Lithium battery and its preparation and control method, battery system, and electric vehicle

Abstract

The lithium battery has a positive electrode and a negative electrode, and the negative electrode material layer of the negative electrode is made of a lithium-silicon composite negative electrode active material. When the lithium battery is charged to 100% SOC, the lithium-silicon composite negative electrode active material is a lithium-silicon alloy Li 4.4 The positive electrode comprises a first active positive electrode material and a second active positive electrode material, the first active positive electrode material containing lithium, and the second active positive electrode material comprises elemental sulfur and / or a sulfur-containing compound. The present application also provides methods for preparing and controlling the lithium battery, a battery system including the lithium battery, and an electric vehicle.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This disclosure claims priority to and the benefit of Chinese Patent Application No. 202211742564.3, entitled "LITHIUM BATTERY AND PREPARATION METHOD AND CONTROL METHOD THEREFOR, BATTERY SYSTEM, AND ELECTRIC VEHICLE," filed on December 29, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to the field of lithium battery technology, and in particular to lithium batteries and methods for preparing and controlling the same, battery systems, and electric vehicles. [Background technology]

[0003] Lithium batteries are widely used in portable electronic products such as mobile phones and notebook computers, as well as in new energy vehicles. Currently, the energy density of commercially available lithium batteries based on conventional graphite anodes has reached its limit, making it unable to meet people's increasing demands for battery life and standby power. Due to the high theoretical specific capacity of lithium metal and silicon-based anode materials, they are considered to be the preferred choice for next-generation high-energy density battery anode materials.

[0004] In the actual use of new energy vehicles, there may be various mode requirements for endurance mileage. However, existing lithium batteries using lithium metal or silicon-based negative electrode materials can hardly meet users' requirements for various endurance mileage modes and can hardly withstand deep discharge. Summary of the Invention

[0005] In view of this, the present disclosure provides a lithium battery, a preparation method and control method thereof, a battery system, and an electric vehicle to solve the problem that current lithium batteries cannot meet users' demands for various endurance mileage modes and have insufficient over-discharge resistance.

[0006] Specifically, according to a first aspect, the present disclosure provides a lithium battery, the lithium battery comprising: a positive electrode comprising a first positive electrode active material and a second positive electrode active material, wherein the first positive electrode active material comprises elemental lithium and the second positive electrode active material comprises elemental sulfur and / or a sulfur-containing compound; A negative electrode including a negative electrode material layer, the negative electrode material layer including a lithium-silicon composite negative electrode active material, and when a lithium battery is charged to SOC 100%, the lithium-silicon composite negative electrode active material is a lithium-silicon alloy Li 4.4 a negative electrode containing Si and elemental lithium; Includes:

[0007] The lithium battery provided in the first aspect of the present disclosure has a negative electrode comprising a lithium-silicon composite negative electrode active material and a positive electrode comprising both a first positive electrode active material and a second positive electrode active material. This allows the lithium battery to exhibit high energy density and long cycle life characteristics as required, and also has good over-discharge resistance. The lithium battery can provide an emergency mileage during over-discharge without significant damage to the battery's positive electrode structure or significant impact on the battery's cycle life.

[0008] In some implementations, the lithium intercalation onset potential of the second active positive electrode material is equal to or lower than the lithium intercalation cutoff potential of the first active positive electrode material, and the lithium intercalation cutoff potential of the second active positive electrode material is higher than the potential at which the transition metal element in the first active positive electrode material undergoes an irreversible reduction reaction.

[0009] In some embodiments, the first positive electrode active material contains one or more of lithium transition metal oxides and lithium-containing phosphates, and / or the sulfur-containing compound contains one or more of metal sulfides and sulfonated polyacrylonitrile. The metal element in the metal sulfide contains one or more of lithium, molybdenum, copper, silver, titanium, zinc, manganese, iron, cobalt, and nickel.

[0010] In some embodiments, the mass of the second positive electrode active material is 1.6% to 22% of the mass of the first positive electrode active material.

[0011] In some embodiments, when the lithium battery is charged to 100% SOC, the molar fraction of elemental lithium in the lithium-silicon composite negative electrode active material ranges from 15% to 95%.

[0012] In some embodiments, when the lithium battery is charged to a level not exceeding the first SOC threshold, the lithium-silicon composite negative electrode active material does not contain elemental lithium, and the lithium-silicon alloy Li x Si is included. 0 < x ≤ 4.4, and the first SOC threshold ranges from SOC15% to SOC95%.

[0013] In some embodiments, the surface of the negative electrode material layer has a protective layer, or the surface of the lithium-silicon composite negative electrode active material has a protective layer. The protective layer contains a polymer matrix and a lithium salt.

[0014] In some embodiments, the polymer matrix contains one or more of polyethylene oxide, polysiloxane, polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, and their derivatives and copolymers. The lithium salt contains one or more of lithium nitrate, lithium sulfide, lithium chloride, lithium bromide, lithium iodide, lithium fluoride, and lithium phosphate.

[0015] In some implementations, the lithium battery further includes an electrolyte, wherein the solvent in the electrolyte includes at least one of a non-halogenated ether solvent and a fluorinated ether solvent.

[0016] According to a second aspect, the present disclosure further provides a method for preparing a lithium battery, comprising the steps of:

[0017] A silicon-based material layer containing a silicon-based material is formed on the negative electrode current collector, and the lithium metal and silicon-based material layer are hot-pressed in an inert atmosphere, resulting in an in situ reaction between the lithium metal and the silicon-based material to form a negative electrode material layer containing a lithium-silicon composite negative electrode active material, thereby obtaining a negative electrode.

[0018] A positive electrode is provided, the positive electrode including a first active positive electrode material and a second active positive electrode material, the first active positive electrode material including elemental lithium, and the second active positive electrode material including elemental sulfur and / or a sulfur-containing compound.

[0019] When the negative electrode and positive electrode are assembled into a lithium battery and the lithium battery is charged to SOC 100%, the lithium-silicon composite negative electrode active material is converted into the lithium-silicon alloy Li 4.4 Includes Si and elemental lithium.

[0020] The preparation method of the lithium battery has a simple process and is easy to control.

[0021] In some implementations, in the anode, the lithium-silicon composite anode active material is a lithium-silicon alloy, Li x Contains Si and does not contain elemental lithium. x≦4.4.

[0022] In some implementations, the silicon-based material includes one or more of elemental silicon, silicon oxide, and silicon-based non-lithium alloys.

[0023] In some implementations, the lithium metal is a thin lithium film. The method further includes forming a protective layer on the surface of the silicon-based material layer before hot-pressing the lithium metal and the silicon-based material layer in an inert atmosphere, or forming a protective layer on the surface of the negative electrode material layer after forming the negative electrode material layer. The protective layer includes a polymer matrix and a lithium salt.

[0024] According to a third aspect, the present disclosure provides a control method for the aforementioned lithium battery, the control method including:

[0025] When a command is received to instruct the lithium battery to enter the first preset mode, the charge cutoff voltage for charging the lithium battery is V h The control is performed so that

[0026] V h >V s V s In this case, elemental lithium is not deposited on the negative electrode of the lithium battery. The charging voltage of the lithium battery is V s From V h When the negative electrode active material is between 4.4 Includes Si and elemental lithium.

[0027] The control method is used to charge the aforementioned lithium battery, so that it can be ensured that the lithium battery can meet the long cycle life requirements for high-frequency normal durability and can also meet the low-frequency durability requirements.

[0028] In some implementations, when a command is received indicating that the lithium battery should enter the second preset mode, the charge cutoff voltage for charging the lithium battery is V s The control is performed so that

[0029] In some implementations, during charging of the lithium battery, the charging voltage of the lithium battery is V sIf a command is received instructing the lithium battery to enter the first preset mode when V is reached, the lithium battery will continue to h and if a command instructing the lithium battery to enter the first preset mode is not received, charging of the lithium battery is controlled to be stopped.

[0030] According to a fourth aspect, the present disclosure provides another control method for the aforementioned lithium battery, the control method including:

[0031] When a command instructing the lithium battery to enter the third preset mode is received, the lithium battery is controlled to be discharged to a first discharge threshold voltage V1, which is the potential V at which the transition metal element in the first positive electrode active material undergoes an irreversible reduction reaction. R That's all.

[0032] The control method can be used to discharge the aforementioned lithium battery, so that in an emergency when the lithium battery's circuit is about to be exhausted, the second positive electrode active material is activated to ensure that the lithium battery can continue to output power and provide durable driving range in the emergency.

[0033] In some implementations, when the voltage of the discharging lithium battery is close to a second discharge threshold voltage V2, if a command is received instructing the lithium battery to enter a third preset mode, the lithium battery is controlled to continue discharging to a first discharge threshold voltage V1, where V2>V1, and V2 is equal to the lithium insertion cutoff potential of the first positive electrode active material.

[0034] In some implementations, V1 is expressed as V1=βV R The following is satisfied: 1.0≦β≦1.5.

[0035] According to a fifth aspect, the present disclosure further provides a battery management system including a memory and a processor, the memory storing program instructions, and the processor being adapted to load the program instructions and execute the method for controlling a lithium battery according to the third aspect of the present disclosure and / or execute the method for controlling a lithium battery according to the fourth aspect of the present disclosure.

[0036] According to a sixth aspect, the present disclosure further provides a battery system for an electric vehicle, the battery system including a battery management system and at least one lithium battery according to the first aspect of the present disclosure.

[0037] The electric vehicle uses a battery system having the aforementioned lithium batteries, and the charge cut-off voltage for charging each lithium battery and the discharge cut-off voltage for discharging each lithium battery may be adjusted according to the actual endurance mileage requirements of the electric vehicle.

[0038] In some implementations, if the battery management system recognizes that the electric vehicle should operate in the first mode before or during charging of the lithium battery, it sets the charging cutoff voltage for charging the lithium battery to V h The control is configured to be such that:

[0039] V h is the upper limit charging voltage that a lithium battery can withstand, and V h >V s V s In this case, elemental lithium is not deposited on the negative electrode of the lithium battery. s From V h When the negative electrode active material is between 4.4 Includes Si and elemental lithium.

[0040] In some implementations, the battery management system sets a charging cutoff voltage for charging the lithium battery to V if it recognizes that the electric vehicle should operate in the second mode before or during charging of the lithium battery. sThe control is configured so that the endurance driving distance of the electric vehicle in the second mode is shorter than the endurance driving distance of the electric vehicle in the first mode.

[0041] In some implementations, the battery management system is configured to control a discharge cutoff voltage for discharging the lithium battery to be V1 when it is recognized that the electric vehicle should operate in a third mode in which the second positive electrode active material can achieve capacity before or during discharging the lithium battery.

[0042] V1 is equal to or higher than the potential at which the transition metal element in the first positive electrode active material undergoes an irreversible reduction reaction.

[0043] In some implementations, the battery management system is a battery management system according to a fifth aspect of the present disclosure.

[0044] According to a seventh aspect, the present disclosure further provides an electric vehicle, the electric vehicle having a battery system according to the sixth aspect of the present disclosure. [Brief explanation of the drawings]

[0045] [Figure 1A] 1A-1D are two schematic diagrams of the structure of a lithium battery according to one embodiment of the present disclosure. [Figure 1B] 1A-1D are two schematic diagrams of the structure of a lithium battery according to one embodiment of the present disclosure. [Figure 2] FIG. 1 illustrates a discharge curve of a lithium battery according to one embodiment of the present disclosure. [Figure 3] 1 is a schematic diagram of an electric vehicle structure according to one embodiment of the present disclosure. [Figure 4] FIG. 2 is a schematic diagram of another configuration of an electric vehicle according to an embodiment of the present disclosure. [Figure 5A] FIG. 1 shows a curve illustrating the relationship between negative electrode voltage and specific capacity of a lithium battery during a two-stage discharge process according to one embodiment of the present disclosure. [Figure 5B]FIG. 1 shows curves illustrating the relationship between negative electrode voltage and specific capacity of a lithium battery during a three-stage discharge process according to one embodiment of the present disclosure. [Figure 6] 1 is a schematic diagram of the structure of a lithium battery according to one embodiment of the present disclosure. [Figure 7] FIG. 1 is a schematic diagram of a battery management system according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0046] In the actual use of new energy vehicles, various mode requirements for endurance mileage may exist, such as a high-frequency daily mode to ensure that the battery has a long cycle life and a suitable high energy density, a low-frequency holiday mode to ensure that the battery has a higher energy density, and a low-frequency emergency mode to allow the battery to be deeply discharged to provide endurance mileage in an emergency and avoid failures caused by unexpected power depletion. However, existing lithium batteries using lithium metal or silicon-based negative electrode materials can hardly meet users' requirements for various endurance mileage modes, for example, they rarely have a high-energy-density holiday mode and can hardly withstand deep discharge. In consideration of this, embodiments of the present disclosure provide a lithium battery, a preparation method and control method thereof, a battery system, and an electric vehicle.

[0047] The following describes in detail the technical solutions in the embodiments of the present disclosure with reference to the accompanying drawings.

[0048] Referring to FIGS. 1A, 1B, and 6, one embodiment of the present disclosure provides a lithium battery. In the lithium battery 100, the positive and negative electrodes are in the form of electrode sheets. In other words, the lithium battery 100 includes a negative electrode sheet 10 and a positive electrode sheet 20, a separator 30 positioned between the positive electrode sheet 20 and the negative electrode sheet 10, and an electrolyte 40. Generally, the negative electrode sheet 10 includes a negative electrode current collector 11 and a negative electrode material layer 12 disposed on at least one surface of the negative electrode current collector 11. The negative electrode material layer 12 includes a lithium-silicon composite negative electrode active material, an optional conductive agent, a binder, and the like. Similarly, the positive electrode sheet 20 includes a positive electrode current collector 21 and a positive electrode material layer 22 disposed on at least one surface of the positive electrode current collector 21. The positive electrode material layer 22 includes a positive electrode active material, an optional conductive agent, a binder, and the like. The positive electrode material layer 22 may be a single coating layer or may have a superposed structure of two or more coating layers.

[0049] In the present disclosure, the lithium-silicon composite negative electrode active material includes elemental lithium and elemental silicon. When the lithium battery 100 is charged to a state of charge (SOC) of 100%, the lithium-silicon composite negative electrode active material is a lithium-silicon alloy Li 4.4 Includes Si and elemental lithium.

[0050] "The battery is charged to 100% SOC" refers to the state where the active lithium in the positive electrode of the battery is completely extracted. Specifically, it means that the positive electrode of the battery is charged to 100% SOC, that is, the battery is in a fully charged state. When the lithium battery of the present disclosure is fully charged, the positive electrode capacity of the battery is fully exerted. In addition to enabling the active lithium ions extracted from the positive electrode to be stored in the negative electrode in the form of a lithium-silicon alloy, the active lithium ions can further be deposited on the negative electrode in the form of elemental lithium. This "deposited lithium" part is active lithium and can exert its capacity. Thus, the energy density of the battery is very high. In addition, during the discharge of the battery, the active elemental lithium exerts its capacity earlier than the lithium-silicon alloy. When the battery is charged to 100% SOC, elemental lithium is deposited on the negative electrode. Therefore, the amount of the lithium-silicon alloy material Li x Si(0 < x ≦ 4.4) is less than that of the conventional negative electrode material, and the volume fraction of the lithium-silicon alloy material in the battery may be smaller. As a result, the energy density of the battery is improved. In addition, when the lithium battery is charged to a lower SOC, elemental lithium is not deposited on the negative electrode of the battery, the lithium-silicon composite negative electrode active material does not contain elemental lithium, and the negative electrode end is the lithium-silicon alloy Li x Si only exerts its capacity. The battery is charged and discharged at such a low SOC. As a result, the battery can have a long cycle life.

[0051] The positive electrode sheet of the battery in the present disclosure includes a first positive electrode active material and a second positive electrode active material. The first positive electrode active material includes elemental lithium, and the second positive electrode active material includes elemental sulfur and / or a sulfur-containing compound. The first positive electrode active material is a conventional positive electrode active material containing elemental lithium used in lithium batteries. The phrase "the first positive electrode active material includes elemental lithium" refers to the first positive electrode active material containing elemental lithium even when the SOC of the lithium battery is not 100%. In other words, even when lithium ions are not completely extracted from the positive electrode sheet but are transferred to the negative electrode sheet upon charging the battery, the first positive electrode active material itself contains elemental lithium. The second positive electrode active material is a sulfur-based active material used in lithium-sulfur batteries. The negative electrode of the battery in the present disclosure includes the aforementioned lithium-silicon composite negative electrode active material (lithium-silicon alloy Li x A certain amount of lithium (stored in the form of silicon) is pre-stored in the negative electrode, and this pre-stored lithium is not fully extracted during the battery's normal discharge mode. Thus, in an emergency, the pre-stored lithium in the negative electrode and the second positive electrode active material in the positive electrode sheet form a pair of primary batteries, releasing this portion of the pre-stored lithium, providing a durable driving range in an emergency and resolving the problem of breakdowns due to unexpected power depletion. It can be understood that if the negative electrode active material of a lithium battery is a material without pre-stored lithium, such as graphite, elemental silicon, or silicon oxide, the lithium battery does not have over-discharge resistance. Deep over-discharge can cause damage to the solid electrolyte membrane (SEI) on the negative electrode side, dissolution of the copper-based current collector, and other problems, which can further lead to battery gas generation, cycle decay, internal short circuits, and other problems. In addition, the pre-stored lithium extracted from the negative electrode during emergency mode can cause specific damage to the silicon negative electrode structure and interface, leading to side reactions and other problems. Therefore, the pre-stored lithium may simply be used less frequently. This effectively maintains the cycle life of the entire lithium battery.

[0052] Therefore, the lithium battery in this embodiment of the present disclosure can be charged in a state where the negative electrode does not precipitate elemental lithium during charging, resulting in a long cycle life. Furthermore, the lithium battery may also be charged in a state where elemental lithium is precipitated during charging, thereby achieving a higher energy density. Additionally, during discharge of the lithium battery, the lithium-silicon composite negative electrode active material can release specific capacity in the presence of a second positive electrode active material, if desired. Therefore, this lithium battery can be considered to have a long cycle life, high energy density, and over-discharge resistance. This can meet the requirements of various endurance mileage modes of electric vehicles and eliminate concerns about electric vehicle mileage.

[0053] In some implementations of the present disclosure, during discharge of a lithium battery, the lithium intercalation onset potential of the second positive electrode active material is less than the lithium intercalation cutoff potential V of the first positive electrode active material. L The lithium intercalation cutoff potential of the second positive electrode active material is equal to or less than the potential V at which the transition metal element in the first positive electrode active material undergoes an irreversible reduction reaction. R Higher than V L is the potential of the first positive electrode active material at the end of the reversible reduction reaction of the transition metal element in the first positive electrode active material, and is also the discharge cutoff voltage in the normal discharge mode of the lithium battery. In the case where the second positive electrode active material is not present, the discharge voltage of the battery is V L If the first positive electrode active material is less than 0.05 V (in other words, when the battery is in an over-discharged state), the structure of the first positive electrode active material may be damaged to some extent. This may significantly reduce the cycle performance of the battery. However, in the present disclosure, a second positive electrode active material that satisfies the above-mentioned condition is introduced. In this way, during discharge of a lithium battery, the second positive electrode active material participates in energy release only after the active lithium ions are released from the first positive electrode active material to the negative electrode, and the lithium insertion onset potential of the second positive electrode active material is V. R(Generally, the lithium insertion start potential of the positive electrode material is higher than the lithium insertion cutoff potential of the positive electrode material.) In this way, the lithium ions extracted from the negative electrode are better prevented from excessively reducing the transition metal elements in the first positive electrode active material, which can prevent the destruction of the positive electrode structure, the generation of battery gas, and the subsequent impact on the battery cycle.

[0054] At the stage where the second positive electrode active material is involved in the energy release of the lithium battery (i.e., when the lithium battery is in an over-discharged state), the discharge voltage of the lithium battery is V L V from below R Specifically, the discharge voltage of a lithium battery drops to αV L From βV R α is a constant greater than 0 and less than or equal to 1, such as 0.7, 0.8, 0.9, 0.95, or 1.0, and is preferably a constant close to 1.0. β is a constant greater than or equal to 1, such as 1.0, 1.1, 1.2, 1.3, or 1.5. For example, when the first positive electrode active material is a lithium ternary oxide material (such as lithium-nickel-cobalt-manganese oxide), V L may be set to 2.5 V. When the first positive electrode active material is lithium iron phosphate or lithium iron manganese phosphate, V L may be set to 2.0 V. In the case of lithium iron phosphate, the potential during the irreversible reduction reaction (also called overreduction) of the transition metal element during the discharge of the battery specifically refers to the voltage corresponding to the reduction of +2-valent Fe ions to +1-valent or 0-valent Fe. When the first positive electrode active material includes at least two (≧2) materials, V L is the lowest lithium intercalation cutoff potential of the first positive electrode active materials, and V R It can be understood that is the maximum potential at which the transition metal elements in the plurality of first positive electrode active materials undergo a reduction reaction during discharge of the lithium battery.

[0055] In this embodiment of the present disclosure, the first positive electrode active material may include, but is not limited to, one or more of lithium transition metal oxides and lithium-containing phosphates. The lithium transition metal oxides may include one or more of lithium monoxides (such as lithium cobalt oxide, lithium manganese oxide, and lithium nickel oxide), lithium binary oxides (such as lithium nickel manganese oxide and lithium nickel cobalt oxide), lithium ternary oxides (such as lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide), and lithium multi-element oxides. The lithium phosphates may include one or more of lithium iron phosphate, lithium manganese iron phosphate, and the like. The lithium phosphates may be undoped or modified by doping, and may or may not have a surface coating.

[0056] In one implementation of the present disclosure, the sulfur-containing compound includes one or more of a metal sulfide and sulfurized polyacrylonitrile (SPAN), and the metal element in the metal sulfide includes one or more of lithium (Li), molybdenum (Mo), copper (Cu), silver (Ag), titanium (Ti), zinc (Zn), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), etc. In some implementations, the second positive electrode active material is selected from the group consisting of S, Li2S, Mo6S8, CuS, MnS, FeS2, CoS2, NiS2, Fe 0.5 Co 0.5 S2, and SPAN.

[0057] In this implementation of the present disclosure, the mass of the second positive electrode active material may be 1.6% to 22% of the mass of the first positive electrode active material. The introduction of an appropriate amount of sulfur-based positive electrode active material does not excessively increase the internal resistance of the positive electrode side of the lithium battery, and also reduces the discharge current in a normal discharge mode (i.e., voltage V L This helps ensure that the lithium battery has a certain over-discharge resistance in emergencies when the battery is nearly depleted, without excessively reducing the energy density of the lithium battery in the discharge mode (mode in which the battery is discharged to the full capacity).

[0058] In some implementations of the present disclosure, as shown in FIG. 1A, in the positive electrode sheet 20, the second positive electrode active material and the first positive electrode active material are located on the same positive electrode material layer 22. The second positive electrode active material and the first positive electrode active material may be uniformly dispersed on the positive electrode material layer 22 having specific pores. The two materials are arranged on the same layer, so that when the battery is in an over-discharged state, the second positive electrode active material can be rapidly activated to easily exhibit its capacity. In some other implementations of the present disclosure, as shown in FIG. 1B, the positive electrode sheet 20 includes a first positive electrode coating 221 containing a first positive electrode active material and a second positive electrode coating 222 containing a second positive electrode active material, which are arranged in a laminated manner, and the second positive electrode coating 222 is spaced apart from the positive electrode current collector 21. The first positive electrode coating 221 and the second positive electrode coating 222 arranged in a laminated manner form a positive electrode material layer 22 on one side of the positive electrode sheet 20. The sulfur-based positive electrode active material with low conductivity is arranged spaced apart from the positive electrode current collector 21 to prevent the sulfur-based positive electrode active material from affecting the electron transfer in the positive electrode sheet 20. The second positive electrode coating 222 may also contain the first positive electrode active material.

[0059] In one implementation of the present disclosure, when the lithium battery 100 is charged to a level not exceeding the first SOC threshold value, the lithium-silicon composite negative electrode active material does not contain elemental lithium. In this case, the lithium-silicon composite negative electrode active material contains a lithium-silicon alloy that can be represented by the chemical general formula Li x Si, where 0 < x ≦ 4.4. The "first SOC threshold value" refers to the critical SOC value when the battery is charged until elemental lithium begins to precipitate at the negative electrode end, that is, when the lithium-silicon alloy in the negative electrode of the battery becomes completely saturated with lithium ions (specifically, the lithium-silicon alloy becomes Li 4.4 Si), and not all of the active lithium ions are extracted from the positive electrode side.

[0060] If the battery is charged below the first SOC threshold, the battery's negative electrode will not deposit lithium, the lithium battery's energy density will not be fully realized, and the negative electrode terminal will become a lithium-silicon alloy, Li x Only the capacity of Si is exerted, and as a result, the volume expansion tolerated by the negative electrode terminal is also weak, and side reactions between the negative electrode and the electrolyte are minor. In this way, the lithium battery can withstand multiple charge / discharge cycles at a relatively low energy density (still significantly higher than the energy density of current batteries using graphite as the negative electrode), i.e., has a longer cycle life. Therefore, the lithium battery provided in the present disclosure can take into account both the characteristics of "long cycle life" and "high energy density," and the two characteristics may be freely selected with reference to the battery management system of the lithium battery to meet the cycle requirements over the entire life of an electric vehicle.

[0061] In one embodiment of the present disclosure, when a lithium battery is charged to an SOC of 100%, the lithium-silicon composite negative electrode active material has an adjustable elemental lithium fraction, where the mole fraction of elemental lithium in the lithium-silicon composite negative electrode active material ranges from 15% to 95%, and specifically may be 18%, 20%, 22%, 25%, 30%, 35%, 40%, 42%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 92%, etc. Correspondingly, the aforementioned first threshold value may be appropriately adjusted based on the mole fraction of elemental lithium, and the cycle life and specific high energy density value of the lithium battery may be appropriately adjusted. Optionally, the first SOC threshold may be in the range of SOC 15% to SOC 95%, and may specifically be SOC 18%, SOC 20%, SOC 22%, SOC 25%, SOC 30%, SOC 35%, SOC 40%, SOC 42%, SOC 45%, SOC 50%, SOC 55%, SOC 60%, SOC 65%, SOC 70%, SOC 75%, SOC 80%, SOC 85%, SOC 90%, SOC 95%, etc.

[0062] Figure 2 shows the discharge curve of a lithium battery using a lithium-silicon composite anode active material. The discharge curve of a lithium battery has a discharge inflection point, which refers to the minimum value of dV / dQ in the discharge curve. Before the inflection point, the energy density of the battery (i.e., the product of the battery voltage and the battery level) is relatively high, and the lithium-silicon alloy Li 4.4 The capacity of both the silicon and elemental lithium is realized, with the elemental lithium capacity being realized first. After the inflection point, which corresponds to a state where the battery's SOC is low during charging, the negative electrode is filled with the lithium-silicon alloy Li. x Only the capacity of Si is utilized, and the battery's energy density is low, but the battery's cycle life is long.

[0063] In some implementations of the present disclosure, when the lithium battery 100 is charged to 100% SOC, the lithium-silicon composite negative electrode active material is a mixture of elemental lithium and lithium-silicon alloy Li 4.4 In this case, the lithium-silicon composite anode active material contains only lithium and silicon elements (in other words, the lithium-silicon composite anode active material may be formed by pressing elemental silicon and lithium metal in situ). Thus, the lithium-silicon alloy Li 4.4 The mole fraction of Si ranges from 5% to 85%.

[0064] The lithium battery in this disclosure contains, when fully charged, elemental lithium and Li 4.4 The aforementioned lithium-silicon composite anode active material containing Si is used, and therefore the N / P (ratio of the anode capacity to the cathode capacity of a lithium battery) of the lithium battery is less than 1. In this way, the volume fraction and mass fraction of the anode active material in the lithium battery can be small, resulting in a significant improvement in the energy density of the battery. The anode capacity corresponding to N is the ratio of lithium inserted into the anode to the lithium-silicon alloy Li 4.4 This refers to the negative electrode capacity when Si is formed and elemental lithium is not deposited, i.e., the negative electrode capacity corresponding to the first SOC threshold mentioned above.

[0065] Optionally, in the lithium battery 100, the volume ratio of the lithium-silicon composite negative electrode active material to the positive electrode active material ranges from 0.1375 to 0.825. The ratio of the thickness of the positive electrode sheet 20 to the thickness of the negative electrode sheet 10 ranges from 8:1 to 4:3. In this way, the N / P ratio of the lithium battery can be better ensured to be less than 1, facilitating an improvement in the energy density of the battery.

[0066] In some implementations of the present disclosure, the surface of the negative electrode material layer 12 further includes a protective layer 13 (see FIG. 1A ), or the surface of the lithium-silicon composite negative electrode active material includes a protective layer 13. The protective layer 13 includes a polymer matrix and a lithium salt. The protective layer 13 is substantially insoluble in the battery's electrolyte 40. The protective layer 13 guides the flow of lithium ions, controls their uniform deposition on the surface of the negative electrode sheet 10, effectively suppresses the growth of lithium dendrites on the surface of the negative electrode sheet 10, and prevents the lithium dendrites from penetrating the separator and causing an internal short circuit in the battery. In particular, when a lithium battery is charged to a high SOC where elemental lithium may be deposited on the negative electrode, the protective layer 13 reduces the side effects of elemental lithium deposition and effectively suppresses side reactions between elemental lithium and the electrolyte 40, thereby improving cycle performance and safety.

[0067] 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 ionic 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), etc. In some implementations, the protective layer may further include an inorganic filler to increase lithium ion permeation paths, improve mechanical properties, etc. The inorganic filler may be at least one of an oxide (e.g., silicon dioxide, aluminum oxide, titanium dioxide), a hydroxide (e.g., aluminum hydroxide, magnesium hydroxide), and a salt.

[0068] The electrolyte 40 of the lithium battery 100 generally includes a solvent and a second lithium salt. In this implementation of the present disclosure, the solvent in the electrolyte 40 of the lithium battery 100 is a non-carbonate solvent. Specifically, the solvent in the electrolyte 40 includes an ether solvent, specifically, at least one of a non-halogenated ether solvent and a fluorinated ether solvent. The side reaction between the carbonate solvent and the lithium metal negative electrode is rapid, easily generating sharp lithium dendrites in the battery negative electrode, which may penetrate the battery separator and cause the battery to spontaneously ignite. The ether solvent has high compatibility with lithium metal, and the side reaction between the ether solvent and lithium metal is much less likely than the side reaction between the carbonate solvent and lithium metal. The ether solvent effectively suppresses the consumption of active lithium during cycling, while improving the uniformity and density of lithium ion deposition and preventing the formation of sharp lithium dendrites that may penetrate the battery separator and pose a safety risk.

[0069] Optionally, the non-halogenated ether solvent may be selected from one or more of, but not limited to, 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, and the like. Optionally, 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, 2,2,3,3,3- The fluoroisopropyl ether may be selected from one or more of, but is not limited to, 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.

[0070] The second lithium salt in electrolyte 40 may be selected from, but is not limited to, one or more of lithium bis(fluorosulfonyl)imide (LiN(SOF)), lithium bis(trifluoromethylsulfonyl)imide (Li(CFSO)N), lithium bis(perfluoroethylsulfonyl)imide (Li(CFSO)N), lithium bis(oxalatoborate) (LiB(C0), LiBOB), lithium trifluoromethylsulfonate (LiCFSO), lithium perfluorobutylsulfonate (LiCFSO), tris(trifluoromethylsulfonyl)methyl lithium LiC(CFSO), and the like.

[0071] In this implementation of the present disclosure, the lithium-silicon composite negative electrode active material in the negative electrode sheet 10 may be formed by in situ pressing a silicon-based material and lithium metal. The silicon-based material may include, but is not limited to, one or more of elemental silicon, silicon oxide, silicon-based non-lithium alloys (such as silicon-germanium alloys, silicon-magnesium alloys, silicon-copper alloys, silicon-iron alloys, etc.), and the like.

[0072] In some implementations, the negative electrode material layer 12 containing the lithium-silicon composite negative electrode active material is formed by in-situ hot-pressing a lithium thin film (lithium foil or a lithium thin film attached to a release film) with an initial negative electrode material layer containing a silicon-based material. In this case, the lithium element of the lithium thin film may be completely transferred to the initial negative electrode material layer and react with the silicon-based material in situ to form the lithium-silicon composite negative electrode active material. In some other implementations, the lithium-silicon composite negative electrode active material is formed by in-situ pressing a mixture of lithium metal powder and a silicon-based material (which may be a wet slurry or a dry powder). In this case, the negative electrode material layer 12 may be formed by coating a mixed slurry of the silicon-based material and lithium powder on a negative electrode current collector, drying and pressing, and then reacting in situ on the negative electrode current collector to form a negative electrode material layer containing the lithium-silicon composite negative electrode active material. Alternatively, a mixture of lithium powder and silicon-based materials is pressed in-situ to form a lithium-silicon composite anode active material, and a slurry containing the lithium-silicon composite anode active material is coated, dried, and pressed to form an anode sheet.

[0073] When it is necessary to form the negative electrode material layer 12 having the protective layer 13 on its surface, the lithium thin film attached to the release film and the silicon-based material layer having the protective layer on its surface (the silicon-based material layer is the aforementioned initial negative electrode material layer including a silicon-based material and an optional binder and conductive agent) may be hot-pressed in situ. In another implementation of the present disclosure, the negative electrode material layer 12 having the protective layer 13 on its surface may alternatively be obtained by forming a protective layer on the surface of the negative electrode material layer 12 including the lithium-silicon composite negative electrode active material.

[0074] In the present disclosure, the negative electrode current collector 11 and the positive electrode current collector 21 are independently selected from elemental metal foils or alloy foils. For example, the negative electrode current collector 11 may be specifically copper foil, and the positive electrode current collector 21 may be specifically aluminum foil. The binder and conductive agent in the negative electrode sheet 10 and the positive electrode sheet 20 are materials commonly used in the battery field. For example, each conductive agent may be independently selected from one or more of conductive carbon black (such as acetylene black or ketjen black), carbon nanotubes, carbon fiber, graphite, and furnace black. Each binder may be independently selected from one or more of styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyolefins (such as polyethylene and polypropylene), sodium carboxymethyl cellulose (CMC), sodium alginate, and the like.

[0075] The lithium battery provided in this embodiment of the present disclosure includes a lithium-silicon composite anode active material. As a result, the proportion of the lithium-silicon composite anode active material in the lithium battery is low, facilitating an improvement in the battery's energy density. In particular, the deposition of elemental lithium at high SOC can improve the battery's energy density. When the battery is charged to a low SOC, the anode does not deposit lithium, resulting in better cycle performance. In addition, the combination of the lithium-silicon composite anode active material with a sulfur-based second cathode active material improves the lithium battery's over-discharge resistance and provides a durable driving range in emergency situations. Therefore, the lithium battery according to this embodiment of the present disclosure can meet the requirements of various electric vehicle applications and significantly reduce concerns about driving range.

[0076] An embodiment of the present disclosure further provides a method for preparing the aforementioned lithium battery, including the following steps:

[0077] S01: A silicon-based material layer is formed on an anode current collector, and the lithium metal and silicon-based material layer are hot-pressed in an inert atmosphere, resulting in an in situ reaction between the lithium metal and the silicon-based material to form an anode material layer containing a lithium-silicon composite anode active material, thereby obtaining an anode sheet.

[0078] S02: A positive electrode sheet is provided, the positive electrode sheet including a first positive electrode active material and a second positive electrode active material, the first positive electrode active material including elemental lithium, and the second positive electrode active material including elemental sulfur and / or a sulfur-containing compound.

[0079] S03: When the negative electrode sheet and the positive electrode sheet are assembled into a lithium battery, and the lithium battery is charged to SOC 100%, the lithium-silicon composite negative electrode active material is the lithium-silicon alloy Li 4.4 It contains silicon and elemental lithium, and the mole fraction of elemental lithium in the lithium-silicon composite anode active material ranges from 15% to 95%.

[0080] In step S01, a silicon-based material layer may be formed on one surface or both opposing surfaces of the negative electrode current collector. Correspondingly, a negative electrode material layer containing a lithium-silicon composite negative electrode active material may also be formed on one surface or both opposing surfaces of the negative electrode current collector. For the principle of forming the negative electrode material layer, please refer to the previous description in this disclosure. The silicon-based material layer may be formed by coating, drying, and rolling a mixed slurry containing a silicon-based material, a conductive agent, and a binder. The silicon-based material may include, but is not limited to, elemental silicon, silicon oxide, silicon-based non-lithium alloys (such as silicon-germanium alloys, silicon-magnesium alloys, silicon-copper alloys, and silicon-iron alloys), other silicon compounds (such as fluorine-containing silicon oxides, lithium hexafluorosilicate, silicon carbide, and silicon boride), etc.

[0081] In the negative electrode material layer prepared in step S01, the lithium-silicon composite negative electrode active material is a lithium-silicon alloy Lix It contains Si and does not contain elemental lithium. x ≤ 4.4. When the silicon-based material used contains elements other than silicon (such as oxygen and fluorine), the lithium-silicon composite negative electrode active material correspondingly contains that element as well. For example, when the silicon-based material used is elemental silicon and the battery is charged to a level below the aforementioned first SOC threshold, the lithium-silicon composite negative electrode active material is the lithium-silicon alloy Li x Si only. When the lithium battery is charged to SOC 100%, the lithium-silicon composite negative electrode active material is elemental lithium and Li 4.4 contains only Si. For example, when the silicon-based material is silicon oxide and the battery is charged to a level below the aforementioned first SOC threshold, the lithium-silicon composite negative electrode active material may contain at least one of Li2O, Li2SiO3, etc., and the lithium-silicon alloy Li x Si (0 < x < 4.4). When the lithium battery is charged to SOC 100%, the lithium-silicon composite negative electrode active material contains at least one of Li2O, Li2SiO3, etc., and Li 4.4 Si and elemental lithium.

[0082] In some implementations of the present disclosure, in step S01, a protective layer may be formed on the surface of the silicon-based material layer before hot-pressing the lithium metal and silicon-based material layer in an inert atmosphere. When the silicon-based material layer and lithium metal having the protective layer on its surface are hot-pressed in situ, the protective layer and silicon-based material layer exhibit a porous structure under hot-pressing. The lithium element of the lithium metal penetrates into the silicon-based material layer and reacts with the silicon-based material in situ to form a lithium-silicon composite negative electrode active material, ultimately forming a negative electrode material layer having the protective layer. The negative electrode material layer includes a lithium-silicon composite negative electrode active material. In some other implementations of the present disclosure, a protective layer may alternatively be formed on the surface of the negative electrode material layer after the negative electrode material layer is formed. For the composition of the protective layer, see the previous description of the present disclosure. The protective layer may be formed by liquid coating, vapor deposition, electrodeposition, or the like.

[0083] In some implementations of the present disclosure, the lithium metal used in the hot-pressing with the silicon-based material layer may be a thin lithium film, specifically a lithium foil, or a thin lithium film attached to a release film, optionally attached to a release film to avoid loss of elemental lithium due to direct contact between the lithium metal and the hot-pressing device.

[0084] In step S02, the method for preparing the positive electrode sheet is not limited. In some implementations, the positive electrode sheet may be prepared by the following method: a mixed slurry containing a first positive electrode active material, a conductive agent, and a binder is coated on a positive electrode current collector, and after drying, an initial positive electrode material layer is formed on the positive electrode current collector. A second positive electrode active material is deposited on the surface of the initial positive electrode material layer to obtain a positive electrode material layer containing the first positive electrode active material and the second positive electrode active material. The positive electrode material layer is then pressed to obtain a positive electrode sheet. In some other implementations, the positive electrode sheet may alternatively be prepared by coating a mixed slurry containing the first positive electrode active material, the second positive electrode active material, a conductive agent, and a binder on a positive electrode current collector, followed by drying and pressing.

[0085] In some other implementations of the present disclosure, the first and second positive electrode active materials are not necessarily on the same layer. For example, the positive electrode sheet 20 shown in FIG. 1B may be obtained by using the following method: At least one surface of a positive electrode current collector 21 is coated sequentially with a first positive electrode coating slurry containing the first active material and a second positive electrode coating slurry containing the second positive electrode active material. After drying and pressing, a first positive electrode coating 221 and a second positive electrode coating 222 are sequentially arranged in a layered manner on at least one surface of the positive electrode current collector 21 to obtain a positive electrode sheet.

[0086] In step S03, the lithium battery assembly process specifically includes: stacking a positive electrode sheet, a separator, and a negative electrode sheet in order to form a bare battery core, placing the bare battery core in a battery casing, injecting an electrolyte, and sealing the battery casing to obtain a lithium battery.

[0087] The lithium battery preparation method provided in this embodiment of the present disclosure has a simple process and is easy to control.

[0088] The control method for a lithium battery provided in this embodiment of the present disclosure may specifically include a charge control method and a discharge control method.

[0089] Specifically, the charging control method for a lithium battery includes:

[0090] When a command is received to instruct the lithium battery to enter the first preset mode, the charge cutoff voltage for charging the lithium battery is V h The control is performed so that

[0091] V h >V s V s In this case, the negative electrode sheet of the lithium battery does not deposit elemental lithium. s From V h When the negative electrode active material is between 0.01 and 0.1, the lithium-silicon composite negative electrode active material contains elemental lithium.

[0092] The "command to instruct the lithium battery to enter the first preset mode" may be a command to instruct the lithium battery to enter the first preset mode, or may be a signal to enable the controller to control the lithium battery to enter the first preset mode. The first preset mode is a mode in which the lithium battery is charged, specifically, charging up to SOC 100%. In this case, the negative electrode is Li 4.4 It can be understood that when the lithium battery is subsequently required to exhibit high energy density characteristics, the lithium battery is charged in the first preset mode.

[0093] The charging voltage of the lithium battery is V s When the charging voltage is V, the lithium-silicon composite anode active material does not contain elemental lithium. s If V is greater than 1, the lithium-silicon composite anode active material contains elemental lithium. s V can be recognized as the critical battery voltage when a lithium battery is charged to the point where elemental lithium begins to deposit on the negative electrode (i.e., when the battery is charged to a level where the first SOC threshold is reached). hV is also the upper limit of the charging voltage that a lithium battery can withstand. h is the battery voltage when a lithium battery is fully charged (i.e., charged to 100% SOC), i.e., the cutoff voltage corresponding to the maximum capacity that can be exerted by the positive electrode, and is sometimes called the rated voltage.

[0094] If a lithium battery needs to have long cycle life characteristics, elemental lithium must not be deposited in the negative electrode of the lithium battery. In other words, the lithium-silicon composite negative electrode active material does not contain elemental lithium. Charging cutoff voltage V s In this case, the lithium battery is not fully charged but is only charged to a relatively low SOC, which results in a weaker volume expansion endured by the negative electrode and a smaller side reaction between the negative electrode and the electrolyte. Therefore, the lithium battery can withstand a large number of charge / discharge cycles, i.e., has a long cycle life. When a lithium battery needs to demonstrate high energy density characteristics, the charge cutoff voltage of the lithium battery is V. h During battery discharge, the battery discharge voltage is V h From V s When the negative electrode is between 4.4 The battery contains silicon and a specific amount of elemental lithium. The energy density provided by the battery is very high. To provide power, V h When a lithium battery that has been charged to 0.5 V is used (i.e., when the lithium battery is discharged), the endurance driving distance that the lithium battery can provide is correspondingly longer. In this way, the lithium battery can exhibit long cycle life characteristics and high energy density characteristics as needed, and can meet both high-frequency daily endurance driving distance requirements and low-frequency long endurance driving distance requirements.

[0095] In some implementations of the present disclosure, during charging of the lithium battery, if a command is received instructing the lithium battery to enter the second preset mode, the charging cutoff voltage for charging the lithium battery is V sThe "command to instruct the lithium battery to enter the second preset mode" may be a command to instruct the lithium battery to enter the second preset mode, or may be a signal to enable the controller to control the lithium battery to enter the second preset mode. The second preset mode is another mode in which the lithium battery is charged, specifically, a V in which elemental lithium is not deposited on the negative electrode sheet. s This refers to charging up to the second preset mode. When a lithium battery needs to demonstrate long cycle life characteristics, it is understood that the lithium battery is charged in the second preset mode. The second preset mode is also the most commonly used charging mode for lithium batteries.

[0096] In some implementations of the present disclosure, during charging of the lithium battery, the charging voltage of the lithium battery is V s If a command is received instructing the lithium battery to enter the first preset mode when V is reached, the lithium battery will continue to h The charging of the lithium battery is controlled to be stopped if a command instructing the lithium battery to enter the first preset mode is not received. In this case, when the lithium battery s When charged to V h This determines whether to charge up to V h is used as a charging cutoff voltage to reduce the number of times the battery needs to be charged, thereby ensuring a longer overall service life for the lithium battery.

[0097] Additionally, whether the lithium battery needs to exhibit high energy density characteristics may be remotely enabled by the user during charging or a mode selection setting may be performed prior to charging so that the lithium battery enters a first pre-set mode for charging, as will be described in more detail later in this disclosure.

[0098] In this disclosure, when a lithium battery needs to exhibit long cycle life characteristics, the charge cutoff voltage V for charging the lithium battery every time is s may be the same or different. s does not have to be a fixed value and can be adjusted to V without compromising the long cycle life of the battery. s is the charge cutoff voltage, V ... s and V h To narrow the gap between the charging cutoff voltage V h The battery life may be determined based on the number of times the battery is charged, thereby ensuring that the lithium battery has a long mileage with long life characteristics.

[0099] In the present disclosure, a method for controlling discharge of a lithium battery includes:

[0100] When a command instructing the lithium battery to enter the third preset mode is received, the lithium battery is controlled to be discharged to a first discharge threshold voltage V1, which is the potential V at which the transition metal element in the first positive electrode active material undergoes an irreversible reduction reaction during discharge. R That's all.

[0101] The "command to instruct the lithium battery to enter the third preset mode" may be a command to instruct the lithium battery to enter the third preset mode, or a signal that enables the controller to control the lithium battery to enter the third preset mode. The third preset mode is a mode in which the lithium battery is discharged. When the second positive electrode active material needs to demonstrate capacity during battery discharge, the lithium battery is discharged in the third preset mode. Because the discharge voltage U of the lithium battery is low when the second positive electrode active material is demonstrating capacity (i.e., the power of the lithium battery is extremely low), the third preset mode is sometimes called an "emergency discharge mode."

[0102] Generally, when the discharge voltage U of the lithium battery is low, the battery management system of the lithium battery sends a command to an electric vehicle (e.g., an electric vehicle) using the lithium battery regarding whether to enable the third preset mode (i.e., whether the second positive electrode active material needs to demonstrate its capacity). After receiving a feedback command from the electric vehicle, the battery management system may control the lithium battery to discharge to V1 based on the feedback command confirming the activation of the third preset mode, thereby causing the second positive electrode active material to demonstrate its capacity. The feedback command to the electric vehicle may be issued by a user of the electric vehicle (e.g., an electric vehicle) pressing a mode button on the vehicle operation panel. When the second positive electrode active material demonstrates its capacity, the discharge voltage of the lithium battery decreases from the lithium intercalation start potential of the second positive electrode active material to V1. In this way, while the second positive electrode active material is demonstrating its capacity, excessive reduction of the transition metal element in the first positive electrode active material and damage to the structure of the transition metal element can be prevented, thereby avoiding gas generation within the battery and subsequent battery cycles.

[0103] In addition, if the feedback command received by the battery management system is to not enable the third preset mode, that is, to not enable the second positive electrode active material to exert its capacity, the battery management system sets the discharge cut-off voltage for discharging the lithium battery to V L Furthermore, when a feedback command to not enable the third preset mode is received, the discharge voltage of the lithium battery is controlled to be V L When the feedback command to not enable the third preset mode is received, the lithium battery is controlled to stop discharging if the discharge voltage of the lithium battery is V L If the voltage is higher than V, the lithium battery will continue to L until lithium is fully intercalated into the first positive electrode active material, providing energy for the electric vehicle in a normal discharge mode.

[0104] In some implementations of the present disclosure, when the voltage of the lithium battery during discharging is close to a second discharge threshold voltage V2, if a command is received instructing the lithium battery to enter a third preset mode, the lithium battery is controlled to continue discharging to a first discharge threshold voltage V1. V2 is the lithium insertion cutoff potential V of the first positive electrode active material. L For a definition of V1, see the above description. When the lithium battery enters the third preset mode, the second cathode active material exerts a capacity that allows the lithium battery to continue to output power.

[0105] Generally, when the discharge voltage of a lithium battery is low, the second positive electrode active material of the lithium battery needs to be used to develop capacity. Thus, the frequency of activating the emergency discharge mode to develop the capacity of the second positive electrode active material can be reduced. The process of the second positive electrode active material developing capacity can also be referred to as the over-discharge or deep-discharge process of the lithium battery. The voltage U of the lithium battery during discharge can be acquired by using a collection module in the battery management system of the lithium battery. The term "close to" above can be understood to mean fluctuating around V2, for example, being equal to or less than V2 or slightly greater than V2. In some embodiments, the relationship between the discharge voltage U and V2 can be determined by collecting multiple discharge voltage data of the lithium battery over a short period of time. For example, the discharge voltage of the lithium battery is collected every 10 seconds within 30 seconds. If all three collected real-time discharge voltage data are equal to or less than V2, the influence of battery operational fluctuations can be eliminated, and the battery power can be considered to be nearly depleted. Whether to activate the emergency discharge mode can be considered. For example, the battery management system can push a command regarding whether to activate the emergency discharge mode to an electric vehicle using a lithium battery.

[0106] V2 is the lithium insertion cutoff potential V of a specific first positive electrode active material. L V Lis also the discharge cutoff voltage in the normal discharge mode of a lithium battery. As described above in this disclosure, if the first active cathode material is a lithium ternary oxide material (such as lithium-nickel-cobalt-manganese oxide), V2 may be set to 2.5 V. If the second active cathode material is lithium iron phosphate or lithium iron manganese phosphate, V2 may be set to 2.0 V. If the first active cathode material includes at least two different materials, V2 may be set based on the material with the lowest lithium insertion cutoff potential; for example, if the first active cathode material includes both lithium iron phosphate and lithium-nickel-cobalt-manganese oxide, V2 may be set to 2.0 V.

[0107] V1 is sometimes called the discharge cut-off voltage in emergency discharge mode for lithium batteries. R β may be β times the potential at which the transition metal element in the first positive electrode active material undergoes an irreversible reduction reaction, where β is a constant equal to or greater than 1, such as 1.0, 1.1, 1.2, 1.3, or 1.5. When the first positive electrode active material includes one or more substances, V1 is determined based on the substance at which the transition metal element in the first positive electrode active material has the highest potential at which the transition metal element undergoes an irreversible reduction reaction, and V R may be the maximum value of the potential during the irreversible reduction reaction of the transition metal element in the plurality of first positive electrode active materials.

[0108] It should be noted that the charging method of the lithium battery before discharging is not taken into consideration in the above-mentioned lithium battery discharge control method. For example, if the charging cutoff voltage during charging of the lithium battery is V s Is it V? H The only concern is whether the second cathode active material needs to provide capacity during discharge, regardless of whether it is present or absent. If so, the discharge cutoff voltage of the battery is controlled to be V1.

[0109] An embodiment of the present disclosure further provides a battery management system 110 for the aforementioned lithium battery. See Fig. 7. The battery management system 110 includes a memory 112 and a processor 111. The memory 112 stores program instructions, and the processor 111 is adapted to load the program instructions and execute the charge control method and / or the discharge control method described in the aforementioned embodiment of the present disclosure.

[0110] An embodiment of the present disclosure further provides a battery system 250 for an electric vehicle. The battery system 250 includes a battery management system 110 and a plurality of lithium batteries 100 according to the first aspect of the present disclosure. The aforementioned lithium batteries 100 may also be referred to as "cells."

[0111] The battery system 250 may be used in an electric vehicle 300 and may communicate with a drive unit 301 of the electric vehicle 300. The electric vehicle 300 may be, for example, an electric car, an electric motorcycle, an electric bicycle, or an electric boat. If the electric vehicle 300 is an electric car, the drive unit 301 of the electric vehicle 300 may be an electric motor.

[0112] In some implementations, the battery system 250 includes at least one battery unit, and each first battery unit includes one or more of the aforementioned lithium batteries 100 and one battery management system 110. See FIG. 3 . The battery system 250 of the electric vehicle 300 includes only a first battery unit 1. The first battery unit 1 includes a battery management system 110 and multiple lithium batteries 100. The first battery unit 1 may be a “module-less” battery pack or a “module-equipped” battery pack. When the first battery unit 1 is a “module-equipped” battery pack, the multiple lithium batteries 100 may be connected in series, parallel, or a combination thereof to form a modular battery pack. The battery management system 110 is configured to monitor status information such as the voltage, current, internal resistance, and temperature of each lithium battery 100 and control the charge / discharge status of each lithium battery 100.

[0113] If the battery system 250 of the electric vehicle 300 includes only the first battery unit 1, the lithium battery may be controlled to be fully charged or charged to a lower SOC during charging based on the actual endurance mileage requirement of the electric vehicle, which can meet the long endurance mileage requirement as needed and ensure a long cycle life under the short endurance mileage requirement.

[0114] Specifically, before or during charging of the lithium battery 100, when it is recognized that the electric vehicle 300 should operate in the first mode, the battery management system 110 sets the charging cutoff voltage of the lithium battery 100 to V h The control is configured so that V h is the upper limit charging voltage that a lithium battery can withstand, and V h >V s V s In this case, elemental lithium is not deposited on the negative electrode of the lithium battery. s From V h When the negative electrode active material of the lithium battery 100 is between Li 4.4 Contains Si and elemental lithium.

[0115] When the electric vehicle operates in the first mode, V h It can be seen that a lithium battery 100 charged to 1000 V can be discharged to provide power to an electric vehicle, and the battery exhibits a high energy density. 4.4 The Si and the SI jointly provide energy, and the electric vehicle 300 has a long-endurance driving range. The first mode is sometimes called a "long-endurance mode." In addition, in this case, the negative electrode of the lithium battery precipitates elemental lithium, which has a particular impact on the cycle life of the lithium battery. Therefore, the operation frequency of the first mode is relatively low. Typically, the first mode needs to be activated when driving long distances on holidays. The first mode is sometimes called a "holiday mode."

[0116] In this implementation of the present disclosure, the battery management system 110 sets the charging cutoff voltage for charging the lithium battery to V when it recognizes that the electric vehicle 300 should operate in the second mode before or during charging of the lithium battery 100. s The control is configured so that V s The meaning of V is as described above in this disclosure. s In this case, elemental lithium is not deposited on the negative electrode of the lithium battery 100, and the lithium battery 100 has a long cycle life characteristic. The durable driving distance of the electric vehicle 300 in the second mode is shorter than the durable driving distance of the electric vehicle 300 in the first mode.

[0117] The "endurance driving distance in the second mode" is, to be precise, the V s The term "endurance driving distance in the first mode" refers to the endurance driving distance provided by discharging the first battery unit 1 including one or more lithium batteries charged up to V h It refers to the distance that can be provided by discharging the first battery unit 1, which includes one or more lithium batteries, charged up to V. h >V s Therefore, the endurance mileage of the electric vehicle 300 in the second mode is shorter than the endurance mileage of the electric vehicle 300 in the first mode. The second mode is sometimes referred to as the "short endurance mode," and the first mode is sometimes referred to as the "long endurance mode." For example, the endurance mileage of the electric vehicle in the second mode may be 400 km to 800 km, and the endurance mileage of the electric vehicle in the first mode may be 800 km to 1,200 km. In addition, the second mode is a mode that is more frequently used by electric vehicles, such as for daily short-distance commuting, and is also referred to as the "daily mode."

[0118] When it is recognized that the electric vehicle needs to operate in the short endurance mode, the first battery unit 1 charges the lithium battery to an upper limit charging voltage V hInstead, the first battery unit is controlled to charge to a lower SOC. This ensures that elemental lithium is not deposited on the negative electrode of the lithium battery and helps the lithium battery in the first battery unit achieve long cycle life characteristics. When it is recognized that the electric vehicle needs to operate in long endurance mode, the lithium battery is charged to 100% SOC, ensuring that the first battery unit achieves high energy density characteristics. In this way, although the cycle life of the lithium battery in the "long endurance mode" is not as long as the cycle life in the "short endurance mode," because the "long endurance mode" is used less frequently, the first battery unit of the electric vehicle as a whole can have more low SOC cycles and full charge cycles, thereby providing the electric vehicle with a longer endurance driving distance as needed. In other words, the energy density of the lithium battery 100 in the second mode is lower than the energy density of the lithium battery 100 in the first mode. The cycle life of the lithium battery 100 in the second mode is longer than the cycle life of the lithium battery 100 in the first mode.

[0119] During charging of the lithium battery, if the battery management system 110 does not receive a command to enable the first operating mode for the electric vehicle 300, the charging cutoff voltage for charging the lithium battery 100 defaults to V s During or before charging of the lithium battery 100, if the battery management system 110 receives a command to enable the first operating mode for the electric vehicle 300, the charging cutoff voltage for charging the lithium battery is V h The control is performed so that

[0120] Regarding the "command to enable the first operating mode for the electric vehicle 300," the mode selection setting may be performed before charging, or the command may be remotely enabled during charging. Specifically, the command may be issued by a user of the electric vehicle pressing a mode button on a vehicle operation panel, or by a user remotely operating a smart terminal capable of communicating with the vehicle (for example, when the charging voltage of the lithium battery is V sWhen approaching a target, the vehicle's intelligent network system will push information to the user, such as whether to enable long-endurance mode.

[0121] In this implementation of the present disclosure, the battery management system 110 is further configured to control the lithium battery 100 to be discharged to a first discharge threshold voltage V1 when it is determined that the electric vehicle 300 should operate in a third mode in which the second positive electrode active material of the lithium battery 100 can demonstrate its capacity before or during the discharge of the first battery unit 1. V1 is equal to or greater than the potential of the first positive electrode active material of the lithium battery 100 during the irreversible reduction reaction of the transition metal element in the first positive electrode active material of the lithium battery 100.

[0122] In the third mode, the electric vehicle 300 requires the second positive active material of the lithium battery 100 to provide power to the electric vehicle 300. In this case, the battery is relatively deeply discharged, which is a rare situation that typically occurs when the lithium battery 100 is low in power. Therefore, the third mode is sometimes referred to as an "emergency discharge mode."

[0123] The command to enable the third operating mode for the electric vehicle 300 can be obtained by the battery management system 110 before or during discharge, specifically by a user pressing a mode button on the operation panel of the electric vehicle 300 or by a user remotely operating a smart terminal capable of communicating with the vehicle. In some embodiments, the battery management system 110 first pushes a query command to the electric vehicle 300 regarding whether to enable the third operating mode. After receiving a feedback command of "confirm enabling the third mode" given by the electric vehicle 300, the battery management system 110 controls the discharge cut-off voltage of the lithium battery 100 to be V1 based on the feedback command.

[0124] In some implementations of the present disclosure, the battery management system 110 is configured to control the lithium battery 100 to continue discharging down to the first discharge threshold voltage V1 when the discharge voltage of the lithium battery 100 approaches the second discharge threshold voltage V2 and when it is recognized that the electric vehicle 300 should operate in a third mode in which the second positive electrode active material of the lithium battery 100 exerts its capacity. In this way, the frequency of activating the emergency discharge mode to exert the capacity of the second positive electrode active material can be reduced.

[0125] In some other implementations, see FIG. 4 . The battery system 250 of the electric vehicle 300 further includes a second battery unit 2. The second battery unit 2 includes a plurality of second cells 200. The second cells 200 are different from the aforementioned lithium battery 100, e.g., high-rate lithium batteries. The negative electrode active material of the second cells 200 may include graphite and / or silicon-based materials. The silicon-based materials include one or more of elemental silicon, silicon oxide, silicon-based alloys, and silicon-carbon composite materials. The second cells 200 are conventional lithium batteries that do not use lithium metal (elemental lithium and / or lithium-silicon alloys) as the negative electrode active material, and the energy density of the second cells 200 is lower than the energy density of the lithium battery 100 provided in the first embodiment of the present disclosure.

[0126] Similar to the above-described first battery unit 1, in addition to the plurality of second cells 200, the second battery unit 2 may further include a second battery management system 210 for monitoring the charge / discharge states of the second cells 200. Optionally, the second battery management system 210 may be integrated into the same controller as the above-described battery management system 110. The battery management system 110 may be electrically connected to the BMS of the second battery unit. For example, the battery management system 110 may be connected to the second battery unit via a CAN bus.

[0127] According to various durability requirements of the electric vehicle 300, only the second battery unit 2 may be selected to power the electric vehicle 300, only the first battery unit 1 may be selected to power the electric vehicle 300, or both the first battery unit 1 and the second battery unit 2 may be selected to power the electric vehicle 300. When the first battery unit 1 is used for power supply, each lithium battery 100 in the first battery unit 1 has a charging cut-off voltage V s or V h When the first battery unit 1 is discharged, each lithium battery 100 typically reaches a cut-off voltage V L or, if necessary, to a cut-off voltage V1.

[0128] Specifically, the second battery unit 2 is particularly suitable for providing power to the electric vehicle 300 together with the first battery unit 1 to meet the power requirements of the electric vehicle 300 in an emergency.

[0129] Embodiments of the present disclosure are further described below with reference to several embodiments.

[0130] Embodiment 1 The preparation method of the lithium battery includes the following steps:

[0131] (1) Preparation of the positive electrode sheet The positive electrode active material is ternary NCM622 (chemical formula: LiNi 0.6 Co 0.2 Mn 0.2 960g of O2, 30g of PVDF binder, 5g of acetylene black conductive agent, and 5g of carbon fiber conductive agent were added to 2000g of N-methylpyrrolidone (NMP) solvent and then stirred in a vacuum mixer to form a stable and uniform cathode slurry. The cathode slurry was uniformly and intermittently coated on both opposing surfaces of aluminum foil (aluminum foil size: width 160mm, thickness 16μm) and then dried at a temperature of 100°C to form a ternary cathode material layer.

[0132] Next, the aluminum foil with the aforementioned ternary material layers on both surfaces was placed in sulfur vapor for evaporation, infiltrating the ternary cathode material layer with elemental sulfur and forming a composite cathode coating on each of the aluminum foil's two surfaces. Each composite cathode coating on each side of the aluminum foil contained elemental sulfur and NCM622, with the mass of elemental sulfur being 3 wt% of the mass of NCM622. The aluminum foil with the composite cathode coating formed on each side was then pressed into a sheet using a roller press, cut into rectangular electrode sheets measuring 48 mm x 56 mm, and tabs were spot-welded across the width to obtain cathode sheets for battery assembly.

[0133] (2) Preparation of electrolyte In a glove compartment filled with argon (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. Then, bis(fluorosulfonyl)imide lithium LiN(SO2F2) was added to the mixed solution to obtain an electrolyte with a bis(fluorosulfonyl)imide lithium LiN(SO2F2) content of 60 wt%.

[0134] (3) Preparation of negative electrode sheet First, 1000g of silicon dioxide powder was added to 2000g of water, followed by 50g of polyacrylic acid (PAA) binder and 20g of acetylene black conductive agent. The mixture was stirred vigorously to form a uniform and stable negative electrode slurry. Using a slit coating device, the negative electrode slurry was evenly and intermittently coated onto both sides of a copper foil (copper foil size: width 160mm, thickness 8μm). The coating was then dried at 393K. After roller pressing, a 60μm-thick silicon dioxide negative electrode material layer was formed on the copper foil, resulting in the negative electrode sheet SA1.

[0135] b. First, 200g of PEO with a molecular weight of 600,000 was added to 2000g of acetonitrile, followed by 16g of nano-alumina powder and 10g of anhydrous lithium nitrate powder. The mixture was vigorously stirred until a uniform and stable protective layer slurry was obtained. The protective layer slurry was evenly and intermittently coated onto negative electrode sheet SA1, resulting in negative electrode sheet SA2.

[0136] c. In the glove compartment (H2O content ≤ 5 ppm, O2 content ≤ 5 ppm), a lithium film (lithium film thickness 15 μm) coated on a polyethylene terephthalate (PET) release film was placed on the negative electrode sheet SA2, so that the protective layer was in contact with the lithium film. By hot pressing, all lithium elements on the lithium film were transferred to the negative electrode sheet SA2, obtaining the negative electrode sheet SA3. The negative electrode material layer of the negative electrode sheet SA3 was 78 μm thick, and the lithium-silicon negative electrode active material contained a lithium-silicon alloy and Li2O. The negative electrode sheet SA3 was cut into rectangular electrode sheets measuring 49 mm x 57 mm, and tabs were spot-welded across the width to obtain the negative electrode sheets for battery assembly.

[0137] (4) Battery assembly The positive electrode sheet obtained in step (1) and the negative electrode sheet for assembling the battery obtained in step (3) were alternately stacked together with a separator to obtain a bare battery core. The positive electrode sheet and the negative electrode sheet were separated by the separator. The bare battery core was placed in an aluminum-plastic film outer package and the electrolyte prepared in step (2) was injected. The outer package was then vacuum-sealed, left at 60°C for 48 hours, pressurized at 60°C, repackaged, degassed, and volume-divided to obtain the lithium battery of embodiment 1.

[0138] When the lithium battery of embodiment 1 is charged to SOC 100%, the lithium-silicon composite negative electrode active material is a mixture of elemental lithium and lithium-silicon alloy Li 4.4The mole fraction of elemental lithium is 23%, and the lithium-silicon alloy Li 4.4 The mole fraction of Si is 71%.

[0139] A charge-discharge cycle test is performed on the lithium battery according to the first embodiment of the present disclosure in the following manner.

[0140] The lithium battery of embodiment 1 is subjected to a charge-discharge cycle test at 25±1°C using a LAND CT 2001C secondary battery performance tester. The steps of a normal low SOC cycle (sometimes referred to as "normal charge and normal discharge") are as follows: The lithium battery is left for 10 minutes, and first, the lithium battery is charged at a constant current of 0.33C to a charge cutoff voltage V s The lithium battery is charged to 3.95V, then charged at a constant voltage of 0.05C, and the lithium battery is left for 10 minutes. Then the lithium battery is charged at a constant current of 0.33C until it reaches the normal discharge cut-off voltage V L The lithium battery was charged to 2.5 V, which is the charge cutoff voltage V. This is one normal low SOC cycle. The high energy density cycle (sometimes called "high charge and normal discharge") involves the following steps: the lithium battery is left for 10 minutes, and then the lithium battery is first charged to the charge cutoff voltage V at a constant current of 0.2 C. h The lithium battery is charged to 4.25V, then charged at a constant voltage of 0.05C, and the lithium battery is left for 10 minutes. Then the lithium battery is charged at a constant current of 0.33C until it reaches the normal discharge cut-off voltage V L The lithium battery was charged to 2.5V, which is the charge cut-off voltage V, at a constant current of 0.2C. This constitutes one high-energy cycle. The high-energy charging steps include: the lithium battery was left for 10 minutes, and then the lithium battery was first charged to 2.5V, which is the charge cut-off voltage V, at a constant current of 0.2C. h The lithium batteries were charged to 4.25 V, which is the standard voltage, and then charged at a constant voltage of 0.05 C. The over-discharge steps included: the lithium batteries were charged to the corresponding cut-off voltage according to a normal low SOC cycle system or a high energy density cycle system, and then the lithium batteries were discharged at a constant current of 0.33 C to the over-discharge cut-off voltage of 0.8 V.

[0141] Specifically, the charge / discharge system of embodiment 1 is as follows: (1) First, 10 cycles of normal charge and normal discharge are performed, followed by one cycle of high-charge and normal discharge; (2) 5 cycles of normal charge and normal discharge are performed, followed by one cycle of normal charge and over-discharge; (3) 5 cycles of normal charge and normal discharge are performed, followed by one cycle of high-charge and normal discharge; (4) 10 cycles of normal charge and normal discharge are performed, followed by one cycle of high-charge and over-discharge. This constitutes one cycle. The above operations (1) to (4) are repeated until the battery discharge capacity during the low SOC cycle is less than 80% of the discharge capacity during the first low SOC cycle. The number of cycles is the cycle life of the lithium battery. The energy density during the first high-charge and discharge of the lithium battery was also tested as the ultimate energy density of the battery. The relevant results are summarized in Table 1.

[0142] Embodiment 2 A lithium battery different from that of embodiment 1 is provided, in which in step (3), 800g of silicon powder is used instead of silicon oxide powder, and the thickness of the lithium film coated on the PET release film is 12 μm.

[0143] When the lithium battery of embodiment 2 is fully charged, the mole fraction of elemental lithium in the lithium-silicon composite negative electrode active material is 24%, and the mole fraction of lithium-silicon alloy Li 4.4 The mole fraction of Si is 76%.

[0144] The lithium battery of the second embodiment is subjected to a charge-discharge cycle test according to the charge-discharge system provided in the first embodiment.

[0145] Embodiment 3 A lithium battery different from that of embodiment 1 is provided, in which in step (3), 800g of silicon powder is used instead of silicon oxide powder, and the thickness of the lithium film coated on the PET release film is 10μm.

[0146] When the lithium battery of embodiment 3 is fully charged, the mole fraction of elemental lithium in the lithium-silicon composite negative electrode active material is 18%, and the mole fraction of lithium-silicon alloy Li 4.4 The mole fraction of Si is 82%.

[0147] The lithium battery of the third embodiment is subjected to a charge-discharge cycle test according to the charge-discharge system provided in the first embodiment.

[0148] Embodiment 4 A lithium battery different from the first embodiment is provided, and a positive electrode sheet is prepared according to the following steps: ternary positive electrode active material NCM811 (chemical formula: LiNi 0.8 Co 0.1 Mn 0.1 955g of O2, 30g of PVDF binder, 10g of acetylene black conductive agent, 5g of carbon fiber conductive agent, and 93.6g of Mo6S8 were added to 2700g of NMP and stirred uniformly to obtain a positive electrode slurry. The positive electrode slurry was coated on opposite sides of aluminum foil and dried at 100°C to form a positive electrode layer. Each positive electrode coating on both sides of the aluminum foil contained NCM811 and Mo6S8, with the mass of Mo6S8 being 9.8 wt% of the mass of NCM811. The aluminum foil with the positive electrode layer on each side was then pressed into a sheet using a roller press and cut into rectangular electrode sheets measuring 48mm x 56mm. Tabs were spot-welded across the width to obtain the positive electrode sheets for battery assembly.

[0149] The lithium battery of the fourth embodiment is subjected to a charge-discharge cycle test according to the charge-discharge system provided in the first embodiment.

[0150] Embodiment 5 A lithium battery different from the first embodiment is provided. A positive electrode sheet is prepared according to the following steps. 957 g of positive electrode active material (i.e., iron manganese phosphate lithium), 30 g of PVDF binder, 8 g of acetylene black conductive agent, 5 g of carbon fiber conductive agent, and 46.8 g of Mo6S8 were added to 2200 g of NMP and stirred uniformly to obtain a positive electrode slurry. The positive electrode slurry was coated on opposing surfaces of an aluminum foil and dried at a temperature of 100°C to form a positive electrode material layer. Each positive electrode coating contained NCM811 and Mo6S8, with the mass of Mo6S8 being 4.9 wt% of the mass of the lithium manganese phosphate. The aluminum foil with the positive electrode material layer on each side was then pressed into a sheet using a roller press and then cut into rectangular electrode sheets measuring 48 mm x 56 mm. Tabs were spot-welded across the width to obtain a positive electrode sheet for battery assembly.

[0151] The lithium battery of embodiment 5 is charged and discharged according to the same charge and discharge system as embodiment 1, except that the charge cut-off voltage V during the normal low SOC cycle is s is 3.88V, and the discharge cut-off voltage V L is 2.0 V, and the charge cutoff voltage V during high energy density cycling h is 4.3V, and the discharge cut-off voltage V L is 2.0V, and the discharge cutoff voltage during overdischarge remains at 0.8V.

[0152] Embodiment 6 A lithium battery different from embodiment 5 is provided, and a positive electrode sheet is prepared according to the following steps: A first cathode active material (960 g of iron manganese lithium phosphate, 30 g of PVDF binder, 5 g of acetylene black conductive agent, and 5 g of carbon fiber conductive agent) was added to 2,100 g of NMP and stirred uniformly to obtain a first cathode slurry. A second cathode active material (100 g of Mo6S8, 5 g of PVDF binder, 3 g of acetylene black conductive agent, and 3 g of carbon fiber conductive agent) was added to 300 g of NMP and stirred uniformly to obtain a second cathode slurry. A spray-type two-layer coating method was used, in which the first cathode slurry was placed on the lower die head and the second cathode slurry was placed on the upper die head. The first and second cathode slurries were simultaneously coated on opposite surfaces of an aluminum foil and dried at a temperature of 100°C, forming two cathode material layers on each opposite surface of the aluminum foil. The cathode coating closest to the aluminum foil was the first cathode coating formed by the first cathode slurry. The areal density parameters of the two-layer coating were controlled so that the mass of Mo6S8 was 14 wt% of the mass of the lithium iron phosphate. The aluminum foil was then pressed into a sheet using a roller press, then cut into rectangular electrode sheets measuring 48 mm x 56 mm, and tabs were spot-welded across the width to obtain cathode sheets for battery assembly.

[0153] The lithium battery of the sixth embodiment is subjected to a charge-discharge cycle test according to the charge-discharge system provided in the first embodiment.

[0154] To highlight the beneficial effects of embodiments of the present disclosure, the following comparative examples are provided in particular.

[0155] Comparative Example 1 When a lithium battery different from that of the first embodiment is prepared, and in step (1) a positive electrode sheet is prepared, the ternary positive electrode material layer is formed by drying, and then directly rolled.

[0156] The lithium battery of Comparative Example 1 is subjected to a charge-discharge cycle test according to the charge-discharge system provided in the first embodiment.

[0157] Comparative Example 2 A lithium battery different from that of embodiment 1 is provided, in which in step (3), the prepared negative electrode sheet SA1 is directly used as the negative electrode sheet DS1 for assembling the lithium battery of comparative example 2, the negative electrode of comparative example 2 does not contain lithium metal, and in step (1), the electrolyte solvent is an ester solvent, specifically a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 4:6.

[0158] The charge-discharge cycle test method for the lithium battery prepared in Comparative Example 2 is as follows. Five lithium batteries were prepared and subjected to a charge-discharge cycle test at 25±1°C and 0.33C in a LAND CT 2001C secondary battery performance tester. The steps are as follows: the battery is left for 10 minutes, and then the battery is first charged at a constant current of 0.33C to a charge cutoff voltage of 4.2V, then charged at a constant voltage of 4.2V to a cutoff voltage of 0.05C. The battery is left for 10 minutes, and then discharged at a constant current to 2.5V. This constitutes one charge-discharge cycle. The above charge-discharge steps are repeated until the discharge capacity of the battery during the cycle is less than 80% of the initial discharge capacity. The number of cycles is the cycle life of the lithium battery. The capacity retention rate at cycle number n is recorded, and the ratio of the battery energy density at cycle number n to the initial energy density is used as the energy retention rate of the lithium battery.

[0159] 5A and 5B, Fig. 5A shows a curve illustrating the relationship between the negative electrode voltage and the specific capacity of a lithium battery during a two-stage discharge process according to embodiment 1 of the present disclosure. Fig. 5B shows a curve illustrating the relationship between the negative electrode voltage and the specific capacity of a lithium battery during a three-stage discharge process.

[0160] From Figure 5A, in the daily mode (i.e., when the lithium battery is V sIn the second mode (where the battery is charged to a temperature of 100°C), the negative electrode of the battery is converted to a lithium-silicon alloy, Li, during discharge. x It can be seen that only Si (x≦4.4) exhibits a capacity of 10 ... 4.4 Si is Li x The negative electrode voltage rises until the negative electrode changes to Si (x≦4.4). During this process, the volume expansion endured by the negative electrode is weak, and the side reaction between the negative electrode and the electrolyte is small, so the battery can maintain a long cycle life. In addition, the energy density of the lithium battery made by this process is higher than that of the lithium battery using graphite as the negative electrode. In everyday operation, Li 4.4 Not all of the lithium elements in Si are extracted during discharge, and some lithium still remains as Li x It can be recognized that the lithium is pre-stored in Si. When the positive electrode of the lithium battery further includes the second positive electrode active material, in the emergency discharge mode, the lithium continues to be stored in Li x The extracted lithium may be extracted into the second positive electrode active material, and the extracted lithium may be inserted into the second positive electrode active material, resulting in the lithium battery continuing to release energy. Additionally, in emergency discharge mode, the previously stored lithium extracted from the negative electrode may damage the structure of the lithium-silicon alloy material. To maintain a long cycle life of the entire battery, this mode should be enabled only infrequently. In Figure 5A, the specific capacity of the negative electrode is 810 mAh / g in daily mode and 1750 mAh / g in emergency mode. The mass fraction of the second positive electrode active material relative to the first positive electrode active material is adjusted to achieve the specific capacity of the negative electrode in both daily mode and emergency mode.

[0161] From FIG. 5B, it can be seen that in the holiday mode (i.e., the first mode mentioned above), an electric vehicle using a lithium battery has a longer endurance driving range. To enable the battery to develop a higher energy density, during charging, the Li 4.4In addition to silicon, some lithium exists in the form of elemental lithium in the negative electrode, which can maintain a high specific capacity and a high output voltage, potentially making the energy density of a lithium battery very high. During battery discharge, the lithium-silicon alloy Li 4.4 The capacity of both Si and elemental lithium is demonstrated, with elemental lithium demonstrating capacity first (voltage at the negative electrode relative to lithium is 0), followed by the lithium-silicon alloy Li 4.4 Si is Li x It exerts its capacity until it is converted to Si (same as in the everyday mode in Figure 5A), and then Li x The lithium pre-stored in the Si provides capacity (in other words, the second positive electrode active material provides capacity, just like in the emergency discharge mode of Figure 5A). In addition, the problem of the battery's negative electrode swelling is more serious in the holiday mode than in the daily mode. Therefore, to extend the overall cycle life of the battery, it is also preferable not to use this mode frequently. In Figure 5B, the specific capacity of the negative electrode is 1350 mAh / g in the holiday mode and 1750 mAh / g in the emergency mode. Li when the battery is fully charged 4.4 The mole fraction of elemental lithium to Si can be adjusted, and as a result, the specific capacity and energy density of the negative electrode in holiday mode can be adjusted.

[0162] In order to strongly support the beneficial effects brought about by the technical solutions in the embodiments of the present disclosure, the following electrochemical performance tests are carried out on the lithium battery respectively. The test results are shown in Table 1. [Table 1]

[0163] From Table 1, it can be seen that the battery of Comparative Example 1, in which no sulfur-based compound is introduced into the positive electrode sheet, has insufficient over-discharge resistance. After undergoing a charge-discharge system including an over-discharge process, the battery's cycle life drops sharply. Compared to Comparative Example 1, in which the positive electrode sheet does not contain elemental sulfur or sulfide, the battery of Embodiment 1 of the present disclosure still has a relatively long cycle life and good over-discharge resistance, despite using a charge-discharge system including an over-discharge process. In this case, high-energy-density charging can be performed as needed to provide higher energy, and over-discharge can be performed as needed to provide the electric vehicle with durable mileage in emergencies. Additionally, the battery of Comparative Example 2, which uses only silicon dioxide material in the negative electrode sheet, does not contain a lithium-silicon alloy and cannot be charged or discharged according to the charge-discharge system of Embodiment 1 of the present disclosure. The battery's energy density is very low and its over-discharge resistance is also insufficient. Similarly, compared to Comparative Example 1, the batteries of Embodiments 2 to 4 of the present disclosure, which use a ternary material as the first positive electrode active material, also have both long cycle life and high ultimate energy density. Additionally, the batteries of Examples 5 and 6 using lithium manganese iron phosphate as the first positive electrode active material have similar performance and provide different endurance mileages for electric vehicles as needed.

[0164] The above description is an exemplary implementation of the present disclosure, and the description is specific and detailed. It should be noted that those skilled in the art may make various improvements and refinements without departing from the principles of the present disclosure, and the improvements and refinements also fall within the scope of protection of the present disclosure.

Claims

1. A lithium battery (100), a cathode (20) comprising a first cathode active material and a second cathode active material, wherein the first cathode active material comprises elemental lithium and the second cathode active material comprises elemental sulfur and / or a sulfur-containing compound; A negative electrode (10) comprising a negative electrode material layer (12), the negative electrode material layer (12) comprising a lithium-silicon composite negative electrode active material, wherein when the lithium battery (100) is charged to an SOC of 100%, the lithium-silicon composite negative electrode active material is a lithium-silicon alloy Li ４．４ a negative electrode (10) comprising Si and elemental lithium; A lithium battery (100) comprising:

2. 2. The lithium battery (100) of claim 1, wherein the lithium intercalation onset potential of the second positive electrode active material is equal to or lower than the lithium intercalation cutoff potential of the first positive electrode active material, and the lithium intercalation cutoff potential of the second positive electrode active material is higher than the potential at which a transition metal element in the first positive electrode active material undergoes an irreversible reduction reaction.

3. 3. The lithium battery (100) of claim 1 or 2, wherein the first positive electrode active material comprises one or more of a lithium transition metal oxide and a lithium-containing phosphate, and / or the sulfur-containing compound comprises one or more of a metal sulfide and a sulfurized polyacrylonitrile, and the metal element in the metal sulfide comprises one or more of lithium, molybdenum, copper, silver, titanium, zinc, manganese, iron, cobalt, and nickel.

4. 4. The lithium battery (100) of claim 1, wherein the mass of the second positive electrode active material is 1.6% to 22% of the mass of the first positive electrode active material.

5. 5. The lithium battery (100) of claim 1, wherein the mole fraction of elemental lithium in the lithium-silicon composite anode active material ranges from 15% to 95% when the lithium battery (100) is charged to the 100% SOC.

6. When the lithium battery (100) is charged to a level that does not exceed a first SOC threshold, the lithium-silicon composite negative electrode active material does not comprise the elemental lithium and is a lithium-silicon alloy Li ｘ 6. The lithium battery (100) of claim 1, comprising: Si; 0<x≦4.4; and the first SOC threshold ranges from 15% SOC to 95% SOC.

7. 7. The lithium battery (100) according to claim 1, wherein a surface of the negative electrode material layer (12) has a protective layer (13), or a surface of the lithium-silicon composite negative electrode active material has a protective layer (13), the protective layer (13) comprising a polymer matrix and a lithium salt.

8. 8. The lithium battery (100) of claim 7, 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.

9. 9. The lithium battery (100) of any one of claims 1 to 8, further comprising an electrolyte (40), wherein the solvent in the electrolyte (40) comprises at least one of a non-halogenated ether solvent and a fluorinated ether solvent.

10. 1. A method for preparing a lithium battery, comprising: forming a silicon-based material layer comprising a silicon-based material on a negative electrode current collector, and hot-pressing the lithium metal and the silicon-based material layer in an inert atmosphere, so that the lithium metal and the silicon-based material react in situ to form a negative electrode material layer comprising a lithium-silicon composite negative electrode active material, thereby obtaining a negative electrode; providing a positive electrode, the positive electrode comprising a first active positive electrode material and a second active positive electrode material, the first active positive electrode material comprising elemental lithium and the second active positive electrode material comprising elemental sulfur and / or a sulfur-containing compound; Assembling the negative electrode and the positive electrode to form a lithium battery, wherein when the lithium battery is charged to an SOC of 100%, the lithium-silicon composite negative electrode active material becomes a lithium-silicon alloy Li ４．４ Si and elemental lithium; A preparation method comprising:

11. In the negative electrode, the lithium-silicon composite negative electrode active material is a lithium-silicon alloy Li ｘ 11. The method of claim 10, comprising Si and not comprising elemental lithium, wherein x≦4.

4.

12. 12. The method of claim 10 or 11, wherein the silicon-based material comprises one or more of elemental silicon, silicon oxide, and silicon-based non-lithium alloys.

13. 13. The preparation method according to claim 10, wherein the lithium metal is a lithium thin film, and the method further comprises forming a protective layer on a surface of the silicon-based material layer before hot pressing the lithium metal and the silicon-based material layer in the inert atmosphere, or forming a protective layer on a surface of the negative electrode material layer after the negative electrode material layer is formed, the protective layer comprising a polymer matrix and a lithium salt.

14. When a command is received indicating that the lithium battery enters the first preset mode, the charge cutoff voltage for charging the lithium battery is set to V ｈ and controlling the temperature so that the temperature is equal to or greater than the predetermined temperature. V ｈ >V ｓ and V ｓ In this case, elemental lithium is not deposited on the negative electrode of the lithium battery, and the charging voltage of the lithium battery is V ｓ From V ｈ When the lithium-silicon composite negative electrode active material is between Li ４．４ 10. The method of claim 1, comprising: Si and the elemental lithium.

15. When a command is received indicating that the lithium battery enters a second preset mode, the charging cutoff voltage for charging the lithium battery is set to V ｓ The method for controlling a lithium battery according to claim 14, comprising controlling the battery so that:

16. During charging of the lithium battery, the charging voltage of the lithium battery is V ｓ , if the instruction is received that the lithium battery enters the first preset mode, the lithium battery continues to V ｈ 16. The method of claim 14 or 15, further comprising: controlling the lithium battery to be charged to a predetermined value up to a predetermined value; and controlling the lithium battery to stop charging if the command instructing the lithium battery to enter the first preset mode is not received.

17. When a command is received indicating that the lithium battery should enter a third preset mode, the lithium battery is discharged to a first discharge threshold voltage V １ and controlling the discharge of the power supply voltage to V １ is a potential V at which the transition metal element in the first positive electrode active material undergoes an irreversible reduction reaction. Ｒ The method for controlling a lithium battery according to any one of claims 1 to 9.

18. The voltage of the lithium battery during discharge is equal to or exceeds a second discharge threshold voltage V ２ If the instruction to cause the lithium battery to enter the third preset mode is received when the lithium battery is close to the first discharge threshold voltage V １ and controlling the discharge of the power supply voltage to V ２ >V １ and V ２ 18. The method of claim 17, wherein:

19. V １ V １ = βV Ｒ 19. The method for controlling a lithium battery according to claim 17 or 18, wherein the following is satisfied and 1.0≦β≦1.

5.

20. 20. A battery management system (110) comprising a memory (112) and a processor (111), wherein the memory (112) stores program instructions, and the processor (111) is adapted to load the program instructions and to perform the method for controlling a lithium battery according to any one of claims 14 to 16 and / or the method for controlling a lithium battery according to any one of claims 17 to 19.

21. A battery system (250) for an electric vehicle comprising a battery management system (110) and at least one lithium battery (100) according to any one of claims 1 to 9.

22. If the battery management system (110) recognizes that the electric vehicle should operate in a first mode before or during charging of the lithium battery (100), it sets a charging cutoff voltage for charging the lithium battery (100) to V ｈ and configured to control the V ｈ is the upper limit charging voltage that the lithium battery (100) can withstand, and V ｈ >V ｓ and V ｓ In this case, elemental lithium is not deposited on the negative electrode of the lithium battery (100), and the voltage of the lithium battery (100) is V ｓ From V ｈ When the lithium-silicon composite negative electrode active material is between Li ４．４ 22. The battery system (250) of claim 21, comprising Si and said elemental lithium.

23. If the battery management system (110) recognizes that the electric vehicle should operate in a second mode before or during charging of the lithium battery (100), it sets the charging cutoff voltage for charging the lithium battery (100) to V ｓ and wherein an endurance driving range of the electric vehicle in the second mode is shorter than an endurance driving range of the electric vehicle in the first mode.

24. When the battery management system (110) recognizes that the electric vehicle should operate in a third mode in which the second positive electrode active material can demonstrate its capacity before or during the discharge of the lithium battery (100), it sets a discharge cutoff voltage for discharging the lithium battery (100) to V １ and configured to control the V １ is equal to or greater than the potential at which a transition metal element in the first positive electrode active material undergoes an irreversible reduction reaction.

25. The battery system (250) of any one of claims 21 to 24, wherein the battery management system (110) is the battery management system (110) of claim 20.

26. An electric vehicle (300) comprising a battery system (250) according to any one of claims 21 to 25.

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