Positive electrode active material for secondary battery, and secondary battery

Abstract

A positive electrode active material for a secondary battery, the positive electrode active material containing a lithium metal composite oxide having a crystal structure attributable to space group Fm-3m, the lithium metal composite oxide containing Li, a first positive element M1, and a second positive element M2, 50 at% or more of the first positive element M1 being Mn, the content of the second positive element in the lithium metal composite oxide being 10 ppm to 1000 ppm by mass, and the content of the lithium metal composite oxide being 10 ppm to 1000 ppm by mass. The number of atoms mLi of Li contained in the lithium metal composite oxide and the number of atoms mM1 of the first positive element satisfy 1.2 < = mLi / mM1 < = 2.0, and the crystallite size of the lithium metal composite oxide is within the range of 1-1000 nm.

Description

[0001] Cross-referencing of related applications

[0002] This disclosure claims priority to Japanese Patent Application No. 2023-170612, filed on September 29, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to positive electrode active materials for secondary batteries and secondary batteries. Background Technology

[0004] Secondary batteries, especially lithium-ion secondary batteries, are expected to serve as power sources for small-scale civilian applications, energy storage devices, and electric vehicles due to their high output and high energy density. As the positive electrode active material in lithium-ion secondary batteries, a composite oxide of lithium and a transition metal (such as cobalt) is used. High capacity can be achieved by replacing a portion of the cobalt with nickel.

[0005] On the other hand, in recent years, in response to the demand for high energy density, Li with rock salt structure has been used... 1+x Mn 1-x O2-based Li-excess lithium metal composite oxides have attracted attention.

[0006] Patent document 1 discloses a positive electrode active material comprising a lithium transition metal composite oxide, wherein the lithium transition metal composite oxide has a crystal structure belonging to space group Fm-3m and is composed of the formula Li 1+x Nb y Me z A p O2 (Me is a transition metal containing Fe and / or Mn, 0 < x < 1, 0 < y < 0.5, 0.25 ≤ z < 1, A is an element other than Nb and Me, 0 ≤ p ≤ 0.2, but Li 1+p Fe 1-q Nb q (Except for cases where O2 is present and 0.15 < p ≤ 0.3, 0 < q ≤ 0.3).

[0007] Prior art literature

[0008] Patent Document 1: Japanese Patent No. 6197029 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] In Patent Document 1, high capacity can be achieved by controlling the composition (i.e., adding Nb). However, the capacity improvement is insufficient and there is room for improvement.

[0011] Methods for solving problems

[0012] In view of the above, one aspect of this disclosure relates to a positive electrode active material for secondary batteries, comprising a lithium metal composite oxide having a crystal structure belonging to space group Fm-3m, wherein the lithium metal composite oxide comprises Li, a first positive element M1 different from Li, and a second positive element M2 different from Li and the first positive element M1, wherein the first positive element M1 is at least 50 atomic percent Mn, and the content of the second positive element M2 in the lithium metal composite oxide is 10 ppm to 100 ppm by mass. 0 ppm, the number of Li atoms mLi contained in the lithium metal composite oxide and the number of atoms mM1 of the first positive element contained in the lithium metal composite oxide satisfy 1.2≤mLi / mM1≤2.0, the crystallite size of the lithium metal composite oxide is in the range of 1 nm to 1000 nm, or, in the X-ray diffraction (XRD) pattern of the lithium metal composite oxide obtained by CuKα rays, the half-width of the diffraction peaks belonging to the (200) plane is in the range of 0.1° to 2.5° based on 2θ.

[0013] Another aspect of this disclosure relates to a secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator between the positive electrode and the negative electrode, wherein the positive electrode comprises the aforementioned positive electrode active material for a secondary battery.

[0014] The effects of the invention

[0015] According to this disclosure, high-energy-density secondary batteries can be realized.

[0016] The novel features of the invention are set forth in the appended claims. Regarding both structure and content, the invention can be better understood in conjunction with other objects and features of the invention, through the following detailed description with reference to the accompanying drawings. Attached Figure Description

[0017] Figure 1 This is a schematic perspective view of a partial cut-off of a secondary battery according to one embodiment of this disclosure.

[0018] Figure 2A This is a graph showing the relationship between mLi / mM and initial discharge capacity corresponding to Table 1.

[0019] Figure 2B This is a graph showing the relationship between mLi / mM and initial discharge capacity corresponding to Table 2.

[0020] Figure 2C This is a graph showing the relationship between mLi / mM and initial discharge capacity corresponding to Table 3.

[0021] Figure 2DThis is a graph showing the relationship between mLi / mM and initial discharge capacity corresponding to Table 4.

[0022] Figure 2E This is a graph showing the relationship between mLi / mM and initial discharge capacity corresponding to Table 5.

[0023] Figure 2F This is a graph showing the relationship between mLi / mM and initial discharge capacity corresponding to Table 6. Detailed Implementation

[0024] The following description illustrates embodiments of the present disclosure using examples, but the disclosure is not limited to these examples. In the following description, specific numerical values ​​or materials are sometimes illustrated, but other numerical values ​​or materials can be applied as long as the effects of the present disclosure are achieved. In this specification, references such as "numerical value A to numerical value B" include both numerical value A and numerical value B, and can be replaced with "numerical value A or higher and numerical value B or lower." In the following description, when lower and upper limits of numerical values ​​related to specific physical properties or conditions are illustrated, any combination of any illustrated lower limit and any illustrated upper limit can be used, as long as the lower limit is not higher than the upper limit. When multiple materials are illustrated, one can be selected for use alone, or two or more can be combined.

[0025] Furthermore, this disclosure includes a combination of matters described in two or more claims selected from the plurality of claims in the appended claims. That is, matters described in two or more claims selected from the plurality of claims in the appended claims can be combined, provided that no technical contradiction arises.

[0026] In the following explanation, the term “containing ~ (or including ~)” includes expressions such as “containing ~ (or including ~)”, “essentially composed of ~”, and “composed of ~”.

[0027] Secondary batteries include at least non-aqueous electrolyte secondary batteries such as lithium-ion batteries and lithium metal secondary batteries, as well as all-solid-state batteries that use solid electrolytes.

[0028] The embodiments of this disclosure relate to a positive electrode active material for secondary batteries, comprising a lithium metal composite oxide (hereinafter also referred to as "lithium metal composite oxide (Fm)") having a crystal structure belonging to space group Fm-3m. The lithium metal composite oxide (Fm) has, for example, a crystal structure based on a rock salt structure belonging to space group Fm-3m, such as a crystal structure similar to that of rock salt represented by NaCl. Oxygen atoms are arranged at the anion sites of such a crystal structure, and Li atoms and metal atoms other than Li can be irregularly arranged at the cation sites.

[0029] Lithium metal composite oxides (Fm) can be rock-salt structured oxides based on Li and Mn composite oxides. 1+x Mn 1-x O2-based lithium metal composite oxides with Li excess. Furthermore, the Li excess state refers to a state in which the number of Li atoms in the lithium metal composite oxide (Fm) is greater than the total number of atoms of the other metal elements.

[0030] The crystal structure of lithium metal composite oxide (Fm) can be determined, for example, from the X-ray diffraction pattern measured using a powder X-ray diffraction apparatus (e.g., an X-ray diffraction apparatus manufactured by Rigaku Corporation).

[0031] Lithium metal oxide (Fm) contains Li, a first positron element M1 (different from Li), and a second positron element M2 (different from Li and the first positron element). The total amount of all metal elements contained in lithium metal oxide (Fm) corresponds to the sum of the total amount of Li, the total amount of the first positron element M1, and the total amount of the second positron element M2 contained in lithium metal oxide (Fm). The first positron element M1 contains at least Mn. Mn is the main component of the first positron element M1, and more than 50 atomic percent of the first positron element M1 is Mn.

[0032] Furthermore, the ratio of the number of Li atoms mLi contained in the lithium metal composite oxide (Fm) to the number of Mn atoms mMn contained in the lithium metal composite oxide (Fm) (mLi / mMn) preferably satisfies 1.7≤mLi / mM≤2.5, and more preferably satisfies 1.8≤mLi / mM≤2.3.

[0033] The first positive element M1 may contain element Mm in addition to Mn. Element Mm is a positive element other than Li and Mn. Furthermore, a positive element (positively charged element, electropositive element) is an element other than hydrogen that can form cations, typically a metallic element (including so-called half-metal elements). The first positive element M1 is the main element constituting the crystal structure. Therefore, the elements contained in the first positive element M1 need to be included in the lithium metal composite oxide (Fm) at a considerably high concentration. When the lithium metal composite oxide (Fm) contains multiple elements as element Mm, the concentration of each element in element Mm is preferably, for example, 6 atomic% or more of the first positive element M1, and may also be 10 atoms.

[0034] By controlling the ratio (mLi / mM1) of the number of Li atoms (mLi) in the lithium metal composite oxide (Fm) to the number of atoms (mM1) of the first positive element in the lithium metal composite oxide, the capacity of the lithium metal composite oxide (Fm) can be increased. Specifically, a high capacity can be obtained when 1.2 ≤ mLi / mM1 ≤ 2.0 is satisfied. Furthermore, it is preferable that 1.2 ≤ mLi / mM1 ≤ 1.8 is satisfied, more preferably that 1.3 ≤ mLi / mM1 ≤ 1.7 is satisfied, and even more preferably that 1.4 ≤ mLi / mM1 ≤ 1.6 is satisfied.

[0035] The second positron element M2 is a trace component, but not an impurity; it is an effective component for improving the capacity of lithium metal composite oxide (Fm). That is, by controlling the content of the second positron element M2 in the lithium metal composite oxide (Fm), the capacity of the lithium metal composite oxide (Fm) can be further increased. Specifically, the content of the second positron element M2 in the lithium metal composite oxide (Fm), on a mass basis, is 10 ppm to 1000 ppm, preferably 30 ppm to 1000 ppm. The content of the second positron element M2 can be 30 ppm to 750 ppm by mass, or 100 ppm to 500 ppm by mass.

[0036] The second positive element M2 is, for example, at least one selected from Fe, Ca, Cr, Na, Al, Si, Mg, Cu, Zn, Pb, and Sb, and is particularly preferred to be at least one selected from Fe, Ca, Na, and Mg. When the lithium metal composite oxide (Fm) contains two or more second positive elements M2, the total content of all two or more second positive elements M2 should be in the range of 10 ppm to 1000 ppm by mass.

[0037] As a preferred example, the following lithium metal composite oxide (Fm) can be cited.

[0038] (1) The contents of Fe, Ca, Na and Mg are 0~500ppm, 0~500ppm, 0~500ppm and 0~500ppm respectively, and the total of Fe, Ca, Na and Mg is 50ppm~1000ppm of lithium metal composite oxide (Fm).

[0039] (2) The contents of Fe, Ca, Na and Mg are 0~300ppm, 0~300ppm, 0~300ppm and 0~300ppm respectively, and the total of Fe, Ca, Na and Mg is 30ppm~750ppm of lithium metal composite oxide (Fm).

[0040] (3) The contents of Fe, Ca, Na and Mg are 0~200ppm, 0~200ppm, 0~200ppm and 0~200ppm respectively, and the total of Fe, Ca, Na and Mg is 30ppm~500ppm of lithium metal composite oxide (Fm).

[0041] (4) The contents of Fe, Ca, Na and Mg are 0~100ppm, 0~100ppm, 0~100ppm and 0~100ppm respectively, and the total of Fe, Ca, Na and Mg is 30ppm~300ppm of lithium metal composite oxide (Fm).

[0042] The reason for increasing the capacity of lithium metal composite oxide (Fm) by including the second positive element M2 in trace amounts is unclear. One possible reason is that by forming a dielectric layer composed of an oxide of the second positive element M2 on at least a portion of the surface of the lithium metal composite oxide (Fm), the electron orbital energy on the surface of the lithium metal composite oxide (Fm) changes due to the change in electric field distribution, which promotes the tunneling movement of electrons (charge transfer reaction) that accompanies the movement of lithium ions between the electrolyte and the lithium metal composite oxide (Fm).

[0043] One embodiment of this disclosure relates to a lithium metal composite oxide (Fm) that, in order to achieve improved charge / discharge efficiency and high energy density, satisfies 1.2 ≤ mLi / mM ≤ 2.0, and the crystallization of the lithium metal composite oxide (Fm) satisfies at least one of the following conditions (A) and (B). Alternatively, both conditions (A) and (B) may be satisfied.

[0044] When neither condition (A) nor (B) is satisfied, it is difficult to obtain high capacity within the range of 1.2 ≤ mLi / mM ≤ 2.0. That is, the range of mLi / mM ratio that reflects high capacity is different when at least one of conditions (A) and (B) is satisfied, and when neither condition (A) nor (B) is satisfied.

[0045] Condition (A): The crystallite size of lithium metal composite oxide (Fm) is in the range of 1 nm to 1000 nm.

[0046] Condition (B): In the X-ray diffraction (XRD) pattern of lithium metal composite oxide (Fm) obtained using CuKα rays, the half-width of the diffraction peaks belonging to the (200) plane is in the range of 0.1° to 2.5° based on 2θ.

[0047] Under condition (A), the crystallite size of the lithium metal composite oxide (Fm) can be less than 100 nm or less than 80 nm. Furthermore, the crystallite size of the lithium metal composite oxide is preferably 4 nm or more, but can be 5 nm or more or 6 nm or more. The crystallite size of the lithium metal composite oxide (Fm) can be 4 nm to 1000 nm, 5 nm to 1000 nm, 3 nm to 200 nm, 4 nm to 80 nm, or 5 nm to 80 nm. The upper and lower limits of the above crystallite size can be combined arbitrarily.

[0048] The lithium metal composite oxide (Fm) can contain two or more particle groups with different crystallite sizes in the range of 1 nm to 200 nm. That is, the particle size distribution based on the volume of the crystallite size can have multiple peaks. In this case, it is preferable to contain at least a particle group with a crystallite size in the range of 10 nm to 200 nm. Each particle group accounts for more than 10% and more than 30% of the total volume of the lithium metal composite oxide (Fm). In addition, the total volume of such particle groups accounts for more than 50% of the total volume of the lithium metal composite oxide (Fm).

[0049] When a lithium metal composite oxide contains two or more particle groups with different crystallite sizes, it may contain at least a first particle group with a first crystallite size d1 in the range of 10 nm to 200 nm and a second particle group with a second crystallite size d2 that is less than 30% and less than 20% of d1.

[0050] The first particle swarm exhibits a peak in the volumetric particle size distribution based on the crystallite size. The first crystallite size d1 can be below 100 nm or below 50 nm. For example, the first crystallite size d1 can be 20 nm to 100 nm or 20 nm to 50 nm.

[0051] The second particle swarm exhibits a broad peak in the volumetric particle size distribution based on the crystallite size. The second crystallite size d2 can be greater than 3 nm or greater than 4 nm. For example, the second crystallite size d2 can be 3 nm to 10 nm or 4 nm to 7 nm.

[0052] Generally, lithium metal composite oxides with large crystallite size and well-developed crystal structure generally exhibit improved capacity. On the other hand, it is believed that small lithium metal composite oxides (Fm) with crystallite size below 100 nm have significantly increased capacity due to the increased area of ​​grain boundaries, which promotes the release and storage of lithium ions.

[0053] Crystallite sizes below 200 nm were calculated using the Scherrer formula based on the half-width of the diffraction peaks belonging to the (200) plane in the X-ray diffraction (XRD) pattern of lithium metal composite oxide (Fm) obtained using CuKα rays. In the X-ray diffraction (XRD) pattern of lithium metal composite oxide (Fm) obtained using CuKα rays, the half-width of the diffraction peaks belonging to the (200) plane, in 2θ reference, can be in the range of, for example, 0.1° to 1.8°. The half-width of sharp peaks can be in the range of 0.2° to 0.5°. The half-width of broad peaks can be in the range of 2.0° to 2.2°. The crystallite size of larger particle groups cannot be calculated using the X-ray diffraction (XRD) pattern of CuKα rays, but can be actually measured in scanning electron microscopy (SEM) observation of particles with characteristic shapes of single-crystal particles (the edges of straight lines along the crystal growth plane, and the shape of edges at certain angles). The cross-section of lithium metal composite oxide (Fm) particles can be observed using a scanning electron microscope (SEM). The maximum diameter of more than 30 microcrystals with a maximum diameter of more than 100 nm can be measured using vernier calipers and averaged to calculate the result.

[0054] The following shows an example of preferred conditions for XRD determination.

[0055] Measuring radius: 150mm

[0056] Diverging slit (DS): 1.25°

[0057] Under the condition (B) that the particle size distribution based on the volume of the crystallite size has one main peak, in the X-ray diffraction (XRD) pattern of lithium metal composite oxide (Fm) obtained using CuKα rays, the half-width at half-maximum (WWHM) of the diffraction peak belonging to the (200) plane, based on 2θ, can be less than 1.0°, less than 0.8°, or less than 0.5°. The WWHM of the diffraction peak, based on 2θ, can be greater than 0.2° or greater than 0.3°. The WWHM of the diffraction peak belonging to the (200) plane, based on 2θ, can be 0.2°~1.0°, 0.3°~0.8°, or 0.3°~0.5°. The upper and lower limits of the above WWHM can be arbitrarily combined.

[0058] Lithium metal composite oxides (Fm) satisfying at least one of conditions (A) and (B) can be synthesized by calcining a mixture of raw materials at a temperature of 700°C to 1300°C (calcination method), and then pulverizing the calcined product. After sufficient crystallization through calcination, the crystallite size can be controlled within the range of 1 nm to 1000 nm through appropriate pulverization. Lithium metal composite oxides (Fm) satisfying at least one of conditions (A) and (B) can also be described, in a sense, as lithium metal composite oxides (Fm) synthesized by the calcination method.

[0059] Furthermore, the Li-excess crystal structure, which is similar to the rock salt structure belonging to the space group Fm-3m, is believed to have a greater capacity improvement effect by reducing the crystallite size to below 1000 nm compared to the crystal structure that clearly belongs to the space group Fm-3m.

[0060] When the first positive element M1 contains Mm in addition to Mn, the ratio of the number of Mn atoms mMn contained in the lithium metal composite oxide (Fm) to the number of Mm atoms mMm contained in the lithium metal composite oxide (Fm) (mMn / mMm) is, for example, 1 or more and 15 or less, preferably 1 or more and 12 or less, may be greater than 1 and less than 12, or may be 2 or more and less than 12.

[0061] Element Mm may, for example, contain at least one selected from Ti, Ge, Ga, Ni, Co, Sn, Nb, Mo, Bi, V, Y, Zr, K, Pt, Au, Ag, Ru, Ta, W, La, Ce, Pr, Gd, Sm, Eu, Yb, Dy, and Er. Preferably, element Mm contains at least one selected from Ti, Co, Nb, and Ni. 50 atomic percent, 80 percent, or 100 percent of element Mm may be selected from at least one of Ti, Co, Nb, and Ni. However, in lithium metal composite oxide (Fm), element Mm preferably accounts for at least 6 atomic percent of the first positive element M1. For example, in the case where Ti is included in the lithium metal composite oxide (Fm), the content of Ti may be at least 6 atomic percent of element Mm.

[0062] In element Mm, Ti is particularly preferred, and can be set to be 50 atomic percent or more, and further 80 atomic percent or more, or 100% Ti. Ti has the function of stabilizing crystal structures based on rock salt structures belonging to space group Fm-3m, and increasing the capacity of lithium metal composite oxides (Fm).

[0063] By enabling the coexistence of Mn and Ti, charge-discharge efficiency can be significantly improved, and high energy density can be achieved. The rationale is not yet clear, but one possible reason is that in lithium metal composite oxides, Ti can utilize Ti with empty d-orbitals.4+ It exists in the form of [a specific structure]. In this case, it is believed that rock salt structures with high symmetry are prone to stability, and that the rock salt structure can remain stable even after repeated charging and discharging.

[0064] The ratio (mMn / mTi) of the number of Mn atoms (mMn) in the lithium metal composite oxide (Fm) to the number of Ti atoms (mTi) in the lithium metal composite oxide (Fm) can be 2 or more, 3 or more, 4 or more, and preferably 5 or more. Furthermore, mMn / mTi can be 15 or less, 10 or less, and preferably 7 or less. The range of mMn / mTi can be, for example, 2 to 30, 2 to 15, or 2.5 to 7.

[0065] Lithium metal composite oxides (Fm) can contain fluorine (F). In the aforementioned crystal structure, fluorine can substitute oxygen atoms at the anion sites. This stabilizes the excess Li state, resulting in higher capacity. Furthermore, the average discharge potential increases through the substitution of fluorine atoms.

[0066] In lithium metal composite oxides (Fm), the arrangement of Li cation sites is irregular, and the Li binding states are diverse, resulting in a wide voltage distribution associated with Li release. Therefore, it is difficult to utilize the lower potential side of the voltage distribution as capacity. However, by introducing fluorine atoms, the voltage distribution associated with Li release shifts towards the higher potential side, making it easier to utilize the lower potential side as capacity. This further increases the available capacity.

[0067] Lithium metal composite oxides (Fm) can, for example, be composed of Li a Mn b M1 c O d F e This is indicated. However, the labeling of the second positive element M2, which is a trace component, is omitted in the above composition formula. In this case, it is preferable to satisfy 1≤a≤1.4, 0.5≤b≤0.9, 0≤c≤0.4, 1.33≤d≤2, 0≤e≤0.67, and 1.7≤d+e≤2.2. e+f is usually less than 2, and can be less than 1.94, less than 1.9, or less than 1.8. It is acceptable to satisfy 0<c / b≤1.

[0068] As shown in the above composition, some oxygen atoms at the anion sites can be replaced by fluorine atoms. This stabilizes the Li-excess (a>1) state, resulting in high capacity. Furthermore, as mentioned above, the average discharge potential increases, further enhancing the usable capacity.

[0069] The lattice constant α of lithium metal composite oxides (Fm) preferably has a value of 4.09 Å or higher and 4.16 Å or lower. In this case, a significant increase in capacity can be achieved. The detailed reason is not yet clear, but it is speculated that when the lattice constant α is within the above range, the crystal structure is more easily stabilized, which facilitates the tunneling of electrons (charge transfer reaction) accompanying the movement of lithium ions between the electrolyte and the active material. The aforementioned lattice constant α can be 4.10 Å or higher and 4.15 Å or lower.

[0070] The lattice constant 'a', representing the length of the lattice along the 'a' axis of the lithium metal composite oxide, can be determined using Rigaku Corporation's benchtop X-ray diffractometer "MiniFlex" and the comprehensive powder X-ray analysis software "PDXL". Furthermore, in X-ray diffraction measurements using the aforementioned X-ray diffractometer, the X-ray source is CuKα rays, and the measurement range for 2θ is 10° to 100°.

[0071] Furthermore, the lattice constant *a* obtained using the integrated powder X-ray analysis software "PDXL" is followed by a value in parentheses, which represents the error to the third decimal place. For example, in the case of 4.115(2) Å, it means that the lattice constant *a* is 4.113 Å or more and 4.117 Å or less. In this disclosure, a lattice constant *a* of 4.09 Å or more and 4.16 Å or less means that, within the aforementioned error range, the lattice constant *a* is included in the range of 4.09 Å or more and 4.16 Å or less.

[0072] Lithium metal composite oxide (Fm) is preferably obtained by sintering a mixture of raw materials containing elements constituting lithium metal composite oxide (Fm). Sintering the raw material mixture allows for the efficient synthesis of lithium metal composite oxide (Fm) even in mass production. Sintering promotes the growth of crystals similar to rock salt structures belonging to space group Fm-3m, resulting in lithium metal composite oxides with large crystallite sizes. The lithium metal composite oxide (Fm) synthesized by sintering has high particle hardness and is mostly blocky; by performing a pulverization process, the crystallite size can be controlled within the range of 1 nm to 1000 nm.

[0073] When a pulverization process is performed, lithium metal composite oxide (Fm) can contain two or more particle groups with different crystallite sizes in the range of 1 nm to 200 nm. Furthermore, lithium metal composite oxide (Fm) can contain at least a particle group with crystallite sizes in the range of 10 nm to 200 nm. That is, the volumetric particle size distribution has both sharp and broad peaks, with the sharp peaks belonging to the first particle group with a first crystallite size d1 in the range of 10 nm to 200 nm, and the broad peaks belonging to the second particle group with a smaller second crystallite size d2. Lithium metal composite oxide (Fm) has high hardness, making it difficult to pulverize to achieve uniform crystallite sizes; therefore, it is considered easy to form such a particle size distribution. Lithium metal composite oxide (Fm) with sharp and broad peaks in the volumetric particle size distribution can also be described from one perspective as lithium metal composite oxide (Fm) synthesized by a sintering method.

[0074] In addition, several lithium metal composite oxides (Fm) have been reported to be synthesized in the laboratory by applying high shear forces to the raw material mixture using a stirring device such as a ball mill without calcining the mixture. However, the lithium metal composite oxides (Fm) synthesized without calcining the raw material mixture have small crystallite sizes, making it difficult to achieve crystallite sizes of 3 nm or larger, or 5 nm or larger. Furthermore, it is impossible to achieve a volumetric particle size distribution with sharp and broad peaks.

[0075] <Method for manufacturing lithium metal composite oxide (Fm)>

[0076] As raw materials for the elements constituting lithium metal composite oxides, oxides of Mn, oxides of element Mm, lithium oxides, lithium salts, lithium manganese oxide (LiMnO2), lithium titanate, Li2O, Co2O3, TiO2, Mn2O3, etc., can be used. Lithium fluoride (LiF) can be used as a fluorine source. The types and mixing ratios of raw materials can be appropriately selected according to the desired composition described above.

[0077] The firing atmosphere of the raw material mixture can vary depending on the desired composition of the lithium metal composite oxide (Fm) or the type of raw material, and can be, for example, an inert atmosphere (e.g., in an Ar atmosphere) or an oxidizing atmosphere (e.g., in air or in the presence of oxygen). It is preferable to allow the atmosphere gas to circulate. The raw material mixture can be fired while being stirred. For example, a firing furnace equipped with a fluidized bed can be used to fire the raw material mixture while stirring.

[0078] The firing temperature of the raw material mixture can vary depending on the composition of the desired lithium metal composite oxide (Fm) or the type of raw material, for example, it can be above 700°C, preferably above 900°C and below 1300°C.

[0079] If the lithium metal composite oxide (Fm) obtained by sintering is in the form of bulk particles, the bulk particles can be crushed. In this case, a stirring device capable of applying a large shear force to the particles, such as a ball mill or bead mill, can be used.

[0080] Next, a detailed description of the secondary battery according to the embodiments of this disclosure will be provided. The secondary battery, for example, includes a positive electrode, a negative electrode, an electrolyte, and a separator.

[0081] [positive electrode]

[0082] The positive electrode comprises a positive current collector and a positive electrode additive layer formed on the surface of the positive current collector and containing positive active material. The above-described positive electrode for a secondary battery is used as the positive electrode. The positive electrode additive layer can be formed, for example, by dispersing a positive electrode additive containing positive active material, a binder, etc., in a dispersion medium, coating the resulting positive electrode slurry onto the surface of the positive current collector, and then drying it. The dried coating can be calendered as needed. The positive electrode additive layer can be formed on one surface or on both surfaces of the positive current collector.

[0083] The positive electrode mixture layer contains a positive electrode active material as an essential component, and can include binders, tackifiers, conductive agents, positive electrode additives, etc., as optional components. Commonly known materials can be used as binders, tackifiers, and conductive agents.

[0084] As the positive electrode active material, it comprises the aforementioned lithium metal composite oxide (Fm) having a crystal structure similar to that of rock salt belonging to space group Fm-3m. The lithium metal composite oxide (Fm) is, for example, a secondary particle formed by the aggregation of multiple primary particles. The particle size of the primary particles is generally 0.01 μm to 1 μm. The average particle size of the secondary particles of the lithium metal composite oxide (Fm) is, for example, 10 μm or less, or 1 μm or less, preferably 0.05 μm to 10 μm or 0.05 μm to 1 μm. Here, the average particle size of the lithium metal composite oxide (Fm) refers to the median particle size (D50) where the cumulative frequency in the volumetric particle size distribution reaches 50%, measured using a laser diffraction particle size distribution measuring device. The diameter (D90) where the cumulative frequency in the volumetric particle size distribution of the lithium metal composite oxide (Fm) reaches 90% can be 1 μm to 10 μm. Furthermore, in the volume-based particle size distribution of lithium metal composite oxide (Fm), the cumulative frequency of the diameter (D10) that becomes 10% can be less than 0.03 μm.

[0085] The BET surface area of ​​the composite oxide is preferably 0.01 m². 2 / g~15m 2 Within the range of / g.

[0086] In addition, the content of elements constituting the composite oxide can be determined by inductively coupled plasma optical emission spectrometry (ICP-AES), electron probe microanalysis (EPMA), or energy dispersive X-ray diffraction (EDX).

[0087] As a positive electrode active material, other known lithium metal oxides, not the aforementioned lithium metal composite oxides, can be mixed in with the lithium metal composite oxide having a crystal structure similar to that of the rock salt described above. Examples of other lithium metal oxides include Li. a CoO2, Li a NiO2, Li a MnO2, Li a Co b Ni 1-b O2, Li a Co b M 1-b O c Li a Ni 1- b M b O c Li a Mn2O4, Li a Mn 2-b M b Lithium transition metal composite oxides such as O4, LiMePO4, and Li2MePO4F. M is selected from at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B. Me contains at least one transition element (e.g., at least one selected from Mn, Fe, Co, and Ni). The values ​​are 0 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.9, and 2.0 ≤ c ≤ 2.3. Furthermore, the value 'a', representing the molar ratio of lithium, increases or decreases according to charge and discharge conditions.

[0088] The shape and thickness of the positive current collector can be selected from the shape and range based on the negative current collector. Examples of materials for the positive current collector include stainless steel, aluminum, aluminum alloy, and titanium.

[0089] [negative electrode]

[0090] The negative electrode, for example, includes a negative current collector and may have a negative active material layer formed on the surface of the negative current collector. The negative active material layer can be formed, for example, by dispersing a negative electrode mixture containing a negative active material, a binder, etc., in a dispersion medium, coating the resulting negative electrode slurry onto the surface of the negative current collector, and then drying it. The dried coating can be calendered as needed. That is, the negative active material can be a mixture layer. Alternatively, lithium metal foil or lithium alloy foil can be attached to the negative current collector. The negative active material layer can be formed on one surface or on both surfaces of the negative current collector.

[0091] The negative electrode active material layer contains a negative electrode active material as an essential component, and can include binders, conductive agents, tackifiers, etc., as optional components. Commonly known materials can be used as binders, conductive agents, and tackifiers.

[0092] The negative electrode active material includes materials that electrochemically absorb and release lithium ions, lithium metal, and / or lithium alloys. Carbon materials and alloy materials can be used as materials for electrochemically absorbing and releasing lithium ions. Examples of carbon materials include graphite, easily graphitized carbon (soft carbon), and difficult-to-graphitize carbon (hard carbon). Among these, graphite, which exhibits excellent charge-discharge stability and low irreversible capacity, is preferred. Examples of alloy materials include materials containing at least one metal capable of forming an alloy with lithium, such as silicon, tin, silicon alloys, tin alloys, and silicon compounds. Silicon oxide or tin oxide, formed by combining these with oxygen, can also be used.

[0093] As silicon-containing alloy materials, for example, lithium-ion conductive phases and silicon composite materials in which silicon particles are dispersed in the lithium-ion conductive phase can be used. As the lithium-ion conductive phase, for example, silicon oxide phases, silicate phases, and / or carbon phases can be used. The main component of the silicon oxide phase (e.g., 95-100% by mass) can be silicon dioxide. Among these, composite materials composed of silicate phases and silicon particles dispersed in the silicate phase are preferred in terms of high capacity and low irreversible capacity.

[0094] The silicate phase may contain at least one element selected from Group 1 and Group 2 elements of the long-period periodic table. Examples of Group 1 and Group 2 elements from the long-period periodic table include lithium (Li), potassium (K), sodium (Na), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). Other elements may include aluminum (Al), boron (B), lanthanum (La), phosphorus (P), zirconium (Zr), and titanium (Ti). Lithium-containing silicate phases (hereinafter also referred to as lithium silicate phases) are preferred due to their small irreversible capacity and high initial charge / discharge efficiency.

[0095] The lithium silicate phase can be any oxide phase containing lithium (Li), silicon (Si), and oxygen (O), but may also contain other elements. The atomic ratio of O to Si in the lithium silicate phase (O / Si) is, for example, greater than 2 and less than 4. Preferably, O / Si is greater than 2 and less than 3. The atomic ratio of Li to Si in the lithium silicate phase (Li / Si) is, for example, greater than 0 and less than 4. The lithium silicate phase can have the following structure: Li 2z SiO 2+z The composition is represented by (0 < z < 2). z preferably satisfies the relationship 0 < z < 1, and more preferably z = 1 / 2. Elements other than Li, Si and O that can be included in the lithium silicate phase include, for example, iron (Fe), chromium (Cr), nickel (Ni), manganese (Mn), copper (Cu), molybdenum (Mo), zinc (Zn), aluminum (Al), etc.

[0096] The carbon phase can be composed of amorphous carbon with low crystallinity (i.e., non-crystalline carbon). Amorphous carbon can be hard carbon, soft carbon, or something else entirely.

[0097] As the negative current collector, non-porous conductive substrates (such as metal foils) or porous conductive substrates (such as meshes, grids, perforated plates, etc.) can be used. Examples of materials that can be used as the negative current collector include stainless steel, nickel, nickel alloys, copper, and copper alloys.

[0098] [Electrolytes]

[0099] The electrolyte can be a liquid electrolyte (electrolyte), a gel electrolyte, or a solid electrolyte. A liquid electrolyte is, for example, an electrolyte containing a non-aqueous solvent and a salt dissolved in the non-aqueous solvent. The concentration of the salt in the electrolyte is, for example, 0.5 mol / L or more and 2 mol / L or less. The electrolyte may contain known additives.

[0100] Gel electrolytes comprise a salt and a matrix polymer, or a salt, a non-aqueous solvent, and a matrix polymer. As a matrix polymer, for example, a polymer material that gels by absorbing a non-aqueous solvent is used. Examples of polymer materials include fluoropolymers, acrylic resins, polyether resins, and polyethylene oxide.

[0101] As a solid electrolyte, materials known in all-solid-state lithium-ion secondary batteries (such as oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.) are used.

[0102] For example, liquid non-aqueous electrolytes are prepared by dissolving a salt in a non-aqueous solvent. The salt is an electrolyte salt that undergoes ion dissociation in the electrolyte; for example, it may contain lithium salts. Electrolytes can contain various additives. Electrolytes are typically used directly in liquid form, but they can also be used in a state where flowability is restricted by gelling agents or similar methods.

[0103] As a non-aqueous solvent, cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, and chain carboxylic acid esters can be used, for example. Examples of cyclic carbonates include propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC). Examples of chain carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone (GVL). Examples of chain carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP). One non-aqueous solvent can be used alone, or two or more can be used in combination.

[0104] Examples of non-aqueous solvents include cyclic ethers, chain ethers, nitriles such as acetonitrile, and amides such as dimethylformamide.

[0105] Examples of cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-epoxybutane, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-eucalyptol, crown ethers, etc.

[0106] Examples of chain ethers include 1,2-dimethoxyethane, dimethyl ether, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, etc.

[0107] These solvents can be fluorinated solvents in which some hydrogen atoms are replaced by fluorine atoms. Fluorinated ethylene carbonate (FEC) can be used as a fluorinated solvent.

[0108] As lithium salts, lithium salts containing chloric acid (LiClO4, LiAlCl4, LiB) can be used, for example. 10 Cl 10Lithium salts include those containing fluorine acids (LiPF6, LiPF2O2, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, LiCF3CO2, etc.), lithium salts containing fluorinated imides (LiN(FSO2)2, LiN(CF3SO2)2, LiN(CF3SO2)(C4F9SO2), LiN(C2F5SO2)2, etc.), and lithium halides (LiCl, LiBr, LiI, etc.). Lithium salts can be used alone or in combination of two or more.

[0109] The concentration of lithium salt in the electrolyte can be above 1 mol / L and below 2 mol / L, or above 1 mol / L and below 1.5 mol / L. By controlling the lithium salt concentration within the above range, an electrolyte with excellent ionic conductivity and moderate viscosity can be obtained. However, the lithium salt concentration is not limited to the above.

[0110] Electrolytes may contain other known additives. Examples of additives include 1,3-propanesulfonyl lactone, methylbenzene sulfonate, cyclohexylbenzene, biphenyl, diphenyl ether, and fluorobenzene.

[0111] [Septum]

[0112] The separator lies between the positive and negative electrodes. It possesses high ion permeability, moderate mechanical strength, and insulation properties. Microporous membranes, woven fabrics, and non-woven fabrics can be used as separators. Polyolefins such as polypropylene and polyethylene are preferred as separator materials.

[0113] As an example of a secondary battery structure, one could exemplify a structure in which an electrode assembly consisting of a positive and negative electrode wound together with a separator, and a non-aqueous electrolyte, is housed within an outer casing. Alternatively, instead of a wound electrode assembly, other electrode assemblies could be used, such as a stacked electrode assembly where the positive and negative electrodes are layered together with a separator. Secondary batteries can be, for example, cylindrical, square, coin-shaped, button-shaped, or laminated, among other forms.

[0114] Figure 1 This is a schematic perspective view of a partially cut-off square secondary battery according to one embodiment of this disclosure.

[0115] The battery comprises a square-shaped battery casing 4, an electrode assembly 1 housed within the battery casing 4, and a non-aqueous electrolyte (not shown). The electrode assembly 1 has a strip-shaped negative electrode, a strip-shaped positive electrode, and a separator between them. The negative electrode current collector is electrically connected to the negative terminal 6 disposed on the sealing plate 5 via a negative electrode lead 3. The negative terminal 6 is insulated from the sealing plate 5 by a resin gasket 7. The positive electrode current collector is electrically connected to the back of the sealing plate 5 via a positive electrode lead 2. That is, the positive electrode is electrically connected to the battery casing 4, which also serves as the positive terminal. The periphery of the sealing plate 5 fits into the open end of the battery casing 4, and the fitting is laser-welded. The sealing plate 5 has an injection hole for the non-aqueous electrolyte, which is blocked by a sealing plug 8 after electrolyte injection.

[0116] Furthermore, the structure of the secondary battery can be cylindrical, coin-shaped, button-shaped, etc., with a metal battery casing, or it can be a laminated battery with a battery casing made of laminated sheets that serve as a barrier layer and resin sheets. In this disclosure, there are no particular limitations on the type, shape, etc., of the secondary battery.

[0117] (Postscript)

[0118] Based on the above description, the following technical solution is disclosed.

[0119] (Technical Solution 1)

[0120] A positive electrode active material for secondary batteries comprises a lithium metal composite oxide having a crystal structure that can be classified into space group Fm-3m.

[0121] The lithium metal composite oxide comprises Li, a first positive element M1 different from Li, and a second positive element M2 different from Li and the first positive element M1.

[0122] More than 50% of the atoms of the first positive element M1 are Mn.

[0123] The content of the second positive element M2 in the lithium metal composite oxide is 10 ppm to 1000 ppm by mass.

[0124] The number of Li atoms (mLi) in the lithium metal composite oxide and the number of atoms of the first positive element (mM1) in the lithium metal composite oxide satisfy 1.2 ≤ mLi / mM1 ≤ 2.0.

[0125] The crystallite size of the lithium metal composite oxide is in the range of 1 nm to 1000 nm, or, in the X-ray diffraction (XRD) pattern of the lithium metal composite oxide obtained using CuKα rays, the half-width of the diffraction peaks belonging to the (200) plane is in the range of 0.1° to 2.5° based on 2θ.

[0126] (Technical Solution 2)

[0127] According to the positive electrode active material for secondary batteries described in technical solution 1, the lithium metal composite oxide further contains F.

[0128] (Technical Solution 3)

[0129] According to technical solution 1 or 2, the positive electrode active material for secondary batteries, the second positive element M2 contains at least one selected from Fe, Ca, Cr, Na, Al, Si, Mg, Cu, Zn, Pb and Sb.

[0130] (Technical Solution 4)

[0131] The positive electrode active material for secondary batteries according to any one of technical solutions 1 to 3

[0132] The first positive element M1, in addition to Mn, also contains element Mm.

[0133] The Mm is selected from at least one of Ti, Ge, Ga, Ni, Co, Sn, Nb, Mo, Bi, V, Y, Zr, K, Pt, Au, Ag, Ru, Ta, W, La, Ce, Pr, Gd, Sm, Eu, Yb, Dy, and Er.

[0134] (Technical Solution 5)

[0135] According to the positive electrode active material for secondary batteries described in technical solution 4, the Mm contains at least Ti.

[0136] (Technical Solution 6)

[0137] The positive electrode active material for secondary batteries as described in technical solution 4 or 5

[0138] The lithium metal composite oxide is composed of the formula Li a Mn b Mm c O d F e express,

[0139] It satisfies 1≤a≤1.4, 0.5≤b≤0.9, 0≤c≤0.4, 1.33≤d≤2, 0≤e≤0.67, and 1.7≤d+e≤2.

[0140] (Technical Solution 7)

[0141] According to technical solution 6, the positive electrode active material for secondary batteries satisfies 0 < c / b ≤ 1.

[0142] (Technical Solution 8)

[0143] A secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator between the positive electrode and the negative electrode.

[0144] The positive electrode comprises any one of the technical solutions 1 to 7, which is a positive electrode active material for secondary batteries.

[0145] The present disclosure will now be described in detail based on embodiments and comparative examples, but the present disclosure is not limited to the following embodiments.

[0146] <Reference Examples 1-60>

[0147] [The production of the positive electrode]

[0148] The following method was used to synthesize a lithium metal composite oxide (Fm) containing Mn and Ti as the first positive element M1. Manganese oxide (Mn₂O₃), lithium carbonate (Li₂CO₃), and titanium oxide (TiO₂) were mixed with additives to obtain the compositions shown in Tables 1-7. The compositions were calculated assuming Li has a +1 valence, Mn a +3 valence, Ti a +4 valence, and O a -2 valence. The mixture was calcined at 950°C for 10 hours to obtain the lithium metal composite oxide (Fm).

[0149] The sintered lithium metal composite oxide (Fm) was pulverized under various conditions using a planetary ball mill. The conditions were varied in rotation speed (150–500 rpm) and processing time (3–24 hours). As an example, the case of lithium metal composite oxide (Fm) No. 1 was described. The sintered lithium metal composite oxide (Fm) was fed into a planetary ball mill (Fritsch Premium-Line P7, rotation speed: 300 rpm, container: 45 mL, balls: φ3 mm Zr balls) and treated at room temperature in a dry atmosphere for 12 hours (24 cycles of 0.5 hours of operation followed by a 10-minute stop). This yielded lithium metal composite oxide (Fm) with the specified crystallite size.

[0150] The obtained lithium metal composite oxide (Fm) was analyzed by measuring and examining the X-ray diffraction pattern using a CuKα powder X-ray diffraction apparatus. Based on the number and position of the XRD peaks, it was confirmed that a lithium metal composite oxide (Fm) with a crystal structure based on the rock salt type belonging to the space group Fm-3m was formed. Furthermore, the half-width of the diffraction peaks of the lithium metal composite oxide (Fm) belonging to the (200) plane was determined. The crystallite size was calculated from the half-width using the Scherrer formula. The lattice constant α of the lithium metal composite oxide (Fm) obtained by the described method is shown in the table.

[0151] The obtained lithium metal composite oxide (Fm), acetylene black, and polyvinylidene fluoride were mixed in a solid component mass ratio of 7:2:1, and N-methyl-2-pyrrolidone (NMP) was used as the dispersion medium to prepare a positive electrode slurry. Next, the positive electrode slurry was coated onto a positive electrode current collector made of aluminum foil. After drying and compressing the coating, it was cut into the specified electrode size to obtain the positive electrode.

[0152] [Preparation of Electrolytes]

[0153] A non-aqueous electrolyte is prepared by adding LiPF6 as a lithium salt to a mixed solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) are mixed in a specified volume ratio.

[0154] [Creation of the experimental cell]

[0155] A test unit was fabricated using the aforementioned positive electrode and a negative electrode made of lithium metal foil. The positive and negative electrodes were arranged opposite each other through a separator to form an electrode body, which was then housed in a coin-shaped outer container. Electrolyte was injected into the outer container, which was then sealed to obtain a coin-shaped experimental secondary battery.

[0156] [evaluate]

[0157] (Initial discharge capacity)

[0158] The secondary battery was charged at a constant current of 0.1C at room temperature until the battery voltage reached 4.95V, and then charged at a constant voltage of 4.95V until the current reached 0.01C. The charging capacity was calculated. Then, after a 20-minute pause, the battery was discharged at a constant current of 0.1C until the battery voltage reached 2.5V, and the discharge capacity was measured. The discharge capacity per unit mass of lithium metal composite oxide (Fm) is shown in the table. A maximum of three measurements were performed using the same method, and the average value was calculated. The results are shown in the tables. Additionally, the relationship between mLi / mM (mMn+mTi) and the initial discharge capacity corresponding to each table is shown in the table. Figures 2A-2F .

[0159] Table 1

[0160]

[0161] Table 2

[0162]

[0163] Table 3

[0164]

[0165] Table 4

[0166]

[0167] Table 5

[0168]

[0169] Table 6

[0170]

[0171] Table 7

[0172]

[0173] As shown in Tables 1-7, when the lithium metal composite oxide (Fm) satisfies 1.2≤mLi / mM≤2.0 and its crystallite size is in the range of 1nm~1000nm, the initial discharge capacity is significantly improved.

[0174] <Examples 1-2, Comparative Examples 1-7>

[0175] Next, to investigate the effect of the second positive element M2, lithium metal composite oxides (Fm) containing Mn and Ti as the first positive element M1 and Ca, Na, Mg, and Fe as the second positive element M2 were synthesized at the contents shown in Table 8 (mass basis content in lithium metal composite oxides (Fm)). Specifically, manganese oxide (Mn2O3), lithium carbonate (Li2CO3), and titanium oxide (TiO2) were mixed with the feed composition shown in Table 7, and the oxide of the specified second positive element M2 was mixed into the mixture so that the content of the second positive element M2 was the value shown in Table 8. The resulting mixture was calcined at 950°C for 10 hours, and lithium metal composite oxides (Fm) A1~A2 of the examples and lithium metal composite oxides (Fm) B1~B7 of the comparative examples were obtained in the same manner as the above-mentioned reference examples.

[0176] The obtained lithium metal composite oxide (Fm) was analyzed by measuring and analyzing the X-ray diffraction pattern using a CuKα-ray powder X-ray diffraction apparatus. Based on the number and position of the XRD peaks, it was confirmed that a lithium metal composite oxide (Fm) with a crystal structure based on the rock salt type belonging to the space group Fm-3m was formed. In addition, sharp diffraction peaks and broad diffraction peaks belonging to the (200) plane of the lithium metal composite oxide (Fm) were observed in the X-ray diffraction pattern. The half-width at half-maximum (WWHM) of the sharp peaks was 0.2°~0.5°, and the WWHM of the broad peaks was 2.0°~2.2°. The crystallite size was calculated from the WWHM based on the Scherrer formula, and it was 20~65 nm in the sharp peaks and 3~9 nm in the broad peaks. In addition, the lattice constant α of the lithium metal composite oxide (Fm) obtained by the above method was calculated to be 4.09~4.16 Å.

[0177] Table 8

[0178]

[0179] Table 8 shows that the capacity is increased by including trace amounts of the second positive element M2. It also shows that if the content of the second positive element M2 is too low, the capacity-increasing effect is small. On the other hand, it shows that if the content of the second positive element M2 exceeds 1000 ppm, the capacity decreases.

[0180] Industry availability

[0181] The positive electrode active material for secondary batteries disclosed herein enables the provision of secondary batteries with high energy density. The secondary batteries disclosed herein can be used as main power sources for mobile communication devices, portable electronic devices, and the like.

[0182] The present invention has been described in conjunction with the currently preferred embodiments, but this disclosure should not be construed as restrictive. Various changes and modifications will be apparent to those skilled in the art upon reading the foregoing disclosure. Therefore, the appended claims should be interpreted as including all changes and modifications without departing from the true spirit and scope of the invention.

[0183] Explanation of reference numerals in the attached figures

[0184] 1: Electrode assembly, 2: Positive lead, 3: Negative lead, 4: Battery casing, 5: Sealing plate, 6: Negative terminal, 7: Gasket, 8: Sealing plug.

Claims

1. A positive electrode active material for secondary batteries, comprising a lithium metal composite oxide having a crystal structure belonging to space group Fm-3m. The lithium metal composite oxide comprises Li, a first positive element M1 different from Li, and a second positive element M2 different from Li and the first positive element M1. More than 50% of the atoms of the first positive element M1 are Mn. The content of the second positive element M2 in the lithium metal composite oxide is 10 ppm to 1000 ppm by mass. The number of Li atoms (mLi) in the lithium metal composite oxide and the number of atoms of the first positive element (mM1) in the lithium metal composite oxide satisfy 1.2 ≤ mLi / mM1 ≤ 2.

0. The crystallite size of the lithium metal composite oxide is in the range of 1 nm to 1000 nm, or, in the X-ray diffraction pattern (XRD) obtained by using CuKα rays on the lithium metal composite oxide, the half-width of the diffraction peaks belonging to the (200) plane is in the range of 0.1° to 2.5° based on 2θ.

2. The positive electrode active material for secondary batteries according to claim 1, The lithium metal composite oxide also contains F.

3. The positive electrode active material for secondary batteries according to claim 1, The second positive element M2 contains at least one selected from Fe, Ca, Cr, Na, Al, Si, Mg, Cu, Zn, Pb, and Sb.

4. The positive electrode active material for secondary batteries according to claim 1, The first positive element M1, in addition to Mn, also contains element Mm. The Mm is selected from at least one of Ti, Ge, Ga, Ni, Co, Sn, Nb, Mo, Bi, V, Y, Zr, K, Pt, Au, Ag, Ru, Ta, W, La, Ce, Pr, Gd, Sm, Eu, Yb, Dy, and Er.

5. The positive electrode active material for secondary batteries according to claim 4, The Mm contains at least Ti.

6. The positive electrode active material for secondary batteries according to claim 4, The lithium metal composite oxide is composed of the formula Li a Mn b Mm c O d F e express, It satisfies 1≤a≤1.4, 0.5≤b≤0.9, 0≤c≤0.4, 1.33≤d≤2, 0≤e≤0.67, and 1.7≤d+e≤2.

7. The positive electrode active material for secondary batteries according to claim 6, The condition 0 < c / b ≤ 1 is satisfied.

8. A secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator between the positive electrode and the negative electrode. The positive electrode comprises the positive electrode active material for secondary batteries as described in any one of claims 1 to 7.

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