High-voltage lithium ion battery electrolyte and lithium ion battery

Abstract

The embodiment of the invention relates to an electrolyte of a high-voltage lithium ion battery and the lithium ion battery, and belongs to the technical field of lithium ion batteries. The electrolyte comprises an organic solvent, a lithium salt and an additive, the additive comprises a cyclotrisiloxane additive and an alkene nitrile additive; the structural formula of the cyclotrisiloxane additive is # imgabs 0 # olefinic nitrile additive is # imgabs 1 #. The electrolyte disclosed by the invention contains the olefinic nitrile additive, and the olefinic nitrile additive can be subjected to oxidative decomposition reaction prior to a solvent, so that a uniform and compact CEI film containing an element B is formed on the surface of the positive electrode material, and the positive electrode material is protected; the cyano group contained in the alkene nitrile additive can be adsorbed on the surface of the positive electrode material, and forms stable complexation with positive electrode metal ions, so that the dissolution of the positive electrode metal ions is inhibited, the side reaction of the electrolyte is slowed down, and the cycle life of the high-voltage lithium ion battery is effectively prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a high-voltage lithium ion battery electrolyte and a lithium ion battery. Background Art

[0002] In recent years, with the rapid development of 3C digital products, electric vehicles and energy storage systems, people have put forward higher demands on the energy density of lithium-ion batteries. Among them, the use of high-voltage positive electrode materials is an important means to improve the energy density of lithium-ion batteries.

[0003] Under high voltage, the positive electrode material structure of lithium-ion batteries is unstable and has high oxidation activity. The existing electrolyte is easily catalytically oxidized and decomposed to produce a large amount of gas. In addition, during the battery cycle, the positive electrode transition metal ions are easily dissolved into the electrolyte, and the negative electrode reduction deposition hinders Li + The migration of electrolytes causes the SEI film to rupture, which intensifies the occurrence of side reactions at the interface between the electrode and the electrolyte, resulting in accelerated capacity decay of the battery cell, shorter cycle life, and deterioration of the battery cell performance. Summary of the invention

[0004] In view of the above analysis, the embodiments of the present invention aim to provide a high voltage lithium ion battery electrolyte and a lithium ion battery, so as to solve the problem that the electrolyte in the existing high voltage lithium ion battery is prone to side reactions with the electrodes, resulting in poor battery cycle life.

[0005] On the one hand, an embodiment of the present invention provides an electrolyte for a high-voltage lithium-ion battery, comprising: an organic solvent, a lithium salt, and an additive; the additive comprises a cyclotrisiloxane additive and an olefin nitrile additive; the structural formula of the cyclotrisiloxane additive is:

[0006]

[0007] The structural formula of olefin nitrile additives is:

[0008]

[0009] Among them, R 1 -R 8 They are independently selected from hydrogen, halogen, cyano, C1-C10 unsubstituted or substituted alkyl, C1-C10 unsubstituted or substituted alkoxy, C2-C10 unsubstituted or substituted alkenyl, C2-C10 unsubstituted or substituted alkynyl, C6-C10 unsubstituted or substituted aryl; the values ​​of n include 1, 2, and 3.

[0010] Furthermore, the high voltage lithium ion battery is a high voltage LCO battery of 4.5V and above.

[0011] Further, the olefin nitrile additive includes at least one of the following compounds:

[0012]

[0013] Further, the cyclotrisiloxane additive includes at least one of the following compounds:

[0014]

[0015] Furthermore, the mass of the olefin nitrile additive accounts for 0.1% to 2% of the total mass of the electrolyte.

[0016] Furthermore, the mass of the cyclotrisiloxane additive accounts for 0.1% to 3% of the total mass of the electrolyte.

[0017] Furthermore, the additive also includes: at least one of 1,3-propane sultone, 1,3-sultone, 1,4-butane sultone, vinyl sulfate, vinylene carbonate, vinyl ethylene carbonate, tris(trimethylsilane)borate, tris(trimethylsilane)phosphate, adiponitrile, succinonitrile, ethylene glycol dipropionitrile ether, 1,3,6-hexanetrinitrile, succinic anhydride, maleic anhydride, citraconic anhydride and methylene disulfonate.

[0018] Furthermore, the total mass of the additive is 5% to 20% of the electrolyte.

[0019] Furthermore, the mass of the lithium salt accounts for 10% to 20% of the total mass of the electrolyte.

[0020] Further, the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium tetrafluoroborate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethylsulfonyl imide, lithium bisoxalatoborate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium difluorooxalatophosphate and lithium tetrafluorooxalatophosphate.

[0021] On the other hand, an embodiment of the present invention further provides a lithium-ion battery, comprising: a positive electrode, a negative electrode and the electrolyte of the above embodiment.

[0022] Preferably, the high voltage lithium ion battery is a high voltage LCO battery of 4.5V or above.

[0023] The present invention can achieve at least one of the following beneficial effects:

[0024] 1. The electrolyte of the present invention contains olefin nitrile additives, which can undergo oxidation decomposition reaction on the positive electrode surface before the solvent to form a CEI film containing B, which protects the positive electrode material. At the same time, the cyanide group forms a stable complex with the positive electrode metal ion, which reduces the occurrence of side reactions between the positive electrode material and the electrolyte, thereby improving the cycle life of the lithium ion battery at high voltage. The electrolyte of the present invention is particularly suitable for high-voltage LCO system lithium ion batteries with an operating voltage of 4.5V or above, and can significantly improve the cycle life of the high-voltage lithium ion battery.

[0025] 2. The electrolyte of the present invention also contains cyclotrisiloxane additives, which can form films at both positive and negative electrodes, and the film components are rich in silicates, so that the interface film has good lithium ion conductivity, better stability and mechanical strength.

[0026] 3. The combined use of cyclotrisiloxane additives and olefin nitrile additives in the present invention can significantly improve the long cycle life of lithium-ion batteries. Using olefin nitrile additives alone can easily lead to large film formation resistance, poor compatibility with the negative electrode, and thus deterioration of room temperature cycle performance.

[0027] 4. The present invention ensures that the cycle performance of the lithium-ion battery is significantly improved by controlling the mass percentage of the cyclotrisiloxane additive and the olefin nitrile additive in the electrolyte within an appropriate range; avoids adding too little, which leads to unstable film formation of the interface film and poor protection of the positive and negative electrodes; avoids adding too much, which leads to excessive film formation impedance, which deteriorates the battery performance and increases the cost of the electrolyte.

[0028] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be achieved and obtained through the contents particularly pointed out in the description. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the present invention clearer, exemplary embodiments of the present invention are described below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. For the sake of clarity and conciseness, not all features of the actual implementation are described in the specification.

[0030] The embodiment of the present invention provides an electrolyte for a high-voltage lithium-ion battery, which includes: an organic solvent, a lithium salt, and an additive. The additive includes a cyclotrisiloxane additive and an olefin nitrile additive, and the structural formula of the cyclotrisiloxane additive is:

[0031]

[0032] The structural formula of olefin nitrile additives is:

[0033]

[0034] Among them, R 1 -R 8 They are independently selected from hydrogen, halogen, cyano, C1-C10 unsubstituted or substituted alkyl, C1-C10 unsubstituted or substituted alkoxy, C2-C10 unsubstituted or substituted alkenyl, C2-C10 unsubstituted or substituted alkynyl, C6-C10 unsubstituted or substituted aryl; the values ​​of n include 1, 2, and 3.

[0035] The electrolyte of the present invention contains olefin nitrile additives, which can undergo oxidative decomposition reaction before the solvent, forming a CEI film containing B element on the surface of the positive electrode material, thereby protecting the positive electrode material. At the same time, the cyanide group forms a stable complex with the positive electrode metal ion, thereby reducing the occurrence of side reactions between the positive electrode material and the electrolyte, thereby improving the cycle life of the lithium ion battery at high voltage.

[0036] Among them, the olefin nitrile additive has a BC=C structure, which is easy to polymerize into a film on the positive electrode surface, making the interface film more resilient, more uniform and dense in shape, and having a better protective effect; and the additive contains the B element, which can further optimize the interface film components, and form an interface film containing the B element on the positive electrode surface, thereby improving the stability of the interface film. The cyanide group contained in the olefin nitrile additive can be adsorbed on the surface of the positive electrode material, and by forming a stable complex with the positive electrode metal ion, the dissolution of the positive electrode metal ion is inhibited, and the occurrence of electrolyte side reactions is slowed down. The olefin nitrile additive shown in the structural formula II of the present invention can protect the positive electrode material from these directions, and through the synergistic effect of the BC=C structure and the cyanide group, the dissolution of the positive electrode metal ion is slowed down, thereby effectively improving the cycle life of the lithium ion battery. In addition, the carbon-carbon double bond contained in the olefin nitrile additive can also participate in the negative electrode film formation, and also has a certain protective effect on the negative electrode.

[0037] It should be noted that the complexing protection ability of olefin nitrile additives for positive electrode metal ions has a certain relationship with the number of cyano groups. The olefin nitrile additives of the present invention contain at least two cyano groups. Compared with some nitrile compounds containing only one cyano group, the olefin nitrile additives of the present invention have a higher cyano density and a better protective effect on the positive electrode material.

[0038] The electrolyte of the present invention also contains cyclotrisiloxane additives, which can form films on both positive and negative electrodes, and the film components are rich in silicates, so that the interface film has good lithium ion conductivity, better stability and mechanical strength.

[0039] The cyclotrisiloxane additive and the olefin nitrile additive used in combination in the present invention can significantly improve the long cycle life of the lithium ion battery, avoiding the problem that the use of olefin nitrile additives alone easily leads to large film formation impedance, poor compatibility with the negative electrode, and thus deterioration of room temperature cycle performance.

[0040] In some embodiments, the olefin nitrile additive is preferably at least one of the following compounds:

[0041]

[0042] The olefin nitrile additive of the present invention also contains F element, which can react with Li + The reaction generates more LiF in the interface film, further improving the stability of the interface film and reducing the interface impedance, which is beneficial to the uniform deposition of lithium ions and inhibits the formation of lithium dendrites, thereby further improving the cycle life of lithium-ion batteries.

[0043] In some embodiments, the cyclotrisiloxane additive is preferably at least one of the following compounds:

[0044]

[0045] In some embodiments, the mass of the olefin nitrile additive accounts for 0.1% to 2% of the total mass of the electrolyte, for example, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, etc. The present invention controls the amount of olefin nitrile additive added within a suitable range to avoid adding too little, which results in poor film stability, insufficient cyanide groups, and insignificant protection effect; and to avoid adding too much, which results in increased electrolyte cost, excessive film impedance, and is not conducive to the insertion and extraction of lithium ions, but instead deteriorates the battery cycle performance.

[0046] Preferably, the mass of the olefin nitrile additive accounts for 0.5-1% of the total mass of the electrolyte, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc.

[0047] In some embodiments, the mass of the cyclotrisiloxane additive accounts for 0.1% to 3% of the total mass of the electrolyte. If the amount added is too little, it is easy to cause poor film stability and ineffective protection of the positive and negative electrodes; if the amount added is too much, it is easy to cause excessive film impedance, which is not conducive to the insertion and extraction of lithium ions, deteriorating the performance of the lithium-ion battery and increasing the cost of the electrolyte.

[0048] Preferably, the mass of the cyclotrisiloxane additive accounts for 0.5-2% of the total mass of the electrolyte, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, etc.

[0049] In some embodiments, the additives further include conventional additives, which include: 1,3-propane sultone (PS), 1,3-sultone (PST), 1,4-butane sultone (BS), vinyl sulfate (DTD), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), tris(trimethylsilyl) borate (TMSB), tris(trimethylsilyl) phosphate (TMSP), adiponitrile (ADN), succinonitrile (SN), ethylene glycol dipropylene glycol ether (DENE), 1,3,6-hexanetrinitrile (HTCN), succinic anhydride (SA), maleic anhydride (MA), citraconic anhydride (CTA) and at least one of methylene methane disulfonate (MMDS).

[0050] Adding conventional additives to the electrolyte of the present invention, for example, adding PS, can improve the cycle performance through film-forming effect, and can introduce S element into the interface film, optimize the interface film components, and improve the stability of the interface film.

[0051] In some embodiments, the total mass of the additives accounts for 5% to 20% of the total mass of the electrolyte, to avoid excessive additives resulting in excessive film formation impedance at the interface between the electrode and the electrolyte, resulting in poor battery performance; to avoid too few additives resulting in poor film formation stability and poor battery cycle performance.

[0052] In some embodiments, the lithium salt includes lithium hexafluorophosphate (LiPF 6 ), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorooxalatoborate (LiODFB), lithium tetrafluoroborate (LiBF 4 ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalatoborate) (LiBOB), lithium hexafluoroantimonate (LiSbF 6 ) lithium hexafluoroarsenate (LiAsF 6 ), lithium difluorooxalate phosphate (LiDFOP) and lithium tetrafluorooxalate phosphate (LiTFOP) or a combination of two or more thereof.

[0053] Preferably, the lithium salt comprises LiPF 6 、LiPO 2 F 2 , a combination of at least two of LiBOB and LiODFB.

[0054] In some embodiments, the mass of lithium salt accounts for 10% to 20% of the total mass of the electrolyte. If the lithium salt content is too low or too high, it will have a relatively large impact on the viscosity and conductivity of the electrolyte, affecting the transmission of lithium ions, which is not conducive to the performance of lithium-ion batteries.

[0055] In some embodiments, the organic solvent includes any one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl trifluoroethyl carbonate (FEMC), fluoroethylene carbonate (FEC), diethyl carbonate (DEC), propyl propionate (PP), ethyl propionate (EP), methyl propionate (MP), propyl acetate (PA), ethyl acetate (EA), ethyl butyrate (EB), γ-butyrolactone (GBL), γ-valerolactone (GVL), and δ-valerolactone (DVL), or a combination of two or more thereof.

[0056] Preferably, the organic solvent is a combination of three or more of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC).

[0057] In some embodiments, the mass of the organic solvent accounts for 60% to 85% of the total mass of the electrolyte.

[0058] The electrolyte of the present invention is suitable for high-voltage lithium-ion batteries. Preferably, the high-voltage lithium-ion battery is a high-voltage LCO battery of 4.5V or above, that is, a lithium-ion battery using lithium cobalt oxide (LCO) as the positive electrode material.

[0059] Under high voltage, the Co ions in the LCO positive electrode material are easily dissolved into the electrolyte, and the SEI film is destroyed by reduction at the negative electrode, resulting in degradation of the performance of the battery cell, and the higher the working voltage, the more obvious the dissolution of Co ions. The electrolyte in the present invention includes olefin nitrile additives, in which the cyanide group is preferentially adsorbed on the surface of the LCO material, occupying the metal active sites on the surface of the LCO, and the cyanide group has a strong coordination ability, which can form a stable complex with the high-valent metal ions of the positive electrode material, inhibiting the dissolution of Co ions. In addition, the electrolyte in the present invention also includes cyclotrisiloxane additives, which can form a stable CEI / SEI interface film in combination with olefin nitrile additives, slow down the dissolution of Co ions, and inhibit the deposition of Co ions on the surface of the negative electrode, thereby inhibiting the occurrence of side reactions on the positive and negative electrode surfaces.

[0060] On the other hand, an embodiment of the present invention further provides a lithium ion battery. The lithium ion battery comprises a positive electrode, a negative electrode, a separator and the electrolyte in the above embodiment.

[0061] The electrolyte of the present invention includes olefin nitrile additives, which can react with oxidation and decomposition on the surface of the positive electrode material in preference to the solvent to form a CEI film containing B; cyano groups are adsorbed on the surface of the positive electrode material to form a stable complex with the positive electrode metal ions, which plays a dual protective role in inhibiting the dissolution of the positive electrode metal ions and slowing down the occurrence of electrolyte side reactions. However, olefin nitrile additives have a large film-forming impedance and poor compatibility with the negative electrode, and are prone to deterioration of room temperature cycle performance when used alone. For this reason, cyclotrisiloxane additives are also added to the electrolyte of the present invention, and such substances can form films at both the positive and negative electrodes, and the film components are rich in silicates, so that the interface film has good lithium ion conductivity, better stability and mechanical strength; olefin nitrile additives and cyclotrisiloxane additives are used in combination to significantly improve the long cycle life of lithium ion batteries.

[0062] In some embodiments, the active material in the positive electrode is one or more of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, ternary or lithium-rich manganese-based.

[0063] Preferably, the high voltage lithium ion battery is a high voltage LCO battery of 4.5V or above.

[0064] In some embodiments, the active material in the negative electrode is one or more of natural graphite, artificial graphite, and silicon-carbon composite material.

[0065] The electrolyte and lithium ion battery of the present invention are further described below with reference to specific embodiments.

[0066] Example 1

[0067] The electrolyte of this embodiment includes: 2wt% conventional additive PS, 2wt% cyclotrisiloxane additive shown in structural formula I-1, 1wt% olefin nitrile additive shown in structural formula II-1, 13.5wt% LiPF 6 and 0.5wt%LiPO 2 F 2 , and the rest are organic solvents.

[0068] The above electrolyte is used to prepare a lithium-ion battery, and the specific process is as follows.

[0069] 1. Preparation of electrolyte

[0070] Organic solvents ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), and propyl propionate (PP) were mixed according to the ratio of EC:PC:DEC:FEC:PP:=1:1:2:1:5, and 13.5 wt% LiPF was added in sequence after mixing evenly. 6 and 0.5wt%LiPO 2 F 2, add conventional additives and special additives after they are fully dissolved, wherein the conventional additive is 2wt% PS, and the special additive is 2wt% cyclotrisiloxane additive I-1 and 1wt% olefin nitrile additive II-1, and mix thoroughly and dissolve them for later use.

[0071] 2. Preparation of positive electrode

[0072] Lithium cobalt oxide positive electrode active material (LCO), conductive carbon black (Super-P), carbon nanotubes (CNT) and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97.9:0.5:0.5:1.1, and then dispersed in N-methyl-2-pyrrolidone (NMP), and stirred thoroughly to obtain positive electrode slurry. The positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and after drying, it is rolled and die-cut to obtain a positive electrode sheet.

[0073] 3. Preparation of negative electrode

[0074] The negative electrode active material graphite, conductive carbon black (Super-P), binder styrene butadiene rubber (SBR) and thickener carboxymethyl cellulose (CMC) are mixed in a mass ratio of 97.3:0.3:1.3:1.1, and then dispersed in deionized water to obtain a negative electrode slurry. The negative electrode slurry is evenly coated on the negative electrode current collector copper foil, and after drying, it is rolled and die-cut to obtain a negative electrode sheet.

[0075] 4. Preparation of lithium-ion batteries

[0076] The positive and negative electrode sheets and the separator prepared by the above method are stacked in order, wherein the separator is located between the positive and negative electrode sheets. The stacked battery cells are fixed with tape, and packaged after cold pressing to form lithium-ion batteries with a thickness of 4.6 mm, a length of 85 mm, and a width of 50 mm. The battery cells are vacuum-baked at 80°C for 24 hours to obtain battery cells to be injected with liquid. In a glove box with a dew point controlled below -40°C, the prepared electrolyte is injected into the battery cells. After standing at high temperature for 24 hours and at room temperature for 12 hours, formation, secondary sealing and capacity separation are carried out to complete the battery production.

[0077] Example 2

[0078] The difference from Example 1 is that the cyclotrisiloxane additive in the electrolyte is 0.5 wt % of compound I-1, and the rest is the same.

[0079] Example 3

[0080] The difference from Example 1 is that the cyclotrisiloxane additive in the electrolyte is 0.1 wt % of compound I-1, and the rest is the same.

[0081] Example 4

[0082] The difference from Example 1 is that the cyclotrisiloxane additive in the electrolyte is 3 wt % of compound I-1, and the rest is the same.

[0083] Example 5

[0084] The difference from Example 1 is that the olefin nitrile additive in the electrolyte is 0.5 wt % of compound II-1, and the rest is the same.

[0085] Example 6

[0086] The difference from Example 1 is that the olefin nitrile additive in the electrolyte is 0.1 wt % of compound II-1, and the rest is the same.

[0087] Example 7

[0088] The difference from Example 1 is that the olefin nitrile additive in the electrolyte is 2 wt % of compound II-1, and the rest is the same.

[0089] Example 8

[0090] The difference from Example 1 is that the cyclotrisiloxane additive in the electrolyte is 2 wt % of compound I-2, and the rest is the same.

[0091] Example 9

[0092] The difference from Example 1 is that the cyclotrisiloxane additive in the electrolyte is 2 wt % of compound I-3, and the rest is the same.

[0093] Example 10

[0094] The difference from Example 1 is that the olefin nitrile additive in the electrolyte is 1 wt % of compound II-2, and the rest is the same.

[0095] Comparative Example 1

[0096] The difference from Example 1 is that the electrolyte of this comparative example does not contain siloxane additives, that is, does not contain 2 wt % of compound I-1, and the rest is the same.

[0097] Comparative Example 2

[0098] The difference from Example 1 is that the electrolyte of this comparative example does not contain olefin nitrile additives, that is, does not contain 1 wt % of compound II-1, and the rest is the same.

[0099] Comparative Example 3

[0100] The difference from Example 1 is that the electrolyte of this comparative example does not contain 2 wt % of Compound I-1 and 1 wt % of Compound II-1, and the rest is the same.

[0101] Comparative Example 4

[0102] The difference from Example 1 is that the cyclotrisiloxane additive is 0.05 wt % of compound I-1, and the rest is the same.

[0103] Comparative Example 5

[0104] The difference from Example 1 is that the cyclotrisiloxane additive is 3.5 wt % of compound I-1, and the rest is the same.

[0105] Comparative Example 6

[0106] The difference from Example 1 is that the olefin nitrile additive is 0.05 wt % of compound II-1, and the rest is the same.

[0107] Comparative Example 7

[0108] The difference from Example 1 is that the olefin nitrile additive is 3 wt % of compound II-1, and the rest is the same.

[0109] The lithium ion batteries prepared in the embodiments and comparative examples were subjected to cycle performance tests.

[0110] Cyclic performance test at 4.5V: At 25°C, the lithium-ion battery was charged to 4.5V at 0.5C constant current and constant voltage, with a cut-off current of 0.05C, and then discharged to 3.0V at 0.5C constant current. The initial discharge capacity was recorded as C 0 , repeat the charge and discharge 500 times, and record the discharge capacity of the 500th cycle as C 1 , calculate the capacity retention rate of room temperature cycle according to the following formula: Capacity retention rate = C 1 / C 0 × 100%. The test results are shown in Table 1.

[0111] Cyclic performance test at 4.53V: At 25°C, the lithium-ion battery was charged to 4.53V at 0.5C constant current and constant voltage, with a cut-off current of 0.05C, and then discharged to 3.0V at 0.5C constant current. The initial discharge capacity was recorded as C 2 , repeat the charge and discharge 500 times, and record the discharge capacity of the 500th cycle as C 3 , calculate the capacity retention rate of room temperature cycle according to the following formula: Capacity retention rate = C 3 / C 2 × 100%. The test results are shown in Table 1.

[0112] Table 1 Types and contents of electrolyte additives and lithium-ion battery performance test results

[0113]

[0114] It can be seen from Comparative Examples 1-3 and Examples 1-10 that the addition of cyclotrisiloxane additives and olefin nitrile additives to the electrolyte significantly improves the room temperature cycle performance of the lithium ion battery, wherein the combined use of cyclotrisiloxane additives and olefin nitrile additives is more effective than the use of them alone. The room temperature cycle capacity retention rate of the battery after 500 cycles at a high voltage of 4.5V is above 82%, and the room temperature cycle capacity retention rate after 500 cycles at a high voltage of 4.53V is mostly above 80%. This is because when the two are used together, both the positive and negative electrode materials are effectively protected, and the occurrence of electrode-electrolyte interface side reactions is effectively slowed down, which is beneficial to the long cycle life of the lithium ion battery at high voltage.

[0115] It can be seen from Comparative Examples 1-3 and Examples 1-10 that the addition amount of cyclotrisiloxane additives and olefin nitrile additives within the range set by the present invention can significantly improve the cycle performance of lithium-ion batteries. Among them, it can be seen from Examples 1 to 4 that the more cyclotrisiloxane additives are added, the more obvious the battery cycle performance improvement effect is. When the addition amount continues to increase, the battery cycle performance improvement effect is slightly reduced due to the large film formation impedance. It can be seen from Examples 1 and Examples 5 to 7 that the more olefin nitrile additives are added, the more obvious the battery cycle performance improvement effect is. When the addition amount continues to increase, the battery cycle performance improvement effect is slightly reduced due to the large film formation impedance.

[0116] It can be seen from Comparative Example 4, Comparative Example 6, and Example 1 that when the amount of cyclotrisiloxane additives or olefin nitrile additives added is too small, the film formation stability of the electrode-electrolyte interface is poor, the protection effect is not obvious, and the battery cycle performance is poor; it can be seen from Comparative Example 5, Comparative Example 7, and Example 1 that when the amount of cyclotrisiloxane additives or olefin nitrile additives added is too much, due to the excessive film formation impedance, it is not conducive to the insertion and removal of lithium ions, the battery cycle performance is not further improved, and the battery cycle performance is worse than that of Examples 1 to 7, and the cost of the electrolyte is increased.

[0117] From Comparative Example 1, Examples 1, 8, and 9, it can be seen that adding cyclotrisiloxane additives represented by structural formulas I-2 and I-3 to the electrolyte can also improve the cycle performance of lithium-ion batteries, among which compound I-3 has a more obvious improvement effect. This is because the double bonds in compound I-2 polymerize to form a denser interface film, which increases the interface impedance; compound I-3 has -CF 3 The interfacial film generated by the action of the groups is rich in LiF, which is conducive to the uniform deposition of lithium ions and further improves the stability of the interfacial film.

[0118] It can be seen from Comparative Example 2, Example 1 and Example 10 that adding compound II-2 to the electrolyte also improves the cycle performance. However, because compound II-2 contains four cyano groups, the battery impedance increases, which is not conducive to improving the room temperature cycle performance.

[0119] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. An electrolyte for a high voltage lithium ion battery, characterized in that: include: An organic solvent, a lithium salt, and an additive; the additive comprises a cyclotrisiloxane additive and an olefin nitrile additive; The structural formula of the cyclotrisiloxane additive is: The structural formula of the olefin nitrile additive is: Wherein, R1-R8 are independently selected from hydrogen, halogen, cyano, C1-C10 unsubstituted or substituted alkyl, C1-C10 unsubstituted or substituted alkoxy, C2-C10 unsubstituted or substituted alkenyl, C2-C10 unsubstituted or substituted alkynyl, C6-C10 unsubstituted or substituted aryl; the value of n includes 1, 2, and 3.

2. The electrolyte according to claim 1, characterized in that The olefin nitrile additive comprises at least one of the following compounds:

3. The electrolyte according to claim 1, characterized in that The cyclotrisiloxane additive includes at least one of the following compounds:

4. The electrolyte according to any one of claims 1 to 3, characterized in that The mass of the olefin nitrile additive accounts for 0.1% to 2% of the total mass of the electrolyte.

5. The electrolyte according to claim 4, characterized in that The mass of the cyclotrisiloxane additive accounts for 0.1% to 3% of the total mass of the electrolyte.

6. The electrolyte according to claim 1, characterized in that The additive also includes: at least one of 1,3-propane sultone, 1,3-sultone, 1,4-butane sultone, vinyl sulfate, vinylene carbonate, vinyl ethylene carbonate, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, adiponitrile, succinonitrile, ethylene glycol dipropionitrile ether, 1,3,6-hexanetrinitrile, succinic anhydride, maleic anhydride, citraconic anhydride and methylene methane disulfonate.

7. The electrolyte according to claim 6, characterized in that The total mass of the additive is 5% to 20% of the electrolyte.

8. The electrolyte according to claim 1, characterized in that The mass of the lithium salt accounts for 10% to 20% of the total mass of the electrolyte.

9. The electrolyte according to any one of claims 1 to 8, characterized in that: The high voltage lithium ion battery is a high voltage LCO battery of 4.5V and above.

10. A lithium ion battery, characterized in that: include: A positive electrode, a negative electrode and an electrolyte according to any one of claims 1 to 9; Preferably, the lithium-ion battery is a high-voltage LCO battery of 4.5V or above.

Images