Electrolyte and lithium-ion battery containing electrode interface modification additive

Abstract

The present invention discloses an electrolyte and a lithium-ion battery containing an electrode interface modification additive, and relates to the technical field of lithium-ion batteries. The electrolyte comprises: a conductive salt of lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(fluorosulfonyl)imide; an additive of lanthanum nitrate, the mass fraction of which in the electrolyte is 0.05%-0.30%; and a solvent of an ether-ester mixed organic solvent. The lithium-ion battery operates at a cut-off voltage of 4.5 V, and comprises a positive electrode material, a negative electrode material, and the electrolyte. The electrolyte system of the present invention has good compatibility, and the lithium-ion battery supported by it can achieve good cycle performance and good safety, and the 0.2C first cycle coulombic efficiency can reach 91.9%.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to an electrolyte containing an electrode interface modification additive and a lithium ion battery. Background Art

[0002] Lithium-ion batteries, a popular application in portable electronic devices, power batteries, and large-scale energy storage, offer broad development prospects due to their high energy density, long cycle life, low self-discharge, low carbon footprint, and lack of memory effect. To overcome the technical barriers to lithium-ion battery development, such as battery life and safety, developing the next generation of lithium-ion batteries with high safety, high energy density, and extended life is a major challenge urgently needed in the field of secondary battery technology.

[0003] Higher energy density means that the battery charging cut-off voltage needs to be increased, thereby obtaining a higher battery specific capacity. 0.6 Co 0.2 Mn 0.2 For example, O2 has a charge cut-off voltage of up to 4.5V. The widely used electrolyte is a carbonate-based electrolyte with lithium hexafluorophosphate as the conductive salt. It has strong water sensitivity, a narrow temperature range, and the conductive salt is easy to decompose (decomposition potential 4.2V vs Li / Li + , the decomposition products will catalyze the carbonate ring opening), which can easily lead to an increase in side reactions at the positive and negative electrode interfaces, lithium salt consumption, and reduced interface conductivity, accelerating the generation of negative electrode lithium dendrites and the dissolution and structural collapse of the positive electrode materials, further causing problems such as increased internal resistance of the battery, battery heating, and a sudden drop in capacity, and even major safety accidents such as the internal diaphragm of the battery being pierced by dendrites and the battery short circuiting and catching fire. On the other hand, an excessively high charge cut-off voltage can lead to dissolution and corrosion of the positive electrode aluminum current collector, especially in high-voltage-resistant lithium bis(trifluoromethylsulfonyl)imide (LiTFSI)-based electrolytes. Therefore, it is crucial to develop battery technology that has both high-voltage stability and uniform charge transfer during the electrochemical process at the positive and negative electrode interfaces.

[0004] As the "circulating blood" of lithium-ion batteries, electrolytes are usually composed of conductive salts, solvents and functional additives, and play a vital role in solid-liquid interface and bulk mass transfer. In order to optimize the electrochemical process of the electrode, starting from the electrolyte is one of the strategies with the most research value and research space. Among them, selecting appropriate electrolyte additives is the main way to regulate the electrolyte. Specific additives can achieve the following effects on the solvent-solute coordination structure, Li +Direct regulation of the solvation / desolvation process at the solid-liquid interface, the interphase of the interfacial solid electrolyte membrane, etc. Conventional organic additives usually have only a single effect, such as film-forming additives, which mostly form organic fragments; or they cannot achieve the coordinated regulation of the positive and negative electrode interface films, that is, they can only unilaterally obtain a window with a more stable oxidation or reduction potential than carbonates, and there is no absolute advantage at both poles. Such additives will still lead to low coulombic efficiency in the first cycle of the battery and uneven solid electrolyte membrane, which will cause interface treatment Li + Problems such as ion flow transmission and uneven distribution of power lines. In this state, the battery will have uneven deposition of lithium at the negative electrode and the generation of lithium dendrites during long-term cycling. The dendrites pierce the diaphragm, which will cause positive and negative short circuits inside the battery, instantaneous heat release and thermal runaway. At high charging cut-off voltages, the positive electrode active material is deeply delithiated, the positive electrode current collector dissolves and corrodes, and the electrode material produces diffusion-induced stress corrosion. Ultimately, the mechanical stress inside the active material and the effective contact area of ​​the binder caused by the corrosion of the current collector decrease, and the two together cause the electrode to pulverize, crack and fail. At the same time, the microcracks generated in the electrode increase its contact area with the electrolyte, increase the adverse reactions at the solid-liquid interface and the consumption and pollution of the electrolyte, thereby generating huge interfacial charge transfer resistance. In order to achieve Li in lithium-ion batteries at high cut-off voltages + In order to ensure the uniform transmission of ion flow and the uniform distribution of stress in electrode materials, new electrode interface modification additives that can be applied to organic systems are urgently needed to achieve stable and safe operation of lithium-ion batteries.

[0005] The choice of electrolyte additives is not limited to molecular compounds, ionic compounds can also participate in interface regulation. The KongLong research group studied the battery performance of LiNO3 as an electrolyte additive, and the ternary nickel-cobalt-manganese NCM811 battery showed a high-voltage performance of 4.4V. The Ali Coskun research group used LiNO3 as an additive to prepare lithium-sulfur batteries, but the capacity retention rate after 50 cycles at 0.1C was only 70.7%. The Suo Liumin research group used LiAlO2, Li2CO3, Li2SiO3, and Li3PO4 as electrolyte additives to prevent corrosion of the Al current collector, but they were only used to explore the life of aqueous batteries, and these types of ionic compounds are not soluble in organic solvents.

[0006] Based on the above content, it is necessary to conduct in-depth research on the application of ionic compounds as electrolyte additives for lithium-ion batteries and consider their use as electrolyte additives for electrode interface modification in high-voltage systems. Summary of the Invention

[0007] Aiming at the deficiencies of the prior art, the present invention provides an electrolyte and a lithium-ion battery containing an electrode interface modification additive. Lanthanum nitrate (La(NO3)3) is used as the electrode interface modification additive to ensure stable operation of the lithium-ion battery at a cutoff voltage of 4.5 V.

[0008] To this end, the first aspect of the present invention provides an electrolyte containing an electrode interface modification additive, comprising:

[0009] The conductive salt is lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(fluorosulfonyl)imide;

[0010] The additive is lanthanum nitrate, and the mass fraction of the lanthanum nitrate in the electrolyte is 0.05%-0.30%;

[0011] The solvent is an ether-ester mixed organic solvent.

[0012] Furthermore, the mass fraction of the lanthanum nitrate in the electrolyte is 0.08%-0.20%.

[0013] Furthermore, the mass fraction of the lanthanum nitrate in the electrolyte is 0.10%-0.15%.

[0014] Furthermore, the ether-ester mixed organic solvent is prepared by mixing ethylene glycol dimethyl ether, fluoroethylene carbonate and ethyl methyl carbonate in a volume ratio of (0.9-1.1): (0.9-1.1): (2-4).

[0015] Furthermore, the ether-ester mixed organic solvent is prepared by mixing ethylene glycol dimethyl ether, fluoroethylene carbonate and ethyl methyl carbonate in a volume ratio of 1:1:3.

[0016] Furthermore, the concentration of the lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(fluorosulfonyl)imide in the electrolyte is 0.1 mol / L-2 mol / L.

[0017] Furthermore, the concentration of the lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(fluorosulfonyl)imide in the electrolyte is 0.9 mol / L-1.1 mol / L.

[0018] Furthermore, the electrolyte is used for a lithium-ion battery with a cut-off voltage of 4.5V.

[0019] Furthermore, the preparation method of the electrolyte includes:

[0020] The lanthanum nitrate hexahydrate is fully dehydrated;

[0021] The dried anhydrous lanthanum nitrate was transferred into an inert atmosphere glove box for thorough grinding;

[0022] In an inert atmosphere glove box, ethylene glycol dimethyl ether, fluoroethylene carbonate and ethyl methyl carbonate are mixed to prepare the ether-ester mixed organic solvent;

[0023] The lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(fluorosulfonyl)imide is added to the ether-ester mixed solvent to prepare a mixed organic electrolyte, and the mixture is stirred at room temperature. During the stirring process, the ground anhydrous lanthanum nitrate is slowly added to the mixed organic electrolyte, and the mixture is fully stirred and allowed to stand to obtain the electrolyte containing the electrode interface modification additive.

[0024] A second aspect of the present invention provides a lithium-ion battery, wherein the lithium-ion battery operates at a cut-off voltage of 4.5V, and the lithium-ion battery comprises a positive electrode material, a negative electrode material, and the above-mentioned electrolyte;

[0025] The positive electrode material is selected from any one of nickel-cobalt-manganese ternary positive electrode or lithium nickel manganese oxide; the negative electrode material is selected from any one of graphite or lithium metal.

[0026] Compared with the prior art, the present invention has at least the following beneficial effects:

[0027] The present invention provides an electrolyte containing an electrode interface modification additive, wherein the additive La(NO3)3 has a regulating effect on both the positive and negative electrode interfaces of a lithium-ion battery, and uses ether to improve the solubility of the additive, and uses ester to improve the interface film-forming ability and provide ideal low-temperature performance. Through the synergistic effect of the ionic compound additive La(NO3)3 and the ether-ester mixed electrolyte, a stable interface structure is constructed by the additive, and uniform deposition of negative electrode lithium is simultaneously induced. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments described in the embodiments of the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0029] Figure 1 The substances that may exist after the dissociation of La(NO3)3 in an ether-ester mixed solvent at 0°C-50°C provided by the embodiment of the present invention (corresponding to La / La 3+ ) relative to Li / Li + The equilibrium potential of

[0030] Figure 2 Cyclic voltammetry curves of the lithium ion battery electrolyte relative to the active electrode Al in Example 1, Comparative Example 1 and Comparative Example 5 of the present invention;

[0031] Figure 3The constant potential time-current curves of the positive electrode current collector of the lithium ion battery in Example 1, Comparative Example 1 and Comparative Example 5 of the present invention are shown;

[0032] Figure 4 The impedance Nyquist plots of the positive electrode current collector of the lithium ion battery in Example 1 of the present invention and Comparative Example 1 are shown;

[0033] Figure 5 Schematic diagram of the morphology of the positive electrode current collector of the lithium ion battery in Example 1, Example 4 and Comparative Example 1 of the present invention;

[0034] Figure 6 Graph showing the change in overpotential of the lithium symmetric battery over time in Example 4, Comparative Example 3 and Comparative Example 4 of the present invention;

[0035] Figure 7 Schematic diagram of the first cycle of the NCM622||Li battery at 0.2C in Example 1 of the present invention (a), and schematic diagram of the macroscopic morphology of the lithium negative electrode of Comparative Example 1 and Example 1 (b). DETAILED DESCRIPTION

[0036] In order to better understand the above technical solution, the technical solution of the embodiment of the present application is described in detail below through the accompanying drawings and specific embodiments. It should be understood that the embodiment of the present application and the specific features in the embodiment are detailed descriptions of the technical solution of the embodiment of the present application, rather than limitations on the technical solution of the present application. In the absence of conflict, the embodiment of the present application and the technical features in the embodiment can be combined with each other.

[0037] According to a first aspect of an embodiment of the present invention, there is provided an electrolyte solution containing an electrode interface modification additive, comprising:

[0038] The conductive salt is lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(fluorosulfonyl)imide;

[0039] The additive is lanthanum nitrate, and the mass fraction of lanthanum nitrate in the electrolyte is 0.05%-0.30%;

[0040] The solvent is an ether-ester mixed organic solvent.

[0041] The electrolyte containing the electrode interface modification additive provided by the embodiment of the present invention, the additive La(NO3)3 has a regulating effect on the positive and negative electrode interfaces of the lithium ion battery: assisting the positive electrode current collector to produce Al(NO3)3 precipitation to effectively prevent the conductive salt LiTFSI from corroding and dissolving the Al matrix, effectively blocking the electrochemical and chemical corrosion paths, and reducing the coulomb efficiency loss caused by current collector corrosion; assisting the formation of the negative electrode interface film, cleaning the copper current collector surface, and avoiding the active Li caused by the formation of the solid electrolyte membrane in the early activation process. + loss, reducing the overpotential of lithium deposition at the negative electrode.

[0042] The electrolyte of the embodiment of the present invention uses ether to improve the solubility of the additive, and uses ester to improve the interfacial film-forming ability and provide ideal low-temperature performance. Through the synergistic effect of the ionic compound additive La(NO3)3 and the ether-ester mixed electrolyte, a stable interface structure is constructed by the additive, and the uniform deposition of the negative electrode lithium is simultaneously induced. The positive and negative electrode interfaces maintain good ionic conductivity, and the electrolyte liquid phase maintains a stable solvation structure. Therefore, the electrolyte of the embodiment of the present invention can be used for lithium-ion batteries with a cut-off voltage of 4.5V.

[0043] Among them, the mass fraction of the additive lanthanum nitrate in the electrolyte is preferably 0.08%-0.20%, the mass fraction of the additive lanthanum nitrate in the electrolyte is more preferably 0.10%-0.15%, and the mass fraction of the additive lanthanum nitrate in the electrolyte is most preferably 0.10%.

[0044] In one feasible embodiment, the ether-ester mixed organic solvent is prepared by mixing ethylene glycol dimethyl ether, fluoroethylene carbonate, and ethyl methyl carbonate in a volume ratio of (0.9-1.1):(0.9-1.1):(2-4). Preferably, the ether-ester mixed organic solvent is prepared by mixing ethylene glycol dimethyl ether, fluoroethylene carbonate, and ethyl methyl carbonate in a volume ratio of 1:1:3.

[0045] Specifically, solvents for lithium-ion battery electrolytes must combine safety (high flash point), conductivity (low melting point, high dielectric constant), environmental friendliness, cost-effectiveness, and compatibility. To achieve stable and high-performance lithium-ion batteries, a mixture of at least two organic solvents is necessary to leverage their strengths and compensate for their weaknesses, achieving excellent battery performance. Ethylene glycol dimethyl ether has a melting point of -58°C, a flash point of -2°C, a surface tension of 21.3 dyne / cm, and a dielectric constant of 7.3. Fluoroethylene carbonate has a melting point of 18°C, a flash point of 120°C, and a dielectric constant of 102. It is widely used as a film-forming additive in lithium-ion batteries to form a low-impedance, densely structured solid electrolyte interface film and prevent further decomposition of the electrolyte. It can also be used as a metal surface treatment agent to improve metal corrosion resistance. Ethyl methyl carbonate has a melting point of -14°C, a surface tension of 25.9 dyne / cm, and a dielectric constant of 2.9. It possesses both methyl and ethyl structures, combining the properties of both dimethyl and diethyl carbonate.

[0046] Considering these requirements and characteristics, a mixed organic solvent was created by combining these three elements: Ethylene glycol dimethyl ether's low melting point and low surface tension ensure low-temperature fluidity; fluoroethylene carbonate's high flash point provides high-temperature stability, while its high dielectric constant ensures lithium salt dissociation (solubility); the fluorine atoms in its structure facilitate wetting within the battery cell, while also providing excellent solid electrolyte membrane-forming properties; and ethyl methyl carbonate combines the advantages of current commercial linear carbonate solvents (dimethyl carbonate and diethyl carbonate) in electrolytes. The resulting ether-ester mixed solvent offers excellent solute-salt dissociation, a wide liquidus temperature range, and interfacial film-forming properties, ensuring high electrolyte stability and providing guidance for the development of other mixed solvents. Compared to other solvent systems, these three are primary products in the synthetic process, making their acquisition relatively simple and inexpensive, while also ensuring excellent solvent properties.

[0047] In one feasible embodiment, the concentration of lithium bis(trifluoromethylsulfonyl imide) and / or lithium bis(fluorosulfonyl imide) in the electrolyte is 0.1 mol / L to 2 mol / L. Preferably, the concentration of lithium bis(trifluoromethylsulfonyl imide) and / or lithium bis(fluorosulfonyl imide) in the electrolyte is 0.9 mol / L to 1.1 mol / L. More preferably, the concentration of lithium bis(trifluoromethylsulfonyl imide) and / or lithium bis(fluorosulfonyl imide) in the electrolyte is 1 mol / L.

[0048] Specifically, lithium bis(trifluoromethanesulfonyl)imide has good electrochemical stability (high voltage stability, >4.5V vsLi / Li + ) and high electrical conductivity (up to 0.01S / cm), even at low temperatures (such as -30°C) the electrical conductivity can still reach 10 -3 S / cm, its flash point (>100℃) is higher than the currently widely used LiPF6 (25℃), and its operating temperature range is wide. It is insensitive to trace water in organic systems, while the currently widely used LiPF6 is highly water-sensitive. When it comes into contact with water, it releases harmful substances such as HF acid and PF5 gas, which is not conducive to the stability of the internal components of the battery. Similarly, lithium bis(fluorosulfonyl)imide has strong electrochemical stability, a wide temperature range, high solubility, good hydrolysis resistance, and high conductivity (the strong electron-withdrawing properties of fluoride ions weaken the coordination effect of anions and cations, thereby making Li + Lithium bis(trifluoromethylsulfonyl imide) and lithium bis(fluorosulfonyl imide) can effectively reduce the interfacial resistance at low temperatures and reduce the capacity loss during battery aging. They have a good effect on stabilizing the electrode interface, improving battery capacity and electrochemical performance, and extending battery life.

[0049] Considering that the cost of lithium-ion battery liquid electrolyte accounts for 15%-20% of the total cost, of which the solute (lithium salt) accounts for 40%-50% of the electrolyte cost, the solvent accounts for approximately 30%, and the additives account for 10%-30%. The amount of solute and solvent added is relatively large (especially for large-scale energy storage devices, where the amount of electrolyte used is measured in kilograms). To control the production cost of lithium-ion batteries, it is necessary to control the amount of solute. At the same time, to ensure the ionic conductivity of the electrolyte, the addition of lithium salt needs to provide a sufficient number of carriers and a high ion mobility. The balance between these two factors produces the electrolyte's ionic conductivity. The number of charge carriers in the electrolyte is determined by the dissociation effect of the solute lithium salt, and is dominated by the ion mobility and the intrinsic viscosity of the electrolyte. As research on lithium-ion battery electrolytes continues to deepen, it is known that high lithium salt concentration (>3 mol / L) corresponds to high cost, high viscosity, low ion mobility, low wettability of the diaphragm material, and high risk of solvent depletion. The preferred 1 mol / L lithium salt can provide the best bulk conductivity and cost-effectiveness.

[0050] In one feasible embodiment, the preparation method of the electrolyte containing the electrode interface modification additive includes:

[0051] The lanthanum nitrate hexahydrate is fully dehydrated;

[0052] The dried anhydrous lanthanum nitrate was transferred into an inert atmosphere glove box for thorough grinding;

[0053] In an inert atmosphere glove box, ethylene glycol dimethyl ether, fluoroethylene carbonate and ethyl methyl carbonate were mixed to prepare an ether-ester mixed organic solvent;

[0054] Lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(fluorosulfonyl)imide are added to an ether-ester mixed solvent to prepare a mixed organic electrolyte, which is stirred at room temperature. During the stirring process, ground anhydrous lanthanum nitrate is slowly added to the mixed organic electrolyte, which is fully stirred and then allowed to stand to obtain an electrolyte containing an electrode interface modification additive.

[0055] A second aspect of an embodiment of the present invention provides a lithium-ion battery operating at a cutoff voltage of 4.5V, comprising a positive electrode material, a negative electrode material, and the aforementioned electrolyte. The positive electrode material is selected from a nickel-cobalt-manganese ternary positive electrode or lithium nickel manganese oxide; and the negative electrode material is selected from graphite or lithium metal.

[0056] The electrolyte system provided by the embodiment of the present invention has good compatibility, and the lithium-ion battery supported by it can achieve good cycle performance and good safety, and the battery's 0.2C first cycle coulombic efficiency can reach 91.9%.

[0057] Unless otherwise specified, in the embodiment of the present invention, the preparation method of the ternary nickel-cobalt-manganese positive electrode sheet is as follows: the positive electrode active material LiNi 0.6 Co0.2 Mn 0.2 O2, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 7:1:1, placed in an agate mortar and ground for more than 40 minutes, then added to N-methyl-2-pyrrolidone (NMP) and magnetically stirred for 4 hours to make a slurry. The slurry is evenly coated on the positive electrode aluminum current collector, dried in a vacuum drying oven at 80°C for 12 hours, and then sliced ​​to obtain the positive electrode sheet.

[0058] The positive electrode shell, negative electrode shell, stainless steel gasket, and spring were purchased from Dongguan Kelude Experimental Equipment Technology Co., Ltd., model CR2032. The positive electrode current collector aluminum foil, negative electrode current collector copper foil, negative electrode lithium metal electrode sheet, and separator (model Celgard 2500) were also purchased from Dongguan Kelude Experimental Equipment Technology Co., Ltd.

[0059] Example 1 An electrolyte containing an electrode interface modification additive and a preparation method thereof

[0060] (1) Electrolyte

[0061] The conductive salt is lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), and the conductive salt concentration is 1 mol / L;

[0062] The additive is lanthanum nitrate, with a mass fraction of 0.10%;

[0063] The solvent is an ether-ester mixed organic solvent, specifically ethylene glycol dimethyl ether (DME), fluoroethylene carbonate (FEC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:3.

[0064] (2) Preparation method

[0065] The steps include:

[0066] (1) Dehydrate 10 g of lanthanum nitrate hexahydrate (La(NO3)3·6H2O) and dry it in a vacuum oven at 40°C for 8 h.

[0067] (2) The dried anhydrous lanthanum nitrate (La(NO3)3) was transferred into an inert atmosphere glove box and ground using an agate mortar for more than 30 minutes;

[0068] (3) In an inert atmosphere glove box, DME, FEC, and EMC were prepared into an ether-ester mixed organic solvent at a volume ratio of 1:1:3;

[0069] (4) Add 2.871 g of conductive salt LiTFSI to a certain amount of ether-ester mixed organic solvent, adjust the volume to 10 mL and weigh it. The conductive salt concentration is 1 mol / L and stir at room temperature for 6 h. During the stirring process, slowly add 0.1% by mass of La(NO3)3. After sufficient stirring, let it stand for the next step.

[0070] (5) The mixed solution after standing was used as the electrolyte to assemble NCM622||Li half-cell, Li||Al battery, Li||Cu battery, and Li||Li symmetric battery.

[0071] (3) Test methods

[0072] Battery performance test:

[0073] The assembled NCM622||Li battery was left to rest for 12 hours before cycling performance testing using a Blue Power battery testing system. First, constant voltage charging at 3.9V was performed to eliminate stray current until the current rate was less than 0.05C (1C = 200mAh / g). Then, 50 cycles of charge and discharge were performed at a rate of 0.2C. The first-cycle coulombic efficiency was calculated as the first-cycle discharge specific capacity divided by the first-cycle charge specific capacity.

[0074] The assembled Li||Li symmetrical battery was left to stand for 12 hours and then tested using a blue battery test system for time-voltage curves at a constant current (0.5 mA / cm 2 ) Charge and discharge 200 times, the charge and discharge step time is set to 2 hours, and then constant current (1mA / cm 2 ) Charge and discharge 300 times, and the charge and discharge step time is set to 1 hour.

[0075] The assembled Li||Cu battery was left to stand for 12 hours and then tested using a blue battery test system for time-voltage curves at a constant current (0.5 mA / cm 2 ) first discharge, then charge for 1 cycle and then discharge once, the upper limit of charging voltage is 1V, the discharge step time is set to 10 hours, and then constant current (0.5mA / cm 2 ) Discharge first and then charge for 10 cycles. The charging and discharging time is set to 2 hours.

[0076] Electrochemical behavior test:

[0077] The assembled Li||Al battery was left to stand for 12 hours, and the AC impedance, cyclic voltammetry curve, and time-current curve of the working electrode Al were measured using a Chenhua electrochemical workstation CHI760E. The cyclic voltammetry scan rate was 10mV / s; the AC impedance frequency range was 0.01Hz-10 5 Hz, amplitude 0.5 mV; time-current curves were obtained using voltages of 3.8 V, 4.0 V, 4.2 V, and 4.5 V, with polarization times of 1 hour, respectively.

[0078] Example 2

[0079] The difference from Example 1 is that the mass fraction of La(NO3)3 is 0.05%.

[0080] Example 3

[0081] The difference from Example 1 is that the mass fraction of La(NO3)3 is 0.15%.

[0082] Example 4

[0083] The difference from Example 1 is that the mass fraction of La(NO3)3 is 0.20%.

[0084] Example 5

[0085] The difference from Example 1 is that the mass fraction of La(NO3)3 is 0.30%.

[0086] Example 6

[0087] The difference from Example 1 is that the solvents used are DME, FEC and EMC in a volume ratio of 1:1:2.

[0088] Example 7

[0089] The difference from Example 1 is that the solvents used are DME, FEC and EMC in a volume ratio of 1:1:4.

[0090] Comparative Example 1

[0091] The difference from Example 1 is that La(NO3)3 is not added.

[0092] Comparative Example 2

[0093] The difference from Example 1 is that the mass fraction of La(NO3)3 is 0.35%.

[0094] Comparative Example 3

[0095] The difference from Example 1 is that the mass fraction of La(NO3)3 is 0.40%.

[0096] Comparative Example 4

[0097] The difference from Example 1 is that the solvent is DME.

[0098] Comparative Example 5

[0099] The difference from Example 1 is that the solvents are DME and FEC, and the volume ratio of the two is 1:1.

[0100] Comparative Example 6

[0101] The difference from Example 1 is that the solvents used are DME, FEC and EMC in a volume ratio of 1:1:6.

[0102] Comparative Example 7

[0103] The difference from Example 1 is that the solvents used are DME, FEC and EMC in a volume ratio of 1:1:8.

[0104] Table 1 Performance of electrolytes and lithium-ion batteries based on Examples 1-7 and Comparative Examples 1-7

[0105]

[0106] Results and Discussion

[0107] according to Figure 1 It was found that La(NO3)3 is soluble in organic solvents and can dissociate into La 3+ and NO3 - , both of which are beneficial to the interface modification of the electrode. The present invention uses La(NO3)3 as an electrolyte additive to help build a stable and uniform positive and negative electrode interface. La / La 3+ The standard electrode potential is 0.66 V vs Li / Li + , there may be La 3+ The reduction potential of LaF3 and La(NO3)3 is higher than that of Li / Li + Therefore, La 3+ Can be preferentially deposited in lithium-ion batteries, + Pre-clean the negative electrode surface to replace the Li consumed during the activation process + The material on the surface of the negative electrode copper current collector is reduced to prevent the loss of active lithium and achieve uniform lithium deposition. The presence of LaF3 depends on the anion exchange in the solvation structure of LiTFSI and La(NO3)3 to form La(TFSI)3 defluorination. According to thermodynamic calculations, the spontaneous conversion of LaF3 and LiNO3 to LiF and La(NO3)3 means that LaF3 is basically not present in the chemical environment, thus avoiding the superposition of electrode side reactions.

[0108] Nitrate anion (NO3 - ) has an electron donor number (DN) of 21.1 kcal / mol, which is much higher than TFSI. - The DN number is 5.4kcal / mol, so NO3 - It can capture Al that is corroded by dissolution due to high voltage operation of LiTFSI batteries. 3+, and realize anion and cation coordination. According to the theory of hard and soft acid-base, aluminum nitrate Al(NO3)3 is more stable than Al(TFSI)3 and then forms a precipitate on the Al surface, interrupting the contact between LiTFSI in the electrolyte and the Al matrix, thereby achieving passivation protection of the positive electrode interface. Figure 2 The cyclic voltammetry curve shows that the oxidation potential of Al in the Li||Al of Example 1 is 5.85V vs Li / Li + ) is much larger than that of Comparative Example 1 (3.6V vs Li / Li + ) and Comparative Example 5 (5V vs Li / Li + ). At the same potential, the current density of Example 1 is smaller than that of Comparative Example 1 and Comparative Example 5, that is, the rate of anodic dissolution or electrolyte oxidation reaction is slower. Although the anodic dissolution current density is lower in Comparative Example 5 than in Comparative Example 1, serious dissolution corrosion still exists. In addition, the current density increases (the increase is also large) when the scanning potential changes from positive scanning to negative scanning in Comparative Example 1 and Comparative Example 5. This indicates that the high potential stimulates the rapid dissolution of Al and the decomposition reaction of the electrolyte. Therefore, even when the Al dissolution current continues to increase during negative scanning, it cannot be offset by the reverse current of the external circuit.

[0109] From the time-current curve Figure 3 It can be seen that the La(NO3)3 additive in Example 1 effectively reduces the oxidation current of Al under a high voltage of 4.5V. The current density corresponding to the step potential scan of Comparative Example 1 increases with increasing potential, which means that high voltage stimulates the dissolution of Al anode. In Example 1 and Comparative Example 5, cathode reduction currents (current density less than 0) appear at different potentials, which means that the voltage does not induce the "electron loss" reaction of the Al electrode itself (no Al→Al 3+ This result and Figure 2 The curves of Al electrode are consistent at this potential (3.8V, 4.0V, 4.2V, 4.5V vs Li / Li + ) is in a stable state. 4.5V vsLi / Li + The absolute value of the current density of Comparative Example 5 is smaller than that of Example 1, which also means that at a higher voltage (5 V), Comparative Example 5 cannot inhibit the anodic dissolution of Al (the current will show an anodic current and gradually increase).

[0110] By AC impedance Figure 4 It can be seen that Example 1 has a larger interface reaction resistance than Comparative Example 1. The impedance modulus of the real part (Z') and imaginary part (Z'') of the AC impedance of Example 1 and Comparative Example 1 is smaller than that of Example 1. The surface of Al in Example 1 has good passivation ability (low ionic conductivity, Al is not easily converted to Al 3+ ) can effectively inhibit the dissolution and corrosion of the matrix.

[0111] Depend on Figure 5 It can be seen that the surface of the positive electrode current collector of the lithium ion battery in Example 1 did not change after various high-voltage polarization treatments. The surface of Comparative Example 1 showed micron-scale pitting pits, and the corrosion points were concentrated and continuous (as shown by the white arrows in the figure). This feature indicates that the positive electrode Al current collector of Comparative Example 1 will continue to dissolve and perforate in the LiTFSI electrolyte, which is manifested as irreversible capacity loss in NCM622||Li. More new substances appeared on the surface of Example 4. Figure 6 From the symmetrical battery time-voltage curve, it can be seen that La(NO3)3 is in excess at this time, which is not conducive to the optimization of interface performance. However, Example 4 still has advantages over Comparative Example 4. Comparative Example 4 shows obvious polarization phenomenon at 1 mA. This polarization is caused by the side reaction of the electrode-electrolyte interface during the repeated deposition-stripping of lithium. Figure 6 , Comparative Example 3 at 0.5 mA / cm 2 The voltage is relatively stable during charge and discharge, 1mA / cm 2 During the charge and discharge, the electrodes were severely polarized. The ohmic impedance and charge transfer resistance inside the symmetrical battery increased sharply, causing the battery voltage to increase to 0.40V. The battery electrolyte was exhausted and the battery was about to break due to excessive voltage. 2 When charging and discharging at this level, severe polarization occurs (voltage fluctuation is large (exceeding ±0.5V), that is, the electrode reaction overpotential is extremely large), and the battery circuit is terminated. Similarly, in Example 4, at 0.5mA / cm 2 During the charge and discharge process, a large overpotential (more than ±0.5V) was also observed. However, as the charge and discharge process progressed, the voltage gradually decreased and stabilized. 2 The voltage remains relatively stable during charge and discharge. Nevertheless, the overpotential of Example 4 still leads to a short circuit on the surface of the lithium metal electrode, which is not conducive to long-term cycling of the battery.

[0112] according to Figure 7 a. The NCM622||Li battery of Example 1 exhibited a first cycle coulombic efficiency of 91.90% at 0.2C, and a first cycle discharge capacity of 214.5 mAh / g. The macroscopic morphology of the negative electrode lithium surface in the Li||Al battery is shown in FIG. Figure 7 As shown in Figure b, the surface of the lithium negative electrode of Example 1 has a metallic luster, while black matter appears on the lithium negative electrode of Comparative Example 1, indicating that the dissolution of the positive electrode current collector Al in the electrolyte without additives will lead to uneven deposition of lithium and side reactions of the electrolyte.

[0113] The performance of the battery and the positive electrode Al current collector in the electrolyte of Examples 1-7 and Comparative Examples 1-7, such as the oxidation onset potential, is shown in Table 1. The first cycle discharge capacity of Examples 1-7 is between 208 mAh / g and 216 mAh / g, and the first cycle coulombic efficiency is above 80.00% (better than Comparative Examples 2-7). The Al oxidation onset potential in Li||Al is higher than that in Example 2 (4.5 V vs Li / Li + ) are all greater than 5V. Example 1-7 The first-cycle deposition overpotential of the metal in Li||Cu increases with the increase of the amount of La(NO3)3 added. This potential value corresponds to Li + (Example 2) or La 3+ Deposition potential. + →Li 0 The electrons are obtained in La metal (by Figure 1 It can be seen that La 3+ →La 0 Prioritizes Li + The surface deposition of Li2O3 corresponds to a large overpotential. + The smaller the deposition onset overpotential, the more favorable it is for the negative electrode Li + Gain electrons and become Li 0 In Example 2, only 0.05% La(NO3)3 was added, and the battery's first cycle coulombic efficiency and Al oxidation starting potential (4.5V vs Li / Li + ) indicates that the dissolution of Al reduces the interfacial stability and the overall performance of the battery. Even if the metal deposition starting potential is the lowest, it cannot guarantee the normal long-term operation of the battery. Therefore, a balance must be struck between the metal deposition starting overpotential and the Al oxidation starting potential to ensure both the stability of the positive electrode Al and the negative electrode Li + The deposition has a small energy barrier, so the addition of La(NO3)3 in an appropriate amount provides the preferential deposition of La even with a higher deposition overpotential, which can provide a basis for the deposition of Li + Pre-clean the negative electrode surface to replace the Li consumed during the activation process + The material on the surface of the negative electrode copper current collector is reduced to prevent the loss of active lithium and achieve uniform lithium deposition, which is specifically manifested in high Coulombic efficiency and neat Li negative electrode morphology.

[0114] The first-cycle discharge capacity of Comparative Examples 1-7 is between 153mAh / g and 222mAh / g, and the low first-cycle discharge capacity of Comparative Examples 2-3 is caused by the excess of La(NO3)3. The first-cycle coulomb efficiency of Comparative Examples 1-7 is below 80.00% (except Comparative Example 1), and the first-cycle deposition overpotential of the metal in Li||Cu is too large and does not have an advantage. The starting potential of Al oxidation in Li||Al presents different values. The Al in Comparative Example 1 undergoes anodic dissolution at 3.6V, the Al in Comparative Examples 4-5 undergoes anodic dissolution above 4.5V, and the Al in Comparative Examples 2-3 and Comparative Examples 6-7 can remain stable below 5V. The low first-cycle coulomb efficiency of Comparative Examples 2-7 is caused by the anodic dissolution of the positive electrode Al or the excessively high deposition energy barrier of the negative electrode Li during charging. Al→Al 3+ The contributed charge capacity is irreversible, so the capacity loss is manifested as low discharge capacity. The battery performance of Comparative Example 1 is superior, but its Al oxidation starting potential is 3.6V vsLi / Li + , which means that Al dissolution does not reach the NCM622 charging platform ( Figure 7 Medium charging platform 4.0V vs Li / Li + ), which is extremely detrimental to the stable operation of the battery. According to the barrel effect, Example 1 clearly has obvious advantages and has a good effect on improving the stability of the electrode interface and optimizing battery performance.

[0115] In summary, the present invention proposes an electrolyte and lithium-ion battery containing an electrode interface modification additive. Among them, La(NO3)3 after vacuum drying is added to an ether-ester mixed organic solvent of DME, FEC, and EMC (volume ratio 1:1:3). The addition of 0.1% mass fraction of La(NO3)3 can increase the 0.2C first coulomb efficiency of the NCM622||Li battery to 91.90%, the first cycle discharge capacity is 214.5mAh / g, Al(NO3)3 precipitation can be formed on the Al surface of the positive electrode current collector, and the Al oxidation potential is increased to above 5V. La appears at the negative electrode in Li||Li and Li||Al batteries. 3+ The preferential deposition of active lithium avoids loss of active lithium (significantly improving initial coulombic efficiency), demonstrates uniform lithium deposition, and inhibits side reactions. Lithium-ion batteries prepared using the electrolyte containing the electrode interface modification additive of the present invention exhibit compatibility between the positive and negative electrodes, enabling interface control at both the positive and negative electrodes and ensuring stable battery operation.

[0116] It is easy for those skilled in the art to understand that, under the premise of no conflict, the above-mentioned advantageous methods can be freely combined and superimposed. The above is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application. The above is only a preferred embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and variations can be made without departing from the technical principles of the present application. These improvements and variations should also be regarded as the scope of protection of the present application.

Claims

1. An electrolyte containing an electrode interface modification additive, characterized in that: include: The conductive salt is lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(fluorosulfonyl)imide; The additive is lanthanum nitrate, and the mass fraction of the lanthanum nitrate in the electrolyte is 0.05%-0.30%; The solvent is an ether-ester mixed organic solvent; wherein the ether-ester mixed organic solvent is prepared by mixing ethylene glycol dimethyl ether, fluoroethylene carbonate and ethyl methyl carbonate in a ratio of (0.9-1.1): (0.9-1.1): (2-4) by volume.

2. The electrolyte containing the electrode interface modification additive according to claim 1, characterized in that: The mass fraction of the lanthanum nitrate in the electrolyte is 0.08%-0.20%.

3. The electrolyte containing the electrode interface modification additive according to claim 2, characterized in that: The mass fraction of the lanthanum nitrate in the electrolyte is 0.10%-0.15%.

4. The electrolyte containing the electrode interface modification additive according to claim 1, characterized in that: The ether-ester mixed organic solvent is prepared by mixing ethylene glycol dimethyl ether, fluoroethylene carbonate and ethyl methyl carbonate in a volume ratio of 1:1:

3.

5. The electrolyte containing the electrode interface modification additive according to claim 1, characterized in that: The concentration of the lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(fluorosulfonyl)imide in the electrolyte is 0.1 mol / L-2 mol / L.

6. The electrolyte containing the electrode interface modification additive according to claim 5, characterized in that: The concentration of the lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(fluorosulfonyl)imide in the electrolyte is 0.9 mol / L-1.1 mol / L.

7. The electrolyte containing the electrode interface modification additive according to claim 1, characterized in that: The electrolyte is used for a lithium-ion battery with a cut-off voltage of 4.5V.

8. The electrolyte containing the electrode interface modification additive according to any one of claims 1 to 7, characterized in that: The preparation method of the electrolyte comprises: The lanthanum nitrate hexahydrate is fully dehydrated; The dried anhydrous lanthanum nitrate was transferred into an inert atmosphere glove box for thorough grinding; In an inert atmosphere glove box, ethylene glycol dimethyl ether, fluoroethylene carbonate and ethyl methyl carbonate are mixed to prepare the ether-ester mixed organic solvent; The lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(fluorosulfonyl)imide is added to the ether-ester mixed solvent to prepare a mixed organic electrolyte, and the mixture is stirred at room temperature. During the stirring process, the ground anhydrous lanthanum nitrate is slowly added to the mixed organic electrolyte, and the mixture is fully stirred and allowed to stand to obtain the electrolyte containing the electrode interface modification additive.

9. A lithium-ion battery, characterized in that: The lithium-ion battery operates at a cutoff voltage of 4.5 V, and the lithium-ion battery comprises a positive electrode material, a negative electrode material, and the electrolyte according to any one of claims 1 to 8; The positive electrode material is selected from any one of nickel-cobalt-manganese ternary positive electrode or lithium nickel manganese oxide; the negative electrode material is selected from any one of graphite or lithium metal.

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