Irregular Rock Salt-Type Cathode Material and Method for Producing the Same

Abstract

The improved disordered rock salt type containing Mn is found to be produced by a method including mixing a lithium compound with a metal precursor compound containing Mn having an oxidation state of 2 to form a mixture, and heating the mixture to a certain temperature to form a disordered rock salt type structure. This method can achieve an improvement in cycle life by changing the metal redox and oxygen redox of the disordered rock salt type.

Description

Technical Field

[0001] The present invention relates to the field of battery technology.

Background Art

[0002] Lithium metal oxides are used to formulate cathode materials for lithium-ion batteries. Cathodes are derived from several basic crystallographic structural types, such as spinel-type, olivine-type, and layered oxide structures. The layered oxide structure includes a lithium-excess type structure in which additional lithium is present within the structure.

[0003] Recently, disordered rock-salt type structures, such as those formed from certain lithium metal oxides, have attracted attention. Compounds represented by the following formula: xLi 3 NbO 4 ·(1-x)LiMO 2 (1) (wherein M is a divalent or trivalent cation) have been shown to be a promising class of transition metal oxides for use as cathodes in lithium-ion batteries. The compounds of formula (1) are considered to have a disordered rock-salt type in which the random atomic arrangement of lithium and transition metal ions is filled in the closest cubic structure. These disordered rock-salt type compositions provide the ability to contain up to three lithium atoms per formula unit, which is more than conventional lithium-excess type layered materials. Formula (1) can be represented as converted to Li x M y N z O w and.

[0004] The disordered rock-salt type structure is an attractive cathode material for next-generation lithium-ion batteries because it has a higher specific energy density (e.g., a higher theoretical energy density) than state-of-the-art cathode materials such as layered lithium metal oxide structures. For example, certain disordered rock-salt type structure materials have a theoretical weight energy density of about 1120 Wh / kg, while LiMn 2 O 4The active material has a theoretical weight energy density of about 492 Wh / kg, and LiMn 1.5 Ni 0.5 O 4 has a theoretical weight energy density of about 691 Wh / kg. This energy density is particularly attractive when relatively low-cost raw materials such as manganese are used as components of the disordered rock salt-type structure. Thus, the disordered rock salt-type material can achieve a relatively high energy density at a relatively low material cost. To achieve an equivalent energy density, known cathode materials require relatively high-cost raw materials such as cobalt or nickel.

[0005] The problem with the disordered rock salt-type material is its relatively low conductivity. It has been reported that reducing the size of the disordered rock salt-type particles by milling and then re-aggregating the milled particles improves the conductivity by shortening the transport paths of electrons and ions (Patent Document 1).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

[0007] It has been found that an improved disordered rock salt-type material can be formed by using a metal in a precursor compound that is in a lower oxidation (valence) state before heating. The mechanism is not fully clear. It has been found that the formed particles have a smaller particle size or crystallite size than those formed using a precursor compound containing a metal in a higher oxidation state when other variables are equivalent.

[0008] Exemplarily, the method includes mixing a lithium compound with a metal precursor compound containing Mn in an oxidation state of 2 to form a mixture, and heating the mixture to a certain temperature to form a disordered rock salt structure. Also, Mn in an oxidation state of 2 may be formed as follows. In the absence of a lithium compound up to a certain temperature, a mixture containing a Mn compound having an oxidation state greater than 2 and at least one other metal precursor compound is formed to form a precursor (also referred to as an intermediate precursor). This formed intermediate precursor contains Mn having a reduced oxidation state of 2. The resulting intermediate precursor is then mixed with a lithium source, heated, and a disordered rock salt type may be formed.

[0009] This method can produce a disordered rock salt type having a metal redox capacity and an oxygen redox capacity, where the metal redox capacity is greater than the oxygen redox capacity. Similarly, the method can produce a disordered rock salt type having a metal redox capacity that is at least partially due to the presence of Mn in a reduced 2+ valence state, which is thought to contribute to, but is not limited to, an increase in the metal redox capacity and an improvement in cycle life. For example, the method can enable the formation of a disordered rock salt type containing Li, Mn, and O, with at least 1 mol% of Mn in the 2+ valence state. The valence state and the proportion of Mn in the 2+ valence state can be determined by known methods such as X-ray absorption spectroscopy, as described in Phys. Rev. B 94, 155117, 12 October 2016. Desirably, for essentially all of the Mn present in the disordered rock salt type, at least 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, or 50% is in the 2+ valence state.

[0010] The disordered rock salt type can be used in the electrodes of an electrochemical cell. The disordered rock salt type material may be used to form a cathode. The electrochemical cell utilizing the disordered rock salt type material may be a primary or secondary lithium ion battery. The lithium ion battery is desirably a secondary battery.

Brief Description of the Drawings

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Embodiments for Carrying Out the Invention

[0012] The following definitions apply to some of the aspects described with respect to some embodiments of the present invention. These definitions may also be extended in this specification. Each term is further explained and illustrated throughout the description, drawings, and examples. Any interpretation of the terms in this description shall be considered in view of the complete description, drawings, and examples presented in this specification.

[0013] Unless the context clearly dictates otherwise, the singular forms "a", "an", and "the" include the plural. Thus, for example, a reference to an object can include a plurality of objects unless the context clearly dictates otherwise.

[0014] The rate "C" refers to either the discharge current as a fraction or multiple of the "1C" current value at which a battery (in a substantially fully charged state) would be substantially fully discharged in 1 hour, or the charge current as a fraction or multiple of the "1C" current value at which a battery (in a substantially fully discharged state) would be substantially fully charged in 1 hour, depending on the context.

[0015] If certain battery characteristics can vary with temperature, such characteristics are specified at 30 degrees Celsius unless a clear contrary determination is made by context.

[0016] The ranges set forth herein include their endpoints. Thus, for example, the range from 1 to 3 includes the values 1 and 3, as well as intermediate values.

[0017] In the disordered rock salt-type composition, both lithium and transition metals occupy the octahedral sites of the cubic close-packed lattice. In an electrochemical reaction, the diffusion of lithium proceeds by lithium hopping from one octahedral site to another via intermediate tetrahedral sites. Lithium in the intermediate tetrahedral sites is in an activated state in lithium diffusion. The activated tetrahedral lithium ions share faces with the following four octahedral sites: (i) the site previously occupied by the lithium ion itself, (ii) the vacancy to which the lithium ion moves, and (iii and iv) two sites that can be occupied by lithium, transition metal, or vacancy.

[0018] Using this method, a disordered rock salt-type useful for making battery cathodes containing Mn, such as those known in the art (e.g., U.S. Patent No. 10,280,092), can be made. This method can perform long annealing, but the crystal grains of the disordered rock salt-type are small or relatively small. For example, when all other things are equal, this method achieves the same or smaller crystal grain or particle size compared to a method that does not use a manganese +2 precursor compound, even when heated for a longer time (i.e., 2, 5, or 10 times at the same temperature). This enables a more robust method for forming the disordered rock salt-type.

[0019] An exemplary disordered rock salt type can be any that contains Mn as described in U.S. Application No. 15 / 222,377 (now U.S. Patent No. 10,280,092), which is incorporated herein by reference in its entirety. Other disordered rock salt types as described in U.S. Patent Nos. 10,811,671; 9,692,043; 9,093,712; 9,083,062; 8,722,250; 8,535,832; 10,833,322; 10,497,928; 9,865,872; and 9,780,363 may be useful if they contain Mn and are incorporated herein by reference. Disordered rock salt type compositions generally contain lithium, a transition metal, and oxygen. One or more of the transition metal or oxygen sites may be doped to improve electrochemical performance. In a non-limiting example, the oxygen site is doped with fluorine. The general formula for doping at the oxygen site is as follows. Li x N y M z O 2-a F a (i) Here, 1.0 < x < 1.65, 0 ≤ y < 0.55, 0.1 < z < 1, 0 ≤ a < 0.5, N is one of Ti, Ta, Zr, W, Nb, or Mo, and M is one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Zr, Y, Mo, Ru, Rh, Sn, Bi, or Sb (provided that Mn is present only when). Other dopants such as Na and Mg may be incorporated in place of Li at low concentrations such as 0.1 mol% to 10 mol% of the existing Li and dopants. These compositions exhibit excellent specific capacity or energy density, such as approximately 350 mAh / g at 55 °C and C / 40, and approximately 300 mAh / g at 30 °C and C / 15. The disordered rock salt type may be one in which "a" is zero. As described in the co-pending application entitled "Disordered Rocksalt Material and Method of Forming" filed simultaneously with this specification by Tanghong Yi, which is incorporated herein by reference, other anions can be further incorporated in place of O and / or F. Desirably, the disordered rock salt type is one in which N is Nb and M is Mn and Ti. When Mn and Ti are present, it may be desirable for Mn / Ti to be 1 to 50, 25, or 10. When fabricating the cathode, the disordered rock salt type may be mixed with other additives that can introduce useful properties to bond or improve the conductivity of the disordered rock salt type powder. For example, the disordered rock salt type can be mixed with or coated with carbon microparticles to improve conductivity. Usually, the weight amount of carbon is such that the weight ratio of disordered rock salt type / carbon is 100, 50, 30, 20, 10 to about 2 or 5.

[0020] This method can generate a disordered rock salt type that exhibits a metal redox capacity and an oxygen redox capacity, where the metal redox capacity is greater than the oxygen redox capacity. The capacity contributed by the transition metal is obtained as a gradient curve from 0 to about 150 mAh / g in the capacity Q (mAh / g) versus voltage (V) curve (voltage from about 3 volts to 4.2 volts). Subsequently, the capacity obtained in the high voltage plateau is understood to be due to oxygen anions (up to about 4.5 volts). The metal redox capacity, all other things being essentially equal, is at least 5%, 10%, or more less than the oxygen redox capacity as measured by the area under the dQ / dV curve when compared to a disordered rock salt type cathode not made by this method.

[0021] Surprisingly, it has been found that when making an improved disordered rock salt type containing Mn, it can be made by mixing a lithium compound with a metal precursor compound containing Mn (where Mn has an oxidation state of 2) to form a mixture. For example, the mixture contains MnO or a mixed metal oxide in which at least a portion of the Mn is in the oxidation state 2. Examples include MnO, MnCO 3 , Mn 3 O 4 , Mn(NO 3 ) 2 . Desirably, at least 25 wt%, 50 wt%, 75 wt%, 90 wt% of essentially all of the metal precursor compounds containing Mn present in the mixture have Mn in the oxidation state 2. The Mn precursor present in the mixture may simply be MnO.

[0022] The mixture can be formed by any suitable method, such as the methods known in the art, such as those disclosed in U.S. Patent Publication No. 2022 / 0059816, which is exemplary and incorporated herein by reference. To form the mixture, the metal precursor compound and the lithium compound are mixed based on the desired composition of the disordered rock salt type. One or more of the precursors can be metal compounds containing oxygen, fluorine, and one or more of P, S, and N, such as oxides, hydroxides, oxynitrides, nitrides, nitrates, sulfides, sulfates, phosphates, phosphites, fluorides, and combinations thereof. As an example of a precursor, as long as there is a sufficient amount of the Mn precursor having an oxidation state of 2 as described above, Mn 2 O 3 , LiOH, Nb 2 O 5 , LiF, NbF 5 and the like can be included. The mixture can include one or more compounds that can introduce substitutions of O or F, such as those having S, P, N, or combinations thereof.

[0023] Mn having an oxidation state of 2 is Mn having an oxidation state greater than 2 (e.g., Mn 2 O 3) can be formed by mixing it with other metal precursor compounds that can have the same stoichiometric ratio desired in an irregular rock salt type or a part of an irregular rock salt type. A mixture of an Mn compound having an oxidation state greater than 2 and at least one other metal precursor compound can be made by any suitable method as described herein when making the desired irregular rock salt type. The intermediate mixture is then heated to a temperature to achieve at least a partially mixed metal compound (e.g., 50%, 75%, 90% - all of Mn having an oxidation state of 2) in the absence of lithium and in a certain atmosphere (e.g., an inert atmosphere or an oxygen-containing atmosphere) to form an intermediate precursor. Optionally, the intermediate precursor can be heated in an oxygen-containing atmosphere free of lithium to form a mixed metal oxide intermediate containing Mn having an oxidation state of 2. Any useful temperature and time can be used to form the intermediate precursor. Generally, for the formation of the intermediate precursor, the temperature, atmosphere, and holding time as described for forming the irregular rock salt type can be employed, but desirably, it is oxygen-free. If useful, higher temperatures may be used, but this may require additional or multiple milling to achieve the desired particle size when mixing with the lithium compound.

[0024] Desirably, the precursors may be mixed in a liquid such as water or an organic solvent in a desired amount to achieve the desired non-stoichiometric rock salt type to produce a suspension (one or more of the precursors may be dissolved and precipitated upon removal of the solvent). Milling can be carried out by any method useful for achieving the desired particle size, examples of which include a micro media mill, a planetary mill, or other grinding methods (e.g., a stirred mill, an ultrasonic induction mill, or a vibration mill). The particles can have an average particle size of up to 2 micrometers, 1 micrometer, 400 nanometers (nm), 200 nm, or 100 nm to 5 or 10 nm. An example of a suitable micro bead mill is the Buhler PML2 mill (Buhler Group). Suitable milling may be carried out with a commercially available stirred mill such as those available from Buhler Group (Germany) and Netzsch GmbH (Germany), a sonic mill available from Resodyn Corporation. (Butte, Montana), and a planetary mill available from Glen Mills Inc., (Clifton, New Jersey) and Retsch GmbH (Germany). The size may be determined by any suitable method, such as a method known in the art including, for example, a method by micrograph or a method by laser light scattering.

[0025] The milling media can be anything useful for milling the ceramic particles without causing the mixture to revert to its original composition or intended contribution. The milling media can be of any useful shape, such as spherical, elliptical, or cylindrical. Desirably, the milling media is spherical. The milling media can be ceramic, metal, or a ceramic-metal composite (e.g., WC / Co). The milling media can be anything useful for milling the precursor without causing detrimental mixing. Examples of milling media include cubic stabilized zirconia (e.g., stabilized with one or more of Mg, Ca, Y, Ce, Al, and Hf), zircon, silicon carbide, WC / Co, and mixed carbides such as those described in U.S. Patent No. 5,563,107 and International Publication No. 2004 / 110699 (incorporated herein by reference), including those containing zirconium. Suitable cubic stabilized zirconia milling media can be obtained from Chemco Advanced Material (Suzhou) Co., Ltd., (Suzhou, China). Similarly, self-milling, such as the use of metal oxides desired in the composition, can be used as the milling media.

[0026] The suspension of precursor particles can then be dried by any suitable method, such as spray drying. Other drying methods, including evaporation, heating, application of vacuum, critical fluid drying, or freeze drying, can be employed. Spray drying can be carried out using any known commercially available spray dryer, such as a mini spray dryer, e.g., the Buchi B-290 model.

[0027] Next, the dried mixture of precursor particles can be heated to the annealing temperature. At the annealing temperature, the precursors react to form an irregular rock salt type. Desirably, the temperature and time are such that the resulting irregular rock salt type does not melt into a monolithic melt, but retains the form of the dried mixture, such as the spray-dried aggregates of the precursor particles. The annealing temperature can be 500 °C, from 750 °C to 900 °C, 1000 °C, or 1200 °C. The annealing temperature can be held for any useful time, such as 10 minutes, 1 hour, 2 hours, 3 hours, or from 5 hours to 12 hours, or 24 hours. Surprisingly, even with a longer annealing time, the crystal growth of the mixtures of the present invention is substantially suppressed compared to mixtures having only Mn precursors in the oxidation state 3. That is, it has been found that the particles maintain a small size and improved performance such as improved cycle life and conductivity due to that small size. Further, since the particles can maintain a smaller size at a certain temperature, the stoichiometry can be more precisely adjusted using different oxygen-containing atmospheres (i.e., the partial pressure of oxygen over a longer time, which can vary during annealing to form the irregular rock salt type). For example, annealing is carried out at a high temperature such as 750 °C to 1200 °C for the time to form the irregular rock salt type under a low-oxygen or oxygen-free (inert gas such as a noble gas or nitrogen) atmosphere, but then the temperature is lowered and annealing is carried out at a lower temperature (e.g., less than 750 °C to about 400 °C or 500 °C) under an oxygen-containing atmosphere such as air, dry air, or oxygen in nitrogen or an inert gas at any desired partial pressure. In other words, two or more annealing temperatures may be employed to form the irregular rock salt type. The holding time for each annealing temperature can be any of the above.

[0028] Annealing may be carried out in any suitable atmosphere, which may be static, flowing, or a combination thereof, and may be varied according to the holding temperature employed in the method. The atmosphere may be a noble gas, nitrogen, air, or dry air, and any combination for achieving the desired partial pressures of one or more gases. The annealing conditions may be selected based on the composition of the rock-salt-type precursor.

[0029] The rock-salt-type formed can be mixed in any way involving milling other components useful for making electrodes, as described herein in a suitable manner. For example, carbon may be added. Carbon can be added via a suspension and spray-dried to form spray-dried particles. Carbon can include acetylene black, carbon black, carbon fiber, graphite, carbon nanotubes, KJ600, etc. Carbon may be milled in a ratio where the rock-salt-type powder predominates and the carbon precursor is in a minor amount. For example, the rock-salt-type and carbon may each be present in amounts such that the weight ratio of the rock-salt-type to carbon can be from 100 / 1, 50 / 1, 30 / 1, 20 / 1, or 10 / 1 to 5 / 1, 1.5 / 1, or 1 / 1.

[0030] The rock-salt-type can be used to form a cathode by any suitable method such as those known in the art. For example, the rock-salt-type powder may be mixed with a binder such as a polymer useful for making a cathode (e.g., a polyfluoropolymer such as polyvinylidene fluoride) and one or more solvents to form a slurry. Non-limiting examples of one or more solvents can be aprotic polar solvents such as N-methyl-2-pyrrolidinone (NMP). Next, the slurry may be deposited on a metal current collector (e.g., stainless steel, aluminum, or any suitable conductive metal sheet), and the solvent removed to form the cathode.

[0031] Desirably, the irregular rock salt type cathode has an average secondary particle size of at least 1 to 20 micrometers. Each of the secondary particles is an aggregate of primary particles. The primary particles of the DRS desirably have the aforementioned average particle size and may contain other particles that can be useful, such as increasing conductivity (e.g., carbon or other inorganic high ion conductivity particles).

[0032] The irregular rock salt type cathode may be used in a rechargeable lithium ion battery cell. The battery cell includes a cathode, an anode, a separator, and an electrolyte. The battery or battery cell may be formed in any suitable atmosphere, such as those common in the art. For example, a high purity argon atmosphere may be used to limit unwanted mixing from chemical species present in the atmosphere.

Examples

[0033] Example 1: The irregular rock salt type material is synthesized in multiple steps. Typically, the stoichiometric amounts of precursors of all oxides (Mn 2 O 3 , TiO 2 , and Nb 2 O 5 ) that do not contain lithium precursors are mixed and milled with ceramic beads in deionized water using a Micromedia Buhler mill to form a ~10% solid suspension and then spray dried. The dried mixture of oxides is annealed at 1000 °C for 12 hours in an inert atmosphere to form an intermediate precursor (trigonal, R-3). Here, Mn is considered to be essentially in the Mn+2 oxidation state based on the X-ray diffraction pattern shown in Figure 1 with reference to melanostibite. The annealed powder is mixed with lithium precursors (Li 2 CO 3 and LiF), and ball milled for 3 hours using a planetary ball mill with a zirconia medium to prepare a mixture of lithium compounds and intermediate metal oxides. This mixture is then annealed at 900 °C under an argon flow for 12 hours to obtain the irregular rock salt type phase shown in Figure 2.

[0034] Example 2 Precursors of the same stoichiometric amounts (MnO, Li 2 CO 3 , LiF, Nb 2 O 5 , and other dopants in oxide or fluoride form) were mixed in deionized water to form a suspension, which was ball-milled in a planetary ball mill in the same manner as in Example 1 to prepare a homogeneous mixture of all the precursors containing lithium compounds. The mixture was dried in air at 100 °C for 12 hours and then annealed under an argon flow at 900 °C for 12 hours to obtain an irregular rock salt type.

[0035] Comparative Example 1: The same stoichiometric amounts of metal and lithium precursors were formed into a mixture in the same manner as in Example 2, but MnO was replaced with Mn 2 O 3 . The particles remaining in the formed irregular rock salt type are shown in Figure 3. It is clear from Figures 2 and 3 that the particle size in Example 1 is significantly smaller compared to Comparative Example 1. Figure 4 shows the X-ray diffraction patterns of the irregular rock salt types of Example 1 and Comparative Example 1. It is clear from the X-ray diffraction patterns that there is a difference in the lattice parameter, as indicated by the shift in the peak position (see the peaks around 43° and 63° 2θ). X-ray diffraction was measured using a Rigaku Miniflex benchtop X-Ray diffractometer.

[0036] The irregular rock salt types of Example 1 and the comparative example were milled with the same carbon nanotubes in a planetary ball mill using a zirconia medium at a ratio of 93:7 (powder to carbon ratio) to fabricate the cathode. The battery cell for testing the electrochemical behavior was a glove box (M-Braun, O 2and a humidity content <0.1 ppm). The cathode is prepared by mixing irregular rock salt-type powder with poly(vinylidene fluoride) (Sigma Aldrich) and 1-methyl-2-pyrrolidinone (Sigma Aldrich) and conductive carbon to a ratio of active material:carbon:PVDF = 90:7:3. The resulting slurry is deposited on a stainless steel current collector and dried to form a composite cathode film (about 2 mg / cm 2 ). For the anode, a thin Li foil is cut to the required size. Each cell contained a composite cathode film, a polypropylene separator, and a lithium foil anode. Lithium hexafluorophosphate (LiFP 6 ) is contained in an electrolyte mixture of an additive and ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (1.0 M LiPF 6 ) in EC / EMC (1:2 v / v) is used. The cells are sealed and cycled at 30 °C between 1.5 and 4.6 V at a C / 20 formation rate and a C / 3 cycle rate (where 1 C = 300 mAh / g).

[0037] The disordered rock salt type of Example 1 shows a higher capacity from transition metal redox and a lower capacity from oxygen anion redox. This is shown below by the shift capacity where a high voltage plateau of 150 - 200 mAh / g is observed. The capacity due to the transition metal is a gradient curve of 0 to about 150 mAh / g. Thereafter, the capacity obtained at the high voltage plateau is due to oxygen anions. The disordered rock salt type of Comparative Example 1 shows a capacity of about 130 mAh / g from metal redox and about 186 mAh / g from oxygen redox, while the disordered rock salt type of Example 1 shows a metal redox capacity of about 170 mAh / g and an oxygen redox capacity of about 120 mAh / g during the initial charge. Compared with the disordered rock salt type of Example 1, the larger charge capacity from anion redox for the disordered rock salt type of Comparative Example 1 is clearly shown by the larger area under the peak near 4.5 V (see Fig. 5 showing the initial charge and discharge of cells employing the disordered rock salt types of Example 1 and Comparative Example 1). The initial charge and discharge are at a C rate of C / 20. The cycle life is determined by repeating the cycles at 30 °C with C / 3 charge and discharge. The results are shown in Fig. 6. Here, it is clear that the battery cell using the disordered rock salt type of Example 1 shows an improved cycle life compared to the battery cell using the disordered rock salt type of Comparative Example 1.

Claims

1. A method comprising: mixing a lithium compound with a metal precursor compound containing Mn in oxidation state 2 to form a mixture; and heating the mixture to a certain temperature to form an irregular rock salt type.

2. The method according to claim 1, wherein the metal precursor compound contains MnO.

3. The metal precursor compound is a mixed metal oxide intermediate containing Mn having the oxidation state 2, and the mixed metal oxide is A Mn compound having an oxidation state greater than 2 is mixed with at least one other metal precursor compound up to a certain temperature to form an intermediate precursor mixture. The method according to claim 1, comprising: heating the intermediate precursor mixture to an intermediate temperature in an intermediate atmosphere in the absence of lithium to form the mixed metal oxide intermediate containing Mn having oxidation state 2.

4. The Mn compound having an oxidation state greater than 2 is Mn ２ O ３ The method according to claim 3.

5. The method according to claim 3, wherein the intermediate atmosphere is air.

6. The method according to claim 1, wherein the heating is carried out in an atmosphere that is essentially devoid of oxygen.

7. The method according to claim 1, wherein the mixing of the lithium compound and the metal precursor compound includes grinding the lithium compound and the metal precursor compound together.

8. The aforementioned irregular rock salt type has formula (i), Li ｘ N ｙ M ｚ O ２－ａ F ａ (i) Here, 1.0 < x < 1.65, 0 ≤ y < 0.55, 0.1 < z < 1, 0 ≤ a < 0.5, N is one of Ti, Ta, Zr, W, Nb, or Mo, and M is one or more of Mn and Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Al, Zr, Y, Mo, Ru, Rh, Sn, Bi, or Sb. The method according to any one of claims 1 to 7.

9. An irregular rock salt type having a metal redox capacity and an oxygen redox capacity, wherein the metal redox capacity is greater than the oxygen redox capacity, the irregular rock salt type contains Mn, and at least 50% by mass of the Mn exists in a valence state of 2+.

10. The irregular rock salt type according to claim 9, wherein the metal redox capacity is at least 10% greater than the oxygen redox capacity.

11. The aforementioned irregular rock salt type has formula (i), Li ｘ N ｙ M ｚ O ２－ａ F ａ (i) Here, 1.0 < x < 1.65, 0 ≤ y < 0.55, 0.1 < z < 1, 0 ≤ a < 0.5, N includes one or more of Ti, Ta, Zr, W, Nb, or Mo, and M includes Mn and one or more of Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Al, Zr, Y, Mo, Ru, Rh, Sn, Bi, or Sb. Irregular rock salt type according to claim 9 or 10.

12. The irregular rock salt type according to claim 11, wherein "a" is zero.

13. A composition comprising an irregular rock salt type containing Li, Mn, and O, wherein at least 50% by mass of the present Mn is in a valence state of 2+.

14. The composition according to claim 13, wherein at least 75% by mass of the Mn present is in the valence state 2+.

15. The aforementioned irregular rock salt type has formula (i), Li ｘ N ｙ M ｚ O ２－ａ F ａ (i) Here, 1.0 < x < 1.65, 0 ≤ y < 0.55, 0.1 < z < 1, 0 ≤ a < 0.5, N includes one or more of Ti, Ta, Zr, W, Nb, or Mo, and M includes Mn and one or more of Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Al, Zr, Y, Mo, Ru, Rh, Sn, Bi, or Sb. The composition according to claim 13 or 14.

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