JP7647838B2 - Recycled lithium-ion secondary batteries - Google Patents

Description

The present invention relates to a method for regenerating lithium-ion secondary batteries and regenerated lithium-ion secondary batteries.

In recent years, due to growing international environmental awareness, eco-friendly vehicles, such as hybrid vehicles and plug-in hybrid vehicles, which emit less carbon dioxide, are becoming more and more popular. There is a strong demand for the development of lithium-ion secondary batteries with excellent output characteristics and charge/discharge cycle characteristics as batteries for eco-friendly vehicles.

A common type of lithium-ion secondary battery is the non-aqueous electrolyte secondary battery. Non-aqueous electrolyte secondary batteries are composed of a positive electrode, a negative electrode, and an electrolyte, and the positive electrode and negative electrode use a material that allows lithium intercalation, that is, the reversible insertion and removal of lithium ions. By placing an electrolyte between the positive electrode and the negative electrode, electrochemical energy can be obtained by utilizing the oxidation-reduction reaction that occurs when lithium ions are inserted and removed from the positive electrode and the negative electrode.

Positive electrode active materials for lithium ion secondary batteries include lithium cobalt composite oxide (LiCoO ₂ ), which is relatively easy to manufacture, lithium nickel composite oxide (LiNiO ₂ ), which uses nickel, which is cheaper than cobalt, and lithium manganese composite oxide (LiMn ₂ O ₄ ), which uses manganese, as well as lithium metal composite oxides such as lithium nickel manganese cobalt composite oxide (NMC) and lithium nickel cobalt aluminum composite oxide (NCA).

For automotive use, the most important factor is cost, so inexpensive carbon-based materials are used as negative electrode active materials, but for battery testing and evaluation, metallic lithium, lithium alloys, lithium metal oxides, or metals that form alloys with lithium can also be used.

Recently, all-solid-state secondary batteries using solid electrolytes have also been attracting much attention. All-solid-state secondary batteries are composed of a positive electrode, a negative electrode, and a lithium ion conductive solid electrolyte, and as the active materials for both the positive and negative electrodes, materials capable of desorbing and inserting lithium ions are used, as in the above case. In particular, all-solid-state batteries using lithium metal composite oxides with a layered or spinel structure as the positive electrode active material can obtain a high voltage of 4.5 V or more, and are therefore expected to be batteries with high energy density.

As mentioned above, the lithium metal composite oxide used in the positive electrode active material contains a large amount of valuable metals such as lithium, nickel, manganese, and cobalt. For this reason, attempts have been made to recover these valuable metals from lithium ion batteries (used lithium ion secondary batteries) that have deteriorated due to long-term use. In particular, the need to recover valuable metals from used lithium ion secondary batteries is expanding further, supported by the atmosphere promoting the 3Rs (reduce: reducing waste), reuse (reuse), and recycle (recovery and reuse).

For example, Patent Document 1 discloses a method for recovering valuable metals from a positive electrode active material for a lithium ion secondary battery, which comprises a first step of adding a mineral acid or a mixture of a mineral acid and hydrogen peroxide to a positive electrode active material for a lithium ion secondary battery, and then separating the eluate, a second step of contacting the separated eluate with an organic solvent containing a metal extractant to perform an extraction and separation process, and a third step of contacting the organic solvent phase of the extract with a mineral acid to perform back extraction and separation.

Patent Document 2 discloses a method for recovering cobalt from lithium-ion batteries, which includes a magnetic separation process in which crushed powder from lithium-ion batteries obtained by crushing after firing is sieved to a predetermined particle size or less, and then the crushed powder is magnetically separated into magnetized and non-magnetized materials; a first extraction process in which cobalt contained in the positive electrode plates that constitute the lithium-ion batteries is extracted and separated using a first acidic solvent; and a second extraction process in which cobalt contained in the magnetized materials separated by the magnetic separation process and cobalt contained in the extraction residue floating or precipitated in the first acidic solvent are extracted and separated using a second acidic solvent.

Patent Document 3 discloses a method for recovering valuable metals from lithium-ion batteries, which includes a dismantling step for dismantling lithium-ion batteries, a cleaning step for washing the battery dismantled materials with alcohol or water to remove the electrolytic solution and electrolyte, a positive electrode active material stripping step for immersing the washed battery dismantled materials in an aqueous sulfuric acid solution to strip the positive electrode active material from the positive electrode substrate, a leaching step for leaching the stripped positive electrode active material with an acidic solution in the presence of a fixed carbon-containing material, a neutralization step for separating and removing aluminum and copper from the resulting leachate by neutralization, a nickel/cobalt recovery step for separating and recovering nickel and cobalt from the leachate after the neutralization step, and a lithium recovery step for concentrating the lithium in the remaining aqueous solution by solvent extraction and back extraction, and then separating and recovering lithium as a solid lithium carbonate.

Patent Document 4 discloses a method for leaching valuable metals from a positive electrode active material of a lithium ion battery made of a composite oxide composed of transition metals including at least manganese, the method comprising a first step of dissolving components of the positive electrode active material that are soluble in a sulfuric acid solution in an aqueous solution to which sulfuric acid has been added, and a second step of adding hydrogen peroxide to the sulfuric acid leaching slurry solution without performing solid-liquid separation after the first step, thereby further leaching unleached components remaining in the sulfuric acid leaching slurry.

Patent Document 5 discloses a method for regenerating a lithium composite oxide, which comprises the steps of preparing a lithium composite precursor from which lithium has been partially extracted electrochemically or chemically, and reacting the lithium composite precursor from which lithium has been partially extracted with a lithium compound.

Japanese Patent Application Publication No. 10-287864 JP 2004-214025 A JP 2007-122885 A JP 2012-072488 A JP 2016-085953 A

In promoting the 3R activities mentioned above, the order of priority is first reduce, second reuse, and third recycle, from the perspective of minimizing consumption of energy such as electricity and heat, as well as water and various other resources.

However, Patent Documents 1 to 4 each disclose a technique for separating and recovering valuable metals from the positive electrode active material contained in the positive electrode plate of a lithium-ion secondary battery. In other words, all of the techniques disclosed in Patent Documents 1 to 4 are limited to those related to recycling, which is the last resort, and no consideration has been given to techniques that can reduce and reuse the lithium-ion secondary battery itself.

In addition, Patent Document 5 describes a technology in which a lithium composite precursor from which some lithium has been extracted is reacted with a lithium compound to regenerate a lithium composite oxide, but this is merely the regeneration of the lithium composite oxide, which is the positive electrode active material. In other words, this does not correspond to a technology that can reduce and reuse the lithium ion secondary battery itself. Moreover, the technology disclosed in Patent Document 5 involves a firing process using a lithium compound, and it cannot be said that it has sufficiently reduced energy and resources. Furthermore, Patent Document 5 does not describe in detail how to recover the lithium composite precursor from which some lithium has been extracted in solid form from the positive electrode plate of a used, depleted lithium ion secondary battery. In other words, when it comes to lithium ion secondary batteries, the technology disclosed in Patent Document 5 is nothing more than a technology related to recycling.

In view of the problems inherent in the above-mentioned conventional technology, one aspect of the present invention aims to provide a method for regenerating lithium-ion secondary batteries that allows the lithium-ion secondary batteries themselves to be reused.

In order to solve the above problems, according to one aspect of the present invention,
A preparation step of discharging a depleted lithium ion secondary battery, which is a lithium ion secondary battery that has been charged and discharged multiple times, to prepare a lithium ion secondary battery prepared for regeneration;
A first exchange step of exchanging a used negative electrode of the prepared lithium ion secondary battery with a lithium supplementary electrode containing lithium to obtain a lithium ion secondary battery before regeneration;
a regeneration step of discharging the pre-regenerated lithium ion secondary battery to obtain a regenerated lithium ion secondary battery;
and a second exchange step of exchanging the lithium replenishment electrode of the regenerated lithium ion secondary battery with the used negative electrode or an unused negative electrode to obtain a regenerated lithium ion secondary battery.

According to one aspect of the present invention, it is possible to provide a method for regenerating a lithium ion secondary battery that allows the lithium ion secondary battery itself to be reused.

FIG. 1 is a process flow diagram showing a method for regenerating a lithium ion secondary battery according to one embodiment of the present invention. FIG. 1 is a schematic diagram illustrating a regenerated lithium-ion secondary battery according to one embodiment of the present invention.

Hereinafter, the form for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiment, and various modifications and substitutions can be made to the following embodiment without departing from the scope of the present invention.
[Method for Regenerating Lithium-Ion Secondary Battery]
In examining a method for regenerating a lithium ion secondary battery that can reuse the lithium ion secondary battery itself, the inventors of the present invention have conducted extensive research into the mechanism of deterioration and consumption of a lithium ion secondary battery, particularly the behavior of lithium that contributes to an intercalation reaction, which is particularly important. As a result, they have found that the main factors that inactivate the lithium (lithium ions) of a lithium ion secondary battery, that is, turn it into inactive lithium that does not contribute to an intercalation reaction, are the immobilization of lithium due to the occurrence of cation mixing caused by the positive electrode side, and the immobilization of lithium due to the formation of a solid electrolyte interphase (SEI) film caused by the negative electrode side.

Then, the inventors discovered that by supplementing the lithium that no longer contributes to the intercalation reaction due to the above immobilization (hereinafter also referred to as "inactive lithium") with new lithium, it is possible to recover the discharge capacity and regenerate the lithium ion secondary battery without damaging its morphology, thus completing the present invention.

Here, we will first explain the mechanism of deterioration and consumption of lithium-ion secondary batteries.
1. Aging and depletion of lithium ion secondary batteries When a lithium ion secondary battery is charged and discharged, an intercalation reaction occurs inside the lithium ion secondary battery, in which lithium ions are inserted and removed from the positive and negative electrodes. However, repeated charging and discharging may result in inactive lithium that no longer contributes to the intercalation reaction as described above. Depending on the amount of inactive lithium, the charge and discharge capacity of the lithium ion secondary battery may decrease, leading to aging and depletion.

The main factors for the deterioration and consumption of such lithium ion secondary batteries, that is, the main factors for deactivating the lithium contained in the lithium ion secondary batteries, are contained in both the positive electrode side and the negative electrode side.
(1) Main factor on the positive electrode side First, regarding the positive electrode side, when a positive electrode active material with a high nickel composition ratio is used in a lithium ion secondary battery, a high capacity density can be obtained, but the proportion of divalent nickel ions also increases. Therefore, in the space group R-3m of the crystal of the positive electrode active material, for example, a monovalent lithium ion present at the 3a site and a divalent nickel ion present at the 3b site are easily replaced, which is called cation mixing.

Cation mixing is thought to occur for the following reasons (A) and (B). (A) The ionic radius of monovalent lithium ions and the ionic radius of divalent nickel ions are very close to each other. (B) In the firing process of manufacturing the positive electrode active material, an increase in divalent nickel ions due to insufficient oxygen concentration in the furnace, or excessive firing, such as a high firing temperature or long firing time, increases damage to the positive electrode active material.

When cation mixing occurs, the lithium site occupancy rate of the positive electrode active material, i.e., the proportion of lithium occupying the 3a site, for example, decreases, and the amount of lithium inserted and removed during charging and discharging decreases, resulting in a decrease in capacity density. When the lithium site occupancy rate of the positive electrode active material decreases, nickel is more likely to occupy, for example, the 3a site of the space group R-3m in place of lithium than manganese or cobalt. For this reason, the lithium that no longer occupies the 3a site will occupy the 3b site where nickel was located.

Although the effect of the above-mentioned cation mixing on lithium is partial and limited, on the other hand, for example, lithium that occupies the 3b site instead of nickel ions is immobilized and can hardly contribute to charging and discharging, becoming inactive lithium. Moreover, metal ions that occupy the 3a site instead of lithium are also immobilized, which results in a loss of the area in which lithium can be inserted into the positive electrode active material.

Here, the case of a positive electrode active material having a high nickel composition ratio and a crystal space group of R-3m has been described as an example, but even in the case of a positive electrode active material for lithium ion secondary batteries having other metals or other space groups, when repeatedly charged and discharged, cation mixing may occur similarly, and inactive lithium may be generated. In the following description, the case of a positive electrode active material having a crystal space group of R-3m may be described as an example, but the regeneration method for lithium ion secondary batteries of this embodiment can be applied not only to lithium ion secondary batteries having such a positive electrode active material, but also to various lithium ion secondary batteries.
(2) Main Factors on the Negative Electrode Side Next, regarding the negative electrode side, when a lithium ion secondary battery is repeatedly charged and discharged, a thin film with a thickness of less than 50 nm, called a solid electrolyte interphase (SEI) film, is formed on the surface of the negative electrode by the reductive decomposition of the electrolyte. The SEI film is a complex containing multiple inorganic lithium compounds and organic lithium compounds, such as lithium fluoride, lithium alkyl carbonate, lithium carbonate, and lithium oxide, which contain lithium, carbon, oxygen, fluorine, phosphorus, silicon, and the like, and is formed on the surface of the negative electrode by the reductive decomposition of the electrolyte.

The SEI coating has ionic conductivity but no electronic conductivity, allowing it to moderately absorb lithium ions into the negative electrode while suppressing the decomposition of the electrolyte on the negative electrode. For this reason, if there were no SEI coating, the decomposition of the electrolyte would be accelerated, which would ultimately lead to the battery ceasing to operate, so it is preferable for a certain amount of SEI coating to be formed.

However, when the lithium-ion secondary battery is repeatedly charged and discharged, the thickness of the SEI film may change. If the thickness of the SEI film becomes too thin, the electrolyte decomposition reaction may proceed too quickly. Conversely, if the film thickness becomes too thick, the electrical resistance may increase, and lithium may be used to form the SEI film itself, and lithium may be captured and fixed inside the SEI film, resulting in a decrease in charge and discharge capacity. If the thickness of the SEI film changes when the lithium-ion secondary battery is repeatedly charged and discharged in this way, it may have a negative effect on the life and efficiency of the battery. Therefore, in order to improve the performance of the lithium-ion secondary battery, it is preferable to stably control the thickness of the SEI film.

However, the detailed mechanism of SEI film formation is currently unknown and its control is extremely difficult; therefore, if methods for evaluating SEI films are further improved and the mechanism is elucidated, it is believed that this will be of great help in improving the performance of lithium-ion secondary batteries in the future.
(3) Depleted Lithium-Ion Secondary Battery In this way, unused lithium-ion secondary batteries become depleted lithium-ion secondary batteries due to the effects of cation mixing on the positive electrode side and the formation of an SEI film on the negative electrode side when used for a long period of time. However, once either cation mixing or the formation of an SEI film occurs, the lithium immobilized by them loses its function of contributing to the intercalation reaction and cannot be restored. For this reason, in order to restore a depleted lithium-ion secondary battery to the state of an unused lithium-ion secondary battery as much as possible and regenerate it, it is necessary to replenish the deficient amount of immobilized lithium by some method.

Based on the above findings, the inventors of the present invention have completed a method for regenerating a lithium ion secondary battery. The method for regenerating a lithium ion secondary battery according to the present embodiment will be described below.
2. Regenerating Method for Lithium-Ion Secondary Battery The regenerating method for the lithium-ion secondary battery according to this embodiment will be described.

The method for regenerating a lithium ion secondary battery according to the present embodiment can be carried out according to the flow chart shown in FIG. 1 and can include the following steps.
A preparation process for discharging a depleted lithium ion secondary battery, which is a lithium ion secondary battery that has been charged and discharged multiple times, to prepare a lithium ion secondary battery ready for regeneration.
A first exchange process in which a used negative electrode, which is the negative electrode of the lithium ion secondary battery prepared for regeneration, is exchanged for a lithium supplementary electrode containing lithium to produce a lithium ion secondary battery before regeneration treatment.
A regeneration process in which the pre-regenerated lithium-ion secondary battery is discharged to produce a regenerated lithium-ion secondary battery.
A second exchange step of exchanging the lithium refill electrode of the regenerated lithium ion secondary battery with a used negative electrode or an unused negative electrode to obtain a regenerated lithium ion secondary battery.
As described above, according to the study by the inventors of the present invention, at least a part of the lithium contained in a depleted lithium ion secondary battery, which is a lithium ion secondary battery that has been charged and discharged multiple times, is fixed by cation mixing on the positive electrode side or by the SEI coating on the negative electrode side, and becomes inactive lithium. Therefore, in order to regenerate such a depleted lithium ion secondary battery, it is necessary to replenish the deficient amount of fixed lithium.

Therefore, the inventors of the present invention investigated ways to replenish lithium.

As a result, it was found that it is possible to replenish the fixed lithium deficiency by using a lithium replenishment electrode that contains lithium and can supply and replenish lithium. In other words, it was found that it is possible to remove the used negative electrode from a depleted lithium ion secondary battery, replace it with a lithium replenishment electrode, and use the lithium replenishment electrode to replenish lithium.

They then discovered that by replenishing lithium using a lithium refill electrode, it is possible to create a regenerated lithium-ion secondary battery that recovers the discharge capacity without compromising the shape of the original depleted lithium-ion secondary battery.

The regeneration method for lithium ion secondary batteries according to this embodiment can be applied to both liquid and solid electrolytes. Therefore, the use of a solid electrolyte reduces the effects of SEI film formation on the negative electrode, and the method can also be applied to all-solid-state secondary batteries, which are said to be less susceptible to deterioration.

Each step of the method for regenerating a lithium ion secondary battery according to the present embodiment will be described in detail below. Note that the name of each step is followed by the step number in FIG.
(1) Preparation process (S11)
In the preparation step, a depleted lithium ion secondary battery, which is a lithium ion secondary battery that has been charged and discharged multiple times, can be discharged to become a lithium ion secondary battery prepared for regeneration.

In a lithium ion secondary battery, by repeatedly charging and discharging, a portion of the lithium that contributes to the intercalation reaction is inactivated, becoming inactive lithium that does not contribute to the intercalation reaction during charging and discharging. Then, such a lithium ion secondary battery that has been repeatedly charged and discharged becomes a depleted lithium ion secondary battery that contains the inactive lithium.

Therefore, in the preparation step (S11), the depleted lithium ion secondary battery is first discharged, and lithium other than the inactive lithium is moved from the negative electrode to the positive electrode, thereby preparing a lithium ion secondary battery for regeneration.

As mentioned above, once lithium is inactivated by cation mixing or the formation of an SEI film, the resulting inactive lithium is deprived of its functionality and cannot be restored to its original state. Furthermore, in the case of cation mixing, for example, in the space group R-3m of the crystals of the positive electrode active material, the area in which lithium can be inserted is also reduced due to the metal occupying the 3a site instead of the lithium that should be inserted.

The purpose of the preparation process is therefore to move lithium other than inactive lithium to an area not affected by cation mixing, for example, within the 3a site, by discharging. However, if the depleted lithium ion secondary battery has already been discharged and lithium other than inactive lithium has moved from the negative electrode to the positive electrode, the already performed discharge serves as the preparation process, and it is not necessary to carry out a new preparation process.

As described above, the configuration of the depleted lithium ion secondary battery is not particularly limited, and the depleted lithium ion secondary battery may be either a lithium ion secondary battery using an electrolytic solution as the electrolyte, or a so-called all-solid-state battery using a solid electrolyte as the electrolyte. That is, the depleted lithium ion secondary battery may have a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a separator, and an electrolytic solution, or may have a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and a solid electrolyte. In either case, any optional components may be further included as necessary.

The composition of the positive electrode active material of the positive electrode of the depleted lithium ion secondary battery is not particularly limited, but the method of regenerating the lithium ion secondary battery of this embodiment is particularly effective in the case of a positive electrode active material that is prone to cation mixing due to repeated charging and discharging. For this reason, the depleted lithium ion secondary battery has a positive electrode that contains a positive electrode active material, and it is preferable that the positive electrode active material contains nickel and cobalt.

As described above, one or more of the positive electrode active material and the SEI coating formed on the surface of the negative electrode of the depleted lithium ion secondary battery contain inactive lithium, which is lithium that does not contribute to the intercalation reaction during charging and discharging of the depleted lithium ion secondary battery. In the positive electrode active material, for example, as described above, inactive lithium is contained in the 3b site of the space group R-3m of the crystal of the positive electrode active material.
(2) First exchange step (S12)
In the first exchange step, the used negative electrode of the prepared lithium ion secondary battery is exchanged for a lithium supplementary electrode containing lithium, to obtain a lithium ion secondary battery before regeneration treatment.

In the above preparation process, lithium other than inactive lithium contained in the exhausted lithium ion secondary battery is moved to an area not affected by cation mixing, for example, in the 3a site, which is a lithium site. However, the area of the positive electrode of the exhausted lithium ion secondary battery where lithium, such as the lithium used in the formation of the SEI film itself and the lithium fixed inside the SEI film, was supposed to be inserted is still in an empty state. The purpose of this process is to replace the used negative electrode, which is the negative electrode used in the exhausted lithium ion secondary battery, with a lithium refill electrode, which is a lithium supply source, in order to insert new lithium into the area of the positive electrode where lithium can be inserted in the regeneration process described below. Since the lithium refill electrode is an electrode for refilling lithium, it is preferable that it contains lithium. As the lithium refill electrode, for example, an electrode having one or more materials selected from metallic lithium, lithium alloy, lithium metal oxide, etc. can be used.

In addition, lithium-containing lithium refill electrodes are not generally used in vehicles and the like from the viewpoint of cost, etc., and have only been used as negative electrode active materials for battery testing and evaluation, such as performance evaluation of positive electrode active materials using half cells. However, the purpose of the lithium refill electrodes containing lithium is to refill new lithium into a lithium ion secondary battery, and after refilling is completed, they are replaced with the original used negative electrode or unused negative electrode as described below, so that costs can be sufficiently suppressed even when such lithium-containing lithium refill electrodes are used.
(3) Regeneration process (S13)
In the regeneration process, the pre-regenerated lithium ion secondary battery is discharged to produce a regenerated lithium ion secondary battery.

Specifically, the pre-regenerated lithium ion secondary battery obtained in the first exchange step is discharged, and new lithium is moved from the lithium replenishment electrode to the positive electrode, thereby obtaining a regenerated lithium ion secondary battery. In the regeneration step, the pre-regenerated lithium ion secondary battery in which the lithium replenishment electrode is disposed is discharged, and new lithium ions are supplied from the lithium replenishment electrode. For this reason, for example, in the space group R-3m of the crystals of the positive electrode active material, new lithium can be inserted and replenished into the vacant portion of the 3a site in the region not affected by cation mixing.
(4) Second exchange step (S14)
In the second exchange step, the lithium refill electrode of the regenerated lithium ion secondary battery is exchanged with a used negative electrode or an unused negative electrode to obtain a regenerated lithium ion secondary battery.

The lithium refill electrode of a regenerated lithium-ion secondary battery can be replaced with a used negative electrode, which is the original negative electrode used in the depleted lithium-ion secondary battery, or with an unused negative electrode to create a regenerated lithium-ion secondary battery.

If the lithium refill electrode is used as the negative electrode as it is, lithium dendrites, i.e., dendritic lithium deposits, will grow over a long period of repeated charging and discharging, and these deposits may damage or penetrate the separator, etc., and in some cases may cause an internal short circuit. In addition, this is a large burden in terms of cost, so it is preferable to replace it with a used or unused negative electrode.

As the used negative electrode and the unused negative electrode, an electrode containing carbon can be suitably used. That is, the used negative electrode and the unused negative electrode can contain carbon.

Note that an SEI coating may be formed on the surface of the used negative electrode. For this reason, it is preferable to analyze the SEI coating in advance, and if there is a defect such as the SEI coating being too thick, to replace it with an unused negative electrode. It is also preferable to replace the used negative electrode with an unused negative electrode if it is thought that the capacity for absorbing lithium is insufficient.

The method of analyzing the SEI coating is not particularly limited, but may be, for example, cross-section polishing-field emission scanning electron microscope (CP-FE-SEM), focused ion beam processing-in-lens scanning electron microscope (FIB-in-lens SEM), X-ray photoelectron spectroscopy (X-ray photoelectron spectroscopy), hard X-ray photoemission spectroscopy (HAXPES), focused ion beam processing-transmission electron microscope-electron energy loss spectroscopy (FIB-TEM-EELS), or other analysis and evaluation devices such as these.

In the second replacement step, if the decrease in electrolyte due to decomposition is significant, it is preferable to replenish the electrolyte, and in the case of an all-solid-state secondary battery, if the solid electrolyte has deteriorated, it is preferable to replace it with an unused one. In addition, if necessary, the separator should also be inspected, and if any abnormality is found, it is preferable to replace it with an unused one.

The method for regenerating a lithium-ion secondary battery according to this embodiment has been described in detail above, but this technology does not only regenerate a depleted lithium-ion secondary battery once, but can also regenerate it multiple times. In other words, for example, it is possible to repeat the cycle of use → depletion → regeneration → reuse for the same lithium-ion secondary battery many times.

In this way, according to the method for regenerating a lithium ion secondary battery of the present embodiment, the lithium ion secondary battery can be regenerated any number of times, and the lithium ion secondary battery can be reused.
[Recycled lithium-ion secondary battery]
Next, the regenerated lithium ion secondary battery of this embodiment will be described.

The regenerated lithium ion secondary battery of this embodiment can be manufactured by regenerating a depleted lithium ion secondary battery using the regeneration method for lithium ion secondary batteries described above. For this reason, some of the matters already described will not be described.

The regenerated lithium ion secondary battery of this embodiment is a regenerated lithium ion secondary battery that has been regenerated after being an unused lithium ion secondary battery that has been charged and discharged multiple times to become a depleted lithium ion secondary battery.
The regenerated lithium ion secondary battery of this embodiment contains a larger amount of lithium than an unused lithium ion battery, and the amount of active lithium that contributes to the intercalation reaction during charging and discharging of the regenerated lithium ion secondary battery can be made larger than that of a depleted lithium ion secondary battery. Furthermore, the amount of inactive lithium that does not contribute to the intercalation reaction can be made equal to or less than that of a depleted lithium ion secondary battery.

Figure 2 is a schematic diagram showing a regenerated lithium-ion secondary battery according to this embodiment.

The regenerated lithium ion secondary battery 20 of this embodiment can have a positive electrode 21, a negative electrode 22, and an electrolyte 23. The electrolyte 23 can be an electrolytic solution or a solid electrolyte. As shown in FIG. 2, the regenerated lithium ion secondary battery 20 can have a separator 24 and a housing 25 for housing the electrodes, etc., as necessary.

As described above, in a lithium ion secondary battery, by repeatedly charging and discharging the battery, a portion of the lithium that contributes to the intercalation reaction is inactivated, and the lithium becomes inactive and does not contribute to the intercalation reaction during charging and discharging. A lithium ion secondary battery that has been repeatedly charged and discharged in this manner becomes a depleted lithium ion secondary battery that contains the inactive lithium.

When regenerating a depleted lithium-ion secondary battery, first, in the first exchange step described above, the used negative electrode of the depleted lithium-ion secondary battery is replaced with a lithium refill electrode. Next, in the regeneration step, the shortage of lithium corresponding to the inactive lithium derived from the SEI coating, in other words, the shortage of lithium corresponding to the inactive lithium other than that derived from cation mixing in the positive electrode, is replenished with new lithium. After that, in the second exchange step, the lithium refill electrode is replaced with the original used negative electrode or an unused negative electrode to produce a regenerated lithium-ion secondary battery.

Therefore, the regenerated lithium ion secondary battery of this embodiment contains inactive lithium 211 in the positive electrode 21, which is generated by cation mixing by charging and discharging an unused lithium ion secondary battery multiple times. In addition, the positive electrode 21 further contains new active lithium 212 that is replenished by the above-mentioned regeneration. Note that in FIG. 2, the inactive lithium 211 and the new active lithium 212 are shown diagrammatically, and do not mean that these lithiums exist in a localized manner as shown in FIG. 2.

In other words, because the final regenerated lithium-ion secondary battery has been replenished with lithium in the regeneration process, the amount (total amount) of lithium contained before it is reused as a lithium-ion secondary battery will exceed that of an unused lithium-ion secondary battery immediately after its initial manufacture. For the same reason, the regenerated lithium-ion secondary battery can contain more lithium than a depleted lithium-ion secondary battery before regeneration. The total amount of lithium referred to here is the sum of the active lithium that contributes to the intercalation reaction and the inactive lithium.

In addition, in a regenerated lithium-ion secondary battery, active lithium that contributes to the intercalation reaction is replenished in the regeneration process as described above. Therefore, the amount of active lithium that contributes to the intercalation reaction exceeds that of a depleted lithium-ion secondary battery. However, in a depleted lithium-ion secondary battery, as described above, some of the lithium sites of the positive electrode are occupied by other metals such as nickel due to cation mixing. Therefore, in the regeneration process, the amount of active lithium cannot be restored to the same amount as in an unused lithium-ion secondary battery, and the amount of active lithium in a regenerated lithium-ion secondary battery is less than that of an unused lithium-ion secondary battery.

Furthermore, in a regenerated lithium-ion secondary battery, the amount of inactive lithium can be made equal to or less than that of a depleted lithium-ion secondary battery. However, the amount of inactive lithium cannot be made as small as that of an unused lithium-ion secondary battery that contains very little inactive lithium, so in a regenerated lithium-ion secondary battery, the amount of inactive lithium is greater than that of an unused lithium-ion battery.

In the regenerated lithium-ion secondary battery of this embodiment, which is a regenerated depleted lithium-ion secondary battery, the initial discharge capacity can be made larger than the discharge capacity of the depleted lithium-ion secondary battery immediately before the regeneration process by replenishing active lithium in the regeneration process as described above.

In particular, the discharge capacity recovery rate calculated by the following formula (1) can be made 10% or more.
{(CB)/(AB)}×100(%)...(1)
A: Initial discharge capacity (mAh/g) of an unused lithium-ion secondary battery
B: Discharge capacity (mAh/g) of the exhausted lithium ion secondary battery immediately before the regeneration process
C: Initial discharge capacity of the regenerated lithium ion secondary battery (mAh / g)
In the regeneration process, the lithium replenishment electrode used to supply new lithium can be used not only once but repeatedly many times, and the negative electrode can basically be reused as the original negative electrode. Therefore, with the regenerated lithium ion secondary battery of this embodiment, it is possible to reuse the lithium ion secondary battery itself without disassembling or dismantling the lithium ion secondary battery, reducing new consumption of energy and resources as much as possible.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

First, a comparative example, which serves as a blank test for the examples, will be described.
[Comparative Example 1]
An unused lithium ion secondary battery having an NMC-based positive electrode active material and a negative electrode having a carbon-based negative electrode active material was charged and discharged 2000 times to obtain a depleted lithium ion secondary battery. The NMC-based positive electrode active material is an oxide containing Li, Ni, Mn, and Co as metal elements, and contains Ni, Mn, and Co in a ratio of Ni:Mn:Co=8:1:1 in terms of the material amount. The material amount ratio of Li to metals other than Li is Li/metal=1.05. The depleted lithium ion secondary battery has a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator, and an electrolyte, and the SEI coating formed on the surface of the positive electrode active material and the negative electrode contains inactive lithium. The same applies to the other examples and comparative examples below.

In addition, in the depleted lithium ion secondary battery used in this comparative example, all lithium other than the inactive lithium had already been transferred to the positive electrode, and the preparation process had already been carried out, making it a lithium ion secondary battery that was prepared for regeneration. For this reason, the following operations from the first exchange process onwards were carried out.

The used negative electrode of the lithium-ion secondary battery prepared for regeneration was replaced with a lithium refill electrode (first replacement process). An unused carbon-based negative electrode that does not contain lithium was used as the lithium refill electrode to replace the used negative electrode.

Next, the pre-recycled lithium-ion secondary battery was discharged to carry out the recycle process (recycle process). This resulted in a recycle-processed lithium-ion secondary battery.

Then, the lithium refill electrode was replaced with the used negative electrode of the prepared lithium ion battery, and the electrolyte was also replenished to obtain a regenerated lithium ion secondary battery (second replacement process).

The discharge capacity recovery rate of the regenerated lithium ion secondary battery was calculated from the initial discharge capacity of an unused lithium ion secondary battery, the discharge capacity of the exhausted lithium ion secondary battery immediately before the regeneration process, and the initial discharge capacity of the regenerated lithium ion secondary battery according to the following formula (1).
{(CB)/(AB)}×100(%)...(1)
A: Initial discharge capacity (mAh/g) of an unused lithium-ion secondary battery
B: Discharge capacity (mAh/g) of the exhausted lithium ion secondary battery immediately before the regeneration process
C: Initial discharge capacity of the regenerated lithium ion secondary battery (mAh / g)
The discharge capacity was determined by leaving each battery for about 12 hours after preparation, charging the battery to a cutoff voltage of 4.3 V with a current density of 0.05 mA/ ^cm2 for the positive electrode after stabilizing the open circuit voltage OCV, and then discharging the battery to a cutoff voltage of 2.5 V after a 10-minute pause. The discharge capacity immediately before the regeneration process of the exhausted lithium ion secondary battery was measured in the same manner at any timing after the open circuit voltage stabilized.

As a result, as shown in Table 1, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 0%.
[Comparative Example 2]
As the positive electrode active material of the unused lithium ion secondary battery, an NMC-based positive electrode active material was used, which is an oxide containing Li, Ni, Mn, and Co as metal elements, and contains Ni, Mn, and Co in a ratio of Ni:Mn:Co=6:2:2 in terms of substance amount, and has a substance amount ratio of Li to metal other than Li of Li/metal=1.04. Apart from the above, the lithium ion secondary battery was consumed and regenerated in the same manner as in Comparative Example 1.

As a result, as shown in Table 1, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 0%.
[Comparative Example 3]
As the positive electrode active material of the unused lithium ion secondary battery, an NCA-based positive electrode active material was used, which is an oxide containing Li, Ni, Co, and Al as metal elements, and contains Ni, Co, and Al in a ratio of Ni:Co:Al=9:0.7:0.3 in terms of substance amount, and the substance amount ratio of Li to metals other than Li is Li/metal=1.01. Apart from the above, the lithium ion secondary battery was consumed and regenerated in the same manner as in Comparative Example 1.

As a result, as shown in Table 1, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 0%.
[Comparative Example 4]
As the positive electrode active material of the unused lithium ion secondary battery, an NCA-based positive electrode active material was used, which is an oxide containing Li, Ni, Co, and Al as metal elements, and contains Ni, Co, and Al in a ratio of Ni:Co:Al=8.2:1.5:0.3 in terms of substance amount, and the substance amount ratio of Li to metals other than Li is Li/metal=1.02. Except for the above points, the lithium ion secondary battery was consumed and regenerated in the same manner as in Comparative Example 1.

As a result, as shown in Table 1, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 0%.
[Comparative Example 5]
After the regeneration treatment by discharging, the original negative electrode was not returned, and an unused carbon-based negative electrode was used as it was, but the same procedure as in Comparative Example 1 was performed. That is, the second exchange step was not performed, and the regenerated lithium ion secondary battery obtained in the regeneration step was used as a regenerated lithium ion secondary battery.

As a result, as shown in Table 1, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 0%.
[Comparative Example 6]
As the positive electrode active material of the unused lithium ion secondary battery, an NMC-based positive electrode active material was used, which is an oxide containing Li, Ni, Mn, and Co as metal elements, and contains Ni, Mn, and Co in a ratio of Ni:Mn:Co=6:2:2 in terms of substance amount, and has a substance amount ratio of Li to metal other than Li of Li/metal=1.04. Apart from the above, the lithium ion secondary battery was consumed and regenerated in the same manner as in Comparative Example 5.

As a result, as shown in Table 1, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 0%.
[Comparative Example 7]
As the positive electrode active material of the unused lithium ion secondary battery, an NMC-based positive electrode active material was used, which is an oxide containing Li, Ni, Mn, and Co as metal elements, and contains Ni, Mn, and Co in a ratio of Ni:Mn:Co=2:2:6 in terms of substance amount, and has a substance amount ratio of Li to metal other than Li of Li/metal=1.05. Apart from the above, the lithium ion secondary battery was consumed and regenerated in the same manner as in Comparative Example 5.

As a result, as shown in Table 1, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 0%.
[Comparative Example 8]
As the positive electrode active material of the unused lithium ion secondary battery, an NMC-based positive electrode active material was used, which is an oxide containing Li, Ni, Mn, and Co as metal elements, and contains Ni, Mn, and Co in a ratio of Ni:Mn:Co=2.5:5:2.5 in terms of substance amount, and the substance amount ratio of Li to metals other than Li is Li/metal=1.05. Apart from the above, the lithium ion secondary battery was consumed and regenerated in the same manner as in Comparative Example 5.

As a result, as shown in Table 1, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 0%.
[Comparative Example 9]
As the positive electrode active material of the unused lithium ion secondary battery, an NCA-based positive electrode active material was used, which is an oxide containing Li, Ni, Co, and Al as metal elements, and contains Ni, Co, and Al in a ratio of Ni:Co:Al=9:0.7:0.3 in terms of substance amount, and the substance amount ratio of Li to metals other than Li is Li/metal=1.01. Apart from the above, the lithium ion secondary battery was consumed and regenerated in the same manner as in Comparative Example 5.

As a result, as shown in Table 1, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 0%.
[Comparative Example 10]
As the positive electrode active material of the unused lithium ion secondary battery, an NCA-based positive electrode active material was used, which is an oxide containing Li, Ni, Co, and Al as metal elements, and contains Ni, Co, and Al in a ratio of Ni:Co:Al=8.2:1.5:0.3 in terms of substance amount, and the substance amount ratio of Li to metals other than Li is Li/metal=1.02. Except for the above points, the lithium ion secondary battery was consumed and regenerated in the same manner as in Comparative Example 5.

As a result, as shown in Table 1, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 0%.
[Comparative Example 11]
As the positive electrode active material of the unused lithium ion secondary battery, an NCA-based positive electrode active material was used, which is an oxide containing Li, Ni, Co, and Al as metal elements, and contains Ni, Co, and Al in a ratio of Ni:Co:Al=7.6:1.4:1.0 in terms of substance amount, and the substance amount ratio of Li to metals other than Li is Li/metal=1.06. Apart from the above, the lithium ion secondary battery was consumed and regenerated in the same manner as in Comparative Example 5.

As a result, as shown in Table 1, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 0%.
[Example 1]
In Comparative Example 1, which was positioned as a blank test, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 0%, so the regenerated lithium ion secondary battery of Comparative Example 1 was used as a depleted lithium ion secondary battery as it was.

In the first replacement process, an electrode made of metallic lithium was used as the lithium replacement electrode to replace the negative electrode used.

Other than the above, the preparation process, first exchange process, regeneration process, and second exchange process were carried out in the same manner as in Comparative Example 1.

As a result, as shown in Table 1, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 64%.
[Example 2]
In Comparative Example 2, which was positioned as a blank test, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 0%, so the regenerated lithium ion secondary battery of Comparative Example 2 was used as a depleted lithium ion secondary battery as it was.

In the first replacement process, an electrode made of metallic lithium was used as the lithium replacement electrode to replace the negative electrode used.

Other than the above, the preparation process, first exchange process, regeneration process, and second exchange process were carried out in the same manner as in Comparative Example 2.

As a result, as shown in Table 1, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 73%.
[Example 3]
In Comparative Example 3, which was positioned as a blank test, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 0%, so the regenerated lithium ion secondary battery of Comparative Example 3 was used as a depleted lithium ion secondary battery as it was.

In the first replacement process, an electrode made of metallic lithium was used as the lithium replacement electrode to replace the negative electrode used.

Other than the above, the preparation process, first exchange process, regeneration process, and second exchange process were carried out in the same manner as in Comparative Example 3.

As a result, as shown in Table 1, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 12%.
[Example 4]
In Comparative Example 4, which was positioned as a blank test, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 0%, so the regenerated lithium ion secondary battery of Comparative Example 4 was used as a depleted lithium ion secondary battery as it was.

In the first replacement process, an electrode made of metallic lithium was used as the lithium replacement electrode to replace the negative electrode used.

Other than the above, the preparation process, first exchange process, regeneration process, and second exchange process were carried out in the same manner as in Comparative Example 4.

As a result, as shown in Table 1, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 43%.
[Example 5]
In Comparative Example 5, which was positioned as a blank test, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 0%, so the regenerated lithium ion secondary battery of Comparative Example 5 was used as a depleted lithium ion secondary battery as it was.

In the first exchange process, an electrode made of metallic lithium was used as a lithium replenishment electrode to replace the used negative electrode, and in the second exchange process, the lithium replenishment electrode was replaced with an unused carbon electrode.

Other than the above, the preparation process, first exchange process, regeneration process, and second exchange process were carried out in the same manner as in Comparative Example 5.

As a result, as shown in Table 1, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 80%.
[Example 6]
In Comparative Example 6, which was positioned as a blank test, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 0%, so the regenerated lithium ion secondary battery of Comparative Example 6 was used as a depleted lithium ion secondary battery as it was.

In the first exchange process, an electrode made of metallic lithium was used as a lithium replenishment electrode to replace the used negative electrode, and in the second exchange process, the lithium replenishment electrode was replaced with an unused carbon electrode.

Other than the above, the preparation process, first exchange process, regeneration process, and second exchange process were carried out in the same manner as in Comparative Example 6.

As a result, as shown in Table 1, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 83%.
[Example 7]
In Comparative Example 7, which was positioned as a blank test, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 0%, so the regenerated lithium ion secondary battery of Comparative Example 7 was used as a depleted lithium ion secondary battery as it was.

In the first exchange process, an electrode made of metallic lithium was used as a lithium replenishment electrode to replace the used negative electrode, and in the second exchange process, the lithium replenishment electrode was replaced with an unused carbon electrode.

Other than the above, the preparation process, first exchange process, regeneration process, and second exchange process were carried out in the same manner as in Comparative Example 7.

As a result, as shown in Table 1, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 96%.
[Example 8]
In Comparative Example 8, which was positioned as a blank test, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 0%, so the regenerated lithium ion secondary battery of Comparative Example 8 was used as a depleted lithium ion secondary battery as it was.

In the first exchange process, an electrode made of metallic lithium was used as a lithium replenishment electrode to replace the used negative electrode, and in the second exchange process, the lithium replenishment electrode was replaced with an unused carbon electrode.

Other than the above, the preparation process, first exchange process, regeneration process, and second exchange process were carried out in the same manner as in Comparative Example 8.

As a result, as shown in Table 1, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 90%.
[Example 9]
In Comparative Example 9, which was positioned as a blank test, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 0%, so the regenerated lithium ion secondary battery of Comparative Example 9 was used as a depleted lithium ion secondary battery as it was.

In the first exchange process, an electrode made of metallic lithium was used as a lithium replenishment electrode to replace the used negative electrode, and in the second exchange process, the lithium replenishment electrode was replaced with an unused carbon electrode.

Other than the above, the preparation process, first exchange process, regeneration process, and second exchange process were carried out in the same manner as in Comparative Example 9.

As a result, as shown in Table 1, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 21%.
[Example 10]
In Comparative Example 10, which was positioned as a blank test, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 0%, so the regenerated lithium ion secondary battery of Comparative Example 10 was used as a depleted lithium ion secondary battery as it was.

In the first exchange process, an electrode made of metallic lithium was used as a lithium replenishment electrode to replace the used negative electrode, and in the second exchange process, the lithium replenishment electrode was replaced with an unused carbon electrode.

Other than the above, the preparation process, first exchange process, regeneration process, and second exchange process were carried out in the same manner as in Comparative Example 10.

As a result, as shown in Table 1, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 48%.
[Example 11]
In Comparative Example 11, which was positioned as a blank test, the discharge capacity recovery rate of the regenerated lithium ion secondary battery was 0%, so the regenerated lithium ion secondary battery of Comparative Example 11 was used as a depleted lithium ion secondary battery as it was.

In the first exchange process, an electrode made of metallic lithium was used as a lithium replenishment electrode to replace the used negative electrode, and in the second exchange process, the lithium replenishment electrode was replaced with an unused carbon electrode.

Other than the above, the preparation process, first exchange process, regeneration process, and second exchange process were carried out in the same manner as in Comparative Example 11.

As a result, the discharge capacity recovery rate of the regenerated lithium-ion secondary battery was 72%, as shown in Table 1.

空（ブランク）試験の位置付けであった比較例１～比較例１１については、再生リチウムイオン二次電池における放電容量回復率が全て０％であり、供給できる新たなリチウムイオンを含まない未使用の炭素系負極では、リチウム補充用電極として機能しないことが確認できた。

For Comparative Examples 1 to 11, which were positioned as blank tests, the discharge capacity recovery rates in the regenerated lithium-ion secondary batteries were all 0%, and it was confirmed that an unused carbon-based negative electrode that does not contain new lithium ions that can be supplied does not function as a lithium replenishment electrode.

In contrast, for Examples 1 to 11, the discharge capacity recovery rates of the regenerated lithium-ion secondary batteries were in the range of approximately 10% to 100%, and it was confirmed that the discharge capacity was recovered in all Examples.

Furthermore, after the regeneration process by discharging, in Examples 1 to 4, in which the original negative electrode was returned to its original state, and in Examples 5 to 11, in which an unused carbon-based negative electrode was used, the discharge capacity recovery rate in the latter tended to be higher than that in the former.

The reason for this is still unclear, but in the former case, it is possible that the original negative electrode is not only affected by the formation of an SEI film, but that lithium has been immobilized in some way in the negative electrode itself. In other words, the capacity of a used negative electrode to absorb lithium is reduced compared to an unused carbon-based negative electrode, and it is thought that the entire amount of lithium after the new lithium is replenished is not absorbed.

From another perspective, if the discharge capacity recovery rates of the latter Examples 5 and 6 (NMC-based) and Examples 9 and 10 (NCA-based) are taken as the standard (zero), it can be said that the discharge capacity recovery rates of the former Examples 1 and 2 (NMC-based) are in the range of -15% to -10%, and the discharge capacity recovery rate of the former Examples 3 and 4 (NCA-based) is in the range of -10% to -5%. Therefore, it can be said that this range corresponds to the capacity at which the negative electrode used can no longer absorb lithium.

The regenerated lithium-ion secondary batteries obtained in Examples 1 to 11 were replenished with new active lithium during the replacement process.

As a result, the regenerated lithium-ion secondary batteries obtained in Examples 1 to 11 all contain a greater amount of lithium than unused lithium-ion secondary batteries and depleted lithium-ion secondary batteries before regeneration.

In addition, these recycled lithium-ion secondary batteries have a greater amount of active lithium than the depleted lithium-ion secondary batteries before regeneration, but less than that of unused lithium-ion secondary batteries, and the amount of inactive lithium is greater than that of unused lithium-ion secondary batteries but less than that of depleted lithium-ion secondary batteries.

These results confirm that the method for recycling lithium-ion secondary batteries and the recycled lithium-ion secondary batteries of this embodiment are extremely effective, and that the lithium-ion secondary batteries themselves can be reused without disassembling or dismantling the lithium-ion secondary batteries, reducing new consumption of energy and resources as much as possible.

As explained above, the method for recycling lithium-ion secondary batteries and the recycled lithium-ion secondary batteries of this embodiment are suitable for the atmosphere promoting global 3R activities, and are not only very environmentally friendly technologies, but are also expected to play a major role in the future in terms of industrial use.

S11 Preparation process S12 First exchange process S13 Regeneration process S14 Second exchange process

Claims (4)

A regenerated lithium ion secondary battery (excluding those having an insertion port for inserting an electrode having metallic lithium for replenishing lithium) that is obtained by regenerating an unused lithium ion secondary battery after being charged and discharged multiple times to become a depleted lithium ion secondary battery ,
The amount of lithium contained is greater than that of the unused lithium ion secondary battery,
the amount of active lithium contributing to the intercalation reaction during charging and discharging of the regenerated lithium ion secondary battery is greater than that of the depleted lithium ion secondary battery;
A regenerated lithium ion secondary battery, the amount of inactive lithium not contributing to the intercalation reaction being equal to or less than that of the depleted lithium ion secondary battery. The amount of lithium contained is greater than that of the depleted lithium ion secondary battery,
the amount of active lithium is less than that of the unused lithium ion secondary battery;
2. The regenerated lithium ion secondary battery of claim 1, wherein the amount of inactive lithium is greater than that of the unused lithium ion secondary battery. The regenerated lithium ion secondary battery according to claim 1 or 2, wherein the initial discharge capacity is greater than the discharge capacity of the depleted lithium ion secondary battery immediately before the regeneration process. The regenerated lithium ion secondary battery according to any one of claims 1 to 3, wherein the discharge capacity recovery rate calculated by the following formula (1) is 10% or more.
{(CB)/(AB)}×100(%)...(1)
A: initial discharge capacity (mAh/g) of the unused lithium ion secondary battery
B: Discharge capacity (mAh/g) of the exhausted lithium ion secondary battery immediately before the regeneration treatment
C: Initial discharge capacity (mAh/g) of the regenerated lithium ion secondary battery

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