Lithium secondary battery

Abstract

[Problem] To provide a means capable of improving cycle characteristics in a lithium-precipitation-type lithium secondary battery having a negative electrode intermediate layer containing nickel particles. [Solution] A lithium secondary battery comprising a power-generating element comprising: a positive electrode having a positive electrode active material layer containing a positive electrode active material; a negative electrode which has a negative electrode current collector and in which lithium metal precipitates on the negative electrode current collector during charging; a solid electrolyte layer which is interposed between the positive electrode and the negative electrode and contains a solid electrolyte; and a negative electrode intermediate layer which is present adjacent to a surface of the solid electrolyte layer on the negative electrode current collector side and contains Ni particles having Ni (OH)2 on the surface thereof.

Description

Lithium secondary battery

[0001] The present invention relates to a lithium secondary battery.

[0002] In recent years, much research and development has been done on lithium secondary batteries that use oxide- or sulfide-based solid electrolytes, which are materials primarily composed of ionic conductors that allow ions to be conducted in a solid state.

[0003] Conventionally, as one type of lithium secondary battery, a so-called lithium deposition type is known in which lithium metal is deposited on a negative electrode current collector during the charging process (for example, N. Suzuki, N. Yasuhiro, S. Fujiki, R. Omoda, T. Shiratuki, T. Watanabe, and Y. Aihara Adv. Energy Sustainability Res. 2021, 2, 2100066). During the charging process of such a lithium deposition type lithium secondary battery, lithium metal is deposited between the solid electrolyte layer and the negative electrode current collector. At this time, dendrites grow from the lithium metal layer and penetrate the solid electrolyte layer, which can cause a short circuit.

[0004] This document discloses a technique for disposing a layer containing carbon black (negative electrode intermediate layer) between a negative electrode current collector and a solid electrolyte layer, which constitute the power generating element of a lithium secondary battery. According to this document, this configuration allows lithium metal to be deposited as a lithium metal layer between the negative electrode intermediate layer and the negative electrode current collector during charging, and the negative electrode intermediate layer serves as a protective layer for the lithium metal layer. Furthermore, this document investigates negative electrode intermediate layers containing carbon black and various metal particles, and reveals that the use of a negative electrode intermediate layer containing nickel particles exhibits good discharge capacity. However, it also reports that the use of a negative electrode intermediate layer containing nickel particles results in poor cycle performance due to the high current density of the nickel particles, which causes short circuits after repeated charge and discharge.

[0005] In view of the above-mentioned conventional techniques, an object of the present invention is to provide a means for improving the cycle characteristics of a lithium deposition type lithium secondary battery having a negative electrode intermediate layer containing nickel particles.

[0006] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, in a lithium secondary battery equipped with a lithium deposition type power generating element having a negative electrode intermediate layer containing nickel particles, it has been found that Ni(OH) ２ The present inventors have found that the above problems can be solved by incorporating the above compound, and have completed the present invention.

[0007] That is, one embodiment of the present invention is a battery comprising: a positive electrode having a positive electrode active material layer containing a positive electrode active material; a negative electrode having a negative electrode current collector, on which lithium metal is deposited during charging; a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte; and a Ni(OH) ２ and a negative electrode intermediate layer containing Ni particles having a surface thereof.

[0008] Fig. 1 is a cross-sectional view schematically showing the overall structure of a stacked-type (internal parallel connection type) lithium secondary battery (stacked-type secondary battery) according to one embodiment of the present invention. Fig. 2 is a cross-sectional view showing the structure of nickel (Ni 2p ３／２ ) spectra were analyzed by peak separation to identify three species (Ni(OH) ２ 1 is a graph illustrating that the peaks of the SiO 2 film can be separated into those of NiO and Ni.

[0009] One aspect of the present invention is a battery comprising: a positive electrode having a positive electrode active material layer containing a positive electrode active material; a negative electrode having a negative electrode current collector, on which lithium metal is deposited during charging; a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte; and a Ni(OH) ２The lithium secondary battery according to this embodiment is a lithium deposition type lithium secondary battery having a negative electrode intermediate layer containing nickel particles, and is provided with a power generating element having the negative electrode intermediate layer containing nickel particles.

[0010] Hereinafter, a secondary battery according to the present embodiment will be described with reference to the accompanying drawings. The technical scope of the present invention should be determined based on the claims and is not limited to the following embodiments. In the description of the drawings, the same elements are given the same reference numerals, and redundant description will be omitted. In addition, the dimensional proportions in the drawings are exaggerated for the convenience of explanation and may differ from the actual proportions.

[0011] FIG. 1 is a cross-sectional view schematically illustrating the overall structure of a stacked-type (internal parallel connection type) lithium secondary battery (hereinafter also referred to simply as a "stacked-type secondary battery") according to one embodiment of the present invention. FIG. 1 shows a cross section of the stacked-type secondary battery during charging. The stacked-type secondary battery 10a shown in FIG. 1 has a structure in which a substantially rectangular power-generating element 21, where charge and discharge reactions actually proceed, is sealed inside a laminate film 29, which is a battery exterior. The power-generating element 21 has a structure in which a negative electrode, a solid electrolyte layer 17, and a positive electrode are stacked. The negative electrode has a structure in which a negative electrode current collector 11' and a negative electrode active material layer 13 made of lithium metal deposited on the surface of the negative electrode current collector 11' are stacked. A negative electrode intermediate layer 14 is disposed adjacent to the surface of the negative electrode active material layer 13 facing the solid electrolyte layer 17. The positive electrode has a structure in which a positive electrode active material layer 15 is disposed on the surface of a positive electrode current collector 11". The negative electrode, solid electrolyte layer, and positive electrode are laminated in this order, with the negative electrode intermediate layer 14 and the positive electrode active material layer 15 facing each other with the solid electrolyte layer 17 interposed therebetween. As a result, adjacent negative electrodes, solid electrolyte layers, and positive electrodes constitute one unit cell layer 19. Therefore, the stacked secondary battery 10a shown in FIG. 1 can be said to have a structure in which a plurality of unit cell layers 19 are laminated and electrically connected in parallel. A negative electrode current collector 25 and a positive electrode current collector 27 that are electrically connected to the respective electrodes (negative electrode and positive electrode) are attached to the negative electrode current collector 11' and the positive electrode current collector 11", respectively, and are structured so as to be sandwiched between the ends of the laminate film 29 and extended to the outside of the laminate film 29. A constraining pressure is applied to the stacked secondary battery 10a in the stacking direction of the power generating element 21 by a pressure member (not shown). Therefore, the volume of the power generating element 21 is kept constant.

[0012] The main components of the lithium secondary battery according to this embodiment will be described below.

[0013] [Current Collector] The current collector (negative electrode current collector, positive electrode current collector) has the function of mediating the movement of electrons from the electrode active material layer (negative electrode active material layer, positive electrode active material layer). There are no particular limitations on the material constituting the current collector. For example, metals such as aluminum, nickel, iron, stainless steel, titanium, and copper, as well as conductive resins, can be used as the material constituting the current collector. There are also no particular limitations on the thickness of the current collector, but an example is 10 to 100 μm.

[0014] [Negative Electrode Active Material Layer] The lithium secondary battery according to this embodiment is a so-called lithium deposition type in which lithium metal is deposited on the negative electrode current collector during the charging process. The layer of lithium metal deposited on the negative electrode current collector during this charging process is the negative electrode active material layer of the lithium secondary battery according to this embodiment. Therefore, the thickness of the negative electrode active material layer increases as the charging process progresses, and the thickness of the negative electrode active material layer decreases as the discharging process progresses. Although the negative electrode active material layer does not need to be present during full discharge, in some cases, a negative electrode active material layer composed of a certain amount of lithium metal may be present during full discharge. Furthermore, the thickness of the negative electrode active material layer (lithium metal layer) during full charge is not particularly limited, but is typically 0.1 to 1000 μm.

[0015] [Negative Electrode Intermediate Layer] The negative electrode intermediate layer is a layer adjacent to the surface of the solid electrolyte layer facing the negative electrode current collector, and is composed of Ni(OH). ２ The negative electrode intermediate layer preferably has electrical conductivity as a whole. In this specification, the volume resistivity of the negative electrode intermediate layer is measured using an electrode resistance measurement system (manufactured by Hioki E.E. Corporation, product name: RM2610). In addition, in this specification, "Ni particles" refers to particles consisting of at least one of simple Ni and molecules containing Ni atoms.

[0016] The negative electrode intermediate layer is Ni(OH) ２ Although the mechanism by which the inclusion of Ni particles having Ni(OH) on the surface improves the cycle characteristics of lithium deposition-type lithium secondary batteries is not completely clear, it is thought that the Ni(OH) ２This is thought to be because the presence of water or metal hydroxides in the negative electrode intermediate layer improves the wettability of the negative electrode intermediate layer to lithium, allowing lithium metal to be more uniformly deposited on the current collector surface. Generally, in lithium deposition-type batteries, the presence of water or metal hydroxides in the negative electrode intermediate layer irreversibly converts lithium to lithium oxide, reducing the amount of lithium available for discharge and lowering the battery capacity. Therefore, it has been common knowledge in the technical field that the inclusion of water or metal hydroxides should be strictly prevented. In contrast, according to the study by the present inventors, it was surprisingly found that the lithium deposition-type lithium secondary battery according to the present embodiment does not contain Ni(OH), a metal hydroxide, in the negative electrode intermediate layer. ２ Despite the fact that the battery contains lithium, no decrease in battery capacity due to irreversible conversion to lithium oxide was observed.

[0017] Ni(OH) ２ The average primary particle diameter of the Ni particles having on their surface is, for example, less than 1000 nm, preferably 500 nm or less, more preferably 300 nm or less, even more preferably 100 nm or less, and particularly preferably 80 nm or less. The lower limit of the average primary particle diameter of the Ni particles is not particularly limited, but is, for example, 10 nm or more, preferably 20 nm or more, even more preferably 30 nm or more, and even more preferably 40 nm or more. In this specification, the average particle diameter of the particles refers to the 50% cumulative diameter (D50) of particle diameters (the longest distance between any two points on the outline of the observed particles) of 50 particles measured by observation with a scanning electron microscope (SEM).

[0018] Ni(OH) in the broad sense ２ Ni(OH) exists in two forms: α-Ni(OH) ２ (Ni(OH) ２ ・2H ２ O) and β-Ni(OH) ２ (Ni(OH) ２ Among these, from the viewpoint of suppressing the generation of lithium that cannot participate in the reaction and the resulting decrease in battery capacity, Ni(OH) contained in the negative electrode intermediate layer is preferred. ２ is β-Ni(OH)２ In one embodiment of the present invention, the β-Ni(OH) ２ The content of Ni(OH) on the surface of the Ni particle ２ It is, for example, 80 mol % or more, more preferably 90 mol % or more, even more preferably 95 mol % or more, particularly preferably 99 mol % or more, and most preferably 100 mol % based on the total molar amount of

[0019] Ni(OH) on the surface of Ni particles ２ The content of Ni(OH) on the surface of the Ni particle is, for example, 1 mol% or more, preferably 10 mol% or more, more preferably 20 mol% or more, even more preferably 40 mol% or more, and particularly preferably 70 mol% or more, based on the total molar amount of Ni atoms on the surface of the Ni particle. ２ The upper limit of the content of Ni(OH) on the surface of the Ni particle is not particularly limited, but may be, for example, 100 mol % or less, 90 mol % or less, or 80 mol % or less, based on the total molar amount of Ni atoms on the surface of the Ni particle. ２ When the content is within the above range, non-uniform deposition of lithium metal can be sufficiently suppressed.

[0020] In one embodiment, the surface of the Ni particle may further contain nickel oxide (NiO) and / or elemental Ni (also simply referred to as "Ni" in this specification). The content of NiO on the surface of the Ni particle is, for example, 99 mol% or less, preferably 80 mol% or less, more preferably 70 mol% or less, even more preferably 20 mol% or less, and particularly preferably 10 mol% or less, relative to the total molar amount of Ni atoms on the surface of the Ni particle. The lower limit of the content of NiO on the surface of the Ni particle is not particularly limited, but may be, for example, 0 mol% or more, more than 0 mol%, 1 mol% or more, 5 mol% or more, or 10 mol% or more, relative to the total molar amount of Ni atoms on the surface of the Ni particle. When the content of NiO on the surface of the Ni particle is within the above range, non-uniform precipitation of lithium metal can be sufficiently suppressed. The Ni content on the surface of the Ni particles is, for example, 95 mol% or less, preferably 60 mol% or less, more preferably 20 mol% or less, even more preferably 10 mol% or less, particularly preferably 1 mol% or less, or even 0 mol%, relative to the total molar amount of Ni atoms on the surface of the Ni particles. The lower limit of the Ni content on the surface of the Ni particles is not particularly limited, but may be, for example, 0 mol% or more, more than 0 mol%, 1 mol% or more, 3 mol% or more, or 5 mol% or more relative to the total molar amount of Ni atoms on the surface of the Ni particles. When the Ni content on the surface of the Ni particles is within the above range, it is possible to sufficiently suppress uneven precipitation of lithium metal.

[0021] The Ni(OH) on the surface of the Ni particles ２ In this specification, as an index of the content ratio of Ni, NiO, or Ni, the Ni content (Ni 2p ３／２ The peak area corresponding to the chemical state of the compound (III) is used. The specific measurement method is described in the Examples section below.

[0022] The Ni (Ni 2p ３／２ ) spectrum, as shown in Figure 2, three types (Ni(OH) ２, NiO, and Ni), and the area of ​​each peak can be calculated by peak separation analysis. The ratio of the peak areas corresponds to the ratio of the amounts of substances (molar ratio) of each species. Utilizing this, in the present invention, the peak area of ​​each peak (respectively Ni(OH) ２ (A1 is NiO, A2 is Ni, and A3 is Ni) and the ratio of the area of ​​A1, A2, or A3 to the sum of the areas of A1 to A3, defined as (A1, A2, or A3) / (A1+A2+A3), is calculated. This area ratio is used to calculate the ratio of Ni(OH) to the total molar amount of Ni atoms on the Ni surface. ２ , NiO, or Ni content (mol %).

[0023] Ni(OH) ２ The method for preparing Ni particles having Ni(OH) on the surface thereof is not particularly limited, and a conventionally known method can be appropriately selected. ２ As a method for preparing Ni particles having Ni(OH) on the surface, there is a method of subjecting Ni particles made of Ni and / or NiO to superheated steam treatment. The superheated steam treatment is carried out using a superheated steam generator, and ultrapure water is preferred as the steam source. In addition, by appropriately selecting the superheated steam temperature, steam velocity, and steam exposure time, it is possible to obtain Ni(OH) on the surface of the Ni particles. ２ It is possible to adjust the content of

[0024] The negative electrode intermediate layer is made of Ni(OH). ２ It is preferable that the Ni particles further contain a carbon material in addition to the Ni particles having the above-mentioned surface. The carbon material can contribute to suppressing the generation and growth of dendrites. Specific examples of the carbon material include carbon black (specifically, acetylene black, Ketjen Black (registered trademark), furnace black, channel black, thermal lamp black, etc.), carbon nanotubes (CNT), graphite, hard carbon, etc. Among these, carbon black is preferred, and at least one selected from the group consisting of acetylene black, Ketjen Black (registered trademark), furnace black, channel black, and thermal lamp black is more preferred.

[0025] The carbon material may be contained in the negative electrode intermediate layer in the form of carbon particles. This can further suppress the generation and growth of dendrites. The average primary particle diameter of the carbon particles is, for example, 200 nm or less, preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 45 nm or less. There is no particular lower limit for the average primary particle diameter of the carbon particles, but it is preferably 10 nm or more, more preferably 20 nm or more, and even more preferably 25 nm or more.

[0026] The content of Ni particles in the negative electrode intermediate layer may be 10 to 90 mass%, preferably 25 to 75 mass%, more preferably 30 to 60 mass%, even more preferably 40 to 60 mass%, and even more preferably 50 to 60 mass%, relative to 100 mass% of the total amount of Ni particles and carbon material in the negative electrode intermediate layer. When the content of Ni particles in the negative electrode intermediate layer is within the above range, the cycle characteristics of the lithium secondary battery can be further improved. Furthermore, the content of Ni particles in the negative electrode intermediate layer may be, for example, 5 to 90 mass%, preferably 20 to 70 mass%, more preferably 25 to 60 mass%, even more preferably 35 to 60 mass%, and even more preferably 40 to 55 mass%, relative to 100 mass% of the total amount of the negative electrode intermediate layer.

[0027] The negative electrode intermediate layer may be composed of only Ni particles or a mixture of Ni particles and carbon particles, as long as a free-standing film can be produced using only Ni particles or a mixture of Ni particles and carbon particles. However, a binder may also be included if necessary. The type of binder is not particularly limited, and binders known in the art can be used as appropriate. Examples include polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen elements), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and carboxymethyl cellulose.

[0028] The binder content in the negative electrode intermediate layer is not particularly limited, but is preferably in the range of 1 to 15 mass% and more preferably in the range of 5 to 10 mass% relative to 100 mass% of the total amount of the negative electrode intermediate layer. If the binder content is 1 mass% or more, a negative electrode intermediate layer with sufficient strength can be formed. If the binder content is 15 mass% or less, a negative electrode intermediate layer with sufficient lithium ion conductivity can be formed.

[0029] The thickness of the negative electrode intermediate layer is not particularly limited, but is preferably 1 to 50 μm, more preferably 5 to 40 μm, and even more preferably 10 to 30 μm. When the thickness of the negative electrode intermediate layer is 1 μm or more, the function of the negative electrode intermediate layer can be fully exhibited. When the thickness of the negative electrode intermediate layer is 50 μm or less, a decrease in energy density can be suppressed.

[0030] [Solid Electrolyte Layer] The solid electrolyte layer is interposed between the negative electrode and the positive electrode and contains a solid electrolyte (usually as a main component). The solid electrolyte contained in the solid electrolyte layer is not particularly limited, and any solid electrolyte known in the art can be appropriately adopted, for example, a sulfide solid electrolyte and an oxide solid electrolyte. This solid electrolyte exhibits excellent lithium ion conductivity, and is therefore preferably a sulfide solid electrolyte containing an S element, more preferably a sulfide solid electrolyte containing an Li element, an M element, and an S element, wherein the M element contains at least one element selected from the group consisting of P, Si, Ge, Sn, Ti, Zr, Nb, Al, Sb, Br, Cl, and I, and even more preferably a sulfide solid electrolyte containing an S element, an Li element, and an P element. One example is LPS (Li ２ S-P ２ S ５ ), Li ６ P.S. ５ X (wherein X is Cl, Br or I), Li ７ P ３ S １１ , Li ３．２ P ０．９６ S and Li ３ P.S. ４These sulfide solid electrolytes are preferably used because they have excellent lithium ion conductivity.

[0031] The ionic conductivity (e.g., Li ion conductivity) of the sulfide solid electrolyte at room temperature (25°C) is, for example, 1 × 10 −５ S / cm or more, and preferably 1×10 −４ The ionic conductivity of the solid electrolyte can be measured by an AC impedance method.

[0032] Examples of the shape of the solid electrolyte include particulate shapes such as spherical shapes and oval spherical shapes, thin films, etc. When the solid electrolyte is particulate, its average particle size (D50) is not particularly limited, but is preferably 0.01 μm or more and 40 μm or less, more preferably 0.1 μm or more and 20 μm or less, and even more preferably 0.5 μm or more and 10 μm or less.

[0033] The content of the solid electrolyte in the solid electrolyte layer is preferably 50 to 100 mass %, more preferably 90 to 100 mass %.

[0034] The solid electrolyte layer may further contain a binder in addition to the solid electrolyte. The binder is not particularly limited, and a known binder can be used as appropriate. For example, the binder described above for the negative electrode intermediate layer can be similarly employed. The content of the binder in the solid electrolyte layer is not particularly limited, and is, for example, 1 to 10 mass %.

[0035] The thickness of the solid electrolyte layer varies depending on the intended configuration of the lithium secondary battery, but is usually 0.1 to 1000 μm, and preferably 10 to 100 μm.

[0036] [Positive Electrode Active Material Layer] The positive electrode active material layer essentially contains a positive electrode active material, and may contain a solid electrolyte, a binder, and a conductive additive as needed.

[0037] The type of the positive electrode active material contained in the positive electrode active material layer is not particularly limited, but may be LiCoO ２ , LiMnO ２ , LiNiO ２, LiVO ２ , Li(Ni-Mn-Co)O ２ Layered rock salt active materials such as LiMn ２ O ４ , LiNi ０．５ Mn １．５ O ４ Spinel-type active materials such as LiFePO ４ , LiMnPO ４ Olivine type active materials such as Li ２ FeSiO ４ , Li ２ MnSiO ４ Examples of oxide active materials other than those mentioned above include Si-containing active materials such as Li ４ Ti ５ O １２ Among them, Li(Ni-Mn-Co)O ２ Also, those in which part of these transition metals has been replaced with other elements (hereinafter simply referred to as "NMC composite oxides") are preferably used as the positive electrode active material.

[0038] In addition, a sulfur-based positive electrode active material is also one of the preferred embodiments. Examples of the sulfur-based positive electrode active material include particles or thin films of organic sulfur compounds or inorganic sulfur compounds, and any material can be used as long as it is capable of releasing lithium ions during charging and absorbing lithium ions during discharging by utilizing the oxidation-reduction reaction of sulfur.

[0039] The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but is, for example, preferably 30 to 99 mass %, more preferably 40 to 95 mass %, and even more preferably 45 to 90 mass %.

[0040] The positive electrode active material layer preferably further contains a solid electrolyte. The specific form of the solid electrolyte contained in the positive electrode active material layer may be the same as that described in the solid electrolyte layer section. A sulfide solid electrolyte is preferably used because it has excellent lithium ion conductivity and a low bulk modulus, allowing it to follow the volume change of the positive electrode active material during charge and discharge. The content of the solid electrolyte in the positive electrode active material layer is not particularly limited, but is, for example, 1 to 70 mass%, preferably 3 to 60 mass%, and more preferably 5 to 55 mass%.

[0041] The binder used in the positive electrode active material layer is not particularly limited, and known binders can be used as appropriate. For example, the binders described above for the negative electrode intermediate layer can be used. The content of the binder in the positive electrode active material layer is not particularly limited, and is, for example, 1 to 10 mass%.

[0042] The conductive additive used in the positive electrode active material layer is not particularly limited, and for example, carbon such as carbon black (specifically, acetylene black, Ketjen Black (registered trademark), furnace black, channel black, thermal lamp black, etc.) can be used. The content of the conductive additive in the positive electrode active material layer is not particularly limited, and is, for example, 1 to 30 mass%.

[0043] The thickness of the positive electrode active material layer varies depending on the intended configuration of the lithium secondary battery, but is usually 0.1 to 1000 μm, preferably 10 to 300 μm.

[0044] Although one embodiment of the lithium secondary battery of the present invention has been described above, the present invention is not limited to the configuration described in the above embodiment, and can be modified as appropriate based on the claims.

[0045] The following embodiments are also included within the scope of the present invention: a lithium secondary battery according to claim 1 having the features of claim 2; a lithium secondary battery according to claim 2 having the features of claim 3; a lithium secondary battery according to claim 2 or 3 having the features of claim 4; a lithium secondary battery according to any one of claims 1 to 4 having the features of claim 5; a lithium secondary battery according to claim 5 having the features of claim 6; a lithium secondary battery according to claim 6 having the features of claim 7; and a lithium secondary battery according to claim 6 or 7 having the features of claim 8.

[0046] The present invention will be described in more detail below with reference to examples. However, the technical scope of the present invention is not limited to the following examples. Note that the following operations were carried out in a glove box with an argon atmosphere at a dew point of −68° C. or less. Furthermore, the instruments and devices used in the glove box were thoroughly dried beforehand.

[0047] <Preparation of Ni particles> Nickel nanoparticles (average particle size: 70 nm) were subjected to superheated steam treatment using a superheated steam generator. Ultrapure water was used as the steam source, and the superheated steam temperature was 180°C, the steam velocity was 1.0 m / s, and the steam exposure time was the value shown in Table 1 below. In this way, Ni particles a to g with partial hydroxides on the surface were obtained.

[0048] <Ni(OH) present on the surface of Ni particles ２ The elemental composition of the surface (region at a depth of 0 to 5 nm) of each of the Ni particles a to g prepared above was analyzed using X-ray photoelectron spectroscopy under the following measurement conditions. The mole percentage of Ni(OH) relative to the total molar amount of Ni atoms was calculated. ２ The content was calculated as a mole percentage. The obtained values ​​are shown in Table 1 below.

[0049] (Measurement conditions) Apparatus name: X-ray photoelectron spectrometer VersaProbe III manufactured by ULVAC-PHI, Inc. X-ray source: Monochromated Al Kα ray 50 W Photoelectron take-off angle: 45° Measurement area: 200 μmφ.

[0050] The nickel (Ni 2p ３／２) spectra are of three species (Ni(OH) ２ , NiO, and Ni), and the area of ​​each peak can be calculated by peak separation analysis. The ratio of the peak areas corresponds to the ratio of the amounts of substances (molar ratio) of each species. Utilizing this, the peak area of ​​each peak (respectively Ni(OH) ２ A1 is defined as A1, NiO as A2, and Ni as A3. The ratio of the area of ​​A1 to the sum of the areas of A1 to A3, defined as A1 / (A1+A2+A3), is calculated, and this is used as the ratio of Ni(OH) to the total molar amount of Ni atoms on the Ni surface. ２ (In Table 1 and Table 2 described later, "Ni(OH) on the Ni surface" refers to the content (mol%) of ２ The results are shown in Table 1 below. Note that the results of similar measurements on nickel nanoparticles that were not subjected to the above superheated steam treatment are also shown in Table 1 below.

[0051]

[0052] <Examples of Test Cell Preparation> [Example 1] (Preparation of Positive Electrode) In a glove box with an argon atmosphere having a dew point of −68° C. or less, LiNi as a positive electrode active material was ０．８ Mn ０．１ Co ０．１ O ２ , acetylene black as a conductive additive, and Li as a solid electrolyte. ６ P.S. ５ Cl was weighed out to a mass ratio of 90:1:9. These were mixed using an agate mortar and then further stirred and mixed using a planetary ball mill. 2 parts by mass of styrene-butadiene rubber (SBR) as a binder was added to 100 parts by mass of the obtained mixed powder, and mesitylene was added as a solvent and mixed to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to the surface of an aluminum foil as a positive electrode current collector, dried, and pressed to obtain a positive electrode having a positive electrode active material layer (thickness 120 μm) on the surface of the positive electrode current collector.

[0053] (Preparation of Solid Electrolyte Layer) In a glove box with an argon atmosphere having a dew point of −68° C. or less, Li as a solid electrolyte was ６ P.S.５ A solid electrolyte slurry was prepared by adding 2 parts by mass of SBR as a binder to 100 parts by mass of Cl, and adding mesitylene as a solvent and mixing them. The solid electrolyte slurry was applied to the surface of a stainless steel foil as a support and dried to obtain a solid electrolyte layer (thickness: 30 μm).

[0054] (Preparation of Negative Electrode Intermediate Layer) The Ni particles a prepared above and carbon black nanoparticles (average particle diameter: 35 nm) were weighed and mixed so that the Ni particle content (Ni content) was the value shown in Table 2 below. Here, in Table 2 below, the Ni content is a value calculated according to the following formula (1).

[0055]

[0056] Next, 7 parts by mass of polyvinylidene fluoride (PVDF) as a binder and N-methyl-2-pyrrolidone (NMP) as a solvent were added to 93 parts by mass of the resulting mixture to prepare a negative electrode intermediate layer slurry. The resulting negative electrode intermediate layer slurry was applied to the surface of a stainless steel foil as a negative electrode current collector and dried to obtain a negative electrode intermediate layer (thickness 10 μm). The resulting laminate was punched out to a diameter of 10 mm and used to prepare the following test cell.

[0057] (Preparation of test cell) A positive electrode active material layer formed on the surface of an aluminum foil (positive electrode current collector) and a solid electrolyte layer formed on the surface of a stainless steel foil were stacked so that the exposed surface of the positive electrode active material layer and the exposed surface of the solid electrolyte layer faced each other, and transferred by cold isostatic pressing (CIP; 700 MPa, 25 ° C, 1 minute). After peeling off the stainless steel foil adjacent to the solid electrolyte layer, the solid electrolyte layer and the negative electrode intermediate layer formed on the surface of the stainless steel foil (negative electrode current collector) were stacked so that the exposed surface of the solid electrolyte layer and the exposed surface of the negative electrode intermediate layer faced each other, and transferred by cold isostatic pressing (CIP; 80 ° C, 500 MPa, 1 minute). Finally, an aluminum positive electrode tab and a nickel negative electrode tab were bonded to each of the aluminum foil (positive electrode current collector) and the stainless steel foil (negative electrode current collector) using an ultrasonic welding machine, and the resulting laminate was placed inside an aluminum laminate film and vacuum sealed to obtain a test cell, which is a lithium deposition type lithium secondary battery.

[0058] [Examples 2 to 14] Test cells of Examples 2 to 14 were prepared in the same manner as in Example 1, except that the type of Ni particles used in the above (preparation of the negative electrode intermediate layer) was changed to those shown in Table 2 below.

[0059] Comparative Example 1 A test cell for Comparative Example 1 was produced in the same manner as in Example 1, except that the type of Ni particles used in the above (production of the negative electrode intermediate layer) was changed to nickel nanoparticles that had not been subjected to superheated steam treatment.

[0060] <Cycle Durability Test> Leads were connected to the negative electrode current collector and the positive electrode current collector of the test cell (before the first charge) prepared in the above Examples and Comparative Examples, respectively, and a cycle durability test was performed while applying a constraining pressure of 3 MPa in the stacking direction of the test cell using a pressure member. At this time, CC charge / discharge at a charge / discharge rate of 0.5 C was repeated 100 times at 60°C in the cell voltage range of 2.5 V to 4.3 V. In addition, to confirm the capacity of the cycle test, before the first cycle (t ０ ), after the 50th cycle, and after the 100th cycle (t １００ The battery was charged and discharged at a charge / discharge rate of 0.1 C (CC-CV charge (0.02 C cutoff) / CC discharge). A 30-minute rest period was provided between each charge and discharge. Before the first cycle (t ０ ) discharge capacity after the 100th cycle (t １００ The percentage of the discharge capacity of the battery was calculated as the capacity retention rate [%]. The results are shown in Table 2 below.

[0061]

[0062] From the results shown in Table 2, in a lithium secondary battery having a negative electrode intermediate layer containing Ni particles, Ni(OH) ２ It has been found that the inclusion of Ni(OH) on the surface suppresses the decrease in discharge capacity with the progress of charge-discharge cycles. ２ It can be seen that when Ni particles not containing Zn were used in the negative electrode intermediate layer, the discharge capacity decreased significantly as the charge-discharge cycle progressed.

[0063] REFERENCE SIGNS LIST 10a laminated secondary battery, 11' negative electrode current collector, 11" positive electrode current collector, 13 negative electrode active material layer, 14 negative electrode intermediate layer, 15 positive electrode active material layer, 17 solid electrolyte layer, 19 single cell layer, 21 power generating element, 25 negative electrode current collector, 27 positive electrode current collector, 29 laminate film.

Claims

a positive electrode having a positive electrode active material layer containing a positive electrode active material; a negative electrode having a negative electrode current collector, on which lithium metal is deposited during charging; a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte; Existing adjacent to the surface of the solid electrolyte layer on the side of the negative electrode current collector, Ni(OH) ２ A negative electrode intermediate layer containing Ni particles having on the surface, and A lithium secondary battery comprising a power generation element having the above. 　 The content of Ni(OH) on the surface of the Ni particles ２ is 10 mol% or more with respect to the total molar amount of Ni atoms on the surface of the Ni particles when measuring a region with a depth of 5 nm from the surface of the Ni particles using X-ray photoelectron spectroscopy (XPS). The lithium secondary battery according to claim 1. 　 The lithium secondary battery according to claim 2, wherein the content is 20 mol% or more. 　 The lithium secondary battery according to claim 3, wherein the content is 40 mol% or more. 　 The lithium secondary battery according to any one of claims 1 to 4, wherein the negative electrode intermediate layer further contains a carbon material. 　 The lithium secondary battery according to claim 5, wherein the content ratio of the Ni particles in the negative electrode intermediate layer is 10 to 90% by mass with respect to 100% by mass of the total amount of the Ni particles and the carbon material in the negative electrode intermediate layer. 　 The lithium secondary battery according to claim 6, wherein the content ratio is 25 to 75% by mass. 　 The lithium secondary battery according to claim 7, wherein the content ratio is 30 to 60% by mass.

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