Lithium battery and preparation method thereof

Abstract

The invention relates to the technical field of batteries, in particular to a lithium battery and a preparation method thereof. The lithium battery comprises a positive plate, a negative plate, a diaphragm and an electrolyte, wherein the positive plate comprises a positive current collector and a positive active material layer arranged on at least one side surface of the positive current collector; the positive electrode active material layer contains a lithium supplement agent and an organic flame retardant A; the lithium supplement agent comprises a lithium-rich material and elemental sulfur coating at least part of the surface of the lithium-rich material; in the lithium supplement agent, the molar content of elemental sulfur is not lower than 1 / 4 of the oxygen release molar weight of the lithium-rich material; the diaphragm is arranged between the positive plate and the negative plate and comprises a base film and an aramid fiber coating arranged on at least one side surface of the base film; the aramid fiber coating contains an organic flame retardant B; and the electrolyte contains a flame retardant C and an electron-withdrawing functional additive. The lithium battery provided by the invention has high safety.

Description

TECHNICAL FIELD

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

[0002] In order to improve the initial efficiency of the battery and optimize the stability of the positive electrode material to improve the cycle performance of the battery, adding a lithium supplement is an effective technical means. The lithium supplement supplements the lithium loss in the first charge and discharge, reduces the structural changes caused by the long-term vacancy of lithium in the positive electrode, and is beneficial to the cycle performance. However, the lithium supplement is often accompanied by an oxygen release process during the lithium supplement process, which causes electrolyte side reactions and gas production. The electrolyte side reaction products form a CEI film on the surface of the positive electrode active material, increasing the battery impedance; gas production will affect the formation process of the battery interface film, which is not conducive to the formation of a dense and stable interface film. In some technologies, a small amount of transition metal sulfide is added to the positive electrode by mechanical mixing to absorb the oxygen released by the positive electrode, but this technology is not conducive to the rate and cycle life of the battery.

[0003] The main causes of battery thermal runaway include large-area internal short circuit and oxygen release from the positive electrode causing chain side reactions. The main measures to solve the safety problem of lithium-ion batteries in the prior art include: increasing the internal resistance to reduce or cut off the current; flame retardant; inhibiting lithium dendrites; material optimization, etc. (1) For the way of increasing the internal resistance to reduce or cut off the current, it includes coating a safety coating with chemical degradation between the current collector and the positive electrode and coating a safety coating with high-temperature expansion function PTC between the current collector and the positive electrode, etc. The safety coating with chemical degradation generally includes adhesive substances, conductive substances and special sensitive substances to high temperature and high pressure. The special sensitive substances to high temperature and high pressure degrade under high temperature and high pressure, destroy the conductive network of the safety layer, block the electron conduction, increase the internal resistance, and even cut off the current to prevent thermal runaway. For example, some technologies introduce a safety layer containing special sensitive substances (such as polymers containing monosaccharide structural units, substances containing monosaccharide structural units and ester groups, and polymeric esterification products of polysaccharides) into the positive electrode sheet of the lithium-ion battery, which solves the safety problem of lithium-ion batteries during overcharging and achieves higher safety and electrochemical performance; for example, some technologies set PTC electrode sheets in the battery cell of the lithium-ion battery, which solves the problem of thermal runaway of lithium-ion batteries under overcharging, short circuit or high temperature conditions, and achieves high safety of the battery. The experimental results show that the battery does not swell and explode during testing, and the surface temperature is controlled within a reasonable range. (2) The way of flame retardant mainly adds flame retardant in the positive and negative electrodes and the electrolyte. Some technologies add nanoscale resin solid flame retardant to the positive electrode material of the lithium-ion battery, which solves the problem of thermal runaway of lithium-ion batteries under misuse conditions, improves the safety of the battery and reduces the cost, and achieves more stable battery performance; some technologies add compounds containing sulfonyl groups to the electrolyte of the lithium-ion battery to form an interfacial film, which solves the problem of lithium dendrite formation and strong flammability in lithium-ion batteries, improves the cycle performance and safety of the battery, and achieves more efficient battery use and safety. (3) The way of inhibiting lithium dendrites mainly includes adding additives to the electrolyte to inhibit lithium dendrites or modifying the structure of the battery cell. Some technologies add nitrogen and nitrogen compounds to the electrolyte of the lithium-ion battery to generate Li3N to prevent the diffusion of lithium precipitation and exclude oxygen and carbon dioxide, which solves the problem of impedance caused by uneven distribution of electrolyte and increased swelling force in the battery, prolongs the service life of the battery and improves the safety; some technologies set a barrier layer in the bending area of the wound battery to block at least part of the ions released from the positive electrode sheet from embedding into the negative electrode sheet in the bending area.(4) Material optimization mainly includes electrolyte optimization and improving the thermal stability of the insulating film. For example, some technologies use non-aqueous electrolytes with 10%-60% high oxidation potential solvents in lithium-ion batteries, combined with carbonate solvents, to solve the problem of insufficient electrochemical and safety performance of lithium-ion batteries at high voltage and high temperature, achieving better kinetic and safety performance. Some technologies add at least one additive A from the following categories to the electrolyte of lithium-ion batteries: phosphate ester compounds containing unsaturated bonds, cyclic compounds containing -SO2- bonds, and cyclic siloxane compounds containing unsaturated bonds, to control their properties. Diffusion rate has solved the problem of balancing energy density and cycle performance in lithium-ion batteries, improving safety and stability and reducing the risk of gas generation at high temperatures. Some technologies have solved the problem of unstable cycle performance of lithium-ion batteries under high voltage by increasing the lithium salt concentration and the type of conductive lithium salt in the lithium-ion battery, achieving high energy density and improved safety performance, and significantly extending the cycle life of the battery. Some technologies have solved the safety and rate performance problems of traditional lithium-ion batteries by using polyolefin separators and buffer gels in lithium-ion batteries, achieving stable operation in high-temperature environments and normal power supply after puncture.

[0004] However, increasing internal resistance, reducing or cutting off current results in a slow response and cannot prevent internal short circuits caused by diaphragm rupture, nor can it effectively block free radical chain reactions. Flame retardancy is the last line of defense, but it is insufficient to prevent triggering internal short circuits. Suppressing lithium dendrites cannot fundamentally prevent internal short circuits caused by diaphragm rupture or effectively block free radical chain reactions. Material optimization and other technical measures have not fundamentally solved the two problems mentioned above. Summary of the Invention

[0005] To address the problems of side reactions and gas generation in the electrolyte caused by oxygen release during lithium replenishment, and the inability of existing lithium batteries to fundamentally prevent internal short circuits caused by separator rupture and effectively block free radical chain reactions, this invention provides a lithium battery and its preparation method. This lithium battery effectively absorbs oxygen atoms containing lone pairs of electrons released during lithium replenishment, reducing electrolyte side reactions and forming a CEI film at the positive electrode interface, thus lowering impedance. It also suppresses chain reactions caused by oxygen release during thermal runaway, inhibiting high-temperature short circuits and effectively suppressing thermal runaway. Furthermore, it possesses excellent safety characteristics against overcharge, over-discharge, and short circuits, improving battery safety without affecting battery electrical performance and enhancing cycle performance.

[0006] The first aspect of the present invention provides a lithium battery, the lithium battery comprising a positive electrode, a negative electrode, a separator and an electrolyte;

[0007] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector; the positive active material layer contains a lithium supplement agent and an organic flame retardant A; the lithium supplement agent includes a lithium-rich material and elemental sulfur coated on at least a portion of the surface of the lithium-rich material; in the lithium supplement agent, the molar content of the elemental sulfur is not less than one-quarter of the molar amount of oxygen released by the lithium-rich material;

[0008] The separator is disposed between the positive electrode and the negative electrode, and the separator includes a base film and an aramid coating disposed on at least one side of the base film; the aramid coating contains an organic flame retardant B;

[0009] The electrolyte contains flame retardant C and electron-absorbing additives.

[0010] In some embodiments, the molar content of elemental sulfur in the lithium replenishing agent is not less than one-quarter and not more than one-third of the molar amount of oxygen released by the lithium-rich material.

[0011] In some embodiments, organic flame retardant A and organic flame retardant B each independently comprise a fluororubber-based flame retardant.

[0012] In some of these embodiments, the fluororubber flame retardant includes at least one of fluorinated phosphazene rubber, fluorinated acrylate rubber, and tetrafluoropropylene rubber.

[0013] In some embodiments, the fluorinated rubber flame retardant includes fluorinated phosphazene rubber.

[0014] In some of these embodiments, the fluorinated phosphazene rubber includes at least one of trifluoroethoxyphosphazene rubber, octafluoropentoxyphosphazene rubber, and o-allylphenoxyphosphazene rubber.

[0015] In some embodiments, the flame retardant C comprises a fluorinated flame retardant.

[0016] In some embodiments, the fluorinated flame retardant includes at least one of potassium perfluorobutyl sulfonate, ammonium perfluorooctanoate, perfluoroether, and ethoxypentafluorocyclotriphosphazene.

[0017] In some of these embodiments, the electron-withdrawing functional additive comprises a compound having a core element with empty orbitals.

[0018] In some embodiments, the electron-withdrawing functional additive includes boron-containing compounds.

[0019] In some of these embodiments, the boron-containing compound includes at least one of borate esters, electron-deficient boranes, cycloboroxanes, boron complexes, and lithium borates.

[0020] In some embodiments, the borate ester includes at least one selected from trimethyl borate, triethyl borate, tripropyl borate, tri(trimethylalkyl)borate, tri(2-cyanoethyl)borate, and (2,2,2-trifluoroethyl)borate.

[0021] In some of these embodiments, the electron-deficient borane includes tris(pentafluorophenyl)borane.

[0022] In some of these embodiments, the cycloboroxane comprises and / or 2,4,6-trimethoxycycloboroxane.

[0023] In some of these embodiments, the boron complex comprises boron pyridine trifluoride.

[0024] In some of these embodiments, the lithium borate includes at least one of lithium oxalate borate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium difluorobis(trifluoromethyl)borate, and lithium fluorobis(pentafluoroethyl)borate.

[0025] In some embodiments, the positive electrode active material layer also contains a binder and a conductive agent.

[0026] In some embodiments, the positive electrode active material in the positive electrode active material layer includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganese oxide.

[0027] In some embodiments, the lithium-rich material includes lithium iron ferrite and / or lithium nickel ferrite.

[0028] In some embodiments, the electrolyte in the electrolyte solution includes lithium hexafluorophosphate.

[0029] In some of these embodiments, the base film comprises a polyolefin base film.

[0030] In some embodiments, the lithium supplement is present in a mass content of 1%-5% in the positive electrode active material layer.

[0031] In some embodiments, the organic flame retardant A has a mass content of 1%-3% in the positive electrode active material layer.

[0032] In some embodiments, the organic flame retardant B has a mass content of 1%-5% in the aramid coating.

[0033] In some embodiments, the flame retardant C has a mass content of 0.1%-5% in the electrolyte.

[0034] In some embodiments, the electron-withdrawing functional additive is present in the electrolyte at a mass content of 0.1%-5%.

[0035] In some embodiments, when one side of the separator is provided with an aramid coating and the other side is not provided with an aramid coating, the aramid coating is provided on the surface of the base membrane facing the positive electrode.

[0036] In some of these embodiments, the aramid coating has a porous structure.

[0037] In some embodiments, the thickness of the aramid coating is 1 μm-5 μm.

[0038] A second aspect of the present invention provides a method for preparing a lithium battery, the method comprising:

[0039] Preparation of positive electrode sheet: A positive electrode slurry containing positive electrode active material, the lithium supplementer and organic flame retardant A is coated on at least one side of the positive electrode current collector, and then dried;

[0040] Preparation of negative electrode sheet: The negative electrode slurry is coated on at least one side of the negative electrode current collector and then dried;

[0041] Preparation of the diaphragm: A mixture containing aramid and organic flame retardant B is coated on at least one side of the base membrane, and then dried and washed with water to obtain a diaphragm with an aramid coating on at least one side.

[0042] Battery assembly: The electrolyte, the positive electrode, the separator, and the negative electrode are assembled to obtain a lithium battery;

[0043] The lithium replenishing agent comprises a lithium-rich material and elemental sulfur coated on at least a portion of the surface of the lithium-rich material, wherein the molar content of the elemental sulfur in the lithium replenishing agent is not less than one-quarter of the molar amount of oxygen released by the lithium-rich material; the electrolyte contains flame retardant C and electron-withdrawing functional additives.

[0044] In some of these embodiments, the surface of the separator facing the positive electrode has an aramid coating during battery assembly.

[0045] In some of these embodiments, the mixture also contains a pore-forming agent.

[0046] In some embodiments, the pore-forming agent includes at least one of NaCl, NaSO4, and LiOH.

[0047] In some embodiments, the mass of the pore-forming agent is 20%-45% of the mass of the aramid fiber.

[0048] In some embodiments, the contact conditions during the preparation of the lithium replenishing agent include: being carried out in the presence of an inert atmosphere, a contact temperature of 115-125°C, and a contact time of not less than 30 minutes.

[0049] Implementing the technical solution of the present invention has at least the following beneficial effects:

[0050] In this invention, the positive electrode lithium replenisher chemically captures oxygen atoms released by the lithium-rich material through elemental sulfur coating, suppressing side reactions and preventing gas production. Oxygen atoms that the elemental sulfur fails to capture are inactivated by organic flame retardant A. Any remaining oxygen atoms are finally captured by flame retardant C and electron-withdrawing additives in the electrolyte. These three components synergistically suppress gas production, preventing the formation of an SEI film at the positive electrode interface. On the other hand, the aramid coating containing organic flame retardant B in the separator enhances puncture resistance at high temperatures, preventing internal short circuits. The final organic flame retardant A in the positive electrode, the organic flame retardant B in the separator, the flame retardant C in the electrolyte, and the electron-withdrawing additives prevent the chain reaction caused by high-temperature oxygen release from the positive electrode material and suppress heat generation, synergistically improving battery safety. Detailed Implementation

[0051] In this invention, organic flame retardant A, organic flame retardant B, and flame retardant C are used only to indicate that they are flame retardants present in different components or materials, and there are no special limitations on the designations A, B, and C.

[0052] As mentioned in the background section, adding lithium replenishers is an effective technique to improve battery initial efficiency and optimize cathode material stability to enhance battery cycle performance. However, lithium replenishment often involves oxygen release during the replenishment process, causing electrolyte side reactions and gas generation. These side reaction products form a CEI film on the surface of the cathode active material, increasing battery impedance. Gas generation also affects the formation of the battery interface film, hindering the formation of a dense and stable interface film. Some technologies use mechanical mixing to add a small amount of transition metal sulfides to the cathode to absorb oxygen release, but adding transition metal sulfides does not... The main reasons for the poor battery performance, such as rate and cycle life, are as follows: (1) The added transition metal sulfide additives are uniformly distributed on the positive electrode. The reactants generated after oxidation will form CEI on the surface of the active material, which increases the battery interface resistance and is detrimental to the battery rate and cycle life; (2) The effective coverage of the surface of the active material or the lithium supplement is low, which cannot effectively suppress most oxygen atoms from reacting with the electrolyte and producing gas. The by-reaction products will be deposited on the surface of the active material to form or thicken CEI, which increases the battery internal resistance and is detrimental to the battery performance, such as rate and cycle life.

[0053] As mentioned in the background section, existing technologies primarily address the safety issues of lithium-ion batteries through measures such as increasing internal resistance, reducing or cutting off current, flame retardancy, suppressing lithium dendrite formation, and material optimization. However, research has shown that while increasing internal resistance, reducing or cutting off current, and flame retardancy are the last line of defense to protect the battery after thermal runaway, increasing internal resistance and reducing or cutting off current have slow responses and cannot prevent internal short circuits caused by separator rupture or effectively block free radical chain reactions. Flame retardancy is the last line of defense, but it is insufficient to prevent triggering internal short circuits. Suppressing lithium dendrite formation focuses more on safety measures at the end of battery cycles and cannot fundamentally prevent internal short circuits caused by separator rupture or effectively block free radical chain reactions. Material optimization mainly affects the window of battery safety and is one of the foundations for improving battery safety, but it does not fundamentally solve the two problems mentioned above.

[0054] Therefore, the key to improving battery safety is to prevent the battery temperature from rising to the self-heating initiation temperature, and more importantly, to prevent it from rising further from the self-heating initiation temperature to the thermal runaway initiation temperature. The key to preventing the battery temperature from rising from the self-heating initiation temperature to the thermal runaway initiation temperature is: 1) avoiding triggering internal short circuits; 2) suppressing side reactions such as oxygen evolution at the positive electrode and effectively blocking free radical chain reactions to slow down the energy release rate.

[0055] This invention, developed through in-depth research, demonstrates that uniformly coating the surface of the lithium replenisher with a layer of elemental sulfur can effectively absorb the oxygen released from the lithium replenisher, suppress gas generation from side reactions in the electrolyte, and reduce battery impedance. Simultaneously, adding a flame retardant to the positive electrode effectively blocks side reactions caused by oxygen evolution at the positive electrode and effectively inhibits free radical chain reactions. This also helps to capture unadsorbed oxygen atoms released by the lithium replenisher and prevents gas generation from electrolyte decomposition. Furthermore, coating the separator with a solvent-based aramid coating effectively improves the puncture strength of the separator at high temperatures, suppressing short circuits. Adding flame retardant components to the aramid coating effectively reduces the crosstalk between positive and negative electrode materials caused by oxygen evolution at the positive electrode. Furthermore, adding flame retardant additives and electron-withdrawing additives to the electrolyte can prevent chain reactions caused by high-temperature oxygen release from the positive electrode material and suppress heat generation, synergistically improving battery safety.

[0056] In view of this, the first aspect of the present invention provides a lithium battery, which includes a positive electrode, a negative electrode, a separator, and an electrolyte;

[0057] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector; the positive active material layer contains a lithium replenishing agent and an organic flame retardant A; the lithium replenishing agent includes a lithium-rich material and elemental sulfur coated on at least part of the surface of the lithium-rich material; in the lithium replenishing agent, the molar content of elemental sulfur is not less than one-quarter of the molar amount of oxygen released by the lithium-rich material.

[0058] A separator is disposed between the positive electrode and the negative electrode. The separator includes a base membrane and an aramid coating disposed on at least one side of the base membrane. The aramid coating contains an organic flame retardant B.

[0059] The electrolyte contains flame retardant C and electron-absorbing additives.

[0060] In this invention, coating the surface of the lithium replenishing agent with elemental sulfur effectively reacts the atomic oxygen released during the lithium replenishment process with the elemental sulfur to form lithium sulfate, which is deposited on the surface of the lithium replenishing agent particles. This suppresses side reactions in the electrolyte. Simultaneously, the generated substance does not accumulate on the surface of the positive electrode active material, preventing increased impedance. Any unreacted atomic oxygen is adsorbed by organic flame retardant A or by electron-withdrawing additives in the electrolyte, minimizing the impact of atomic oxygen. Furthermore, in this system, the lithium replenishing agent particles, after lithium replenishment, function to a certain extent as an organic flame retardant; that is, when the battery releases oxygen at high temperatures at the positive electrode, the organic... Flame retardant A forms the first barrier against free radical chain reactions. The lithium replenishing agent particles also play a role. Then, the electron-withdrawing additives in the electrolyte can adsorb atomic oxygen containing lone pairs of electrons, reducing activity. In addition, flame retardant C in the electrolyte is the last barrier to inhibit free radical chain reactions. At the same time, the aramid coating on the separator and the addition of organic flame retardant B can effectively improve the high-temperature puncture resistance of the separator and the crosstalk of harmful substances to the negative electrode, improve the high-temperature short-circuit resistance, and improve safety. The above measures work together to effectively improve battery safety.

[0061] Therefore, the lithium battery of this invention can effectively absorb oxygen atoms containing lone pairs of electrons released during the lithium replenishment process, reduce electrolyte side reactions and form a CEI film at the positive electrode interface, thereby reducing impedance; at the same time, it has good safety characteristics such as protection against overcharge, over-discharge, and short circuit, can effectively suppress thermal runaway, improve battery safety, and does not affect the battery's electrical performance, and is also beneficial to the battery's cycle performance.

[0062] [Positive electrode tablets]

[0063] This invention involves coating at least a portion of the surface of a lithium-rich material in the positive electrode with a lithium supplement agent of elemental sulfur and an organic flame retardant A. The synergistic effect of these two agents can better enhance the safety of lithium batteries. Furthermore, a certain amount of elemental sulfur on the surface of the lithium-rich material is required to effectively capture the oxygen release from the lithium supplement agent, which causes side reactions and gas production. However, research has found that when the content of elemental sulfur is too high, it will negatively affect the battery performance. The reason for this is that when there is too much elemental sulfur, there will be excess elemental sulfur, which will form polysulfides during the charge and discharge process and dissolve in the electrolyte, migrating to the negative electrode. There, it will continue to cause side reactions, negatively impacting the battery performance. In addition, elemental sulfur interacts with the lithium replenishing agent, specifically with the oxygen released by the lithium-rich material, to capture the oxygen released by the lithium-rich material. However, research has found that the coating amount of elemental sulfur is not limited to a 1:1 molar ratio with the oxygen released by the lithium-rich material, but is not higher than one-third of the molar amount of oxygen released by the lithium-rich material. This results in better overall performance of the lithium battery. In some embodiments, the molar content of elemental sulfur in the lithium replenishing agent is not less than one-quarter of the molar amount of oxygen released by the lithium-rich material, and not higher than one-third of the molar amount of oxygen released by the lithium-rich material.

[0064] In this invention, the molar amount of oxygen released by lithium-rich materials refers to how many moles of oxygen can be released per mole of lithium supplement (specifically, lithium-rich materials).

[0065] In this invention, "the lithium replenishing agent includes lithium-rich material and elemental sulfur coated on at least a portion of the surface of the lithium-rich material" means that the elemental sulfur as a coating layer can completely coat the lithium-rich material or coat a portion of the surface of the lithium-rich material, preferably completely coat it.

[0066] Lithium-rich materials, as lithium replenishers, can compensate for the loss of active lithium during the first charge and discharge of lithium batteries due to the formation of a solid electrolyte interface (SEI) at the negative electrode, thereby improving the battery's initial efficiency, increasing its specific energy, and enhancing its cycle stability. The lithium-rich material can be any lithium-rich material in the art suitable for use as the positive electrode. In some embodiments, the lithium-rich material includes, but is not limited to, lithium-rich lithium iron ferrite (LFO) and / or lithium-rich lithium nickel oxide (LNO).

[0067] According to the present invention, the content of the lithium replenishing agent can be determined by considering factors such as the first-efficiency loss of the negative electrode, the effective lithium replenishing capacity of the lithium replenishing agent, and the battery energy density. The content of the lithium replenishing agent in the positive electrode active material layer of the present invention can be selected within a wide range. In some embodiments, the mass content of the lithium replenishing agent in the positive electrode active material layer is 1%-5%, for example, 1%, 2%, 2.5%, 3%, 4%, 5%, or any combination of two of the above values.

[0068] In this invention, controlling the content of lithium replenishing agent within the above-mentioned range can better improve the battery's initial efficiency, increase the battery's specific energy, and improve the battery's cycle stability.

[0069] According to the present invention, in some embodiments, organic flame retardant A includes fluororubber-based flame retardants.

[0070] In this invention, when the organic flame retardant A includes a fluorinated rubber flame retardant, it can better form a barrier in the positive electrode active material layer, for example, by intertwining with the binder in the positive electrode active material layer to form a barrier, it can more effectively block the side reactions caused by oxygen evolution at the positive electrode and effectively block the free radical chain reaction. At the same time, it can also supplement and capture oxygen atoms released by the lithium supplementer that have not been adsorbed by elemental sulfur and avoid the decomposition of the electrolyte to produce gas.

[0071] According to the present invention, in some embodiments, the fluorinated rubber flame retardant includes at least one of fluorinated phosphazene rubber, fluorinated acrylate rubber, and tetrafluoropropylene rubber.

[0072] In this invention, the above-mentioned fluorinated rubber flame retardant can effectively block free radical chain reactions and slow down the energy release rate.

[0073] According to the present invention, in some embodiments, the fluorinated rubber flame retardant includes fluorinated phosphazene rubber.

[0074] In this invention, fluorinated phosphazene rubber is a type of highly efficient halogen-free flame retardant that combines phosphorus, nitrogen and fluorine elements to form a composite function. Its molecules contain phosphorus, nitrogen and fluorine elements, all of which have flame retardant functions. In this invention, fluorinated phosphazene rubber is used as organic flame retardant A. While effectively blocking free radical chain reactions and slowing down the energy release rate, its structure is stable and has minimal impact on the battery's electrical performance.

[0075] According to the present invention, fluorinated phosphazene rubber, also known as fluoroalkoxyphosphazene elastomer, is a polymeric elastomer whose main molecular chain consists of alternating phosphorus and nitrogen atoms, with fluoroalkoxy groups on the phosphorus atoms. The specific type of fluorinated phosphazene rubber is not particularly limited as long as the purpose of the present invention can be achieved. In some embodiments, fluorinated phosphazene rubber includes at least one of trifluoroethoxyphosphazene rubber, octafluoropentoxyphosphazene rubber, and o-allylphenoxyphosphazene rubber (fluorophosphazene rubber). The following embodiments of the present invention use trifluoroethoxyphosphazene rubber as an example to illustrate the advantages of the present invention, but this does not represent a limitation of the present invention.

[0076] According to the present invention, the content of organic flame retardant A in the positive electrode active material layer can be selected within a wide range. In some embodiments, the mass content of organic flame retardant A in the positive electrode active material layer is 1%-3%, for example, 1%, 1.5%, 2%, 2.5%, 3%, or any combination of two of the above values.

[0077] In this invention, the content of organic flame retardant A is controlled within the above-mentioned range. Organic flame retardant A can effectively capture oxygen atoms that elemental sulfur cannot capture, block free radical chain reactions and inactivate free radicals, while having minimal impact on battery electrical performance.

[0078] The positive electrode active material layer is a core component of the positive electrode sheet of a lithium battery. The redox reaction (energy storage and release) that occurs in the battery mainly takes place on the positive electrode active material layer. As those skilled in the art know, the positive electrode active material is the primary component providing the positive electrode active material layer for redox reactions. As long as the purpose of this invention is achieved, there are no special restrictions on the specific selection of the positive electrode active material in the positive electrode active material layer. It can be layered oxides, spinel oxides, polyanionic oxides, lithium-rich manganese-based materials, etc. In some embodiments, the positive electrode active material in the positive electrode active material layer includes, but is not limited to, at least one of lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), lithium iron phosphate (LFP), and lithium manganese oxide (LMO). In the following embodiments of this invention, lithium nickel cobalt manganese oxide (NCM) is used as an example to illustrate the advantages of this invention, but this does not represent a limitation of the invention. Furthermore, the content of the positive electrode active material in the positive electrode active material layer can be selected from conventional contents in the art. As an example, the mass content of the positive electrode active material in the positive electrode active material layer is 85%-96%.

[0079] To establish a conductive network between the positive electrode active materials and between the positive electrode active materials and the current collector, providing an electron transport channel, in some embodiments, the positive electrode active material layer also contains a conductive agent. The specific type of conductive agent is not particularly limited and may include conductive carbon black, carbon nanotubes, graphene, etc. As an example, the conductive agent is conductive carbon black. Furthermore, the content of the conductive agent in the positive electrode active material layer can be selected as needed; generally, the mass content of the conductive agent in the positive electrode active material layer is 0.5%-5%.

[0080] According to the present invention, in some embodiments, the positive electrode active material layer further contains a binder. The binder may be of conventional types in the art, including but not limited to vinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR). Furthermore, the content of the binder in the positive electrode active material layer can be selected as needed, generally the mass content of the binder in the positive electrode active material layer is 0.5%-5%.

[0081] As an example, the positive electrode active material layer also contains a binder and a conductive agent, with the conductive agent having a mass content of 0.5%-5% and the binder having a mass content of 0.5%-5% in the positive electrode active material layer.

[0082] In this invention, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. This means that the positive electrode sheet can have a positive active material layer disposed on any one side of the positive current collector, or it can have a positive active material layer disposed on both sides of the positive current collector. Preferably, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on both sides of the positive current collector.

[0083] There are no special restrictions on the specific type of positive electrode current collector, which is generally aluminum-based, such as aluminum foil.

[0084] In this invention, the thickness of the positive electrode active material layer is a conventional thickness in the art, for example, 10-150 micrometers. This invention does not impose any special restrictions on this, so it will not be described in detail.

[0085] [Negative electrode plate]

[0086] The present invention does not have any particular limitation on the selection of negative electrode sheet, and can be any negative electrode sheet that can be used in lithium batteries in the art. It generally includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, preferably including a negative electrode current collector and a negative electrode active material layer disposed on both sides of the negative electrode current collector.

[0087] The negative electrode active material layer generally includes a negative electrode active material, a conductive agent, and a binder. Specific types of active materials include, but are not limited to, graphite, silicon-based materials, and lithium titanate; specific types of conductive agents include, but are not limited to, conductive carbon black, carbon nanotubes, and graphene; and binders include, but are not limited to, vinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR). The general mass ratio of negative electrode active material, conductive agent, and binder is (80-98):(1-10):(1-10).

[0088] There are no special restrictions on the specific type of negative electrode current collector, but it is generally copper-based, such as copper foil.

[0089] The thickness of the negative electrode active layer is a conventional thickness in the art, such as 10-120 micrometers. This invention does not have any special limitations on this, so it will not be described in detail.

[0090] [Septum]

[0091] The separator, positioned between the positive and negative electrodes, does not participate in the electrochemical reaction itself, but plays a crucial role in the battery's safety, performance, and lifespan. The separator in this invention uses an aramid-coated separator and contains flame-retardant components, which improves puncture resistance at high temperatures, suppresses internal short circuits, and reduces the impact of crosstalk between positive and negative electrodes from byproducts, thus enhancing battery safety.

[0092] According to the present invention, in some embodiments, organic flame retardant B includes fluororubber-based flame retardants.

[0093] According to the present invention, in some embodiments, the fluorinated rubber flame retardant includes at least one of fluorinated phosphazene rubber, fluorinated acrylate rubber, and tetrafluoropropylene rubber.

[0094] According to the present invention, in some embodiments, the fluorinated rubber flame retardant includes fluorinated phosphazene rubber.

[0095] According to the present invention, fluorinated phosphazene rubber includes at least one selected from trifluoroethoxyphosphazene rubber, octafluoropentoxyphosphazene rubber, and o-allylphenoxyphosphazene rubber. The following embodiments of the present invention use trifluoroethoxyphosphazene rubber as an example to illustrate the advantages of the present invention, but do not represent a limitation thereof.

[0096] According to the present invention, the content of organic flame retardant B in the aramid coating can be selected within a wide range. In some embodiments, the mass content of organic flame retardant B in the aramid coating is 1%-5%, for example, 1%, 2%, 3%, 4%, 5%, or any combination of two of the above values.

[0097] In this invention, the aramid involved in the aramid coating can be any type of aramid in the art, including but not limited to para-aramid (aramid 1414) and / or meta-aramid (aramid 1313). This invention does not have any special restrictions on this, so they will not be described in detail.

[0098] According to the present invention, the base membrane is the core foundation layer of the entire membrane structure, and it can be any material feasible in the art. In some embodiments, the base membrane includes a polyolefin base membrane, such as a PE base membrane.

[0099] In this invention, the separator includes a base membrane and an aramid coating disposed on at least one side of the base membrane. This means that one side of the separator is provided with an aramid coating, and the other side may be provided with an aramid coating or may not be provided with an aramid coating. Preferably, no aramid coating is provided. More preferably, the surface of the base membrane in the separator facing the positive electrode needs to be provided with an aramid coating. That is, in some embodiments, when one side of the separator is provided with an aramid coating and the other side is not provided with an aramid coating, the aramid coating is disposed on the surface of the base membrane facing the positive electrode.

[0100] According to the present invention, in some embodiments, the aramid coating has a porous structure.

[0101] In this invention, the aramid coating has a porous structure that allows lithium ions in the electrolyte to pass through freely and shuttle back and forth between the positive and negative electrodes during charging and discharging, forming a current loop.

[0102] According to the present invention, the thickness of the aramid coating can be selected within a wide range. In some embodiments, the thickness of the aramid coating is 1μm-5μm, such as 1μm, 2μm, 3μm, 4μm, 5μm, etc.

[0103] Electrolyte

[0104] Electrolytes can provide mobile ions through electrolytes and provide a medium for ion transport through solvents. The electrolyte of this invention contains flame-retardant additives and additives with electron-withdrawing functions. The two work together to effectively block free radical chain reactions, slow down the energy release rate, improve battery safety, and prevent battery thermal runaway.

[0105] In this invention, the electrolyte in the electrolyte solution can be any electrolyte in the art, including but not limited to lithium hexafluorophosphate; the concentration of the electrolyte is generally 0.5-1.5 mol / L, for example 0.5 mol / L, 0.8 mol / L, 1 mol / L or 1.5 mol / L, etc.

[0106] In this invention, the solvent is the medium for dissolving components such as electrolytes to form a homogeneous solution. It can be a conventional type in the art, such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC). The solvent can be used alone or in combination. As an example, the solvent is EC, EMC, and DEC in a mass ratio of 1:1:1.

[0107] According to the present invention, in some embodiments, flame retardant C includes fluorinated flame retardants, specifically including small-molecule fluorinated flame retardants.

[0108] According to the present invention, in some embodiments, the preferred fluorinated flame retardant includes at least one selected from potassium perfluorobutyl sulfonate, ammonium perfluorooctanoate, perfluoroether, and ethoxypentafluorocyclotriphosphazene. Preferably, it includes at least ethoxypentafluorocyclotriphosphazene.

[0109] Examples of fluorinated flame retardants include ethoxypentafluorocyclotriphosphazene and potassium perfluorobutylsulfonate. There are no special restrictions on the ratio between the two; for example, the mass ratio of ethoxypentafluorocyclotriphosphazene to potassium perfluorobutylsulfonate is 15:4.

[0110] According to the present invention, the content of flame retardant C in the electrolyte can be selected within a wide range as long as the purpose of the present invention can be achieved. In some embodiments, the mass content of flame retardant C in the electrolyte is 0.1%-5%, for example, 0.1%, 0.5%, 1%, 2%, 2.8%, 3.2%, 4%, 5%, or any combination of two of the above values.

[0111] In this invention, controlling the content of flame retardant C within the above-mentioned range can better prevent the chain reaction caused by high-temperature oxygen release from the positive electrode material and suppress heat generation; thus synergistically improving battery safety.

[0112] According to the present invention, the core element of the electron-withdrawing functional additive has empty orbitals, which can adsorb oxygen atoms by interacting with the lone pair electrons in oxygen atoms through the empty orbitals, thereby reducing the chemical activity of oxygen atoms, suppressing side reactions and gas production. In some embodiments, the electron-withdrawing functional additive includes boron-containing compounds.

[0113] According to the present invention, boron-containing compounds refer to compounds containing boron, which can adsorb oxygen atoms and reduce the chemical activity of oxygen atoms. In some embodiments, boron-containing compounds include at least one of borate esters, electron-deficient boranes, cycloboroxanes, boron complexes, and lithium borates.

[0114] Borate esters generally refer to those formed by the dehydration condensation of boric acid and alcohol. As long as the purpose of this invention can be achieved, there is no particular limitation on the specific type of borate ester. In some embodiments, borate esters include at least one of trimethyl borate (TMB), triethyl borate (TEB), tripropyl borate (TPB), tri(trimethylalkyl)borate (TMSB), tri(2-cyanoethyl)borate (TCEB), and (2,2,2-trifluoroethyl)borate (TTFEB).

[0115] According to the present invention, electron-deficient boranes generally contain strong electron-withdrawing groups and have strong Lewis acidity. In some embodiments, electron-deficient boranes include, but are not limited to, tris(pentafluorophenyl)borane.

[0116] Cycloboroxanes generally refer to six-membered rings formed by acid dehydration condensation. In some embodiments, cycloboroxanes are, but are not limited to, (TPFPB) and / or 2,4,6-trimethoxycycloboroxane (TMBX).

[0117] According to the present invention, boron complexes generally refer to adducts formed by coordination with Lewis bases, and in some embodiments, boron complexes include boron trifluoride pyridine.

[0118] According to the present invention, lithium borate generally refers to lithium salts of boron anions. In some embodiments, lithium borate includes at least one of lithium oxalate borate, lithium difluorooxalate borate, lithium tetrafluoroborate (BF4), lithium difluorobis(trifluoromethyl)borate (BF2(CF3)2), and lithium fluorobis(pentafluoroethyl)borate (BF2(C2F5)2).

[0119] According to the present invention, as long as the purpose of the present invention can be achieved, the content of the electron-withdrawing functional additive in the electrolyte can be selected within a wide range. In some embodiments, the mass content of the electron-withdrawing functional additive in the electrolyte is 0.1%-5%, for example, 0.1%, 0.5%, 1%, 2%, 2.8%, 3.2%, 4%, 5%, or any two of the above values, preferably 0.3%-3%.

[0120] In preparing lithium batteries, the present invention can be carried out by selecting the required raw materials and the amount of raw materials added according to the battery preparation operation process in the art, or by preparing lithium batteries according to the lithium battery preparation method provided in the second aspect of the present invention below. The specific raw materials used in the lithium battery preparation method provided in the second aspect of the present invention can correspond to the types and contents of components in the battery product provided in the first aspect of the present invention. Therefore, the second aspect of the present invention does not further explain or list the specific components of some raw materials.

[0121] According to some embodiments of the present invention, a second aspect of the present invention provides a method for preparing a lithium battery, the method comprising:

[0122] Preparation of positive electrode sheet: A positive electrode slurry containing positive electrode active material, lithium supplementer and organic flame retardant A is coated on at least one side of the positive electrode current collector and then dried;

[0123] Preparation of negative electrode sheet: The negative electrode slurry is coated on at least one side of the negative electrode current collector and then dried;

[0124] Preparation of the diaphragm: A mixture containing aramid and organic flame retardant B is coated on at least one side of the base membrane, and then dried and washed with water to obtain a diaphragm with an aramid coating on at least one side.

[0125] Battery assembly: The electrolyte, positive electrode, separator, and negative electrode are assembled to obtain a lithium battery.

[0126] The lithium replenishing agent includes lithium-rich material and elemental sulfur coated on at least part of the surface of the lithium-rich material, and the molar content of elemental sulfur in the lithium replenishing agent is not less than one-quarter of the molar amount of oxygen released by the lithium-rich material; the electrolyte contains flame retardant C and electron-withdrawing functional additives.

[0127] [Preparation of lithium supplement]

[0128] In this invention, the lithium replenishing agent can be selected from the corresponding lithium-rich materials and elemental sulfur, as well as their amounts, according to the lithium replenishing agent required in the battery. As an example, the preparation of the lithium replenishing agent can be carried out in the following manner.

[0129] According to some embodiments of the present invention, the method for preparing the lithium supplement includes: contacting a lithium-rich material with elemental sulfur such that elemental sulfur coats at least a portion of the surface of the lithium-rich material; and the molar content of elemental sulfur is not less than one-quarter of the molar amount of oxygen released by the lithium-rich material.

[0130] According to the present invention, in some embodiments, the molar content of elemental sulfur is not less than one-quarter of the molar amount of oxygen released by the lithium-rich material and not more than one-third of the molar amount of oxygen released by the lithium-rich material.

[0131] In this invention, it was found that when the molar amount of elemental sulfur is less than one-quarter of the molar amount of oxygen released by the lithium replenisher, it cannot effectively capture the side reactions and gas production caused by the oxygen release of the lithium replenisher; when the molar amount of elemental sulfur is greater than one-third of the molar amount of oxygen released by the lithium replenisher, there will be an excess of elemental sulfur, which will form polysulfides during the charging and discharging process and dissolve in the electrolyte and migrate to the negative electrode, where it will continue to cause side reactions and have a negative impact on battery performance.

[0132] According to the present invention, in some embodiments, the mass of the lithium supplement is 1%-6% of the mass of the positive electrode active material, for example, 1%, 2%, 3%, 4%, 5.5% or 6%.

[0133] In this invention, in order to at least partially coat the surface of the lithium-rich material with elemental sulfur, preferably completely coat the surface of the lithium-rich material, the lithium-rich material and elemental sulfur can be in contact at a temperature above the melting point of elemental sulfur. In some embodiments, the contact conditions include 115-125°C, for example 115°C, 118°C, 120°C, 123°C or 125°C.

[0134] According to the present invention, in order to ensure that elemental sulfur is at least partially coated on the surface of the lithium-rich material, preferably completely coated on the surface of the lithium-rich material, the contact time is generally not less than 30 minutes. That is, in some embodiments, the contact conditions include: the contact time is not less than 30 minutes.

[0135] According to the present invention, in order to enable elemental sulfur to be more uniformly coated on the surface of lithium-rich materials, the contact can be dynamic, for example, contact under stirring conditions.

[0136] According to the present invention, after molten elemental sulfur comes into full contact with lithium-rich materials, it can be cooled to room temperature so that elemental sulfur coats the surface of lithium-rich materials.

[0137] According to the present invention, in order to avoid the influence of oxygen during the contact process between lithium-rich materials and elemental sulfur, in some embodiments, the contact conditions include: the contact is carried out in the presence of an inert atmosphere. The inert atmosphere includes, but is not limited to, nitrogen or argon.

[0138] As an example, the preparation of lithium replenishment agent includes: mixing lithium-rich material with elemental sulfur under stirring conditions for at least 30 minutes at a temperature of 115-125°C in an inert atmosphere, and then cooling the temperature to room temperature under stirring conditions to obtain lithium replenishment agent.

[0139] [Preparation of the positive electrode]

[0140] In this invention, the corresponding raw material components and their contents can be selected for preparation based on the types and contents of each component in the positive electrode sheet of the battery corresponding to the first aspect.

[0141] According to the present invention, in some embodiments, organic flame retardant A includes fluororubber-based flame retardants.

[0142] According to the present invention, in some embodiments, the fluorinated rubber flame retardant includes at least one of fluorinated phosphazene rubber, fluorinated acrylate rubber, and tetrafluoropropylene rubber.

[0143] According to the present invention, in some embodiments, the selection of fluorinated rubber flame retardants and positive electrode active materials can correspond to the fluorinated rubber flame retardants in the lithium batteries provided in the first aspect of the present invention. The present invention has no special limitations in this regard, so it will not be elaborated further.

[0144] As an example, fluorinated rubber flame retardants include trifluoroethoxyphosphazene rubber.

[0145] As an example, positive electrode active materials include lithium nickel cobalt manganese oxide (NCM).

[0146] According to the present invention, in some embodiments, the mass of organic flame retardant A is 1% to 3.5% of the mass of the positive electrode active material, for example, 1%, 1.5%, 2%, 2.5%, 3.5%, or any combination of two of the above values.

[0147] According to the present invention, in some embodiments, the positive electrode slurry further contains a binder and a conductive agent. The specific selection and amount of the binder and conductive agent can correspond to the binder and conductive agent in the lithium battery provided in the first aspect of the present invention. The present invention has no special limitations in this regard, so it will not be described in detail.

[0148] According to the present invention, the positive electrode slurry containing positive electrode active material, lithium supplementer and organic flame retardant A refers to the slurry obtained by mixing positive electrode active material, lithium supplementer and organic flame retardant A with solvent. In order to achieve uniform mixing, grinding or other methods can generally be used for mixing. The selection of solvent and solid content of positive electrode slurry can also be selected in accordance with conventional methods in the art. The present invention has no special restrictions on these aspects, so they will not be elaborated further.

[0149] As an example, the solid content of the positive electrode slurry can be 45-60 wt%, and the solvent can be NMP solvent.

[0150] According to the present invention, the coating and drying methods can be carried out in accordance with conventional operations in the art. Generally, a positive electrode sheet is obtained after drying. Alternatively, a positive electrode sheet can be obtained by rolling and slitting after drying as needed.

[0151] As an example, the preparation of the positive electrode sheet includes: preparing a slurry by mixing positive electrode active material, conductive agent, binder, lithium supplementer and organic flame retardant A in a mass ratio of (93.5-87.5):3:1.5:(1-5):(1-3), and preparing the positive electrode sheet by coating, drying, rolling and slitting.

[0152] As an example, the preparation of the positive electrode sheet includes: preparing a slurry by mixing the positive electrode active material NCM, conductive agent SP, binder polyvinylidene fluoride, lithium supplementer and organic flame retardant A trifluoroethoxyphosphazene rubber in a mass ratio of (93.5-87.5):3:1.5:(1-5):(1-3), and preparing the positive electrode sheet by coating, drying, rolling and slitting.

[0153] [Preparation of the negative electrode]

[0154] According to the present invention, the negative electrode sheet can be prepared in accordance with conventional methods in the art, generally by mixing the negative electrode active material, conductive agent, and binder with a solvent to prepare the corresponding slurry. The specific proportions of the negative electrode active material, conductive agent, and binder can correspond to the proportions of each component in the negative electrode active material layer of the negative electrode sheet of the first aspect of the present invention. The present invention does not impose any special limitations on this, and therefore will not be elaborated further.

[0155] According to the present invention, the coating and drying methods can be carried out in accordance with conventional operations in the art. Generally, a negative electrode sheet is obtained after drying. Alternatively, a negative electrode sheet can be obtained by rolling and slitting after drying as needed.

[0156] As an example, the preparation of the negative electrode sheet includes: mixing the negative electrode active material with a conductive agent, adding a binder (e.g., PVDF) and a solvent (e.g., NMP) to obtain a negative electrode slurry, coating it onto a negative electrode current collector, and preparing the negative electrode sheet by drying, rolling, and slitting.

[0157] [Preparation of the diaphragm]

[0158] In this invention, the corresponding raw material components and their contents can be selected for preparation according to the types and contents of each component in the separator of the battery corresponding to the first aspect.

[0159] A mixture containing aramid and organic flame retardant B is coated onto at least one side of a base film, and then dried and washed with water to obtain a diaphragm with an aramid coating on at least one side.

[0160] According to the present invention, the mixture containing aramid and organic flame retardant B refers to a solution obtained by dissolving aramid and flame retardant in a solvent and then adding or not adding other components. The specific choice of solvent is not particularly limited in the present invention, as long as it can solvent aramid and organic flame retardant B, including but not limited to at least one of N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO), hexamethylphosphoramide (HMPA), triethyl phosphate (TEP), trimethyl phosphate (TMP), tetramethylurea (TMU), and tripropylene glycol, preferably dimethylacetamide (DMAC); the amount of solvent used is generally such that the mass concentration of aramid is 3%-10%.

[0161] According to the present invention, in some embodiments, the organic flame retardant B includes a fluororubber flame retardant, the specific selection and content of which may correspond to the fluororubber flame retardant in the diaphragm in the first aspect of the present invention, for example, the mass of the organic flame retardant B independently is 1%-5% of the mass of the aramid.

[0162] According to the present invention, in some embodiments, the mixture further contains a pore-forming agent.

[0163] The present invention adds a pore-forming agent to an aramid solvent, and the pore-forming agent can be washed away after subsequent water washing, thereby forming an aramid coating with a porous structure.

[0164] According to the present invention, in some embodiments, the pore-forming agent includes at least one of NaCl, NaSO4 and LiOH.

[0165] According to the present invention, in some embodiments, the mass of the pore-forming agent is 20%-45% of the mass of the aramid fiber, for example 20%, 30%, 40% or 45%.

[0166] According to the present invention, coating the mixture on at least one side of the base film means that the mixture can be coated on one side of the base film or on both sides of the base film, preferably on one side of the base film, and more preferably on the side of the base film facing the positive electrode pair. The coating method can be a conventional method in the art, such as a microgravure coating method.

[0167] As an example, the preparation of the diaphragm includes: dissolving aramid and organic flame retardant B in a solvent under stirring conditions, then adding a pore-forming agent, stirring evenly, coating the diaphragm onto the surface of a base film using a microgravure coating method, drying, and washing with water to remove the pore-forming agent to obtain the diaphragm.

[0168] [Preparation of Electrolyte]

[0169] The electrolyte is formed by dissolving an electrolyte and optionally other components in a suitable solvent. These other components contain flame retardant C and electron-withdrawing functional additives, the specific selection of which can be referred to the electrolyte provided in the first aspect of the invention. Specifically, in some embodiments, flame retardant C comprises a fluorinated flame retardant, preferably including at least one of potassium perfluorobutyl sulfonate, ammonium perfluorooctanoate, perfluoroethers, and oxypentafluorocyclotriphosphazene; in some embodiments, the electron-withdrawing functional additive comprises a compound having a core element with empty orbitals, preferably including boron-containing compounds; in some embodiments, the mass content of flame retardant C in the electrolyte is 0.1%-5%, and in some embodiments, the mass content of the electron-withdrawing functional additive in the electrolyte is 0.1%-5%.

[0170] According to the present invention, the electrolyte of the present invention can be obtained by mixing the electrolyte, flame retardant C, electron-withdrawing functional additive and the corresponding solvent. As an example, the preparation of the electrolyte includes: the electrolyte solvent is made of EC, EMC and DEC in a mass ratio of 1:1:1, the electrolyte is 1 mol / L lithium hexafluorophosphate, and then the electron-withdrawing functional additive is added to the pre-electrolyte formed by mixing the electrolyte and the solvent, and the flame retardant C is mixed evenly to obtain the electrolyte.

[0171] [Battery Assembly]

[0172] According to some embodiments of the present invention, the surface of the separator facing the positive electrode has an aramid coating during battery assembly.

[0173] In this invention, the battery can be assembled according to conventional methods in the art. As an example, a positive electrode, a separator, and a negative electrode are stacked sequentially to form a battery cell, and the surface of the separator facing the positive electrode has an aramid coating. Then, steps including cell casing, drying, electrolyte injection, formation, and capacity testing are performed to prepare a lithium battery. The cell casing, drying, electrolyte injection, formation, and capacity testing are all common processes in the art.

[0174] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0175] In the following examples, unless otherwise specified, the specific techniques or conditions are not indicated, and the techniques or conditions described in the literature in this field or the product instructions shall be followed; if the manufacturers of the materials or instruments used are not indicated, they are all conventional products that can be obtained commercially.

[0176] Example 1

[0177] The preparation method of lithium batteries includes the following steps:

[0178] S1. Preparation of the positive electrode:

[0179] A positive electrode slurry with a solid content of 47 wt% was prepared by using NMP solvent in a mass ratio of NCM, conductive agent SP, binder polyvinylidene fluoride, lithium supplementer, and trifluoroethoxyphosphazene rubber (Hebei Maihan Sealing Parts Co., Ltd.). The slurry was coated on both sides of an aluminum foil current collector, dried, rolled (to a thickness of 95 μm), and slit to prepare a positive electrode sheet. The lithium supplementer was lithium-rich ferrite (LFO). Under an argon atmosphere, at a temperature of 120°C, lithium-rich ferrite (LFO) and elemental sulfur were mixed at a molar ratio of 3.5:1 for 50 min under stirring, based on the molar amount of oxygen released by (LFO). The temperature was then lowered to room temperature under stirring.

[0180] S2, Preparation of the negative electrode:

[0181] Graphite and conductive agent SP were mixed in a mass ratio of 18:1, and then PVDF binder (mass ratio of 1:18 to graphite) and NMP (mass ratio of 18:41.12 to graphite) were added to prepare a negative electrode slurry. The negative electrode slurry was coated on both sides of a copper foil current collector, and then dried, rolled, and slit to prepare a negative electrode sheet.

[0182] S3. Preparation of electrolyte:

[0183] The electrolyte solvent is a combination of EC, EMC and DEC in a mass ratio of 1:1:1; the electrolyte is lithium hexafluorophosphate with a concentration of 1 mol / L in the solvent; 2 wt% TMSB, 3 wt% ethoxypentafluorocyclotriphosphazene, and 0.8 wt% potassium perfluorobutylsulfonate are added to the initial electrolyte mixture.

[0184] S4. Preparation of the diaphragm:

[0185] (1) Preparation of mixture: Aramid (Taihe New Materials Group Co., Ltd.) and trifluoroethoxyphosphazene rubber (3% of the mass of aramid, Hebei Maihan Sealing Parts Co., Ltd.) are dissolved in dimethylacetamide (DMAC) to make the concentration of aramid 5wt%. Then lithium hydroxide is added as a pore-forming agent, and the mass of the pore-forming agent is 35% of the mass of aramid.

[0186] (2) The separator is made of 12-micron PE base film, and the above mixture is coated on the side facing the positive electrode pair with a dry thickness of 2 microns, and then washed with water to obtain the separator;

[0187] S5. The positive electrode, negative electrode and separator are stacked to form a cell, and then processed into a lithium-ion battery with a capacity of 10Ah through processes such as casing, vacuum drying, electrolyte injection, formation and capacity testing.

[0188] Example 2

[0189] The method is the same as in Example 1, except that:

[0190] Based on the molar amount of oxygen released by lithium iron ferrite (LFO), the molar ratio of lithium iron ferrite (LFO) to elemental sulfur is 3:1.

[0191] The rest is the same as in Example 1, and a lithium-ion battery with a capacity of 10Ah is finally prepared.

[0192] Example 3

[0193] The method is the same as in Example 1, except that:

[0194] Based on the molar amount of oxygen released by lithium iron ferrite (LFO), the molar ratio of lithium iron ferrite (LFO) to elemental sulfur is 4:1.

[0195] The rest is the same as in Example 1, and a lithium-ion battery with a capacity of 10Ah is finally prepared.

[0196] Example 4

[0197] The method is the same as in Example 1, except that:

[0198] Replace lithium difluorooxalate borate with TMSB;

[0199] The rest is the same as in Example 1, and a lithium-ion battery with a capacity of 10Ah is finally prepared.

[0200] Example 5

[0201] The method is the same as in Example 1, except that:

[0202] A positive electrode slurry with a solid content of 47 wt% was prepared by using NMP solvent with NCM, conductive agent SP, binder polyvinylidene fluoride, lithium supplementer and trifluoroethoxyphosphazene rubber in a mass ratio of 90.5:3:1.5:2:3; 0.5 wt% TMSB, 3 wt% ethoxypentafluorocyclotriphosphazene, and 1.5 wt% potassium perfluorobutyl sulfonate were added to the initial electrolyte mixture.

[0203] The pore-forming agent is NaSO4, and the mass of the pore-forming agent is 20% of the mass of the aramid fiber;

[0204] The rest is the same as in Example 1, and a lithium-ion battery with a capacity of 10Ah is finally prepared.

[0205] Example 6

[0206] The method is the same as in Example 1, except that:

[0207] Based on the molar amount of oxygen released by lithium iron ferrite (LFO), the molar ratio of lithium iron ferrite (LFO) to elemental sulfur is 2:1.

[0208] The rest is the same as in Example 1, and a lithium-ion battery with a capacity of 10Ah is finally prepared.

[0209] Comparative Example 1

[0210] The method is the same as in Example 1, except that:

[0211] The lithium replenishing agent was replaced with lithium-rich sodium ferrite (LFO), which has no sulfur coating on its surface;

[0212] The rest is the same as in Example 1, and a lithium-ion battery with a capacity of 10Ah is finally prepared.

[0213] Comparative Example 2

[0214] The method is the same as in Example 1, except that:

[0215] Based on the molar amount of oxygen released by lithium iron ferrite (LFO), the molar ratio of lithium iron ferrite (LFO) to elemental sulfur is 5:1.

[0216] The rest is the same as in Example 1, and a lithium-ion battery with a capacity of 10Ah is finally prepared.

[0217] Comparative Example 3

[0218] The method is the same as in Example 1, except that:

[0219] Replace the diaphragm with a regular ceramic 12+2+2 diaphragm (Xingyuan material, SC16-D4(12+2+2));

[0220] The rest is the same as in Example 1, and a lithium-ion battery with a capacity of 10Ah is finally prepared.

[0221] Comparative Example 4

[0222] The method is the same as in Example 1, except that:

[0223] A positive electrode slurry with a solid content of 47 wt% was prepared by using NMP solvent with NCM, conductive agent SP, binder polyvinylidene fluoride and lithium supplementer in a mass ratio of 92.5:3:1.5:3.

[0224] The rest is the same as in Example 1, and a lithium-ion battery with a capacity of 10Ah is finally prepared.

[0225] Comparative Example 5

[0226] The method is the same as in Example 1, except that:

[0227] 5.8 wt% TMSB was added to the initial electrolyte, but ethoxypentafluorocyclotriphosphazene and potassium perfluorobutylsulfonate were not added.

[0228] The rest is the same as in Example 1, and a lithium-ion battery with a capacity of 10Ah is finally prepared.

[0229] Comparative Example 6

[0230] The method is the same as in Example 1, except that:

[0231] The initial electrolyte contains 4.5 wt% ethoxypentafluorocyclotriphosphazene and 1.3 wt% potassium perfluorobutyl sulfonate, but no TMSB is added.

[0232] The rest is the same as in Example 1, and a lithium-ion battery with a capacity of 10Ah is finally prepared.

[0233] Comparative Example 7

[0234] The method is the same as in Example 1, except that the trifluoroethoxyphosphazene rubber used in the preparation of the positive electrode and the separator is replaced with magnesium oxide.

[0235] Performance testing

[0236] The batteries from Examples 1-6 and Comparative Examples 1-7 were subjected to needle penetration, compression, and hot box tests, and their cycle electrical performance was also tested.

[0237] Needle penetration test: Fix a fully charged battery on a fixture, and use a high-temperature resistant steel needle with a diameter of 6mm (needle tip cone angle 45°~60°, needle surface smooth, free of rust, oxide layer and oil stains) to penetrate the battery from a direction perpendicular to the battery plate at a speed of (25±5)mm / s. The penetration position is close to the geometric center of the pierced surface. The steel needle stays in the battery and is observed for one hour.

[0238] Compression test: The test is performed on a fully charged battery. The pressure plate is a semi-cylinder with a radius of 75mm and a length greater than the size of the battery being compressed.

[0239] Compression direction: Apply pressure perpendicular to the direction of the battery plates;

[0240] Extrusion speed: (5±1) mm / s;

[0241] Expansion test: Stop when the voltage reaches 0V, the deformation reaches 30%, or the extrusion pressure reaches 200kN. Observe for one hour.

[0242] Hot chamber test: Place the fully charged battery in the temperature chamber; raise the temperature chamber from room temperature to 130℃±2℃ at a rate of 5℃ / min, maintain this temperature for 30 minutes, and then stop heating. Observe for 1 hour.

[0243] Cyclic test: 1) Discharge at 1C to the discharge termination voltage; 2) Let stand for at least 30 minutes; 3) Charge the lithium-ion battery at a constant current of 1C to the charging termination voltage, then switch to constant voltage charging, and stop charging when the charging termination current drops to 0.05C; 4) Let stand for 1 hour after charging; 5) Discharge at 1C to the discharge termination voltage and record the discharge capacity; Repeat steps 2) to 5) continuously.

[0244] The test results are shown in Table 1.

[0245] Table 1 Test Results

[0246]

[0247]

[0248] As can be seen from the test results in Table 1, the batteries of Examples 1-6 all passed the needle penetration, extrusion and hot box tests, and no gas was generated during the formation process. Furthermore, it can be seen from Examples 1 and Comparative Example 2 that in the batteries of the present invention, excessive elemental S content in the lithium replenishing agent has a certain impact on the battery cycle performance.

[0249] As can be seen from Example 1 and Comparative Examples 1-2, a certain amount of elemental sulfur coating has a significant effect on inhibiting gas formation.

[0250] As can be seen from Example 1 and Comparative Example 3, aramid coating modification has a positive effect on improving safety.

[0251] As can be seen from Example 1 and Comparative Example 4, adding flame retardant additives to the positive electrode can effectively block free radical chain reactions and prevent rapid uncontrolled expansion, thus significantly improving battery safety.

[0252] As can be seen from Example 1 and Comparative Examples 5-6, the additives and flame retardants in the electrolyte have a significant effect on suppressing gas production and improving safety performance.

[0253] As can be seen from Example 1 and Comparative Example 7, compared with inorganic flame retardants, organic flame retardants are more effective in inhibiting free radical chain reactions and improving battery safety in the battery of the present invention.

[0254] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium battery, characterized in that, The lithium battery includes a positive electrode, a negative electrode, a separator, and an electrolyte; The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector; the positive active material layer contains a lithium supplement agent and an organic flame retardant A; the lithium supplement agent includes a lithium-rich material and elemental sulfur coated on at least a portion of the surface of the lithium-rich material; in the lithium supplement agent, the molar content of the elemental sulfur is not less than one-quarter of the molar amount of oxygen released by the lithium-rich material; The separator is disposed between the positive electrode and the negative electrode, and the separator includes a base film and an aramid coating disposed on at least one side of the base film; the aramid coating contains an organic flame retardant B; The electrolyte contains flame retardant C and electron-absorbing additives.

2. The lithium battery according to claim 1, characterized in that, In the lithium replenishing agent, the molar content of elemental sulfur is not less than one-quarter of the molar amount of oxygen released by the lithium-rich material, and not more than one-third of the molar amount of oxygen released by the lithium-rich material. And / or, the organic flame retardant A and the organic flame retardant B each independently comprise a fluororubber-based flame retardant; And / or, the flame retardant C includes a fluorinated flame retardant; And / or, the electron-withdrawing functional additives include compounds with core elements having empty orbitals; And / or, the positive electrode active material layer also contains a binder and a conductive agent; And / or, the positive electrode active material in the positive electrode active material layer includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganese oxide; And / or, the lithium-rich material includes lithium iron ferrite and / or lithium nickel oxide; And / or, the electrolyte in the electrolyte solution includes lithium hexafluorophosphate; And / or, the base film comprises a polyolefin base film.

3. The lithium battery according to claim 2, characterized in that, The fluorinated rubber flame retardant includes at least one of fluorinated phosphazene rubber, fluorinated acrylate rubber, and tetrafluoropropylene rubber. And / or, the fluorinated flame retardant includes at least one of potassium perfluorobutyl sulfonate, ammonium perfluorooctanoate, perfluoroether, and ethoxypentafluorocyclotriphosphazene; And / or, the electron-withdrawing functional additive includes boron-containing compounds.

4. The lithium battery according to claim 3, characterized in that, The fluorinated rubber flame retardant includes fluorinated phosphazene rubber; And / or, the fluorinated phosphazene rubber includes at least one of trifluoroethoxyphosphazene rubber, octafluoropentoxyphosphazene rubber, and o-allylphenoxyphosphazene rubber; And / or, the boron-containing compound includes at least one of borate esters, electron-deficient boranes, cycloboroxanes, boron complexes, and lithium borates.

5. The lithium battery according to claim 4, characterized in that, The borate esters include at least one selected from trimethyl borate, triethyl borate, tripropyl borate, tri(trimethylalkyl)borate, tri(2-cyanoethyl)borate, and (2,2,2-trifluoroethyl)borate. And / or, the electron-deficient borane includes tris(pentafluorophenyl)borane; And / or, the cycloboroxane comprises and / or 2,4,6-trimethoxycycloboroxane; And / or, the boron complex comprises boron trifluoride pyridine; And / or, the lithium borate includes at least one of lithium oxalate borate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium difluorobis(trifluoromethyl)borate, and lithium fluorobis(pentafluoroethyl)borate.

6. The lithium battery according to claim 1, characterized in that, The lithium replenishing agent has a mass content of 1%-5% in the positive electrode active material layer; And / or, the organic flame retardant A has a mass content of 1%-3% in the positive electrode active material layer; And / or, the organic flame retardant B has a mass content of 1%-5% in the aramid coating; And / or, the flame retardant C has a mass content of 0.1%-5% in the electrolyte; And / or, the electron-withdrawing functional additive has a mass content of 0.1%-5% in the electrolyte.

7. The lithium battery according to any one of claims 1-6, characterized in that, When one side of the separator is provided with an aramid coating and the other side is not provided with an aramid coating, the aramid coating is provided on the surface of the base membrane facing the positive electrode sheet; And / or, the aramid coating has a porous structure; And / or, the thickness of the aramid coating is 1μm-5μm.

8. A method for preparing a lithium battery, characterized in that, The preparation method includes: Preparation of positive electrode sheet: A positive electrode slurry containing positive electrode active material, lithium supplementer and organic flame retardant A is coated on at least one side of the positive electrode current collector and then dried; Preparation of negative electrode sheet: The negative electrode slurry is coated on at least one side of the negative electrode current collector and then dried; Preparation of the diaphragm: A mixture containing aramid and organic flame retardant B is coated on at least one side of the base membrane, and then dried and washed with water to obtain a diaphragm with an aramid coating on at least one side. Battery assembly: The electrolyte, the positive electrode, the separator, and the negative electrode are assembled to obtain a lithium battery; The lithium replenishing agent comprises a lithium-rich material and elemental sulfur coated on at least a portion of the surface of the lithium-rich material, wherein the molar content of the elemental sulfur in the lithium replenishing agent is not less than one-quarter of the molar amount of oxygen released by the lithium-rich material; the electrolyte contains flame retardant C and electron-withdrawing functional additives.

9. The method for preparing a lithium battery according to claim 8, characterized in that, During battery assembly, the surface of the separator facing the positive electrode has an aramid coating; And / or, the mixture also contains a pore-forming agent; And / or, the method for preparing the lithium supplement includes: contacting a lithium-rich material with elemental sulfur such that elemental sulfur coats at least a portion of the surface of the lithium-rich material, and the molar content of the elemental sulfur is not less than one-quarter of the molar amount of oxygen released by the lithium-rich material.

10. The method for preparing a lithium battery according to claim 9, characterized in that, The pore-forming agent includes at least one of NaCl, NaSO4, and LiOH; And / or, the mass of the pore-forming agent is 20%-45% of the mass of the aramid fiber; And / or, in preparing the lithium replenishing agent, the contact conditions include: being carried out in the presence of an inert atmosphere, a contact temperature of 115-125°C, and a contact time of not less than 30 minutes.

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