JP2017103008A - Positive electrode active material for all-solid-state lithium ion secondary battery and all-solid-state lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material for an all-solid-state lithium ion secondary battery, with which a charge reaction and a discharge reaction can be smoothly performed and the capacity of the positive electrode active material can be effectively utilized.SOLUTION: A positive electrode active material contains a metal oxide particle and an anion (carbonate radical and/or sulfate radical). The metal oxide has a LiMnOtype crystal structure and is represented by formula (A): Li(MM)O(in the formula, an element Mrepresents a first metal element with a valence of 4, an element Mrepresents a second metal element with a valence of 3, and 0<x≤1/3 and 0.5≤y≤0.8 are satisfied.). The first metal element contains at least Mn, the molar ratio y1 of Mn in the total of the first and second metal elements satisfies 0.5≤y1≤0.8, and the second metal element contains Ni, Co and/or Fe and contains at least Ni. The anion is unevenly distributed on a surface layer of the particle.SELECTED DRAWING: Figure 1

Description

The present invention relates to a positive electrode active material for an all solid lithium ion secondary battery containing a metal oxide having a Li ₂ MnO ₃ type crystal structure and an all solid lithium ion secondary battery using the same.

  Among various secondary batteries being developed, a lithium ion secondary battery (LIB) that can easily obtain a high energy density is considered most promising. On the other hand, with the expansion of battery applications, large batteries such as automobile batteries and stationary batteries are attracting attention. For large batteries, ensuring safety is even more important than small batteries. An all-solid lithium ion secondary battery (all-solid LIB) using an inorganic solid electrolyte is easy to ensure safety even when the size is increased, and it is easy to effectively use the capacity of an active material, compared to LIB using an electrolyte. It is expected.

As a positive electrode active material of all solid LIB, a solid solution positive electrode material obtained by solidifying Li ₂ MnO ₃ and LiM ³ O ₂ (wherein M ³ is a transition metal element such as Ni or Co) has attracted attention. ing. Specific examples of the solid solution positive electrode material include zLi ₂ MnO ₃ — (1-z) LiM ³ O ₂ (wherein z is a molar ratio of Li ₂ MnO _{3 in} the solid solution), or Li _{1 + x1} ( Mn _y2 M ³ _1-y2 ) _1-x1 O ₂ (wherein x1 is an excess amount of lithium and y2 is a molar ratio of Mn to the total of Mn and M ³ ).

For example, Patent Document 1 proposes a solid solution positive electrode material using a solid solution of Li ₂ M ⁴ O ₃ and LiM ⁵ O _2, and Patent Document 2 includes a Li—M ⁵ —Mn-based composite oxide. A solid solution cathode material is disclosed. In these formulas, M ⁴ is a tetravalent metal element, and M ⁵ is a trivalent metal element.

JP 2012-059528 A JP-T-2004-538610

  The solid solution positive electrode materials of Patent Document 1 and Patent Document 2 are not easily activated electrochemically. Therefore, the charge / discharge reaction is not performed reversibly and smoothly, and it is difficult to secure a high capacity for both the charge capacity and the discharge capacity. Such problems are particularly pronounced in all solid LIBs where all electrochemical reactions occur at the solid / solid interface.

  An object of the present invention is to perform a charging reaction and a discharging reaction smoothly in an all-solid-state LIB and effectively use the capacity of a positive electrode active material.

One aspect of the present invention includes metal oxide particles and at least one anion selected from the group consisting of carbonate and sulfate.
The metal oxide has a Li ₂ MnO ₃ type crystal structure and has the following formula (A):
Li _{1 + x} (M ¹ _y M ² _1-y ) _1-x O ₂
(In the formula, element M ¹ is a tetravalent first metal element, element M ² is a trivalent second metal element, and 0 <x ≦ 1/3 and 0.5 ≦ y ≦ 0.8. Satisfaction.)
Represented by
The first metal element includes at least Mn,
The molar ratio y1 of Mn in the total of the first metal element and the second metal element satisfies 0.5 ≦ y1 ≦ 0.8,
The second metal element includes at least one selected from the group consisting of Ni, Co, and Fe, and includes at least Ni,
The present invention relates to a positive electrode active material for an all-solid-state lithium ion secondary battery in which the anions are unevenly distributed in the surface layer of the particles.

Another aspect of the present invention is a positive electrode including the positive electrode active material described above,
A negative electrode containing a negative electrode active material that inserts and desorbs lithium ions;
The present invention relates to an all solid lithium ion secondary battery including a solid electrolyte layer including an inorganic solid electrolyte that is interposed between the positive electrode and the negative electrode and exhibits lithium ion conductivity.

  According to the present invention, charging reaction and discharging reaction can be performed smoothly in all solid LIB. Therefore, since the charge capacity and the discharge capacity can be increased, the capacity of the positive electrode active material can be effectively used.

It is a longitudinal cross-sectional view which shows schematically the electrode group contained in the all-solid-state LIB which concerns on one Embodiment of this invention. It is an O1s peak of the spectrum by the X ray photoelectron spectroscopy (XPS) of the positive electrode active material of Example 1 and Comparative Example 1. It is an O1s peak of the XPS spectrum of the positive electrode active material of Example 2 and Comparative Example 2. It is an O1s peak of the XPS spectrum of the positive electrode active material of Comparative Example 3 and Reference Example 1.

[Cathode active material for all solid LIB]
The positive electrode active material for all-solid-state LIB according to an embodiment of the present invention includes metal oxide particles and at least one anion selected from the group consisting of carbonate groups and sulfate groups. The metal oxide has a Li ₂ MnO ₃ type crystal structure and has the following formula (A):
Li _{1 + x} (M ¹ _y M ² _1-y ) _1-x O ₂
(In the formula, element M ¹ is a tetravalent first metal element, element M ² is a trivalent second metal element, and 0 <x ≦ 1/3 and 0.5 ≦ y ≦ 0.8. It is satisfied.) The first metal element (element M ¹ ) contains at least Mn, and the molar ratio y1 of Mn in the total of the first metal element and the second metal element satisfies 0.5 ≦ y1 ≦ 0.8. The second metal element (element M ² ) includes at least one selected from the group consisting of Ni, Co, and Fe, and includes at least Ni. And the anion is unevenly distributed in the surface layer of particle | grains.

The metal oxide particles having the above composition having a Li ₂ MnO ₃ type crystal structure can insert and desorb Li ions. However, it has low conductivity and is difficult to be activated electrochemically. Therefore, it is difficult to perform the charge / discharge reaction reversibly and smoothly. In the all-solid LIB, the electrochemical reaction in the battery is performed at the solid / solid interface. Therefore, when the metal oxide particles are used as the positive electrode active material, it is further difficult to make the charge / discharge reaction proceed smoothly. Therefore, conventionally, even when such a positive electrode active material is used for the all-solid-state LIB, a sufficient capacity cannot be obtained.

  In the present embodiment, the charge / discharge reaction can be performed reversibly and smoothly by unevenly distributing anions such as carbonate and / or sulfate radicals on the surface layer of the metal oxide particles. This is considered because an anion is unevenly distributed on the surface layer of the metal oxide particles, thereby suppressing the formation of a high resistance layer at the interface between the positive electrode active material and the solid electrolyte. Thus, in this embodiment, since the reversibility of the charge / discharge reaction is increased, the charge capacity and the discharge capacity are improved, and the capacity of the all-solid-state battery can be increased. In addition, since the formation of the high resistance layer is suppressed, cycle characteristics and rate characteristics are also improved. The presence of anions can be grasped by analyzing the composition of the surface layer of the metal oxide particles. Therefore, it is possible to select a non-defective product at the positive electrode active material stage without assembling the battery and conducting a charge / discharge test.

  In this embodiment, anions are unevenly distributed on the surface layer of the metal oxide particles, but the surface layer of the particles refers to a region from the surface of the particles to a depth that can be analyzed by XPS spectrum. The surface layer of the particle is, for example, a region from the particle surface to a depth of 10 nm.

In LIB using an electrolytic solution, for example, a positive electrode active material having a crystal structure belonging to the space group R-3m such as LiCoO ₂ is used. When LiCoO ₂ particles containing anions such as carbonate radicals are used as the positive electrode active material in the LIB using the electrolyte and the all-solid LIB, the charge / discharge reaction is inhibited. That is, it can be said that the effect of uneven distribution of anions on the surface layer is completely different depending on the crystal structure of the positive electrode active material and the difference in battery system.

The positive electrode active material according to this embodiment will be described in more detail.
(Metal oxide particles)
In general, the crystal structure of the Li ₂ MnO ₃ type (monoclinic crystal) belongs to the space group C2 / m, and the LiMO ₂ type (hexagonal crystal) (where M is a combination of Mn and Ni and / or Co) The crystal structure belongs to the space group R-3m. All of these have a layered rock salt structure and can form a solid solution. The solid solution as described above includes at least a Li ₂ MnO ₃ type crystal structure and has a high theoretical capacity. The metal oxide described above has an inactive Li ₂ MnO ₃ type crystal structure as a whole, but is considered to be activated by the solid solution of the metal oxide having the LiMO ₂ type crystal structure.

As the metal oxide containing the first metal element and the second metal element, Li ₂ M ¹ O ₃ having a Li ₂ MnO ₃ type crystal structure and the above LiMO ₂ type crystal structure are used from the viewpoint of increasing the capacity. A solid solution with LiM ² O ₂ having the following is promising. The solid solution of Li ₂ M ¹ O ₃ and LiM ² O ₂ can contain more Li than the total amount of the first metal element and the second metal element in terms of molar ratio. Such a solid solution has a Li ₂ MnO ₃ type crystal structure as a whole, and can be represented by the above formula (A).

  In the formula (A), x satisfies 0 <x ≦ 1/3, preferably 0.10 ≦ x ≦ 0.30, and more preferably 0.14 ≦ x ≦ 0.26. When x is in such a range, the capacity of the metal oxide can be increased and charging / discharging can be performed stably.

  The molar ratio y of the first metal element to the total of the first metal element and the second metal element is 0.5 ≦ y ≦ 0.8, and preferably 0.6 ≦ y ≦ 0.8. When y is in such a range, the capacity and the electrochemical activity are easily balanced.

  The first metal element contained in the metal oxide only needs to contain at least Mn, may contain only Mn, and may contain Mn and a first metal element other than Mn. Examples of the first metal element other than Mn include at least one selected from the group consisting of Ti and Zr. The first metal element only needs to be tetravalent in average valence. As the first metal element, only Mn or a combination of Mn and Ti is preferable, and among them, only Mn is preferable.

The molar ratio y1 of Mn in the total of the first metal element and the second metal element satisfies 0.5 ≦ y1 ≦ 0.8. When the molar ratio y1 is less than 0.5, the capacity derived from Li ₂ MnO ₃ is reduced, and a contribution as a solid solution positive electrode material cannot be obtained, and when it exceeds 0.8, the contribution of Li ₂ MnO ₃ becomes too large. , The activity decreases electrochemically. From the viewpoint of the balance between capacity and electrochemical activity, the molar ratio y1 preferably satisfies 0.6 ≦ y1 ≦ 0.8 or 0.6 ≦ y1 ≦ 0.7.

The second metal element (element M ² ) contained in the metal oxide contains at least Ni, and may further contain Co and / or Fe. When the second metal element contains Ni, it becomes easy to improve the stability of the crystal structure and the electron conductivity. The second metal element may be Ni alone or a combination of Ni and Co and / or Fe. The element M ² has only to be trivalent in average valence. As a 2nd metal element, the case where only Ni and the case where Ni and Co are included at least are preferable. The latter includes a combination of Ni and Co, and a combination of Ni, Co, and Fe. Although the details are not clear, it is presumed that these combinations increase the structural stability when Li or Li ₂ O is desorbed.

  The ratio of Ni in the second metal element is, for example, 10 to 100 mol%, and preferably 40 to 80 mol% or 50 to 75 mol%. When the ratio of Ni is in such a range, it is more advantageous in terms of increasing the capacity.

  When the second metal element contains Co, the proportion of Co in the second metal element is, for example, 5 to 60 mol%, and preferably 15 to 50 mol% or 25 to 50 mol%. When the ratio of Co is in such a range, it is more advantageous in that the electron conductivity can be easily increased.

Of the metal oxides of the formula (A), those in which the first metal element is Mn are particularly preferable. Such a metal oxide has the following formula (1):
Li _{1 + x} (Mny ₁ M ² _1-y1 ) _1-x O ₂
(In the formula, the elements M ² , x and y 1 are the same as above.)
Can be expressed as

In the above formulas (A) and (1), the metal oxide is described as a dioxide, but the oxygen coefficient “2” may be “2 ± δ”, and the oxygen coefficient is 2 ± δ. The metal oxides of formula (A) and formula (1) are also included in this embodiment. Here, δ is an oxygen excess amount or an oxygen deficiency amount, for example, 0 to 0.2.
Specific examples of the metal oxides of the formula (A) and formula (1) include Li _{1 + x} (Ni _0.3 Co _0.1 Mn _0.6 ) _1-x O ₂ , Li _{1 + x} (Ni _0.2 Co _0.1 Mn _0.7 ) _{1 -x O 2, Li 1 + x} (Ni 0.3 Co 0.1 Mn 0.6) 1-x O 2 and the like.

The average particle diameter of the metal oxide particles is, for example, 4 to 10 μm, and preferably 5 to 9 μm. In the present specification, the average particle size is the median diameter (D ₅₀₎ in volume-based particle size distribution measured using a laser diffraction type particle size distribution measuring apparatus.

(Anion)
The anion unevenly distributed in the surface layer of the metal oxide particles is at least one selected from the group consisting of carbonate groups and sulfate groups. The anion may be contained in the form of a free anion such as CO ₃ ²⁻ or SO ₄ ^2−, but is often included in the form of a metal salt. However, the anion is preferably present in a form other than the transition metal salt in the surface layer of the metal oxide particles. Here, the transition metal salt is a salt of a transition metal and an anion in the first metal element and the second metal element contained in the metal oxide. Examples of forms other than the transition metal salt include an anionic Li salt.

Whether or not the anion is unevenly distributed on the surface layer of the metal oxide particle is determined from the peak P _{1 of} O1s derived from the metal oxide and the peak P _{2 of} O1s derived from the anion located on the higher binding energy side by XPS spectrum. I can confirm. When anions are distributed on the surface layer of the metal oxide particles, the peak P ₂ is detected. When the ratio S ₂ / S ₁ of the area S ₂ of the peak P ₂ to the area S ₁ of the peak P ₁ in the XPS spectrum satisfies, for example, S ₂ / S ₁ ≧ 1.0, the surface layer of the metal oxide particles It can be said that anions are unevenly distributed. Thus, the ratio S ₂ / S ₁ is desirably S ₂ / S ₁ ≧ 1.0, preferably S ₂ / S ₁ ≧ 2.0, and S ₂ / S ₁ ≧ 3. More preferably, it is 0. When the ratio S ₂ / S ₁ is in such a range, since the surface layer of the metal oxide particles contains a large amount of anions, the charge / discharge reaction can be performed smoothly. The upper limit of the ratio S ₂ / S ₁ is not particularly limited, but for example, S ₂ / S ₁ ≦ 10.

The absolute value of the difference in binding energy between the peak P ₁ and the peak P ₂ in the XPS spectrum is, for example, 1 to 4 eV, and may be 1 to 3 eV. Note that the difference between the binding energy of the peak P ₁ and the peak P _2, the absolute value of the difference between the binding energy of the maximum value of the binding energy peak P ₂ of the maximum value of the peak P _1.

In the XPS spectrum of the positive electrode active material, the peak P ₁ is detected, for example, between 528.1 and 531.1 eV, and the peak P ₂ is detected, for example, between 530.5 and 532.5 eV. The peak P ₂ detected between 530.5 and 532.5 eV is derived from anions (carbonate groups and / or sulfate groups), organic oxygen (oxygen bonded to an organic group), and the like. Note that since the amount of organic oxygen is extremely small, the influence on the peak P ₁ can be ignored.

The ratio S ₂ / S ₁ can be obtained from the calculation result obtained by performing waveform separation by peak fitting in the XPS spectrum and calculating the peak areas S ₁ and S ₂ with analysis software. At the time of peak fitting, for example, the background of the XPS spectrum is removed and smoothing is performed by the Shirley method. The peak position of the entire spectrum can be corrected by separating the waveform of carbon C and setting the energy value of the peak of carbon C on the lowest energy side to a reference value (284.6 eV: CC bond). it can. At the time of peak fitting, the number of peaks, the peak position, etc. may be adjusted so as to facilitate analysis while keeping certain rules (such as the peak half-value width not exceeding a certain value). In the spectrum after waveform separation of necessary peaks, the chemical state of each peak can be determined by comparing the energy value at the peak apex position with the value in the database.

  The positive electrode active material according to the present embodiment can be obtained, for example, by firing a mixture containing a precursor containing Li and a precursor containing a first metal element and a second metal element. At this time, for example, by using a carbonate and / or sulfate more than the stoichiometric ratio as a precursor containing Li, a large number of anions can be distributed on the surface layer of the metal oxide particles. As the precursor containing Li, lithium carbonate is preferably used. At this time, the ratio of the atomic ratio of Li to the total of the first metal element and the second metal element is higher than 1.3 which is the stoichiometric ratio, for example, the atomic ratio is 1.4 to 2.0 or It is preferable to use lithium carbonate at a ratio of 1.5 to 1.7. In addition, you may perform baking by a multistep as needed.

  Moreover, when the metal oxide particles obtained by firing are washed with water, anions on the surface layer are reduced. Therefore, it is also preferable to limit the amount and the number of times of water when washing with water. A metal oxide fired without washing with water may be used as the positive electrode active material.

In addition to carbonates and sulfates, nitrates, hydroxides, oxides, halides, and the like can be used as the precursors that are firing raw materials.
As the precursor containing the first metal element and the second metal element, a mixture containing a precursor containing the first metal element and a precursor containing the second metal element may be used. A precursor containing both of the two metal elements may be used. The precursor containing the first metal element and the second metal element may be a coprecipitate obtained by a coprecipitation method from a compound containing each metal element.

  When the metal oxide particles include a plurality of first metal elements, a precursor including each first metal element may be used in combination, or a precursor including a plurality of first metal elements may be used. Similarly, when the metal oxide particles include a plurality of second metal elements, a precursor including each second metal element may be used in combination, or a precursor including a plurality of second metal elements may be used. .

The mixture of precursors may be pulverized at an appropriate stage.
Firing can be performed in an inert gas atmosphere, but is preferably performed in the air. The firing temperature is, for example, 700 to 1000 ° C. When firing is performed in multiple stages, the firing conditions at each stage may be different. For example, the first baking may be performed in the air and the second baking may be performed in an inert gas atmosphere.

[All-solid LIB]
An all-solid LIB according to an embodiment of the present invention includes a positive electrode including the positive electrode active material described above, a negative electrode, and a solid electrolyte layer interposed therebetween.
(Positive electrode)
The positive electrode should just contain the positive electrode active material, and may contain the well-known component used for a positive electrode by all the solid LIB in addition to a positive electrode active material. From the viewpoint of increasing lithium ion conductivity in the positive electrode, the positive electrode preferably includes an inorganic solid electrolyte exhibiting lithium ion conductivity together with the positive electrode active material.

The inorganic solid electrolyte is not particularly limited as long as it exhibits lithium ion conductivity, and an inorganic solid electrolyte such as that used for a solid electrolyte layer in an all-solid LIB can be used. The crystal state of the inorganic solid electrolyte is not particularly limited, and may be crystalline or amorphous. As the inorganic solid electrolyte, a sulfide (sulfide-based inorganic solid electrolyte) is preferable, and a sulfide containing Li and P is more preferable. As the sulfide, for example, Li ₇ P ₃ S ₁₁ , Li ₃ PS ₄ , Li ₁₀ GeP ₂ S ₁₂ , Li ₆ PS ₅ X (X is selected from the group consisting of F, Cl, Br, I and At. At least one kind). These solid electrolytes may be used individually by 1 type, and may use 2 or more types together as needed.

  The proportion of the inorganic solid electrolyte in the total amount of the positive electrode active material and the inorganic solid electrolyte is preferably 5 to 40% by mass, and more preferably 10 to 40% by mass. When the proportion of the inorganic solid electrolyte is in such a range, it is easy to ensure high lithium ion conductivity of the positive electrode.

The positive electrode may include a positive electrode current collector and a positive electrode active material or a positive electrode mixture supported on the positive electrode current collector. The positive electrode mixture is a mixture containing a positive electrode active material and an inorganic solid electrolyte.
As the positive electrode current collector, any positive electrode current collector can be used without particular limitation as long as it is used as a positive electrode current collector of all solid LIB. Examples of the form of such a positive electrode current collector include metal foils, plate-like bodies, powder aggregates, and the like, and a material obtained by forming a film of the positive electrode current collector may be used. The metal foil may be an electrolytic foil, an etched foil, or the like.

Examples of the material of the positive electrode current collector include aluminum, magnesium, stainless steel, titanium, iron, cobalt, zinc, tin, and alloys thereof.
The thickness of the positive electrode is, for example, 50 to 200 μm.
The positive electrode can be obtained, for example, by compressing a positive electrode active material or a positive electrode mixture. The positive electrode may be formed by forming a layer of a positive electrode active material or a positive electrode mixture on the surface of the positive electrode current collector.

(Negative electrode)
The negative electrode includes a negative electrode active material. The negative electrode active material is not particularly limited as long as lithium ions can be inserted and desorbed, and a known negative electrode active material used in LIB can be used. For example, in addition to a carbonaceous material that can insert and desorb lithium ions, a simple substance, alloy, or compound of a metal or a semimetal that can insert and desorb lithium ions can be used. Examples of the carbonaceous material include graphite, hard carbon, and amorphous carbon. Examples of simple metals and metalloids and alloys include lithium metal, alloys, and Si. Examples of the compound include oxides, sulfides, nitrides, hydrates, silicides (such as lithium silicide), and the like. Examples of the oxide include titanium oxide and silicon oxide. A negative electrode active material may be used individually by 1 type, and may be used in combination of 2 or more type. For example, silicon oxide and a carbonaceous material may be used in combination.

  In addition to the negative electrode active material, the negative electrode may include known components used for the negative electrode in all solid LIB. As in the case of the positive electrode, from the viewpoint of increasing lithium ion conductivity in the negative electrode, the negative electrode preferably contains an inorganic solid electrolyte exhibiting lithium ion conductivity together with the negative electrode active material. As such an inorganic solid electrolyte, it can select from what was illustrated about the positive electrode suitably. The ratio of the inorganic solid electrolyte to the total amount of the negative electrode active material and the inorganic solid electrolyte can be appropriately selected from the range described as the ratio of the inorganic solid electrolyte to the total amount of the positive electrode active material and the inorganic solid electrolyte.

  The negative electrode may include a negative electrode current collector and a negative electrode active material or a negative electrode mixture supported on the negative electrode current collector. The negative electrode mixture is a mixture containing a negative electrode active material and an inorganic solid electrolyte. Examples of the form of the negative electrode current collector include those described for the positive electrode current collector. Examples of the material for the negative electrode current collector include copper, nickel, stainless steel, titanium, and alloys thereof.

The thickness of the negative electrode is, for example, 50 to 200 μm.
The negative electrode can be produced according to the case of the positive electrode, using a negative electrode active material or a negative electrode mixture, and if necessary, a negative electrode current collector.

(Solid electrolyte layer)
The solid electrolyte layer interposed between the positive electrode and the negative electrode includes an inorganic solid electrolyte that exhibits lithium ion conductivity. As such an inorganic solid electrolyte, the inorganic solid electrolyte illustrated about the positive electrode is mentioned, A sulfide is preferable.

The solid electrolyte layer can be formed by compressing the inorganic solid electrolyte. The solid electrolyte layer can contain known additives used for the solid electrolyte layer of the all-solid LIB, if necessary.
The thickness of the solid electrolyte layer is, for example, 20 to 200 μm.

  FIG. 1 is a longitudinal sectional view schematically showing an electrode group included in the all solid LIB according to the present embodiment. The electrode group 1 included in the all-solid LIB includes a positive electrode 2, a negative electrode 4, and a solid electrolyte layer 3 interposed therebetween. The positive electrode 2 includes a positive electrode current collector 2b and a positive electrode mixture layer 2a supported thereon. The negative electrode 4 includes a negative electrode current collector 4b and a negative electrode mixture layer 4a supported thereon. The positive electrode 2 and the negative electrode 4 are disposed so that the positive electrode mixture layer 2a and the negative electrode mixture layer 4a face each other. The solid electrolyte layer 3 is disposed between the positive electrode mixture layer 2a and the negative electrode mixture layer 4a. The solid electrolyte layer 3 includes a lithium ion conductive inorganic solid electrolyte.

  The positive electrode mixture layer 2 a, the negative electrode mixture layer 4 a, and the solid electrolyte layer 3 have a disk shape having substantially the same size, and are stacked with the solid electrolyte layer 3 sandwiched therebetween to form a cylindrical laminate 6. ing. The insulator 5 is attached to the side surface of the multilayer body 6 so as to cover the side surface of the negative electrode mixture layer 4a and the side surface of the solid electrolyte layer 3 on the negative electrode mixture layer 4a side. The positive electrode current collector 2b and the negative electrode current collector 4b are circular metal foils that are larger in size than the positive electrode mixture layer 2a and the negative electrode mixture layer 4a. The positive electrode current collector 2b and the negative electrode current collector 4b are formed to have substantially the same size as the stacked body 6 with the insulator 5 attached.

The all solid LIB can be produced by housing the electrode group in a cell case. One end of a lead is connected to each of the positive electrode and the negative electrode of the electrode group. The other end of the lead is electrically connected to an external terminal exposed to the outside of the cell case.
The all-solid LIB is not limited to the example shown in FIG. 1, but may be various types such as a round shape, a cylindrical shape, a square shape, and a thin layer flat type. The electrode group may include a plurality of positive electrodes and / or a plurality of negative electrodes.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
(1) Synthesis of positive electrode active material Metal oxide a1: Li _{1 + x} (Ni _0.2 Co _0.1 Mn _0.7 ) _1-x O ₂ was synthesized by the following procedure.
Ni (NO ₃ ) ₂ .9H ₂ O, Co (NO ₃ ) ₂ .6H ₂ O, and MnCl ₂ .4H ₂ O in such an amount that the Ni: Co: Mn atomic ratio is 2: 1: 7 The precursor aqueous solution was prepared by dissolving in distilled water. This precursor aqueous solution was dropped into a sodium hydroxide aqueous solution kept at 20 ° C. in a thermostatic bath over several hours, thereby generating a Ni—Co—Mn coprecipitate. The obtained mixture was taken out from the thermostatic bath, and the coprecipitate was aged by stirring while blowing air at room temperature for 2 days. The coprecipitate was then filtered off and washed with distilled water to remove sodium hydroxide.

  An amount of lithium carbonate (0.2125 mol) such that the Li / (Ni + Co + Mn) ratio was 1.7 was dispersed in distilled water. The obtained dispersion and coprecipitate were placed in a mixer and stirred. The resulting mixture was dried at 50 ° C. for 2 days. The dried product was pulverized mechanically and then fired at 900 ° C. for 5 hours in the air to synthesize the target metal oxide a1 (0.25 mol per batch).

From the XRD pattern of the metal oxide a1, the metal oxide a1 is composed of a monoclinic Li ₂ MnO ₃ type unit cell (space group C2 / m) single phase and is a Li ₂ MnO ₃ —LiM ² O ₂ solid solution. It was confirmed. No impurities were observed from the XRD pattern. The composition of the metal oxide a1 analyzed from the XRD pattern was Li _{1 + x} (Ni _0.2 Co _0.1 Mn _0.7 ) _1-x O ₂ (x = 0.25).

(2) Production of all-solid LIB All-solid LIB shown in FIG. 1 was produced by the following procedure.
(A) Production of Solid Electrolyte Layer 3 A cylindrical die (inner diameter 10 mm, height 30 mm) made of cold die steel (SKD) was placed upright, and a short pin serving as a bottom plate was inserted into the bottom of the cylindrical die. In this state, 50 mg of Li ₂ S (70 mol%)-P ₂ S ₅ (30 mol%) solid solution (composition: Li ₇ P ₃ S ₁₁ ), which is a lithium ion conductive solid electrolyte, is layered in a cylindrical mold. did. Then, a solid electrolyte layer is formed by inserting a cylindrical long pin having a size matched to the inner diameter of the cylindrical mold from the top of the cylindrical mold into the inside and pressurizing once at a pressure of 188 MPa in the thickness direction of the layer. 3 was produced.

(B) Production of Negative Electrode Mixture Layer 4a Graphite and Li ₂ S (70 mol%)-P ₂ S ₅ (30 mol%) solid solution were sufficiently mixed in a mortar using a mass ratio of 6: 4. 16 mg of the obtained mixture was filled in layers on the solid electrolyte layer 3 in the cylindrical mold produced in (a). And the negative mix layer 4a was produced by press-pressing 3 times in the thickness direction of a layer. The pressure of the pressure press was 188 MPa per time.

  Next, the cylindrical mold was placed so that the cylindrical pin was turned upside down, the short pin was taken out, the short pin was inserted into the negative electrode mixture layer 4a side, and the short pin became the bottom. Next, the solid electrolyte layer 3 and the negative electrode mixture layer 4a were pressed from the solid electrolyte layer 3 side using a long pin. In this way, a space surrounded by the inner wall of the cylindrical mold was formed on the solid electrolyte layer 3 on the side opposite to the negative electrode mixture layer 4a.

(C) Production of Positive Electrode Mixture Layer 2a The metal oxide a1 and Li ₂ S (70 mol%)-P ₂ S ₅ (30 mol%) solid solution obtained in (1) above were used at a mass ratio of 7: 3. The mixture was obtained by thoroughly mixing in a mortar. 20 mg of the mixture was filled in layers on the solid electrolyte layer 3 in the cylindrical mold, and the positive electrode mixture layer 2a was press-pressed three times in the order of 376 MPa, 752 MPa, and 1050 MPa in the thickness direction of the layer, respectively. Was made.

(D) Assembly of all-solid LIB A laminate 6 in a state in which the solid electrolyte layer 3 is sandwiched between the positive electrode mixture layer 2a and the negative electrode mixture layer 4a formed as in (a) to (c) Removed from the mold.
On one surface of a copper foil (vertical 20 mm × horizontal 20 mm, thickness 100 μm) as the negative electrode current collector 4b, an insulator 5 (inner diameter 11 mm, height 50 μm) having a hole in the center was disposed. And the laminated body 6 (outer diameter 10 mm) was accommodated in the hole of the insulator 5 so that the negative mix layer 4a might contact | connect the negative electrode collector 4b. Next, an electrode group 1 was prepared by placing an aluminum foil (vertical 20 mm × horizontal 20 mm, thickness 20 μm) as the positive electrode current collector 2 b on the positive electrode mixture layer 2 a of the laminate 6. The insulator 5 is disposed so as to suppress contact between the negative electrode mixture layer 4a and the negative electrode current collector 4b, and the positive electrode mixture layer 2a and the positive electrode current collector 2b.
The electrode group 1 was accommodated in a laminate cell having a negative electrode lead and a positive electrode lead, and the gas in the cell was sealed while being sucked with a vacuum pump. In this way, an all-solid LIB was produced.

(3) Evaluation (a) XPS spectrum measurement of positive electrode active material The XPS spectrum of the positive electrode active material (metal oxide a1) obtained in (1) above was measured to confirm the O1s peak. In the XPS spectrum, the peak P ₁ derived from the metal oxide is 528.1 to 531.1 eV, and the peak P ₂ derived from CO ₃ ²⁻ , organic oxygen, and SO ₄ ²⁻ is 530.5 to 532. Each was confirmed at .5 eV. In above procedure, determine the peak area S ₂ of the peak area of the peak P ₁ S ₁ and the peak P _2, from these values, to determine the ratio S ₂ / S _1. As the analysis software, SpecSurf (JEOL Ltd.) was used.

(B) Charge capacity, discharge capacity and capacity maintenance rate of all-solid-state LIB battery All-solid-state LIB was maintained at 25 ° C. in a thermostat and pressurized at 58.8 MPa. In this state, in the current 0.02 mA / cm ^2, and charged to the charging end voltage 4.7V, then in the current 0.02 mA / cm ^2, and discharged to the discharge termination voltage 2.0 V. The charge capacity and discharge capacity (initial discharge capacity) at this time were determined.
The above charging and discharging were repeated 10 cycles, the discharge capacity at the 10th cycle was determined, and the capacity retention rate (%) with respect to the initial discharge capacity was determined.

Comparative Example 1
A metal oxide was synthesized in the same manner as in Example 1 except that lithium carbonate (0.14 mol) was used in such an amount that the Li / (Ni + Co + Mn) ratio was 2.0. Then, the obtained metal oxide was washed with distilled water, filtered, and dried at 100 ° C. to obtain a target metal oxide b1.

From the XRD pattern of the metal oxide b1, the metal oxide b1 is composed of a monoclinic Li ₂ MnO ₃ type unit cell (space group C2 / m) single phase and is a Li ₂ MnO ₃ —LiM ² O ₂ solid solution. It was confirmed. No impurities were observed from the XRD pattern. The composition of the metal oxide b1 analyzed from the XRD pattern was Li _{1 + x} (Ni _0.2 Co _0.1 Mn _0.7 ) _1-x O ₂ (x = 0.26).
An all-solid LIB was prepared and evaluated in the same manner as in Example 1 except that the metal oxide b1 was used as the positive electrode active material instead of the metal oxide a1.

Example 2
Ni (NO ₃ ) ₂ .9H ₂ O, Co (NO ₃ ) ₂ .6H ₂ O, and MnCl ₂ .4H ₂ O in such an amount that the Ni: Co: Mn atomic ratio is 3: 1: 6. A metal oxide a2 was synthesized in the same manner as in Example 1 except that lithium carbonate was used in such an amount that the Li / (Ni + Co + Mn) ratio was 1.6.

From the XRD pattern of the metal oxide a2, the metal oxide a2 is substantially composed of a monoclinic Li ₂ MnO ₃ type unit cell (space group C2 / m) single phase, and Li ₂ MnO ₃ —LiM ² O ₂ solid solution. It was confirmed that. No impurities were observed from the XRD pattern. The composition of the metal oxide a2 analyzed from the XRD pattern was Li _{1 + x} (Ni _0.3 Co _0.1 Mn _0.6 ) _1-x O ₂ (x = 0.25).
An all-solid LIB was prepared and evaluated in the same manner as in Example 1 except that the metal oxide a2 was used as the positive electrode active material instead of the metal oxide a1.

Comparative Example 2
A metal oxide was synthesized in the same manner as in Example 2 except that lithium carbonate (0.14 mol) was used in such an amount that the Li / (Ni + Co + Mn) ratio was 2.0. Then, the obtained metal oxide was washed with distilled water, filtered, and dried at 100 ° C. to obtain a target metal oxide b2.

From the XRD pattern of the metal oxide b2, the metal oxide b2 is composed of a monoclinic Li ₂ MnO ₃ type unit cell (space group C2 / m) single phase and is a Li ₂ MnO ₃ —LiM ² O ₂ solid solution. It was confirmed. No impurities were observed from the XRD pattern. From the XRD pattern, the composition of the metal oxide b2 was Li _{1 + x} (Ni _0.3 Co _0.1 Mn _0.6 ) _1-x O ₂ (x = 0.23).
An all-solid LIB was prepared and evaluated in the same manner as in Example 1 except that the metal oxide b2 was used as the positive electrode active material instead of the metal oxide a1.

Comparative Example 3
Commercially available LiCoO ₂ (metal oxide b3) was prepared. From the XRD pattern, it was confirmed that the metal oxide b3 consists of a hexagonal crystal (space group R-3m) single phase and does not have a Li ₂ MnO ₃ type crystal structure. Mn molar ratio y1 of metal oxide b3 was 0.0. Further, no impurity was observed from the XRD pattern.
The metal oxide b3 was used as the positive electrode active material instead of the metal oxide a1, and the mass of the mixture when layered in Example 2 (2) (b) was changed to 15 mg. Except for these, an all-solid LIB was prepared in the same manner as in Example 1. Evaluation was performed in the same manner as in Example 1 except that the current value was 0.1 mA / cm ² and the end-of-charge voltage was 4.2 V.

Reference example 1
The metal oxide b1 used in Comparative Example 3 was fired in an air stream at 700 ° C., which is higher than the decomposition temperature of lithium carbonate (690 ° C.) for 15 hours, to obtain a metal oxide c1. From the XRD pattern, it was confirmed that the metal oxide c1 consists of a hexagonal crystal (space group R-3m) single phase and does not have a Li ₂ MnO ₃ type crystal structure. Mn molar ratio y1 of metal oxide c1 was 0.0. Further, no impurity was observed from the XRD pattern. The composition of the metal oxide b3 analyzed from the XRD pattern was LiCoO ₂ .
An all-solid LIB was prepared and evaluated in the same manner as in Comparative Example 3 except that the metal oxide c1 was used instead of the metal oxide b3.

  For Example 2, Comparative Examples 1 to 3, and Reference Example 1, the XPS spectrum of the positive electrode active material was measured in the same manner as in Example 1. FIG. 2 is an O1s peak of the XPS spectrum of the metal oxide a1 of Example 1 and the metal oxide b1 of Comparative Example 1. FIG. 3 is an O1s peak of the XPS spectrum of the metal oxide a2 of Example 2 and the metal oxide b2 of Comparative Example 2. FIG. 4 shows O1s peaks of XPS spectra of the metal oxide b3 of Comparative Example 3 and the metal oxide c1 of Reference Example 1.

In FIG. 2, the peaks P ₁ of the metal oxides a1 and b1 are denoted by P ₁ (a1) and P ₁ (b1), respectively, and the peaks P ₂ of the metal oxides a1 and b1 are respectively represented by P ₂ (a1) and P ₂ (b1). In FIG. 3, the peak P ₂ of the metal oxide a2 is indicated by P ₂ (a2), and the peak P ₁ of the metal oxide b2 is indicated by P ₁ (b2). In the metal oxides a1 and a2 of Examples 1 and 2 and the metal oxide b3 of Comparative Example 3, the peak P ₁ of the metal oxide of 528.1 to 531.1 eV is small, and the carbonate group is smaller than the peak P _1. And a peak P _{2 of} 530.5 to 532.5 eV derived from sulfite and sulfate radicals is remarkably large. On the other hand, in the metal oxides b1 and b2 of Comparative Examples 1 and 2, the peak P ₂ derived from the carbonate or sulfate radical is small, and the peak P ₁ derived from the metal oxide is remarkably large. From these, in the metal oxides of Examples 1 and 2 and Comparative Example 3, anions such as carbonate radicals and sulfate radicals are segregated on the surface layer, and the metal oxides of Comparative Examples 1 and 2 and Reference Example 1 It can be said that the surface layer contains a large amount of metal oxide rather than anions.

  The evaluation results of Examples 1-2, Comparative Examples 1-3, and Reference Example 1 are shown in Table 1 together with the composition of the positive electrode active material. Examples 1 and 2 were represented by A1 and A2, Comparative Examples 1, 2, and 3 were represented by B1, B2, and B3, respectively, and Reference Example 1 was represented by C1.

As shown in Table 1, in Comparative Examples 1 and 2 where anions such as carbonate radicals and sulfate radicals are not unevenly distributed on the surface layer, the peak area ratio S ₂ / S ₁ in the XPS spectrum is significantly larger than in the Examples. Small and less than 1. In such a comparative example, the charge capacity was extremely small and no discharge capacity was obtained. That is, the cells of Comparative Examples 1 and 2 could not be substantially charged and discharged.

On the other hand, in the example in which anions are unevenly distributed on the surface layer, the ratio S ₂ / S ₁ is remarkably large. As shown in Table 1, in the example, a large charge capacity was obtained, and a certain amount of discharge capacity could be secured. That is, the cell of the example could be charged / discharged as an all-solid LIB. Further, in the batteries of Examples 1 and 2, a high capacity retention rate of 100% was obtained even after 10 cycles of charge / discharge.

In LiCoO ₂ having a hexagonal crystal (space group R-3m) crystal structure, the discharge capacity of Comparative Example 3 in which anions are unevenly distributed in the surface layer is lower than that in Reference Example 1 in which uneven distribution is not present. It was. That is, in Comparative Example 3 and Reference Example 1, charge / discharge behaviors completely different from those in Examples using metal oxides having different crystal structures were shown. Since Comparative Example 3 and Reference Example 1 and Examples differ not only in the positive electrode active material but also in the charge end voltage and charge / discharge current value, the charge / discharge capacities cannot be generally compared. However, the theoretical capacity is larger in Examples (360 to 365 mAh / g) than Comparative Example 3 and Reference Example 1 (260 to 273 mAh / g), which is advantageous. In addition, the capacity retention rate after repeating the charge / discharge cycle 10 times was as low as 79% in Comparative Example 3 and 72% in Reference Example 1.

  The positive electrode active material according to the present invention can be charged and discharged by using it as an all-solid LIB. Therefore, the all-solid-state LIB is useful for various applications that require high safety.

1: electrode group, 2: positive electrode, 2a: positive electrode mixture layer, 2b: positive electrode current collector, 3: solid electrolyte layer, 4: negative electrode, 4a: negative electrode mixture layer, 4b: negative electrode current collector, 5: insulation Body, 6: Laminated body

Claims (7)

Comprising metal oxide particles and at least one anion selected from the group consisting of carbonate and sulfate radicals,
The metal oxide has a Li ₂ MnO ₃ type crystal structure and has the following formula (A):
Li _{1 + x} (M ¹ _y M ² _1-y ) _1-x O ₂
(In the formula, element M ¹ is a tetravalent first metal element, element M ² is a trivalent second metal element, and 0 <x ≦ 1/3 and 0.5 ≦ y ≦ 0.8. Satisfaction.)
Represented by
The first metal element includes at least Mn,
The molar ratio y1 of Mn in the total of the first metal element and the second metal element satisfies 0.5 ≦ y1 ≦ 0.8,
The second metal element includes at least one selected from the group consisting of Ni, Co, and Fe, and includes at least Ni,
A positive electrode active material for an all-solid-state lithium ion secondary battery, wherein the anions are unevenly distributed in the surface layer of the particles.   The positive electrode active material for an all-solid-state lithium ion secondary battery according to claim 1, wherein the second metal element includes at least Ni and Co.   The positive electrode active material for an all-solid-state lithium ion secondary battery according to claim 1, wherein the molar ratio y1 satisfies 0.6 ≦ y1 ≦ 0.7. In the spectrum of the positive electrode active material by X-ray photoelectron spectroscopy, the area S ₁ of the peak P ₁ of O1s derived from the metal oxide and the area S ₂ of the peak P ₂ of O1s derived from the anion are S _The positive electrode active material for an all-solid-state lithium ion secondary battery according to any one of claims 1 to 3, satisfying ₂ / S ₁ ≥1.0. The positive electrode active material for an all-solid-state lithium ion secondary battery according to claim 4, wherein the area S ₁ and the area S ₂ satisfy S ₂ / S ₁ ≧ 2.0. A positive electrode comprising the positive electrode active material according to claim 1;
A negative electrode containing a negative electrode active material that inserts and desorbs lithium ions;
An all solid lithium ion secondary battery comprising a solid electrolyte layer including an inorganic solid electrolyte interposed between the positive electrode and the negative electrode and exhibiting lithium ion conductivity.   The all-solid-state lithium ion secondary battery according to claim 6, wherein the inorganic solid electrolyte is a sulfide.

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