A method for capacity recovery of a lithium-ion secondary battery

Abstract

The present application provides a method for recovering the capacity of a lithium-ion secondary battery, which comprises the following steps: (1) providing a lithium-ion secondary battery with capacity attenuation; (2) providing a capacity recovery agent, wherein the capacity recovery agent comprises a p-phenylenediamine compound, a lithium salt, and an organic solvent, wherein the organic solvent is used to dissolve the p-phenylenediamine compound and the lithium salt; (3) injecting the capacity recovery agent into the lithium-ion secondary battery; (4) causing the capacity recovery agent to react inside the lithium-ion secondary battery; and (5) pouring out the liquid mixture inside the lithium-ion secondary battery after the reaction, and injecting an electrolyte into the lithium-ion secondary battery.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion secondary batteries, and in particular to a method for recovering the capacity of a lithium ion secondary battery, and a lithium ion secondary battery obtained by the method. Background Art

[0002] In recent years, the application of lithium-ion secondary batteries has become increasingly widespread. They are widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. However, with repeated use, the capacity of lithium-ion secondary batteries gradually decreases, affecting their service life and safety. Currently, in-depth research on the capacity recovery of lithium-ion secondary batteries that have undergone capacity decay is lacking. Summary of the Invention

[0003] The object of the present invention is to provide a method for efficiently and accurately restoring the capacity of a lithium-ion secondary battery using a capacity recovery agent, and the capacity recovery agent does not remain in large quantities inside the secondary battery, thereby ensuring the cycle stability of the secondary battery in subsequent use.

[0004] In order to achieve the above object, the present application provides a method for recovering the capacity of a lithium-ion secondary battery, which comprises the following steps:

[0005] (1) Providing a lithium-ion secondary battery with capacity fading;

[0006] (2) providing a capacity recovery agent, wherein the capacity recovery agent comprises a p-phenylenediamine compound, a lithium salt, and an organic solvent, wherein the organic solvent is used to dissolve the p-phenylenediamine compound and the lithium salt;

[0007] (3) injecting the capacity recovery agent into the lithium-ion secondary battery;

[0008] (4) causing the capacity recovery agent to react inside the lithium-ion secondary battery;

[0009] (5) Pour out the liquid mixture inside the lithium ion secondary battery after the reaction, and inject the electrolyte into the lithium ion secondary battery.

[0010] Therefore, the present application effectively restores the capacity of the lithium-ion secondary battery by using a specific type of capacity recovery agent and replacing the electrolyte with a new one after the capacity recovery agent reacts, while ensuring the cycle stability of the secondary battery in subsequent use.

[0011] In any embodiment, in step (1), the capacity-faded lithium-ion secondary battery is an active lithium-faded battery, and the capacity to be restored for the capacity-faded lithium-ion secondary battery is C, and the calculation method of C is:

[0012] C=C2+C3-C1,

[0013] Where C2=C1 / (1-P1),

[0014] in,

[0015] P1 is the active lithium loss rate of the lithium-ion secondary battery with capacity decay;

[0016] C1 is the discharge capacity of the lithium-ion secondary battery in the current state with capacity decay;

[0017] C2 is the discharge capacity of the lithium-ion secondary battery when the positive electrode material accommodates active lithium to the maximum extent;

[0018] C3 is the capacity that the lithium-ion secondary battery with capacity decay needs to be charged before its capacity is restored;

[0019] The above capacities are all measured in Ah.

[0020] Thus, the capacity that needs to be restored by the lithium-ion secondary battery can be accurately calculated, thereby performing targeted and precise regulation on the capacity recovery of the lithium-ion secondary battery.

[0021] In any embodiment, the active lithium loss rate P1 of the capacity-faded lithium-ion secondary battery is greater than or equal to 5%. Thus, the capacity of the lithium-ion secondary battery can be restored using the method of the present invention.

[0022] In any embodiment, in step (2), the added mass m1 of the p-phenylenediamine compound in the capacity recovery agent and the capacity C required to be restored of the lithium-ion secondary battery with capacity decay satisfy:

[0023] m1=C*M1*1000 / (M li *3860), of which

[0024] M1 represents the relative molecular mass of p-phenylenediamine compounds, g / mol,

[0025] M li represents the relative atomic mass of lithium atom, g / mol,

[0026] 3860 represents the gram capacity of lithium metal, mAh / g.

[0027] In any embodiment, in step (2), the added mass m2 of the lithium salt in the capacity recovery agent and the capacity C required to be restored of the capacity-faded lithium-ion secondary battery satisfy:

[0028] m2=C*M2*1000 / (n*M li *3860), of which

[0029] M2 represents the relative molecular mass of lithium salt, g / mol,

[0030] n represents the number of lithium atoms in the lithium salt,

[0031] M li represents the relative atomic mass of Li atom, g / mol,

[0032] 3860 represents the gram capacity of lithium metal, mAh / g.

[0033] Thus, the required masses of the p-phenylenediamine compound and the lithium salt can be accurately calculated, thereby precisely controlling the recovered capacity of the lithium-ion secondary battery.

[0034] In any embodiment, the p-phenylenediamine compound is selected from compounds of Formula 1 and / or Formula 2:

[0035]

[0036] Wherein, R1, R2, R3, and R4 are each independently a linear or branched alkyl group having 1 to 3 carbon atoms, or hydrogen; and R5 and R6 are each independently hydrogen or a linear or branched alkyl group having 1 to 3 carbon atoms. Thus, the p-phenylenediamine compound, together with the lithium salt, reacts with the delithiated positive electrode, generating a positive electrode lithium replenishment reaction, thereby restoring the capacity of the lithium-ion secondary battery.

[0037] In any embodiment, the lithium salt is selected from one or more of lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(difluorosulfonylimide), LiCl, and LiBr. Thus, the lithium salt, together with the p-phenylenediamine compound, reacts with the delithiated positive electrode, generating a positive electrode lithium replenishment reaction, thereby restoring the capacity of the lithium-ion secondary battery.

[0038] In any embodiment, the capacity restoration agent comprises 0.5-15% by weight of the p-phenylenediamine compound and 0.5-15% by weight of the lithium salt, preferably 0.5-6% by weight; these amounts are based on the total mass of the capacity restoration agent. The specific amounts of lithium salt and p-phenylenediamine compound in the capacity restoration agent provide the agent with a moderate viscosity, allowing for better reaction with the battery's internal electrodes, thereby restoring the capacity of the lithium-ion secondary battery.

[0039] In any embodiment, in step (2), the organic solvent comprises a cyclic carbonate and a low-viscosity solvent. Thus, the organic solvent with a specific composition can better dissolve the lithium salt and the p-phenylenediamine compound, thereby restoring the capacity of the lithium-ion secondary battery.

[0040] In any embodiment, the cyclic carbonate is ethylene carbonate (EC) or propylene carbonate (PC), or a combination thereof; the cyclic carbonate is present in an amount of 10-30% by weight based on the total weight of the organic solvent. Thus, the cyclic carbonate has a high dielectric constant, which ensures that the lithium salt and the p-phenylenediamine compound have a high solubility in the organic solvent.

[0041] In any embodiment, the low-viscosity solvent is one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl propionate, ethyl butyrate, ethyl propionate, propyl butyrate, tetrahydrofuran, and 1,3-dioxolane; and the content of the low-viscosity solvent is 70-90% by weight, based on the mass of the organic solvent. Thus, the specific type and content of the low-viscosity solvent can alleviate the excessive viscosity of the cyclic carbonate, allowing the interior of the battery to be fully wetted, thereby ensuring capacity recovery of the lithium-ion secondary battery.

[0042] In any embodiment, in step (4), the capacity recovery agent is allowed to react inside the lithium ion secondary battery by standing at 20-60° C. Under the reaction conditions, the capacity recovery agent fully infiltrates the interior of the lithium ion secondary battery, ensuring capacity recovery of the lithium ion secondary battery.

[0043] In any embodiment, in step (4), the capacity recovery agent can be caused to react inside the lithium-ion secondary battery by ultrasound or heating. This can accelerate the infiltration of the capacity recovery agent into the internal electrode of the lithium-ion secondary battery, accelerate the reaction speed, and improve the efficiency of the secondary battery capacity recovery.

[0044] In any embodiment, in step (5), after the liquid mixture inside the lithium-ion secondary battery after the reaction is poured out, an organic detergent is injected for cleaning, followed by vacuum drying, and finally, an electrolyte is injected into the lithium-ion secondary battery. In this way, no capacity recovery agent remains inside the battery, thereby ensuring the cycle stability and safety of the lithium-ion secondary battery after capacity recovery.

[0045] The second aspect of the present application provides a lithium ion secondary battery, characterized in that it is a lithium ion secondary battery obtained by the method described in the first aspect of the present application, and the positive electrode active material of the lithium ion secondary battery is at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and olivine structure lithium phosphate, optionally,

[0046] The lithium-containing phosphate with an olivine structure is at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0047] A third aspect of the present application provides a battery module including the secondary battery according to the second aspect of the present application.

[0048] A fourth aspect of the present application provides a battery pack comprising the battery module of the third aspect of the present application.

[0049] The fifth aspect of the present application provides an electrical device comprising at least one selected from the secondary battery of the second aspect of the present application, the battery module of the third aspect of the present application, or the battery pack of the fourth aspect of the present application.

[0050] The present application adds a capacity recovery agent containing a specific type and content of p-phenylenediamine compounds and lithium salts to a lithium-ion secondary battery with capacity attenuation, thereby replenishing active lithium to the positive electrode plate inside the lithium-ion secondary battery, ensuring efficient and precise control of the capacity recovery of the lithium-ion secondary battery; and replacing the electrolyte with a new one after the capacity recovery agent reacts, thereby eliminating the impact of the capacity recovery agent on the safety and cycle stability of the subsequent operation of the lithium-ion secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is a flow chart of a method according to a preferred embodiment of the present application. DETAILED DESCRIPTION

[0052] Below, the capacity recovery method of the lithium-ion secondary battery of the present application, the corresponding secondary battery, battery module, battery pack and electrical device are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0053] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0054] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0055] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0056] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0057] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0058] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0059] At present, lithium-ion secondary batteries are widely used in various fields and are used in huge quantities. However, their capacity gradually decays due to repeated charge and discharge during use. Most of the existing technical solutions are to add lithium supplement additives to the battery cells of fresh batteries, so that the initial active lithium content of the battery cells is higher; but there is no mention of the recovery of the battery capacity after decay. Regarding the capacity recovery of secondary batteries with capacity decay, those skilled in the art have done very little research. It is only mentioned that a capacity recovery agent can be added to the secondary batteries with capacity decay, but the degree of capacity recovery is limited and it is impossible to achieve precise capacity recovery regulation. Moreover, the capacity recovery agent still exists in the electrolyte system after the capacity is recovered, which will affect the later cycle stability of the battery cell. After extensive research, the inventors found that the method of the first aspect of the present invention can efficiently and accurately restore the capacity of lithium-ion secondary batteries by precisely controlling the addition of a specific type and content of capacity recovery agent and replacing the electrolyte, and the capacity recovery agent does not remain inside the secondary battery, thereby ensuring the cycle stability of the secondary battery in subsequent use.

[0060] Method for restoring capacity of lithium-ion secondary battery

[0061] In one embodiment of the present application, see Figure 1 , the present application proposes a method for recovering the capacity of a lithium-ion secondary battery, which comprises the following steps:

[0062] (1) Providing a lithium-ion secondary battery with capacity fading;

[0063] (2) providing a capacity recovery agent, wherein the capacity recovery agent comprises a p-phenylenediamine compound, a lithium salt, and an organic solvent, wherein the organic solvent is used to dissolve the p-phenylenediamine compound and the lithium salt;

[0064] (3) injecting the capacity recovery agent into the lithium-ion secondary battery;

[0065] (4) causing the capacity recovery agent to react inside the lithium-ion secondary battery;

[0066] (5) Pour out the liquid mixture inside the lithium ion secondary battery after the reaction, and inject the electrolyte into the lithium ion secondary battery.

[0067] Although the mechanism is still unclear, the applicant has unexpectedly discovered that by using a capacity recovery agent containing a p-phenylenediamine compound and a lithium salt, and replacing the electrolyte with a new one after the capacity recovery agent reacts, the present application effectively restores the capacity of a lithium-ion secondary battery while ensuring the cyclic stability of the secondary battery during subsequent use. Specifically, taking a lithium iron phosphate lithium-ion secondary battery as an example, the lithium ions in the p-phenylenediamine compound and the lithium salt react with the iron phosphate in the delithiated positive electrode to form lithium iron phosphate. During this reaction, the lithium in the lithium salt acts as an external lithium source and is incorporated into the positive electrode through an oxidation-reduction reaction, thereby increasing the total amount of active lithium available within the secondary battery, thereby achieving capacity recovery of the secondary battery.

[0068] The term "active lithium" refers to lithium ions within the battery that can participate in redox reactions during the charge and discharge process.

[0069] In some embodiments, in step (1), the capacity-faded lithium-ion secondary battery is an active lithium-faded battery, and the capacity to be restored for the capacity-faded lithium-ion secondary battery is C, and the calculation method of C is:

[0070] C=C2+C3-C1,

[0071] Where C2=C1 / (1-P1),

[0072] in,

[0073] P1 is the active lithium loss rate of the lithium-ion secondary battery with capacity decay;

[0074] C1 is the discharge capacity of the lithium-ion secondary battery in the current state with capacity decay;

[0075] C2 is the discharge capacity of the lithium-ion secondary battery when the positive electrode material accommodates active lithium to the maximum extent;

[0076] C3 is the capacity that the lithium-ion secondary battery with capacity decay needs to be charged before its capacity is restored;

[0077] The above capacities are all measured in Ah.

[0078] Thus, the capacity that needs to be restored by the lithium-ion secondary battery can be accurately calculated, thereby performing targeted and precise regulation on the capacity recovery of the lithium-ion secondary battery.

[0079] The “active lithium decay battery” is a secondary battery in which the active lithium in the positive electrode gradually decreases after the initial formation and / or during use.

[0080] The calculation method of the active lithium loss rate P1 of the lithium-ion secondary battery with capacity decay is as follows:

[0081] Active lithium loss rate P1 = (C20-C10) / C20;

[0082] C10 is 154.025mm 2 The capacity of the active lithium in the current state of the battery cathode; C20 is 154.025mm 2 The capacity of the battery cathode that can hold active lithium.

[0083] The test methods for C10 and C20 are as follows:

[0084] Take the cathode electrode of the fully charged battery and use the punching machine to punch the cathode electrode into an area of 154.025mm 2 A coin cell containing this cathode and lithium was prepared using a disc of the same size. The coin cell was charged using the charging process shown in Table 1, and its charge capacity was recorded as C10. The coin cell was discharged and then recharged using the process shown in Table 2, and its recharge capacity was recorded as C20 (this does not consider the loss of active lithium due to loss of cathode active material). The values of U1 and U2 for different lithium-ion secondary batteries are shown in Table 3.

[0085] Table 1 Button battery charging process

[0086]

[0087] Note: “0.04C” means a current of 0.04 times the capacity.

[0088] Table 2 Discharge and recharge process of button battery

[0089]

[0090] Table 3 U1 and U2 of different lithium-ion secondary batteries

[0091] positive electrode active material <![CDATA[U1(V)]]> <![CDATA[U2(V)]]> lithium iron phosphate 3.75 2 NCM532 4.25 2.8 lithium cobalt oxide 4.25 2.8 lithium manganate 4.3 2.5

[0092] When the secondary battery recovers its capacity in a fully discharged state, C3 is 0 Ah, and C=C2-C1.

[0093] In some embodiments, the active lithium loss rate P1 of the capacity-faded lithium-ion secondary battery is greater than or equal to 5%. Therefore, the method of the present invention can be used to restore the capacity of the lithium-ion secondary battery.

[0094] In some embodiments, in step (2), the added mass m1 of the p-phenylenediamine compound in the capacity recovery agent and the capacity C required to be restored of the capacity-faded lithium-ion secondary battery satisfy the following relationship:

[0095] m1=C*M1*1000 / (M li *3860),

[0096] in

[0097] M1 represents the relative molecular mass of p-phenylenediamine compounds, g / mol,

[0098] M li represents the relative atomic mass of lithium atom, g / mol,

[0099] 3860 represents the gram capacity of lithium metal, mAh / g.

[0100] In some embodiments, in step (2), the added mass m2 of the lithium salt in the capacity recovery agent and the capacity C required to be restored of the capacity-faded lithium-ion secondary battery satisfy:

[0101] m2=C*M2*1000 / (n*M li *3860),

[0102] in

[0103] M2 represents the relative molecular mass of lithium salt, g / mol,

[0104] n represents the number of lithium atoms in the lithium salt,

[0105] M li represents the relative atomic mass of Li atom, g / mol,

[0106] 3860 represents the gram capacity of lithium metal, mAh / g.

[0107] Thus, the required masses of the p-phenylenediamine compound and the lithium salt can be accurately calculated, thereby precisely controlling the recovered capacity of the lithium-ion secondary battery.

[0108] In some embodiments, the p-phenylenediamine compound is selected from compounds of Formula 1 and / or Formula 2:

[0109]

[0110] Wherein, R1, R2, R3, and R4 are each independently a linear or branched alkyl group having 1 to 3 carbon atoms, or hydrogen, preferably a methyl group, an ethyl group, or hydrogen; R5 and R6 are each independently hydrogen, a linear or branched alkyl group having 1 to 3 carbon atoms, preferably hydrogen, a methyl group, or an ethyl group. Preferably, the p-phenylenediamine compound is tetramethyl-p-phenylenediamine (TMPD), N,N-dimethyl-p-phenylenediamine, and N,N-diethyl-p-phenylenediamine.

[0111] In some embodiments, the lithium salt is selected from one or more of lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(difluorosulfonylimide), LiCl, and LiBr; preferably lithium hexafluorophosphate, lithium perchlorate, and LiBr.

[0112] During the charging process of lithium-ion secondary batteries, the following reactions occur at the positive electrode:

[0113] LiMO2--Li 1-X MO2+xLi + +xe-.

[0114] After the loss of active lithium, there is a delithiation state in the positive electrode. 1-X MO2, after the capacity recovery agent is injected into the battery, the lithium salt and the p-phenylenediamine compound (taking TMPD as an example) react with the delithiated positive electrode to produce a positive electrode lithium replenishment reaction:

[0115] Li 1-x MO2+XLi + +TMPD------LiMO2+TMPD .+

[0116] This increases the total active lithium content of the battery system, allowing the capacity of the lithium-ion secondary battery to be restored, thereby effectively extending the battery's service life.

[0117] In some embodiments, the capacity restoration agent comprises a p-phenylenediamine compound at a concentration of 0.5-15% by weight, preferably 0.5-5% by weight, and a lithium salt at a concentration of 0.5-15% by weight, preferably 0.5-6% by weight; all of these concentrations are based on the total mass of the capacity restoration agent. Consequently, the specific concentrations of lithium salt and p-phenylenediamine in the capacity restoration agent ensure a moderate viscosity, allowing for better reaction with the internal electrode plates, thereby restoring the capacity of the lithium-ion secondary battery. For a given lithium-ion secondary battery capacity, the lower the lithium salt concentration in the capacity restoration agent, the greater the total amount of capacity restoration agent required. Therefore, the lithium salt concentration should not be less than 0.5% by weight. Furthermore, the higher the lithium salt concentration, the greater the viscosity of the solvent restoration agent, making it difficult for the capacity restoration agent to diffuse across the electrode plates, resulting in uneven distribution of the capacity restoration effect on the cathode electrode plates. This can even result in the central portion of the electrode plate failing to react with the capacity restoration agent, preventing capacity restoration. Therefore, the lithium salt concentration should not be greater than 15% by weight.

[0118] In some embodiments, in step (2), the organic solvent comprises a cyclic carbonate and a low-viscosity solvent. Cyclic carbonate has a high dielectric constant, which can ensure that the diphenylenediamine compound and the lithium salt have a large solubility in the organic solvent, so that the addition of a small amount of capacity recovery agent can also achieve the expected capacity recovery effect. However, cyclic carbonate has a high viscosity, which will affect the diffusion of the capacity recovery agent between the pole pieces, so that the pole pieces cannot be well infiltrated and cannot participate in the reaction; or it reduces the reaction time of the middle position with the solvent recovery agent, so that the middle part of the pole piece cannot be well activated. At this time, a low-viscosity solvent is added to reduce the viscosity of the system so that the pole piece is fully infiltrated, thereby ensuring that the pole piece is fully activated.

[0119] In some embodiments, the cyclic carbonate is ethylene carbonate (EC) or propylene carbonate (PC), or a combination thereof, preferably ethylene carbonate; the cyclic carbonate content is 10-30% by weight, preferably 20-30% by weight, based on the total mass of the organic solvent. Thus, the specific type of cyclic carbonate further ensures that the lithium salt and p-phenylenediamine compound have a high solubility in the organic solvent, thereby enabling the desired capacity recovery effect to be achieved even with the addition of a small amount of capacity recovery agent.

[0120] In some embodiments, the low-viscosity solvent is one or more of dimethyl carbonate (DMC), diethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl propionate, ethyl butyrate, ethyl propionate, propyl butyrate, tetrahydrofuran, and 1,3-dioxolane; preferably dimethyl carbonate; the content of the low-viscosity solvent is 70-90% by weight, preferably 70-80% by weight, based on the mass of the organic solvent. Thus, the specific type and content of the low-viscosity solvent can alleviate the excessive viscosity of the cyclic carbonate, allowing the interior of the battery to be fully wetted, thereby ensuring capacity recovery of the lithium-ion secondary battery.

[0121] In some embodiments, in step (3), the capacity recovery agent is injected into the capacity-faded lithium-ion battery. Before the capacity recovery agent is injected, the electrolyte in the battery can be poured out, or the capacity recovery agent can be directly injected without pouring out the electrolyte. Preferably, the electrolyte in the battery is poured out before the capacity recovery agent is injected. Those skilled in the art should know that when the capacity of the lithium-ion battery is severely attenuated, there is very little free electrolyte remaining in the battery. At this time, the capacity recovery agent can be directly injected into the battery. The method of injecting the capacity recovery agent can be any method known to those skilled in the art, such as injection by a syringe.

[0122] In some embodiments, in step (4), the capacity recovery agent is allowed to react within the lithium-ion secondary battery by standing at a temperature of 20-60° C., preferably 20-45° C. Typically, the standing time is 24-72 hours, preferably 45-55 hours. Under the reaction conditions, the capacity recovery agent fully infiltrates the interior of the lithium-ion secondary battery, ensuring capacity recovery of the lithium-ion secondary battery.

[0123] In some embodiments, in step (4), the capacity recovery agent can be reacted inside the lithium-ion secondary battery by ultrasound or heating. In some embodiments, ultrasound can be applied at a frequency of 25KHz-80KHz, preferably 40KHz, for 2-4 hours, preferably 2 hours, to accelerate the reaction of the capacity recovery agent inside the lithium-ion secondary battery. In some embodiments, heating can be performed in an oven at 20-45°C for 2 hours to accelerate the reaction of the capacity recovery agent inside the lithium-ion secondary battery. In this way, the infiltration of the capacity recovery agent into the internal pole piece of the lithium-ion secondary battery can be accelerated, the reaction speed can be accelerated, and the efficiency of the secondary battery capacity recovery can be improved.

[0124] In some embodiments, in step (5), after the liquid mixture inside the lithium-ion secondary battery after the reaction is poured out, an organic detergent is injected for cleaning, followed by vacuum drying, and finally, an electrolyte is injected into the lithium-ion secondary battery. In this way, no capacity recovery agent remains inside the battery, thereby ensuring the cycle stability and safety of the lithium-ion secondary battery after capacity recovery.

[0125] In some embodiments, the organic cleaning agent is the same as the low-viscosity solvent described above, preferably DMC. After cleaning with the organic cleaning agent, the secondary battery is vacuum dried, typically at 20-45°C, preferably room temperature, under a vacuum of -0.08 to -0.1 MPa. The vacuum drying is typically performed for 0.2-1 hour, preferably 0.5 hours.

[0126] In some embodiments, by implementing the method of the present application, the capacity recovery rate of the lithium-ion secondary battery is 0.5%-25%.

[0127] The capacity recovery rate P of the secondary battery is calculated by the following formula:

[0128] P = (Ca - Cb) / Cb * 100%;

[0129] in

[0130] Cb is the discharge capacity of the battery before capacity recovery, measured in Ah;

[0131] Ca is the discharge capacity of the battery after capacity recovery, measured in Ah.

[0132] The test methods for Ca and Cb are as follows:

[0133] At 25°C, the lithium-ion secondary battery was charged at a constant current of 0.04C to U 10 , let it sit for 5 minutes, and then discharge it at 0.04C to U 20 The obtained discharge capacity is recorded as the initial discharge capacity C0, where U 10 and U 20 The values of are shown in Table 4.

[0134] Table 4 U of different lithium-ion secondary batteries 10 and U 20

[0135] positive electrode active material <![CDATA[U 10 (V)]]> <![CDATA[U 20 (V)]]> lithium iron phosphate 3.65 2.5 NCM532 4.25 2.8 lithium cobalt oxide 4.25 2.8 lithium manganate 4.25 2.5

[0136] Repeat the above steps three times for the same battery, and record the battery's discharge capacity (Cn) after the nth discharge. Take the average of these three discharge capacities as the battery's discharge capacity (Cb) before capacity recovery. After the battery's capacity has recovered, repeat the above charge and discharge process three more times; take the average of these three discharge capacities as the battery's discharge capacity (Ca) after capacity recovery.

[0137] The testing method for the capacity C1 of the lithium-ion secondary battery in the current state with capacity fading is the same as the testing method for Cb.

[0138] The second aspect of the present application provides a lithium ion secondary battery, characterized in that it is a lithium ion secondary battery obtained by the method described in the first aspect of the present application, and the positive electrode active material of the lithium ion secondary battery is at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and olivine structure lithium phosphate, optionally,

[0139] The lithium-containing phosphate with an olivine structure is at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0140] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0141] [Positive electrode]

[0142] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the positive electrode active material of the first aspect of the present application.

[0143] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0144] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0145] In some embodiments, the positive electrode active material can be a positive electrode active material for a battery known in the art. As an example, the positive electrode active material is lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05O2), at least one of an olivine-structured lithium-containing phosphate, optionally, the olivine-structured lithium-containing phosphate may include but is not limited to lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. However, the present application is not limited to these materials, and other traditional materials that can be used as battery positive electrode active materials can also be used. These positive electrode active materials can be used alone or in combination of two or more.

[0146] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0147] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0148] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0149] [Negative electrode]

[0150] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0151] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0152] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0153] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0154] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0155] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0156] In some embodiments, the negative electrode film layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0157] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0158] [Electrolytes]

[0159] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0160] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0161] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0162] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0163] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0164] [Isolation film]

[0165] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0166] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0167] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0168] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0169] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate. Preferably, the outer packaging of the secondary battery is a soft shell.

[0170] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape.

[0171] In some embodiments, secondary battery products of different shapes include a box body and a secondary battery of the present invention encapsulated in the box body. The box body may include a shell and a cover plate. The shell may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell has an opening connected to the receiving cavity, and the cover plate can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly through a winding process or a lamination process. The electrolyte is infiltrated into the electrode assembly to form a secondary battery cell of the present invention. The secondary battery cell is encapsulated in the receiving cavity. The number of secondary battery cells contained in the secondary battery may be one or more, and those skilled in the art can select according to specific actual needs.

[0172] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0173] In a battery module, multiple secondary batteries can be arranged in sequence along the length of the battery module. Of course, they can also be arranged in any other manner. Furthermore, the multiple secondary batteries can be fixed by fasteners.

[0174] Optionally, the battery module may further include a housing having an accommodation space, and the plurality of secondary batteries are accommodated in the accommodation space.

[0175] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0176] A battery pack may include a battery box and multiple battery modules disposed within the box. The battery box comprises an upper case and a lower case. The upper case can be placed over the lower case to form an enclosed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0177] In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0178] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0179] The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module may be used.

[0180] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0181] Example

[0182] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0183] Example 1

[0184] (1) Take a lithium-ion secondary battery with capacity decay; measure the active lithium loss rate P1 of the secondary battery as 20% according to the method described in the manual, and measure the discharge capacity C1 of the secondary battery in its current state as 116 mAh. The battery cell after the test is in a fully discharged state, that is, the capacity C3 that the secondary battery needs to be charged before its capacity is restored is 0. Then, calculate the capacity C that needs to be restored for the lithium-ion secondary battery with capacity decay as 29 mAh according to the following formula:

[0185] C=C2+C3-C1,

[0186] Where C2=C1 / (1-P1),

[0187] in,

[0188] P1 is the active lithium loss rate of the lithium-ion secondary battery with capacity decay;

[0189] C1 is the discharge capacity of the lithium-ion secondary battery in the current state with capacity decay;

[0190] C2 is the discharge capacity of the lithium-ion secondary battery when the positive electrode material accommodates active lithium to the maximum extent;

[0191] C3 is the capacity that the lithium-ion secondary battery with capacity decay needs to be charged before its capacity is restored;

[0192] The above capacities are all measured in Ah;

[0193] (2) Based on the capacity C required to be restored for the secondary battery obtained in step (1), the added mass m1 of tetramethyl-p-phenylenediamine is calculated to be 0.178 g:

[0194] m1=C*M1*1000 / (M li *3860), of which

[0195] M1 represents the relative molecular mass of p-phenylenediamine compounds, g / mol,

[0196] M li represents the relative atomic mass of lithium atom, g / mol,

[0197] 3860 represents the gram capacity of lithium metal, mAh / g.

[0198] Calculate the added mass m2 of lithium hexafluorophosphate to be 0.164g:

[0199] m2=C*M2*1000 / (n*Mli*3860), where

[0200] M2 represents the relative molecular mass of lithium salt, g / mol,

[0201] n represents the number of lithium atoms in the lithium salt,

[0202] M li represents the relative atomic mass of Li atom, g / mol,

[0203] 3860 represents the gram capacity of lithium metal, mAh / g.

[0204] The aforementioned amounts of tetramethyl-p-phenylenediamine and lithium hexafluorophosphate were dissolved in 16.058 g of a mixed solvent of ethylene carbonate and dimethyl carbonate in a mass ratio of 3:7 to provide a capacity recovery agent.

[0205] (3) Use a tool to cut open a corner of the soft-pack secondary battery cell and pour out the electrolyte. Then use a syringe to inject 10g of the capacity recovery agent obtained in step (2) into the lithium-ion secondary battery cell. Then use a heat sealer to seal the cell at 140°C for 10 seconds.

[0206] (4) leaving the battery cell at 25° C. for 48 hours to allow the capacity recovery agent to react inside the lithium-ion secondary battery;

[0207] (5) Cut open a corner of the battery cell from step (4) and pour out the liquid mixture inside the lithium-ion secondary battery after the reaction. Then inject 10g of DMC into the battery cell and soak it for 30 minutes, then pour it out. Repeat the above operation 6 times. Then dry the battery cell at 25℃ and vacuum at -0.1MPa for 30 minutes. Then inject the electrolyte into the battery cell. Then seal the battery cell using a heat sealer at 140℃ for 10 seconds.

[0208] Example 2-18

[0209] The same steps as in Example 1 were followed, except for the type and mass of the mixed solvent in the solvent recovery agent, the ratio of the different solvents in the mixed solvent, the battery charge state before recovery, and the reaction conditions. See Table 1 for details.

[0210] Comparative Example 1

[0211] The same steps as in Example 1 were performed, except that step (5) was not performed.

[0212] Comparative Example 2

[0213] The same steps as in Example 1 were followed, except that no p-phenylenediamine compound was added.

[0214] Comparative Example 3

[0215] The same procedure as in Example 1 was followed except that no lithium salt was added.

[0216] Comparative Example 4

[0217] The same steps as in Example 1 were followed, except that the p-phenylenediamine compound and the lithium salt were not added.

[0218] Table 1

[0219]

[0220]

[0221] Battery performance test

[0222] The discharge capacities of the batteries after capacity recovery in the above embodiments and comparative examples were tested before and after capacity recovery according to the method described in the specification, and the corresponding capacity recovery rates P were calculated. The results are recorded in Table 2.

[0223] Table 2

[0224]

[0225]

[0226] According to the above results, it can be seen that the capacity recovery rates of the lithium-ion secondary batteries of Examples 1-20 of the present invention all reach the ideal range after the capacity is restored by the method of the present invention, and the cycle retention rate of the battery after 500 cycles at 25°C after capacity recovery is still maintained at a high level (above 80%).

[0227] In contrast, in Comparative Example 1, where the capacity recovery agent was used directly without removing the reaction mixture after reaction, the capacity cycle retention rates were lower than those in the examples. Comparative Examples 2-4, where the capacity recovery agent did not contain lithium salts or p-phenylenediamine compounds, showed essentially no change in battery capacity after treatment using the same method as the present invention, failing to achieve the desired battery capacity recovery effect.

[0228] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for recovering the capacity of a lithium-ion secondary battery, characterized in that: The following steps are included: (1) Provide lithium-ion secondary batteries with capacity fading; (2) providing a capacity recovery agent, wherein the capacity recovery agent comprises a p-phenylenediamine compound, a lithium salt, and an organic solvent, wherein the organic solvent is used to dissolve the p-phenylenediamine compound and the lithium salt; (3) injecting the capacity recovery agent into the lithium-ion secondary battery; (4) causing the capacity recovery agent to react inside the lithium-ion secondary battery; (5) Pour out the liquid mixture inside the lithium-ion secondary battery after the reaction, and inject electrolyte into the lithium-ion secondary battery. In the capacity recovery agent, the content of the p-phenylenediamine compound is 0.5-15% by weight, and the content of the lithium salt is 0.5-15% by weight, and the above contents are based on the total mass of the capacity recovery agent.

2. The method according to claim 1, characterized in that In the step (1), the capacity-faded lithium-ion secondary battery is an active lithium-faded battery, and the capacity to be restored for the capacity-faded lithium-ion secondary battery is C. The calculation method of C is: C=C2+C3-C1, Where C2=C1 / (1-P1), in, P1 is the active lithium loss rate of the lithium-ion secondary battery with capacity decay; C1 is the discharge capacity of the lithium-ion secondary battery in the current state with capacity decay; C2 is the discharge capacity of the lithium-ion secondary battery when the positive electrode material can accommodate active lithium to the maximum extent; C3 is the capacity that the lithium-ion secondary battery with capacity decay needs to be charged before its capacity is restored; The above capacities are all measured in Ah.

3. The method according to claim 1, characterized in that The active lithium loss rate P1 of the lithium-ion secondary battery with capacity decay is greater than or equal to 5%.

4. The method according to claim 2, characterized in that In the step (2), the added mass m1 of the p-phenylenediamine compound in the capacity recovery agent and the capacity C required to be restored of the lithium-ion secondary battery with capacity decay satisfy: m1=C*M1*1000 / (M li *3860), of which, M1 represents the relative molecular mass of p-phenylenediamine compounds, g / mol, M li represents the relative atomic mass of lithium atom, g / mol, 3860 represents the gram capacity of lithium metal, mAh / g.

5. The method according to claim 2, characterized in that In step (2), the added mass m2 of the lithium salt in the capacity recovery agent and the capacity C required to be restored of the capacity-faded lithium-ion secondary battery satisfy: m2=C* M2*1000 / (n*M li *3860), of which, M2 represents the relative molecular mass of lithium salt, g / mol, n represents the number of lithium atoms in the lithium salt, M li represents the relative atomic mass of Li atom, g / mol, 3860 represents the gram capacity of lithium metal, mAh / g.

6. The method according to claim 1, characterized in that The p-phenylenediamine compound is selected from the compounds of Formula 1 and / or Formula 2: and / or Formula 1 Formula 2; Wherein, R1, R2, R3 and R4 are each independently a straight-chain or branched alkyl group having 1 to 3 carbon atoms or hydrogen; R5 and R6 are each independently hydrogen or a straight-chain or branched alkyl group having 1 to 3 carbon atoms.

7. The method according to claim 1, characterized in that The lithium salt is selected from one or more of lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(difluorosulfonylimide), LiCl, and LiBr.

8. The method according to claim 1, characterized in that In the capacity recovery agent, the content of the lithium salt is 0.5-6 wt %, based on the total mass of the capacity recovery agent.

9. The method according to claim 1, characterized in that In step (2), the organic solvent comprises a cyclic carbonate and a low-viscosity solvent.

10. The method according to claim 9, characterized in that The cyclic carbonate is ethylene carbonate (EC) or propylene carbonate (PC) or a combination thereof; the content of the cyclic carbonate is 10-30% by weight, based on the total weight of the organic solvent.

11. The method according to claim 9 or 10, characterized in that The low-viscosity solvent is one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl propionate, ethyl butyrate, ethyl propionate, propyl butyrate, tetrahydrofuran, and 1,3-dioxolane; the content of the low-viscosity solvent is 70-90% by weight, based on the mass of the organic solvent.

12. The method according to claim 1, characterized in that In step (4), the capacity recovery agent is allowed to react inside the lithium ion secondary battery by standing at 20-60°C.

13. The method according to claim 1, wherein In step (4), the capacity recovery agent may be reacted inside the lithium-ion secondary battery by ultrasound or heating.

14. The method according to claim 1, wherein In step (5), after the liquid mixture inside the lithium ion secondary battery after the reaction is poured out, an organic cleaning agent is injected for cleaning, and then vacuum drying is performed, and finally an electrolyte is injected into the lithium ion secondary battery.

15. A lithium ion secondary battery, characterized in that: It is a lithium ion secondary battery obtained by the method described in any one of claims 1 to 14, wherein the positive electrode active material of the lithium ion secondary battery is at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and olivine structure lithium-containing phosphate.

16. The lithium-ion secondary battery according to claim 15, characterized in that The lithium-containing phosphate with an olivine structure is at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

17. A battery module, characterized in that: The secondary battery according to claim 15 or 16 is included.

18. A battery pack, characterized in that: A battery module comprising the battery module according to claim 17.

19. An electrical device, characterized in that: The battery comprises at least one selected from the lithium-ion secondary battery according to claim 15 or 16, the battery module according to claim 17, or the battery pack according to claim 18.

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