Method for recovering the capacity of a lithium-ion secondary battery

Abstract

The present application provides a method for restoring capacity of a lithium-ion secondary battery, which includes the steps of: (1) providing a lithium-ion battery with a faded capacity; (2) providing a capacity recovery agent including lithium iodide and an organic solvent, where the organic solvent is used to dissolve the lithium iodide; (3) injecting the capacity recovery agent into the lithium-ion battery with a faded capacity; (4) reacting the capacity recovery agent inside the lithium-ion battery; and (5) pouring out the liquid mixture inside the lithium-ion battery after the reaction, and injecting an electrolyte into the lithium-ion battery.

Description

Technical Field

[0001] The present invention relates to the field of lithium-ion secondary batteries, and more specifically to a method for recovering the capacity of a lithium-ion secondary battery and a lithium-ion secondary battery obtained by this method.

Background Art

[0002] In recent years, as the application range of lithium-ion secondary batteries (also called "lithium-ion batteries") has become increasingly wide, lithium-ion batteries are widely used in energy storage power systems such as hydraulic, thermal, wind, and solar power plants, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. However, since lithium-ion secondary batteries are repeatedly used, their capacity gradually decreases, affecting their service life and safety. Currently, there is still a lack of in-depth research on the capacity recovery of lithium-ion secondary batteries with attenuated capacity.

Summary of the Invention

[0003] An object of the present invention is to provide a method for efficiently and accurately recovering the capacity of a lithium-ion secondary battery by using a capacity recovery agent that does not remain in large quantities inside the secondary battery and guarantees the cycle stability of subsequent use of the secondary battery.

[0004] To achieve the above object, the present application The first aspect provides a method for recovering the capacity of a lithium-ion secondary battery, which comprises: (1) providing a lithium-ion battery with attenuated capacity; (2) providing a capacity recovery agent containing lithium iodide and an organic solvent, wherein the organic solvent is used to dissolve the lithium iodide; (3) injecting the capacity recovery agent into the lithium-ion battery with attenuated capacity; (4) reacting the capacity recovery agent inside the lithium-ion battery; (5) discharging the liquid mixture inside the lithium-ion battery after the reaction, and injecting an electrolyte into the lithium-ion battery.

[0005] Thereby, the present application effectively restores the capacity of the lithium-ion secondary battery by using a specific type of capacity recovery agent and replacing it with a new electrolyte after the capacity recovery agent has reacted, and guarantees the cycle stability of subsequent use of the secondary battery.

[0006] In any of the embodiments, in step (1), the lithium-ion secondary battery with the attenuated capacity is an active lithium attenuated battery, the capacity that needs to be recovered for the lithium-ion battery with the attenuated capacity is C, and the calculation method of C is C = C2 + C3 - C1, where C2 = C1 / (1 - P1), where P1 is the active lithium loss rate of the lithium-ion battery with the attenuated capacity, C1 is the discharge capacity of the current state of the lithium-ion battery with the attenuated capacity, C2 is the discharge capacity corresponding to when the positive electrode material activity of the lithium-ion battery accommodates lithium to the maximum extent, C3 is the capacity that needs to be charged by charging before the capacity recovery of the lithium-ion battery with the attenuated capacity, Each of the above capacities is calculated based on Ah.

[0007] Thereby, the capacity that needs to be recovered for the lithium-ion secondary battery can be accurately calculated, and thereby accurate adjustment and control with a clear aim can be performed for the capacity recovery of the lithium-ion secondary battery.

[0008] In any of the embodiments, the active lithium loss rate P1 of the lithium-ion battery with the attenuated capacity is 5% or more. Thereby, the capacity of the lithium-ion secondary battery can be recovered by using the method of the present invention.

[0009] In any of the embodiments, in step (2), the added mass m of lithium iodide in the capacity recovery agent and the capacity C that needs to be recovered of the lithium-ion battery with attenuated capacity satisfy: m = C * M * 1000 / (n * M li * 3860), where: M represents the relative molecular mass of lithium iodide, g / mol; n represents the number of lithium atoms in lithium iodide; M li represents the relative atomic mass of Li atoms, g / mol; 3860 is the gram capacity of lithium metal, mAh / g.

[0010] Thereby, the mass of lithium iodide required can be accurately calculated, and thereby the recovery capacity of the lithium-ion secondary battery can be accurately controlled.

[0011] In any of the embodiments, in the capacity recovery agent of step (2), the content of lithium iodide is 0.5 - 15% by weight, optionally 0.5 - 6% by weight, calculated based on the total mass of the capacity recovery agent. Thereby, a specific content of lithium iodide in the capacity recovery agent can react better with the electrode plates inside the battery, thereby recovering the capacity of the lithium-ion secondary battery.

[0012] In any of the embodiments, in step (2), the organic solvent includes a cyclic carbonate and a low-viscosity solvent. Thereby, the specifically combined organic solvent can dissolve lithium iodide better, thereby recovering the capacity of the lithium-ion secondary battery.

[0013] In any of the embodiments, the cyclic carbonate is ethylene carbonate (EC) or propylene carbonate (PC) or a combination thereof, and the content of the cyclic carbonate is 10 - 30% by weight, calculated based on the total mass of the organic solvent. Thereby, the cyclic carbonate has a high dielectric constant and can ensure that lithium iodide has a relatively high solubility in the organic solvent.

[0014] In any of the embodiments, 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, 1,3-dioxolane, and the content of the low-viscosity solvent is 70 - 90% by weight, calculated based on the mass of the organic solvent. Thereby, the low-viscosity solvent of a specific type and content can alleviate the problem that the viscosity of the cyclic carbonate is too high, fully infiltrate the inside of the battery, and thereby ensure the capacity recovery of the lithium-ion secondary battery.

[0015] In any of the embodiments, in step (4), the capacity recovery agent is reacted inside the lithium-ion secondary battery by standing at 20 - 60°C. Under the reaction conditions, the capacity recovery agent can fully infiltrate the inside of the lithium-ion secondary battery and ensure the capacity recovery of the lithium-ion secondary battery.

[0016] In any of the embodiments, in step (4), the capacity recovery agent can be reacted inside the lithium-ion battery by ultrasonic waves or heating. Thereby, the infiltration of the capacity recovery agent into the electrode plate inside the lithium-ion secondary battery can be accelerated, the reaction rate can be accelerated, and the efficiency of the capacity recovery of the secondary battery can be improved.

[0017] In any of the embodiments, in step (5), after pouring out the liquid mixture inside the lithium-ion secondary battery after the reaction, an organic cleaning agent is injected for cleaning, and then vacuum drying is performed, and finally an electrolyte is injected into the lithium-ion battery. Thereby, the capacity recovery agent is prevented from remaining inside the battery, and the cycle stability and safety after the capacity recovery of the lithium-ion secondary battery are ensured.

[0018] The second aspect of the present application provides a lithium-ion secondary battery, which is a lithium-ion secondary battery obtained by the method described in the first aspect of the present application. 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 lithium-containing phosphate with an olivine structure. Optionally, The lithium-containing phosphate with an olivine structure is characterized by being 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 manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

[0019] The third aspect of the present application provides a battery module, which includes the secondary battery of the second aspect of the present application.

[0020] The fourth aspect of the present application provides a battery pack, which includes the battery module of the third aspect of the present application.

[0021] The fifth aspect of the present application provides a power consumption device, which includes 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.

[0022] This application adds a capacity recovery agent containing lithium iodide to a lithium-ion secondary battery with attenuated capacity, replenishes active lithium to the positive electrode plate inside the lithium-ion secondary battery, activates the inactive lithium of the negative electrode, ensures highly efficient and accurate control over the capacity recovery of the lithium-ion secondary battery, replaces it with a new electrolyte after the capacity recovery agent has reacted, and eliminates 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

[0023]

Figure 1

Embodiments for Carrying Out the Invention

[0024] Hereinafter, with appropriate reference to the drawings, embodiments specifically disclosing the method for recovering the capacity of the lithium-ion secondary battery of this application, the corresponding secondary battery, battery module, battery pack, and electrical device will be described in detail. However, detailed descriptions that are not necessary may be omitted. For example, detailed descriptions of well-known matters and duplicate descriptions of structures that are actually the same may be omitted. This is to avoid making the following description unnecessarily long and to enable those skilled in the art to easily understand. Note that the drawings and the following description are provided to enable those skilled in the art to fully understand this application and do not limit the theme described in the claims.

[0025] The "ranges" disclosed in this application are limited in the form of a lower limit and an upper limit. A given range is defined by selecting one lower limit and one upper limit, and the selected lower limit and upper limit define the boundaries of a specific range. The ranges thus defined may or may not include the end values, and any combination is possible, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a particular parameter, it is understood that ranges of 60 - 110 and 80 - 120 are also possible. Also, if the minimum range values 1 and 2 are listed, and the maximum range values 3, 4, and 5 are listed, all ranges of 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5 are possible. In this application, unless otherwise specified, the numerical range "a - b" represents a shortened expression of any combination of real numbers from a to b, where both a and b are real numbers. For example, the numerical range "0 - 5" represents that all real numbers between "0 - 5" have already been listed in this specification, and "0 - 5" is only a shortened expression of combinations of these numbers. Also, when a parameter is expressed as an integer ≧ 2, it is equivalent to disclosing that this parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0026] Unless otherwise specified, all embodiments and alternative embodiments of this application can be combined with each other to form a new technical solution.

[0027] Unless otherwise specified, all technical features and alternative technical features of this application can be combined with each other to form a new technical solution.

[0028] Unless otherwise specified, all steps of this application may be performed in order or randomly, and preferably, they are performed in order. For example, the fact that the method includes steps (a) and (b) means that the method may include steps (a) and (b) performed in order, or steps (b) and (a) performed in order. For example, the fact that the method mentioned above may further include step (c) means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), may include steps (a), (c) and (b), may include steps (c), (a) and (b), etc.

[0029] Unless otherwise specified, "including" and "comprising" mentioned in this application represent an open type and may also be a closed type. For example, the above "including" and "comprising" may further include or comprise other components not listed, or may include or comprise only the listed components.

[0030] Unless otherwise specified, in this application, the term "or" is inclusive. For example, the phrase "A or B" represents "A, B, or both A and B". More specifically, any of the conditions where A is true (or exists) and B is false (or does not exist), where A is false (or does not exist) but B is true (or exists), and where both A and B are true (or exist) satisfy "A or B".

[0031] Currently, lithium-ion secondary batteries are widely used in various fields, and the usage amount is huge. During use, repeated charging and discharging cause the capacity to gradually decay. Most of the conventional technical solutions add lithium replenishing additives to the battery core of a fresh battery to make the initial active lithium content in the battery core relatively high, but do not mention the recovery after the capacity of the battery has decayed. Regarding the capacity recovery of a secondary battery with decayed capacity, the research of those skilled in the art is very little. It only mentions that a capacity recovery agent can be added to a secondary battery with decayed capacity, but the degree of capacity recovery is limited and it is impossible to achieve precise adjustment and control of the capacity recovery. Moreover, the capacity recovery agent still exists in the electrolyte system after the capacity has recovered, which affects the cycle stability of the battery core in the later stage. Through a large amount of research, the inventor has found that the method of the first aspect of the present invention can accurately control the addition of a capacity recovery agent of a specific type and content and replace the electrolyte, so as to accurately recover the capacity of the lithium-ion secondary battery with high efficiency, and the capacity recovery agent does not remain inside the secondary battery, ensuring the cycle stability of the subsequent use of the secondary battery.

[0032] Method for recovering the capacity of a lithium-ion secondary battery In one embodiment of the present application, referring to FIG. 1, the present application provides a method for recovering the capacity of a lithium-ion secondary battery, which includes (1) providing a lithium-ion battery with decayed capacity; (2) providing a capacity recovery agent containing lithium iodide and an organic solvent, wherein the organic solvent is used to dissolve the lithium iodide; (3) injecting the capacity recovery agent into the lithium-ion battery with decayed capacity; (4) reacting the capacity recovery agent inside the lithium-ion battery; (5) pouring out the liquid mixture inside the lithium-ion battery after the reaction and injecting an electrolyte into the lithium-ion battery.

[0033] Although the mechanism is not yet clear, the applicant has unexpectedly discovered the following. This application uses a capacity recovery agent containing lithium iodide and, after the capacity recovery agent has reacted, replaces it with a new electrolyte, thereby effectively recovering the capacity of the lithium-ion secondary battery and ensuring the cycle stability of subsequent use of the secondary battery. Specifically, taking a lithium iron phosphate-based lithium-ion secondary battery as an example, lithium iodide reacts with iron phosphate in the lithium-depleted state cathode to form lithium iron phosphate and triiodide ions (I3 - ), 2Li + +3I - +2FePO4 = 2LiFePO4 + I3 - That is, During this reaction, lithium in lithium iodide enters the cathode through a redox reaction as an additional lithium source, increasing the total amount of available active lithium inside the secondary battery.

[0034] At the same time, at the anode, triiodide ions (I3 - ) can react with inactive lithium (lithium oxide in the SEI film (solid electrolyte interface film) and lithium precipitated from the anode surface) to form soluble LiI, 3Li2O + 3I3 - = 6Li + + IO3 - + 8I - That is, Soluble LiI can also react with FePO4 at the cathode to form LiFePO4, 2Li + I3 - = 2Li + + 3I - That is, Therefore, this realizes the activation of inactive lithium, thereby realizing the capacity recovery of the secondary battery.

[0035] The term "active lithium" represents lithium ions that can participate in the occurrence of redox reactions during charge and discharge in the battery.

[0036] In some embodiments, in the step (1), the lithium-ion secondary battery with the attenuated capacity is an active lithium attenuated battery, the capacity that needs to be restored for the lithium-ion battery with the attenuated capacity is C, and the calculation method of the C is C = C2 + C3 - C1, where C2 = C1 / (1 - P1), where P1 is the active lithium loss rate of the lithium-ion battery with the attenuated capacity, C1 is the discharge capacity of the current state of the lithium-ion battery with the attenuated capacity, C2 is the discharge capacity corresponding to when the cathode material activity of the lithium-ion battery accommodates lithium to the maximum extent, C3 is the capacity that needs to be charged by charging before the capacity recovery of the lithium-ion battery with the attenuated capacity, Each of the above capacities is calculated based on Ah.

[0037] Thereby, the capacity that needs to be restored for the lithium-ion secondary battery can be accurately calculated, and thereby, accurate adjustment and control with a clear aim can be performed for the capacity recovery of the lithium-ion secondary battery.

[0038] The "active lithium attenuated battery" is a secondary battery in which the active lithium of the positive electrode gradually decreases after the first formation and / or during use.

[0039] The calculation method of the active lithium loss rate P1 of the lithium-ion secondary battery with the attenuated capacity is The active lithium loss rate P1 = (C20 - C10) / C20, where C10 is the capacity corresponding to the active lithium of the current state of the battery cathode at 154.025mm 2 and C20 is the capacity corresponding to the active lithium that can be accommodated by the battery cathode at 154.025mm 2 and is the capacity corresponding to the active lithium that can be accommodated by the battery cathode.

[0040] The test methods for C10 and C20 are as follows.

[0041] Take the cathode plate of the fully discharged battery and use a sheet punching machine to punch the cathode plate into a circular sheet with an area of 154.025 mm 2 of this size 、 Manufacture this cathode and lithium button battery. Charge the button battery, and record its charge capacity as C10 as shown in Table 1. After discharging and then charging the above button battery, record its recharge capacity as C20 as shown in Table 2 (here, the loss of active lithium due to the loss of cathode active material is not considered). Here, refer to Table 3 for the U1 and U2 values of different lithium-ion secondary batteries.

[0042]

Table 1

[0043]

Table 2

[0044]

Table 3

[0045] When the secondary battery recovers its capacity in a fully discharged state, C3 is 0 Ah, and C = C2 - C1.

[0046] In some embodiments, the loss rate P1 of active lithium in the lithium-ion secondary battery with the attenuated capacity is 5% or more. Thereby, the capacity of the lithium-ion secondary battery can be recovered using the method of the present invention.

[0047] In some embodiments, in step (2), the added mass m of lithium iodide in the capacity recovery agent and the capacity C that needs to be recovered of the lithium-ion battery with the attenuated capacity satisfy m = C * M * 1000 / (n * M li * 3860), where M represents the relative molecular mass of lithium iodide, in g / mol, n represents the number of lithium atoms in lithium iodide, M li represents the relative atomic mass of a Li atom, in g / mol, 3860 is the gram capacity of lithium metal, in mAh / g.

[0048] Thereby, the mass of the required lithium iodide can be accurately calculated, thereby accurately controlling the recovery capacity of the lithium-ion secondary battery.

[0049] In some embodiments, in the capacity recovery agent, the content of lithium iodide is 0.5-15 wt%, optionally 0.5-6 wt%, calculated based on the total mass of the capacity recovery agent. Thereby, a specific content of lithium iodide in the capacity recovery agent reacts better with the electrode plate inside the battery, thereby recovering the capacity of the lithium-ion secondary battery. When the capacity that needs to be recovered by the lithium-ion secondary battery is constant, the lower the concentration of lithium iodide in the capacity recovery agent, the greater the total amount of the required capacity recovery agent. Therefore, it is difficult for the concentration of lithium iodide to be lower than 0.5 wt%. At the same time, the higher the concentration of lithium iodide, the greater the viscosity of the solvent recovery agent, whereby the capacity recovery agent is difficult to diffuse on the electrode plate, and the capacity recovery effect of the cathode electrode plate is unevenly distributed, and ultimately the middle part of the electrode plate cannot react with the capacity recovery agent and cannot recover the capacity. Therefore, it is difficult for the concentration of lithium iodide to be higher than 15 wt%.

[0050] In some embodiments, in step (2), the organic solvent includes a cyclic carbonate and a low-viscosity solvent. The cyclic carbonate has a high dielectric constant and can ensure that lithium iodide has a relatively high solubility in the organic solvent, so that even if a small amount of capacity recovery agent is added, the expected capacity recovery effect can be achieved. However, the cyclic carbonate has a relatively high viscosity, which affects the diffusion of the capacity recovery agent between the electrodes, preventing the middle position of the electrode from being well infiltrated, unable to participate in the reaction, or reducing the reaction time between the middle position and the solvent recovery agent, so that the middle part of the electrode cannot be well activated. At this time, a low-viscosity solvent is added to reduce the viscosity of the system and fully infiltrate the electrode, thereby ensuring that the electrode is fully activated.

[0051] In some embodiments, the cyclic carbonate is ethylene carbonate (EC) or propylene carbonate (PC) or a combination thereof, preferably ethylene carbonate. The content of the cyclic carbonate is 10-30% by weight, preferably 20-30% by weight, calculated based on the total mass of the organic solvent. Thereby, a specific type of cyclic carbonate further ensures that lithium iodide has a relatively high solubility in the organic solvent, so that even if a small amount of capacity recovery agent is added, the expected capacity recovery effect can be achieved.

[0052] In some embodiments, the low-viscosity solvent is one or more of dimethyl carbonate (DMC), 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, 1,3-dioxolane, preferably dimethyl carbonate. The content of the low-viscosity solvent is 70-90% by weight, preferably 70-80% by weight, calculated based on the mass of the organic solvent. Thereby, a specific type and content of the low-viscosity solvent can alleviate the problem that the viscosity of the cyclic carbonate is too high, fully infiltrate the inside of the battery, and thereby guarantee the capacity recovery of the lithium-ion secondary battery.

[0053] In some embodiments, in step (3), the capacity recovery agent is injected into the lithium-ion battery with attenuated capacity. Before injecting the capacity recovery agent, the electrolyte in the battery may be drained, or the capacity recovery agent may be directly injected without draining the electrolyte. Preferably, the electrolyte in the battery is drained before injecting the capacity recovery agent. As should be understood by those skilled in the art, when the capacity attenuation of the lithium-ion battery is severe, the free electrolyte remaining in the battery is very little, and at this time, the capacity recovery agent can be directly injected into the battery. The injection method of the capacity recovery agent may be any method known to those skilled in the art, such as injection with a syringe.

[0054] In some embodiments, in step (4), the capacity recovery agent is reacted inside the lithium-ion battery by standing at 20-60°C, preferably at a temperature of 20-45°C. Generally, the standing time is 24-72 hours, preferably 45-55 hours. Under the said reaction conditions, the capacity recovery agent can fully infiltrate the inside of the lithium-ion secondary battery and guarantee the capacity recovery of the lithium-ion secondary battery.

[0055] In some embodiments, in step (4), the capacity recovery agent can be reacted inside the lithium-ion battery by ultrasonic waves or heating. In some embodiments, ultrasonic waves can be applied at a frequency of 25 KHz - 80 KHz, preferably 30 - 50 KHz for 2 - 4 h, preferably 2 h, thereby accelerating 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 1 - 4 h, thereby accelerating the reaction of the capacity recovery agent inside the lithium-ion secondary battery. Thereby, the infiltration of the capacity recovery agent into the electrode plate inside the lithium-ion secondary battery can be accelerated, the reaction rate can be accelerated, and the efficiency of capacity recovery of the secondary battery can be improved.

[0056] In some embodiments, in step (5), after pouring out the liquid mixture inside the lithium-ion battery after the reaction, an organic cleaning agent is injected for cleaning, and then vacuum drying is performed, and finally an electrolyte is injected into the lithium-ion battery. Thereby, the capacity recovery agent is prevented from remaining inside the battery, and the cycle stability and safety after capacity recovery of the lithium-ion secondary battery are guaranteed.

[0057] In some embodiments, the organic cleaning agent is the same as the above low-viscosity solvent, preferably DMC. After cleaning using the organic cleaning agent, generally at 20 - 45 °C, preferably at room temperature, the secondary battery is vacuum dried at a vacuum degree of -0.08 to -0.1 MPa. Generally, vacuum drying is performed for 0.2 - 1 hour, preferably 0.5 hour.

[0058] In some embodiments, by implementing the method of the present application, the capacity recovery rate of the lithium-ion secondary battery is 0.5% - 15%.

[0059] The capacity recovery rate P of the secondary battery is calculated by the formula P = (Ca - Cb) / Cb * 100%, where Cb is the discharge capacity of the battery before capacity recovery, calculated based on Ah, Ca is the discharge capacity of the battery after capacity recovery and is calculated based on Ah.

[0060] The test methods for Ca and Cb are as follows.

[0061] At 25 °C, charge the lithium-ion secondary battery at a constant current of 0.04C to U 10 then let it stand for 5 min, and then discharge it at 0.04C to U 20 and record the obtained discharge capacity as the initial discharge capacity C0. Here, the values of U 10 and U 20 refer to Table 4.

[0062]

Table 4

[0063] Repeat the above steps three times for the same battery, and simultaneously record the discharge capacity Cn of the battery after the nth time. Take the average value of the three discharge capacities as the discharge capacity Cb of the battery before capacity recovery. After recovering the capacity of the battery, repeat the above charge-discharge process three times, and take the average value of the three discharge capacities as the discharge capacity Ca of the battery after capacity recovery.

[0064] The test method for the current state capacity C1 of the lithium-ion secondary battery with attenuated capacity is the same as the test method for Cb.

[0065] The second aspect of this application provides a lithium-ion secondary battery, which is a lithium-ion secondary battery obtained by the method described in the first aspect of this application. 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-structured lithium-containing phosphate. Optionally, The lithium-containing phosphate of the olivine structure is characterized by being 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 manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

[0066] Generally, a secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During charging and discharging of the battery, active ions are intercalated and deintercalated reciprocally between the positive electrode plate and the negative electrode plate. The electrolyte serves to conduct ions between the positive electrode plate and the negative electrode plate. The separator is installed between the positive electrode plate and the negative electrode plate, mainly serving to prevent short circuit between the positive and negative electrodes and allowing ions to pass through.

[0067] [Positive Electrode Plate] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, and the positive electrode film layer contains the positive electrode active material of the first aspect of the present application.

[0068] As an example, the positive electrode current collector has two surfaces facing each other in its own thickness direction, and the positive electrode film layer is provided on either one or both of the two opposing surfaces of the positive electrode current collector.

[0069] In some embodiments, the positive electrode current collector may employ a metal foil sheet or a composite current collector. For example, as the metal foil sheet, an aluminum foil may be employed. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer material substrate (such as substrates of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0070] In some embodiments, the cathode active material can employ a cathode active material used in batteries known in the art. By way of example, the cathode active material can be lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which may be abbreviated as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which may be abbreviated as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which may be abbreviated as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which may be abbreviated as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which may be abbreviated as NCM811), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05 O2), and at least one of olivine-structured lithium-containing phosphates. Optionally, the olivine-structured lithium-containing phosphate may include at least one of lithium iron phosphate (e.g., LiFePO4 (which may be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon, but is not limited thereto. However, the present application is not limited to these materials, and conventional materials that can be used as other battery cathode active materials may also be used. These cathode active materials may be used alone or in combination of two or more.

[0071] In some embodiments, the positive electrode film layer further selectively contains an adhesive. For example, the adhesive may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0072] In some embodiments, the positive electrode film layer further selectively contains 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.

[0073] In some embodiments, the positive electrode plate can be manufactured in the following manner. Components for manufacturing the positive electrode plate, such as the positive electrode active material, conductive agent, adhesive, 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 processes such as drying and cold pressing, a positive electrode plate is obtained.

[0074] [Negative electrode plate] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, and the negative electrode film layer contains a negative electrode active material.

[0075] For example, the negative electrode current collector has two opposing surfaces in its own thickness direction, and the negative electrode film layer is disposed on either one or both of the two opposing surfaces of the negative electrode current collector.

[0076] In some embodiments, the negative electrode current collector may employ a metal foil sheet or a composite current collector. For example, a copper foil may be employed as the metal foil sheet. The composite current collector has a polymer material-based layer and a polymer material Base layerIt may include a metal layer formed on at least one surface thereof. The composite current collector may be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer material substrate (such as substrates of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0077] In some embodiments, the negative electrode active material can employ a negative electrode active material known in the art for use in batteries. By way of example, the negative electrode active material may include at least one material among artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be selected from at least one of silicon alone, silicon oxide, silicon carbon composite, silicon nitride composite, and silicon alloy. The tin-based material may be selected from at least one of tin alone, tin oxide, and tin alloy. However, this application is not limited to these materials, and conventional materials that can be used as other battery negative electrode active materials may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0078] In some embodiments, the negative electrode film layer further selectively includes an adhesive. The adhesive 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).

[0079] In some embodiments, the negative electrode film layer further selectively includes a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0080] In some embodiments, the negative electrode film layer further selectively includes other auxiliaries, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0081] In some embodiments, the negative electrode plate can be manufactured in the following manner. Components for manufacturing the negative electrode plate, such as the negative electrode active material, the conductive agent, the adhesive, and any other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry. The negative electrode slurry is coated on the negative electrode current collector, and after undergoing processes such as drying and cold pressing, a negative electrode plate is obtained.

[0082] [Electrolyte] The electrolyte functions to conduct ions between the positive electrode plate and the negative electrode plate. This application is not specifically limited to the type of electrolyte and can be selected according to demand. For example, the electrolyte may be liquid, gel-like, or all-solid.

[0083] In some embodiments, an electrolytic solution is employed as the electrolyte. The electrolytic solution includes an electrolyte salt and a solvent.

[0084] 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 difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

[0085] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl 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, sulfolane, dimethyl sulfone, ethyl methyl sulfone, and diethyl sulfone.

[0086] In some embodiments, the electrolyte further selectively contains additives. For example, the additives may include negative electrode film-forming additives and positive electrode film-forming additives, and may further include additives that can improve some performances of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high-temperature or low-temperature performance of the battery, and the like.

[0087] [Separator] In some embodiments, the secondary battery further includes a separator. The present application is not particularly limited to the type of the separator, and any known porous structure separator with good chemical stability and mechanical stability may be selected.

[0088] In some embodiments, the material of the separator may be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, and there is no particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, and there is no particular limitation.

[0089] In some embodiments, the positive electrode plate, the negative electrode plate, and the separator can be manufactured into an electrode assembly by a winding process or a lamination process.

[0090] In some embodiments, the secondary battery may include an exterior body. This exterior body may be used to package the electrode assembly and the electrolyte.

[0091] In some embodiments, the exterior body of the secondary battery may be a rigid case, such as a rigid plastic case, an aluminum case, a steel case, etc. The exterior body of the secondary battery may be a pouch, such as a bag-shaped pouch. The material of the pouch may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate. A preferred exterior body of the secondary battery is a pouch.

[0092] This application is not particularly limited to the shape of the secondary battery, and it may be cylindrical, square, or any other arbitrary shape.

[0093] In some embodiments, secondary battery products of different shapes include a housing and the secondary battery of the present invention packaged within the housing. The housing may include a case and a cover plate. Here, the case may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates surround to form a receiving cavity. The case has an opening communicating with the receiving cavity, and the cover plate can cover the opening so as to seal the receiving cavity. The positive electrode plate, the negative electrode plate, and the separator can form an electrode assembly by a winding process or a lamination process. The electrolyte is infiltrated into the electrode assembly to form the secondary battery cell of the present invention. The secondary battery cell is packaged within the receiving cavity. The number of secondary battery cells included may be one or more, and those skilled in the art can specifically select according to actual needs. Into the pond The number of secondary battery cells included may be one or more, and those skilled in the art can select specifically according to actual needs.

[0094] In some embodiments, the secondary battery may be assembled into a battery module, and the number of secondary batteries included in the battery module may 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.

[0095] In a battery module, a plurality of secondary batteries may be arranged in order along the longitudinal direction of the battery module. Of course, they may be arranged in any other manner. Further, these plurality of secondary batteries may be fixed by fasteners.

[0096] Optionally, the battery module may further include a housing having an accommodation space, and the plurality of secondary batteries are accommodated in this accommodation space.

[0097] In some embodiments, the battery module may be further assembled into a battery pack. The number of battery modules included in the battery pack may be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0098] The battery pack may include a battery box and a plurality of battery modules installed in the battery box. The battery box includes an upper housing and a lower housing. The upper housing covers the lower housing and can form a sealed space for accommodating the battery module. The plurality of battery modules may be arranged in the battery box in any manner.

[0099] In addition, the present application further provides a power consumption device, and the power consumption device includes at least one of the secondary battery, battery module, or battery pack according to the present application. The secondary battery, battery module, or battery pack may be used as a power source of the power consumption device or as an energy storage unit of the power consumption device. The power consumption device may include, but is not limited to, mobile devices (such as mobile phones, notebook computers, 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.

[0100] As the power consumption device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0101] This power consumption device is, for example, a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the demand for high output and high energy density of the secondary battery of this power consumption device, a battery pack or a battery module can be adopted.

[0102] As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. This device generally requires thinning and can adopt a secondary battery as a power source.

[0103] Examples Hereinafter, examples of the present application will be described. The examples described below are illustrative only and are merely for interpreting the present application and should not be construed as a limitation on the present application. When specific technologies or conditions are not specified in the examples, the technologies or conditions described in the literature in this field or as described in the product specification are followed. The reagents or instruments used are all ordinary products that can be obtained commercially when the manufacturer is not specified.

[0104] Example 1 (1) Take one lithium iron phosphate secondary battery with attenuated capacity, measure that the active lithium loss rate P1 of the secondary battery is 20% by the method described in the specification, and measure that the discharge capacity C1 of the current state of the battery is 116 mAh. The tested battery core is in a fully discharged state, that is, the capacity C3 that needs to be charged by charging before the capacity recovery of the battery is 0. Then, it is calculated by the following formula that the capacity C that needs to be recovered for the lithium iron phosphate battery with attenuated capacity is 29 mAh, C = C2 + C3 - C1, where C2 = C1 / (1 - P1), where Here P1 is the active lithium loss rate of the lithium iron phosphate battery with attenuated capacity, C1 is the discharge capacity of the current state of the lithium iron phosphate battery with attenuated capacity, C2 is the discharge capacity corresponding to the case where the cathode material of the lithium iron phosphate battery accommodates the maximum amount of active lithium. C3 is the capacity that needs to be charged by charging before the capacity recovery of the lithium iron phosphate battery with the attenuated capacity. Each of the above capacities is calculated based on Ah. (2) Based on the capacity C that needs to be recovered of the lithium iron phosphate battery obtained in step (1), calculate that the added mass m of lithium iodide is 0.146 g. m = C * M * 1000 / (n * M li * 3860), where M represents the relative molecular mass of lithium iodide, g / mol. n represents the number of lithium atoms in lithium iodide. M li represents the relative atomic mass of Li atoms, g / mol. 3860 represents the gram capacity of lithium metal, mAh / g.

[0105] Dissolve the above amount of lithium iodide in a mixed solvent of ethylene carbonate and dimethyl carbonate with a mass ratio of 3:7 of 14.6 g to provide a capacity recovery agent. (3) Use a tool to shear a corner of the battery core of the pouch lithium iron phosphate battery and pour out the electrolyte. Subsequently, use a syringe to inject 10 g of the capacity recovery agent obtained in step (2) into the battery core of the lithium-ion secondary battery. Then use a heat sealer to seal the battery core, and the packaging conditions are 140 °C and 10 s.

[0106] (4) Let the above battery core stand at 25 °C for 48 h to react the capacity recovery agent inside the lithium iron phosphate battery. (5) One corner of the battery core in step (4) was sheared, and the liquid mixture inside the lithium iron phosphate battery after the reaction was poured out. Subsequently, 10 g of DMC was injected into the battery core, soaked for 30 min, and then poured out. The above operations were repeated 6 times. Then the battery core was dried at 25°C under a vacuum of -0.1 MPa for 30 min. Subsequently, electrolyte was injected into the battery core. Then the battery core was sealed using a heat sealer, and the packaging conditions were 140°C and 10 s.

[0107] Example 2 - 18 Except for changing the type, mass of the mixed solvent in the solvent recovery agent, the ratio of different solvents in the mixed solvent, the type of battery, the state of charge of the battery before recovery, and the reaction conditions, it was carried out according to the same steps as in Example 1. Details are shown in Table 1.

[0108] Comparative Example 1 It was carried out according to the same steps as in Example 1, except that the electrolyte was not poured out in step (3) and step (5) was not carried out.

[0109] Comparative Example 2 It was carried out according to the same steps as in Example 1, except that lithium iodide was not added.

[0110]

Table 5

[0111] Battery performance test For the batteries after capacity recovery in the above examples and comparative examples, the discharge capacity before and after capacity recovery was tested by the method described in the specification, and the corresponding capacity recovery rate P was calculated. The results are shown in Table 2.

[0112]

Table 6

[0113] As can be seen from the above results, after the lithium-ion secondary batteries of Examples 1-17 of the present invention were subjected to capacity recovery by the method of the present invention, the capacity recovery rate of each of them reached an ideal range (all were 5% or more, and ultimately reached 20% or more), and the cycle retention rate after 500 cycles at 25°C of the battery after capacity recovery still maintained a relatively high level (80% or more).

[0114] In comparison, the capacity recovery agent of Comparative Example 1 had a capacity recovery rate of 13% when directly used without pouring out the reaction mixture after the reaction, but the cycle retention rate was only 80%, both of which were lower than those of the examples. The capacity recovery agent of Comparative Example 2 did not contain lithium iodide, and after the battery was treated using the same method as the present invention, the capacity of the battery hardly changed, and the effect of battery capacity recovery could not be realized.

Claims

1. A method for restoring the capacity of a lithium-ion battery, comprising: (1) providing a lithium-ion battery with a decreased capacity; (2) providing a capacity restoration agent containing lithium iodide and an organic solvent, wherein the organic solvent is used to dissolve the lithium iodide; (3) injecting the capacity restoration agent into the lithium-ion battery with the decreased capacity; (4) reacting the capacity restoration agent inside the lithium-ion battery; (5) pouring out the liquid mixture inside the lithium-ion battery after the reaction and injecting an electrolyte into the lithium-ion battery. The method for restoring the capacity of a lithium-ion battery is characterized by the above steps.

2. In the step (1), the lithium-ion secondary battery with the decreased capacity is an active lithium-decayed battery. The capacity to be restored of the lithium-ion battery with the decreased capacity is C. The calculation method of C is: C = C2 + C3 - C1, where C2 = C1 / (1 - P1), and here, P1 is the active lithium loss rate of the lithium-ion battery with the decreased capacity; C1 is the discharge capacity of the current state of the lithium-ion battery with the decreased capacity; C2 is the discharge capacity corresponding to when the positive electrode material activity of the lithium-ion battery accommodates lithium to the maximum extent; C3 is the capacity that needs to be charged by charging before the capacity of the lithium-ion battery with the decreased capacity is restored. Each of the above capacities is calculated based on Ah. The method according to claim 1 is characterized by the above.

3. The active lithium loss rate P1 of the lithium-ion battery with the decreased capacity is 5% or more. The method according to claim 1 or 2 is characterized by the above.

4. In the step (2), the added mass m of lithium iodide in the capacity restoration agent and the capacity C that needs to be restored of the lithium-ion battery with the decreased capacity satisfy: m = C * M * 1000 / (n * M li * 3860) is satisfied, where M represents the relative molecular mass of lithium iodide, g / mol; n represents the number of lithium atoms in lithium iodide; M li represents the relative atomic mass of Li atoms, g / mol, and 3860 is the gram capacity of lithium metal, mAh / g. The method according to claim 2 is characterized by the above.

5. In the capacity restoration agent in the step (2), the content of lithium iodide is 0.5 - 15% by weight, calculated based on the total mass of the capacity restoration agent. The method according to claim 1 or 2 is characterized by the above.

6. In the step (2), the organic solvent contains a cyclic carbonate and a low-viscosity solvent, and the method according to claim 1 or 2 is characterized in that.

7. The cyclic carbonate is ethylene carbonate (EC) and / or propylene carbonate (PC), and the content of the cyclic carbonate is 10-30% by weight, calculated based on the mass of the organic solvent, and the method according to claim 6 is characterized in that.

8. 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, 1,3-dioxolane, and the content of the low-viscosity solvent is 70-90% by weight, calculated based on the total mass of the organic solvent, and the method according to claim 6 is characterized in that.

9. In the step (4), the capacity recovery agent is reacted inside the lithium-ion battery by standing at 20-60°C, and the method according to claim 1 or 2 is characterized in that.

10. In the step (4), the capacity recovery agent can be reacted inside the lithium-ion battery by ultrasonic waves or heating, and the method according to claim 8 is characterized in that.

11. In the step (5), after pouring out the liquid mixture inside the lithium-ion battery after the reaction, an organic cleaning agent is injected for cleaning, and then vacuum drying is performed, and finally an electrolyte is injected into the lithium-ion battery, and the method according to claim 1 or 2 is characterized in that.

12. The positive electrode active material of the lithium-ion 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 lithium-containing phosphate with an olivine structure, and the method according to claim 1 or 2 is characterized in that.

Images