A high-voltage fast-charging lithium ion secondary battery

Abstract

The application discloses a high-voltage fast-charging lithium ion secondary battery, which comprises a positive electrode, a negative electrode, a diaphragm and an electrolyte, wherein the electrolyte comprises a main lithium salt, a nonaqueous solvent and an additive, the additive comprises a novel composite lithium salt, the novel composite lithium salt at least comprises a pyrosulfate boron trifluoride composite lithium salt with a structure shown in the following formula (I-1): the novel composite lithium salt accounts for 0.02-5.0 wt% of the total mass of the electrolyte; and the negative electrode comprises an active substance capable of reversibly absorbing and releasing lithium ions, and the specific surface area of the active substance is 0.1-20 m 2 / g. The electrolyte and the negative electrode material of the application interact to build a low-impedance lithium ion migration channel, thereby improving the fast-charging and low-temperature performance of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion secondary batteries, in particular to a high-voltage fast-charging lithium ion secondary battery containing a pyrosulfate boron trifluoride composite lithium salt and a hard carbon negative electrode. BACKGROUND

[0002] At present, the energy replenishment anxiety of new energy vehicles during long-distance travel has become the core problem of vehicle owners, therefore, the low-temperature fast-charging performance of batteries is increasingly concerned. The internal impedance of the battery is one of the important standards for evaluating the fast-charging and low-temperature performance of lithium ion batteries. Excessive internal impedance can cause large internal polarization of the battery during charging and discharging, thereby affecting the capacity of the battery, and generating more side reactions under extreme conditions. Once the internal polarization of the battery is large during the rate charging process, overpotential is easily generated, leading to irreversible lithium precipitation in the negative electrode, further causing capacity attenuation and safety decline of the battery.

[0003] Electrochemical impedance spectroscopy is a commonly used evaluation method for testing the internal impedance of the battery. Lu et al. (The timescale identification decoupling complicated kinetic processes in lithium batteries[J]. Joule, 2022, 6(6): 1172-1198.) summarized the method of using relaxation time distribution function to decouple electrochemical impedance spectroscopy data, and roughly divided the sources of internal impedance of the battery into ohmic impedance (R0), liquid-solid interfacial impedance (R sei ), charge transfer impedance (R ct ), diffusion impedance (R w ), etc. In different battery systems, the relaxation time (frequency domain) of each type of impedance source is relatively close, so the relaxation time distribution function can be directly used to decouple and distinguish the impedance types. Through electrochemical impedance spectroscopy analysis, it is found that the diffusion impedance dominated by solid-phase diffusion accounts for a large part of the internal impedance of the battery. The battery can simplify the internal positive electrode, electrolyte, separator, negative electrode, electrolyte and solid phase formed by the negative electrode reaction as a series circuit during charging and discharging, therefore, the impedance of any component is too high, which is easy to cause the battery to have a short board, thereby affecting the fast-charging performance and low-temperature performance of the battery. Among them, the solid phase formed by the negative electrode, electrolyte (mainly additives) and negative electrode reaction (SEI film) has the most critical impact on the internal impedance of the battery.

[0004] Therefore, it is necessary and urgent to propose a scheme that can simultaneously solve the problem of excessive impedance of electrolyte, negative electrode, and solid phase formed by electrolyte and negative electrode reaction, and apply it to lithium ion secondary batteries to improve the fast-charging performance and low-temperature performance. SUMMARY

[0005] Fulfulfate boron trifluoride complex lithium salt is a new type of electrolyte additive developed by the applicant, which can improve the cycle performance, high temperature storage performance and low temperature performance of the battery. Further research has found that the fulfulfate boron trifluoride complex lithium salt has the effect of reducing the liquid-solid interfacial impedance and charge transport impedance in the battery, but when it is used with different negative active materials, the improvement effect on the fast charging performance and low temperature performance of the battery is quite different.

[0006] In order to solve the above technical problems, the present application proposes a high-voltage fast-charging lithium ion secondary battery which is interacted by fulfulfate boron trifluoride complex lithium salt and specific negative active material, which can construct a low-impedance lithium ion migration channel, thereby improving the fast-charging performance and low-temperature performance of the battery.

[0007] The purpose of the present application is achieved by the following technical solutions:

[0008] A high-voltage fast-charging lithium ion secondary battery, comprising a positive electrode, a negative electrode, a separator and an electrolyte, the electrolyte comprising a main lithium salt, a non-aqueous solvent and an additive, the additive comprising:

[0009] A new composite lithium salt, the new composite lithium salt at least comprising a fulfulfate boron trifluoride complex lithium salt of the following formula (I-1):

[0010]

[0011] The new composite lithium salt accounts for 0.02-5.0wt% of the total mass of the electrolyte; preferably, it accounts for 0.1-2.0wt% of the total mass of the electrolyte;

[0012] And the negative electrode comprises:

[0013] An active material capable of reversibly absorbing and releasing lithium ions, the specific surface area of the active material being 0.1-20.0m 2 / g; preferably, the specific surface area of the active material is 0.5-10.0m 2 / g.

[0014] When the active material is a single substance, the specific surface area of the single substance needs to meet the above limitation;

[0015] When the active material is two or more substances, the specific surface area of any one of the substances needs to meet the above limitation.

[0016] When the new composite lithium salt and the negative active material with the above specific surface area coexist, the purpose of constructing a low impedance, stable and permeable lithium ion migration channel can be achieved, thereby improving the battery fast charging performance and low temperature performance. If the specific surface area of the negative active material is too low, the path of lithium ion migration inside the negative active material will be too long, thereby increasing the difficulty of lithium ion solid phase diffusion, increasing the battery diffusion impedance and the battery internal impedance, and reducing the battery fast charging performance and low temperature performance; if the specific surface area of the negative active material is too high, too much electrolyte will participate in the generation process of the liquid-solid interface, increasing the side reaction, increasing the number of irreversible lithium ions, thickening the interface, increasing the battery internal impedance, and reducing the battery fast charging performance and low temperature performance.

[0017] The active material of the negative electrode is selected from a carbon material and / or a silicon material; the carbon material is selected from at least one of natural graphite, artificial graphite and hard carbon, and the silicon material is selected from silicon and / or silicon monoxide.

[0018] The specific types of the carbon material are commonly used materials in the field of secondary batteries, wherein the natural graphite refers to a graphite material with inconsistent particle diameters or a wide particle diameter distribution, and generally has defects on the surface. The lithium ion secondary battery prepared therefrom generally has more side reactions and relatively poor cycle performance, but has the advantages of low price and wide commercial application; the artificial graphite refers to a graphite material prepared or selected by artificial, and has basically consistent particle diameters or a relatively narrow particle diameter distribution compared with the natural graphite, and has better compatibility with the electrolyte and better use performance, but has a higher price and is commonly used in the field of high-performance lithium ion secondary batteries such as high-end new energy vehicles; the hard carbon refers to a carbon material that is difficult to graphitize at a temperature of 2500°C or above, and has a highly disordered carbon layer structure and an open void structure, and all of them can be directly purchased on the market.

[0019] Further, the active material of the negative electrode at least includes the hard carbon, and the mass content of the hard carbon is 0.1-100%. Preferably, the mass content of the hard carbon in the active material of the negative electrode is 1-50%; more preferably, the mass content of the hard carbon in the active material of the negative electrode is 5-20%.

[0020] The active material of the negative electrode includes the hard carbon, which can significantly improve the diffusion capacity of lithium ions in the negative electrode and has excellent reaction kinetics. At the same time, the electrolyte of the present application has good compatibility with the negative electrode material, which is helpful to form a stable and permeable liquid-solid interface during the first charge and discharge process of the battery, thereby improving the fast charging performance of the battery.

[0021] Further research shows that the size of the diffusion impedance is mainly determined by the state of the solid phase material in the lithium ion secondary battery, and although it is distributed throughout the frequency domain, its main components are distributed in the low frequency region (1-0.01 Hz frequency domain). Therefore, the proportion of the low frequency region (1-0.01 Hz frequency domain) AC impedance to the full frequency domain (10000-0.01 Hz) AC impedance is an important means to measure the diffusion impedance of the whole battery internal impedance, and is also an important indicator to measure the fast charging performance of the battery.

[0022] Through the interaction of the pyrosulfate-boron trifluoride complex lithium salt and the specific negative electrode active material, the AC impedance of the lithium ion secondary battery in the 1-0.01 Hz frequency domain accounts for 40-80% of the AC impedance in the 10000-0.01 Hz frequency domain. Further, the AC impedance of the lithium ion secondary battery in the 1-0.01 Hz frequency domain accounts for 60-70% of the AC impedance in the 10000-0.01 Hz frequency domain.

[0023] Specifically, the AC impedance is measured at 0-45℃, at 20%-80% state of charge of the battery. In a specific embodiment, the AC impedance resistance value in different frequency domains can be measured at room temperature, at about 50% state of charge of the battery.

[0024] In addition, the positive electrode, the negative electrode, the separator, and the liquid-solid interface formed by the interaction of the electrolyte and the positive and negative electrodes all have an impact on the charge transfer impedance. Among them, the impact of the separator is small, so the separator in the common lithium ion secondary battery can be used. Preferably, the separator is selected from at least one of polyolefin separators, polyester separators, cellulose separators, and polyimide separators, and the separator can be further processed using ceramic coating technology. The positive electrode material in the common lithium ion secondary battery is used in the present application. Although the positive electrode material has a certain impact on the charge transfer impedance, in order to improve the energy density of the battery, the high-voltage battery system is used in the present application, so there are certain limitations in the selection of the positive electrode material. Preferably, the active material of the positive electrode is selected from at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide, lithium nickel oxide, layered lithium manganate, spinel lithium manganate, and nickel manganate material.

[0025] Generally, the electrolyte additive and the liquid-solid interface formed by the interaction of the additive and the negative electrode have a great impact on the size of the charge transfer impedance of the lithium ion secondary battery. The process of lithium ion migration from the liquid-solid interface to the solid phase of the negative electrode material is the main component of the charge transfer impedance, and the AC impedance part is partially distributed in the medium-low frequency region of 1-0.1 Hz, and partially overlaps with the diffusion impedance. Through the decoupling data mentioned in the present application, it is found that within the above-mentioned test temperature and state of charge range of the present application, the charge transfer impedance accounts for 20-40% of the AC impedance in the 10000-0.01 Hz full frequency domain.

[0026] Due to the difference of the preparation process parameters of the new composite lithium salt, the new composite lithium salt further comprises at least one of the compounds represented by the following formula (I-2), (I-3), (I-4), (I-5), (I-6):

[0027]

[0028]

[0029]

[0030] and the new composite lithium salt contains at least 80.0wt% of the pyrosulfate boron trifluoride composite lithium salt represented by the formula (I-1). Preferably, the new composite lithium salt contains 80.0-95.0wt% of the pyrosulfate boron trifluoride composite lithium salt represented by the formula (I-1), and the rest is at least one of the compounds (I-2), (I-3), (I-4), (I-5) or (I-6).

[0031] According to the above high-voltage fast-charging lithium ion secondary battery, the additive further comprises a base additive selected from at least one of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, tris(trimethylsilyl) phosphate, 1,3-propane sultone, 1,3-propene sultone, vinyl sulfate, lithium difluorophosphate, lithium bisfluorosulfonylimide, succinic anhydride, adipodinitrile, cyclohexylbenzene, lithium difluorophosphate bisoxalate, or lithium difluoroboric acid oxalate, and the mass percentage of any base additive in the electrolyte is 0.1-5.0wt%, preferably 0.1-2.0wt%.

[0032] In a specific embodiment, the base additive is lithium difluoroboric acid oxalate (LiDFOB) and lithium difluorophosphate (LiDFP), each accounting for 0.1%-2.0% of the total mass of the electrolyte, and through the interaction with the new composite lithium salt and the negative electrode active material, the fast-charging performance and low-temperature performance of the lithium ion secondary battery can be further improved.

[0033] In another embodiment, the base additive is fluoroethylene carbonate (FEC), vinyl sulfate (DTD) and tris(trimethylsilyl) phosphate (TMSP), each accounting for 0.1%-2.0% of the total mass of the electrolyte, and through the interaction with the new composite lithium salt and the negative electrode active material, the fast-charging performance and low-temperature performance of the lithium ion secondary battery can be further improved.

[0034] According to the high-voltage fast-charging lithium ion secondary battery, the main lithium salt is at least one selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bisoxalate borate, lithium difluoro oxalate borate, lithium bisfluorosulfonimide, lithium bis-trifluoromethylsulfonimide, lithium tetrafluoro oxalate phosphate, lithium trioxalate phosphate or lithium difluoro bisoxalate phosphate, and the molar concentration is 0.1-4.0 mol / L.

[0035] According to the high-voltage fast-charging lithium ion secondary battery, the non-aqueous solvent is at least one selected from C3-C6 carbonate compounds, C3-C8 carboxylate compounds, sulfone compounds, ether compounds, nitrile compounds.

[0036] Preferably, the C3-C6 carbonate compounds are at least one selected from vinyl carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl-2,2,2-trifluoroethyl; the C3-C8 carboxylate compounds are at least one selected from γ-butyrolactone, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, propyl acetate, propyl propionate, 2,2-difluoroethyl acetate; the sulfone compounds are at least one selected from tetramethylene sulfone, dimethyl sulfoxide, dimethyl sulfone, diethyl sulfone; the ether compounds are selected from triethylene glycol dimethyl ether and / or tetraethylene glycol dimethyl ether; the nitrile compounds are at least one selected from acetonitrile, succinonitrile, adiponitrile, 1,3,6-hexanetricarbonitrile, p-fluorobenzonitrile, 1,2-bis(cyanoethoxy)ethane.

[0037] Preferably, the non-aqueous solvent is a mixture of at least two of vinyl carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, γ-butyrolactone, ethyl acetate, ethyl propionate, propyl propionate, succinonitrile, adiponitrile, 1,3,6-hexanetricarbonitrile.

[0038] According to the high-voltage fast-charging lithium ion secondary battery, the negative electrode further comprises auxiliary materials such as current collectors, conductive agents, and binders. Since the selection of the auxiliary materials has no significant effect on the interaction between the electrolyte and the negative electrode mentioned in the present application, the present application has no limitation on the types of the auxiliary materials, and any known auxiliary materials can be used.

[0039] The active material of the positive electrode can be a common positive electrode material of lithium ion secondary batteries. Preferably, the active material of the positive electrode is at least one selected from lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide, lithium nickel oxide, layered lithium manganese oxide, spinel lithium manganese oxide, and lithium nickel manganese oxide material. Further preferably, the active material of the positive electrode is at least one selected from lithium nickel cobalt manganese oxide, lithium cobalt oxide, or lithium nickel oxide material.

[0040] The high-voltage fast-charging lithium ion secondary battery has excellent low-temperature fast-charging performance, and the constant current charging ratio is greater than or equal to 75% under the working voltage of 1-6C charging rate and 4.2-5.0V cutoff; further, the constant current charging ratio of the lithium ion secondary battery is greater than or equal to 90% under the working voltage of 2-4C charging rate and 4.25-4.45V cutoff.

[0041] Compared with the prior art, the present application has the beneficial effects of:

[0042] 1. The present application uses a new type of composite lithium salt and a specific negative electrode to strengthen the interaction between the electrolyte and the negative electrode, solves the problem of excessive solid-phase impedance formed by the reaction of the electrolyte, the negative electrode and the electrolyte and the negative electrode, and thus improves the fast-charging performance and low-temperature performance of the lithium ion secondary battery.

[0043] 2. The present application uses a relaxation time distribution function to decouple and distinguish the components and their sizes in the internal impedance of the lithium ion secondary battery, and verifies that only when the electrolyte and the negative electrode of the present application are used at the same time, the prepared lithium secondary battery can have the effects of reducing the charge transfer impedance and the diffusion impedance. Although the mechanism of how the electrolyte and the negative electrode affect the charge transfer impedance and the diffusion impedance is not clear and controversial, through analysis of the experimental results, it is speculated that the new type of composite lithium salt and the specific negative electrode of the present application synergistically form a stable and ion-permeable electrolyte-negative electrode channel during the preparation of the battery, thereby improving the electrochemical performance of the lithium ion secondary battery. DETAILED DESCRIPTION

[0044] The present application will be further described below in conjunction with specific embodiments, but the present application is not limited to these specific embodiments. Those skilled in the art should realize that the present application encompasses all alternatives, improvements and equivalents within the scope of the claims.

[0045] In the examples and comparative examples of the present application, the types of new composite lithium salts include the following:

[0046] Composite lithium salt A1: containing 95wt% of compound I-1 and 5wt% of compound I-2;

[0047] Composite lithium salt A2: containing 90wt% of compound I-1, 6wt% of compound I-2 and 4wt% of compound I-3.

[0048] In the examples and comparative examples of the present application, natural graphite, artificial graphite, hard carbon, silicon and silicon monoxide are purchased from Ningbo Sunson Co., Ltd.

[0049] Example 1

[0050] The embodiment provides a preparation method of a lithium ion secondary battery, and specifically comprises the following steps.

[0051] Preparation of the positive plate

[0052] The positive active material lithium nickel cobalt manganese oxide LiNi 0.7 Co 0.2 Mn 0.1 O2, conductive carbon black Super-P and a binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 93:4:3, and then they are dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive slurry. The slurry is uniformly coated on both sides of an aluminum foil current collector, and then the positive plate is obtained after drying, calendering and vacuum drying, and welding of an aluminum lead wire by using an ultrasonic welding machine.

[0053] Preparation of the negative plate

[0054] The negative active material, conductive carbon black, a binder styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) are mixed in a mass ratio of 92:2:3:3, and then they are dispersed in deionized water to obtain a negative slurry. The slurry is coated on both sides of a copper foil current collector, and then the negative plate is obtained after drying, calendering and vacuum drying, and welding of a nickel lead wire by using an ultrasonic welding machine. The specific surface area of the negative active material is 20 m 2 / g.

[0055] Preparation of the battery cell

[0056] A polyethylene microporous film with a thickness of 20 μm is placed between the positive plate and the negative plate as a separator, and then the sandwich structure composed of the positive plate, the negative plate and the separator is wound, and the battery cell is obtained after packaging in an aluminum plastic film.

[0057] Preparation of the electrolyte

[0058] Vinyl carbonate (EC), diethyl carbonate (DEC) and methyl ethyl carbonate (EMC) are mixed in a mass ratio of EC:DEC:EMC=3:2:5, and then lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonylimide (LiFSI) are added to a molar concentration of 0.75 mol / L and 0.25 mol / L respectively to form a basic electrolyte. 5.0% of the composite lithium salt A1 is added based on the total mass of the electrolyte.

[0059] Liquid injection and formation of the battery cell

[0060] The electrolyte prepared in this example was injected into the battery cell in a glove box with moisture less than 10 ppm, and the amount of electrolyte was enough to fill the voids in the battery cell. Then the formation was carried out as follows: 0.01C constant current charging for 30 min, 0.02C constant current charging for 60 min, 0.05C constant current charging for 90 min, 0.1C constant current charging for 240 min, then after 1 hr of standing, shaping and sealing, further constant current charging to 4.40V at a current of 0.2C, and after 24 hrs of standing at room temperature, constant current discharging to 3.0V at a current of 0.2C.

[0061] On the basis of Example 1, the composite lithium salt in the electrolyte and its content, and the negative active material and its content were changed, and the other operations were unchanged, and the lithium ion secondary batteries were prepared according to the following Table 1 electrolyte and negative active material formulation table:

[0062] Table 1 Electrolyte and negative active material formulation table

[0063]

[0064]

[0065] On the basis of Example 6, the electrolyte formulation was changed, the negative active material and its content were unchanged, and the other operations were unchanged, and the lithium ion secondary batteries were prepared according to the following Table 2 electrolyte formulation table:

[0066] Table 2 Electrolyte formulation table

[0067]

[0068] II. Electrochemical performance test

[0069] The performances of the above lithium secondary batteries were tested, including:

[0070] (1) AC impedance test:

[0071] This test was carried out at room temperature 25℃, and the secondary battery was preferentially charged to 50% SOC in the charged state, and an electrochemical workstation with electrochemical impedance spectrum test function was used to test the AC impedance of the secondary battery, the initial frequency was 10000Hz, the cutoff frequency was 0.01Hz, the perturbation voltage was ±0.01V, the test points were not less than 60, the impedance data Z n (n is the test frequency) at each test frequency was obtained, and the ratio c% of the AC impedance from 1 to 0.01 Hz to the AC impedance from 10000 to 0.01 Hz was calculated according to the following formula:

[0072] c% = (Z 0.01 -Z1) / (Z 0.01 -Z 10000 ) x 100%;

[0073] The ratio mainly reflects the case that the diffusion impedance accounts for the battery impedance, and also contains the case that part of the charge transport impedance accounts for the battery impedance.

[0074] (2) Low temperature performance test:

[0075] ① Low temperature discharge capacity: at room temperature (25℃), charge the battery to 4.45V at 1C current, and then constant voltage charge until the current drops to 0.05C, then discharge to 2.8V at 1C current, record the room temperature discharge capacity C1. Repeat the above charging step to 4.45V, then reduce the ambient temperature to -20℃, and place the battery at ambient temperature for 5 hours, which achieves the purpose of cooling the battery. Then discharge to 2.5V at 0.5C current, record the discharge capacity C2, and the capacity retention rate R1:

[0076] R1 = C2 / C1*100%.

[0077] ② Low temperature DCIR impedance: fast charging performance test: at room temperature (25℃), adjust the battery to 50% SOC at 0.2C current, then reduce the ambient temperature to -20℃, and place the battery at ambient temperature for 5 hours, which achieves the purpose of cooling the battery. Then discharge at 1C current I1 for 30s, and record the voltage value V1 at the last 1s and the voltage value V2 at the 30th s, and calculate the low temperature DCIR impedance R2 according to the following formula:

[0078] R2 = (V1-V2) / I1.

[0079] (3) Rate charge performance test

[0080] At room temperature (25℃), charge the battery to 4.45V at 4C rate, then constant voltage charge until the current drops to 0.1C, record the total charge capacity C3 and the constant current charge capacity C4, and calculate the battery constant current rush-in ratio R3 according to the following formula:

[0081] R3 = C4 / C3*100%.

[0082] The specific test results are shown in Table 3 as follows:

[0083] Table 3 Electrochemical test results

[0084]

[0085] Comparing the examples 1-2 and the comparative examples 1-2 in the above table 3, on the basis of using the specific surface area negative electrode material in the secondary battery, it is necessary to simultaneously use the electrolyte containing 0.02-5.0wt% of the new composite lithium salt, so as to obtain the interaction of the specific negative electrode and the electrolyte, thereby reducing the diffusion impedance ratio and the charge transfer impedance ratio of the battery, and improving the fast charging performance and the low temperature performance of the battery under high voltage.

[0086] Comparing the example 6 and the comparative example 5 in the above table 3, the lithium salt additive used in the application can only play the effect of improving the fast charging performance and the low temperature performance of the secondary battery.

[0087] Comparing the examples 1-4 and the comparative examples 3-4 in the above table 3, on the basis of using the specific electrolyte additive in the secondary battery, simultaneously using the negative electrode active material with the specific surface area of 0.1-20.0m 2 / g can play the interaction of the specific negative electrode and the electrolyte, thereby reducing the diffusion impedance ratio and the charge transfer impedance ratio of the battery, and improving the fast charging performance and the low temperature performance of the battery under high voltage. If the specific surface area is too small, the active site on the negative electrode active material is too small, which is not conducive to the occurrence of the negative electrode-electrolyte interaction; if the specific surface area is too large, the new composite lithium salt cannot participate in the negative electrode-electrolyte interface interaction, thereby affecting the stability of the interface.

[0088] Comparing the examples 1-4 or the examples 10-12 in the above table 3, when the amount of the new composite lithium salt is further reduced to 0.1-2.0wt%, the fast charging performance and the low temperature performance of the secondary battery can be further improved.

[0089] Comparing the examples 1-4 or the examples 10, 13-14 in the above table 3, when the specific surface area of the negative electrode active material is further reduced to 0.5-10.0m 2 / g, the fast charging performance and the low temperature performance of the secondary battery can be further improved.

[0090] In the application, the new composite lithium salt and the negative electrode active material interact, so the amount of the new composite lithium salt and the specific surface area of the negative electrode active material affect each other, when the specific surface area of the negative electrode active material changes within the range of the application, the amount of the new composite lithium salt also needs to change within the range of the application, so as to match the best performance effect.

[0091] Comparing Example 10 and Comparative Examples 5-6 in Table 3 above, when a specific kind and specific surface area of negative electrode material is used, if the amount of the new composite lithium salt is too small, it is difficult to form a dense and permeable interface phase, so that other lithium salts and / or solvents in the electrolyte participate in the interface phase film forming reaction, increase the interface impedance, and are not conducive to fast charging performance and low temperature performance; if the amount of the new composite lithium salt is too large, it is easy to form an interface phase that is too dense during battery production, which is not conducive to the transmission of lithium ions, and is also not conducive to fast charging performance and low temperature performance.

[0092] Comparing Examples 5-9 and Comparative Examples 15-18 in Table 3 above, when hard carbon is used as one of the active negative electrode materials, it helps to further improve the ion conductivity of the negative electrode and produce a more stable and permeable lithium ion transmission channel with the new composite lithium salt, thereby further improving the fast charging performance and low temperature performance of the battery.

[0093] Comparing Example 6 and Examples 19-21 in Table 3 above, adding 0.1% to 2.0% by weight of other lithium salts of different types to the base electrolyte helps to further improve the fast charging performance and low temperature performance of the battery.

[0094] Comparing Example 6 and Examples 22-23 in Table 3 above, adding 0.1% to 2.0% by weight of different types of base additives to the base electrolyte helps to further improve the fast charging performance and low temperature performance of the battery.

Claims

1. A high-voltage fast-charging lithium-ion secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, the electrolyte comprising a main lithium salt, a nonaqueous solvent, and an additive, characterized in that: The additive comprises: The new composite lithium salt comprises at least a pyrosulfate boron trifluoride composite lithium salt with the structure shown in the following formula (I-1): The new composite lithium salt accounts for 0.02-5.0wt% of the total mass of the electrolyte; The negative electrode comprises: An active material capable of reversibly absorbing and releasing lithium ions, the specific surface area of the active material being 0.1 to 20.0 m 2 / g.

2. The high voltage fast-charge lithium ion secondary battery of claim 1, wherein: The specific surface area of the active substance is 0.5 to 10.0 m 2 / g.

3. The high voltage fast charge lithium ion secondary battery of claim 1, wherein: The active material of the negative electrode is selected from carbon material and / or silicon material; the carbon material is selected from at least one of natural graphite, artificial graphite and hard carbon, and the silicon material is selected from silicon and / or silicon monoxide.

4. The high voltage fast charge lithium ion secondary battery of claim 3, wherein: The active material of the negative electrode comprises at least hard carbon, and the mass content of the hard carbon is 0.1-100%.

5. The high voltage fast charge lithium ion secondary battery of claim 4, wherein: The active material of the negative electrode comprises hard carbon, and the mass content of the hard carbon is 5-20%.

6. The high voltage fast charge lithium ion secondary battery of claim 1, wherein: The new composite lithium salt accounts for 0.1-2.0wt% of the total mass of the electrolyte.

7. The high voltage fast charge lithium ion secondary battery as claimed in any one of claims 1 to 6, wherein: The AC impedance of the lithium ion secondary battery in the frequency range of 1-0.01Hz accounts for 40-80% of the AC impedance in the frequency range of 10000-0.01Hz.

8. The high voltage fast charge lithium ion secondary battery of claim 7, wherein: The AC impedance of the lithium ion secondary battery in the frequency range of 1-0.01Hz accounts for 60-70% of the AC impedance in the frequency range of 10000-0.01Hz.

9. The high voltage fast charge lithium ion secondary battery of claim 1, wherein: The new composite lithium salt further comprises at least one of the following compounds with the structures shown in the following formulae (I-2), (I-3), (I-4), (I-5) and (I-6): The new composite lithium salt comprises at least 80.0wt% of the pyrosulfate boron trifluoride composite lithium salt with the structure shown in the formula (I-1).

10. The high voltage fast charge lithium ion secondary battery of claim 9, wherein: The new composite lithium salt comprises 80.0-95.0wt% of the pyrosulfate boron trifluoride composite lithium salt with the structure shown in the formula (I-1), and the rest is at least one of the compounds (I-2), (I-3), (I-4), (I-5) and (I-6).

11. The high voltage fast charge lithium ion secondary battery of claim 1, wherein: The additive further comprises a base additive selected from at least one of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, tris(trimethylsilyl) phosphate, 1,3-propane sultone, 1,3-propene sultone, vinyl sulfate, lithium difluorophosphate, lithium bisfluorosulfonylimide, succinic anhydride, adipodinitrile, cyclohexylbenzene, lithium difluorophosphate bisoxalate or lithium difluoroboric acid oxalate, and the mass percentage content of any base additive in the electrolyte is 0.1-5.0wt%.

12. The high voltage fast charge lithium ion secondary battery of claim 1, wherein: The main lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bisoxalate borate, lithium difluoroboric acid oxalate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethylsulfonylimide, lithium tetrafluoro-oxalate phosphate, lithium tri-oxalate phosphate or lithium difluoro-bis-oxalate phosphate, and the molar concentration thereof is 0.1-4.0mol / L.

13. The high voltage fast charge lithium ion secondary battery of claim 1, wherein: The non-aqueous solvent is selected from at least one of C3-C6 carbonate compounds, C3-C8 carboxylic acid ester compounds, sulfone compounds, ether compounds and nitrile compounds; The C3-C6 carbonate compound is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, and methyl-2,2,2-trifluoroethyl carbonate; the C3-C8 carboxylic acid ester compound is selected from at least one of gamma-butyrolactone, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, propyl acetate, propyl propionate, and 2,2-difluoroethyl acetate; the sulfone compound is selected from at least one of tetramethylurea, dimethyl sulfoxide, and diethyl sulfoxide; the ether compound is selected from triethylene glycol dimethyl ether and / or tetraethylene glycol dimethyl ether; and the nitrile compound is selected from at least one of acetonitrile, butanedinitrile, hexanedinitrile, 1,3,6-hexanetricarbonitrile, p-fluorobenzonitrile, and 1,2-bis(cyanoethoxy)ethane.

14. The high voltage fast charge lithium ion secondary battery of claim 1, wherein: The active material of the positive electrode is selected from at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide, lithium nickel oxide, layered lithium manganate, spinel lithium manganate, or nickel manganese acid lithium material.

15. The high voltage fast charge lithium ion secondary battery of claim 1, wherein: The lithium ion secondary battery has a constant current charge input ratio ≥75% under constant current constant voltage charging at a 1-6C charge rate and a 4.2-5.0V cutoff operating voltage.

16. The high voltage fast charge lithium ion secondary battery of claim 15, wherein: The lithium ion secondary battery has a constant current charge input ratio ≥90% under constant current charging at a 2-4C charge rate and a 4.25-4.45V cutoff operating voltage.

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