Positive electrode material and solid-state battery

Abstract

Achieve a high-performance solid-state battery. 【Solution】A positive electrode material is provided, the composition formula of which is represented by Li2Co 1-n M n P2O7, and the element M is Mg or Zn. For example, the composition n of the element M is set in the range of 0 < n ≤ 0.5, and as an example, n = 0.5. Such a positive electrode material Li2Co 1-n M n P2O7 (M = Mg, Zn) is used as the positive electrode material of the positive electrode layer 10 of a solid-state battery 1 including a positive electrode layer 10, a negative electrode layer 20, and an electrolyte layer 30 provided therebetween. Thereby, a high-performance solid-state battery 1 is realized, which exhibits excellent cycle life and high energy density.

Description

[Technical Field]

[0001] This invention relates to a positive electrode material and a solid-state battery. [Background technology]

[0002] The chemical formula is LiFePO4 or LiFe (1-x) M x P (1-x) O 2(2-x) A technique is known for using lithium transition metal oxides, represented by (where M is a predetermined transition metal, etc.), as positive electrode materials for lithium-ion batteries (Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2007 / 103179 [Overview of the project] [Problems that the invention aims to solve]

[0004] A solid-state battery includes opposing positive and negative electrode layers and an electrolyte layer between them. The positive electrode material used in the positive electrode layer affects the performance of the solid-state battery. Depending on the positive electrode material used in the positive electrode layer, a solid-state battery with sufficient performance may not be obtainable.

[0005] In one aspect, the present invention aims to realize a high-performance solid-state battery. [Means for solving the problem]

[0006] In one embodiment, the compositional formula is Li2Co 1-n M n A positive electrode material is provided, represented as P2O7, where M is Mg or Zn. In another embodiment, a solid-state battery is provided that uses the positive electrode material described above. [Effects of the Invention]

[0007] On one side, it becomes possible to realize a high-performance solid-state battery.

Brief Description of the Drawings

[0008] [Figure 1] It is a diagram for explaining a configuration example of a solid-state battery. [Figure 2] It is a diagram for explaining solid solution energy. [Figure 3] It is a diagram for explaining the volume change rate. [Figure 4] It is a diagram for explaining voltage.

Modes for Carrying Out the Invention

[0009] First, a configuration example of a solid-state battery will be described. FIG. 1 is a diagram for explaining a configuration example of a solid-state battery. FIG. 1 schematically shows a cross-sectional view of a main part of an example of a solid-state battery.

[0010] The solid-state battery 1 shown in FIG. 1 includes a positive electrode layer 10 and a negative electrode layer 20, and an electrolyte layer 30 provided therebetween. For example, the solid-state battery 1 is a lithium-ion battery (also referred to as a "lithium-ion secondary battery", etc.) capable of charge and discharge. FIG. 1 shows the basic structural part of such a lithium-ion battery.

[0011] An electrolyte material is used for the electrolyte layer 30. The electrolyte material of the electrolyte layer 30 includes a solid electrolyte. For example, an oxide solid electrolyte is used for the solid electrolyte of the electrolyte layer 30. As the oxide solid electrolyte of the electrolyte layer 30, for example, LAGP, which is one type of NASICON (Na super ionic conductor)-type (also referred to as "NASICON-type") oxide solid electrolyte, is used. LAGP is an oxide solid electrolyte represented by the composition formula Li 1+y Al y Ge 2-y (PO4)3 (0 < y ≦ 1).

[0012] In addition, various oxide solid electrolytes may be used for the solid electrolyte of the electrolyte layer 30, such as LAGP in which some of the constituent elements are substituted with other elements, or LAPP represented by the composition formula Li9Al3(P2O7)3(PO4)2, or LAPP in which some of its constituent elements are substituted with other elements. Furthermore, the solid electrolyte of the electrolyte layer 30 is not limited to oxide solid electrolytes; sulfide solid electrolytes such as Li2S-P2S5 may also be used.

[0013] A positive electrode material is used in the positive electrode layer 10. The positive electrode material of the positive electrode layer 10 includes a positive electrode active material. Details of the positive electrode material of the positive electrode layer 10 will be described later. In addition to the positive electrode material, the positive electrode layer 10 may further contain a solid electrolyte. For example, the solid electrolyte of the positive electrode layer 10 may be the same type of material as the solid electrolyte used in the electrolyte layer 30. The positive electrode layer 10 may further contain a conductive additive such as a carbon material.

[0014] The negative electrode layer 20 uses a negative electrode material. The negative electrode material of the negative electrode layer 20 includes a negative electrode active material. Examples of negative electrode materials used in the negative electrode layer 20 include TiO2 and Nb2O5. Materials such as lithium or lithium-containing alloys may be used as the negative electrode material of the negative electrode layer 20. In addition to the negative electrode material, the negative electrode layer 20 may further contain a solid electrolyte. For example, the solid electrolyte of the negative electrode layer 20 may be the same type of material as the solid electrolyte used in the electrolyte layer 30. The negative electrode layer 20 may further contain a conductive additive such as a carbon material.

[0015] The solid-state battery 1 has a configuration in which a positive electrode layer 10 is provided on one side of an electrolyte layer 30 and a negative electrode layer 20 is provided on the other side. The solid-state battery 1 is manufactured by firing a laminate, in which the electrolyte layer 30 is interposed between the positive electrode layer 10 and the negative electrode layer 20, in a predetermined atmosphere at a predetermined temperature.

[0016] For example, pastes are prepared to form each of the layers: the electrolyte layer 30, the positive electrode layer 10, and the negative electrode layer 20. These pastes are coated and dried in a predetermined stacking order to form the laminate. The formed laminate is then fired in a predetermined atmosphere at a predetermined temperature for the purpose of removing organic components and sintering the solid electrolyte. For example, a solid-state battery 1 is manufactured in this manner.

[0017] A current collector (not shown) may be connected to the positive electrode layer 10 and the negative electrode layer 20 of the solid-state battery 1, respectively. For example, a laminate is formed including the positive electrode layer 10 and the negative electrode layer 20, which have been coated with the paste described above onto the current collector and dried, and an electrolyte layer 30, and then fired to manufacture the solid-state battery 1 including the current collector.

[0018] Furthermore, electrodes (not shown) may be connected to the positive electrode layer 10 and the negative electrode layer 20 of the solid-state battery 1, respectively. In this case, the solid-state battery 1 may be in the form of a chip-type battery that can be mounted on other electronic components such as a circuit board using the electrodes connected to the positive electrode layer 10 and the negative electrode layer 20, respectively.

[0019] The solid battery 1 is not limited to the form of a chip-type battery; it may also be housed in a bag-shaped laminate film (outer casing) to form a thin battery. Alternatively, the solid battery 1 may be housed in a coin-type, cylindrical, or rectangular battery case (outer casing) to form a coin-type battery, cylindrical battery, rectangular battery, etc.

[0020] During charging of the solid-state battery 1, Li is conducted from the positive electrode layer 10 to the negative electrode layer 20 via the electrolyte layer 30 and absorbed. During discharging of the solid-state battery 1, Li is conducted from the negative electrode layer 20 to the positive electrode layer 10 via the electrolyte layer 30 and absorbed. In the solid-state battery 1, charging and discharging operations are realized by this conduction of Li.

[0021] Figure 1 illustrates a solid-state battery 1 (basic structure) that includes one electrolyte layer 30, one positive electrode layer 10, and one negative electrode layer 20, but the number of each of the electrolyte layer 30, positive electrode layer 10, and negative electrode layer 20 is not limited to one. The solid-state battery 1 may have a structure in which the electrolyte layer 30 is interposed between a pair of positive electrode layers 10 and negative electrode layers 20, and may include one or more layers of each of the electrolyte layer 30, positive electrode layer 10, and negative electrode layer 20.

[0022] Here, we will further describe the positive electrode layer 10 of the solid-state battery 1 as described above. Generally, known cathode materials that can be used in the cathode layer 10 include layered rock salt type, spinel type, and olivine type cathode materials. Among these, the olivine type cathode material, represented by the compositional formula Li2MP2O7(M=Mn,Fe,Co), is considered promising as a next-generation cathode material because it exhibits a higher operating voltage compared to LiMPO4(M=Mn,Fe,Co), which is composed of the same elements.

[0023] The energy density of a battery is expressed as the product of voltage and capacity, and improving the operating voltage is effective in increasing energy density. Among the olivine-type cathode materials Li2MP2O7, Li2CoP2O7 (also called "LCPO"), which uses Co as element M, exhibits an operating voltage of 5V class. By using this as a cathode material, it becomes possible to realize a solid-state battery 1 that exhibits high energy density.

[0024] Conventional positive electrode materials such as LCPO used in the positive electrode layer 10 of a solid-state battery 1 undergo repeated volume changes during charging and discharging of the solid-state battery 1 due to the desorption and insertion of Li and the change in the valence state of the transition metal. Volume changes in the positive electrode material can cause strain and internal stress in the positive electrode layer 10. Strain and internal stress in the positive electrode layer 10 may lead to cracks in the positive electrode layer 10 and delamination from other components (electrolyte layer 30, current collector, electrodes, etc.), and may further reduce the charge-discharge cycle life of the solid-state battery 1.

[0025] In the solid-state battery 1 in which the positive electrode layer 10 is laminated with the electrolyte layer 30 and the negative electrode layer 20, the volume change of the positive electrode material used in the positive electrode layer 10 can affect the performance of the solid-state battery 1. Therefore, suppressing the volume change of the positive electrode material used in the positive electrode layer 10 is effective for improving the performance of the solid-state battery 1.

[0026] In view of such points, here, a positive electrode material having the following configuration is used as the positive electrode material, and a positive electrode material capable of suppressing the volume change accompanying charge and discharge is realized. Further, a high-performance solid-state battery 1 using such a positive electrode material in the positive electrode layer 10 is realized.

[0027] That is, here, as the positive electrode material of the positive electrode layer 10 of the solid-state battery 1, the composition formula is Li2Co 1-n M n A positive electrode material represented by P2O7 and in which the element M is Mg or Zn is used. The composition n of the element M is set, for example, in the range of 0 < n ≤ 0.5.

[0028] This positive electrode material Li2Co 1-n M n P2O7 (M = Mg, Zn) has a structure in which a part of Co in the conventional olivine-type positive electrode material Li2CoP2O7 (LCPO) in which Li, Co, P, and O are contained in a ratio of 2:1:2:7 is substituted with Mg or Zn.

[0029] The positive electrode material Li2Co 1-n M n P2O7, as will be described later, has a volume change accompanying charge and discharge (desorption and insertion of Li) suppressed as compared with the conventional LCPO in which a part of Co is not substituted with Mg or Zn. Such a positive electrode material Li2Co 1-n M n When P2O7 (M = Mg, Zn) is used in the positive electrode layer 10 of the solid-state battery 1, the generation of strain and internal stress in the positive electrode layer 10 accompanying charge and discharge is suppressed. Thereby, the generation of cracks and peeling of the positive electrode layer 10 due to strain and internal stress is suppressed. Therefore, a solid-state battery 1 showing excellent cycle life is realized.

[0030] Furthermore, Li2Co is a cathode material in which a portion of the Co in the conventional olivine-type cathode material LCPO is replaced with Mg or Zn. 1-n M n As will be discussed later, P2O7 (M=Mg,Zn) exhibits improved operating voltage compared to LCPO. Such a positive electrode material Li2Co 1-n M n By using P2O7 (M=Mg,Zn) in the positive electrode layer 10 of the solid-state battery 1, a solid-state battery 1 exhibiting high energy density is realized.

[0031] The positive electrode layer 10 contains the positive electrode material Li2Co 1-n M n By using P2O7(M=Mg,Zn), a high-performance solid-state battery 1 is realized that exhibits excellent cycle life and high energy density.

[0032] Below, the positive electrode material Li2Co 1-n M n P2O7 (M=Mg,Zn) will be further explained with reference to comparative examples and examples. [Comparative Example 1] Li 2-x A model for CoP2O7 (x=0,0.5,1.0,1.5,2.0) was prepared. The model for x=0 is Li2CoP2O7, i.e., the LCPO model, where Li is not extracted. For 0.5≦x, multiple models were prepared by changing the site where Li is extracted. Using the prepared models as initial models, structural optimization was performed using molecular dynamics calculations with machine learning force fields, and the lattice volume and energy were calculated. The rate of volume change was calculated based on the obtained lattice volume. The voltage was calculated based on the obtained energy.

[0033] [Example 1] Li2Co 1-n Mg nWe prepared models for P2O7 (n=0, 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875, 1). When n=0, it is the Li2CoP2O7 model, i.e., the LCPO model. When n=1, it is the Li2MgP2O7 model. For 0.125≦n≦0.875, we prepared multiple models with different arrangement patterns of Co and Mg. Using the prepared models as initial models, we performed structural optimization using molecular dynamics calculations with machine learning force fields and calculated the energy. From the obtained energy, we calculated the solid solution energy.

[0034] [Example 2] Li2Co 1-n Zn n We prepared models for P2O7 (n=0, 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875, 1). When n=0, it is the model for Li2CoP2O7, i.e., the LCPO model. When n=1, it is the model for Li2ZnP2O7. For 0.125≦n≦0.875, we prepared multiple models with different arrangement patterns of Co and Zn. Using the prepared models as initial models, we performed structural optimization using molecular dynamics calculations with machine learning force fields and calculated the energy. From the obtained energy, we calculated the solid solution energy.

[0035] [Example 3] Li 2-x Co 0.5 Mg 0.5 A model for P2O7 (x=0,0.5,1.0,1.5,2.0) was prepared. When x=0, it is Li2Co where Li has not been extracted. 0.5 Mg 0.5 This is a model of P2O7. For 0.5 ≤ x, multiple models were prepared by changing the site from which Li is extracted. Using one of the prepared models as the initial model, structural optimization was performed using molecular dynamics calculations with machine learning force fields, and the lattice volume and energy were calculated. The rate of volume change was calculated based on the obtained lattice volume. The voltage was calculated based on the obtained energy.

[0036] [Example 4] Li 2-x Co0.5 Zn 0.5 A model for P2O7 (x=0,0.5,1.0,1.5,2.0) was prepared. When x=0, it is Li2Co where Li has not been extracted. 0.5 Zn 0.5 This is a model of P2O7. For 0.5 ≤ x, multiple models were prepared by changing the site from which Li is extracted. Using one of the prepared models as the initial model, structural optimization was performed using molecular dynamics calculations with machine learning force fields, and the lattice volume and energy were calculated. The rate of volume change was calculated based on the obtained lattice volume. The voltage was calculated based on the obtained energy.

[0037] [Solid solution energy] Li2Co in Example 1 1-n Mg n P2O7 and Li2Co from Example 2 1-n Zn n The solid solution energy of P2O7 will be described.

[0038] In Example 1, the compositional formula was Li2Co 1-n M n In P2O7, the element M is Mg, and Li2Co 1-n Mg n A P2O7 model (n=0,0.125,0.25,0.375,0.5,0.625,0.75,0.875,1) is provided.

[0039] In Example 2, the compositional formula is Li2Co 1-n M n In P2O7, element M is Zn, and Li2Co 1-n Zn n A P2O7 model (n=0,0.125,0.25,0.375,0.5,0.625,0.75,0.875,1) is provided.

[0040] Li2Co in Example 1 1-n Mg n P2O7 and Li2Co from Example 2 1-n Zn nFor each P2O7, the energy of the optimal structure at each composition n is calculated. From the obtained energy, the solid solution energy [eV] is calculated according to equation (1) below (Reference: ISIJ International, Vol. 60 (2020), No. 12, pp. 2963-2972 (equation (1))).

[0041] Solid solution energy = E' - {(1-n) × E(Li2CoP2O7) + n × E(Li2MP2O7)} ... (1) In formula (1), E' is the Li2Co of Example 1. 1-n Mg n P2O7 and Li2Co from Example 2 1-n Zn n This represents the energy when the elemental composition n of M(Mg,Zn) in P2O7 is in the range of 0.125 ≤ n ≤ 0.875.

[0042] In formula (1), E(Li2CoP2O7) is the Li2Co from Example 1. 1-n Mg n P2O7 and Li2Co from Example 2 1-n Zn n This is the energy when the elemental composition n of P2O7 (Mg,Zn) is n=0 (LCPO).

[0043] In formula (1), E(Li2MP2O7) is Li2Co from Example 1. 1-n Mg n P2O7 and Li2Co from Example 2 1-n Zn n This is the energy when the elemental composition n of M(Mg,Zn) in P2O7 is n=1 (Li2MgP2O7,Li2ZnP2O7).

[0044] Figure 2 illustrates solid solution energy. Figure 2 shows Li2Co 1-n M n This shows the relationship between the elemental composition n[-] of M(Mg,Zn) in P2O7 and the solid solution energy [eV].

[0045] Figure 2 shows the Li2Co of Example 1.1-n Mg n P2O7 (M = Mg) and Li2Co of Example 2 1-n Zn n For P2O7 (M = Zn) and P2O7 (M = Mg), the solid solution energies calculated for each composition n are plotted. In Figure 2, the plot is further fitted with a curve. From the fitting curve in Figure 2, Li2Co of Example 1 1-n Mg n P2O7 and Li2Co of Example 2 1-n Zn n P2O7 all tend to have the minimum solid solution energy at n = 0.5.

[0046] Here, when a part of Co in LCPO (Li2CoP2O7) is substituted with Mg or Zn, the amount of Co contributing to charge and discharge relatively decreases, so the theoretical capacity decreases. Also, when a part of Co in LCPO is substituted with Mg or Zn, along with the relative decrease in the amount of Co, the crystal structure becomes unstable, and there is concern that decomposition or precipitation of impurities may occur during charge and discharge.

[0047] Regarding this point, as described above, Li2Co of Example 1 1-n Mg n P2O7 and Li2Co of Example 2 1-n Zn n P2O7 all have the minimum solid solution energy at n = 0.5, and it can be said that n = 0.5 is the solid solution limit. That is, Li2Co of Example 1 1-n Mg n P2O7 and Li2Co of Example 2 1-n Zn n P2O7 can be synthesized while suppressing the decrease in capacity accompanying the relative decrease in the amount of Co and suppressing the destabilization of the crystal structure, etc. in the range of 0 < n ≤ 0.5, and among them, it can be said that n = 0.5 is the optimum value.

[0048] 〔Volume change rate〕 Li of Comparative Example 1 2-x CoP2O7, Li of Example 3 2-x Co 0.5 Mg 0.5P2O7 and Li of Example 4 2-x Co 0.5 Zn 0.5 The volume change rate of P2O7 will be described.

[0049] In Comparative Example 1, the compositional formula Li 1-n M n representing the extraction of Li from P2O7 (desorption of Li accompanying charging), 2-x Co 1-n M n with the composition n of element M in P2O7 set to n = 0, Li 2-x models of CoP2O7 (x = 0, 0.5, 1.0, 1.5, 2.0) are prepared. That is, a model representing the extraction of Li from Li2CoP2O7 (LCPO) is prepared.

[0050] In Example 3, the compositional formula Li 1-n M n representing the extraction of Li from P2O7 (desorption of Li accompanying charging), 2-x Co 1-n M n with element M in P2O7 being Mg and its composition n set to n = 0.5, Li 2-x Co 0.5 Mg 0.5 models of P2O7 (x = 0, 0.5, 1.0, 1.5, 2.0) are prepared.

[0051] In Example 4, the compositional formula Li 1-n M n representing the extraction of Li from P2O7 (desorption of Li accompanying charging), 2-x Co 1-n M n with element M in P2O7 being Zn and its composition n set to n = 0.5, Li 2-x Co 0.5 Zn 0.5 models of P2O7 (x = 0, 0.5, 1.0, 1.5, 2.0) are prepared.

[0052] Li of Comparative Example 1 2-x CoP2O7, Li of Example 3 2-x Co 0.5 Mg 0.5P2O7 and Li of Example 4 2-x Co 0.5 Zn 0.5 For each P2O7, the lattice volume is calculated by varying x to reduce the amount of Li, that is, by reproducing the charged state.

[0053] Figure 3 illustrates the rate of volume change. Figure 3(A) shows capacity [mAh / g] (charging capacity) and volume [Å]. 3 This shows the relationship with the cell volume. Figure 3(B) shows the volume change rate [%] for Comparative Example 1, Example 3, and Example 4.

[0054] Li in Comparative Example 1 2-x CoP2O7, Li from Example 3 2-x Co 0.5 Mg 0.5 P2O7 and Li of Example 4 2-x Co 0.5 Zn 0.5 For P2O7, when the lattice volume is calculated while increasing x and decreasing the amount of Li (reproducing the charged state), a plot of volume against capacity according to x (charged state) is obtained, as shown in Figure 3(A).

[0055] Furthermore, for Examples 3 and 4, since the amount of Co is half that of Comparative Example 1, half of the theoretical volume is plotted, i.e., the volume until x in the Li composition 2-x becomes x=1.0.

[0056] From the change in volume with respect to capacity shown in Figure 3(A), the rate of volume change [%] can be calculated according to the following equation (2). Volume change rate = {(V'-V) / V} × 100 ... (2) In equation (2), V is Li of Comparative Example 1. 2-x CoP2O7, Li from Example 3 2-x Co 0.5 Mg 0.5 P2O7 and Li of Example 4 2-x Co 0.5 Zn 0.5 This is the volume of the Li component in P2O7 when x = 0 (before charging), where x is the value of the Li component 2-x.

[0057] In equation (2), V' is Li of Comparative Example 1. 2-x CoP2O7, Li from Example 3 2-x Co 0.5 Mg 0.5 P2O7 and Li of Example 4 2-x Co 0.5 Zn 0.5 This is the volume of the Li composition 2-x in P2O7 when x is in the range of 0.5 ≤ x ≤ 2.0 (during charging) (for example, the volume when x = 1.0).

[0058] Based on the relationship shown in Figure 3(A), the Li of Comparative Example 1 can be calculated using equation (2). 2-x CoP2O7, Li from Example 3 2-x Co 0.5 Mg 0.5 P2O7 and Li of Example 4 2-x Co 0.5 Zn 0.5 Figure 3(B) shows the rate of change in volume of P2O7 at x=1.0 relative to the volume at x=0.

[0059] From Figure 3(B), the Li of Comparative Example 1 2-x In CoP2O7, the volume change rate is -4.4% (x=1.0). In contrast, Li 2-x Example 3: Li in CoP2O7 where 50% of the Co is replaced with Mg. 2-x Co 0.5 Mg 0.5 In P2O7, the volume change rate can be suppressed to -1.6% (x=1.0). 2-x Example 4 shows Li in CoP2O7 where 50% of the Co is replaced with Zn. 2-x Co 0.5 Zn 0.5 In P2O7, the rate of volume change can be suppressed to -2.2% (x=1.0).

[0060] Based on these findings, Li 2-x Co 1-n M n P2O7 or Li2Co before charging 1-n M n According to P2O7(M=Mg,Zn), volume changes can be effectively suppressed.

[0061] Here, Li 2-x Co 1-n M n P2O7 or Li2Co before charging 1-n M n Regarding Li2CoM(P2O7) (M = Mg, Zn), when n = 0.5 is taken as an example, similarly, in the range of 0 < n ≤ 0.5, the effect of suppressing volume change can be obtained.

[0062] Therefore, when Li2CoM(P2O7) (M = Mg, Zn) is used as the positive electrode material in the positive electrode layer 10 of the solid battery 1, the generation of strain and internal stress in the positive electrode layer 10 accompanying charge and discharge can be suppressed, and the generation of cracks and peeling in the positive electrode layer 10 caused by strain and internal stress can be suppressed. Thereby, a solid battery 1 showing excellent cycle life is realized. 1-n M n

[0063] 〔Voltage〕 The voltage of LiCoP2O7 of Comparative Example 1, LiCoMgP2O7 of Example 3, and LiCoZnP(2O7) of Example 4 will be described. 2-x CoP2O7, LiCo of Example 3 2-x Co 0.5 Mg 0.5 P2O7 and LiCo of Example 4 2-x Co 0.5 Zn 0.5 P2O7 will be described.

[0064] In Comparative Example 1, a model of LiCoMP2O7 (x = 0, 0.5, 1.0, 1.5, 2.0) with the composition n of the element M in LiCoMP2O7 set to n = 0, which represents the extraction of Li from Li2CoMP2O7 (Li desorption accompanying charging), is prepared. That is, a model representing the extraction of Li from Li2CoP2O7 (LCPO) is prepared. 1-n M n Li extraction from P2O7 (Li desorption accompanying charging) is represented by the composition formula Li<00S0182>Co 1-n M n P2O7 2-x CoP2O7(x = 0, 0.5, 1.0, 1.5, 2.0) is prepared. That is, a model representing the extraction of Li from Li2CoP2O7 (LCPO) is prepared.

[0065] In Example 3, the extraction of Li from Li2CoMP2O7 (Li desorption accompanying charging) is represented by the composition formula Li 1-n M n P2O72-x Co 1-n M n Let the element M in P2O7 be Mg, and its composition n be n=0.5. 2-x Co 0.5 Mg 0.5 A model for P2O7 (x=0,0.5,1.0,1.5,2.0) is provided.

[0066] In Example 4, Li2Co 1-n M n Compositional formula Li represents the abstraction of Li from P2O7 (desorption of Li during charging) 2-x Co 1-n M n Let the element M in P2O7 be Zn, and its composition n be n=0.5. 2-x Co 0.5 Zn 0.5 A model for P2O7 (x=0,0.5,1.0,1.5,2.0) is provided.

[0067] Li in Comparative Example 1 2-x CoP2O7, Li from Example 3 2-x Co 0.5 Mg 0.5 P2O7 and Li of Example 4 2-x Co 0.5 Zn 0.5 For each P2O7, the energy is calculated by varying x to reduce the amount of Li, that is, by reproducing the charged state.

[0068] From the energy obtained, the voltage [VvsLi / Li] is calculated according to equation (3) below. + The following is calculated (Reference: Electrochemistry, Vol. 76 (2008), No. 10, pp. 752-762 (Equation (1))).

[0069] Voltage=-{E'-xE(Li)-E} / xF...(3) In equation (3), E is Li of Comparative Example 1. 2-x CoP2O7, Li from Example 3 2-x Co 0.5 Mg 0.5 P2O7 and Li of Example 42-x Co 0.5 Zn 0.5 This is the energy of the Li atom in P2O7 when x = 0 (before charging), where x is the value of the Li composition 2-x.

[0070] In equation (3), E' is Li of Comparative Example 1. 2-x CoP2O7, Li from Example 3 2-x Co 0.5 Mg 0.5 P2O7 and Li of Example 4 2-x Co 0.5 Zn 0.5 This is the energy (during charging) when the x in the Li composition 2-x in P2O7 is in the range of 0.5 ≤ x ≤ 2.0.

[0071] In equation (3), E(Li) is the energy of the Li metal. In equation (3), x is the number of Li atoms that were removed. In equation (3), F is the Faraday constant.

[0072] In equation (3), the unit conversion to voltage is performed by dividing -{E'-xE(Li)-E} by xF. Figure 4 is a diagram illustrating voltage. Figure 4(A) shows capacity [mAh / g] (charging capacity) and voltage [VvsLi / Li + The relationship between [VvsLi / Li] is shown. Figure 4(B) shows the voltage [VvsLi / Li] for Comparative Example 1, Example 3 and Example 4. + This indicates [...].

[0073] Figure 4(A) shows the Li of Comparative Example 1. 2-x CoP2O7, Li from Example 3 2-x Co 0.5 Mg 0.5 P2O7 and Li of Example 4 2-x Co 0.5 Zn 0.5 For each P2O7, the voltage relative to the capacity corresponding to x (charge state) is plotted.

[0074] Furthermore, for Examples 3 and 4, since the amount of Co is half that of Comparative Example 1, the plotted values ​​represent half of the theoretical capacity, i.e., the voltage until x in the Li composition 2-x becomes x=1.0.

[0075] Figure 4(A) shows the Li of Comparative Example 1. 2-x CoP2O7, Li from Example 3 2-x Co 0.5 Mg 0.5 P2O7 and Li of Example 4 2-x Co 0.5 Zn 0.5 The relationship between the capacitance and voltage of P2O7 around x=1.0 is shown in an enlarged view and illustrated.

[0076] Li in Comparative Example 1 2-x CoP2O7, Li from Example 3 2-x Co 0.5 Mg 0.5 P2O7 and Li of Example 4 2-x Co 0.5 Zn 0.5 Figure 4(B) shows the voltage of P2O7 when x = 1.0.

[0077] From Figure 4(B), the Li of Comparative Example 1 2-x In CoP2O7, the voltage is 5.39V (x=1.0). In contrast, Li 2-x Example 3: Li in CoP2O7 where 50% of the Co is replaced with Mg. 2-x Co 0.5 Mg 0.5 In P2O7, when the State of Charge (SOC) is 100%, the voltage increases to 5.48V (x=1.0). 2-x Example 4 shows Li in CoP2O7 where 50% of the Co is replaced with Zn. 2-x Co 0.5 Zn 0.5 In the P2O7, the voltage increases to 5.60V (x=1.0) when the SOC is at 100%.

[0078] Based on these findings, Li 2-x Co 1-n M n P2O7 or Li2Co before charging 1-nM n According to P2O7 (M = Mg, Zn), the voltage can be effectively improved.

[0079] In addition, here, Li 2-x Co 1-n M n P2O7 or Li2Co before charging 1-n M n Regarding P2O7 (M = Mg, Zn), taking the case where n = 0.5 as an example, similarly, in the range of 0 < n ≤ 0.5, the effect of improving the voltage can be obtained.

[0080] Therefore, when Li2Co 1-n M n P2O7 (M = Mg, Zn) is used as the positive electrode material in the positive electrode layer 10 of the solid battery 1, the operating voltage is improved compared with LCPO. As a result, the solid battery 1 showing a high energy density is realized.

[0081] 〔Element M〕 From FIG. 3(B), when the element M in Li 2-x Co 1-n M n P2O7 or Li2Co 1-n M n P2O7 is Mg as in Example 3, when the element M in Li 2-x Co 1-n M n P2O7 or Li2Co 1-n M n P2O7 is Zn, compared with the case where the element M in Li

[0082] From FIG. 4(B), when the element M in Li 2-x Co 1-n M n P2O7 or Li2Co 1-n M n P2O7 is Zn as in Example 4, when the element M in Li 2-x Co 1-n M n P2O7 or Li2Co 1-n M nThe voltage can be further improved as compared with the case where element M in P2O7 is Mg.

[0083] Li 2-x Co 1-n M n P2O7 or Li2Co 1-n M n By using elements M of Mg and Zn in P2O7, the volume change can be suppressed and the voltage can be improved as compared with LCPO. Here, it can be said that using element M as Mg is more effective for suppressing the volume change. Also, it can be said that using element M as Zn is more effective for improving the voltage.

[0084] As described above, as a positive electrode material applicable to the positive electrode layer 10 of the solid battery 1, a positive electrode material having a composition formula represented by Li2Co 1-n M n P2O7 is provided, wherein element M is Mg or Zn. That is, a positive electrode material Li2Co 1-n M n P2O7 having a structure in which a part of Co in LCPO is substituted with Mg or Zn is provided. The composition n of element M is set, for example, in the range of 0 < n ≤ 0.5.

[0085] For such a positive electrode material Li2Co 1-n M n P2O7, the volume change associated with the desorption and insertion of Li can be suppressed as compared with LCPO. Therefore, when the positive electrode material Li2Co 1-n M n P2O7 is used for the positive electrode layer 10 of the solid battery 1, the distortion and internal stress generation of the positive electrode layer 10 associated with the charge and discharge (desorption and insertion of Li) of the solid battery 1 can be suppressed, and the generation of cracks and peeling of the positive electrode layer 10 due to the distortion and internal stress can be suppressed. Thereby, a solid battery 1 showing excellent cycle life is realized.

[0086] Also, for the positive electrode material Li2Co 1-n M n P2O7, the operating voltage is improved as compared with LCPO. Thereby, a solid battery 1 showing a high energy density is realized. Therefore, by using the cathode material Li2Co 1-n M n P2O7 in the cathode layer 10, a high-performance solid battery 1 that exhibits excellent cycle life and high energy density is realized.

[0087] In addition, within the cathode layer 10 of the solid battery 1 during or after the charge-discharge operation, depending on the charge (desorption of Li) or discharge (insertion of Li) state of the solid battery 1, Li 2-x Co 1-n M n The cathode material having a composition represented by P2O7 may be included. Here, x in the composition 2-x of Li is, for example, in the range of 0 ≦ x ≦ 2.0, or in the range of 0 ≦ x ≦ 1.0. The element M is Mg or Zn. The composition n of the element M is set, for example, in the range of 0 < n ≦ 0.5.

Explanation of Reference Numerals

[0088] 1 Solid battery 10 Cathode layer 20 Anode layer 30 Electrolyte layer

Claims

1. The empirical formula is Li ２ Co １－ｎ M ｎ P ２ O ７ A positive electrode material represented by , where M is Mg or Zn.

2. The positive electrode material according to claim 1, wherein the range of n is 0 < n ≤ 0.

5.

3. A positive electrode layer using the positive electrode material described in claim 1 or 2, The negative electrode layer opposite the positive electrode layer, An electrolyte layer containing a solid electrolyte is provided between the positive electrode layer and the negative electrode layer, A solid-state battery having the following characteristics.

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