JP7079417B2 - How to recover the resistance characteristics of non-aqueous electrolyte secondary batteries - Google Patents

Description

The present invention relates to a method for recovering resistance characteristics of a non-aqueous electrolyte secondary battery.

In recent years, non-aqueous electrolyte secondary batteries such as lithium secondary batteries have been used for portable power sources such as personal computers and mobile terminals, and for driving vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). It is suitably used for power supplies and the like.

When manufacturing a non-aqueous electrolyte secondary battery, by using LiPF ₆ as a supporting salt and LiPO ₂ F ₂ as an additive in the non-aqueous electrolyte, a film is formed on the surface of the negative electrode, and resistance characteristics and the like are deteriorated. It is known that it can be improved (see, for example, Patent Document 1).
Further, it is known that the performance can be recovered by adding a compound containing a fluorophosphate anion to the non-aqueous electrolyte of the non-aqueous electrolyte secondary battery whose performance has deteriorated (see, for example, Patent Documents 2 and 3). ..

Japanese Patent Application Laid-Open No. 2015-018802 International Publication No. 2015/163279 Japanese Unexamined Patent Publication No. 2017-152259

In the above-mentioned Patent Documents 2 and 3 which are the prior arts, although the recovery of the reduced capacity of the non-aqueous electrolyte secondary battery is actually studied, the recovery of the resistance characteristics is actually studied. Not. Therefore, as a result of diligent studies on this point by the present inventor, it has been found that there is room for improvement in these conventional techniques in terms of recovering the resistance characteristics.

Therefore, an object of the present invention is to provide a method capable of effectively recovering the lowered resistance characteristics of the non-aqueous electrolyte secondary battery.

In the method for recovering the resistance characteristics of the non-aqueous electrolyte secondary battery disclosed herein, the non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The non-aqueous electrolyte contains LiPF ₆ and LiPO ₂ F ₂ . A film is formed on the surface of the negative electrode. The method for recovering the resistance characteristics of the non-aqueous electrolyte secondary battery disclosed herein includes a step of acquiring a correlation between the amount of P component in the coating of the non-aqueous electrolyte secondary battery and the amount of Li in the coating. For a non-aqueous electrolyte secondary battery having reduced resistance characteristics, LiPO ₂ F ₂ is added to the non-aqueous electrolyte when the amount of P component with respect to the amount of Li in the coating reaches the standard determined from the correlation. Including the process. The standard is defined in the range in which the amount of P component does not show a linear approximation to the amount of Li in the correlation.

With such a configuration, it is possible to effectively recover the lowered resistance characteristics of the non-aqueous electrolyte secondary battery.

It is sectional drawing which shows typically the internal structure of the lithium secondary battery used in the resistance characteristic recovery method which concerns on one Embodiment of this invention. It is a schematic diagram which shows the structure of the winding electrode body of the lithium secondary battery used in the resistance characteristic recovery method which concerns on one Embodiment of this invention. It is a figure which shows typically the coating film of the surface of the negative electrode of the lithium secondary battery before deterioration. It is a figure which shows typically the coating film of the surface of the negative electrode of the lithium secondary battery which deteriorated. It is a figure which shows typically the coating film of the surface of the negative electrode of the lithium secondary battery to which LiPO ₂ F ₂ was added after the deterioration progressed. It is a graph which shows the relationship between the storage days and the amount of Li obtained in the examination in an Example. It is a graph which shows the relationship between the storage days and the amount of P component obtained in the examination in an Example. It is a graph plotting the amount of Li on the horizontal axis and the amount of P component on the vertical axis for the examination in the examples.

Hereinafter, embodiments according to the present invention will be described. It should be noted that matters other than those specifically mentioned in the present specification and necessary for carrying out the present invention (for example, general configurations and manufacturing processes of non-aqueous electrolyte secondary batteries which do not characterize the present invention). Can be grasped as a design matter of a person skilled in the art based on the prior art in the art. The present invention can be carried out based on the contents disclosed in the present specification and the common general technical knowledge in the art.

In the present specification, the "secondary battery" generally refers to a power storage device capable of being repeatedly charged and discharged, and is a term including a so-called storage battery and a power storage element such as an electric double layer capacitor.

The method for recovering the resistance characteristics of the non-aqueous electrolyte secondary battery according to the present embodiment is a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte is LiPF ₆ . It is applied to a non-aqueous electrolyte secondary battery containing LiPO ₂ F ₂ and having a film formed on the surface of the negative electrode.
The method for recovering the resistance characteristics of the non-aqueous electrolyte secondary battery according to the present embodiment is a step of acquiring a correlation between the amount of P component in the coating of the non-aqueous electrolyte secondary battery and the amount of Li in the coating (hereinafter, "" (Also referred to as "correlation acquisition step") and when the amount of P component with respect to the amount of Li in the coating reaches the standard determined from the above correlation for a non-aqueous electrolyte secondary battery with reduced resistance characteristics, LiPO ₂ F The step of adding ₂ to the non-aqueous electrolyte (hereinafter, also referred to as “addition step”) is included. This criterion is set in the range where the amount of P component does not show a linear approximation to the amount of Li in the above correlation.

Hereinafter, the case where the non-aqueous electrolyte secondary battery to which the resistance characteristic recovery method according to the present embodiment is applied is a lithium secondary battery will be described as an example, but the non-aqueous electrolyte to which the resistance characteristic recovery method is applied will be described. The secondary battery is not limited to the lithium secondary battery. Further, as an example, a square lithium secondary battery provided with a flat wound electrode body will be described. However, the lithium secondary battery may be a lithium secondary battery provided with a laminated electrode body, and may be a cylindrical lithium secondary battery or a laminated lithium secondary battery.

FIG. 1 is a cross-sectional view schematically showing the internal structure of the lithium secondary battery 100 used in the resistance characteristic recovery / recovery method according to the present embodiment. FIG. 2 is a schematic view showing the configuration of the wound electrode body 20 of the lithium secondary battery 100 used in the resistance characteristic recovery method according to the present embodiment.

The lithium secondary battery 100 shown in FIG. 1 is a sealed battery constructed by housing a flat wound electrode body 20 and a non-aqueous electrolyte 80 in a flat square battery case (that is, an outer container) 30. Is. The battery case 30 is provided with a positive electrode terminal 42 and a negative electrode terminal 44 for external connection, and a thin-walled safety valve 36 set to release the internal pressure when the internal pressure of the battery case 30 rises above a predetermined level. There is. Further, the battery case 30 is provided with an injection port (not shown) for injecting the non-aqueous electrolyte 80. The positive electrode terminal 42 is electrically connected to the positive electrode current collector plate 42a. The negative electrode terminal 44 is electrically connected to the negative electrode current collector plate 44a. As the material of the battery case 30, for example, a lightweight metal material having good thermal conductivity such as aluminum is used.

As shown in FIGS. 1 and 2, in the wound electrode body 20, the positive electrode active material layer 54 is formed along the longitudinal direction on one side or both sides (here, both sides) of the long positive electrode current collector 52. The positive electrode sheet 50 and the negative electrode sheet 60 in which the negative electrode active material layer 64 is formed along the longitudinal direction on one side or both sides (here, both sides) of the long negative electrode current collector 62 are two long sheets. It has a form of being overlapped with each other via a separator sheet 70 and wound in the longitudinal direction. The positive electrode active material layer non-formed portion 52a (that is, the positive electrode activity) formed so as to protrude outward from both ends of the winding electrode body 20 in the winding axis direction (that is, the sheet width direction orthogonal to the longitudinal direction). A portion where the positive electrode current collector 52 is exposed without forming the material layer 54) and a portion 62a where the negative electrode active material layer is not formed (that is, a portion where the negative electrode current collector 62 is exposed without forming the negative electrode active material layer 64). A positive electrode current collector plate 42a and a negative electrode current collector plate 44a are joined to each of the above.

As the positive electrode sheet 50 and the negative electrode sheet 60, the same ones used in the conventional lithium secondary battery can be used without particular limitation. A typical aspect is shown below.

Examples of the positive electrode current collector 52 constituting the positive electrode sheet 50 include aluminum foil and the like. Examples of the positive electrode active material contained in the positive electrode active material layer 54 include lithium transition metal oxides (eg, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNiO ₂ , LiCoO ₂ , LiFeO ₂ , LiMn ₂ O). ₄ , LiNi _0.5 Mn _1.5 O ₄ , etc.), lithium transition metal phosphoric acid compounds (eg, LiFePO ₄ , etc.) and the like. The positive electrode active material layer 54 may contain components other than the active material, such as a conductive material and a binder. As the conductive material, for example, carbon black such as acetylene black (AB) or other carbon material (eg, graphite or the like) can be preferably used. As the binder, for example, polyvinylidene fluoride (PVDF) or the like can be used. The lithium secondary battery 100 preferably has a normally operating voltage range of 3.0 V to 4.1 V. Therefore, it is preferable to select a positive electrode active material in which the upper limit potential for normal use of the positive electrode is 4.2 V or less based on lithium.

Examples of the negative electrode current collector 62 constituting the negative electrode sheet 60 include copper foil and the like. As the negative electrode active material contained in the negative electrode active material layer 64, a carbon material such as graphite, hard carbon, or soft carbon can be used. The negative electrode active material layer 64 may contain components other than the active material, such as a binder and a thickener. As the binder, for example, styrene butadiene rubber (SBR) or the like can be used. As the thickener, for example, carboxymethyl cellulose (CMC) or the like can be used.
A film is formed on the surface of the negative electrode sheet 60 (particularly, the surface of the negative electrode active material contained in the negative electrode active material layer 64). The film contains a P component derived from LiPO ₂ F ₂ . In addition, lithium ions are present in the coating film.

Examples of the separator 70 include a porous sheet (film) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. The porous sheet may have a single-layer structure or a laminated structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). A heat-resistant layer (HRL) may be provided on the surface of the separator 70.

The non-aqueous electrolyte 80 contains LiPF ₆ as a supporting salt and LiPO ₂ F ₂ with an additive. The non-aqueous electrolyte 80 also contains a non-aqueous solvent capable of dissolving them. Note that FIG. 1 does not strictly show the amount of the non-aqueous electrolyte 80 injected into the battery case 30.
As the non-aqueous solvent, a known non-aqueous solvent used in the non-aqueous electrolytic solution for a secondary battery can be used without particular limitation, and specifically, for example, carbonates, ethers, esters, nitriles, etc. Solvents, lactones and the like can be used. Of these, carbonates are preferable. Examples of carbonates include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and the like. These can be used alone or in combination of two or more.

The concentration of LiPF ₆ in the non-aqueous electrolyte 80 is preferably 0.7 mol / L or more and 1.3 mol / L or less.
The concentration of LiPO ₂ F ₂ in the non-aqueous electrolyte 80 is not particularly limited, but is preferably 0.05 mol / L or more and 0.5 mol / L or less.

The non-aqueous electrolyte contains, for example, a gas generator such as biphenyl (BP) and cyclohexylbenzene (CHB); a dispersant; and other additives such as a thickener, as long as the effects of the present invention are not significantly impaired. You may be.

This embodiment is a method applied when there are a plurality (particularly a large number) of the same lithium secondary batteries 100, such as a product to be shipped.

The correlation acquisition process will be described. In this step, the correlation between the amount of P component in the coating film of the lithium secondary battery 100 and the amount of Li in the coating film is acquired.
The step can be carried out, for example, as follows.
For a part of an unused lithium secondary battery 100 such as a lithium secondary battery 100 before shipment, an operation for increasing the amount of coating on the surface of the negative electrode 60 such as application of a charge / discharge cycle or storage at a high temperature is performed. implement. This operation corresponds to an operation of deteriorating the lithium secondary battery 100. Then, the amount of P component and the amount of Li in the coating film on the surface of the negative electrode 60 are analyzed. For example, by plotting the amount of P component with respect to the amount of Li, the correlation between the amount of P component in the coating and the amount of Li in the coating can be obtained.
The P component refers to a component derived from LiPO ₂ F ₂ in the coating film.

The amount of Li can be determined, for example, by disassembling the lithium secondary battery 100, taking out the negative electrode 60, and performing ICP emission analysis on the coating film on the surface thereof.
Further, the amount of the P component can be determined, for example, by disassembling the lithium secondary battery 100, taking out the negative electrode 60, and analyzing the coating film on the surface thereof by ion chromatography. In ion chromatography, the amount of P component can be determined as the total amount of components containing P (that is, PO ₄ , PO ₃ F, and PO ₂ F ₂ ). Further, for example, the amount of P component can be obtained by ICP emission analysis.

According to the study of the present inventor, as shown in the study results in the examples described later, the amount of Li in the coating film continuously increases, whereas the amount of P component in the coating film is present. We found that it became saturated in stages. Then, in the correlation between the amount of P component in the film and the amount of Li in the film, the amount of P component initially increases linearly with respect to the amount of Li (that is, the amount of Li and the amount of P component are linearly approximated). However, after that, it was found that the rate of increase in the amount of P component decreased and the linear approximation was not shown. He found that the resistance increased when the linear approximation was no longer shown.

This phenomenon is explained as follows.
A film as shown in FIG. 3 is formed on the negative electrode 60 of the lithium secondary battery 100 before deterioration. That is, on the surface of the negative electrode 60 (specifically, the negative electrode active material), a coating film 66 containing a layer 66A made of a decomposition product of a non-aqueous electrolyte and a layer 66B containing a P component derived from LiPO ₂ F ₂ is formed. It is formed. On the other hand, in the non-aqueous electrolyte, the lithium ion 1 exists in a form solvated with the solvent 2. Here, the layer 66B containing the P component is on the outer surface side of the coating film 66, and the presence of the highly polar P component on the outer surface promotes the desolvation of the lithium ion 1. Therefore, the insertion reaction of lithium ions into the negative electrode active material is smoothly performed, and as a result, the resistance of the lithium secondary battery 100 is lowered.

As the deterioration progresses, a film as shown in FIG. 4 is formed on the negative electrode 60 of the lithium secondary battery 100. That is, as LiPO ₂ F ₂ in the non-aqueous electrolyte is depleted, a layer 66C containing an organic component derived from a non-aqueous solvent is formed on the outermost surface side of the coating film 66. Since the lithium ions are abundant, lithium ions are present in all of the layers 66A to 66C, and the proportion of the P component is reduced in the entire coating 66. The polarity of the organic component is lower than that of the P component, and therefore, the effect of promoting the desolvation of lithium ion 1 by the P component is lost. As a result, the resistance of the lithium secondary battery 100 increases (that is, the resistance characteristics decrease).

Furthermore, the present inventor can add LiPO ₂ F ₂ to the non-aqueous electrolyte at a stage where the above linear approximation is no longer shown in the correlation between the amount of P component in the coating and the amount of Li in the coating. It has been found that it is effective in recovering the resistance characteristics of the lithium secondary battery 100.

Specifically, by newly supplying LiPO ₂ F ₂ into the non-aqueous electrolyte depleted of LiPO ₂ F ₂ , as shown in FIG. 5, the LiPO ₂ F ₂ is formed on the outermost surface side of the coating film 66. A layer 66D containing the derived P component is formed. As a result, the effect of promoting the desolvation of lithium ion 1 by the P component is obtained again, and the resistance characteristic of the lithium secondary battery 100 becomes smaller (that is, the resistance characteristic is restored).

In the prior art, the relationship between the correlation between the amount of P component in the coating and the amount of Li in the coating and the resistance characteristic of the lithium secondary battery 100 has not been grasped. Therefore, if LiPO ₂ F ₂ is added before LiPO ₂ F ₂ is depleted, side reactions due to the excessive presence of LiPO ₂ F ₂ are likely to occur, which may reduce the resistance characteristics. In addition, the resistance characteristics are dominated by the desolvation of lithium ions, but if LiPO ₂ F ₂ is added at an early stage, the thickness of the coating becomes too large, and the resistance due to diffusion of lithium ions in the coating An increase may occur. On the other hand, if the addition of LiPO ₂ F ₂ is too late, the layer of known resistance due to the organic component becomes too thick in the film.
However, according to the resistance characteristic recovery method according to the present embodiment, such a problem can be solved.
As a film-forming agent, vinylene carbonate and the like are known, but since vinylene carbonate has a small effect of reducing resistance, LiPO ₂ F ₂ is used in this embodiment.

Therefore, in the resistance characteristic recovery method according to the present embodiment, a lithium secondary battery 100 whose resistance characteristic is lowered due to use or the like is prepared. The lithium secondary battery 100 is usually the remaining lithium secondary battery 100 that was not used in the correlation acquisition step, and is, for example, a battery that has been shipped and used. The addition step is performed on the lithium secondary battery 100. That is, when the amount of P component with respect to the amount of Li in the coating reaches the standard determined from the above correlation with respect to the lithium secondary battery 100 having reduced resistance characteristics, LiPO ₂ F ₂ is added to the non-aqueous electrolyte 80. do. This criterion is set in the range where the amount of P component does not show a linear approximation to the amount of Li in the above correlation.

Specifically, as described above, the amount of P component initially increases linearly with respect to the amount of Li, and the formula: y (amount of P component) = αx (amount of Li) + β (in the formula, α and β is a coefficient) and can be approximated by a straight line. A standard is set in a range where the amount of P component does not show a linear approximation with respect to the amount of Li, and when the amount of P component reaches this standard, LiPO ₂ F ₂ is added to the non-aqueous electrolyte 80.

This standard can be set, for example, as a value smaller than the calculated value of αx (Li amount) + β by a predetermined amount. Specifically, for example, the standard is a value that is 10% or more smaller than the calculated value of αx (Li amount) + β (that is, the calculated value × 0.9 or less). That is, when the amount of P component is 10% or more smaller than the calculated value, LiPO ₂ F ₂ is added to the non-aqueous electrolyte 80. In particular, it is preferable to add LiPO ₂ F ₂ to the non-aqueous electrolyte 80 when the amount of P component is 10% smaller than the calculated value.
Alternatively, in the range where the amount of P component does not show a linear approximation with respect to the amount of Li, the rate of increase in the amount of P component changes so as to be small. This change appears as a change in the coefficient α representing the slope in the formula: y (P component amount) = αx (Li amount) + β (in the formula, α and β are coefficients). That is, it can be grasped by the differential value of this equation.
Therefore, for example, the case where the differential value of the above equation is equal to or less than a specific numerical value can be used as a reference.

Further, it is not always necessary to actually measure the Li amount and the P component amount to determine whether or not the P component amount has reached the standard. Understand the relationship between other easily measurable characteristics such as battery capacity and the standard, and if it is possible to determine whether or not the standard has been reached, make a judgment using these other characteristics. May be good.

Regarding the addition of LiPO ₂ F ₂ to the non-aqueous electrolyte 80, LiPO ₂ F ₂ may be added to the non-aqueous electrolyte 80 as it is, but LiPO ₂ F ₂ may be added to the non-aqueous solvent used in the non-aqueous electrolyte 80. It is preferable to prepare a dissolved solution and add this solution to the non-aqueous electrolyte 80.
The amount of LiPO ₂ F ₂ added to the non-aqueous electrolyte 80 is not particularly limited, but the amount of P component in the film formed thereafter is within 10% of the calculated value of αx (Li amount) + β. It is preferable to add it so as to have a value (that is, a calculated value × 0.9 or more), and it is more preferable to add it so that the deviation is within 5%.

After adding LiPO ₂ F ₂ to the non-aqueous electrolyte 80, it is not necessary to perform a charging treatment or an aging treatment of leaving it at a high temperature. A layer containing a P component derived from LiPO ₂ F ₂ can be formed on the surface of the coating film by charging during normal use or standing at a high temperature. However, the above treatment is advantageous because the layer containing the P component derived from LiPO ₂ F ₂ is uniformly formed.

As described above, the resistance characteristics of the lithium secondary battery 100 can be restored.
The lithium secondary battery 100 whose resistance characteristics have been restored can be used for various purposes, and may be used again for the same purpose as used, or may be used for another purpose. Suitable applications include drive power supplies mounted on vehicles such as electric vehicles (EVs), hybrid vehicles (HVs), and plug-in hybrid vehicles (PHVs). The lithium secondary battery 100 may also be used in the form of an assembled battery, typically composed of a plurality of batteries connected in series and / or in parallel.
It can also be used as a storage battery for storing electric power.

Hereinafter, examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in such examples.

<Preparation of lithium secondary battery>
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (LNCM) as a positive electrode active material powder, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder are used as LNCM :. A slurry for forming a positive electrode active material layer was prepared by mixing with N-methylpyrrolidone (NMP) at a mass ratio of AB: PVdF = 87: 10: 3. This slurry was applied to both sides of a long aluminum foil in a strip shape, dried, and then roll-pressed to prepare a positive electrode sheet.
The mass ratio of natural graphite (C) as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener in a mass ratio of C: SBR: CMC = 98: 1: 1. To prepare a slurry for forming a negative electrode active material layer by mixing with ion-exchanged water. This slurry was applied to both sides of a long copper foil in a strip shape, dried, and then rolled to prepare a negative electrode sheet.
In addition, two separator sheets (porous polyolefin sheets) were prepared.
The prepared positive electrode sheet and the negative electrode sheet were laminated via a separator sheet to prepare an electrode body.
A current collector was attached to the prepared electrode body, and the current collector was housed in a battery case together with the electrolytic solution and sealed. The non-aqueous electrolyte contains ethylene carbonate (EC), ethylmethyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of EC: EMC: DMC = 1: 1: 1 as a supporting salt. The one in which LiPF ₆ was dissolved at a concentration of 1.1 mol / L and LiPO ₂ F ₂ was dissolved at a concentration of 0.1 mol / L was used.
Next, an activation treatment was performed on this to prepare a lithium secondary battery having a film formed on the surface of the negative electrode.

<Deterioration treatment of lithium secondary battery>
The lithium secondary battery produced above was prepared in a state of 100% SOC and stored in an environment of 60 ° C. to be intentionally deteriorated. The maximum storage period was 100 days.

<Analysis of lithium secondary battery>
The lithium secondary battery before and after storage was disassembled, and the negative electrode was taken out.
The amount of Li was determined by performing ICP emission analysis on the coating film on the surface of the negative electrode.
In addition, the total amount (that is, the amount of P component) of P-based components (that is, PO ₄ , PO ₃ F, and PO ₂ F ₂ ) was determined by ion chromatography.

<Relationship between storage days, Li amount, and P component amount>
FIG. 6 shows the relationship between the number of storage days and the amount of Li obtained by the above examination, and FIG. 7 shows the relationship between the number of storage days and the amount of P component.
From FIG. 6, it can be seen that the amount of Li increases linearly with respect to the square root of the number of storage days. On the other hand, from FIG. 7, it can be seen that the amount of P component does not show a linear increase with respect to the square root of the number of storage days, and the amount of increase gradually decreases and becomes saturated.
From the above, it can be seen that when the number of storage days increases, the increase in the amount of P component behaves differently from the increase in the amount of Li.
Therefore, FIG. 8 shows a graph in which the amount of Li is plotted on the horizontal axis and the amount of P component is plotted on the vertical axis. From this graph, the correlation between the amount of Li and the amount of P component can be grasped. From FIG. 8, it can be seen that the amount of P component can be approximated by a straight line L at first with respect to the amount of Li, and increases linearly. However, as described above, an increase in the amount of P component behaves differently from an increase in the amount of Li. Therefore, when the amount of Li increases by a certain amount or more, the line L deviates from the straight line L as shown by the arrow.

<Examination of addition of LiPO ₂ F ₂ >
A LiPO ₂ F ₂ additive solution in which LiPO ₂ F ₂ was dissolved in a mixed solvent containing EC, EMC and DMC in a volume ratio of EC: EMC: DMC = 1: 1: 1 was prepared.
A plurality of lithium secondary batteries were produced in the same manner as described above, and stored in an environment of 60 ° C. at 100% SOC until the amount of P component did not show a linear approximation with respect to the amount of Li. Then, the LiPO ₂ F ₂ additive solution was injected into each lithium secondary battery. At this time, a plurality of injection amounts of the LiPO ₂ F ₂ additive liquid were changed so that the ratio of the Li amount and the P component amount was changed. In addition, a battery with a zero injection amount (that is, LiPO ₂ F ₂ was not added) was also provided.
Then, the activation treatment was carried out in an environment of 60 ° C.
The resistance of these batteries was measured at −30 ° C. by impedance. The ratio of the resistance values of the other batteries when the resistance value of the battery to which LiPO ₂ F ₂ was not added was 100 was determined. The results are shown in Table 1.
Moreover, these batteries were disassembled, and the amount of Li and the amount of P component were determined. Then, in the obtained Li amount, the ratio (%) in which the P component amount deviates from the value of the straight line L in FIG. 8 was obtained. The results are shown in Table 1.

From the results in Table 1, by adding LiPO ₂ F ₂ to the non-aqueous electrolyte in the range where the amount of P component does not show a linear approximation with respect to the amount of Li, the amount of P component in the coating increases and the lithium secondary It can be seen that the resistance of the battery can be reduced.
Therefore, it can be seen that the reduced resistance characteristics of the non-aqueous electrolyte secondary battery can be recovered by the resistance characteristic recovery method disclosed herein.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The techniques described in the claims include various modifications and modifications of the specific examples exemplified above.

1 Lithium ion 2 Solvent 20 Winding electrode body 30 Battery case 36 Safety valve 42 Positive electrode terminal 42a Positive current collector plate 44 Negative electrode terminal 44a Negative electrode current collector plate 50 Positive electrode sheet (positive electrode)
52 Positive electrode current collector 52a Positive electrode active material layer non-formed portion 54 Positive electrode active material layer 60 Negative electrode sheet (negative electrode)
62 Negative electrode current collector 62a Negative electrode active material layer non-formed portion 64 Negative electrode active material layer 66 Coating 66A Layer made of decomposition products of non-aqueous electrolyte, etc. 66B Layer containing P component derived from LiPO ₂ F ₂ 66C Derived from non-aqueous solvent Layer containing organic component 66D LiPO ₂ Layer containing P component derived from F ₂ 70 Separator sheet (separator)
80 Non-aqueous electrolyte 100 Lithium secondary battery

Claims (1)

It is a method of recovering the resistance characteristics of non-aqueous electrolyte secondary batteries.
The non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte.
The non-aqueous electrolyte contains LiPF ₆ and LiPO ₂ F ₂ .
A film is formed on the surface of the negative electrode.
A step of acquiring a correlation between the amount of P component in the coating film of the non-aqueous electrolyte secondary battery and the amount of Li in the coating film.
For a non-aqueous electrolyte secondary battery having reduced resistance characteristics, LiPO ₂ F ₂ is added to the non-aqueous electrolyte when the amount of P component with respect to the amount of Li in the coating reaches the standard determined from the correlation. Process and
Including
The reference is defined in the range in which the amount of P component does not show a linear approximation to the amount of Li in the correlation.
How to recover the resistance characteristics of non-aqueous electrolyte secondary batteries.

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