Electrochemistry-based battery electrolyte

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to an electrochemistry-based battery electrolyte, which comprises an electrolytic stock solution, and an anti-overcharge additive containing chloroanisole organic matters and biphenyl, the chloroanisole organic matter is subjected to an oxidation-reduction reaction on the surface of the positive electrode to form an oxidation product; biphenyl and the oxidation product are subjected to an electropolymerization reaction, and hydrogen is generated; the multi-layer composite diaphragm is arranged between the positive electrode and the negative electrode and is used for adsorbing the hydrogen; and the positive electrode, the negative electrode, part of the side surfaces of the multi-layer composite diaphragm and the inner wall of the polar plate positioning sleeve are spaced to form a gas accommodating cavity for accommodating hydrogen flowing out of the multi-layer composite diaphragm. According to the invention, polymerization type and redox type substances with different anti-overcharge mechanisms are combined for use, multiple overcharge protection is carried out by virtue of complementary advantages, the electrolyte has higher safety, and the influence of a reaction byproduct hydrogen on the safety of the battery is reduced by virtue of the multilayer composite diaphragm and the polar plate positioning sleeve.

Description

Technical Field

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

[0002] As lithium-ion batteries are increasingly valued as power batteries in electric bicycles, electric vehicles, hybrid electric vehicles and other fields, the battery safety issues that follow cannot be ignored. Lithium-ion batteries are prone to fire and even explosion under extreme conditions such as short circuit, over-discharge, overcharging, heat, and violent impact, which seriously restricts their promotion and application in the field of power batteries. Overcharging of lithium-ion batteries may cause safety hazards when the external protection circuit fails or is abused. Anti-overcharge additives can achieve internal overcharge protection of the battery.

[0003] The electrolyte of lithium-ion batteries is generally composed of electrolyte lithium salts and high-purity organic solvents, and is a carrier for lithium ion migration and charge transfer. From the perspective of function, the anti-overcharge additive added to the electrolyte is a key material that affects the performance of lithium batteries such as anti-overcharge and high specific energy.

[0004] According to the anti-overcharge action principle, anti-overcharge additives can be divided into polymerization type and redox type.

[0005] The working principle of polymer anti-overcharge additives is: when the battery is overcharged, the potential reaches the reaction potential of the polymer, the single molecule is oxidized to produce free radical ions, the free radical ions undergo polymerization in the electrolyte, and the formed polymer is deposited on the diaphragm near the positive electrode and extends to the positive and negative electrodes. At this time, two situations will occur: one is that the polymer forms an electric bridge between the positive and negative electrodes, resulting in a micro short circuit to prevent the voltage from continuing to rise; the other is to completely block the shuttle of ions between the positive and negative electrodes, thereby blocking the electrochemical reaction. Therefore, electropolymer additives are irreversible additives.

[0006] The working principle of the redox type anti-overcharge additive is: no electrochemical reaction occurs at normal voltage of lithium-ion batteries, but when the battery is overcharged, the anti-overcharge additive is oxidized near the positive electrode to form active molecules, which then diffuse to the negative electrode and are reduced to form neutral molecules, and then diffuse to the positive electrode. In this way, it constantly shuttles between the positive and negative electrodes, undergoes redox reactions, consumes the overcharge current, and thus achieves the purpose of anti-overcharge.

[0007] Li Zhijian from Shaanxi University of Science and Technology found that adding 2,3-difluorotoluene to the electrolyte of lithium-ion batteries studied its electrochemical properties as an anti-overcharge additive for organic electrolytes, and conducted linear sweep voltammetry tests, constant current and constant voltage charge and discharge tests, electrochemical impedance analysis, scanning electron microscopy analysis and other tests on lithium-ion batteries. The results show that the additive 2,3-difluorotoluene begins to polymerize when overcharged to 4.85V on a high-voltage battery, which can effectively limit the charging current; the electrolyte battery containing 2,3-difluorotoluene has good room temperature cycle performance in high-voltage ternary batteries, and the capacity retention rate is 67.5% after 100 cycles of 1C charge and discharge.

[0008] At present, many researchers have tried to use new anti-overcharge additives to solve the problem of lithium-ion battery overcharge, and have achieved certain results. However, there are still some problems that need to be solved and paid attention to in this field:

[0009] Li Bingchuan and others from the Beijing Institute of Chemical Reagents believe that the electropolymerization additives currently used in commercial batteries have a high polymerization potential (4.5-5.5V) and a good overcharge protection effect, but they will cause irreversible damage to the battery, and the generated polymers may also become potential safety hazards. Redox pairs as additives to lithium-ion battery electrolytes will not cause permanent damage to the battery, have little effect on the overall performance of the battery, and have great development potential. It is an important work direction to seek redox pair additives with high oxidation starting potential, good solubility, large diffusion coefficient, excellent reversibility and long cycle life. At the same time, it is also a good idea to use electropolymerization additives and redox pair additives together to make up for each other's shortcomings.

[0010] Ma Yulin and others from Harbin Institute of Technology believe that the overcharge performance of lithium-ion batteries involves various components in the battery system, and the simultaneous use of multiple overcharge-resistant components can maximize the overcharge safety of the battery. The use of overcharge-resistant positive electrode materials and suitable overcharge-resistant electrolytes, coupled with battery cells made of voltage-sensitive diaphragms, will be the future trend.

[0011] For example, the invention patent with application number 200910068034.3 only discloses a method for refining biphenyl in a lithium-ion battery overcharge additive.

[0012] Therefore, how to better combine multiple additives with different anti-overcharging mechanisms to achieve better anti-overcharging effect is a technical problem that needs to be solved. Summary of the invention

[0013] To this end, the present invention provides a battery electrolyte based on electrochemistry. Through chloroanisole organic matter and biphenyl, two substances with different anti-overcharge mechanisms, namely polymerization type and redox type, are used in combination. Multiple overcharge protections are performed by virtue of complementary advantages, so that the electrolyte has higher safety. The multi-layer composite diaphragm and the plate positioning sleeve are used to reduce the impact of the reaction by-product hydrogen on the battery safety.

[0014] To achieve the above object, the present invention provides an electrochemical battery electrolyte, characterized in that it comprises:

[0015] The electrolyte stock solution is placed between the positive and negative electrodes of the lithium-ion battery and contains an anti-overcharge additive;

[0016] The anti-overcharge additives include chloroanisole organic matter and biphenyl;

[0017] The chloroanisole organic substance can undergo a redox reaction on the positive electrode surface of the lithium-ion battery to form an oxidation product;

[0018] The biphenyl is capable of undergoing an electropolymerization reaction with the oxidation product and generating hydrogen;

[0019] A multi-layer composite diaphragm is arranged between the positive electrode and the negative electrode to absorb the hydrogen;

[0020] The positive electrode, the negative electrode and the multi-layer composite diaphragm are arranged inside the plate positioning sleeve, and part of the side surfaces thereof are separated from the inner wall of the plate positioning sleeve to form a gas containing cavity, and the gas containing cavity is used to contain the hydrogen flowing out of the multi-layer composite diaphragm.

[0021] Further, the electrolyte solution consists of EC, EMC and DEC;

[0022] The weight percentage of the chloroanisole organic matter in the electrolyte stock solution is 0.1 to 1, and the weight percentage of the biphenyl in the electrolyte stock solution is 1 to 4.

[0023] Further, the multi-layer composite diaphragm includes a polyethylene layer and a polypropylene layer;

[0024] A layer of the polypropylene layer is disposed on each side of the polyethylene layer;

[0025] The outer sides of the two polypropylene layers are coated with a metal organic framework to adsorb the hydrogen.

[0026] In the above scheme, the multi-layer composite membrane of PP / PE / PP has a more uniform microporous structure and better heat resistance than a single-layer membrane, thereby further improving the safety performance of lithium-ion batteries.

[0027] Furthermore, the positive electrode, the negative electrode and the multilayer composite diaphragm are arranged inside the plate positioning sleeve, and part of their side surfaces are separated from the inner wall of the plate positioning sleeve to form a gas accommodating cavity, and the gas accommodating cavity is used to accommodate hydrogen flowing out of the multilayer composite diaphragm.

[0028] Furthermore, a safety valve penetrating through both sides is disposed on the side wall of the electrode plate positioning sleeve, and one end of the safety valve is inserted into the accommodating cavity and aligned with the polyethylene layer.

[0029] Furthermore, at least two electrode groups consisting of the positive electrode, the multilayer composite diaphragm and the negative electrode are arranged in the electrode plate positioning sleeve;

[0030] The positive electrode, the multilayer composite separator and the negative electrode of the electrode group are stacked horizontally in order from low to high;

[0031] A metal diaphragm is disposed on the top surface of the negative electrode, and another electrode group is disposed on the upper side of the metal diaphragm.

[0032] Furthermore, the edge of the positive electrode is connected to the positive electrode terminal, the edge of the negative electrode is connected to the negative electrode terminal, and the inner wall of the plate positioning sleeve is provided with two wiring installation grooves, and the two wiring installation grooves are respectively embedded and installed in the positive electrode terminal and the negative electrode terminal.

[0033] In the above solution, the safety of the battery and the terminal blocks is further ensured through the structural design of the battery.

[0034] Further, the metal organic framework is a zeolite imidazolate framework compound;

[0035] The zeolite imidazolate framework compound is added to a mixed solution of polyvinylidene fluoride and N-methyl-2-pyrrolidone in a mass ratio of 6:100, and stirred evenly to form a slurry, which is then evenly coated on the outer sides of the two polypropylene layers by a coating technique.

[0036] Furthermore, the material of the positive electrode active material coating of the positive electrode is NCM622, and the material of the negative electrode active material coating of the negative electrode is graphite, and the graphite is a defective graphene structure for further adsorbing hydrogen.

[0037] Further, the chloroanisole organic substance is 3-chloroanisole;

[0038] The 3-chloroanisole produces a redox reaction on the electrode surface, and its oxidation product and the biphenyl produce an electropolymerization reaction, and the process of the electropolymerization reaction is specifically as follows:

[0039]

[0040] Furthermore, the anti-overcharge additive also includes 3-fluoroanisole in an amount of 1 to 10 weight percent of the electrolyte stock solution to reduce the exothermic peak value when the lithium-ion battery is overcharged.

[0041] In the above scheme, the oxidation product of 3-chloroanisole and biphenyl, two additives with different anti-overcharge mechanisms, are used simultaneously, and the battery is provided with multiple overcharge protections by virtue of their complementary advantages.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] 1. Through fluoroanisole organic substances, chloroanisole organic substances and biphenyl, the two substances with different anti-overcharge mechanisms, polymerization type and redox type, are used together. With complementary advantages, the battery is protected against multiple overcharges at different temperatures and voltages, making the electrolyte safer.

[0044] 2. The multi-layer composite diaphragm of PP / PE / PP reduces the impact of the reaction by-product hydrogen on battery safety, and the microporous structure is more uniform and has better heat resistance, thereby further improving the safety performance of lithium-ion batteries.

[0045] 3. The structural design of the battery further ensures the safety of the battery and the terminal. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a schematic diagram of the side structure of the multi-layer composite diaphragm;

[0047] Figure 2 A schematic diagram of the cross-sectional structure of a plate positioning sleeve for setting a multi-layer composite diaphragm;

[0048] Figure 3 A schematic diagram of the explosion structure of a plate with a multi-layer composite diaphragm;

[0049] Figure 4 Schematic diagram of the change of electrochemical impedance of the basic electrolyte before and during overcharging;

[0050] Figure 5 It is a schematic diagram of the change of electrochemical impedance of 4% 3-chloroanisole, 0.5% 3-chloroanisole and 3% biphenyl before and during overcharging of the present invention;

[0051] Figure 6 It is a schematic diagram of the change of electrochemical impedance of 8% 3-chloroanisole, 0.5% 3-chloroanisole and 3% biphenyl before and during overcharging of the present invention;

[0052] Figure 7A schematic diagram of voltage, heat flow and current curves of an electrochemical battery electrolyte when overcharged at a constant temperature of 30 degrees according to an embodiment of the present invention;

[0053] Figure 8 Schematic diagram of potentiodynamic scanning polarization curves of the electrolyte with different 3-chloroanisole and biphenyl contents according to an embodiment of the present invention.

[0054] Description of the main components in the figure: 1. Negative electrode; 11. Negative electrode terminal; 2. Positive electrode; 21. Positive electrode terminal; 3. Metal organic framework; 4. Polypropylene layer; 5. Polyethylene layer; 6. Plate positioning sleeve; 61. Fixing sleeve; 7. Safety valve; 8. Electrolyte. DETAILED DESCRIPTION

[0055] In order to make the objects and advantages of the present invention more clearly understood, the present invention is further described below in conjunction with embodiments; 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.

[0056] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0057] It should be noted that, in the description of the present invention, terms such as "up", "down", "left", "right", "inside" and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the drawings. This is merely for the convenience of description and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention.

[0058] In addition, it should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0059] like Figures 1 to 8 As shown, the present invention provides a battery electrolyte based on electrochemistry, which realizes the combined use of two substances with different anti-overcharge mechanisms, namely, polymerization type and redox type, through fluoroanisole organic matter, chloroanisole organic matter and biphenyl, and provides multiple overcharge protections for the battery at different temperatures and voltages by virtue of complementary advantages, so that the electrolyte has higher safety.

[0060] in, Figure 1 It is a schematic diagram of the side structure of the multi-layer composite diaphragm; Figure 2 A schematic diagram of the cross-sectional structure of a plate positioning sleeve for setting a multi-layer composite diaphragm; Figure 3 A schematic diagram of the explosion structure of a plate with a multi-layer composite diaphragm;

[0061] Figure 4 Schematic diagram of the change of electrochemical impedance of the basic electrolyte before and during overcharging; Figure 5 It is a schematic diagram of the change of electrochemical impedance of 4% 3-chloroanisole, 0.5% 3-chloroanisole and 3% biphenyl before and during overcharging of the present invention; Figure 6 It is a schematic diagram of the change of electrochemical impedance of 8% 3-chloroanisole, 0.5% 3-chloroanisole and 3% biphenyl before and during overcharging of the present invention; Figure 7 A schematic diagram of voltage, heat flow and current curves of an electrochemical battery electrolyte when overcharged at a constant temperature of 30 degrees according to an embodiment of the present invention; Figure 8 Schematic diagram of potentiodynamic scanning polarization curves of the electrolyte with different 3-chloroanisole and biphenyl contents according to an embodiment of the present invention.

[0062] Among them, 1. negative electrode; 11. negative electrode terminal; 2. positive electrode; 21. positive electrode terminal; 3. metal organic framework; 4. polypropylene layer; 5. polyethylene layer; 6. plate positioning sleeve; 61. fixing sleeve; 7. safety valve; 8. electrolyte.

[0063] Embodiment 1:

[0064] like Figures 1 to 3 As shown, this embodiment proposes an electrochemical battery electrolyte, including an electrolyte stock solution, which is arranged between the positive electrode 2 and the negative electrode 1 of the lithium-ion battery, and an anti-overcharge additive is added; the anti-overcharge additive includes chloroanisole organic matter and biphenyl; the chloroanisole organic matter can undergo a redox reaction on the surface of the positive electrode 2 of the lithium-ion battery to form an oxidation product; the biphenyl can produce an electropolymerization reaction with the oxidation product and produce hydrogen; a multilayer composite diaphragm is arranged between the positive electrode 2 and the negative electrode 1 to adsorb the hydrogen; the positive electrode 2, the negative electrode 1 and the multilayer composite diaphragm are arranged inside the plate positioning sleeve 6, and part of its side surface is separated from the inner wall of the plate positioning sleeve 6 to form a gas accommodating cavity, and the gas accommodating cavity is used to accommodate the hydrogen flowing out of the multilayer composite diaphragm.

[0065] Furthermore, the multilayer composite membrane comprises a polyethylene layer 5 and a polypropylene layer 4 ; one layer of the polypropylene layer 4 is disposed on each side of the polyethylene layer 5 ; and the outer sides of the two polypropylene layers 4 are coated with the metal organic framework 3 .

[0066] In the above scheme, the multi-layer composite membrane of PP / PE / PP has a more uniform microporous structure and better heat resistance than a single-layer membrane, thereby further improving the safety performance of lithium-ion batteries.

[0067] Furthermore, the positive electrode 2, the negative electrode 1 and the multilayer composite diaphragm are arranged inside the plate positioning sleeve 6, and part of their side surfaces are separated from the inner wall of the plate positioning sleeve 6 to form a gas accommodating cavity, and the gas accommodating cavity is used to accommodate hydrogen flowing out of the multilayer composite diaphragm.

[0068] Furthermore, a safety valve 7 penetrating through both sides is disposed on the side wall of the electrode plate positioning sleeve 6 , and one end of the safety valve 7 is inserted into the accommodating cavity and aligned with the polyethylene layer 5 .

[0069] Furthermore, at least two electrode groups consisting of the positive electrode 2, the multilayer composite diaphragm and the negative electrode 1 are arranged in the electrode plate positioning sleeve 6; the positive electrode 2, the multilayer composite diaphragm and the negative electrode 1 of the electrode group are horizontally stacked in sequence from low to high; a metal diaphragm is arranged on the top surface of the negative electrode 1, and another electrode group is arranged on the upper side of the metal diaphragm.

[0070] Furthermore, the edge of the positive electrode 2 is connected to the positive electrode terminal 21, and the edge of the negative electrode 1 is connected to the negative electrode terminal 11. The inner wall of the plate positioning sleeve 6 is provided with two wiring installation grooves, and the two wiring installation grooves are respectively embedded and installed in the positive electrode terminal 21 and the negative electrode terminal 11.

[0071] In the above solution, the safety of the battery and the terminal blocks is further ensured through the structural design of the battery.

[0072] Furthermore, the metal organic framework 3 is a zeolite imidazolate framework compound; the zeolite imidazolate framework compound is added to a mixed solution of polyvinylidene fluoride and N-methyl-2-pyrrolidone in a mass ratio of 6:100, and stirred evenly to form a slurry, and the slurry is evenly coated on the outer sides of the two polypropylene layers 4 by coating technology.

[0073] Furthermore, the material of the positive electrode active material coating of the positive electrode 2 is NCM622, and the material of the negative electrode active material coating of the negative electrode 1 is graphite, and the graphite is a defective graphene structure for further adsorbing hydrogen.

[0074] Specifically, a fixing sleeve 61 is provided on the outer wall of the plate positioning sleeve 6 to fix the battery at a desired position.

[0075] Specifically, Figures 1 to 3As shown, the positive electrode 2, the multilayer composite membrane and the negative electrode 1 are arranged in horizontal contact in sequence, which enhances the efficiency of the polymerization and redox reactions of the electrolyte. The reaction is further accelerated by setting different cross-sectional areas.

[0076] More specifically, the micropores of the metal organic framework 3 coated on the side of the polypropylene layer 4 close to the positive electrode 2 are more than or larger than the micropores of the metal organic framework 3 coated on the side of the polypropylene layer 4 close to the negative electrode 1, ensuring that the hydrogen byproduct of the polymerization and redox reactions occurring in the positive electrode 2 can be fully adsorbed.

[0077] In this embodiment, the multi-layer composite diaphragm of PP / PE / PP reduces the impact of the reaction byproduct hydrogen on the safety of the battery, and the microporous structure is more uniform and the heat resistance is better, thereby further improving the safety performance of the lithium-ion battery. The structural design of the battery further ensures the safety of the battery and the terminal.

[0078] Embodiment 2:

[0079] like Figures 1 to 8 As shown, this embodiment proposes an electrochemical battery electrolyte based on the first embodiment, including an electrolyte stock solution of a lithium-ion battery composed of EC, EMC, and DEC, and an anti-overcharge additive is added to the electrolyte stock solution. The anti-overcharge additive includes 1 to 10 weight percent of fluoroanisole organic matter, 0.1 to 1 weight percent of chloroanisole organic matter, and 1 to 4 weight percent of biphenyl, which are used to prevent the lithium-ion battery from overcharging.

[0080] Furthermore, the fluoroanisole organic substance is 3-fluoroanisole, which is used to prevent the electrolyte solution from self-decomposing at high temperature. The chemical formula of 3-fluoroanisole is:

[0081]

[0082] Furthermore, the cut-off voltage of the electrolyte solution does not exceed 5V, so that the 3-fluoroanisole can prevent the lithium-ion battery from overcharging and slow down the heat release during overcharging.

[0083] In the above scheme, 3-fluoroanisole undergoes an electropolymerization reaction at the positive electrode, thereby reducing the exothermic peak value of the lithium-ion battery when it is overcharged, and extending the exothermic time to avoid violent exothermic release or even explosion of the battery when it is overcharged.

[0084] Figures 4 to 6It is an electrochemical impedance equivalent fitting diagram drawn by combining the experiment of electrochemical impedance spectroscopy, that is, the curve in the figure is the result of fitting the electrochemical impedance spectrum obtained by the experiment. Specifically, the value fitted by the electrochemical impedance spectrum is the sum of the ohmic impedance R and the resistance of lithium ions passing through the surface of the active material. According to the fitted value, it can be known that the electrochemical impedance of the NCM622 half-cell of different electrolyte systems is basically the same before overcharging, indicating that when overcharging does not occur, the anti-overcharge additive has little effect on the electrochemical impedance of the battery. However, when overcharging occurs, the electrochemical impedance increases, and with the increase of the content of 3-fluoroanisole, the increase of electrochemical impedance is more obvious. The electrochemical impedance of the basic electrolyte, 4% and 8% 3-fluoroanisole added electrolyte after overcharging is 8.45Ω, 20.24Ω and 12.12Ω respectively. The electropolymerized anti-overcharge additive essentially achieves the purpose of overcharge protection by increasing the internal resistance of the battery after action. Therefore, when anti-overcharge performance is prioritized, 4% by weight of 3-chloroanisole, 0.5% by weight of 3-chloroanisole and 3% by weight of biphenyl are preferred.

[0085] See also Figure 7 The heat generation of the battery using the basic electrolyte during the overcharge process is as follows: when the voltage exceeds 4.2V, the heat flow rises slowly, and when the voltage exceeds 4.8V, the heat release rises rapidly. The peak of the heat flow curve appears when the cut-off voltage reaches 5V, and the heat release peak is 140mW / g. After the anti-overcharge additive is introduced, when the voltage reaches about 4.4V, another obvious exothermic peak appears. With the increase of the amount of 3-fluoroanisole added in the anti-overcharge additive, the exothermic peak around 4.4V gradually becomes obvious and dominates the heat release during the overcharge process. This is because the reaction amount of the electropolymerization reaction of 3-fluoroanisole exceeds the reaction amount of the electropolymerization reaction of biphenyl at this potential. Part of the heat is the heat released when the electrical energy is converted into chemical energy during the reaction; the other part of the heat is the electropolymerization reaction product attached to the surface of the positive electrode, which increases the internal resistance of the electrode, consumes the overcharged electrical energy, and directly converts the electrical energy into thermal energy. When the addition amount of 3-fluoroanisole is 5%, the exothermic peak at 4.4V is the strongest, and the peak value is only about 500mW / g, which is far less than the large amount of heat released during thermal runaway caused by overcharging. Therefore, compared with the violent heat release or even explosion when the battery is overcharged, the heat release caused by 3-fluoroanisole is slow, and it is not easy to cause thermal runaway and fire accidents. The exothermic peak at around 4.4V also proves that 3-fluoroanisole undergoes electropolymerization reaction at this potential.

[0086] Specifically, when the positive electrode surface is coated with a composite diaphragm containing a zeolite imidazolate framework compound, since the zeolite imidazolate framework compound has the characteristics of high porosity and adjustable porosity, it can prevent the electropolymerization product from being deposited on the surface of the composite diaphragm and growing along the small pores on the composite diaphragm and gradually penetrating the composite diaphragm, thereby avoiding the micro-short circuit inside the lithium-ion battery. The micro-short circuit bridge increases the resistance of the charge when passing through the composite diaphragm, which, according to Joule's law, causes an increase in the heat release of the battery.

[0087] Further, the chloroanisole organic substance is 3-chloroanisole, and its chemical formula is:

[0088]

[0089] The 3-chloroanisole produces a redox reaction on the electrode surface, and its oxidation product and the biphenyl produce an electropolymerization reaction.

[0090] Further, the process of the electropolymerization reaction between the oxidation product of 3-chloroanisole and biphenyl is specifically as follows:

[0091]

[0092] It should be noted that 3-fluoroanisole does not react with 3-chloroanisole or biphenyl.

[0093] In the above scheme, the battery expansion caused by hydrogen generated when the oxidation product of 3-chloroanisole and biphenyl are used together is avoided.

[0094] Furthermore, the metal organic framework is a zeolite imidazolate framework compound; the electrolyte stock solution contains EC+DEC+EMC with a concentration of 1 mol / L, wherein the mass ratio of EC, DEC and EMC is 1:1:1; the electrolyte stock solution is added with the biphenyl in an amount of 2 to 4 weight percentages, so that the biphenyl undergoes an electropolymerization reaction while undergoing an electropolymerization reaction with the oxidation product of 3-chloroanisole.

[0095] Specifically, the electrolyte stock solution is a 1 mol / L LiPF6 standard electrolyte, and the solvent is ethylene carbonate (EC) + dimethyl carbonate (DMC) + diethyl carbonate (DEC), (V(EC)∶V(DEC):V(DMC)=1∶1∶1). The positive electrode material NCM622 is LiNi 0.6 C o0.2 Mn 0.2 O 2 .

[0096] See also Figure 8The potentiodynamic scanning method uses polarization curves to study the multi-step complex reactions of anti-overcharge additives and the reaction process of mixed anti-overcharge additives on the electrode surface. Figure 8 It can be seen that the polarization curve of the basic electrolyte is basically a straight line before 5V, indicating that no obvious chemical reaction occurs on the electrode surface. The electrolyte with only 3% biphenyl has a peak, corresponding to the electropolymerization reaction of biphenyl at this potential; the mixed electrolyte with 0.25% 3-chloroanisole and 4% 3-fluoroanisole added by volume on the basis of 3% biphenyl has two adjacent small peaks as shown in curve e, indicating that there are two different reactions on the electrode surface in this potential range, which occur successively and overlap but do not overlap completely. When the content of 3-chloroanisole is increased to 0.5%, the two reactions overlap completely and overlap into one peak, as shown in curve d, confirming that two different reactions do occur on the electrode surface with the mixed additive.

[0097] It is understandable that redox additives are generally stable and reversible, and have little effect on battery performance. The battery voltage is limited to the oxidation potential of the additive by consuming excess current inside the battery through redox. Its maximum oxidation current is related to the concentration, diffusion coefficient, electrode cross-sectional area and electrode spacing of the additive. Its shunt voltage limiting capacity is limited, and its overcharge prevention capacity gradually declines until it disappears after multiple cycles, which cannot completely solve the safety problem of battery overcharge. For electropolymer additives, in order to ensure that lithium-ion batteries can be protected in time to prevent safety accidents when overcharged, their concentration in the electrolyte is generally increased, which often increases the irreversible capacity loss of the battery, low charging and discharging efficiency, greatly shortened cycle life and very serious self-discharge phenomenon. The performance of the battery deteriorates sharply after long-term storage and even causes the battery to fail to work normally. Therefore, while ensuring the safety of the battery's overcharge prevention, the concentration of such additives should be minimized to reduce their negative effects. By adding two additives with different overcharge prevention mechanisms, the battery is double-protected from overcharge by virtue of complementary advantages.

[0098] It is understandable that redox additives are generally stable and reversible, and have little effect on battery performance. The battery voltage is limited to the oxidation potential of the additive by consuming excess current inside the battery through redox. Its maximum oxidation current is related to the concentration, diffusion coefficient, electrode cross-sectional area and electrode spacing of the additive. Its shunt voltage limiting capacity is limited, and its overcharge prevention capacity gradually declines until it disappears after multiple cycles, which cannot completely solve the safety problem of battery overcharge. For electropolymer additives, in order to ensure that lithium-ion batteries can be protected in time to prevent safety accidents when overcharged, their concentration in the electrolyte is generally increased, which often increases the irreversible capacity loss of the battery, low charging and discharging efficiency, greatly shortened cycle life and very serious self-discharge phenomenon. The performance of the battery deteriorates sharply after long-term storage and even causes the battery to fail to work normally. Therefore, while ensuring the safety of the battery's overcharge prevention, the concentration of such additives should be minimized to reduce their negative effects. By adding two additives with different overcharge prevention mechanisms, the battery is double-protected from overcharge by virtue of complementary advantages.

[0099] Based on the above experimental phenomena and literature reports, it is reasonable to speculate that when the mixed electrolyte is overcharged, the redox of 3-chloroanisole and the electropolymerization of biphenyl occur on the electrode surface, and both of them protect the battery from overcharge. Figure 8 As shown in the middle curve d, the two small voltage platforms in the charge-discharge test curve correspond to the redox shuttle of 3-chloroanisole and the electropolymerization process of biphenyl. The two overcharge mechanisms work together to prevent the battery from being further overcharged, but due to the presence of biphenyl, the oxidation product of 3-chloroanisole may undergo a new electropolymerization reaction with biphenyl, resulting in the reduction peak of 3-chloroanisole not being obvious when the voltage is swept back.

[0100] Furthermore, the preparation method of the electrochemical battery electrolyte includes: step S1, dissolving the fluoroanisole organic matter in a methanol / ether mixed solution and recrystallizing it twice, and drying it under a vacuum condition of 100 degrees for at least 48 hours for purification; step S2, preparing a battery shell for placing electrodes and injecting the electrolyte stock solution; step S3, mixing the chloroanisole organic matter and the biphenyl to form a mixture, and adding the mixture and the fluoroanisole organic matter purified in step S1 to the electrolyte stock solution.

[0101] Specifically, 1.455 g Co(NO 3 ) 2 6H 2O and 1.642g 2-methylimidazole were dissolved in 40ml methanol solution respectively, and then stirred for 10 minutes respectively to dissolve them. The two solutions were mixed and stirred vigorously for 10 minutes, and then settled at room temperature for 48 hours. The purple precipitate was then filtered and repeatedly rinsed with methanol, and finally dried under 80 degrees vacuum conditions for 24 hours to obtain a zeolite imidazole ester framework compound.

[0102] The zeolite imidazolate skeleton compound was added to a mixed solution of PVDF (polyvinylidene fluoride) and NMP (N-methyl-2-pyrrolidone) in a mass ratio of 6:100, and then stirred evenly for 24 hours to form a uniform slurry. The prepared polyethylene layer / polypropylene layer / polyethylene layer was taken out and the slurry was evenly applied on the surface, and dried at 100 degrees in a vacuum for 12 hours. By controlling the amount of slurry applied, a composite diaphragm with a thickness of about 80 microns was obtained, which was cut into discs with a diameter of 50 mm for battery assembly.

[0103] More specifically, by changing the mass of the zeolite imidazolate framework compound added to the mixed solution, the micropore size of the composite membrane is changed, thereby achieving the coating of a metal organic framework with different hydrogen adsorption capabilities near the positive electrode or the negative electrode.

[0104] In the above scheme, the preparation of a battery electrolyte with stronger overcharge resistance is achieved by utilizing the characteristics of high porosity, uniform pore size, and adjustable porosity of the zeolite imidazolate framework compound.

[0105] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

[0106] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An electrochemical battery electrolyte, characterized in that: include: The electrolyte stock solution is arranged between the positive electrode (2) and the negative electrode (1) of the lithium ion battery, and an anti-overcharge additive is added; The anti-overcharge additives include chloroanisole organic matter and biphenyl; The chloroanisole organic substance can undergo a redox reaction on the surface of the positive electrode (2) of the lithium ion battery to form an oxidation product; The biphenyl is capable of undergoing an electropolymerization reaction with the oxidation product and generating hydrogen; A multi-layer composite diaphragm is arranged between the positive electrode (2) and the negative electrode (1) to absorb the hydrogen; The positive electrode (2), the negative electrode (1) and the multi-layer composite diaphragm are arranged inside the plate positioning sleeve (6), and part of the side surface thereof is separated from the inner wall of the plate positioning sleeve (6) to form a gas containing cavity, and the gas containing cavity is used to contain hydrogen flowing out of the multi-layer composite diaphragm.

2. The electrochemical cell electrolyte according to claim 1, characterized in that: The electrolyte solution consists of EC, EMC and DEC; The weight percentage of the chloroanisole organic matter in the electrolyte stock solution is 0.1 to 1, and the weight percentage of the biphenyl in the electrolyte stock solution is 1 to 4.

3. The electrochemical cell electrolyte according to claim 1, characterized in that: The multi-layer composite diaphragm comprises a polyethylene layer (5) and a polypropylene layer (4); A layer of the polypropylene layer (4) is disposed on each side of the polyethylene layer (5); The outer sides of the two polypropylene layers (4) are coated with a metal organic framework (3) to adsorb the hydrogen.

4. The electrochemical cell electrolyte according to claim 3, characterized in that: The side wall of the electrode plate positioning sleeve (6) is provided with a safety valve (7) penetrating both sides, and one end of the safety valve (7) is inserted into the accommodating cavity and aligned with the polyethylene layer (5).

5. The electrochemical cell electrolyte according to claim 3, characterized in that: The electrode plate positioning sleeve (6) is provided with at least two electrode groups consisting of the positive electrode (2), the multi-layer composite diaphragm and the negative electrode (1); The positive electrode (2), the multilayer composite separator and the negative electrode (1) of the electrode group are stacked horizontally in order from low to high; A metal diaphragm is arranged on the top surface of the negative electrode (1), and another electrode group is arranged on the upper side of the metal diaphragm.

6. The electrochemical cell electrolyte according to claim 3, characterized in that: The edge of the positive electrode (2) is connected to the positive electrode terminal (21), the edge of the negative electrode (1) is connected to the negative electrode terminal (11), and the inner wall of the plate positioning sleeve (6) is provided with two wiring installation grooves, and the two wiring installation grooves are respectively embedded and installed with the positive electrode terminal (21) and the negative electrode terminal (11).

7. The electrochemical cell electrolyte according to claim 3, characterized in that: The metal organic framework (3) is a zeolite imidazolate framework compound; The zeolite imidazolate framework compound is added to a mixed solution of polyvinylidene fluoride and N-methyl-2-pyrrolidone in a mass ratio of 6:100, and stirred evenly to form a slurry, which is then evenly coated on the outer sides of the two polypropylene layers (4) by a coating technique.

8. The electrochemical cell electrolyte according to any one of claims 1 to 7, characterized in that: The material of the positive electrode active material coating of the positive electrode (2) is NCM622, and the material of the negative electrode active material coating of the negative electrode (1) is graphite, and the graphite is a defective graphene structure for further adsorbing hydrogen.

9. The electrochemical cell electrolyte according to any one of claims 1 to 7, characterized in that: The chloroanisole organic substance is 3-chloroanisole; The 3-chloroanisole produces a redox reaction on the electrode surface, and its oxidation product and the biphenyl produce an electropolymerization reaction, and the process of the electropolymerization reaction is specifically as follows:

10. The electrochemical cell electrolyte according to any one of claims 1 to 7, characterized in that: The anti-overcharge additive also includes 3-fluoroanisole in an amount of 1 to 10 weight percent of the electrolyte stock solution, so as to reduce the exothermic peak value when the lithium-ion battery is overcharged.

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