the second mode before or during charging the lithium battery 100 of the first battery unit 1, it sets the end-of-charge voltage for charging the lithium battery 100 of the first battery unit 1 to the V h That is, when charging the lithium battery 100, it can be fully charged. Naturally, before or during charging the lithium battery 100 of the first battery unit 1, if the first charge control device 110 finds that the powered vehicle is operating in the second mode and that the first battery unit 1 and the second battery unit 2 are both supplying power to the powered vehicle 300 in the second mode, it will set the charge end voltage for charging the lithium battery 100 of the first battery unit 1 to the above V s However, in this case, the cruising range of the vehicle in the second mode is controlled by the second battery unit 2 and V h This is shorter than the cruising range that can be provided by the first battery unit 1 charged to 1000mV.

[0070] When the power vehicle 300 does not require a particularly long cruising range (e.g., when using the vehicle for daily commuting), it can power the vehicle using only the low-energy density second battery unit 2, thereby allowing the vehicle to tolerate more charge / discharge cycles and extend its service life. When the vehicle only occasionally requires a long cruising range (e.g., when using the vehicle for long-distance travel on holidays), it can power the vehicle using both the first battery unit 1 and the second battery unit 2, or the first battery unit 1 alone, thereby providing more sufficient power for the vehicle and selectively achieving the goal of a long cruising range without sacrificing the overall cycle life. Therefore, by selectively using different battery units in the battery system according to different cruising ranges, the high-energy density battery units that are used less frequently in the power vehicle can exhibit a long cycle life, allowing the entire battery system to combine a long service life with a long cruising capability.

[0071] The present invention will now be further described with reference to several examples. [Example]

[0072] (1) Manufacturing of positive electrode plates 960g of the positive electrode active material ternary NCM 622, 30g of adhesive PVDF, 5g of conductive agent acetylene black, and 5g of conductive agent carbon fiber were added to 2000g of solvent NMP (nitrogen methyl pyrrolidone), and then stirred with a vacuum mixer to form a stable and uniform positive electrode paste. The positive electrode paste was applied uniformly and intermittently to both sides of an aluminum foil (aluminum foil size: width 160 mm, thickness 16 μm) using a slit coater, then dried at a temperature of 393 K and pressed using a roll press, forming a 135 μm thick positive electrode material layer on the aluminum foil to obtain a positive electrode plate. The positive electrode plate was then cut into a rectangular electrode plate measuring 48 mm × 56 mm, and tabs were spot-welded to the widthwise positions.

[0073] (2) Preparation of electrolyte In a glove box filled with argon gas (H2O content ≦ 5 ppm, O2 content ≦ 5 ppm), ethylene glycol dimethyl ether (DME), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), and difluoroethyl acetate (DFEA) were mixed in a volume ratio of DME:TTE:DFEA = 30:50:20, and then 60 wt% of lithium bisfluorosulfonimide LiN(SO2F)2 was added to the mixed solution to obtain an electrolyte solution.

[0074] (3) Manufacturing of negative electrodes a. First, 1000 g of silicon monoxide powder was added to 2000 g of water, and then 50 g of the adhesive polyacrylic acid (PAA) and 20 g of the conductive agent acetylene black were added. The mixture was vigorously stirred until a uniform and stable negative electrode paste was formed. The negative electrode paste was then uniformly and intermittently applied to both sides of a copper foil (copper foil size: width 160 mm, thickness 8 μm) using a slit coater. The paste was then dried at a temperature of 393 K and pressed using a roll press. After that, a 60 μm-thick silicon monoxide negative electrode material layer was formed on the copper foil, and a negative electrode plate SA1 was obtained.

[0075] b. First, 200 g of PEO with a molecular weight of 600,000 was added to 2,000 g of acetonitrile, and then 16 g of nano-alumina powder and 10 g of anhydrous lithium nitrate powder were added. The mixture was vigorously stirred until a uniform and stable protective layer paste was formed. The protective layer paste was then evenly and intermittently applied to negative electrode plate SA1 to obtain negative electrode plate SA2.

[0076] c) In a glove box (H2O content ≦5 ppm, O2 content ≦5 ppm), the negative electrode plate SA2 was bonded to a 15 μm-thick lithium thin film coated with a PET release film, bringing the protective layer into contact with the lithium thin film. Under the action of a hot press, all of the lithium elements on the lithium thin film were transferred to the negative electrode plate SA2, yielding negative electrode plate SA3. The negative electrode material layer of the negative electrode plate SA3 was 78 μm thick, and the lithium silicon negative electrode active material therein comprised a lithium silicon alloy and Li2O. The negative electrode plate SA3 was cut into rectangular plates measuring 49 mm × 57 mm, and tabs were spot-welded across the width to obtain negative electrodes for battery assembly.

[0077] (4) Battery assembly The positive electrode plate obtained in step (1) and the negative electrode plate obtained in step (3) were alternately stacked together with a separator to obtain a bare cell, with the positive electrode plate and the negative electrode plate separated by the separator. The bare cell was placed in an aluminum plastic film case, and the electrolyte prepared in step (2) was poured into it. After vacuum sealing, the cell was left at 60°C for 48 hours, pressure-formed at 60°C, secondary packaged, evacuated, and graded, and the lithium battery of Example 1 was obtained.

[0078] When the lithium battery of Example 1 is fully charged, the lithium silicon composite negative electrode active material contains lithium element and lithium silicon alloy Li 4.4 The lithium silicon composite negative electrode active material contains Si, and the molar ratio of lithium in the lithium silicon composite negative electrode active material is 23%, and the lithium silicon alloy Li 4.4 The molar ratio of Si is 71%.

[0079] The lithium battery of Example 1 of the present application was subjected to a charge-discharge cycle test by the following method.

[0080] The lithium battery of Example 1 was placed in a LAND CT 2001C secondary battery performance testing device and subjected to a charge-discharge cycle test at 25±1°C. The steps of the first conventional low SOC cycle were as follows: After 10 minutes of rest, the battery was first charged at a constant current of 0.2C until the end-of-charge voltage reached 3.95V, then charged at a constant voltage of 0.05C, left for 10 minutes, and then discharged at a constant current until the voltage reached 3.0V. This constituted one conventional low SOC cycle. This step was repeated 30 times, resulting in a total of 30 conventional low SOC cycles. The steps of the high-energy cycle were as follows: After 10 minutes of rest, the battery was first charged at a constant current of 0.2C until the voltage reached 4.25V, then charged at a constant voltage of 0.05C, left for 10 minutes, and then discharged at a constant current until the voltage reached 3.0V. This constituted one high-energy cycle. One high-energy cycle was performed for every 30 conventional cycles. Each high-energy cycle produces a s =cV b +a×c×K+b×c×(dQ / dV) / (3.6×CA) was used to calibrate the end-of-charge voltage of the next conventional low SOC cycle.

[0081] When the discharge capacity of the battery during the cycle is lower than 80% of the initial discharge capacity, the cycle is terminated, and the cycle number n is the cycle life of the lithium battery. The capacity retention rate at the cycle number n is recorded, and the ratio of the battery energy density at the cycle number n to the initial energy density is defined as the energy retention rate of the lithium battery. [Example]

[0082] The lithium battery differs from Example 1 in that in step (3), 800 g of silicon powder is used instead of silicon monoxide powder, and the thickness of the lithium thin film coated on the PET release film is 12 μm.

[0083] When the lithium battery of Example 2 was fully charged, the molar ratio of lithium in the lithium silicon composite negative electrode active material was 24%, and the molar ratio of lithium silicon alloy Li 4.4The molar ratio of Si is 76%.

[0084] The lithium battery of Example 2 was charged according to the charge-discharge process of Example 1. [Example]

[0085] The lithium battery differs from Example 1 in that in step (3), 800 g of silicon powder is used instead of silicon monoxide powder, and the thickness of the lithium thin film coated on the PET release film is 10 μm.

[0086] In the fully charged state of the lithium battery of Example 3, the molar ratio of lithium element in the lithium silicon composite negative electrode active material was 18%, and the molar ratio of lithium silicon alloy Li 4.4 The molar ratio of Si is 82%.

[0087] The lithium battery of Example 3 was charged according to the charge-discharge process of Example 1. [Example]

[0088] The lithium battery in Example 3 has the same structure as that in Example 3, but differs in that the first conventional low SOC cycle in Example 3, in which "charging was performed at a constant current of 0.2 C until the end-of-charge voltage reached 3.95 V," was changed to an end-of-charge voltage of 4.0 V.

[0089] To highlight the beneficial effects of the examples of the present application, the following comparative examples are provided. (Comparative Example 1)

[0090] The lithium battery differs from Example 1 in that in step (3), the manufactured negative electrode plate SA1 is used as the negative electrode plate DS1 for assembling the lithium battery of Comparative Example 1, the negative electrode of Example 1 does not contain metallic lithium, and in step (2), the solvent of the electrolyte is an ester-based solvent, specifically, a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 4:6.

[0091] The charge-discharge cycle test for the lithium batteries manufactured in Comparative Example 1 was carried out by placing five lithium batteries in a LAND CT 2001C secondary battery performance testing device and conducting a charge-discharge cycle test at 0.2C at 25±1°C. The steps were as follows: After leaving the batteries for 10 minutes, they were first charged at a constant current of 0.2C until the end-of-charge voltage reached 4.2V, then charged at a constant voltage of 4.2V until the end-of-charge voltage reached 0.05C, and then left for 10 minutes, after which they were discharged at a constant current to 3.0V. This constitutes one charge-discharge cycle.

[0092] The above charge / discharge steps are repeated, and when the discharge capacity of the battery during the cycle is lower than 80% of the initial discharge capacity, the cycle is terminated, and the cycle number n is the cycle life of the lithium battery. The capacity retention rate at the cycle number n is recorded, and the ratio of the battery energy density at the cycle number n to the initial energy density is defined as the energy retention rate of the lithium battery. (Comparative Example 2)

[0093] The manufacturing process of the lithium battery differs from that of Example 1 in that in step (3), no protective layer is formed on the negative electrode plate SA1, the negative electrode plate SA1 is thermocompressed with a thin lithium film coated with a PET release film, and the resulting negative electrode plate DS2 is assembled to obtain the lithium battery of Comparative Example 2.

[0094] In order to strongly support the beneficial effects of the technical measures of the present invention, the battery was subjected to energy density (battery volume and discharge energy tests) and cycle life tests. The test results are shown in Table 2. [Table 2]

[0095] As can be seen from Table 2, the lithium battery according to the embodiment of the present application simultaneously exhibits the characteristics of high energy density and long cycle life.

[0096] The above examples merely illustrate some exemplary embodiments of the present application, and although the description is specific and detailed, it should not be understood as limiting the scope of the claims of the present application. It should be noted that a person skilled in the art may make further modifications and improvements without departing from the concept of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present application should be determined based on the scope of the attached claims.

Claims

1. A lithium battery comprising: a positive electrode plate; a negative electrode plate; a separator located between the positive electrode plate and the negative electrode plate; and an electrolyte; wherein a negative electrode material layer of the negative electrode plate contains a lithium silicon composite negative electrode active material, and a protective layer is provided on a surface of the negative electrode material layer or on a surface of the lithium silicon composite negative electrode active material, the protective layer comprising a polymer matrix and a lithium salt; When the lithium battery is fully charged, the lithium silicon composite negative electrode active material is composed of lithium element and lithium silicon alloy Li ４．４ A lithium battery containing Si, wherein the molar ratio of the lithium element in the lithium silicon composite negative electrode active material is 15% to 95%.

2. When the lithium battery is fully charged, the lithium silicon alloy Li ４．４ 2. The lithium battery according to claim 1, wherein the molar ratio of Si is 5% to 85%.

3. 2. The lithium battery of claim 1, wherein the polymer matrix comprises one or more of polyethylene oxide, polysiloxane, polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, and derivatives and copolymers thereof, and the lithium salt comprises one or more of lithium nitrate, lithium sulfide, lithium chloride, lithium bromide, lithium iodide, lithium fluoride, and lithium phosphate.

4. 2. The lithium battery of claim 1, wherein the N / P ratio is less than 1.

5. 2. The lithium battery according to claim 1, wherein the solvent in the electrolyte solution comprises an ether-based solvent, and the ether-based solvent comprises at least one of a non-halogenated ether-based solvent and a fluorinated ether-based solvent.

6. 2. The lithium battery of claim 1, wherein the lithium silicon composite negative electrode active material does not contain elemental lithium when the SOC of the positive electrode charged is lower than a first threshold, and the first threshold is 15% to 95%.

7. A method for manufacturing a lithium battery, comprising: a mixed paste containing a silicon-based material, a conductive agent, and an adhesive is applied to a negative electrode current collector, dried, and roll-pressed to form a silicon-based material layer on the negative electrode current collector; hot-pressing the lithium thin film and the silicon-based material layer so that all lithium elements in the lithium thin film are transferred to the silicon-based material layer and react with the silicon-based material in situ to form a negative electrode material layer containing a lithium silicon composite negative electrode active material, thereby obtaining a negative electrode plate; and forming a protective layer on the surface of the silicon-based material layer before hot pressing the silicon-based material layer and the lithium thin film; or forming a protective layer on the surface of the negative electrode material layer after forming the negative electrode material layer, wherein the protective layer includes a polymer matrix and a lithium salt; and assembling the negative electrode plate to form a lithium battery, When the lithium battery is fully charged, the lithium silicon composite negative electrode active material is a mixture of lithium and a lithium silicon alloy, Li ４．４ The method for producing a lithium battery comprises: containing Si; and the molar ratio of the lithium element in the lithium silicon composite negative electrode active material is 15% to 95%.

8. The method of claim 7 , wherein the silicon-based material comprises at least one of elemental silicon, silicon oxide, silicon-based non-lithium alloys, and other silicon-containing compounds.

9. A power vehicle, wherein the battery system includes at least one first battery unit, the first battery unit including a plurality of lithium batteries according to any one of claims 1 to 6 and a first charge control device.

10. The first charge control device sets a charge end voltage for charging the lithium battery to V before or during charging the lithium battery of the first battery unit and when it is determined that the power vehicle is operating in a first mode. ｓ Controlled to The first charge control device may further set a charge end voltage for charging the lithium battery to V when it is determined that the power vehicle is operating in a second mode before or during charging the lithium battery of the first battery unit. ｈ and V ｈ is the upper limit charging voltage that the lithium battery can tolerate, and V ｓ <V ｈ and V ｓ is the lowest voltage at which elemental lithium does not deposit on the negative electrode of the lithium battery, 10. The powered vehicle of claim 9, wherein the range of the powered vehicle in the first mode is less than the range of the powered vehicle in the second mode.

11. 10. The power vehicle according to claim 9, wherein the battery system further includes at least one second battery unit, the second battery unit including a plurality of second cells, and a negative electrode active material of the second cells including graphite and / or a silicon-based material.

12. When the power vehicle operates in a first mode, power is supplied to the power vehicle only by the second battery unit, and when the power vehicle operates in a second mode, power is supplied to the power vehicle by both the first battery unit and the second battery unit, or power is supplied to the power vehicle only by the first battery unit; 12. The motor vehicle of claim 11, wherein a range in the first mode is less than a range in the second mode.

13. Before or during charging of the first battery unit, when the first charge control device determines that the power vehicle is operating in a second mode and that power is supplied to the power vehicle only by the first battery unit, the first charge control device sets a charge end voltage for charging each lithium battery of the first battery unit to V ｈ and V ｈ 13. The motor vehicle according to claim 12, wherein ≅ is the upper limit charging voltage that can be tolerated by the lithium battery.

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