Non-aqueous electrolyte additive for silicon negative electrode ternary high-voltage lithium battery, non-aqueous electrolyte and silicon negative electrode ternary high-voltage lithium battery

Abstract

The invention provides a non-aqueous electrolyte additive for a silicon negative electrode ternary high-voltage lithium battery, a non-aqueous electrolyte and the silicon negative electrode ternary high-voltage lithium battery. The non-aqueous electrolyte additive comprises fluoroethylene carbonate, vinylene carbonate, a lithium salt additive and an additive A, the additive A has a structure shown in the formula 1, and R1 and R2 are respectively and independently selected from at least one of alkyl, fluoroalkyl, vinyl, allyl, ethynyl, propynyl, acetyl, fluoroacetyl, sulfuryl and methyl isocyanate; additive A also achieves equivalent replacement with vinylene carbonate. The non-aqueous electrolyte additive has the advantages that the non-aqueous electrolyte additive can quickly and well remove water and reduce acid for the non-aqueous electrolyte, the problem of dissolving positive and negative materials by HF (hydrogen fluoride) is solved, and equivalent replacement with vinylene carbonate is realized, so that the problem of overhigh impedance caused by overhigh addition amount of the vinylene carbonate is avoided; and the problem that the SEI film is seriously damaged due to expansion and shrinkage of the silicon material is solved.

Description

Technical Field

[0001] The present disclosure relates to the technical field of ternary high-voltage lithium batteries, and particularly to a non-aqueous electrolyte additive, a non-aqueous electrolyte, and a silicon anode ternary high-voltage lithium battery for a ternary high-voltage lithium battery with a silicon anode. Background Art

[0002] In the ternary high-voltage lithium battery system (>4.3V), there is a problem that lattice oxygen is easily removed. The removed lattice oxygen has extremely strong oxidizing properties and is easy to oxidize the electrolyte to generate gas and water, resulting in an increase in the HF content of the ternary high-voltage electrolyte system, leading to a rapid increase in the acidity of the ternary high-voltage electrolyte system and causing serious deterioration of the cycle performance of the ternary high-voltage lithium battery. Under high-temperature conditions, especially for a ternary high-voltage lithium battery with a silicon anode, since the expansion rate of silicon in the fully lithiated state is more than 300%, it is easy to cause the phenomenon of repeated rupture-regeneration-rupture of the SEI film, accelerating the consumption of the electrolyte and further deteriorating the high-temperature cycle performance of the ternary high-voltage lithium battery.

[0003] In practical applications, some scholars usually add a large amount (mass fraction greater than 10%) of fluoroethylene carbonate (FEC) to solve the above technical problems. However, due to the poor thermal stability of FEC itself, it will react with LiPF6 and ethylene carbonate (EC) at high temperatures, resulting in problems such as an increase in the acidity of the electrolyte, a high gas generation amount, and poor high-temperature cycle performance. Therefore, some other scholars reduce the acidity of the electrolyte by adding water-removing and acid-suppressing additives such as hexamethyldisilazane (HMDS), dicyclohexylcarbodiimide (DCC), and trimethylsilyl phosphate (TMSP) to improve its high-temperature cycle performance. However, the addition of such water-removing and acid-suppressing additives often brings problems of deteriorated cycle performance.

[0004] For this reason, there has also emerged on the market a lithium-ion battery silicon-carbon anode electrolyte containing a mixed additive disclosed in Chinese Patent Document No. CN117712485A, which inhibits the expansion of the silicon-carbon anode of the lithium-ion battery by adding a siloxane additive to improve the cycle performance of the lithium-ion battery; another example is an electrolyte additive and an electrolyte and a lithium-ion battery using the same disclosed in Chinese Patent Document No. CN117594880A, which effectively inhibits the acidity growth of the electrolyte by introducing heteroatoms such as N-Si and lone-pair electrons B, N, O, and improves the stability of the CEI / SEI film under high voltage, thereby improving the high-temperature cycle and high-temperature storage performance of the high-voltage system.

[0005] However, for the non-aqueous electrolytes of some ternary high-voltage lithium-ion batteries with silicon anodes containing FEC, since FEC produces a large amount of water and acid under high temperature and high pressure conditions, simply introducing silicon nitride or silicon oxide cannot quickly capture HF and H2O in the ternary high-voltage lithium-ion batteries with silicon anodes, resulting in the cyclic performance and storage performance of the ternary high-voltage lithium-ion batteries with silicon anodes still not being improved well under high temperature and high pressure; moreover, using silicon nitride additives and silicon oxide additives alone simultaneously will cause a large amount of by-products and affect the cyclic performance of the ternary high-voltage lithium-ion batteries with silicon anodes. Summary of the Invention

[0006] The purpose of the present disclosure is to overcome the deficiencies in the prior art, and to provide a non-aqueous electrolyte additive for a ternary high-voltage lithium-ion battery with a silicon anode, which can quickly capture HF and H2O, achieve a fast and good water removal and acid reduction effect on the non-aqueous electrolyte, reduce the dissolution problem of HF to the positive and negative materials at the same time, and realize an equivalent replacement with vinylene carbonate to avoid the problem of too high impedance caused by too high addition amount of vinylene carbonate; it also slows down the serious problem of SEI film damage caused by the expansion and contraction of silicon materials, and a non-aqueous electrolyte additive, a non-aqueous electrolyte and a ternary high-voltage lithium-ion battery with a silicon anode with low cost.

[0007] The purpose of the present disclosure is achieved through the following technical solutions:

[0008] A non-aqueous electrolyte additive for a ternary high-voltage lithium-ion battery with a silicon anode, comprising fluoroethylene carbonate, vinylene carbonate and a lithium salt additive,

[0009] The electrolyte additive further comprises additive A, and additive A has the following structure of formula 1:

[0010]

[0011] Wherein, R1 and R2 are each independently selected from at least one of an alkyl group, a fluoroalkyl group, a vinyl group, a propenyl group, an ethynyl group, a propynyl group, an acetyl group, a fluoroacetyl group, a sulfonyl group and a methyl isocyanate group;

[0012] When in use, the addition of additive A also realizes an equivalent replacement with vinylene carbonate.

[0013] In one embodiment, the principle of additive A capturing HF and H2O is:

[0014]

[0015] In one embodiment, based on the mass fraction, the usage amount of vinylene carbonate is 0.2% - 2.0%; the usage amount of additive A is 0.1% - 5.0%.

[0016] In one embodiment, the usage amount of the lithium salt additive is 0.5% to 1.0%.

[0017] The usage amount of the fluorinated ethylene carbonate is 0% to 12.0%.

[0018] In one embodiment, the lithium salt additive includes at least one of lithium bis(fluorosulfonyl)imide LiFSI, lithium difluorophosphate LiPO2F2, lithium bis(oxalato)borate LiBOB, and lithium difluoro(oxalato)phosphate LiODFP.

[0019] In one embodiment, the additive A is selected from any one of the following formulas 11 to 13:

[0020]

[0021] A non-aqueous electrolyte includes an electrolyte salt, an organic solvent, and a non-aqueous electrolyte additive for a silicon anode ternary high-voltage lithium battery described in any of the above embodiments.

[0022] In one embodiment, the organic solvent includes at least three of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0023] In one embodiment, the volume ratio of the ethylene carbonate, the propylene carbonate, the dimethyl carbonate, the diethyl carbonate, and the ethyl methyl carbonate is (20 to 40):(0 to 20):(0 to 20):(5 to 20):(30 to 50).

[0024] A silicon anode ternary high-voltage lithium battery includes the non-aqueous electrolyte, a positive electrode, a negative electrode, and a separator described in any of the above embodiments. The positive electrode is Li(Ni x Co y Mn z )O2) (where 0.8 ≤ x, 0 < y ≤ 0.2, 0 < z ≤ 0.2 and x + y + z = 1), and the negative electrode is a graphite-doped silicon carbon material.

[0025] Compared with the prior art, the present disclosure has at least the following advantages:

[0026] 1) Since the additive A contains both Si-O and Si-N groups, it can quickly capture HF and H2O in the silicon anode ternary high-voltage lithium battery, achieving a rapid and good effect of removing water and reducing acid in the non-aqueous electrolyte, ensuring the stability of the non-aqueous electrolyte; and the additive A can form a dense (O—Si—O)n SEI film during charge and discharge, effectively avoiding the dissolution of HF in the positive and negative materials, thereby improving the cycling performance and storage performance of the silicon anode ternary high-voltage lithium battery under high temperature and high pressure.

[0027] 2) Since the addition of additive A can achieve equal replacement with vinylene carbonate, it effectively solves the problem of increased impedance of SEI film caused by excessive addition of vinylene carbonate in silicon negative electrode ternary high-voltage lithium batteries; it also reduces the cost of adding vinylene carbonate to the non-aqueous electrolyte of silicon negative electrode ternary high-voltage lithium batteries. The added vinylene carbonate helps to form a SEI film mainly composed of organic matter on the surface of the silicon negative electrode, so that this film can protect the negative electrode material from further erosion by the non-aqueous electrolyte, thereby reducing the decomposition of the electrolyte salt in the non-aqueous electrolyte; especially in combination with the use of FEC, FEC can also form a SEI film on the surface of the silicon negative electrode, thereby making the SEI film more stable and self-healing, and can more effectively inhibit the structural fragmentation problem caused by the volume expansion of lithium embedding in the silicon negative electrode during the charging and discharging process, that is, it can effectively slow down the damage to the SEI film caused by the expansion and contraction of the silicon material, and there is no need to add additional sulfur-containing additives (1,3-propane sultone) to assist in enhancing the flexibility of the SEI film under high temperature and high pressure to slow down the damage to the SEI film caused by the expansion and contraction of the silicon material.

[0028] 3) Since additive A has the ability to quickly capture HF and H2O, it can effectively avoid the problem of a large amount of by-products caused by using a single silicon nitrogen additive and a single silicon oxygen additive at the same time, or the problem of poor water removal and acid reduction effect caused by using them alone, that is, it can more effectively eliminate the side effects caused by the side reaction products, so that the SEI film formation will be more stable, which is more beneficial to the cycle performance and storage performance. Since additive A can capture H2O in the by-product to effectively inhibit the hydrolysis reaction of the lithium salt additive, thereby reducing the amount of HF generated in the non-aqueous electrolyte, it is particularly suitable for the application of non-aqueous electrolytes for silicon negative electrode ternary high-voltage lithium batteries containing FEC. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 It is the structural formula 1 of the additive A of the present invention. DETAILED DESCRIPTION

[0031] In order to facilitate the understanding of the present disclosure, the present disclosure will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present disclosure are given in the drawings. However, the present disclosure can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present disclosure more thoroughly and comprehensively understood.

[0032] It should be noted that when an element is referred to as "fixed to" another element, it can be directly on the other element or there may also be an intermediate element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an intermediate element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only and do not represent the only implementation.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this disclosure belongs. The terms used in the specification of this disclosure herein are only for the purpose of describing specific implementations and are not intended to limit this disclosure. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0034] The present disclosure provides a non-aqueous electrolyte additive for a silicon anode ternary high-voltage lithium battery, including fluoroethylene carbonate, vinylene carbonate and a lithium salt additive. The electrolyte additive further includes additive A, and additive A has the following structure of formula 1, wherein R1 and R2 are each independently selected from at least one of an alkyl group, a fluoroalkyl group, a vinyl group, an allyl group, an ethynyl group, a propynyl group, an acetyl group, a fluoroacetyl group, a sulfonyl group and a methyl isocyanate group; when in use, the addition of additive A also realizes an equivalent replacement with vinylene carbonate.

[0035] The above-mentioned non-aqueous electrolyte additive for a silicon anode ternary high-voltage lithium battery can quickly capture HF and H2O in the silicon anode ternary high-voltage lithium battery because additive A contains both Si-O and Si-N groups at the same time, realizing a fast and good water removal and acid reduction effect on the non-aqueous electrolyte, and ensuring the stability of the non-aqueous electrolyte; and additive A can form a dense (O—Si—O)n SEI film during the charge and discharge process, effectively avoiding the dissolution of the positive and negative materials by HF, thereby improving the cycle performance and storage performance of the silicon anode ternary high-voltage lithium battery under high temperature and high pressure. And the addition of additive A can realize an equivalent replacement with vinylene carbonate. At the same time, it effectively solves the problem that the impedance of the SEI film increases due to the excessive addition amount of vinylene carbonate in the non-aqueous electrolyte of the silicon anode ternary high-voltage lithium battery; it also reduces the addition cost of vinylene carbonate in the non-aqueous electrolyte of the silicon anode ternary high-voltage lithium battery. Especially in combination with the use of FEC and additive A, it can more effectively inhibit the structural fragmentation problem caused by the volume expansion during lithium insertion and extraction in the silicon anode during the charge and discharge process; and additive A effectively inhibits the hydrolysis reaction of the lithium salt additive, thereby reducing the generation amount of HF in the non-aqueous electrolyte, and is especially suitable for the application of the non-aqueous electrolyte of a silicon anode ternary high-voltage lithium battery containing FEC.

[0036] To better understand the technical solutions and beneficial effects of the present disclosure, the following further elaborates on the present disclosure in detail with specific embodiments. A non-aqueous electrolyte additive for a silicon anode ternary high-voltage lithium battery in an embodiment includes fluoroethylene carbonate, vinylene carbonate, and a lithium salt additive. The electrolyte additive further includes additive A, and additive A has the following structural formula 1:

[0037]

[0038] Wherein, R1 and R2 are each independently selected from at least one of an alkyl group, a fluoroalkyl group, a vinyl group, an allyl group, an ethynyl group, a propargyl group, an acetyl group, a fluoroacetyl group, a sulfonyl group, and a methyl isocyanate group;

[0039] During use, the addition of additive A also realizes an equivalent replacement with vinylene carbonate.

[0040] It can be understood that if vinylene carbonate is used alone, the formed SEI film is mainly composed of organic substances, but it cannot effectively resist the structural fragmentation problem caused by the volume expansion during lithium insertion in the silicon anode during charge and discharge; if FEC is used alone, although the formed SEI film can better resist the structural fragmentation problem caused by the volume expansion during lithium insertion in the silicon anode during charge and discharge to a certain extent, there is a problem that the poor thermal stability leads to an increase in the acidity of the non-aqueous electrolyte.

[0041] Therefore, some scholars will compound and use vinylene carbonate and FEC to better inhibit the problems of the SEI film being non-dense and the structural fragmentation of the SEI film caused by the volume expansion during lithium insertion in the silicon anode ternary high-voltage lithium battery during charge and discharge. However, due to the poor thermal stability of FEC, it will generate more HF and H2O at high temperature (>60 °C) and high voltage (≥4.4 V), and still cannot effectively improve the cycle performance and storage performance of the silicon anode ternary high-voltage lithium battery under high temperature and high voltage conditions.

[0042] To solve the above technical problems, in the present disclosure, by adding additive A, the two groups of Si-O and Si-N of additive A can quickly capture HF and H2O in the ternary high-voltage lithium battery with a silicon negative electrode, effectively solving the problem of high acidity and moisture content of the non-aqueous electrolyte in the ternary high-voltage lithium battery with a silicon negative electrode containing FEC under high-temperature and high-pressure conditions, thereby ensuring the stability of the non-aqueous electrolyte and effectively avoiding the problem of high expansion rate in the ternary high-voltage lithium battery with a silicon negative electrode containing FEC; moreover, additive A can form a dense (O—Si—O)n SEI film during charge and discharge, which helps to improve the elasticity and thermal stability of the SEI film, thus better making up for the deficiencies of the traditional SEI film mainly formed by vinylene carbonate and the SEI film formed by FEC. It not only effectively avoids the dissolution of HF in the positive and negative materials, but also better inhibits the structural fragmentation problem caused by the volume expansion during lithium insertion in the silicon negative electrode during charge and discharge, thereby improving the cycle performance and storage performance of the ternary high-voltage lithium battery with a silicon negative electrode under high temperature and high pressure.

[0043] It can also be understood that due to the addition of additive A, it can achieve an equal replacement with vinylene carbonate while effectively solving the problem of increased impedance of the SEI film caused by excessive addition of vinylene carbonate in the ternary high-voltage lithium battery with a silicon negative electrode; it also reduces the addition cost of vinylene carbonate in the non-aqueous electrolyte of the ternary high-voltage lithium battery with a silicon negative electrode; adding a small amount of vinylene carbonate helps to form a SEI film mainly composed of organic matter on the surface of the silicon negative electrode, and this SEI film can protect the negative electrode material from further erosion by the non-aqueous electrolyte, thereby reducing the decomposition amount of the electrolyte salt in the non-aqueous electrolyte; especially in combination with the use of FEC, FEC can also form a SEI film on the surface of the silicon negative electrode, making the SEI film more stable and self-repairing, and being able to more effectively inhibit the structural fragmentation problem caused by the volume expansion during lithium insertion in the silicon negative electrode during charge and discharge, that is, it can effectively slow down the problem of SEI film damage caused by the expansion and contraction of silicon materials, without the need to additionally add a sulfur-containing additive (1,3-propane sultone) to assist in enhancing the flexibility of the SEI film under high temperature and high pressure to slow down the problem of SEI film damage caused by the expansion and contraction of silicon materials.

[0044] It should be noted that currently, some traditional literatures disclose that the use of silicon nitride additives and silicon oxide additives alone can improve the high-temperature cycle performance and storage performance of ternary high-voltage lithium batteries with a silicon negative electrode containing FEC to a certain extent. However, if the traditional silicon nitride additives and silicon oxide additives are simultaneously added to the non-aqueous electrolyte, a relatively large amount of by-product silicon monofluoride will be generated when the silicon nitride additives and silicon oxide additives capture HF and H2O. The specific description is as follows:

[0045] The reaction pathway of the silicon oxide additive alone when capturing HF and H2O:

[0046]

[0047] Reaction pathways of a single silicon nitride additive when capturing HF and H2O:

[0048]

[0049] It can be seen from the above reaction pathways that when a silicon oxide additive and a silicon nitride additive are separately added, at the same dosage, the amount of by-product silicon monofluoride generated by the silicon nitride additive and the silicon oxide additive when capturing HF and H2O is relatively large. Also, due to the low fluorination degree of silicon monofluoride, it is easy to undergo hydrolysis reaction with organic solvents of carbonate esters or trace water to generate harmful HF by-products, resulting in poor stability and compactness of the (O—Si—O)n-based SEI film; further deteriorating the stability of the non-aqueous electrolyte.

[0050] It can also be understood that it can be seen from the above reaction pathways that when a silicon oxide additive and a silicon nitride additive are separately added, they both react with HF and H2O. However, since the chemical bond energy of silicon nitride (355 kJ / mol) is lower than that of silicon oxide (460 kJ / mol), silicon nitride will preferentially break to generate silicon monofluoride under high temperature and high pressure conditions. At the same time, silicon nitride will accelerate hydrolysis to generate Si-OH under high temperature and high pressure conditions, thus playing a certain role in removing water and reducing acid. However, as the high-temperature storage time prolongs, when the silicon nitride additive is used up, the remaining silicon oxide additive cannot immediately capture HF and H2O, but will break only when the acid value reaches a relatively high level, that is, it cannot achieve rapid capture of HF and H2O. There is a blank time period in the connection of water removal and acid reduction. At this time, the generated HF will attack the SEI film, causing it to be damaged quickly, and then enter the positive and negative materials, resulting in their dissolution, thus accelerating the deterioration of the high-temperature cycling performance and high-temperature storage performance of the silicon anode ternary high-voltage lithium battery; even seriously, when the acid value reaches the value that can damage the silicon oxide additive, the generated HF has completely damaged the SEI film, resulting in the inability of the silicon anode ternary high-voltage lithium battery to operate normally, thus causing the problem of low utilization rate of the silicon nitride additive in capturing HF and H2O.

[0051] To solve the above technical problems, in the present disclosure, oxygen and nitrogen are simultaneously linked to a silicon chain to form additive A of the present disclosure, enabling nitrogen and oxygen to coexist around the same silicon atom to form a Si-O-N structure. The lone pair electrons of nitrogen will affect the electron distribution of the Si-O bond through conjugation or polarization effects, thereby weakening the chemical bond energy of the Si-O bond, effectively shortening the blank time period for water removal and acid reduction connection between Si-O and Si-N, and enabling the Si-O of additive A to quickly start capturing HF and H2O, effectively avoiding the problem of low utilization rate of Si-O of additive A caused by the acid value reaching the value that destroys the silicon-oxygen additive in the traditional case. Moreover, since additive A can quickly capture HF and H2O to form silicon tetrafluoride with a stable structure and a highly dense and stable SEI film under high temperature and high pressure, the cycle performance and storage performance of the silicon anode ternary high-voltage lithium battery are improved.

[0052] Specifically, in one embodiment, the reaction pathways for additive A to capture HF and H2O are as follows:

[0053]

[0054] Thus, since additive A contains Si—O and Si—N, additive A can quickly capture HF and H2O, effectively avoiding the deterioration of the high-temperature cycle performance and high-temperature storage performance of the silicon anode ternary high-voltage lithium battery due to the depletion of Si—N and the inability of Si—O to quickly capture HF and H2O during a long high-temperature storage time; and the formation of highly stable silicon tetrafluoride effectively avoids the problem of side reactions caused by the poor stability of silicon monofluoride; and when additive A captures H2O, it can form (O—Si—O)n, which is beneficial to repairing the damaged SEI film and ensuring the subsequent formation of a stable, dense and self-repairing SEI film, which is more beneficial to the cycle performance and storage performance of the silicon anode ternary high-voltage lithium battery under high temperature and high pressure.

[0055] It can also be understood that since additive A quickly captures H2O in the by-products and reduces the residual amount of H2O, it can effectively inhibit the hydrolysis reaction of the lithium salt additive, thereby reducing the generation amount of HF in the non-aqueous electrolyte, and is particularly suitable for the application of the non-aqueous electrolyte of the silicon anode ternary high-voltage lithium battery containing FEC.

[0056] It can be understood that, compared with general lithium batteries, due to the relatively large volume expansion rate during lithium insertion in silicon anode ternary high-voltage lithium batteries during charge and discharge, the usage amounts of traditionally used vinylene carbonate and FEC are relatively high. That is, the usage amount of vinylene carbonate usually exceeds 2.0%, and the usage amount of FEC exceeds 10%. However, excessive vinylene carbonate or excessive FEC will result in a relatively large amount of HF generated, which causes additive A to more easily capture a relatively large amount of by-product HF and cannot capture H2O well.

[0057] Therefore, in one embodiment, by mass fraction, the usage amount of the vinylene carbonate is 0.2% - 2.0%; the usage amount of additive A is 0.1% - 5.0%. This effectively reduces the usage amounts of vinylene carbonate and fluoroethylene carbonate, thereby effectively reducing the generation amount of by-product HF in the silicon anode ternary high-voltage lithium battery under high temperature and high pressure. Especially in combination with the usage amount of the fluoroethylene carbonate being 0% - 12.0%, in this way, on the one hand, on the premise of reducing the usage amounts of vinylene carbonate and fluoroethylene carbonate, it can still ensure that adding a small amount of vinylene carbonate and fluoroethylene carbonate can form a dense, low-impedance, and high-temperature-stable SEI film, effectively inhibiting the structural fragmentation problem caused by the volume expansion during lithium insertion in the silicon anode during charge and discharge, thereby effectively alleviating the SEI film damage problem caused by the expansion and contraction of the silicon material. On the other hand, it ensures that additive A has the ability to quickly capture HF and H2O simultaneously, achieving a good effect of quickly removing water and reducing acid in the non-aqueous electrolyte, and also ensuring that when additive A captures H2O, it can form (O—Si—O)n, which is beneficial to repairing the damaged SEI film, thereby ensuring that a stable, dense, and self-repairing SEI film can be formed subsequently, and further improving the cycle performance and storage performance of the silicon anode ternary high-voltage lithium battery under high temperature and high pressure.

[0058] In one embodiment, the usage amount of the lithium salt additive is 0.5% - 1.0%.

[0059] It can be understood that the content of fluoroethylene carbonate in traditional silicon anode ternary high-voltage lithium batteries is generally greater than 10%. In this way, although it can effectively inhibit the structural fragmentation problem caused by the volume expansion during lithium insertion in the silicon anode during charge and discharge. However, in actual applications, if the traditional usage amount of fluoroethylene carbonate is used, it will result in a relatively large amount of HF generated by the excessive usage amount of fluoroethylene carbonate, causing additive A to tend to capture HF more, and thus unable to achieve the rapid capture of H2O. And for non-aqueous electrolytes, quickly removing H2O is particularly important.

[0060] It can also be understood that when the usage amount of fluoroethylene carbonate is greater than 8%, it will cause more HF to be generated in the ternary high-voltage lithium battery with a silicon negative electrode under high-temperature and high-pressure conditions, accelerating the rate of Si-N in additive A capturing HF and H2O while reducing the rate of Si-O in additive A capturing HF and H2O. That is, it increases the blank time period for water removal and acid reduction connection between Si-O and Si-N in additive A, and cannot improve the high-temperature cycling performance and storage performance of the ternary high-voltage lithium battery with a silicon negative electrode well, further leading to the problem of low utilization rate of Si-O in additive A; when the usage amount of fluoroethylene carbonate is lower than 5%, too little fluoroethylene carbonate is added and a stable and self-repairing SEI film cannot be formed on the surface of the silicon negative electrode, thus unable to better inhibit the structural fragmentation problem caused by the volume expansion during lithium insertion and extraction in the silicon negative electrode during charge and discharge.

[0061] Therefore, in the present disclosure, by effectively controlling the usage amount of fluoroethylene carbonate to be 5.0% - 8.0%, in coordination with the usage amount of vinylene carbonate to be 0.2% - 2.0%; and the usage amount of additive A to be 0.1% - 5.0%, it enables additive A to have the ability to capture HF and H2O quickly and simultaneously by Si-N and Si-O under these conditions, so as to achieve a rapid and good water removal and acid reduction effect for the ternary high-voltage lithium battery with a silicon negative electrode. At the same time, it also ensures that (O—Si—O)n can be generated relatively quickly when additive A captures H2O, which helps to improve the elasticity and thermal stability of the SEI film, thus realizing the self-repairing property of the SEI film and effectively preventing the by-product HF from passing through the damaged SEI film to damage the materials of the positive and negative electrodes; that is, it realizes the rapid repair of the SEI film, thereby ensuring that a dense and stable SEI film can effectively inhibit the structural fragmentation problem caused by the volume expansion during lithium insertion and extraction in the silicon negative electrode during charge and discharge, effectively improving the cycling performance and storage performance of the ternary high-voltage lithium battery with a silicon negative electrode under high-temperature and high-pressure conditions; at the same time, it also shortens the blank time period for water removal and acid reduction connection between Si-O and Si-N in additive A well, effectively improving the utilization rate of Si-O in additive A.

[0062] Specifically, the usage amount of fluoroethylene carbonate can be 5%, 5.5%, 6%, 6.5%, 7%, 8.0%, etc.

[0063] It can be understood that although reducing the usage amount of fluoroethylene carbonate can, to a certain extent, better reduce the production amount of by-products HF and H2O, the acid generated by fluoroethylene carbonate is relatively strong and is not conducive to the ionization of H2O, thus unable to achieve the rapid repair of the damaged SEI film, resulting in relatively limited improvement in its cycling performance and storage performance under high-temperature and high-pressure conditions.

[0064] Therefore, in the present disclosure, by setting the usage amount relationship of vinylene carbonate, additive A, and fluoroethylene carbonate to satisfy: b = (0.7 - 1.5) - a, c:b = (5 - 10):1, where a is the usage amount of additive A, b is the usage amount of vinylene carbonate, and b ≥ 0.5%; c is the usage amount of fluoroethylene carbonate. In this way, the usage ratio of vinylene carbonate and fluoroethylene carbonate is further coordinated, which is beneficial to the electrolysis of H2O. As a result, the Si—O of additive A can quickly capture H2O to form an SEI film of (O—Si—O)n, which helps to improve the elasticity and thermal stability of the SEI film, thereby realizing the self - rapid repair of the SEI film, effectively preventing the by - product HF from passing through the damaged SEI film and damaging the materials of the positive and negative electrodes; and ensuring that a relatively small amount of vinylene carbonate and fluoroethylene carbonate can form a dense and low - impedance SEI film, thus effectively inhibiting the structural fragmentation problem caused by the volume expansion during lithium insertion and extraction of the silicon negative electrode during charge and discharge; also effectively shortening the blank time period for water removal and acid reduction connection between Si - O and Si - N in additive A, improving the utilization rate of Si—O in additive A; at the same time, additive A can quickly capture HF, achieving a good effect of water removal and acid reduction, and further effectively reducing the deterioration of the high - temperature cycle performance and storage performance of the silicon negative electrode ternary high - voltage lithium battery due to excessive amounts of HF and H2O.

[0065] It can also be understood that when the usage ratios of vinylene carbonate and fluoroethylene carbonate are not appropriate, on the one hand, it is impossible to ensure that a relatively small amount of vinylene carbonate and fluoroethylene carbonate can form a dense and low - impedance SEI film; on the other hand, it will affect the speed of additive A capturing HF and H2O. Therefore, in the present disclosure, by controlling b = (0.7 - 1.5) - a and c:b = (5 - 10):1, it is ensured that the amounts of HF and H2O generated by additive A under such high - temperature and high - pressure conditions are relatively small, creating a relatively weakly acidic environment for additive A, which is beneficial to the electrolysis of H2O. As a result, the Si—O of additive A can quickly capture H2O to form an SEI film of (O—Si—O)n, which helps to improve the elasticity and thermal stability of the SEI film, thereby realizing the self - rapid repair of the SEI film, effectively preventing the by - product HF from passing through the damaged SEI film and damaging the materials of the positive and negative electrodes. At the same time, it is also ensured that additive A can quickly capture HF under such high - temperature and high - pressure conditions. In this way, while ensuring that a dense, low - impedance, high - temperature - stable, and self - reparable SEI film can be formed under the condition of using a relatively small amount of vinylene carbonate and fluoroethylene carbonate, it also achieves a good effect of water removal and acid reduction, and improves the utilization rate of Si—O in additive A; to ensure that the silicon negative electrode ternary high - voltage lithium battery can still maintain a stable and relatively low acidity and extremely low moisture content under long - term high - temperature and high - pressure conditions, thus ensuring the high - temperature and high - pressure long - term cycle performance and storage performance of the silicon negative electrode ternary high - voltage lithium battery.

[0066] In a preferred embodiment, a is 1.0%, b is 0.5%, b = 1.5 - a, and c:b = 10:1.

[0067] In one of the preferred embodiments, the usage amount of additive A is 0.5% to 1.0%.

[0068] In one embodiment, the lithium salt additive includes at least one of lithium bis(fluorosulfonyl)imide LiFSI, lithium difluorophosphate LiPO2F2, lithium bis(oxalato)borate LiBOB, and lithium difluoro(oxalato)phosphate LiODFP.

[0069] In one embodiment, additive A is selected from any one of the following formulas 11 to 13:

[0070]

[0071]

[0072] The present disclosure also provides a non-aqueous electrolyte, including an electrolyte salt, an organic solvent, and a non-aqueous electrolyte additive for a silicon anode ternary high-voltage lithium battery described in any of the above embodiments. The added non-aqueous electrolyte additive for a silicon anode ternary high-voltage lithium battery can effectively inhibit the structural fragmentation problem caused by the volume expansion during lithium insertion and extraction of the silicon anode, and also improve the cycle performance and storage performance of the silicon anode ternary high-voltage lithium battery under high temperature and high pressure, effectively inhibit the hydrolysis reaction of the lithium salt additive, thereby reducing the generation amount of HF in the non-aqueous electrolyte, and is particularly suitable for the application of the non-aqueous electrolyte of a silicon anode ternary high-voltage lithium battery containing FEC.

[0073] In one embodiment, the organic solvent includes at least three of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0074] In one embodiment, based on the total volume of the organic solvent being 100%, the volume ratio of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate is (20 - 40):(0 - 20):(0 - 20):(5 - 20):(30 - 50).

[0075] In one embodiment, the electrolyte salt is LiPF6, and the concentration is 1.0 mol / L to 1.3 mol / L.

[0076] In one embodiment, the usage amount of the electrolyte salt is 10% to 15%.

[0077] In one embodiment, the preparation of the non-aqueous electrolyte comprises the following specific steps: in an argon atmosphere, add vinylene carbonate (VC), fluoroethylene carbonate (FEC), a lithium salt additive, and additive A to a non-aqueous solvent, and finally add LiPF6, and stir at a low temperature within the range of 5 °C to 10 °C for 1 min to 10 min to obtain the non-aqueous electrolyte.

[0078] The present disclosure also provides a ternary high-voltage lithium battery with a silicon anode, comprising the non-aqueous electrolyte, a positive electrode, a negative electrode, and a separator described in any one of the above embodiments. The positive electrode is Li(Ni x Co y Mn z )O2 (where 0.8 ≤ x, 0 < y ≤ 0.2, 0 < z ≤ 0.2 and x + y + z = 1), and the negative electrode is a graphite-doped silicon-carbon material.

[0079] It can be understood that due to the relatively high expansion rate of the ternary high-voltage lithium battery with a silicon anode containing FEC and the relatively large amounts of H2O and HF produced under high temperature and high pressure, some scholars have currently improved the material of the silicon anode itself, such as doping materials with anti-expansion properties, or improved the structural strength and high-temperature resistance of the separator. However, the above improvement methods will result in a relatively high cost of the ternary high-voltage lithium battery with a silicon anode and a relatively complex improvement process, and cannot well meet the production requirements of industrial large quantities at low cost.

[0080] Therefore, in the present disclosure, by introducing additive A, additive A can quickly capture HF and H2O in the ternary high-voltage lithium battery with a silicon anode, achieving a rapid and good water removal and acid reduction effect on the non-aqueous electrolyte, ensuring the stability of the non-aqueous electrolyte; especially in combination with the use of vinylene carbonate and FEC, it is beneficial for additive A to form a dense, stable, and self-repairing (O—Si—O)n SEI film during charge and discharge, which not only effectively avoids the dissolution of the positive and negative materials by HF, but also more effectively inhibits the structural fragmentation problem caused by the volume expansion during lithium insertion and extraction of the silicon anode during charge and discharge, that is, it can effectively slow down the damage of the SEI film caused by the expansion and contraction of the silicon material, thereby improving the cycle performance and storage performance of the ternary high-voltage lithium battery with a silicon anode under high temperature and high pressure; there is no need to use an additional sulfur-containing additive (1,3-propane sultone) to assist in enhancing the flexibility of the SEI film under high temperature and high pressure to slow down the damage problem of the SEI film caused by the expansion and contraction of the silicon material, and it is especially suitable for the application of the non-aqueous electrolyte of the ternary high-voltage lithium battery with a silicon anode containing FEC to better meet the production requirements of industrial large quantities at low cost.

[0081] In a preferred embodiment, Li(Ni x Co y Mn z )O2 is LiNi0.8 Co 0.1 Mn 0.1 O2。

[0082] The following are some specific examples. If "% " is mentioned, it means by weight percentage. It should be noted that the following examples do not exhaust all possible cases, and the materials used in the following examples can be obtained from commercial channels without special instructions.

[0083] Table 1 Non-aqueous electrolyte formulation table

[0084]

[0085]

[0086] Prepare the formulations of Examples 1 to 3 in Table 1 according to the following steps:

[0087] Under an argon atmosphere, add vinylene carbonate (VC), fluoroethylene carbonate (FEC), lithium salt additive and additive A to an organic solvent, then add an electrolyte salt, and stir and mix at 5 °C for 2 min to obtain the non-aqueous electrolytes of Examples 1 to 3.

[0088] Comparative Example 1

[0089] The difference from Example 1 is that the addition of additive A is omitted in Comparative Example 1, and the rest remains unchanged.

[0090] Comparative Example 2

[0091] The difference from Example 1 is that the addition of VC is omitted in Comparative Example 2, and the rest remains unchanged.

[0092] Comparative Example 3

[0093] The difference from Example 1 is that the addition amount of VC in Comparative Example 3 is 1.5%, and the rest remains unchanged.

[0094] Comparative Example 4

[0095] The difference from Example 1 is that the addition amount of additive A in Comparative Example 4 is 1.0%, and the rest remains unchanged.

[0096] Comparative Example 5

[0097] The difference from Example 1 is that Comparative Example 5 uses a separate silicon oxide additive (Chinese Patent Document No. CN117712485A), and the rest remains unchanged.

[0098] Comparative Example 6

[0099] The difference from Example 1 is that Comparative Example 6 uses a separate silicon nitride additive (Chinese Patent Document No. CN117594880A), and the rest remains unchanged.

[0100] Comparative Example 7

[0101] The difference from Example 1 is that Comparative Example 7 uses a separate silicon nitride additive + a separate silicon oxide additive, and the rest remains unchanged.

[0102] The non-aqueous electrolytes prepared in Examples 1 to 3 and Comparative Examples 1 to 7 were applied to lithium-ion batteries with silicon anodes and ternary high-voltage cathodes:

[0103] First, a negative electrode slurry was prepared from a silicon negative electrode material (graphite-doped silicon-carbon material), a conductive agent acetylene black, and binders CMC and SBR in a mass percentage of 94:1:2:3. Then, the negative electrode slurry was coated on a copper foil current collector and vacuum dried to obtain a negative electrode sheet. Next, the positive electrode material NCM811

[0104] (LiNi 0.8 Co 0.1 Mn 0.1 O2), a conductive agent acetylene black, and a binder PVDF were prepared into a positive electrode slurry in a mass ratio of 94:3:3. Then, the positive electrode slurry was coated on an aluminum foil current collector and vacuum dried to obtain a positive electrode sheet. The positive electrode sheet, the negative electrode sheet, a separator (Celgard 2400), and the non-aqueous electrolytes prepared in Examples 1 to 3 or Comparative Examples 1 to 7 were assembled into a cylindrical lithium-ion battery with a silicon anode and a ternary high-voltage cathode, and electrochemical tests were carried out using a Neware charge-discharge test cabinet to obtain the data in Table 2.

[0105] (1) Performance test of cycling 500 times at 45°C:

[0106] At 25°C, the lithium-ion battery was charged at a constant current and voltage of 0.5C (nominal capacity) to 4.4V, left to stand for 30 minutes, and then discharged at a constant current of 1C to 2.8V. The above was one cycle, which was the initial discharge capacity. At 45°C, the battery was charged at a constant current and voltage of 0.5C (nominal capacity) to 4.4V, left to stand for 30 minutes, and then discharged at a constant current of 1C to 2.8V, and the charge-discharge cycle was repeated 500 times. The result was calculated.

[0107] The capacity retention rate (%) of the cylindrical lithium-ion battery with a silicon anode and a ternary high-voltage cathode after N cycles = (discharge capacity of the Nth cycle / initial discharge capacity) × 100%, where N is the number of cycles of the cylindrical lithium-ion battery with a silicon anode and a ternary high-voltage cathode.

[0108] (2) Test of HF content in the non-aqueous electrolyte:

[0109] Store the non-aqueous electrolyte at 60 °C, and use the ice water titration method to measure the HF content at 0 d and 90 d respectively, denoted as HF-0d and HF-90d.

[0110] (3) High-temperature storage performance test at 60 °C:

[0111] At 25 °C, charge the cylindrical silicon anode ternary high-voltage lithium battery at a constant current of 0.5C until the voltage reaches 4.4V, and then charge it at a constant voltage of 4.4V until the current reaches 0.05C. Measure the volume of the cylindrical silicon anode ternary high-voltage lithium battery as V0 and the initial capacity as C0; then place the cylindrical silicon anode ternary high-voltage lithium battery in a 60 °C constant temperature oven for 90 days, take it out and measure the volume of the cylindrical silicon anode ternary high-voltage lithium battery and denote it as V1, and keep the capacity as C1 and the restored capacity as C2.

[0112] The capacity retention rate (%) of the cylindrical silicon anode ternary high-voltage lithium battery after 90 days of storage at 60 °C = (C1 / C0) × 100%;

[0113] The capacity restoration rate (%) of the cylindrical silicon anode ternary high-voltage lithium battery after 90 days of storage at 60 °C = (C2 / C0) × 100%.

[0114] The expansion rate (%) of the cylindrical silicon anode ternary high-voltage lithium battery after 90 days of storage at 60 °C = (V1 - V0) / V0 × 100%.

[0115] (4) Impedance of the SEI film

[0116] Let the battery stand until the open circuit voltage is stable, then use an electrochemical workstation to apply a small AC signal of 5 mV in the frequency range of 10 mHZ - 1000 kHZ and start scanning to record the impedance data.

[0117] (5) Detection of water

[0118] Use the Karl Fischer method for testing. The specific steps are as follows: Store the electrolyte at 60 °C, and use a Karl Fischer moisture analyzer to measure the water content at 0 days and the 90th day respectively, denoted as water-0d and water-90d.

[0119] Table 2 data

[0120]

[0121]

[0122] As can be seen from the data in Table 2 above, the added additive A, while not deteriorating the cycling performance of the silicon anode ternary high-voltage lithium battery, effectively inhibits the increase in the acidity of the non-aqueous electrolyte under high temperature and high pressure, solves the deterioration of the high-temperature performance caused by the oxygen evolution of the silicon anode ternary high-voltage lithium battery; also reduces the usage amount of FEC, thereby reducing the high dependence of the silicon anode on FEC, and to a certain extent alleviates the relatively serious negative impact caused by the thermal instability of FEC, thus significantly improving the cycling performance and storage performance of the silicon anode ternary high-voltage lithium battery under high temperature and high pressure. It also facilitates the formation of a dense, stable and self-repairing (O—Si—O)n SEI film by additive A during the charge and discharge process, more effectively inhibiting the structural fragmentation problem caused by the volume expansion due to lithium insertion during the charge and discharge of the silicon anode. It also reduces the usage amount of vinylene carbonate, effectively solving the problem that the impedance of the SEI film increases due to the excessive addition amount of vinylene carbonate in the silicon anode ternary high-voltage lithium battery, making the comprehensive indexes of Examples 1 to 3 significantly better than those of Comparative Examples 1 to 7. Among them, Example 2 is the best.

[0123] It can be seen from Examples 1 to 3 and Comparative Examples 3 to 4 that when the usage amount relationship of vinylene carbonate, additive A and fluoroethylene carbonate in Examples 1 to 3 satisfies: b = (0.7 - 1.5) - a, c:b = (5 - 10):1, where a is the usage amount of additive A, b is the usage amount of vinylene carbonate, and b ≥ 0.5%, the comprehensive indexes of Examples 1 to 3 are significantly better than those of Comparative Examples 3 to 4.

[0124] It can be seen from Example 1 and Comparative Examples 5 to 7 that when Example 1 uses the compound use of additive A with vinylene carbonate and fluoroethylene carbonate, it can achieve the effect of removing water and reducing acid for a longer time, and has better high-temperature cycling performance and storage performance.

[0125] The above-described embodiments only represent several implementation manners of the present disclosure, and their descriptions are relatively specific and detailed, but should not be construed as limiting the scope of the disclosed patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present disclosure, several modifications and improvements can still be made, and these all belong to the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure patent should be subject to the appended claims.

Claims

1. A non-aqueous electrolyte additive for a silicon anode ternary high-voltage lithium battery, comprising fluoroethylene carbonate, vinylene carbonate and a lithium salt additive, characterized in that the electrolyte additive further comprises additive A, and additive A has the following structure of formula 1: wherein, R1 and R2 are each independently selected from at least one of an alkyl group, a fluoroalkyl group, a vinyl group, an allyl group, an ethynyl group, a propargyl group, an acetyl group, a fluoroacetyl group, a sulfonyl group and a methyl isocyanate group; during use, the addition of additive A also realizes an equal amount replacement with vinylene carbonate.

2. The non-aqueous electrolyte additive for a silicon anode ternary high-voltage lithium battery according to claim 1, wherein The principle of additive A capturing HF and H2O is:

3. The non-aqueous electrolyte additive for a ternary high-voltage lithium battery with a silicon negative electrode according to claim 1, characterized in that, by mass fraction, the usage amount of vinylene carbonate is 0.2% to 2.0%; the usage amount of additive A is 0.1% to 5.0%.

4. The non-aqueous electrolyte additive for a silicon anode ternary high-voltage lithium battery according to claim 3, characterized in that, The usage amount of the lithium salt additive is 0.5% to 1.0%; the usage amount of fluoroethylene carbonate is 0% to 12.0%.

5. The non-aqueous electrolyte additive for a silicon anode ternary high-voltage lithium battery according to claim 1, characterized in that, The lithium salt additive includes at least one of lithium bis(fluorosulfonyl)imide LiFSI, lithium difluorophosphate LiPO2F2, lithium bis(oxalato)borate LiBOB and lithium difluorobis(oxalato)phosphate LiODFP.

6. The non-aqueous electrolyte additive for a silicon anode ternary high-voltage lithium battery according to claim 1, characterized in that, Additive A is selected from any one of the following formulas 11 to 13:

7. A non-aqueous electrolyte, characterized in that, Comprising an electrolyte salt, an organic solvent and the non-aqueous electrolyte additive for a silicon anode ternary high-voltage lithium battery as described in any one of claims 1 to 6.

8. The non-aqueous electrolyte according to claim 7, characterized in that, The organic solvent includes at least three of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

9. The non-aqueous electrolyte according to claim 8, characterized in that, The volume ratio of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate is (20 to 40):(0 to 20):(0 to 20):(5 to 20):(30 to 50).

10. A ternary high-voltage lithium battery with a silicon negative electrode, characterized in that, Comprising the non-aqueous electrolyte, positive electrode, negative electrode and separator according to any one of claims 7 to 9, wherein the positive electrode is Li(Ni x Co y Mn z )O2) (where 0.8 ≤ x, 0 < y ≤ 0.2, 0 < z ≤ 0.2 and x + y + z = 1), and the negative electrode is a graphite-doped silicon carbon material.

Images