Method for restoring capacity of solid lithium ion battery

Abstract

To provide a method for restoring a capacity of a solid lithium ion battery.SOLUTION: The present disclosure provides a method for restoring a capacity of a solid lithium ion battery. The solid lithium ion battery comprises a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer. The negative electrode active material layer has a facing portion facing the positive electrode active material layer with the solid electrolyte layer therebetween and a non-facing portion not facing the positive electrode active material layer with the solid electrolyte layer therebetween. The capacity restoration method comprises a capacity restoration process of moving lithium ions from the non-facing portion to the positive electrode active material layer by charging the solid lithium ion battery at a current value of 0.05 C or lower.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a method for restoring capacity of a solid-state lithium-ion battery. [Background technology]

[0002] In recent years, with the rapid spread of electronic devices such as personal computers and mobile phones, the development of batteries to be used as their power sources has progressed. The automotive industry has also been developing batteries for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery-electric vehicles (BEVs). Among various types of batteries, lithium-ion batteries have the advantage of high energy density, and therefore, various studies on lithium-ion batteries have been conducted.

[0003] For example, Patent Document 1 discloses a secondary battery using silicon as a negative electrode active material, and Patent Document 2 discloses a method for restoring the capacity of a lithium ion secondary battery, which is a liquid battery. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-098419 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-127283 Summary of the Invention [Problem to be solved by the invention]

[0005] In lithium-ion batteries, the area of ​​the negative electrode active material layer may be made larger than the area of ​​the positive electrode active material layer in order to prevent short circuits due to lithium precipitation, etc. In this regard, in batteries that use a solid electrolyte as the electrolyte (solid-state batteries), lithium ions present in the portion of the negative electrode active material layer that does not face the positive electrode active material layer (non-facing portion) may not be fully utilized, resulting in a decrease in battery capacity.

[0006] The present disclosure has been made in consideration of the above-mentioned circumstances, and a main object of the present disclosure is to provide a method for restoring the capacity of a solid-state lithium-ion battery. [Means for solving the problem]

[0007] [1] A method for restoring capacity of a solid-state lithium-ion battery, comprising: the solid-state lithium-ion battery includes a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer; the negative electrode active material layer has a facing portion facing the positive electrode active material layer with the solid electrolyte layer interposed therebetween, and a non-facing portion not facing the positive electrode active material layer with the solid electrolyte layer interposed therebetween, a capacity recovery method for a solid-state lithium ion battery, the method comprising: a capacity recovery treatment in which the solid-state lithium ion battery is charged at a current value of 0.05 C or less, thereby transferring lithium ions from the non-facing portion to the positive electrode active material layer. [Effects of the Invention]

[0008] The present disclosure has the effect of restoring the capacity of a solid-state lithium-ion battery. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating a solid-state lithium-ion battery according to the present disclosure. [Figure 2] 1 is a graph showing the results of examples and comparative examples in the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] The capacity recovery method for a solid-state lithium-ion battery according to the present disclosure will be described in detail below. Note that the drawings shown below are schematic illustrations, and the size and shape of each part are appropriately exaggerated for ease of understanding.

[0011] FIG. 1 is a schematic cross-sectional view illustrating a solid-state lithium-ion battery subjected to the capacity recovery method of the present disclosure. Note that FIG. 1(b) is a view of FIG. 1(a) with a positive electrode current collector 4 and a negative electrode current collector 5 omitted. The solid-state lithium-ion battery 10 shown in FIG. 1(a) includes a positive electrode active material layer 1, a negative electrode active material layer 2, a solid electrolyte layer 3 disposed between the positive electrode active material layer 1 and the negative electrode active material layer 2, a positive electrode current collector 4 that collects electrons from the positive electrode active material layer 1, and a negative electrode current collector 5 that collects electrons from the negative electrode active material layer 2. Also, as shown in FIG. 1(b), the negative electrode active material layer 2 has a facing portion 2A that faces the positive electrode active material layer 1 across the solid electrolyte layer 3, and a non-facing portion 2B that does not face the positive electrode active material layer 1 across the solid electrolyte layer 3. The capacity recovery method of the present disclosure includes a capacity recovery process in which lithium ions are transferred from the non-facing portion 2B to the positive electrode active material layer 1 by charging such a solid-state lithium-ion battery 10 at a current value of 0.05 C or less.

[0012] According to the present disclosure, by charging a solid-state lithium-ion battery including a negative electrode active material layer having a predetermined facing portion and a non-facing portion at a current value of 0.05 C or less, lithium ions can be transferred from the non-facing portion to the positive electrode active material layer, and the capacity of the solid-state lithium-ion battery can be restored.

[0013] When the negative electrode active material layer has a non-facing portion as described above, lithium ions that have migrated from the positive electrode active material layer may seep into (be inserted into) the non-facing portion. In this case, it may be difficult to sufficiently extract (desorb) lithium ions from the non-facing portion, which may result in a decrease in battery capacity. In particular, when the battery is charged and discharged at a high rate, it is thought that extraction of lithium ions becomes even more difficult. In this regard, Patent Document 2 discloses a capacity recovery method for a lithium-ion secondary battery, which is a liquid-based battery. However, for solid-state batteries that use a solid electrolyte as the electrolyte, the ion conduction characteristics are different, so sufficient capacity recovery cannot be expected even if the technology (capacity recovery method) for liquid-based batteries is directly applied to solid-state batteries.

[0014] As a result of extensive research into this point, the present inventors have found that by charging at a current value of 0.05 C or less, that is, by performing a slow charging operation, lithium ions can be sufficiently extracted (desorbed) from the non-facing portions even in solid-state batteries, and have completed the present invention.

[0015] 1. Capacity recovery process The capacity recovery process in the present disclosure is a process for transferring lithium ions from the non-facing portion to the positive electrode active material layer by charging a predetermined solid-state lithium ion battery at a current value of 0.05 C or less. Details of solid-state lithium ion batteries are described in "2. Solid-state lithium ion batteries."

[0016] The current value may be 0.04 C or less, or may be 0.03 C or less. On the other hand, the current value is, for example, 0.01 C or more.

[0017] Furthermore, the state of charge (SOC) of the solid-state lithium-ion battery undergoing the capacity recovery process is not particularly limited. The SOC is, for example, 50% or less, and may be 40% or less, 30% or less, or 20% or less. On the other hand, the SOC may be 0% or greater than 0%. The SOC may be 5% or greater, or 10% or greater.

[0018] Furthermore, it is preferable that the capacity recovery process be performed until the SOC reaches a predetermined value (threshold) or more. The SOC threshold is, for example, 10% or more, or may be 30% or more, 50% or more, or 70% or more. Furthermore, the capacity recovery process may be continued until the SOC reaches 100%.

[0019] The lithium ion extraction rate in the capacity recovery process is, for example, 62% or more, or may be 65% or more, or 70% or more. On the other hand, the lithium ion extraction rate may be 100% or less. The lithium ion extraction rate may be 95% or less, or may be 90% or less. A method for determining the lithium ion extraction rate will be described in the Examples.

[0020] The capacity recovery process may be a single charging process or two or more charging processes (charging cycles). In the latter case, the discharge conditions are not particularly limited, but an example is a method of discharging at a current value higher than 0.05 C until the SOC reaches a predetermined value (for example, an arbitrary value less than 50%). In the latter case, the charging conditions may be different or the same for each cycle, but are preferably the same.

[0021] 2. Solid-state lithium-ion batteries The solid-state lithium-ion battery includes a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer.

[0022] The positive electrode active material layer contains at least a positive electrode active material. The positive electrode active material layer may also contain at least one of a conductive material, a binder, and a solid electrolyte, as needed. Known materials used in lithium-ion batteries can be used for the positive electrode active material, the conductive material, and the binder. The solid electrolyte will be described later.

[0023] The negative electrode active material layer contains at least a negative electrode active material. The negative electrode active material layer may also contain at least one of a conductive material, a binder, and a solid electrolyte, as necessary. The conductive material, the binder, and the solid electrolyte are as described above. The negative electrode active material may also be a known negative electrode active material used in lithium-ion batteries.

[0024] The negative electrode active material layer has a facing portion that faces the positive electrode active material layer via a solid electrolyte layer (described later) and a non-facing portion that does not face the positive electrode active material layer via the solid electrolyte layer. The length of the non-facing portion is not particularly limited, but is, for example, 1 mm or more.

[0025] The solid electrolyte layer contains at least a solid electrolyte and may contain a binder as needed. The binder is as described above. Examples of the solid electrolyte include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, and halide solid electrolytes, and organic solid electrolytes such as gel electrolytes. A solid battery using only an inorganic solid electrolyte as the solid electrolyte is called an all-solid-state battery.

[0026] Furthermore, solid-state lithium-ion batteries typically include a positive electrode current collector and a negative electrode current collector. These components can be made of known materials used in lithium-ion batteries. Solid-state lithium-ion batteries are typically secondary batteries.

[0027] Furthermore, the use of the solid-state lithium-ion battery is not particularly limited, but examples thereof include a power source for a vehicle such as a hybrid electric vehicle (HEV). When used as a power source for a vehicle, the capacity recovery method of the present disclosure can be suitably used during vehicle inspection.

[0028] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0029] [Example 1] (Fabrication of all-solid-state lithium-ion batteries) An all-solid-state battery was fabricated as shown in Figure 1(a). Si was used as the negative electrode active material, nickel-cobalt-manganese lithium oxide was used as the positive electrode active material, and a sulfide solid electrolyte was used as the solid electrolyte. A rubber-based binder was used as the binder, and a carbon-based conductive material was used as the conductive material. The length of the uncoated area was 1 mm.

[0030] (Capacity recovery process) The above all-solid-state lithium-ion battery was repeatedly charged and discharged at 1C (SOC 0% to 100%). This intentionally created a state in which lithium ions seeped into the uncoated areas, resulting in a decrease in battery capacity. The all-solid-state battery with reduced capacity was discharged until the SOC reached 0%. It was then charged at a current value of 0.05C.

[0031] [Example 2, Comparative Examples 1 to 3] The all-solid-state lithium-ion battery with an SOC adjusted to 0% was subjected to a capacity recovery process in the same manner as in Example 1, except that the current value was changed to 0.01 C (Example 2), 0.12 C (Comparative Example 1), 0.25 C (Comparative Example 2), or 0.75 C (Comparative Example 3) and charged.

[0032] [evaluation] Based on X-ray absorption fine structure analysis (XAFS), the valence (oxidation state) of the transition metals in the uncoated area was calculated before and after the capacity recovery treatment. The extraction rate of lithium ions from the uncoated area was calculated from the change in valence before and after the capacity recovery treatment. The results are summarized in Figure 2.

[0033] As shown in FIG. 2, it was shown that by charging at a current value of 0.05 C or less, 60% or more of lithium ions could be extracted (recovered) from the uncoated portion, and it was confirmed that the capacity of the solid-state lithium-ion battery could be sufficiently recovered by the method disclosed herein. [Explanation of symbols]

[0034] 1...Cathode active material layer 2...Negative electrode active material layer 2A…Opposing part 2B…Non-opposing part 3...Solid electrolyte layer 4...Positive electrode current collector 5...Negative electrode current collector 10...Solid-state lithium-ion battery

Claims

[Claim 1] A method for restoring capacity of a solid-state lithium-ion battery, comprising: the solid-state lithium-ion battery comprises a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer; the negative electrode active material layer has a facing portion facing the positive electrode active material layer with the solid electrolyte layer interposed therebetween, and a non-facing portion not facing the positive electrode active material layer with the solid electrolyte layer interposed therebetween, a capacity recovery method for a solid-state lithium ion battery, the method comprising: a capacity recovery treatment in which the solid-state lithium ion battery is charged at a current value of 0.05 C or less, thereby transferring lithium ions from the non-facing portion to the positive electrode active material layer.

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