Cathode active material for lithium-ion secondary battery

Abstract

The present invention relates to an active cathode material for a lithium-ion secondary battery. The active cathode material for a lithium-ion secondary battery comprises a lithium transition metal compound oxide. The crystal structure of the lithium transition metal compound oxide belongs to the space group R-3m. The lithium transition metal compound oxide contains Ni 4+ .

Description

BACKGROUND OF THE INVENTION 1. Field of the invention

[0001] The present invention relates to an active cathode material for a lithium-ion secondary battery. 2. Description of the state of the art

[0002] The Japanese unpublished patent application No. 2008-257992 (JP 2008-257992 A) discloses a lithium nickel cobalt manganese composite oxide with a layer. SUMMARY OF THE INVENTION

[0003] A lithium transition metal compound oxide can exhibit a layered structure. The layered structure comprises 3a sites and 3b sites. The 3a sites and the 3b sites are layered alternately in the c-axis direction. The 3a sites contain lithium ions (Li + The 3b sites contain transition metal ions (TM). If the 3b sites contain a nickel ion (Ni), it is generally assumed that the Ni ion tends to become trivalent (Ni₂). 3+ ) to become.

[0004] JP 2008-257992 A discloses that the valence of Ni ions can be fixed to divalent by ensuring that the occupation rate or degree of occupancy of metal ions other than Ni, cobalt (Co), and manganese (Mn) at the 3b positions is 5% or less. In the battery, the lithium transition metal compound oxide is charged. In a highly charged state, the valence of Ni changes from divalent (Ni) to 3b. 2+ ) to tetravalent (Ni 4+The ionic radius differs between divalent and tetravalent ions. Consequently, the 3b site can contract rapidly along the c-axis in a highly charged state. A sudden contraction of the crystal structure can lead to irreversible structural changes (e.g., transformation into a rock salt structure or similar). Irreversible structural changes are associated with a deterioration of capacity. Therefore, it is possible that the desired cycle properties cannot be achieved.

[0005] The aim of the present invention is to improve the cycle properties. 1. An active cathode material for a lithium-ion secondary battery contains a lithium transition metal compound oxide. The crystal structure of the lithium transition metal compound oxide belongs to the space group R-3m. The lithium transition metal compound oxide contains Ni 4+ .

[0006] The layered structure belongs to the space group R-3m. In the present invention, tetravalent Ni ions are introduced into the crystal structure before the battery is first charged. It is assumed that even if a valence change with respect to the tetravalent Ni occurs during charging, the contraction in the c-axis direction is mitigated because the tetravalent Ni ions are initially present.

[0007] The cycle life is expected to be improved by reducing irreversible structural changes in a highly charged state. In the following, "active cathode material for lithium-ion secondary batteries" can be abbreviated to "active cathode material".

[0008] 2. The active cathode material according to point “1” above may, for example, have the following configuration. The crystal structure includes a 3a site and a 3b site.

[0009] The 3a position contains Li + and Ni2+ The 3b position contains Ni 4+ and Ni 3+ .

[0010] For example, a divalent Ni ion (Ni) can 2+ ) to the 3a site. A phenomenon in which Ni ions are transferred to the 3a site is also referred to as "cation mixing". (CM)" The 3b site can contain tetravalent and trivalent Ni ions.

[0011] 3. The active cathode material according to point “2” above may, for example, comprise the following configuration. The ratio of the amount of Ni 4+ the amount of Ni 3+ The value is between 0.09 and 0.35.

[0012] The following describes the ratio of the amount of substance of Ni 4+ the amount of Ni 3+ also known as molar ratio “Ni 4+ / Ni 3+ “ is designated. If the molar ratio “Ni 4+ / Ni 3+ “If the value is in the range of 0.09 to 0.35, an improvement in cycle characteristics can be expected.

[0013] 4. The active cathode material according to point “2” or “3” above may, for example, comprise the following configuration. The ratio of the amount of Ni 4+ the amount of Ni 2+ The value is between 2.7 and 7.2.

[0014] The following describes the ratio of the amount of substance of Ni 4+ the amount of Ni 2+ also known as molar ratio “Ni 4+ / Ni 2+ “ is designated. If the molar ratio “Ni 4+ / Ni 2+ “If the value is in a range of 2.7 to 7.2, an improvement in cycle characteristics can be expected.

[0015] 5. The active cathode material according to any of the preceding points “1” to “4” may, for example, comprise the following configuration. A composition of the lithium transition metal composite oxide is represented by the general formula “Li z Ni 1-c-a Co c Mn a O d“expressed. In the general formula, “z, a, c and d” satisfy the relationships “0.1 ≤ z ≤ 1.5”, “0.5 ≤ 1-ca ≤ 1.0”, “0 ≤ c ≤ 0.3, 0 ≤ a ≤ 0.3” and “1.5 ≤ d ≤ 2.1”.

[0016] An embodiment of the present invention (hereinafter referred to as "present embodiment") and an example of the present invention (hereinafter referred to as "present example") are described. It should be noted, however, that the present embodiment and the present example do not limit the technical scope of the present invention. The present embodiment and the present example are exemplary in every respect. The present embodiment and the present example are not limiting. The technical scope of the present invention includes all modifications in the sense and scope that correspond to the description of the claims. For example, it is to be expected from the outset that any configurations can be extracted from the present embodiment and combined as desired. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Features, advantages and technical and industrial significance of exemplary embodiments of the invention are described below with reference to the accompanying drawings, in which the same reference numerals denote the same elements, and wherein: Fig. 1 is a diagram showing an example of fitting results in the Rietveld analysis; Fig. 2 is an example of an X-ray absorption fine structure spectrum (XAFS); Fig. 3 is a table that shows the results of experiments; Fig. 4 is a diagram that concerns a relationship, namely the molar ratio “Ni 4+ / Ni 3+ “and the capacity maintenance rate; and Fig. 5 is a diagram that concerns a relationship, namely the molar ratio “Ni 4+ / Ni 2+ “and the capacity maintenance rate.” DETAILED DESCRIPTION OF THE EXECUTION FORMS Terms and expressions

[0018] “Comprising,” “including,” “having,” and variations thereof are open expressions. A configuration expressed as open may or may not contain additional elements beyond those required. The term “consist of” is a closed expression. However, configurations expressed by closed terms may also contain normally associated impurities and additional elements that are irrelevant to the technology in question. The term “essentially consists of” is a semi-closed expression. Configurations expressed by semi-closed terms allow the addition of elements that do not substantially affect the fundamental and novel properties of the technology in question.

[0019] Numerical values ​​can be expressed in significant figures. Measurement values ​​can be mean values ​​of measurements taken over a multiple of cases, unless otherwise specified. The number of measurements can be 3 or more, 5 or more, or 10 or more. In general, the larger the number of measurements, the higher the reliability of the mean. Measurement values ​​can be rounded based on the number of significant figures. Measurement values ​​may include errors or similar limitations related, for example, to the detection limit of a device.

[0020] The devices, software, etc., used for measuring different types of values ​​are merely examples. Objects equivalent to the devices, etc., mentioned as examples can also be used. If equivalent objects are used, the measurement conditions can be adjusted accordingly.

[0021] A space group to which the crystal structure belongs is identified by an X-ray diffraction (XRD) pattern. The measurement conditions can be, for example, as follows. Analysis method: Wide angle Device: SmartLab II (manufactured by Rigaku Corporation) Measuring angle: 10° to 120° Tube: Cuka Tube voltage: 45 kV Tube current: 200 mA Measurement method: Continuous Step: 0.02 Speed: 2° / min IS: 1 / 2 RS: 20 mm Detection mode: 1-dimensional

[0022] If the crystal structure belongs to the space group R-3m, the composition ratio of different types of Ni ions (Ni) 2+ , Ni 3+ , Ni 4+ ) in a lithium transition metal composite oxide is further identified by the following methods. As an example, a case is described in which a lithium transition metal composite oxide has a composition represented by the following general formula. Li z N 1-c-a Co c Mn a O d

[0023] Co at the 3b position is considered trivalent (Co 3+ ) assumed. Mn at the 3b position is assumed to be tetravalent (Mn 4+ ) assumed. Ni, which was transferred to the 3a position, is treated as a binary (Ni 2+ ). A Ni ion at the 3b position is assumed to be trivalent (Ni 3+ ) or tetravalent (Ni 4+ ). considered. If the composition ratio of the trivalent (Ni 3+) Elements “y” is, the above general formula can be rewritten taking into account the configuration of each position as follows. [Li + z Ni 2+ b ] 3a-Stelle [Ni 3+ y Ni 4+ (1-y-c-b-a) Co c Mn a ] 3b-Sielle [O d ] 6c-Stelle

[0024] The average valence of Ni in the lithium transition metal compound oxide is assumed to be "n". The relationship "n(1-ca) = 2b + 3y + 4(1-ycba)" is satisfied. Accordingly, "y = (4 - n)(1-ca) - 2b" is obtained. The composition ratio of Ni 4+ can also be written as “1-ycba” due to the composition ratio “y” of Ni 3+“a” and “c” are identified by composition analysis. “b” is determined by Rietveld analysis of the XRD pattern. “n” is determined by measuring the fine structure of X-ray absorption (XAFS) in the hard X-ray range.

[0025] The composition of the active cathode material can be measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES). A sample solution is prepared by dissolving 0.1 g of the sample (active cathode material) in a mixed acid solution (10 ml) of hydrochloric and sulfuric acid. The sample solution is diluted to a suitable concentration using a volumetric flask. After dilution, the composition analysis is performed using an ICP-AES instrument. For example, the product labeled "PS3520UVDDII (manufactured by Hitachi High-Tech Science Corporation)" or similar can be used.

[0026] The Rietveld analysis is performed on the XRD patterns using the software "GSAS-II". The structure is the space group R-3m (ITA No. 166). The XRD patterns undergo background processing and structure refinement. Optimization is performed by applying the Ni 2+ The composition ratio "b" is set as a variable at position 3a. In general, "0 ≤ b ≤ 0.1" can be set. Thus, "Rwp", one of the refinement indices, is calculated. A quadratic function "αx 2 + βx + γ“ is adjusted to the values ​​of Rwp and b. Fig. Figure 1 is a diagram showing an example of fitting results in Rietveld analysis. Within the refined region of the obtained approximation curve, the x corresponding to the minimum value of Rwp is denoted as Ni. 2+ -Composition ratio “b”. Note that “b / (z + b)” is also referred to as the “CM rate”.

[0027] XAFS measurements can be performed, for example, at the BL5S1 beamline of the Aichi Synchrotron Light Center. A sample is prepared by coating a substrate with an active cathode material. The sample can be part of a battery's cathode plate. A rapid measurement is performed using the transmission method over a measurement time of 3 minutes, yielding an XAFS spectrum at the Ni-K absorption edge. The XAFS spectra are normalized using the Athena software. Fig. This shows an example of an XAFS spectrum. In the normalized XAFS spectrum, the energy at which the absorption is 0.5 is considered the absorption edge energy. The mean valence "n" of Ni in the active cathode material is determined by linear fitting based on the absorption edge energies of standard Ni samples. 2+ , Ni 3+ and Ni 4+ (e.g. NiO, Ni2O3, NiO2 or the like) calculated.

[0028] Stoichiometric formulas are representative examples of compounds. A compound can have a non-stoichiometric composition. For example, "Al₂O₃" is not limited to a compound with a molar ratio of "Al / O = 2 / 3". "Al₂O₃" represents a compound containing Al and O in any molar ratio unless otherwise specified. For example, the compound may be doped with a trace element. Part of the Al and O may be replaced by another element.

[0029] The term "primary particle" refers to a solid particle that is recognized as the smallest unit of a particle and cannot be further subdivided. Primary particles appear to have no particle boundaries in scanning electron microscope (SEM) images. The number of primary particles contained within a single-crystal particle or a polycrystal particle is counted in an SEM image of the powder. The image magnification is, for example, 10,000x. An independently occurring primary particle or an aggregate of 2 to 10 primary particles is considered a single-crystal particle. An aggregate of more than 10 primary particles is considered a polycrystal particle. The proportion of single-crystal particles is determined for 100 particles randomly extracted from the SEM image.

[0030] "D50" denotes the particle size at which the cumulative frequency in a volume-based particle size distribution (cumulative distribution) is 50%. D50 can be measured, for example, by laser diffraction. Similarly, the particle size at which the cumulative frequency is 10% is also referred to as "D10", and the particle size at which the cumulative frequency is 90% is also referred to as "D90". Active cathode material

[0031] The active cathode material is intended for use in a battery. The battery can be a liquid-filled or solid-state battery. The battery can have any structure. For example, the battery can have a wound or laminate-forming element. The battery can, for example, have a unipolar or bipolar structure.

[0032] The active cathode material contains a lithium transition metal compound oxide. The term "lithium transition metal compound oxide" refers to a compound containing Li, a transition metal (TM), and oxygen (O). A crystal structure of the lithium transition metal compound oxide belongs to the space group R-3m. This crystal structure is also referred to as a "layered structure."

[0033] The layer structure comprises 3a sites (Li sites), 3b sites (TM sites), and 6c sites (O sites). The 3a sites contain Li + The 3b sites contain Ni ions. An exchange phenomenon (CM) can occur between some of the Li ions at the 3a sites and some of the Ni ions at the 3b sites. The Ni ions transferred to the 3a sites can be divalent (Ni₂). 2+ The ionic radius of Li + is 0.76 Å. The ionic radius of trivalent Ni ions (Ni) is 0.76 Å. 3+) is 0.56 Å to 0.60 Å. The ionic radius of divalent Ni ions (Ni) 2+ ) is 0.69 Ä. Ni 2+ has an ionic radius that is closer to that of Li + lies as the one of Ni 3+ , and accordingly it is assumed that Ni 2+ within the 3a-position is stable. Thus, the 3a-positions Li + and Ni 2+ contain.

[0034] The 3b places contain Ni 4+ This means that the lithium transition metal compound oxide contains Ni 4+ The presence of Ni 4+ The crystal structure should improve the cycle properties. It is assumed that Ni 4+ Ni cannot be incorporated into the crystal structure by conventional synthesis methods. According to the new findings of the present invention, Ni 4+The 3b site is introduced by supplying an excess amount of Li source during synthesis and performing a suitable washing with water after calcination.

[0035] The 3b position can be used in addition to Ni 4+ also Ni 3+ contained. The molar ratio “Ni 4+ / Ni 3+ “can be, for example, greater than 0, 0.02 or more, 0.04 or more, 0.06 or more, 0.08 or more, 0.09 or more, 0.10 or more, 0.12 or more, 0.14 or more, 0.16 or more, 0.18 or more, 0.20 or more, 0.21 or more, 0.22 or more, 0.24 or more, 0.26 or more, 0.28 or more, 0.30 or more, 0.32 or more, 0.34 or more, 0.35 or more, 0.36 or more, 0.38 or more, 0.40 or more, 0.42 or more, 0.44 or more, 0.46 or more, 0.48 or more, or 0.50 or more. The molar ratio “Ni 4+ / Ni 3+“can be, for example, 5 or less, 4 or less, 3 or less, 2 or less, 1 or less, 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.48 or less, 0.46 or less, 0.44 or less, 0.42 or less, 0.40 or less, 0.38 or less, 0.36 or less, 0.35 or less, 0.34 or less, 0.32 or less, 0.30 or less, 0.28 or less, 0.26 or less, 0.24 or less, 0.22 or less, 0.21 or less, 0.20 or less, 0.18 or less, 0.16 or less, 0.14 or less, 0.12 or less, 0.10 or less, 0.09 or less, 0.08 or less, 0.06 or less, 0.04 or less, or 0.02 or less. For example, if the molar ratio "Ni 4+ / Ni 3+ “If the value is in a range of 0.09 to 0.35, an improvement in cycle characteristics can be expected.

[0036] The molar ratio “Ni 4+ / Ni 2+“can be, for example, greater than 0, 1 or more, 2 or more, 2.4 or more, 2.7 or more, 2.8 or more, 3.2 or more, 3.6 or more, 3.8 or more, 4.0 or more, 4.4 or more, 4.8 or more, 5.2 or more, 5.6 or more, 6.0 or more, 6.4 or more, 6.7 or more, 6.8 or more, 7.2 or more, 7.6 or more, 8.0 or more, 9.0 or more, 10.0 or more, 12.0 or more, 14.0 or more, 16.0 or more, 16.8 or more, 18.0 or more, or 20.0 or more. The molar ratio “Ni 4+ / Ni 2+“can be, for example, 40.0 or less, 30.0 or less, 20.0 or less, 18.0 or less, 16.8 or less, 16.0 or less, 14.0 or less, 12.0 or less, 10.0 or less, 9.0 or less, 8.0 or less, 7.6 or less, 7.2 or less, 6.8 or less, 6.7 or less, 6.4 or less, 6.0 or less, 5.6 or less, 5.2 or less, 4.8 or less, 4.4 or less, 4.0 or less, 3.8 or less, 3.6 or less, 3.2 or less, 2.8 or less, 2.7 or less, 2.4 or less, 2 or less, or 1 or less. For example, if the molar ratio “Ni 4+ / Ni 2+ “If the value is in a range of 2.7 to 7.2, an improvement in cycle characteristics can be expected.

[0037] The 3b position can contain Co, Mn, etc., in addition to Ni. The lithium transition metal compound oxide, for example, can have a composition described by the general formula "Li z Ni 1-c-a Coc Mn a O d The Li-addition ratio "z" can, for example, satisfy a relationship of "0.1 ≤ z ≤ 1.5". The Li-addition ratio "z" can be, for example, 0.4 or more, 0.6 or more, 0.8 or more, 1.0 or more, 1.2 or more, or 1.4 or more. The Li-addition ratio "z" can be, for example, 1.4 or less, or 1.2 or less.

[0038] In the general formula above, the oxygen addition factor "d" can, for example, satisfy a relationship of "1.5 ≤ d ≤ 2.1". The oxygen addition factor "d" can, for example, be 1.6 or more, 1.7 or more, 1.8 or more, 1.9 or more, or 2.0 or more. The oxygen addition ratio "d" can, for example, be 2.0 or less, 1.9 or less, 1.8 or less, 1.7 or less, or 1.6 or less.

[0039] In the general formula above, the Ni content "1-ca" can, for example, satisfy a relationship of "0.5 ≤ 1-ca ≤ 1.0". The Ni content "1-ca" can be, for example, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more. The Ni addition ratio "1-ca" can be, for example, 0.9 or less, 0.8 or less, 0.7 or less, or 0.6 or less. If the Ni addition ratio "1-ca" is 0.5 or more, an increase in discharge capacity can be expected.

[0040] In the general formula above, the co-component "c" can, for example, satisfy a relationship of "0 ≤ c ≤ 0.3". The co-component "c" can, for example, be 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, 0.10 or more, 0.15 or more, 0.20 or more, or 0.25 or more. The co-addition ratio “c” may be, for example, 0.25 or less, 0.20 or less, 0.15 or less, 0.10 or less, 0.09 or less, 0.08 or less, 0.07 or less, 0.06 or less, 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, or 0.01 or less.

[0041] In the general formula above, the Mn fraction “a” can, for example, satisfy a relationship of “0 ≤ a ≤ 0.3”. The Mn fraction “a” can, for example, be 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, 0.10 or more, 0.15 or more, 0.20 or more, or 0.25 or more. The Mn fraction “a” can be, for example, 0.25 or less, 0.20 or less, 0.15 or less, 0.10 or less, 0.09 or less, 0.08 or less, 0.07 or less, 0.06 or less, 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, or 0.01 or less.

[0042] It should be noted that in the above general formula, Mn may be wholly or partially replaced by Al or the like. That is to say, the lithium transition metal compound oxide may, for example, have a composition that can be described by the general formula “Li z Ni1-c-a Co c Al a O d “ is represented. The range of the Al composition ratio “a” is the same as that of the Mn composition ratio “a” described above.

[0043] A dopant may optionally be added to the lithium transition metal composite oxide. The term "dopant" refers to an element other than Li, Ni, Co, Mn, and O. The dopant may, for example, comprise at least one type selected from a group consisting of Zr, Mo, W, Mg, Ca, Na, Fe, Cr, Zn, Si, Sn, Al, and Ag. The composition of the dopant may be, for example, 0.005 or more, 0.01 or more, 0.02 or more, 0.03 or more, or 0.04 or more. Alternatively, the composition of the dopant may be, for example, 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, or 0.01 or less.

[0044] The active cathode material can be in powder form. The D50 value of the active cathode material can be, for example, 1 µm or more, 3 µm or more, 5 µm or more, 10 µm or more, or 15 µm or more. The D50 value of the powder can be, for example, 30 µm or less, 20 µm or less, or 10 µm or less.

[0045] The lithium transition metal composite oxide can be in the form of single-crystal particles. The lithium transition metal composite oxide can also be in the form of polycrystal particles. That is, the active cathode material can contain both single-crystal and polycrystal particles. The polycrystal particles can have essentially the same structure and composition as the single-crystal particles. For example, the active cathode material (powder) can consist of 50% or more of single-crystal particles by number, and the remainder of polycrystal particles. The single-crystal particle percentage can be, for example, 60% or more, 70% or more, 80% or more, or 90% or more. The single-crystal particle percentage can be, for example, 100% or less, 90% or less, or 80% or less.For example, if the proportion of single-crystal particles is 70% or more, an improvement in the cycle characteristics can be expected. This is presumably because single-crystal particles have fewer particle boundaries than polycrystalline particles and are therefore less susceptible to cracking due to charging and discharging (volume changes).

[0046] The probability of cracking is expected to decrease as the number of primary particles comprising a single-crystal particle decreases. For example, the number of primary particles comprising the single-crystal particle may be 9 or less, 8 or less, 7 or less, 6 or less, 5 or less, 4 or less, 3 or less, or 2 or less. Similarly, the number of primary particles comprising the polycrystalline particle may be 15 or more, 20 or more, 25 or more, or 50 or more. For example, if a single-crystal particle is redefined to include 5 or fewer primary particles, the aforementioned proportion refers to the proportion of single-crystal particles after the redefinition.

[0047] The active cathode material (powder) can be a monodisperse system. Since the powder consists mainly of single-crystal particles and is also a monodisperse system, an improvement in the cycle characteristics can be expected. For example, the powder can have a range of 1 or less. The term "range" refers to a value calculated using the formula "(D90 - D10) / D50". It is assumed that the smaller the range, the sharper the particle distribution. The range of the powder can be, for example, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, or 0.5 or less. Alternatively, the range of the powder can be, for example, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, or 0.5 or more. Preparation of the samples

[0048] Fig. Table 3 shows the results of the experiments. Samples No. 1 to No. 8 were prepared according to the following procedures. Production of the precursor

[0049] A raw material solution is prepared by dissolving NiSO4 in ion-exchanged water. The concentration of the raw material solution is 0.2%. It should be noted that if the target substance is, for example, "LiNi", the solution should be 0.2%. 0,90 Co 0,05 Mn 0,05 O2” is a raw material solution produced by dissolving NiSO4, CoSO4 and MnSO4 in deionized water. The mixing ratio of NiSO4, CoSO4 and MnSO4 is adjusted so that it is “Ni / Co / Mn = 90 / 5 / 5 (molar ratio)”.

[0050] A predetermined quantity of an NH3-aqueous solution is placed in a reaction vessel. The gases in the reaction vessel are replaced with nitrogen gas while the contents are stirred. By adding NaOH to the contents of the reaction vessel, the pH of the aqueous solution is adjusted to an alkaline value. The feedstock liquid is added dropwise while the temperature and pH of the aqueous solution are adjusted to be maintained within a specific range (an essentially constant value), resulting in the formation of a precipitate of TM hydroxide (Ni hydroxide). The precipitate is then subjected to dehydration and pre-combustion.

[0051] The pre-firing temperature is 120 °C to 220 °C. The pre-firing time is 4 to 10 hours. The pre-firing pressure is 0.2 MPa to 1.0 MPa.

[0052] After pre-firing, the precipitate is washed with water. A residue (TM-hydroxide) is obtained by filtration. The TM-hydroxide is dried for 12 hours at 110 °C to remove moisture. This produces a precursor (TM-hydroxide). Addition of a lithium source

[0053] A mixture is prepared by mixing the precursor (TM hydroxide) and a lithium compound (LiOH) in an agate mortar. The lithium compound can be, for example, Li₂CO₃ or the like. The ratio of the amount of Li to the total amount of TM (Ni), which is "Li / TM", is shown in the "Li / TM" column in Fig. Figure 3 illustrates this. For example, if “Li / TM” is greater than 1, a molten salt forms during firing, and the crystallization of the lithium transition metal compound oxide can be promoted. This means that the proportion of single-crystal particles in the powder can be expected to be 70% or more. Burn

[0054] The mixture undergoes heat treatment in a kiln to produce active cathode material. The firing temperature ranges from 650 °C to 1100 °C. The firing time is 5 to 15 hours.

[0055] After firing, the active cathode material is ground in an agate mortar until the particle size is 0.2 mm or less. The active cathode material is dispersed in 500 ml of pure water to form a slurry. The slurry is stirred vigorously for a predetermined time. This is called water washing. The water washing time for each sample is shown in the column "Water Washing Time" in Fig. Number 3 was indicated. No water washing was performed at number 7.

[0056] After washing with water, the slurry is filtered through filter paper and a Buchner funnel. The residue is rinsed with 500 ml of pure water to form a cake. The cake is vacuum-dried at 90 °C. After drying, the cake is crushed in an agate mortar to adjust the particle size to a predetermined level. The cake can be further crushed using a laboratory mill, another mill, or similar equipment. This process yields the active cathode material (LiNiO2). The structure and composition of Ni 2+ , Ni 3+ and Ni 4+ are determined for each sample by Rietveld analysis. For example, in Fig. 2 the XAFS spectra of No. 1 and No. 7 are shown. Evaluation

[0057] A laminate cell is manufactured. The term "laminate cell" refers to a cell in which a power-generating element is housed in a pouch made of an aluminum laminate. The configuration of the power-generating element is as follows. Cathode: active cathode material, conductive material (acetylene carbon black) Anode: Anode active material or active material of the anode (natural graphite) Electrolyte: LiPF6 (1 mol / L), EC / DMC / EMC = 3 / 4 / 3 (volume ratio)

[0058] The cathode and anode are produced by applying a slurry to the surface of a substrate (metal foil). A film applicator (with film thickness adjustment function) from Allgood Co. Ltd., for example, is used as the coating device. After application of the slurry, the resulting coating is dried for 5 minutes at 80 °C. Cycle tests were performed on the laminate cell under the following conditions. Ambient temperature: 60 °C Number of cycles: 100 Current rate: 0.3 C Voltage range: 4.25 V to 2.5 V

[0059] At a discharge rate of 1C, the cell's nominal capacity is discharged in 1 hour. 0.3C is 0.3 times 1C. The capacity conservation rate is calculated by dividing the discharge capacity in the 100th cycle by the discharge capacity in the first cycle. It is assumed that the higher the capacity conservation rate, the better the cycle performance. Experimental results

[0060] In Fig. 3, for example, refers to the description “Ni 4+ / Ni total “the proportion of the substance amount of Ni 4+ in the total amount of Ni 2+ , Ni 3+ and Ni 4+ .

[0061] As in Fig. 3 shown, improves the presence of Ni 4+ The structure tends to reflect cyclical characteristics.

[0062] Fig. 4 is a diagram showing the relationship between the molar ratio “Ni 4+ / Ni 3+ “and the capacity conservation rate. If the molar ratio “Ni 4+ / Ni 3+ “Between 0.09 and 0.35, the cycle characteristics tend to improve. In a range where the molar ratio “Ni 4+ / Ni 3+ “If the value exceeds 0.35, the formation of an inactive area in part of the structure is to be expected due to an excessive Li deficiency.

[0063] Fig. 5 is a diagram showing the relationship between the molar ratio “Ni 4+ / Ni 2+ “and the capacity conservation rate. If the molar ratio “Ni 4+ / Ni 2+ “If the value is between 2.7 and 7.2, the cycle characteristics tend to improve.” QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2008-257992 A [0002, 0004]

Claims

[1] Active cathode material for a lithium-ion secondary battery, wherein the active cathode material containing a lithium transition metal composite oxide, wherein the crystal structure of the lithium transition metal compound oxide belongs to a space group R-3m and the lithium transition metal compound oxide Ni 4+ contains. [2] Active cathode material according to claim 1, wherein the crystal structure includes a 3a site and a 3b site, the 3a position Li + and Ni 2+ contains and the 3b position Ni 4+ and Ni 3+ contains. [3] Active cathode material according to claim 2, wherein the ratio of the amount of Ni 4+ the amount of Ni 3+ The value is between 0.09 and 0.

35. [4] Active cathode material according to claim 2 or 3, wherein the ratio of the amount of substance of Ni 4+ to the amount of Ni 2+ 2.7 to 7.

2. [5] Active cathode material according to claim 2 or 3, wherein the composition of the lithium transition metal compound oxide is defined by the general formula Li z N 1-c-a Co c Mn a O d is expressed where, in the general formula, z, a, c and d satisfy the following relationships: 0.1 ≤ z ≤ 1.5, 0.5 ≤ 1-ca ≤ 1.0, 0 ≤ c ≤ 0.3, 0 ≤ a ≤ 0.3 and 1.5 ≤ d ≤ 2.1.

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