JP2009193803A - All-solid lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an all-solid lithium secondary battery in which resistance against lithium ion conduction is made small and output is improved by suppressing formation of a space charge layer at the interface of the negative electrode layer side of a sulfide based solid electrolyte layer. <P>SOLUTION: In the all-solid lithium secondary battery, an electrochemically stable sulfide-based solid electrolyte layer is formed against the negative electrode layer on the negative electrode layer. Between the negative electrode layer and the sulfide-based solid electrolyte layer, an Li ion conductor modified layer which is electrochemically stable and has no electron conductivity against the negative electrode layer is provided, and problems are solved. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an all-solid lithium secondary battery in which a resistance to lithium ion conduction is reduced and output is improved by suppressing formation of a space charge layer at a negative electrode layer side interface of a sulfide-based solid electrolyte layer.

  With the rapid spread of information-related equipment and communication equipment such as personal computers, video cameras, and mobile phones in recent years, the development of secondary batteries that are excellent as power sources, such as lithium secondary batteries, has been regarded as important. In fields other than the information-related equipment and communication-related equipment, for example, in the automobile industry, the development of high-power and high-capacity lithium secondary batteries for electric vehicles and hybrid vehicles as low-emission vehicles has been promoted. ing.

  However, the lithium secondary batteries currently on the market use an organic electrolyte that uses a flammable organic solvent as a solvent.・ Improved materials are necessary.

  In contrast, an all-solid lithium secondary battery in which the liquid electrolyte is changed to a solid electrolyte to make the battery all solid does not use a flammable organic solvent in the battery, so the safety device can be simplified and manufactured. It is considered to be excellent in cost and productivity.

However, a Li ₂ S · SiS ₂ · LiPO ₄ glass electrolyte containing a transition metal such as silicon or germanium as a solid electrolyte or a Li ₂ S · GeS ₂ · P ₂ S ₅ based crystalline sulfide lithium ion conductor, etc. When used at the time of charging at a low current density, silicon, germanium, etc., which are transition metals contained in the electrolyte, are electrochemically reduced on the surface of the carbon electrode having electron conductivity and used for charging and discharging the battery. It inhibited the electrochemical reduction and oxidation reaction of lithium ions, and deteriorated the charge / discharge efficiency. When this reaction is continued, silicon and germanium present in the solid electrolyte are reduced on the surface, and as a result, dendritic lithium silicon alloy or lithium germanium alloy having electron conductivity is deposited and grown. Finally, there was a problem that the positive electrode and the negative electrode were short-circuited.

  In order to solve such a problem, for example, in Patent Document 1, an entire second solid electrolyte layer that does not contain a transition metal is provided between the first sulfide-based solid electrolyte and the lithium metal negative electrode. A solid lithium secondary battery is disclosed. This prevents the first sulfide-based solid electrolyte from being reduced by the second solid electrolyte layer that does not contain a transition metal. However, in such a case, it is necessary to more reliably prevent the reaction between the first sulfide-based solid electrolyte and the lithium metal negative electrode. Therefore, the entire interface between the sulfide-based solid electrolyte and the lithium metal negative electrode is covered. It was necessary to coat with a second solid electrolyte layer not containing a transition metal, or to increase the thickness of the second solid electrolyte layer not containing a transition metal. For this reason, there existed a problem that lithium ion conductivity fell.

Thus, for example, in Non-Patent Document 1, a Li ₂ S—P—S solid electrolyte material that is electrochemically stable with respect to the negative electrode layer without being reduced even when metallic lithium is used for the negative electrode is used. The all-solid lithium secondary battery used is disclosed. However, the Li ₂ migration occurs due to the chemical potential difference between the solid electrolyte material and the negative electrode layer at the Li ₂ S—P—S solid electrolyte material and the metal lithium interface, and a space charge layer is formed. There has been a problem that resistance to lithium ion conduction is increased.

In Non-Patent Document 1, the formation of a space charge layer between the positive electrode layer and the solid electrolyte layer is prevented by interposing LiNbO ₃ between the positive electrode layer and the solid electrolyte layer, thereby increasing the output. Disclosed. However, oxide-based Li ion conductors such as LiNbO ₃ are vulnerable to reduction and cannot be used as a modification layer for the negative electrode layer.

JP 2004-206942 A JP 2005-353309 A JP 2001-52733 A "Solid State Ionics 177 (2006) 2753-2757" "Electrochemistry communications 9 (2007) 1486-1490"

  The present invention has been made in view of the above problems, and by suppressing the formation of a space charge layer at the negative electrode layer side interface of the sulfide-based solid electrolyte layer, the resistance to lithium ion conduction is reduced, and the output An object of the present invention is to provide an all-solid lithium secondary battery with improved resistance.

  To achieve the above object, the present invention provides an all-solid lithium secondary battery in which a sulfide-based solid electrolyte layer that is electrochemically stable with respect to the negative electrode layer is formed on the negative electrode layer, An all solid lithium secondary battery comprising a Li ion conductor modification layer that is electrochemically stable and non-electron-conductive with respect to the negative electrode layer between the negative electrode layer and the sulfide-based solid electrolyte layer I will provide a.

  According to the present invention, by providing the above-described Li ion conductor modification layer, the loss of Li ions accompanying the movement of Li ions from the sulfide-based solid electrolyte layer near the negative electrode layer to the negative electrode layer due to the chemical potential difference is eliminated. It is possible to suppress the formation of the space charge layer at the negative electrode layer side interface of the sulfide-based solid electrolyte layer. This can reduce the resistance to lithium ion conduction and improve the output.

In the above invention, the negative electrode layer preferably has an oxidation-reduction potential of 0.5 V (vsLi / Li ⁺ ) or less. When the negative electrode layer has such a redox potential, the space charge layer is more easily formed and the resistance to lithium ion conduction is also increased. Therefore, in such a case, the present invention can particularly exhibit its excellent effect. Further, by having such a redox potential, higher output can be achieved.

  In the said invention, it is preferable that the said negative electrode layer has at least 1 type chosen from the group which consists of metal Li, graphite, Si, and Sn. When the negative electrode layer has at least one selected from the group consisting of metal Li, graphite, Si, and Sn, the space charge layer is more easily formed and the resistance to lithium ion conduction is also increased. Therefore, in such a case, the present invention can particularly exhibit its excellent effect. Also, by having such a negative electrode layer, it is possible to increase the output of the all solid lithium secondary battery more reliably.

  In the said invention, it is preferable that the said sulfide type solid electrolyte layer does not have a transition metal element. This is because a sulfide-based solid electrolyte layer that is electrochemically stable with respect to the negative electrode layer can be obtained.

  In the said invention, it is preferable that the said sulfide type solid electrolyte layer has Li and S, and has at least 1 type chosen from the group which consists of P, B, and O. This is because a sulfide-based solid electrolyte layer that is more electrochemically stable with respect to the negative electrode layer can be obtained. Furthermore, it is because an all-solid lithium secondary battery with higher output can be obtained.

In the above invention, the Li-ion conductor modifying layer is _Li 3 N, LiCl, and is preferably made of at least one selected from the group consisting of LiF. This is because the effect of suppressing the formation of the space charge layer at the negative electrode layer side interface of the sulfide-based solid electrolyte layer is high.

  In the present invention, an all-solid lithium secondary battery with reduced resistance to lithium ion conduction and improved output by suppressing formation of a space charge layer at the negative electrode layer side interface of the sulfide-based solid electrolyte layer is provided. There is an effect that it can be obtained.

  The all solid lithium secondary battery of the present invention will be described in detail below.

  The all solid lithium secondary battery of the present invention is an all solid lithium secondary battery in which a sulfide-based solid electrolyte layer that is electrochemically stable with respect to the negative electrode layer is formed on the negative electrode layer, and the negative electrode layer And a lithium ion conductor modification layer that is electrochemically stable and has no electron conductivity with respect to the negative electrode layer.

  According to the present invention, since the Li ion conductor modified layer is formed, an increase in the Li ion concentration in the sulfide solid electrolyte layer near the negative electrode layer due to the chemical potential difference is suppressed, and the sulfide solid Formation of the space charge layer at the negative electrode layer side interface of the electrolyte layer can be suppressed. This can reduce the resistance to lithium ion conduction and improve the output. This can be presumed to be due to the following reasons.

  That is, in order to improve the output, those having a large potential difference between the negative electrode layer and the sulfide solid electrolyte layer are usually used as the negative electrode layer and the sulfide solid electrolyte layer. When the potential difference between the negative electrode layer and the sulfide-based solid electrolyte layer is large as described above, the potential difference or chemical potential difference is usually at the solid (negative electrode layer) -solid (sulfide-based solid electrolyte layer) interface. As a result of lithium movement, a space charge layer is formed in the sulfide-based solid electrolyte layer near the negative electrode layer. For this reason, movement of lithium becomes difficult and resistance to lithium ion conduction is increased. In addition, since a Schottky type junction is formed at the interface between the electron-ion mixed conductor (for example, positive electrode active material, negative electrode active material, etc.) and the ion conductor (for example, sulfide-based solid electrolyte), sulfide-based solid The space charge layer on the electrolyte layer side is greatly developed.

  In the present invention, a Li ion conductor modification layer that is electrochemically stable and has no electronic conductivity with respect to the negative electrode layer is formed between the negative electrode layer and the sulfide-based solid electrolyte layer. The Li ion conductor modified layer can suppress the formation of the space charge layer by suppressing the movement of Li ions due to the chemical potential difference. In addition, since the Schottky junction as described above is not formed, the space charge layer on the sulfide solid electrolyte layer side does not develop greatly. For this reason, the resistance to lithium ion conduction can be reduced, thereby improving the output.

Hereinafter, the all solid lithium secondary battery of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic cross-sectional view schematically showing an example of an all-solid lithium secondary battery in the present invention. An all solid lithium secondary battery shown in FIG. 1 includes a negative electrode layer 1, a sulfide solid electrolyte layer 2 that is electrochemically stable with respect to the negative electrode layer 1 formed on the negative electrode layer 1, and a sulfide solid electrolyte. The positive electrode layer 3 disposed so as to sandwich the layer 2 with the negative electrode layer 1 and the negative electrode layer 1 between the negative electrode layer 1 and the sulfide-based solid electrolyte layer 2 are electrochemically stable and electronically conductive. The Li ion conductor modification layer 4 is not included. Usually, a negative electrode current collector 5 is provided on the negative electrode layer 1 and a positive electrode current collector 6 is provided on the positive electrode layer 3 so as to sandwich them, and further, an insulating (battery case) portion is provided so as to cover the side surface. 7 is arranged.

  The all solid lithium secondary battery of the present invention is not particularly limited as long as it has at least the Li ion conductor modified layer, the negative electrode layer, and the sulfide solid electrolyte. Usually, as described above, it has a positive electrode layer, a positive electrode current collector, a negative electrode current collector, a battery case, and the like.

  Hereinafter, the all solid lithium secondary battery of the present invention will be described in detail for each configuration.

1. Li ion conductor modification layer First, the Li ion conductor modification layer used in the present invention will be described. The Li ion conductor modified layer in the present invention is formed between the negative electrode layer and the sulfide-based solid electrolyte layer, and is characterized by being electrochemically stable with respect to the negative electrode layer and having no electron conductivity. To do.

  In the present invention, a Li ion conductor modified layer that is electrochemically stable and has no electron conductivity with respect to the negative electrode layer is formed between the negative electrode layer and the sulfide-based solid electrolyte layer, thereby As described above, the Li ion conductor modification layer can suppress the formation of the space charge layer by suppressing the movement of Li ions due to the chemical potential difference. In addition, since no Schottky junction is formed at the interface between the negative electrode layer and the sulfide-based solid electrolyte layer, the space charge layer on the sulfide-based solid electrolyte layer side does not develop greatly. For this reason, the resistance to lithium ion conduction can be reduced and the output can be improved.

  In the present invention, the Li ion conductor modified layer is characterized in that it is electrochemically stable with respect to the negative electrode layer. Specifically, “chemically stable” means that the Li ion conductor modification layer does not undergo reductive decomposition (does not accept electrons at the potential of the negative electrode). The presence or absence of the above reductive decomposition can be confirmed by examining the presence or absence of a reducing current by cyclic voltammetry.

In the present invention, the Li ion conductor modified layer is characterized by having no electron conductivity. Specifically, the Li ion conductor modified layer has a conductivity of 10 ^−. It is preferably ⁶ S / cm or less, more preferably in the range of 10 ⁻¹⁵ S / cm to 10 ⁻⁷ S / cm. It is preferable that This is because the resistance to lithium ion conduction can be reduced and the output can be improved by making the movement of Li ions more difficult due to the chemical potential difference and suppressing the formation of the space charge layer.

Such materials used for the Li ion conductor modification layer are those that are electrochemically stable and non-electron conductive with respect to the negative electrode layer, and can suppress the formation of the space charge layer. There is no particular limitation as long as it is. Specifically, it is preferably made of at least one selected from the group consisting of Li ₃ N, LiCl, and LiF. This is because the formation of the space charge layer at the negative electrode layer side interface of the sulfide-based solid electrolyte layer can be effectively suppressed. In the present invention, Li ₃ N is particularly preferable.

  As the film thickness of the Li ion conductor modified layer, by suppressing the formation of the space charge layer, the resistance to lithium ion conduction is reduced, and a desired all-solid lithium secondary battery with improved output is obtained. The film thickness is not particularly limited as long as the film thickness can be reduced.

  This film thickness is preferably determined by the chemical potential difference between the negative electrode layer and the sulfide-based solid electrolyte layer, the Li ion conductivity of the Li ion conductor modification layer, and the like, for example, 100 nm or less, especially 50 nm or less. In particular, a range of 30 nm or less is preferable. In addition, as a minimum, it can be 1 nm or more. If it is larger than the above range, the Li ion conduction resistance of the Li ion conductor modification layer itself becomes large, and the output may not be improved. On the other hand, if it is smaller than the above range, a tunnel current may flow, and the formation of the space charge layer may be suppressed, and the output may not be improved.

Specifically, the film thickness of the Li ion conductor modified layer is usually the difference in chemical potential between the negative electrode layer and the sulfide-based solid electrolyte layer, and the Li ion conductivity of the Li ion conductor modified layer. Can be determined. For example, when the negative electrode layer is metal Li, the sulfide-based solid electrolyte layer is Li ₇ P ₃ S ₁₁ , and the Li ion conductor modification layer is Li ₃ N, it is within 100 nm or less, particularly in the range of 1 nm to 30 nm. It is preferable that Further, for example, a negative electrode mixture composed of metal Li, graphite, and a sulfide-based solid electrolyte layer is used for the anode layer, and the sulfide-based solid electrolyte layer is modified with Li ₇ P ₃ S ₁₁ and the Li ion conductor. When the layer is Li ₃ N, it is preferably 30 nm or less, and more preferably in the range of 1 nm to 30 nm.

  In the present invention, a value measured based on image analysis using an electron microscope can be used as the film thickness of the Li ion conductor modification layer.

  In the present invention, the Li ion conductor modification layer is formed at the interface between the negative electrode layer and the sulfide-based solid electrolyte layer, but by suppressing the formation of the space charge layer, lithium ions are formed. As long as the desired all-solid lithium secondary battery with reduced resistance to conduction and improved output can be obtained, it may be partially formed on the interface, or formed on the entire interface. It may be what was done. Usually, it is preferable that the Li ion conductor modification layer is formed more on the interface, and it is particularly preferable that the Li ion conductor modification layer be formed on the entire interface. This is because the formation of the space charge layer can be suppressed over the entire interface, and the resistance to lithium ion conduction can be further reduced and the output can be improved.

2. Next, the negative electrode layer in the present invention will be described. The negative electrode layer in the present invention is formed on a sulfide-based solid electrolyte layer that is electrochemically stable with respect to the negative electrode layer as described later.

  In the present invention, the negative electrode layer is usually one having a large potential difference from the sulfide-based solid electrolyte layer in order to increase the electromotive force. Thus, when the difference in electrochemical potential of Li ions between the negative electrode layer and the sulfide-based solid electrolyte layer is large, the space charge as described above is formed at the interface between the negative electrode layer and the sulfide-based solid electrolyte layer. A layer is easily formed, and resistance to lithium ion conduction is increased. In the present invention, even when such a negative electrode layer is used, Li at the interface between the negative electrode layer and the sulfide-based solid electrolyte layer is electrochemically stable with respect to the negative electrode layer and has no electron conductivity. By having the ion conductor modification layer, the formation of the space charge layer is suppressed, the resistance to lithium ion conduction is reduced, and thereby a desired all-solid lithium secondary battery with improved output can be obtained. It is.

The negative electrode layer used in the present invention is not particularly limited as long as it has a function as a negative electrode layer. Usually, as described above, in order to increase the electromotive force, A material having an oxidation-reduction potential that increases the potential difference from the sulfide-based solid electrolyte layer is used. Specifically, the negative electrode layer preferably has an oxidation-reduction potential of 0.5 V (vsLi / Li ⁺ ) or less. When the negative electrode layer has such a redox potential, the space charge layer is more easily formed and the resistance to lithium ion conduction is also increased. Therefore, in such a case, the present invention can particularly exhibit its excellent effect. Further, the electromotive force of the all-solid lithium secondary battery can be increased by increasing the potential difference between the negative electrode layer and the sulfide-based solid electrolyte layer.

In the present invention, the negative electrode layer preferably has at least one selected from the group consisting of metals Li, graphite, Si, and Sn as a negative electrode material. Among these, it is preferable to have at least one selected from the group consisting of metal Li and graphite. More reliably, the negative electrode layer can have an oxidation-reduction potential of 0.5 V (vsLi / Li ⁺ ) or less, the space charge layer is more easily formed, and the resistance to lithium ion conduction is also increased. In this case, the present invention can particularly exhibit its excellent effect. Further, this is because the all-solid lithium secondary battery can be further increased in output.

  In addition, the negative electrode layer may be composed of only the negative electrode material, or may be composed of a negative electrode mixture in which the negative electrode material and the solid electrolyte material are mixed. Moreover, in the said negative electrode layer in this invention, in order to improve electroconductivity, you may contain conductive support agents, such as acetylene black, ketjen black, and carbon fiber. In addition, you may form a negative electrode layer using what mixed the said negative electrode material 2 or more types.

  As the film thickness of the negative electrode layer, a film thickness capable of obtaining a desired all-solid lithium secondary battery with reduced resistance to lithium ion conduction and improved output by suppressing the formation of the space charge layer. If it is, it will not specifically limit.

  In the present invention, the film thickness of the negative electrode layer may be a value measured based on image analysis using an electron microscope.

3. Sulfide-based solid electrolyte layer Next, the sulfide-based solid electrolyte layer in the present invention will be described. The sulfide-based solid electrolyte layer in the present invention is formed on the negative electrode layer and is electrochemically stable with respect to the negative electrode layer.

  In the present invention, the sulfide-based solid electrolyte layer is electrochemically stable with respect to the negative electrode layer, so that even when the negative electrode layer having a low redox potential as described above is used, Formation of an alloy or the like due to a reaction between the sulfide-based solid electrolyte layer and the negative electrode layer, and a short circuit due to the alloy or the like can be suppressed.

  Thus, the sulfide solid electrolyte layer is electrochemically stable with respect to the negative electrode layer. However, the space charge layer as described above is easily formed at the interface between the sulfide-based solid electrolyte layer and the negative electrode layer, and the resistance to lithium ion conduction increases. In the present invention, at the interface between the sulfide-based solid electrolyte layer and the negative electrode layer, there is a Li ion conductor modified layer that is electrochemically stable and has no electronic conductivity with respect to the negative electrode layer. It is possible to obtain a desired all-solid lithium secondary battery in which the formation of the space charge layer is suppressed and the resistance to lithium ion conduction is reduced, thereby improving the output.

  In the present invention, the sulfide-based solid electrolyte layer is electrochemically stable with respect to the negative electrode layer. The sulfide-based solid electrolyte layer is Specifically, being electrochemically stable means that the sulfide-based electrolyte layer does not undergo reductive decomposition (does not accept electrons at the potential of the negative electrode). The presence or absence of the above reductive decomposition can be confirmed by examining the presence or absence of a reducing current by cyclic voltammetry.

  The sulfide-based solid electrolyte layer in the present invention is not particularly limited as long as it has a function as a sulfide-based solid electrolyte layer, is formed on the negative electrode layer, and is electrochemically stable with respect to the negative electrode layer. It is not something.

Specifically, the sulfide-based solid electrolyte layer preferably does not have a transition metal element. This is because by not having a transition metal element, a sulfide-based solid electrolyte layer that is electrochemically more stable with respect to the negative electrode layer can be obtained. The sulfide-based solid electrolyte material used for such a sulfide-based solid electrolyte layer only needs to have at least Li (lithium) and S (sulfur), and if necessary, P (phosphorus), B You may have elements, such as (boron) and O (oxygen). _{Specifically,} mention may be made of _{Li 7 P 3 S 11, Li} 2 S, Li 3 PO 4 -Li 2 S-B 2 S 3 _{type, 80Li 2 S-20P 2 S} 5 or the like. Among them, it is preferable to have Li and S and to have at least one selected from the group consisting of P, B, and O. This is because a sulfide-based solid electrolyte layer that is more electrochemically stable with respect to the negative electrode layer can be obtained. Furthermore, because the ion conductivity is improved, a higher-power all-solid lithium secondary battery can be obtained. Examples of such a material include Li ₇ P ₃ S ₁₁ , 80Li ₂ S-20P ₂ S ₅ , Li ₃ PO ₄ —Li ₂ S—B ₂ S ₃ system, and the like.

  Regarding the film thickness of the sulfide-based solid electrolyte layer, by suppressing the formation of the space charge layer, the resistance to lithium ion conduction is reduced, and a desired all-solid lithium secondary battery with improved output is obtained. The film thickness is not particularly limited as long as the film thickness can be reduced.

  In the present invention, the film thickness of the sulfide-based solid electrolyte layer may be a value measured based on image analysis using an electron microscope.

4). Other Configurations In the all solid lithium secondary battery, configurations other than the above-described negative electrode layer, sulfide-based solid electrolyte layer, and Li ion conductor modified layer, such as a positive electrode layer, a positive electrode side Li ion conductor modified layer, and a positive electrode collector. Other configurations such as the electric current collector, the negative electrode current collector, and the battery case will be described in detail below.
(1) Positive electrode layer The positive electrode layer used in the present invention is not particularly limited as long as it has a function as a positive electrode layer, and may be composed of only a positive electrode material. It may be composed of a positive electrode mixture mixed with a solid electrolyte material, and the same materials as those used in a general all solid lithium secondary battery can be used. Moreover, in order to improve electroconductivity, you may contain conductive support agents, such as acetylene black, ketjen black, and carbon fiber.

  The film thickness of the positive electrode layer is not particularly limited, and a film having a thickness similar to that of the positive electrode layer used in a normal all-solid lithium secondary battery can be used.

(2) Positive electrode side Li ion conductor modification layer Next, the positive electrode side Li ion conductor modification layer used for this invention is demonstrated.

  In the present invention, in order to prevent a space charge layer from being formed at the interface between the positive electrode layer and the sulfide-based solid electrolyte layer and increasing resistance to lithium ion conduction, the positive electrode layer and the sulfide are prevented. You may have the positive electrode side Li ion conductor modification layer which is electrochemically stable with respect to the said positive electrode layer, and does not have electronic conductivity in the interface with a system solid electrolyte layer. By having such a positive electrode side Li ion conductor modification layer, formation of a space charge layer at the interface between the positive electrode layer and the sulfide-based solid electrolyte layer is suppressed, and resistance to lithium ion conduction is reduced. Thus, a desired all-solid lithium secondary battery with improved output can be obtained.

The material used for the positive electrode side Li ion conductor modification layer used in the present invention is electrochemically stable and non-electron conductive to the positive electrode layer, and suppresses the formation of the space charge layer. It is not particularly limited as long as it is possible. For example, LiNbO ₃ can be used.

  As the film thickness of the positive electrode side Li ion conductor modification layer, a desired all-solid lithium secondary battery having a reduced resistance to lithium ion conduction and an improved output by suppressing the formation of the space charge layer can be obtained. The film thickness is not particularly limited as long as it can be obtained.

  In the present invention, the positive electrode side Li ion conductor modification layer is formed at the interface between the positive electrode layer and the sulfide-based solid electrolyte layer, but by suppressing the formation of the space charge layer, As long as the desired all-solid lithium secondary battery with reduced resistance to lithium ion conduction and improved output can be obtained, it may be partially formed at the interface, or the entire interface. It may be formed in. Usually, it is preferable that the positive electrode side Li ion conductor modification layer is formed more on the interface, and it is particularly preferable that the positive electrode side Li ion conductor modification layer be formed on the entire interface. This is because the formation of the space charge layer can be suppressed over the entire interface, and the resistance to lithium ion conduction can be further reduced and the output can be improved.

(3) Positive electrode current collector The positive electrode current collector used in the present invention collects current from the positive electrode layer. The positive electrode current collector is not particularly limited as long as it has a function as a positive electrode current collector. The material of the positive electrode current collector is not particularly limited as long as it has conductivity, and examples thereof include SUS, aluminum, nickel, iron, titanium, and carbon. preferable. Furthermore, the positive electrode current collector may be a dense current collector or a porous current collector.

(4) Negative electrode current collector The negative electrode current collector used in the present invention collects the current from the negative electrode layer. The negative electrode current collector is not particularly limited as long as it has a function as a negative electrode current collector. The material for the negative electrode current collector is not particularly limited as long as it has conductivity, and examples thereof include SUS, copper, nickel, and carbon. Among them, SUS is preferable. Furthermore, the negative electrode current collector may be a dense current collector or a porous current collector.

(5) Other Configurations Other configurations other than the above-described members, for example, an insulating part such as a battery case, a resin used for sealing a coin-type battery case, and the like will be described.

  The insulating part, the resin, and the like are not particularly limited, and those similar to a general all solid lithium secondary battery can be used.

  Specifically, examples of the insulating part include an insulating ring and a battery case. As the battery case, generally, a metal case is used, for example, a stainless steel case. Further, the battery case may have a current collector function. Specifically, a case where a battery case made of SUS (stainless steel) is prepared and a part of the battery case is used as a current collector can be exemplified. Moreover, as said resin, resin with a low water absorption rate is preferable, for example, an epoxy resin etc. are mentioned.

5. Others (1) Manufacturing method of all-solid lithium secondary battery The manufacturing method of the all-solid lithium secondary battery of the present invention is not particularly limited as long as it is a method capable of obtaining the all-solid lithium secondary battery. is not. For example, a sulfide-based solid electrolyte layer forming step of forming a sulfide-based solid electrolyte layer by press-molding a sulfide-based solid electrolyte material is performed. Next, a negative electrode material is pressure-bonded onto the negative electrode current collector to form a negative electrode layer, and a negative electrode layer forming step is performed. Furthermore, a Li ion conductor modification layer is formed by forming a Li ion conductor modification layer on the negative electrode layer by flowing a predetermined gas (for example, nitrogen gas, chlorine gas, fluorine gas, etc.) for a predetermined time using the negative electrode layer. Perform the process.

  Next, a positive electrode layer forming step is performed in which a positive electrode mixture composed of a positive electrode material and a solid electrolyte material or only the positive electrode material is placed on the positive electrode current collector and then press-molded to form a positive electrode layer. Next, the negative electrode layer is placed on the sulfide-based solid electrolyte layer so that the Li ion conductor modification layer is in contact with the sulfide-based solid electrolyte layer, and the sulfide-based solid electrolyte layer is further The positive electrode layer is placed so as to be sandwiched between the negative electrode layer. Furthermore, after installing this in, for example, a coin-type battery case, the desired all-solid lithium secondary battery described above is obtained by performing a battery cell forming step of forming a battery cell by sealing with a resin packing. The method etc. can be mentioned.

  The sulfide-based solid electrolyte layer forming step, the negative electrode layer forming step, the Li ion conductor modification layer forming step, the positive electrode layer forming step, and the battery cell forming step are the desired all-solid lithium secondary described above. As long as a battery can be obtained, each process may be performed simultaneously or the order of each process may be changed. Moreover, as long as the desired all-solid lithium secondary battery described above can be obtained, other processes other than the processes described above may be included.

(2) Use Although it does not specifically limit as a use of the all-solid-state lithium secondary battery of this invention, For example, it can use as an all-solid-state lithium secondary battery for motor vehicles, etc.

(3) Shape Examples of the shape of the all solid lithium secondary battery of the present invention include a coin shape, a laminate shape, a cylindrical shape, and a square shape, among which a square shape and a laminate shape are preferable, and a laminate type is particularly preferable.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  Hereinafter, the present invention will be described more specifically with reference to examples.

[Example 1]
(Evaluation cell formation)
First, on the SUS plate as a current collector dried in a glow box having a dew point of −70 ° C. or less for one week or more, a similarly dried metal Li is pressure-bonded to form a negative electrode layer, and dry nitrogen is added for 5 minutes. It was treated with flow (room temperature) to nitrogen and formed Li ion conductor modifying layer (Li 3 _N) on the negative electrode layer.

Li ₇ P ₃ S ₁₁ was used as a sulfide-based solid electrolyte material, and press-molded to form Li ₇ P ₃ S ₁₁ pellets.

Using the obtained negative electrode current collector (SUS), negative electrode layer (metal Li), and Li ion conductor modified layer (Li ₃ N) as a negative electrode body, two negative electrode bodies were used to form Li ₇ P _3. The S ₁₁ pellet was sandwiched so that the Li ion conductor modified layer and the sulfide-based solid electrolyte were in contact with each other to form a symmetric cell to obtain an evaluation cell.

[Example 2]
A symmetric cell was formed as an evaluation cell in the same manner as in Example 1 except that the treatment time in nitrogen was changed to 10 minutes.

[Example 3]
A symmetrical cell was formed as an evaluation cell in the same manner as in Example 1 except that the treatment time in nitrogen was 30 minutes.

[Example 4]
180 mg of graphite and 3.8 mg of metal Li were mixed and heat-treated at 200 ° C. for 16 hours in Ar to intercalate metal Li into graphite. Thereafter, heat treatment was performed at 200 ° C. for 8 hours in N ₂ to form a Li nitride film. After mixing 3.4 mg of the obtained powder and 3.4 mg of the sulfide-based solid electrolyte material, it was placed on a SUS plate as a current collector that was dried in a glow box with a dew point of −70 ° C. or lower for one week or longer. Then, it was press-molded to obtain a negative electrode body.

  A symmetric cell was formed as an evaluation cell in the same manner as in Example 1 except that such a negative electrode body was used.

[Example 5]
A symmetrical cell was formed as an evaluation cell in the same manner as in Example 4 except that the amount of metal Li was 12 mg.

[Comparative Example 1]
A symmetrical cell was formed as an evaluation cell in the same manner as in Example 1 except that the treatment was not performed in nitrogen.

[Comparative Example 2]
A symmetric cell was formed as an evaluation cell in the same manner as in Example 4 except that no metal Li was added.

[Evaluation]
(Impedance measurement)
Impedance was measured using the evaluation cells obtained in Examples 1 to 5, Comparative Example 1 and Comparative Example 2. Further, in Examples 1 to 3 and Comparative Example 1, the interface resistance is obtained from the diameter of the arc whose apex is about 100 kHz of the measured impedance, and the value of ionic conductivity at the lithium nitride interface is used to obtain lithium nitride. The layer thickness was determined. Further, in Example 4, Example 5, and Comparative Example 2, it was assumed that Li was all nitrided from the weight of the metal Li used, and the volume of Li ₃ N was calculated, and nitriding was performed by dividing by the surface area of graphite. The thickness of the lithium layer was determined. FIG. 2 shows the relationship between the obtained impedance (Ω) and Li ₃ N thickness (nm).

  As shown in FIG. 2, when the pressed metal Li was used as the negative electrode layer, the resistance values of Example 1 and Example 2 were significantly lower than those of Comparative Example 1 and showed good values. In addition, Example 3 showed a resistance value comparable to that of Comparative Example 1.

  Moreover, when the negative electrode layer containing graphite was used, Example 4 showed a lower resistance value than Comparative Example 2, and was a good value. Further, the resistance value of Example 5 was larger than that of Comparative Example 2.

In any case, when the Li ₃ N film was formed, the resistance value tended to increase as the Li ₃ N film thickness increased.

From the above results, in the examples, the Li ion conductor modification layer (Li ₃ N film) suppresses the movement of Li ions due to the chemical potential difference between the negative electrode layer and the sulfide-based solid electrolyte layer. By suppressing the formation of the space charge layer at the negative electrode layer side interface of the sulfide-based solid electrolyte layer, the resistance to lithium ion conduction can be reduced and the output can be improved.

In the examples, in the case of Example 1, Example 2, and Example 3 in which the pressed metal Li was used as the negative electrode layer, the thickness of the Li ion conductor modification layer (Li ₃ N film) was changed. It was found that by setting the thickness to 100 nm or less, a better resistance value was exhibited. Further, in the case of Example 4 and Example 5 using the negative electrode layer having graphite, the resistance is further improved by setting the thickness of the Li ion conductor modification layer (Li ₃ N film) to 30 nm or less. It was found to show a value.

It is a schematic sectional drawing which shows typically an example of the all-solid-state lithium secondary battery in this invention. Example 1, Example 2, Example 3, Example 4, Example 5 is a graph showing the relationship between the Li 3 _N thicknesses and impedances of Comparative Example 1, and Comparative Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Negative electrode layer 2 ... Sulfide type solid electrolyte layer 3 ... Positive electrode layer 4 ... Li ion conductor modification layer 5 ... Negative electrode collector 6 ... Positive electrode collector 7 ... Insulation part

Claims (6)

  An all-solid lithium secondary battery in which a sulfide-based solid electrolyte layer that is electrochemically stable with respect to the negative-electrode layer is formed on the negative-electrode layer, between the negative-electrode layer and the sulfide-based solid electrolyte layer An all-solid-state lithium secondary battery comprising a Li ion conductor modification layer that is electrochemically stable and has no electron conductivity with respect to the negative electrode layer. The all-solid-state lithium secondary battery according to claim 1, wherein the negative electrode layer has an oxidation-reduction potential of 0.5 V (vsLi / Li ⁺ ) or less.   3. The all-solid lithium secondary battery according to claim 1, wherein the negative electrode layer has at least one selected from the group consisting of metal Li, graphite, Si, and Sn.   The all-solid-state lithium secondary battery according to any one of claims 1 to 3, wherein the sulfide-based solid electrolyte layer does not contain a transition metal element.   The sulfide type solid electrolyte layer has Li and S, and has at least one selected from the group consisting of P, B, and O. An all-solid lithium secondary battery according to claim 1. The all-solid lithium secondary according to any one of claims 1 to 5, wherein the Li ion conductor modification layer is made of at least one selected from the group consisting of Li ₃ N, LiCl, and LiF. battery.

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