Positive electrode active material and secondary battery

Abstract

A positive electrode active material, in which a phase transition is prevented, and a secondary battery containing this positive electrode active material are provided. An unprecedented synthesis method has been developed in which lithium cobalt oxide particles are treated with a molten salt of MgF₂-LiF₂ as a reaction accelerator to facilitate the diffusion and doping of magnesium into the lithium cobalt oxide bulk and to form a stable coating layer in the particle surface region. Ex-situ XRD analysis confirms that when the modified LiCoO₂ is charged to 4.7 V, the damaging phase transition is prevented, and a novel phase emerges. The modified LiCoO₂ exhibits high electrochemical performance during high-voltage operation.This technology provides a guideline for suppressing fundamental degradation due to the phase transition and achieving ultra-high energy density from LiCoO2 positive electrodes.

Description

Background of the invention 1. Field of the invention

[0001] One embodiment of the present invention relates to an article, a method, or a manufacturing method. The present invention relates to a process, a machine, a product, or a composition of matter. One embodiment of the present invention relates to an energy storage device, a semiconductor device, a display device, a light-emitting device, a lighting device, an electronic device, each comprising a secondary battery, or a manufacturing method thereof.

[0002] It should be noted that electronic devices in this specification refer to all devices including energy storage devices, and that electro-optical devices including energy storage devices, information terminal devices including energy storage devices, and the like are all electronic devices. 2. Description of the state of the art

[0003] The emergence of portable electronic devices, such as smartphones and tablets, has significantly changed human life. The demand for high-capacity secondary batteries is continuously increasing with the continuous integration and enhancement of device functions. Thanks to its excellent energy density, lithium cobalt oxide (LiCoO2; hereinafter also referred to as LCO) remains the most promising candidate for high-capacity lithium-ion batteries widely used in portable devices. Lithium cobalt oxide has a theoretical capacity of 274 mAh / g. However, its highly delithiated state, i.e., a high cut-off voltage state of charge, degrades battery performance, which inevitably leads to the use of the latest lithium cobalt oxide-based products with a cut-off voltage of 4.47 V for full cells. The above full-cell potential corresponds to a potential of approximately 4.55 V versus Li.+ / Li and a discharge capacity of 200 mAh / g.

[0004] Factors such as side reactions on the surface of lithium cobalt oxide, cobalt dissolution, oxygen release, crystal structure changes, and crack formation lead to capacity deterioration during the charge / discharge cycle. To reduce the deterioration at high cut-off voltages, various techniques have been applied to lithium cobalt oxide and lithium cobalt oxide-containing secondary batteries, including element doping, surface coating, and electrolyte solution improvement (Non-Patent Documents 1 to 20).

[0005] Lithium cobalt oxide exhibits an α-NaFeO2 (layered rock salt) crystal structure in the R-3m space group and belongs to the O3 phase, which is characterized by an ABCABC oxygen arrangement sequence. When lithium is extracted from lithium cobalt oxide at high voltage, lithium cobalt oxide undergoes a phase transition from the O3 phase to the H1-3 phase and then to the O1 phase (note that the O1 phase represents an ABAB oxygen arrangement, and the H1-3 phase is a hybrid of the O1 phase and the O3 phase with an ABABCACABCBC oxygen arrangement). This transition brings about a structural change similar to the sliding of the CoO2 plates and creates mechanical stress in the crystal. This structural change can cause crack formation and / or deterioration of crystallinity, which can impair the performance of batteries containing lithium cobalt oxide.Thus, it is important to effectively prevent the phase transition from the O3 phase to the H1-3 phase to achieve a stable charge / discharge cycle when the cut-off voltage is 4.55 V versus Li. + / Li. In general, the phase transition and volume change caused by the electrochemical insertion / extraction of cations are common problems that lead to the deterioration of electrochemical properties. Therefore, effectively mitigating these phenomena is important not only for lithium cobalt oxide, but also for the development of other positive electrode active materials. [Reference][Non-Patent Document] [Non-patent document 1] Tukamoto, H. & West, AR Electronic conductivity of LiCoO2 and its enhancement by magnesium doping. J. Electrochem. Soc. 144, 3164-3168 (1997). [Nicht-Patentdokument 2] Bae, J. G. et al. Structural evolution of Mg-doped single-crystal LiCoO2 cathodes: importance of morphology and Mg-doping sites. ACS Appl. Mater. Interfaces 15, 7939-7948 (2023). [Nicht-Patentdokument 3] Mladenov, M., Stoyanova, R., Zhecheva, E. & Vassilev, S. Effect of Mg doping and MgO-surface modification on the cycling stability of LiCoO2 electrodes. Electrochem. Commun. 3, 410-416 (2001). [Nicht-Patentdokument 4] Jang Y. I. et al. Synthesis and characterization of LiAl y Co 1-y O2 and LiAl y Ni 1-y O2. J. Power Sources 81-82, 589-593 (1999). [Nicht-Patentdokument 5] Luo, W. & Dahn, J. R. Comparative study of Li[Co 1-z Al z ]O2 prepared by solid-state and co-precipitation methods. Electrochim. Acta 54, 4655-4661 (2009). [Nicht-Patentdokument 6] Liu, A., Li, J., Shunmugasundaram, R. & Dahn, J. R. Synthesis of Mg and Mn doped LiCoO2 and effects on high voltage cycling. J. Electrochem. Soc. 164, A1655-A1664 (2017). [Nicht-Patentdokument 7] Zhang, J. N. et al. Trace doping of multiple elements enables stable battery cycling of LiCoO2 at 4.6V. Nat. Energy 4, 594-603 (2019). [Nicht-Patentdokument 8] Kong, W. et al. Unraveling the distinct roles of Mg occupation on Li or Co sites on high-voltage LiCoO2. J. Electrochem. Soc. 168, 030528 (2021). [Nicht-Patentdokument 9] Shim, J-H., Lee, S. & Park, S. S. Effects of MgO coating on the structural and electrochemical characteristics of LiCoO2 as cathode materials for lithium ion battery. Chem. Mater. 26, 2537-2543 (2014). [Nicht-Patentdokument 10] Cho, J., Kim, Y. J. & Park, B. Novel LiCoO2 cathode material with Al2O3 coating for a Li ion cell. Chem. Mater. 12, 3788-3791 (2000). [Nicht-Patentdokument 11] Lee, J. G., Kim, B., Cho, J., Kim, Y. W. & Park, B. Effect of AlPO4-nanoparticle coating concentration on high-cutoff-voltage electrochemical performances in LiCoO2. J. Electrochem. Soc. 151, A801-A805 (2004). [Nicht-Patentdokument 12] Qian, J. et al. Electrochemical surface passivation of LiCoO2 particles at ultrahigh voltage and its applications in lithium-based batteries. Nat. Commun. 9, 4918 (2018). [Nicht-Patentdokument 13] Moon, S. H. et al. TiO2-coated LiCoO2 electrodes fabricated by a sputtering deposition method for lithium-ion batteries with enhanced electrochemical performance. RSC Adv. 9, 7903-7907 (2019). [Nicht-Patentdokument 14] Taguchi, N., Akita, T., Tatsumi, K. & Sakaebe, H. Characterization of MgO-coated-LiCoO2 particles by analytical transmission electron microscopy. J. Power Sources 328, 161-166 (2016). [Nicht-Patentdokument 15] He, Y. et al. A bi-functional strategy involving surface coating and subsurface gradient co-doping for enhanced cycle stability of LiCoO2 at 4.6 V. J. Energy Chem. 77, 553-560 (2023). [Nicht-Patentdokument 16] Orikasa, Y. et al. Origin of surface coating effect for MgO on LiCoO2 to improve the interfacial reaction between electrode and electrolyte. Adv. Mater. Interfaces 1, 1400195 (2014). [Nicht-Patentdokument 17] Yang, X. et al. Pushing lithium cobalt oxides to 4.7 V by latticematched interfacial engineering. Adv. Energy Mater. 12, 2200197 (2022). [Nicht-Patentdokument 18] Takahashi, Y. et al. Structure and electron density analysis of electrochemically and chemically delithiated LiCoO2 single crystals. J. Solid State Chem. 180, 313-321 (2007). [Nicht-Patentdokument 19] Chen, Z., Lu, Z. & Dahn, J. R. Staging phase transitions in Li x CoO2. J. Electrochem. Soc. 149, A1604-A1609 (2002). [Non-Patent Document 20] Van der Ven, A., Aydinol, MK, Ceder, G., Kresse, G. & Hafner, J. First-principles investigation of phase stability in Li x CoO2. Phys. Rev. B 58, 2975-2987 (1998). [Non-Patent Document 21] Momma, K. & Izumi, F. VESTA3 for three-dimensional visualization of crystal, volumetric and morphology data. J. Appl. Crystallogr. 44, 1272-1276 (2011). Summary of the invention

[0006] Magnesium doping and magnesium coating can improve the electrochemical performance of lithium cobalt oxide at high voltage. Recent research has shown that doping with Mg 2+Ions into the lithium sites of lithium cobalt oxide can improve its electrochemical performance by acting as pillars between adjacent CoO2 plates (Non-Patent Documents 14 and 17, etc.). However, studies have failed to achieve sufficient electrochemical reversibility of lithium intercalation / exclusion during high-voltage charging.

[0007] In view of the above, an object of one embodiment of the present invention is to provide a positive electrode active material in which a phase transition due to charge and discharge occurs at a cut-off voltage higher than 4.55 V (versus Li + / Li). Another object of an embodiment of the present invention is to provide a positive electrode active material or a composite oxide that prevents a reduction in discharge capacity due to charge / discharge cycles. Another object of an embodiment of the present invention is to provide a positive electrode active material or a composite oxide that has a crystal structure that is unlikely to be broken by repeated charge and discharge. Another object of an embodiment of the present invention is to provide a positive electrode active material or a composite oxide with high discharge capacity. Another object of an embodiment of the present invention is to provide a secondary battery with high safety or high reliability.

[0008] Another object of an embodiment of the present invention is to provide a positive electrode active material, a composite oxide, an energy storage device or a manufacturing method thereof.

[0009] It should be noted that the description of these objects does not preclude the existence of further objects. In one embodiment of the present invention, it is unnecessary to fulfill all of these objects. Further objects can be derived from the explanation of the description, the drawings, and the claims.

[0010] To solve any of the above problems, the present inventors propose, as an embodiment of the present invention, a method for effectively incorporating magnesium into lithium cobalt oxide through a treatment using molten fluoride salt as an additive. Furthermore, the introduction of nickel and aluminum as additive elements further enhances electrochemical stability.

[0011] In the surface portion of the lithium cobalt oxide after synthesis, a magnesium-rich rock salt structure develops, and a coherent bond to the bulk material is formed. Ex situ X-ray diffraction (XRD) analysis can prove that the lithium cobalt oxide of one embodiment of the present invention undergoes a phase transition into a compressed O3 phase (referred to as "O3' phase" in this specification and the like) at 4.7 V without undergoing a transformation to the H1-3 phase. The lithium cobalt oxide of one embodiment of the present invention achieves excellent results: capacity retentions of 96.4% and 72.7% after 100 cycles at cutoff voltages of 4.6 V and 4.7 V, respectively.

[0012] By using a mixture of a fluorine-substituted organic solvent and propane sultone as the solvent of an electrolyte solution, a secondary battery can exhibit higher charge / discharge cycle performance even at a high cut-off voltage.

[0013] One embodiment of the present invention is a positive electrode active material containing lithium cobalt oxide to which magnesium, fluorine, nickel, and aluminum are added. The positive electrode active material in a discharge state has a layered rock-salt crystal structure belonging to an R-3m space group. The layered rock-salt crystal structure in the discharge state has a c-lattice parameter greater than 14.055 Å and a goodness-of-fit (GOF) of less than or equal to 1.4 when fitted as LiCoO2 with the R-3m space group and subjected to Rietveld refinement. The positive electrode active material includes a surface portion and a bulk region. The surface portion includes a magnesium-rich rock-salt structural region. The magnesium-rich rock-salt structural region is coherently bonded to the bulk region.

[0014] In the above, the c-lattice parameter is preferably less than 14.060 Å.

[0015] Another embodiment of the present invention is a positive electrode active material containing lithium cobalt oxide to which magnesium, fluorine, nickel, and aluminum are added. A narrow-scan spectrum of Mg 1s of the positive electrode active material obtained by X-ray photoelectron spectroscopy exhibits a maximum intensity at a binding energy between a binding energy at which a narrow-scan spectrum of Mg 1s of magnesium oxide obtained by X-ray photoelectron spectroscopy exhibits a maximum intensity and a binding energy at which a narrow-scan spectrum of Mg 1s of magnesium fluoride obtained by X-ray photoelectron spectroscopy exhibits a maximum intensity.

[0016] In the above, the narrow-scan spectrum of Mg 1s of the positive electrode active material obtained by X-ray photoelectron spectroscopy preferably has the maximum intensity at a binding energy of greater than 1303.3 eV and less than 1306.3 eV.

[0017] When a cross section of a particle of the above positive electrode active material is analyzed with an electron beam microanalyzer, it is preferable that Mg / Co (atomic ratio) is greater than or equal to 0.005 and less than or equal to 0.015, and Al / Co (atomic ratio) is less than or equal to 0.005.

[0018] One embodiment of the present invention is a positive electrode active material containing lithium cobalt oxide to which magnesium, fluorine, nickel, and aluminum are added. The positive electrode active material in a discharge state has a layered rock salt crystal structure belonging to an R-3m space group. When a charge / discharge cycle test is conducted in a 25°C environment on a cell in which the positive electrode active material is used for a positive electrode, lithium metal is used for a negative electrode, and a mixture of lithium hexafluorophosphate, ethylene carbonate, and diethyl carbonate with 2 wt.-% vinylene carbonate is used as the electrolyte solution, and then the positive electrode in a discharge state is analyzed by powder X-ray diffraction using a Cu-Kα1 radiation, a peak with a half-width of less than or equal to 0.08° appears within a 2θ range of 18.7° to 19.0°, and a peak with a half-width of less than or equal to 0.12° appears within a 2θ range of 45.0° to 45.3°. In the charge / discharge cycle test, a charge / discharge cycle is repeated 100 times, in which a constant current charge is performed at a current value of 0.5 C (note that 1 C = 200 mA / g) up to a voltage of 4.7 V, a constant voltage charge is performed until the current value reaches 0.05 C, a rest period of 10 minutes is provided, a constant current discharge is performed at a current value of 0.5 C up to a voltage of 2.5 V, and then a rest period of 10 minutes is provided.

[0019] In the above, it is preferable that the volume energy density calculated using the true density of the positive electrode active material is higher than or equal to 4250 Wh / L and the gravimetric energy density calculated using the true density of the positive electrode active material is higher than or equal to 865 Wh / Kg.

[0020] Another embodiment of the present invention is a secondary battery containing the above-described positive electrode active material and an electrolyte solution, and wherein the electrolyte solution contains 1 M LiPF6 dissolved in FEC / MTFP in a volume ratio of 2:8 with 5 wt% PS.

[0021] According to one embodiment of the present invention, a positive electrode active material can be provided in which a phase transition due to charge and discharge occurs at a cut-off voltage higher than 4.55 V (versus Li + / Li). According to another embodiment of the present invention, there can be provided a positive electrode active material or a composite oxide that prevents a reduction in discharge capacity due to charge and discharge cycles. According to another embodiment of the present invention, there can be provided a positive electrode active material or a composite oxide that has a crystal structure that is unlikely to be broken by repeated charge and discharge. According to another embodiment of the present invention, there can be provided a positive electrode active material or a composite oxide with high discharge capacity. According to another embodiment of the present invention, there can be provided a secondary battery with high safety or high reliability.

[0022] According to another embodiment of the present invention, a positive electrode active material, a composite oxide, an energy storage device, or a manufacturing method thereof can be provided.

[0023] It should be noted that the description of these effects does not preclude the existence of further effects. An embodiment of the present invention does not necessarily have to exhibit all of the effects. Further effects will become apparent from and can be derived from the explanation of the description, the drawings, the claims, and the like. Short description of the drawings

[0024] In the accompanying drawings: Fig. 1 is a schematic view illustrating a method for producing a positive electrode active material of an embodiment of the present invention, and a surface and a bulk of the positive electrode active material; Fig. 2 is a flowchart illustrating a manufacturing process of a positive electrode active material of one embodiment of the present invention; Fig. 3A and Fig. 3B are graphs showing DSC results; Fig. 4A to Fig. 4C are graphs showing DSC results; Fig. 5A and Fig. 5B are graphs showing DSC results; Fig. 6 is a schematic view illustrating phase changes in a reference positive electrode material and a positive electrode active material of an embodiment of the present invention; Fig. 7A and Fig. 7B represent calculation models; Fig. 8A to Fig. 8C illustrates a crystal structure of a positive electrode active material of one embodiment of the present invention, and Fig. 8D and Fig. 8E show examples of a lithium arrangement; Fig. 9A to Fig. 9E show examples of a lithium arrangement; Fig. Figure 10 shows an example of a lithium arrangement; Fig. 11A to Fig. 11C show examples of a lithium arrangement; Fig. Figure 12 shows an example of a lithium arrangement; Fig. 13A to Fig. 13D each illustrates a positive electrode of an embodiment of the present invention; Fig. 14A and Fig. 14B illustrates lithium-ion batteries of embodiments of the present invention; Fig. 15A to Fig. 15C illustrates a lithium-ion battery of one embodiment of the present invention; Fig. 16A to Fig. 16D illustrates a lithium-ion battery and energy storage system of embodiments of the present invention; Fig. 17A to Fig. 17C illustrates a lithium-ion battery of one embodiment of the present invention; Fig. 18A to Fig. 18C illustrates a lithium-ion battery of one embodiment of the present invention; Fig. 19A to Fig. 19C illustrate an electric vehicle of an embodiment of the present invention; Fig. 20A to Fig. 20D illustrate transport vehicles of embodiments of the present invention; Fig. 21A to Fig. 21C illustrate a motorcycle and the like of embodiments of the present invention; Fig. 22A to Fig. 22D illustrate electronic devices and the like of embodiments of the present invention; Fig. 23A to Fig. 23D show examples of a space facility; Fig. 24A to Fig. 24C shows XRD patterns of reference positive electrode active materials and a positive electrode active material of an embodiment of the present invention; Fig. 25A to Fig. 25J shows SEM images, HAADF-STEM images, and nanobeam electron diffraction images of a reference positive electrode active material and a positive electrode active material of an embodiment of the present invention; Fig. 26A to Fig. 26J shows SEM images and SEM-EDX mapping images of a positive electrode active material of one embodiment of the present invention in its synthesis steps; Fig. 27A to Fig. 27F shows SEM images and SEM-EDX mapping images of a positive electrode active material of one embodiment of the present invention in its synthesis steps; Fig. 28 shows XPS spectra of a reference positive electrode active material and a positive electrode active material of an embodiment of the present invention; Fig. 29A and Fig. 29B shows XPS spectra of a positive electrode active material of one embodiment of the present invention in its synthesis steps; Fig. 30A to Fig. 30C are STEM-EDX element mapping images of a surface portion of a positive electrode active material of one embodiment of the present invention and diagrams showing results of STEM-EDX line analysis of the surface portion; Fig. 31 shows STEM-EDX element mapping images of a surface portion of a positive electrode active material of one embodiment of the present invention; Fig. 32A and Fig. 32B shows the charge / discharge cycle performance of a half cell containing a reference positive electrode active material and a half cell containing a positive electrode active material of an embodiment of the present invention; Fig. 33A and Fig. 33B are diagrams showing charge / discharge curves and rate performance of a half cell containing a reference positive electrode active material and a half cell containing a positive electrode active material of an embodiment of the present invention; Fig. 34 is a graph showing the rate performance of a half cell containing a reference positive electrode active material and a half cell containing a positive electrode active material of an embodiment of the present invention; Fig. 35A and Fig. 35B are diagrams showing the charge / discharge cycle performance and charge / discharge curves of a half cell containing a reference positive electrode active material and a half cell containing a positive electrode active material of an embodiment of the present invention; Fig. 36A and Fig. 36B are graphs showing the charge / discharge cycle performance of full cells containing a positive electrode active material of one embodiment of the present invention; Fig. 37A to Fig. 37C show ex-situ XRD patterns of a positive electrode in a discharge state containing a reference positive electrode active material and a positive electrode in a discharge state containing a positive electrode active material of an embodiment of the present invention; Fig. 38A to Fig. 38H are SEM images of a reference positive electrode active material and a positive electrode active material of an embodiment of the present invention after cycling; Fig. 39A and Fig. 39B show the cycling performance of positive electrode active materials obtained from SEM images; Fig. 40A to Fig. 40D shows HAADF-STEM images and nanobeam electron diffraction patterns of surface portions of a reference positive electrode active material and a positive electrode active material of an embodiment of the present invention after charge / discharge cycle tests; Fig. 41A to Fig. 41C show ex-situ XRD patterns of positive electrodes in charge states containing a reference positive electrode active material; Fig. 42A to Fig. 42C show ex-situ XRD patterns of positive electrodes in charge states containing a positive electrode active material of one embodiment of the present invention; Fig. 43A to Fig. 43C show ex-situ XRD patterns of positive electrodes in charge states containing a reference positive electrode active material; Fig. 44A to Fig. 44C show ex-situ XRD patterns of positive electrodes in charge states containing a positive electrode active material of one embodiment of the present invention; Fig. 45 is a graph showing dQ / dV curves of a positive electrode active material of one embodiment of the present invention during charge and discharge; Fig. 46A to Fig. 46C show ex-situ XRD patterns of positive electrodes in a charged state containing reference positive electrode active materials and a positive electrode in a charged state containing a positive electrode active material of one embodiment of the present invention; Fig. 47A and Fig. 47B are graphs showing the charge / discharge cycle performance of half cells containing reference positive electrode active materials and a half cell containing a positive electrode active material of one embodiment of the present invention; Fig. 48A to Fig. 48C are diagrams showing ex-situ XRD patterns of positive electrodes in a charged state containing reference positive electrode active materials and a positive electrode in a charged state containing a positive electrode active material of one embodiment of the present invention; Fig. 49A and Fig. 49B are diagrams showing the charge / discharge cycle performance of half cells containing reference positive electrode active materials and a half cell containing a positive electrode active material of one embodiment of the present invention; Fig. 50A and Fig. 50B are graphs showing the charge / discharge cycle performance of half-cells containing reference positive electrode active materials; Fig. 51A and Fig. 51B are diagrams showing the charge / discharge cycle performance of half cells containing reference positive electrode active materials and a half cell containing a positive electrode active material of one embodiment of the present invention; Fig. 52A and Fig. 52B are diagrams showing the charge / discharge cycle performance of half cells containing reference positive electrode active materials and a half cell containing a positive electrode active material of one embodiment of the present invention; Fig. 53 is a graph showing the volume energy densities and gravimetric energy densities of reference positive electrode active materials and a positive electrode active material of an embodiment of the present invention; Fig. 54 shows ex-situ XRD patterns of positive electrodes in discharge states containing a positive electrode active material of one embodiment of the present invention; Fig. 55A and Fig. 55B shows ex-situ XRD patterns of positive electrodes in discharge states containing a positive electrode active material of one embodiment of the present invention; Fig. 56 shows ex-situ XRD patterns of positive electrodes in charge states containing a positive electrode active material of one embodiment of the present invention; and Fig. 57A and Fig. 57B show ex-situ XRD patterns of positive electrodes in charge states containing a positive electrode active material of one embodiment of the present invention. Detailed description of the invention

[0025] Examples of embodiments for implementing the present invention will be described below with reference to the drawings and the like. Note that the present invention should not be construed as limited to the examples of embodiments given below. Embodiments for implementing the invention may be changed as long as they do not deviate from the spirit of the present invention.

[0026] In the drawings, the size, layer thickness, or area is exaggerated in some cases for clarity. Therefore, the size, layer thickness, or area is not limited to the proportions shown.

[0027] The ordinal numbers such as "first" and "second" in this specification and the like are used for convenience and do not indicate the order of steps or the order of superimposed layers. Therefore, for example, an appropriate description can be made even if "first" is replaced with "second," "third," or the like. Furthermore, the ordinal numbers in this specification and the like are not necessarily the same as those used to specify an embodiment of the present invention.

[0028] In this description and the like, a space group is represented using the short symbol of the international notation (or the Hermann-Mauguin notation). In addition, the Miller index is used to express crystal planes and crystal orientations. In crystallography, a prime is placed over a number to express space groups, crystal planes, and crystal orientations; in this description and the like, in some cases, due to formatting constraints, crystal planes, crystal orientations, and space groups are represented by placing a minus sign (-) in front of a number instead of placing a prime over the number.Furthermore, a single direction showing one orientation in a crystal is represented by "[ ]", a set direction showing all equivalent orientations is represented by "< >", a single plane showing a crystal plane is represented by "( )", and a set plane having equivalent symmetry is represented by "{}". A trigonal system represented by the R-3m space group is generally represented by a hexagonal composite lattice for easy understanding of the structure. In some cases, not only (hkl) but also (hkil) are used as the Miller index. Here, i -(h + k). In this specification and the like, a crystal plane or the like in the R-3m space group is represented using a hexagonal composite lattice unless otherwise specified.

[0029] In this specification and the like, depending on an analysis method or the like, the description including a simple term "positive electrode active material" refers to a plurality of positive electrode active material particles in some cases, and to a single positive electrode active material particle in other cases. For example, when the description refers to line analysis using a scanning transmission electron microscope-energy dispersive X-ray (STEM-EDX) detector, STEM-electron energy-loss spectroscopy (STEM-EELS), or electron diffraction, unless otherwise specified, a single positive electrode active material particle is referred to.In contrast, when the description refers to X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), various types of mass spectroscopy, or the like, a plurality of positive electrode active material particles are indicated unless otherwise specified.

[0030] In this description and the like, particles are not necessarily spherical (with a circular cross-section). Other examples of particle cross-sectional shapes include an ellipse, a rectangle, a trapezoid, a triangle, a quadrilateral with rounded corners, and an asymmetric shape. A particle may have an indeterminate shape. Furthermore, a simple term "particle" includes a primary particle and a secondary particle.

[0031] In the case where the characteristics of positive electrode active material particles are described, not all of the particles necessarily exhibit the characteristics. For example, if 50% or more, preferably 70% or more, more preferably 90% or more of three or more randomly selected particles of a positive electrode active material exhibit the advantageous features described below, it can be said that an effect of improving the properties of the positive electrode active material and a secondary battery containing the positive electrode active material is sufficiently obtained.

[0032] The distribution of an element refers to the range in which the element is successively sampled by a successive analysis procedure, as long as the sampled value is not noise. The range in which the element is successively sampled, as long as the sampled value is not noise, can be recast, for example, as the range in which the element is sampled each time the analysis is performed.

[0033] In this specification and the like, an additive element may be reformulated as part of a raw material or a mixture.

[0034] The theoretical capacity of a positive electrode active material refers to the amount of current obtained when all the lithium that can be incorporated into or removed from the positive electrode active material is removed. For example, the theoretical capacity of LiCoO2 is 274 mAh / g, the theoretical capacity of LiNiO2 is 275 mAh / g, and the theoretical capacity of LiMn2O4 is 148 mAh / g.

[0035] The remaining amount of lithium that can be incorporated into and removed from a positive electrode active material is represented by x in a composition formula, e.g., Li x MO2 (here, M is one or more selected from cobalt, nickel, and manganese). In the case of a positive electrode active material in a secondary battery, x can be represented by (theoretical capacity - charge capacity) / theoretical capacity. For example, if a secondary battery containing Li xMO2 as positive electrode active material is charged to 219.2 mAh / g, the positive electrode active material can be charged by Li 0,2 MO2, ie x = 0.2. It should be noted that “x in Li x For example, "MO2 is small" means 0.1 < x ≤ 0.24. Furthermore, the amount of lithium leached from the positive electrode active material with respect to the theoretical capacity is sometimes represented by a depth of charge. In this specification and the like, the depth of charge is equal to 1 - x.

[0036] For example, lithium cobalt oxide to be used for a positive electrode, which has been properly synthesized and almost satisfies the stoichiometric ratio, is LiCoO2 with x of 1. Also, in a secondary battery after completion of discharge, it can be assumed that lithium cobalt oxide therein is LiCoO2 with x of 1. Here, "completion of discharge" means that, for example, the voltage at a current of 100 mA / g or lower is 3.0 V or 2.5 V or lower.

[0037] The charging capacity and / or discharging capacity used to calculate x in Li xCoO2 is used, it is preferable to measure it under conditions where there is no or little influence of a short circuit and / or decomposition of an electrolyte solution, etc. For example, data from a secondary battery that exhibits a sudden change in capacity, which is assumed to be due to a short circuit, must not be used to calculate x.

[0038] The space group of a crystal structure is identified by XRD, electron diffraction, neutron diffraction, or the like. Therefore, in this description and the like, "belonging to a space group" or "being a space group" can be rephrased as "being identified as a space group."

[0039] Furthermore, if the arrangement of anions resembles a cubic close-packed structure, the arrangement can also be considered a cubic close-packed structure. The arrangement of anions forming the cubic close-packed structure refers to a state in which anions in the second layer are located exactly above voids between anions packed in the first layer, and anions in the third layer are arranged at positions that are exactly above voids between the anions in the second layer and not exactly above the anions in the first layer. Consequently, anions do not necessarily form a cubic lattice structure. Actual crystals always have a defect, and therefore analytical results do not necessarily agree with theory.For example, in an electron diffraction pattern or a fast Fourier transform (FFT) pattern of a TEM image, or the like, a point may appear in a position different from a theoretical position. For example, anions can be considered to form a cubic close-packed structure if the orientation deviation from a theoretical position is 5° or less, or 2.5° or less.

[0040] A positive electrode active material to which an additive element for increasing conductivity and / or an additive element for stabilizing a crystal structure is added is sometimes referred to as a composite oxide, a positive electrode part, a positive electrode material, a positive electrode part for a secondary battery, or the like. In this specification and the like, the positive electrode active material of one embodiment of the present invention preferably contains a compound. In this specification and the like, the positive electrode active material of one embodiment of the present invention preferably contains a composition. In this specification and the like, the positive electrode active material of one embodiment of the present invention preferably contains a complex.

[0041] The voltage of a positive electrode generally increases with the increase in the charging voltage of a secondary battery. The positive electrode active material of one embodiment of the present invention has a stable crystal structure even at high voltages. The stable crystal structure of the positive electrode active material in a charged state can prevent a reduction in charging / discharging capacities due to repeated charging and discharging.

[0042] Note that unless otherwise specified, the description assumes that materials (such as a positive electrode active material, a negative electrode active material, an electrolyte, and a separator) of a secondary battery have not deteriorated. A reduction in discharge capacity due to aging treatment and burn-in treatment during the manufacturing process of a secondary battery is not considered deterioration. For example, a state where the discharge capacity is higher than or equal to 97% of the rated capacity of a lithium-ion secondary battery cell and an assembled lithium-ion secondary battery (hereinafter referred to as a lithium-ion secondary battery) can be considered a non-deteriorated state. The rated capacity meets the Japan Industrial Standard (JIS C 8711:2019) in the case of a lithium-ion secondary battery for a portable device.The rated capacities of other lithium-ion secondary batteries meet the above-described JIS, JIS for electric vehicle powertrains, industrial uses, and the like, standards established by the International Electrotechnical Commission (IEC), and the like.

[0043] In this specification and the like, in some cases, materials included in a secondary battery that have not deteriorated are referred to as initial products or materials in an initial state, and materials that have deteriorated (have a discharge capacity of lower than 97% of the rated capacity of the secondary battery) are referred to as products in use, materials in a used state, already used products, or materials in an already used state. (Embodiment 1)

[0044] In this embodiment, features of a manufacturing method of a positive electrode active material of an embodiment of the present invention and the positive electrode active material are described with reference to Fig. 1, Fig. 2, Fig. 3A and Fig. 3B, Fig. 4A to Fig. 4C, Fig. 5A and Fig. 5B, Fig. 6, Fig. 7A and Fig. 7B, Fig. 8A to Fig. 8E, Fig. 9A to Fig. 9E, Fig. 10, Fig. 11A to Fig. 11C and Fig. 12. Note that, for convenience of designation, the positive electrode active material of one embodiment of the present invention is referred to in some cases in the drawings as MFNA-LCO, which includes the initial letters of the names of the additive elements.

[0045] The positive electrode active material of one embodiment of the present invention contains lithium cobalt oxide to which magnesium, fluorine, nickel, and aluminum are added. Note that the composition of the lithium cobalt oxide (LCO or LiCoO2) is not strictly limited to Li:Co:O = 1:1:2.

[0046] The positive electrode active material of one embodiment of the present invention has a layered rock-salt crystal structure belonging to the R-3m space group in a discharge state. This crystal structure has a c-lattice parameter of greater than 14.055 Å and less than 14.060 Å. Note that in the crystal structure analysis of the positive electrode active material in a discharge state, GOF is preferably less than or equal to 2.0, more preferably less than or equal to 1.4.

[0047] To maintain a neutrally charged state even during the intercalation and de-intercalation of lithium ions, a positive electrode active material of a lithium-ion secondary battery must contain a transition metal related to an oxidation-reduction reaction. Preferably, the positive electrode active material of one embodiment of the present invention mainly contains cobalt as the transition metal related to an oxidation-reduction reaction. Using cobalt at higher than or equal to 95 atomic%, preferably higher than or equal to 98 atomic%, more preferably higher than or equal to 99 atomic%, as the transition metal contained in the positive electrode active material leads to many advantages, such as relatively simple synthesis, easy handling, and excellent cycle performance, which is preferable.

[0048] The positive electrode active material of one embodiment of the present invention comprises a surface portion and a bulk portion. The positive electrode active material has a crystal grain boundary in some cases.

[0049] In this specification and the like, the surface portion of the positive electrode active material refers to a region extending from the surface after the bulk in a perpendicular direction or a substantially perpendicular direction less than or equal to 10 nm. The surface portion therefore includes the surface. Note that "substantially perpendicular" refers to a state where an angle is greater than or equal to 80° and less than or equal to 100°. A plane resulting from a closed gap and / or a crack can also be regarded as a surface. The surface portion can also be reformulated as the vicinity of a surface, the region in the vicinity of a surface, or the shell, and includes the outermost surface.

[0050] The bulk refers to a region deeper than the surface portion of the positive electrode active material. The bulk can be reformulated as the inner portion or core.

[0051] A crystal grain boundary refers, for example, to a portion where particles of a positive electrode active material adhere to each other, or a portion where a crystal orientation changes within a positive electrode active material, that is, a portion where a repetition of bright lines and dark lines is discontinuous in a STEM image or the like, a portion having a large number of crystal defects, a portion with a disordered crystal structure, or the like. A crystal defect refers to a defect that can be observed in a cross-sectional transmission electron microscope (TEM) image, a cross-sectional STEM image, or the like, that is, a structure containing another atom between lattices, a void, or the like. A crystal grain boundary can be regarded as a surface defect.The vicinity of a crystal grain boundary refers to a region extending from the crystal grain boundary by less than or equal to 10 nm.

[0052] The positive electrode active material of one embodiment of the present invention contains magnesium, fluorine, nickel, and aluminum, which are additive elements, in the surface portion. Furthermore, the acquisition amounts of the additive elements in the surface portion are preferably higher than those in the bulk.

[0053] In the case where the positive electrode active material of one embodiment of the present invention has a crystal grain boundary, at least some of the additive elements, namely magnesium, fluorine, nickel, and aluminum, are preferably contained in the vicinity of the crystal grain boundary. That is, the detection amount(s) of the additive element(s) in the vicinity of the crystal grain boundary is preferably larger than those in the surface portion and in a portion other than the vicinity of the crystal grain boundary.

[0054] In the bulk positive electrode active material of one embodiment of the present invention, the preferred amount differs among the additive elements. Magnesium is preferably present in a small amount in the bulk to prevent a phase transition described later. Nickel is also preferably present in a small amount in the bulk. In contrast, fluorine and aluminum are preferably absent in the middle portion of the bulk or present in such small amounts that they cannot be detected. This is because the additive elements necessary to prevent phase transition also have adverse effects, such as a reduction in crystallinity and charge / discharge capacities, when present in excessive amounts in the bulk.

[0055] Therefore, when the bulk particle of the positive electrode active material of one embodiment of the present invention is subjected to cross-sectional analysis using an electron probe microanalyzer (EPMA), Mg / Co (atomic ratio) is preferably greater than or equal to 0.005 and less than or equal to 0.015. Furthermore, Ni / Co (atomic ratio) is preferably greater than or equal to 0.002 and less than or equal to 0.05, more preferably greater than or equal to 0.03 and less than or equal to 0.01.

[0056] In the bulk, F / Co (atomic ratio) is preferably less than or equal to 0.01, and fluorine is more preferably not detected. Al / Co (atomic ratio) is preferably less than or equal to 0.005, and aluminum is more preferably not detected.

[0057] Lithium cobalt oxide is susceptible to thermal decomposition in air above 950 °C. However, magnesium oxide (MgO), with a melting point of 2852 °C, is exceptionally thermally stable. When lithium cobalt oxide and magnesium oxide powder are heated below the decomposition temperatures of lithium cobalt oxide, the solid-state reactions tend to be uneven and slow during conventional mixing and baking processes. Therefore, it is difficult to introduce magnesium into lithium cobalt oxide using conventional doping and coating techniques.

[0058] In view of this, the present inventors decided to use molten fluoride salts to facilitate the diffusion and doping of magnesium into the lithium cobalt oxide bulk. This method involves coating the surface portion of lithium cobalt oxide particles with excess magnesium simultaneously with the diffusion of magnesium into the bulk.

[0059] Fig. Figure 1 is a schematic view showing a method for manufacturing the positive electrode active material of one embodiment of the present invention using fluorides as reaction accelerators, as well as the surface and bulk of the positive electrode active material. The surface portion includes a magnesium-rich rock salt structural region, and the rock salt structural region is coherently bonded to the bulk region. The schematic view of the coherent bonding structure was drawn by VESTA (Non-Patent Document 21). The use of fluorides as reaction accelerators enables effective diffusion and doping of the additive element, such as magnesium, into the surface portion of lithium cobalt oxide particles and the bulk.

[0060] The fluorides used as reaction accelerators are preferably fluorides of typical metal elements. For example, lithium fluoride (LiF), sodium fluoride (NaF), potassium fluoride (KF), and a mixture thereof are preferred because these materials have a melting point close to and lower than the decomposition temperature of lithium cobalt oxide, and they offer a high degree of safety. With regard to use in lithium-ion batteries, lithium fluoride is particularly preferred as the fluoride used as a reaction accelerator.

[0061] Fig. Figure 2 is a flowchart illustrating an example of a method for producing the positive electrode active material of one embodiment of the present invention. The six samples with asterisks in the flowchart were analyzed by XPS and SEM-EDX in Example 1. Note that the present invention is not limited to the method in Fig. 2 is limited. For example, any temperature and time are acceptable as long as they are sufficient to melt the fluorides used as reaction accelerators and do not decompose lithium cobalt oxide. The optimal ranges of heating temperature and time may depend on the particle diameter of lithium cobalt oxide as the starting material (hereinafter also referred to as the original LCO). The addition of the additive elements may be performed at a different time or may be performed multiple times. The timing of addition may vary depending on the elements. < <dsc>>

[0062] Here, the results of differential scanning calorimetry (DSC) measurements in Fig. 3A and Fig. 3B, Fig. 4A to Fig. 4C and Fig. 5A and Fig. 5B. DSC measurements were performed using Thermo Plus (EVO2 DSC8271, Rigaku) ​​at a heating rate of 20 °C / min from room temperature to 1000 °C. An alumina shell (ϕ 5 mm × 2.5 mm) and Al2O3 powder were used as a reference.

[0063] Fig. Figure 3A shows the DSC result of the sample in which MgF2 and LiF powders were mixed in a molar ratio of 3:1. The initial melting temperature is 731.4 °C, while the peak melting temperature is 739.3 °C. This result indicates the eutectic point of MgF2 and LiF. Consequently, when exposed to the temperature suggested in this specification and the like (e.g., 900 °C), these compounds undergo a transition from a solid phase to a liquid phase and are transformed into a molten salt.

[0064] Fig. Figure 3B shows the DSC result of the Mg(OH)2 powder. The initial and maximum decomposition temperatures are 357.6 °C and 418.8 °C, respectively.

[0065] Fig. Figure 4A shows the DSC measurement result of original LCO powder. Fig. Figure 4B shows the DSC measurement result of the sample in which original LCO, LiF and MgF2 powder were mixed in a molar ratio of 1:0.003:0.01. Fig. Figure 4C is an enlarged view of the area covered by the dotted rectangle in Fig. 4B. The initial reaction temperature is 778.6 °C and the peak reaction temperature is 814.5 °C. These temperatures are slightly lower than the decomposition temperature of lithium cobalt oxide and higher than the eutectic point of MgF2 and LiF (731.4 °C), which is Fig. 3A. This indicates that the surface of lithium cobalt oxide particles reacts with the magnesium-containing fluoride liquid.

[0066] Fig. Figure 5A shows the DSC result of the sample in which original LCO and Mg(OH)2 powder were mixed in a molar ratio of 1:0.01. Fig. Figure 5B is an enlarged view of the area enclosed by the dotted rectangle in Fig. 5A. The initial reaction temperature is 345.0 °C, while the peak reaction temperature is 363.9 °C.

[0067] As in Fig. 5A and Fig. As shown in Figure 5B, an endothermic peak was observed at 363.9 °C in the DSC result of the mixture of original LCO and Mg(OH)2. This temperature was almost equal to the decomposition temperature of only Mg(OH)2 (357.6 °C) observed in Fig. 3B, and no peaks were observed indicating eutectic points of pristine LCO and Mg(OH)2.

[0068] During the heating process in the Fig. In the manufacturing process shown in Figure 2, the surface portion of lithium cobalt oxide particles and the molten fluoride salt are partially melted, allowing effective diffusion and doping of the additive element, such as magnesium. As a result, a phase change accompanied by the sliding of the CoO2 plates is prevented, allowing the positive electrode active material of one embodiment of the present invention in a highly delithiated state to have a structure different from that of the original LCO in a highly delithiated state.

[0069] Fig. Figure 6 is a diagram illustrating phase changes in the original LCO and the positive electrode active material of one embodiment of the present invention. It is known that LCO changes phase when charged up to 4.55 V (x < 0.3 in Li x CoO2) undergoes a phase transition from the O3 phase to the H1-3 phase. This phase transition entails a structural change similar to the sliding of the CoO2 plates. The volume difference between the two crystal structures is also large. When the H1-3 phase in a charged state and lithium cobalt oxide (O3 phase) in a discharged state contain the same number of cobalt atoms, these structures exhibit a volume difference of greater than 3.5%, typically greater than or equal to 3.9%.

[0070] In contrast, in the positive electrode active material of one embodiment of the present invention, in a highly delithiated state, the presence of magnesium substituted in the lithium layer provides structural support, preventing the sliding of the CoO2 plates and preventing the phase transition from the O3 phase to the H1-3 phase. Furthermore, the sliding is likely initiated at the surface of LCO and could therefore be suppressed by the presence of the magnesium-rich rock salt region in the surface portion of the positive electrode active material of one embodiment of the present invention.

[0071] The positive electrode active material of one embodiment of the present invention is tested at 4.7 V (versus Li + / Li) undergoes a phase transition into a phase referred to in this specification and the like as O3' phase, without being converted into an H1-3 phase.

[0072] The crystal structure of the O3' phase belongs to the R-3m space group, and in the unit cell of the crystal structure of the O3' phase, the coordinates of cobalt and oxygen can be represented by Co (0, 0, 0.5) and O (0, 0, x) within the range of 0.20 ≤ x ≤ 0.22. In the unit cell, the α lattice parameter preferably satisfies 2.798 ≤ a ≤ 2.838 (Å), more preferably 2.808 ≤ a ≤ 2.828 (Å), typically a = 2.818 (Å). The c-lattice parameter preferably satisfies 13.566 ≤ c ≤ 13.766 (Å), more preferably 13.636 ≤ c ≤ 13.696 (Å), typically c = 13.666 (Å).

[0073] In the O3' phase, an ion of cobalt, nickel, magnesium, or the like occupies a site coordinated to six oxygen atoms. Note that a light element, such as lithium or magnesium, sometimes occupies a site coordinated to four oxygen atoms.

[0074] The O3 phase in a discharge state and the O3' phase containing the same number of cobalt atoms have a volume difference of 2.5% or less, in particular 2.2% or less, typically 1.8%.

[0075] Since the positive electrode active material of one embodiment of the present invention is prepared using fluorides as reaction accelerators, fluorine is preferably detected during surface analysis of the positive electrode active material. For example, fluorine is preferably detected by X-ray photoelectron spectroscopy (XPS). Furthermore, a factor indicating that the fluorides have passed through the molten salt stage is preferably the binding energy of the positive electrode active material of one embodiment of the present invention, which is different from that of the compound used as the material.

[0076] For example, a narrow-scan spectrum of Mg 1s of the positive electrode active material of one embodiment of the present invention obtained by XPS preferably has a maximum value at a binding energy different from the binding energies at which the spectra of magnesium oxide and magnesium fluoride have the maximum values. Specifically, the narrow-scan spectrum of Mg 1s of the positive electrode active material of one embodiment of the present invention preferably has the maximum value at a binding energy between the binding energy at which the spectrum of magnesium oxide has the maximum value and the binding energy at which the spectrum of magnesium fluoride has the maximum value.

[0077] In the positive electrode active material of one embodiment of the present invention, the deterioration of the crystal structure is small even after a charge / discharge cycle test at a high cut-off voltage of 4.7 V (versus Li + / Li) is extremely limited, since an adverse phase transition accompanied by the sliding of the CoO2 plates is prevented.

[0078] Specifically, when the charge / discharge cycle test is conducted in a 25°C environment on a cell in which the positive electrode active material of one embodiment of the present invention is used for the positive electrode, lithium metal is used for the negative electrode, and a mixture of lithium hexafluorophosphate, ethylene carbonate, and diethyl carbonate with 2 wt% of vinylene carbonate is used as the electrolytic solution, and then the positive electrode in a discharge state is analyzed by powder X-ray diffraction using a Cu-Kα1 ray, a peak having a half-width of less than or equal to 0.10°, preferably less than or equal to 0.08°, appears within the 2θ range of 18.7° to 19.0°, and a peak having a half-width of less than or equal to 0.12°, preferably less than or equal to 0.09° appears within the 2θ range of 45.0° to 45.3°.In the charge / discharge cycle test here, a charge / discharge cycle is repeated 100 times, in which constant current charging is performed at a current value of 0.5 C (where 1 C = 200 mA / g) to a voltage of 4.7 V, constant voltage charging is performed until the current value reaches 0.05 C, a rest period of 10 minutes is provided, constant current discharging is performed at a current value of 0.5 C to a voltage of 2.5 V, and then a rest period of 10 minutes is provided.

[0079] The positive electrode active material of one embodiment of the present invention withstands a charge / discharge cycle test at a high cutoff voltage, and therefore, the use of the positive electrode active material enables a positive electrode and a secondary battery with high energy density. For example, the volume energy density calculated using the true density of the positive electrode active material can be greater than or equal to 4250 Wh / L, and the gravimetric energy density calculated using the true density of the positive electrode active material can be greater than or equal to 865 Wh / Kg. < <berechnung>>

[0080] An ab initio calculation was performed to obtain evidence of the mechanism blocking the change to the H1-3 phase.

[0081] Two models were created in which all lithium atoms in a lithium layer were removed: in one model, the oxygen arrangement is that of the O3 phase, and in the other model, the oxygen arrangement is that of the H1-3 phase. An O3 phase arrangement model and an H1-3 phase arrangement model, in each of which a magnesium atom was added to the layer from which lithium was completely removed, were also created. For these models, the structure, including the cell size, was optimized, and the energies were compared.

[0082] The calculation was performed using a density functional theory software package "VASP" with a PAW method. During the calculation, an optimization of the structure, including the cell size, was performed. GGA-PBE was used as the exchange-correlation interaction. The degree of spin freedom was not considered. To correct the distributed interaction, a DFT-D3 (BJ) method using the Becke-Johnson damping function was used. A cut-off energy of 1000 eV and a k-point sampling of 3 × 3 × 3 were applied. When calculating the electron state, it was assumed that convergence occurred when the energy change was below 10 -8 eV. Structural relaxation was interrupted when the total force during structure optimization was below 0.001 eV / Å.

[0083] The baseline models used were a model in which the CoO2 layer in LiCoO2 exhibits the O3 phase arrangement (O3 phase arrangement model) and a model in which the CoO2 layer in LiCoO2 exhibits the H1-3 phase arrangement (H1-3 phase arrangement model). The two baseline models each include a layer arrangement consisting of a Li layer, a CoO2 layer, a Li layer, and a CoO2 layer in the cell used for the calculation. In the cell, the number of Li atoms is 24, the number of Co atoms is 24, and the number of O atoms is 48. These two models, in each of which all Li atoms present in one Li layer were removed, leaving only four of the 12 Li atoms in the other Li layer, were formed. These two models are models without Mg. The models without Mg, in which a Mg atom was added to the layer from which all Li atoms were removed, are models with Mg.Finally, the following four models were formed: an "O3-phase arrangement model without Mg", an "H1-3-phase arrangement model without Mg", an "O3-phase arrangement model with Mg", and an "H1-3-phase arrangement model with Mg".

[0084] For these four models, structural optimization, including cell size, was performed and energies were compared. Fig. 7A and Fig. Figure 7B shows the "O3-phase arrangement model with Mg" and the "H1-3-phase arrangement model with Mg" after structural optimization, including cell size. Table 1 shows the energies of the four models. Here, E(H1-3) and E(O3) represent the energies of the H1-3-phase arrangement model and the O3-phase arrangement model, respectively. [Table 1] ohne Mg mit Mg E(H1-3) [eV] -507,77 -515,43 E(O3) [eV] -507,49 -515,50 E(H1-3) - E(O3) [eV] -0,28 0,07

[0085] Without magnesium, the H1-3 phase arrangement model exhibits lower energy; in contrast, with magnesium, the O3 phase arrangement model exhibits lower energy. These results indicate that the presence of magnesium makes the H1-3 phase arrangement difficult to form. While there is no cobalt above and below magnesium in the O3 phase arrangement model with magnesium, there is cobalt above and below magnesium in the H1-3 phase arrangement model. The energy of the H1-3 phase arrangement model with magnesium is presumably higher energy due to the electrostatic repulsion between magnesium and the upper and lower cobalt. Furthermore, magnesium is thought to increase the energy barrier during the sliding of the CoO2 plates.

[0086] This calculation suggests that the transition to the H1-3 phase is prevented by the function of Mg as a pillar. < <li-ordnung>>

[0087] For example, ex-situ XRD measurement, as described above, can determine the coordinates of cobalt and oxygen in the O3' phase. In contrast, because lithium has low X-ray scattering power, XRD cannot analyze whether lithium contained in the O3' phase is ordered or irregular. For example, Fig. 8A, which is a diagram of the O3' phase crystal structure model viewed from the a-axis direction, and Fig. Figure 8B, which is a diagram of the O3' phase crystal structure model viewed from the c-axis direction, assumes that lithium is present in all lithium sites with equal probability.

[0088] However, lithium may actually be ordered in the O3' phase, and the lithium arrangement can potentially be determined by structural analysis combined with another method, such as neutron diffraction. Examples of the x-value in Li x CoO2 and the lithium arrangement, which can be imagined if lithium contained in the O3' phase is ordered, are described using Fig. 8D and Fig. 8E, Fig. 9A to Fig. 9E, Fig. 10, Fig. 11A to Fig. 11C and Fig. 12. These are diagrams of the O3' phase crystal structure model viewed from the c-axis direction. In Fig. 8D and Fig. 8E, Fig. 9A to Fig. 9E, Fig. 10 and Fig. 12, lithium sites are represented by vertices of equilateral triangles, and lithium is represented by hatched circles. For reference, Fig. 8C the overlay of the same diagram as Fig. 8B on a diagram with lithium sites represented by vertices of equilateral triangles.

[0089] Fig. Figure 8D shows an example of a lithium arrangement in a lithium layer, which is conceivable when the O3' phase Li 1 / 3 COO2. In the diagrams below, a hatched parallelogram represents the minimum repeating unit.

[0090] Fig. Figure 8E shows an example of a lithium arrangement in a lithium layer, which is conceivable when the O3' phase Li 1 / 4 CoO2 is.

[0091] Fig. Figure 9A shows an example of a lithium arrangement in a lithium layer, which is conceivable when the O3' phase Li 2 / 9 CoO2 is.

[0092] Fig. 9B to Fig. 9E show examples of a lithium arrangement in a lithium layer, which is conceivable when the O3' phase Li 1 / e CoO2 is.

[0093] Fig. Figure 10 shows an example of a lithium arrangement in three successive lithium layers, which is conceivable when the O3' phase Li 1 / 4 CoO2. To clarify the drawing, equilateral triangles, whose vertices represent lithium sites, are drawn with a solid line in the first layer, a dotted line in the second layer, and a thin solid line in the third layer. Lithium atoms present in the same lithium layer are represented by the same hatching pattern. Fig. 10 can also be viewed as a diagram in which there are three layers, each in Fig. 8E, are superimposed and viewed from the direction of the c-axis.

[0094] Fig. 11A to Fig. 11C represent examples of a lithium arrangement in three successive lithium layers, which is conceivable if the O3' phase Li 1 / 6 CoO2. To distinguish lithium atoms in one layer from those in another, lithium atoms present in the same lithium layer are connected by a line. Fig. 11A to Fig. 11C show three examples of the case where three layers are in Fig. 9D overlay.

[0095] Although Fig. 10 and Fig. 11A to Fig. While Figure 11C shows examples where lithium is present in all lithium layers of the O3' phase, the possible lithium arrangement is not limited to this. It is also conceivable that a layer with lithium and a layer without lithium could alternate between the repeated CoO2 layers.

[0096] Fig. Figure 12 shows an example of a lithium arrangement in four successive lithium layers, which is conceivable when the O3' phase Li 1 / 8 CoO2. The first layer is drawn with a solid line, the second layer is drawn with a dotted line, the third layer is drawn with a thin solid line, and the fourth layer is drawn with a dotted line. Fig. Figure 12 shows an example in which the first layer and the third layer each have the same lithium arrangement as that in Fig. 8E and the second layer and the fourth layer do not contain lithium.

[0097] It should be noted that the lithium arrangement in a plane of the lithium layer or in the c-axis direction is not limited to the above.

[0098] In this specification and the like, a surface of a positive electrode active material refers to a surface of lithium cobalt oxide doped with magnesium or the like. Therefore, the positive electrode active material of one embodiment of the present invention does not contain a material to which a metal oxide adheres that does not have a lithium site that contributes to charge and discharge, such as aluminum oxide (Al2O3), or a carbonate, hydroxy group, or the like that is chemically adsorbed after the positive electrode active material is prepared. The adhered metal oxide refers, for example, to a metal oxide that has a crystal structure different from that of lithium cobalt oxide.

[0099] Furthermore, no electrolyte, no organic solvent, no binder, no conductive material, and no compound derived from any of these adhering to the positive electrode active material are included.

[0100] Since the positive electrode active material of one embodiment of the present invention is a compound containing oxygen and a transition metal into and from which lithium can be intercalated and de-intercalated, an interface between a region where oxygen and cobalt, which is oxidized or reduced due to the intercalation and de-intercalation of lithium, exist and a region where oxygen and cobalt do not exist is regarded as the surface of the positive electrode active material. A plane created by a slip, a closed gap, and / or a crack can also be regarded as the surface of the positive electrode active material. When the positive electrode active material is analyzed, in some cases, a protective film is attached to its surface; however, the protective film is not included in the positive electrode active material.In some cases, a single-layer film or a multi-layer film made of carbon, a metal, an oxide, a resin, or the like is used as the protective film.

[0101] Therefore, for example, in STEM-EDX line analysis, the position of the surface of the positive electrode active material indicates a point where the detection amount of the characteristic X-ray of cobalt is 50% of the sum of the average value Co AVE the detection quantities of the characteristic X-ray radiation of cobalt in the inner section and the average value Co BG of the detection quantities of the characteristic X-rays of cobalt in the background, or a point at which the detection quantity of the characteristic X-rays of oxygen is 50% of the sum of the average value O AVE the detection quantities of the characteristic X-ray radiation of oxygen in the inner section and the average value O BG the detection quantities of the characteristic X-ray radiation of oxygen in the background.It should be noted that when the position of the point at which the detection amount of the characteristic X-ray of cobalt is 50% of the sum of the average value of the detection amounts of the characteristic X-ray of cobalt in the inner portion and the average value of the detection amounts of the characteristic X-ray of cobalt in the background is different from the position of the point at which the detection amount of the characteristic X-ray of oxygen is 50% of the sum of the average value of the detection amounts of the characteristic X-ray of oxygen in the inner portion and the average value of the detection amounts of the characteristic X-ray of oxygen in the background, the difference is likely due to the influence of a carbonate, a metal oxide containing oxygen, or the like adhering to the surface.Therefore, in such a case, the point at which the detection amount of the characteristic X-ray radiation of cobalt becomes 50% of the sum of the average value Co. AVE the detection quantities of the characteristic X-ray radiation of cobalt in the inner section and the average value of CO BG corresponding to the detection amounts of the characteristic X-rays of cobalt in the background, can be used as the position of the surface of the positive electrode active material.

[0102] The average value Co BG The detection amount of the characteristic X-rays of cobalt in the background can be calculated, for example, by determining the average value of the detection amounts in the range from 2 nm, preferably from 3 nm, which lies outside a section near the section where the increase in the detection amount of the characteristic X-rays of cobalt begins. The average value Co AVE The detection quantities of the characteristic X-rays of cobalt in the inner section can be calculated by determining the average value of the detection quantities in the range from 2 nm, preferably from 3 nm, in the depth at which the detection quantities of the characteristic X-rays of cobalt and oxygen are saturated and stabilized, e.g., at a depth that is greater than or equal to 30 nm, preferably more than 50 nm, than the depth at which the increase in the detection quantity of the characteristic X-rays of cobalt begins. The average value O BG the detection quantities of the characteristic X-ray radiation of oxygen in the background and the average value O AVE The detection amounts of the characteristic X-ray radiation of oxygen in the inner section can be calculated in a similar manner.

[0103] To increase the spatial resolution in STEM-EDX line analysis, the beam diameter of an electron beam (also referred to as beam diameter or sample diameter) is preferably small. The beam diameter in STEM-EDX line analysis is preferably less than or equal to 0.3 nm, more preferably less than or equal to 0.2 nm, and even more preferably less than or equal to 0.1 nm.

[0104] The surface of the positive electrode active material in, for example, a cross-sectional scanning transmission electron microscope (STEM) image is a boundary between a region where an image derived from the crystal structure of the positive electrode active material is observed and a region where the image is not observed. The surface of the positive electrode active material is also defined in the cross-sectional STEM image as the outermost surface of a region where an atomic column derived from an atomic nucleus of a metal element with a larger atomic number than lithium among metal elements constituting the positive electrode active material is observed. Alternatively, the surface refers to an intersection point of a tangent drawn on a luminance profile from the surface toward the bulk and an axis in the depth direction in a STEM image.The surface in a STEM image or the like can be determined using additional analysis with higher spatial resolution.

[0105] The spatial resolution of STEM-EDX is approximately 1 nm. Therefore, the maximum value of a profile of an additive element can be shifted by approximately 1 nm. For example, even if the maximum value of the profile of an additive element, such as magnesium, is located outside the surface determined in the manner described above, it can be said that a difference between the maximum value and the surface is within the error margin as long as the difference is less than 1 nm.

[0106] A peak in STEM-EDX line analysis refers to the maximum value of the detection intensity in each element profile or the maximum value of the characteristic X-ray emission of each element. Noise in STEM-EDX line analysis can be defined as a measured value with a half-width less than or equal to the spatial resolution (R), e.g., less than or equal to R / 2.

[0107] The negative impact of noise can be reduced by sampling the same section multiple times under the same conditions. For example, an integrated value obtained by sampling six times can be used as the profile of each element. The number of samples is not limited to six, and an average of measured values ​​obtained by sampling seven or more times can be used as the profile of each element.

[0108] STEM-EDX line analysis can be performed, for example, as follows. First, a protective film is deposited by evaporation over the surface of a positive electrode active material. For example, carbon can be deposited by evaporation using an ion sputtering device (MC1000, manufactured by Hitachi High-Tech Corporation).

[0109] Next, the positive electrode active material is thinned to create a cross-sectional sample for STEM analysis. For example, the positive electrode active material can be thinned using an FIB-SEM device (XVision 200TBS, manufactured by Hitachi High-Tech Corporation). Here, imaging can be performed using a micro probing system (MPS), and the accelerating voltage during final processing can be, for example, 10 kV.

[0110] STEM-EDX line analysis can be performed using, for example, the HD-2700 manufactured by Hitachi High-Tech Corporation as the STEM device and the Octane T Ultra W (with two detectors) manufactured by EDAX Inc. as the EDX detector. In EDX line analysis, the emission current of the STEM device is set in the range of 6 µA to 10 µA, and a portion of the thinned sample that is not located at a deep level and has little unevenness is measured. The magnification is approximately 150,000 times. EDX line analysis can be performed under conditions where drift correction is performed, the line width is 42 nm, the pitch is 0.2 nm, and the number of frames is 6 or more.

[0111] If the surface section contains both magnesium and nickel, divalent nickel could exist more stably in the environment of divalent magnesium. Therefore, even in a highly delithiated state, magnesium dissolution could be prevented, which could contribute to the stabilization of the surface section.

[0112] For a similar reason, when adding the additive element to lithium cobalt oxide in the manufacturing process, magnesium is preferably added in a step before a step in which nickel is added. Alternatively, magnesium and nickel are preferably added in the same step. The reason is as follows: magnesium has a large ionic radius and therefore is likely to remain in the surface portion of lithium cobalt oxide regardless of the step in which magnesium is added; however, nickel can widely diffuse into the inner portion of lithium cobalt oxide if magnesium does not exist. Therefore, if nickel is added before the addition of magnesium, nickel may diffuse into the inner portion of lithium cobalt oxide, and a beneficial amount of nickel may not remain in the surface portion.

[0113] Additive elements that are distributed differently in the depth direction are preferably included simultaneously, in which case the crystal structure of a wider area can be stabilized. For example, in the surface portion of the positive electrode active material of one embodiment of the present invention, the maximum values ​​of the detection amounts of magnesium and nickel are preferably different from the maximum value of the detection amount of aluminum in the depth direction. The maximum value of the detection amount of aluminum is preferably observed in a region of a particle that is further inside than a region of the particle where the maximum values ​​of the detection amounts of magnesium and nickel are observed.

[0114] With such distributions of the additive elements, the crystal structure of a wider area can be stabilized. In the case where magnesium, nickel, and aluminum are included as described above, the surface portion can be sufficiently stabilized by magnesium and nickel; therefore, aluminum is not necessary at the surface. Preferably, aluminum is widely distributed in a deeper area. For example, aluminum is preferably continuously detected in a range extending from a depth of 1 nm from the surface to a depth of 25 nm from the surface.Aluminum preferably disperses widely in a range extending from a depth from the surface of 0 nm to a depth from the surface of 100 nm, more preferably in a range extending from a depth from the surface of 0.5 nm to a depth from the surface of 50 nm, in which case the crystal structure of a wider range can be stabilized.

[0115] When a plurality of additive elements are included as described above, the effects of the additive elements synergistically contribute to further stabilization of the surface portion.

[0116] The additive elements, i.e., magnesium, fluorine, nickel, and aluminum, preferentially form solid solutions with the positive electrode active material. Therefore, for example, in STEM-EDX line analysis, a position where the detection amount of the additive element increases is preferably located at a lower level than a position where the detection amount of cobalt increases, i.e., on the inner portion side of the positive electrode active material.

[0117] In this specification and the like, the depth at which the detection amount of an element increases in STEM-EDX line analysis means the depth at which a measured value that cannot be regarded as noise in terms of intensity, spatial resolution, and the like is successively obtained.

[0118] This embodiment may be appropriately combined with the contents of any of the other embodiments. (Embodiment 2)

[0119] In this embodiment, structures of lithium-ion batteries are described. [Positive electrode]

[0120] A positive electrode comprises a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer contains a positive electrode active material and may further contain a conductive additive and / or a binder. The positive electrode active material described in the above embodiment can be used as the positive electrode active material.

[0121] Fig. Figure 13A shows an example of a schematic cross-sectional view of the positive electrode.

[0122] For example, a metal foil can be used for a current collector 550. The positive electrode can be formed by applying a slurry to the metal foil and drying it. Note that pressing can be performed after drying. The positive electrode is obtained by forming an active material layer over the current collector 550.

[0123] The slurry refers to a material solution used to form an active material layer over the current collector 550, which contains an active material, a binder, and a solvent, preferably also a conductive additive mixed therewith. The slurry may also be referred to as an electrode slurry or active material slurry. In some cases, a slurry for forming a positive electrode active material layer is referred to as a positive electrode slurry, and a slurry for forming a negative electrode active material layer is referred to as a negative electrode slurry.

[0124] A positive electrode active material 561 has functions of absorbing and / or releasing lithium ions due to charge and discharge. For the positive electrode active material 561 used as an embodiment of the present invention, a material with little deterioration due to discharge and charge even at a high charging voltage can be used. In this specification and the like, unless otherwise specified, a charging voltage is shown in terms of the potential of a lithium metal. In this specification and the like, a high charging voltage is, for example, a charging voltage higher than or equal to 4.6 V, preferably higher than or equal to 4.65 V, more preferably higher than or equal to 4.7 V, even more preferably higher than or equal to 4.75 V, and most preferably higher than or equal to 4.8 V.

[0125] For the positive electrode active material 561 used as an embodiment of the present invention, any material can be used as long as it exhibits little deterioration due to discharge and charge even at high charging voltage, and the material described in Embodiment 1 can be used. Note that two or more types of materials with different particle diameters can be used for the positive electrode active material 561 as long as the materials exhibit little deterioration due to discharge and charge even at high charging voltage.

[0126] A conductive additive is also called a conductivity-imparting agent or conductive material, and a carbon material can be used as a conductive additive. A conductive additive is placed between a plurality of active materials, electrically connecting the plurality of active materials and increasing conductivity.It should be noted that in this specification and the like, the term "attached" does not only refer to a state where an active material and a conductive additive are physically in close contact with each other, and includes, for example, the following concepts: the case where a covalent bond occurs, the case where a bond with van der Waals force occurs, the case where a conductive additive covers a part of the surface of an active material, the case where a conductive additive is embedded in the surface roughness of an active material, and the case where an active material and a conductive additive are electrically connected to each other without being in contact with each other.

[0127] Specific examples of carbon materials that can be used as conductive additives include carbon black (e.g., furnace black, acetylene black, or graphite).

[0128] In Fig. Figure 13A shows a carbon black 553 as a conductive additive.

[0129] A binder (a resin) can be mixed into the positive electrode of the lithium-ion battery to adhere the current collector 550, such as metal foil, and the active material to each other. The binder is also called a binding material. Since the binder is a high-molecular material, a large amount of the binder reduces the proportion of the active material in the positive electrode, thereby reducing the discharge capacity of the lithium-ion battery. Therefore, the amount of the mixed binder is preferably minimized. Fig. 13A, an area not filled with the positive electrode active material 561, a second active material 562, or the carbon black 553 indicates a gap or the binder.

[0130] Although Fig. 13A illustrates an example in which the positive electrode active material 561 has a spherical shape, there is no particular limitation. The cross-sectional shape of the positive electrode active material 561 may be, for example, an ellipse, a rectangle, a trapezoid, a pyramid, a polygon with rounded corners, or an asymmetric shape. For example, Fig. 13B illustrates an example in which the positive electrode active material 561 has a polygonal shape with rounded corners.

[0131] For the positive electrode in Fig. 13B, graphene 554 is used as a carbon material, which is used as a conductive additive. In Fig. 13B, a positive electrode active material layer containing the positive electrode active material 561, the graphene 554, and the carbon black 553 is formed over the current collector 550.

[0132] In the step of mixing the graphene 554 and the carbon black 553 to obtain an electrode slurry, the weight of the mixed carbon black is preferably 1.5 times to 20 times, more preferably 2 times to 9.5 times the weight of the graphene.

[0133] When the graphene 554 and the carbon black 553 are mixed within the above range, the carbon black 553 exhibits excellent dispersion stability when preparing a slurry, and thus an aggregate portion is not likely to occur. Furthermore, when the graphene 554 and the carbon black 553 are mixed within the above range, the electrode density can be higher than that of a positive electrode using only the carbon black 553 as a conductive additive. As the electrode density becomes higher, the capacity per unit weight can be increased. In particular, the density of the positive electrode active material layer measured by gravimetry can be higher than or equal to 3.5 g / cc.

[0134] The electrode density is lower than that of a positive electrode containing only graphene as a conductive additive; however, when a first carbon material (graphene) and a second carbon material (acetylene black) are mixed in the above range, rapid charging can be achieved. Therefore, the use of such a mixed conductive additive is particularly effective for lithium-ion batteries for vehicles.

[0135] Fig. Figure 13C shows an example of a positive electrode in which a carbon fiber 555 is used instead of graphene. The Fig. The example shown in Figure 13C differs from the one in Fig. 13B. The use of the carbon fiber 555 can prevent aggregation of the carbon black 553 and increase dispersibility.

[0136] In Fig. 13C, the area not filled with the positive electrode active material 561, the carbon fiber 555, or the carbon black 553 indicates a gap or the binder.

[0137] Fig. Figure 13D shows another example of a positive electrode. Fig. 13C illustrates an example in which the carbon fiber 555 is used in addition to the graphene 554. When both the graphene 554 and the carbon fiber 555 are used, aggregation of the carbon black, such as the carbon black 553, can be prevented, and thus the dispersibility can be further increased.

[0138] In Fig. 13D, the area not filled with the positive electrode active material 561, the carbon fiber 555, the graphene 554, or the carbon black 553 indicates a gap or the binder.

[0139] A lithium-ion battery can be manufactured by placing one of the positive electrodes in Fig. 13A to Fig. 13D, a layered arrangement in which a separator is provided over the positive electrode and a negative electrode is provided over the separator, is accommodated in a container (e.g., an outer part or a metal can) or the like, and the container is filled with a liquid electrolyte (also called an electrolytic solution). <bindemittel>

[0140] A rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, or ethylene-propylene-diene copolymer is preferably used as the binder. A fluororubber can also be used as the binder. <positivelektrodenstromkollektor>

[0141] For the current collector, a material with high conductivity can be used, such as a metal such as stainless steel, gold, platinum, aluminum, or titanium, or an alloy thereof. It is preferable that a material used for the positive electrode current collector does not dissolve at the potential of the positive electrode. Alternatively, it is possible to use an aluminum alloy to which an element for improving heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, is added. A metal element that forms silicide by reacting with silicon can be used. Examples of the metal element that forms silicide by reacting with silicon include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel.The current collector may have a foil-like shape, a plate-like shape, a sheet-like shape, a mesh-like shape, a stamped metal shape, an expanded metal shape, or the like, as required. The current collector preferably has a thickness of greater than or equal to 5 µm and less than or equal to 30 µm. [Negative electrode]

[0142] The negative electrode comprises a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer contains a negative electrode active material and may further contain a conductive additive and a binder. <negativelektrodenaktivmaterial>

[0143] For example, an alloy-based material and / or a carbon material can be used as the negative electrode active material.

[0144] As the carbon material used as the negative electrode active material, one or more selected from graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), a carbon fiber (carbon nanotube), graphene, carbon black, and the like can be used.

[0145] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Spherical graphite with a spherical shape can be used as artificial graphite. For example, MCMB is preferably used because it can have a spherical shape. Furthermore, MCMB is preferably used because it can be relatively lightweight and has a small surface area. Examples of natural graphite include flake graphite and spherical natural graphite.

[0146] Graphite has a low potential, essentially equal to that of a lithium metal (higher than or equal to 0.05 V and lower than or equal to 0.3 V versus Li + / Li) when lithium ions are intercalated into the graphite (while forming a lithium-graphite intercalation compound). For this reason, a lithium-ion battery using graphite can have a high operating voltage. Additionally, graphite is preferred for its advantages, such as a relatively high capacity per unit volume, relatively small volume expansion, lower cost, and a higher level of safety than that of lithium metal.

[0147] As the negative electrode active material, an element that enables charge and discharge reactions through alloying and dealloying reactions with lithium can be used. For example, one or more materials selected from silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, and the like can be used. Such elements have a higher capacity than carbon. In particular, silicon has a high theoretical capacity of 4200 mAh / g. Alternatively, a compound containing one of the above elements can be used. Examples of the compound include SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb and SbSn.For example, an element that enables charge and discharge reactions through alloying and dealloying reactions with lithium and a compound containing the element are in some cases referred to as alloy-based materials.

[0148] In this specification and the like, "SiO" refers to, for example, silicon monoxide. SiO may alternatively be represented by SiOx. Here, it is preferable that x is 1 or has an approximate value of 1. For example, x is preferably greater than or equal to 0.2 and less than or equal to 1.5, more preferably greater than or equal to 0.3 and less than or equal to 1.2.

[0149] As a negative electrode active material, one or more oxides consisting of titanium dioxide (TiO2), lithium titanium oxide (Li4Ti5O 12 ), a lithium-graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5), tungsten oxide (WO2) and molybdenum oxide (MoO2) can be used.

[0150] Alternatively, Li can be used as a negative electrode active material 3-x M x N (M= Co, Ni or Cu) with a Li3N structure, which is a compound nitride of lithium and a transition metal, can be used. For example, Li 2,6 Co 0,4 N3 due to its high discharge capacity (900 mAh / g and 1890 mAh / cm 3 ) preferred.

[0151] A composite nitride of lithium and a transition metal is preferably used. In this case, lithium ions are contained in the negative electrode active material, and therefore, the negative electrode active material can be used in combination with a positive electrode active material that does not contain lithium ions, such as V2O5 or Cr3O8. Note that when a material containing lithium ions is used as the positive electrode active material, the composite nitride of lithium and a transition metal can be used as the negative electrode active material by pre-exposing the lithium ions contained in the positive electrode active material.

[0152] A material that causes a conversion reaction can be used as a negative electrode active material. For example, a transition metal oxide that does not form an alloy with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), or iron oxide (FeO), can be used as a negative electrode active material. Other examples of the material that causes a conversion reaction include oxides such as FeO, CuO, CuO, RuO, and CrO, and sulfides such as CoS. 0,89 , NiS and CuS, nitrides such as Zn3N2, Cu3N and Ge3N4, phosphides such as NiP2, FeP2 and CoP3, and fluorides such as FeF3 and BiF3.

[0153] A combination of two or more of the above negative electrode active materials may be used; for example, a negative electrode active material in which graphite and silicon particles are mixed may be used. The silicon particles refer to silicon powder, which is the negative electrode active material of the lithium-ion secondary battery, and the average diameter in the particle size distribution, that is, the average particle diameter, is approximately 100 nm; the silicon particles are sometimes called nanosilicon particles. To obtain silicon particles to be used, it is preferable that a silicon source is ground and the particle diameters are adjusted to be uniform. The silicon particles may comprise at least one of silicon, silicon oxide, and silicon alloy.Although laser diffraction particle size distribution measurement can typically be used to measure particle size, the measurement is not limited to this. A major axis of a particle's cross-section can be measured by analysis with a scanning electron microscope (SEM), a transmission electron microscope (TEM), or the like.

[0154] For the conductive additive and the binder that may be contained in the negative electrode active material layer, materials similar to those for the conductive additive and the binder that may be contained in the positive electrode active material layer may be used. <negativelektrodenstromkollektor>

[0155] For the negative electrode current collector, copper or the like can be used in addition to a material similar to that of the positive electrode current collector. Note that a material that is not alloyed with charge carrier ions of lithium or the like is preferably used for the negative electrode current collector. [Electrolyte solution]

[0156] The electrolytic solution contains an organic solvent. The organic solvent is not necessarily a liquid at 25°C, but may be a solid at 25°C or a semi-solid at normal temperature. Note that the organic solvent is preferably a liquid in a wide temperature range from subzero temperatures to high temperatures, although one embodiment of the present invention is not limited thereto. The organic solvent may be a liquid, a solid, or a semi-solid in a wide temperature range from subzero temperatures to high temperatures.

[0157] An aprotic organic solvent is preferably used as the organic solvent. For example, one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), 1,3-propanesultone (PS), fluoroethylene carbonate (FEC), methyl 3,3,3-trifluoropropionate (MTFP), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane and sultone can be used, or two or more of these solvents can be used in an appropriate combination in an appropriate ratio.

[0158] PS has a highest occupied molecular orbital (HOMO) level and a lowest unoccupied molecular orbital (LUMO) level equal to those of EC and DEC; therefore, PS is less likely to be oxidized and reduced even at high cut-off voltage, and PS is likely to become a high-molecular compound when decomposed on the surface of the positive electrode active material. Therefore, PS is advantageous in that it is unlikely to become a degradation product with a small molecular weight and be gasified. Therefore, the electrolyte solution preferably contains PS at greater than or equal to 0.1 wt% and less than or equal to 10 wt%, more preferably greater than or equal to 0.25 wt% and less than or equal to 7.5 wt%.

[0159] FEC, which is a cyclic carbonate, has a high dielectric constant and therefore, when used in an organic solvent, has an effect of promoting the dissociation of a lithium salt. On the other hand, since FEC has a substituent with an electron-withdrawing property, a lithium ion is more easily desolved with FEC than with EC. In particular, the solvation energy of a lithium ion in FEC is lower than in EC, which does not have a substituent with an electron-withdrawing property. Therefore, lithium ions are likely to be extracted from the surfaces of a positive electrode active material and a negative electrode active material, which can reduce the internal resistance of a secondary battery. In addition, FEC has a low HOMO level and is therefore not easily oxidized, which means it has high oxidation resistance. In contrast, FEC disadvantageously has a high viscosity.In view of this, a mixed organic solvent containing not only FEC but also MTFP is preferably used for the electrolytic solution. MTFP, which is a linear carbonate, can exhibit an effect of reducing the viscosity of an electrolytic solution or maintaining the viscosity at room temperature (typically 25°C) even at low temperatures (typically 0°C). Furthermore, while the solvation energy in MTFP is lower than in methyl propionate (abbreviation: MP), which does not have a substituent with an electron-withdrawing property, MTFP can solvate a lithium ion when used for the electrolytic solution. In the case where a mixed organic solvent containing both FEC and MTFP is used, y in the volume ratio FEC:MTFP = 1:y preferably satisfies 2 ≤ y ≤ 20, more preferably 4 ≤ y ≤ 9.

[0160] It is preferable that the above-described organic solvent be highly purified and contain a small amount of dust particles or molecules other than constituent molecules of the organic solvent (hereinafter, they are also simply referred to as impurities and include oxygen (O2), water (H2O), and moisture). It is preferable that the organic solvent be subjected to appropriate purification and the generation of a reaction by-product during synthesis be prevented. Specifically, the impurity concentration in the electrolyte is less than or equal to 100 ppm, preferably less than or equal to 50 ppm, more preferably less than 10 ppm. The concentration of moisture among the impurities can be detected by Karl Fischer titration.

[0161] It is also preferable that peaks due to impurities in the above organic solvent are hardly observed by NMR measurement or the like. The term "hardly observed" includes the case where the ratio of the integral area of ​​the peak due to impurities to the integral area of ​​the peak due to the main component (such a ratio is simply referred to as an integral ratio) is less than or equal to 0.005, preferably less than or equal to 0.002. A device used for NMR measurement is not particularly limited, and, for example, "AVANCE III 400" manufactured by Bruker AXS can be used. Among the five peaks of acetonitrile derived from acetonitrile-d3 used in a solvent in 1H NMR measurement, the central peak may be 1.94 ppm.

[0162] For example, in the case of MTFP, it is known that when 1H NMR is measured using an acetonitrile d3 solvent, four peaks appear within the δ range of 3.29 ppm to 3.43 ppm. However, if another peak appears near the above range, for example, another peak appears within the δ range of 3.24 ppm to 3.29 ppm, the peak is likely to be due to impurities. Accordingly, if the ratio of the peak area within the range of 3.24 ppm to 3.29 ppm to the peak area within the range of 3.29 ppm to 3.43 ppm (an integral ratio) is less than or equal to 0.005, preferably less than or equal to 0.002, peaks due to impurities are hardly observed.

[0163] Alternatively, using one or more types of ionic liquids (room-temperature molten salts), which are less likely to burn and evaporate, as the solvent of the electrolyte solution can prevent an energy storage device from exploding and catching fire, even if the energy storage device is short-circuited internally or the internal temperature rises due to overcharging or the like. An ionic liquid contains a cation and an anion, particularly an organic cation and an anion. Examples of the organic cation used for the electrolyte solution include aliphatic onium cations such as a quaternary ammonium cation, a tertiary sulfonium cation, and a quaternary phosphonium cation, and aromatic cations such as an imidazolium cation and a pyridinium cation.Examples of the anion used for the electrolytic solution include a monovalent amide-based anion, a monovalent methide-based anion, a fluorosulfonate anion, a perfluoroalkylsulfonate anion, a tetrafluoroborate anion, a perfluoroalkylborate anion, a hexafluorophosphate anion, and a perfluoroalkylphosphate anion.

[0164] As the electrolyte dissolved in the solvent described above, one of the lithium salts such as LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiIl, Li2SO4, Li2B 10 Cl 10 , Li2B 12 Cl 12 , LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2) (CF3SO2), LiN(C2F5SO2)2 and lithium bis(oxalate)borate (LiB(C2O4)2, LiBOB), or two or more of these lithium salts may be used in appropriate combination in an appropriate ratio.

[0165] The electrolytic solution used for the energy storage device is preferably a highly purified electrolytic solution containing only a small amount of dust particles and elements other than the constituent elements of the electrolytic solution (hereinafter also referred to simply as impurities). Specifically, the weight ratio of impurities to the electrolytic solution is preferably less than or equal to 1%, more preferably less than or equal to 0.1%, even more preferably less than or equal to 0.01%.

[0166] Alternatively, a polymer gel electrolyte obtained by swelling a polymer with an electrolyte solution can be used.

[0167] Using a polymer gel electrolyte improves safety against liquid leakage and the like. Furthermore, a secondary battery can be thinner and lighter.

[0168] As the polymer subjected to gelation, a silicone gel, an acrylic gel, an acrylonitrile gel, a polyethylene oxide-based gel, a polypropylene oxide-based gel, a fluorine-based polymer gel, or the like can be used. For example, a polymer having a polyalkylene oxide structure, such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, or a copolymer containing one of them, can be used. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP), can be used. The resulting polymer can be porous.

[0169] Instead of the electrolyte solution, a solid electrolyte containing an inorganic material, such as a sulfide-based or oxide-based inorganic material, or a solid electrolyte containing a polymer material, such as a polyethylene oxide (PEO)-based polymer material, can be used as an alternative. When using a solid electrolyte, a separator or spacer is unnecessary. Furthermore, the battery can be completely solidified; therefore, there is no possibility of liquid leakage, and the battery's safety is dramatically improved. [Separator]

[0170] When the electrolyte contains a liquid electrolyte, a separator is arranged between the positive electrode and the negative electrode. For example, a fiber containing cellulose such as paper; a nonwoven fabric; a glass fiber; ceramics; a synthetic fiber using nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polypropylene (referred to as PP), polyimide (referred to as PI), polyester, acrylic, polyolefin, or polyurethane; or the like can be used as the separator. The separator may have a porosity in the thickness of greater than or equal to 35% and less than or equal to 90%, preferably greater than or equal to 60% and less than or equal to 85%. A separator using polypropylene may have a porosity of greater than or equal to 35% and less than or equal to 45%.A separator using polyimide can have a porosity of greater than or equal to 75% and less than or equal to 85%. The thickness of the separator is preferably greater than or equal to 10 µm and less than or equal to 80 µm, more preferably greater than or equal to 20 µm and less than or equal to 60 µm. The separator using polyimide is preferred because it has high porosity and a large thickness (typically a thickness of greater than or equal to 50 µm and less than or equal to 60 µm).

[0171] The separator is preferably processed into a pocket-like shape to enclose either the positive electrode or the negative electrode.

[0172] The separator may have a multilayer structure. For example, an organic material film made of polypropylene, polyethylene, or the like may be coated with a ceramic-based material, a fluorine-based material, a polyamide-based material, a mixture thereof, or the like. Examples of the ceramic-based material include alumina particles and silica particles. Examples of the fluorine-based material include PVDF and polytetrafluoroethylene. Examples of the polyamide-based material include nylon and aramid (meta-based aramid and para-based aramid).

[0173] The use of a separator with a multi-layer structure allows the safety of the lithium-ion battery to be maintained even when the total thickness of the separator is small, so that the discharge capacity per volume of the lithium-ion battery can be increased. [Outer part]

[0174] For an outer part included in the lithium-ion battery, for example, a metal material such as aluminum or a resin material can be used. A film-shaped outer part can also be used. As the film, for example, a film having a three-layer structure in which a highly flexible thin metal film made of aluminum, stainless steel, copper, nickel, or the like is provided over a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film made of a polyamide-based resin, a polyester-based resin, or the like is provided as the outer surface of the outer part over the thin metal film can be used.

[0175] This embodiment may be implemented in combination with any of the other embodiments. (Embodiment 3)

[0176] In this embodiment, embodiments of lithium-ion batteries are described. [Laminated lithium-ion battery]

[0177] Fig. 14A and Fig. 14B illustrate embodiments of a laminated lithium-ion battery 500. Fig. 14A and Fig. 14B are external views wherein the lithium-ion battery 500 comprises the electrolyte and separator described in the above embodiments (which are shown in Fig. 14A or Fig. 14B), a negative electrode 506 and a positive electrode 507. In the lithium-ion battery 500, the negative electrode 506 preferably has a larger area than the positive electrode 507. The lithium-ion battery 500 further includes a negative electrode terminal electrode 510 electrically connected to the negative electrode 506, and a positive electrode terminal electrode 511 electrically connected to the positive electrode 507. The electrolyte, the negative electrode 506, and the positive electrode 507 are housed in an outer part 509, and the negative electrode terminal electrode 510 and the positive electrode terminal electrode 511 partially protrude from the outer part 509. An adhesive region 508 is provided in a part of the outer periphery of the outer part 509. Fig. 14A illustrates an embodiment in which the negative electrode terminal electrode 510 and the positive electrode terminal electrode 511 protrude from the same side of the outer part 509, wherein the adhesive region 508 is provided at least on the side from which the terminal electrodes protrude and on two sides adjacent to this side. Fig. 14B illustrates an embodiment in which a side from which the negative electrode terminal electrode 510 protrudes from the outer part 509 and a side from which the positive electrode terminal electrode 511 protrudes from the outer part 509 are opposite each other, wherein the adhesive region 508 is provided at least on the two sides from which the terminal electrodes protrude and on a side located between these sides. In Fig. 14A and Fig. 14B corresponds to a side where the adhesive area 508 is not provided, preferably to a side where the outer part 509 is folded.

[0178] By including the positive electrode active material of one embodiment of the present invention, the laminated lithium ion battery 500 can be a secondary battery with high capacity, high discharge capacity, and excellent cycle performance. [Button cell lithium-ion battery]

[0179] An example of a button cell lithium-ion battery is described. Fig. 15A is an exploded perspective view of a button cell (single-layer flat) lithium-ion battery, Fig. 15B is an exterior view of this, and Fig. 15C is a cross-sectional view of this. Button cell lithium-ion batteries are mainly used in small electronic devices. In this specification and the like, button cell lithium-ion batteries include coin cell lithium-ion batteries.

[0180] For easier understanding, Fig. 15A is a schematic view illustrating the overlap (a vertical relationship and a positional relationship) between components. Therefore, Fig. 15A and Fig. 15B do not fully agree with each other.

[0181] Fig. Fig. 15A illustrates a state in which a positive electrode 304, a negative electrode 307, a spacer 342, and a washer 332 overlap each other and are sealed with a negative electrode can 302 and a positive electrode can 301. Note that Fig. 15A does not depict the electrolyte or separator described in the above embodiments. The spacer 342 and the washer 332 are used when the positive electrode can 301 and the negative electrode can 302 are joined under pressure to protect the inside or to secure the position within the cans. Stainless steel or an insulating material is used for the spacer 342 or the washer 332.

[0182] The positive electrode 304 has a multilayer structure in which a positive electrode active material layer 306 is formed over a positive electrode current collector 305.

[0183] Fig. 15B is a perspective view of a completed button cell lithium-ion battery 300.

[0184] In the button cell lithium-ion battery 300, the positive electrode can 301, which also serves as a positive electrode terminal, and the negative electrode can 302, which also serves as a negative electrode terminal, can be insulated and sealed from each other by a gasket 303 made of polypropylene or the like. The positive electrode 304 includes the positive electrode current collector 305 and the positive electrode active material layer 306 provided in contact with the positive electrode current collector 305. The negative electrode 307 includes a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with the negative electrode current collector 308. The positive electrode can 301 and the negative electrode can 302 are electrically connected to the positive electrode 304 and the negative electrode 307, respectively.

[0185] It should be noted that only one surface of each of the positive electrode 304 and the negative electrode 307 used for the button cell lithium ion battery 300 is provided with an active material layer.

[0186] As in Fig. As shown in Fig. 15C, the positive electrode 304, the negative electrode 307, and the negative electrode can 302 are stacked in this order with the positive electrode can 301 at the bottom, and the positive electrode can 301 and the negative electrode can 302 are then pressure-bonded with the gasket 303 therebetween; as a result, the button cell lithium-ion battery 300 is manufactured.

[0187] By including the positive electrode active material of one embodiment of the present invention, the button cell lithium ion battery 300 can be a secondary battery with high capacity, high discharge capacity, and excellent cycle performance. [Cylindrical lithium-ion battery]

[0188] An example of a cylindrical lithium-ion battery is shown using Fig. 16A. As described in Fig. As shown in Figure 16A, a cylindrical lithium-ion battery 616 includes a positive electrode cap (battery lid) 601 on the top surface and a battery can (outer can) 602 on the side surface and the downward-facing surface. The positive electrode cap 601 and the battery can (outer can) 602 are insulated from each other by a gasket (insulating gasket) 610.

[0189] Fig. Figure 16B schematically shows a cross-section of a cylindrical lithium-ion battery. Fig. The cylindrical lithium-ion battery shown in Figure 16B includes the positive electrode cap (battery lid) 601 on the top surface and the battery can (outer can) 602 on the side surface and the downward-facing surface. The positive electrode cap 601 and the battery can (outer can) 602 are insulated from each other by the gasket (insulating gasket) 610.

[0190] Within the battery can 602, which has a hollow cylindrical shape, there is provided a battery element in which a belt-shaped positive electrode 604 and a belt-shaped negative electrode 606 are wound with an electrolyte layer 605 therebetween. Although not shown, the battery element is wound around a central axis. One end of the battery can 602 is closed, and the other end is open. Within the battery can 602, the battery element in which the positive electrode, the negative electrode, and the separator are wound is provided between a pair of insulating plates 608 and 609 facing each other. The inside of the battery can 602, which is provided with the battery element, is filled with an electrolyte solution (not shown).

[0191] Since a positive electrode and a negative electrode used for a cylindrical storage battery are wound, active materials are preferably formed on both sides of a current collector. It should be noted that, although Fig. 16A to Fig. 16D each illustrates the lithium-ion battery 616 in which the height of the cylinder is greater than the diameter of the cylinder; an embodiment of the present invention is not limited thereto. In the lithium-ion battery, the diameter of the cylinder may be greater than the height of the cylinder. Such a structure can, for example, reduce the size of a lithium-ion battery.

[0192] A positive electrode terminal (positive electrode current collector) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collector) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can be formed using a metal material such as aluminum. The positive electrode terminal 603 and the negative electrode terminal 607 are resistance-welded to a safety valve mechanism 613 and the bottom of the battery can 602, respectively. The safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a positive temperature coefficient (PTC) element 611.The safety valve mechanism 613 disconnects the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the internal pressure of the battery exceeds a predetermined threshold. The PTC element 611, which is a heat-sensitive resistor whose resistance increases with temperature rise, limits the amount of current by increasing the resistance to prevent abnormal heat generation. A barium titanate (BaTiO3)-based ceramic material or the like can be used for the PTC element 611.

[0193] Fig. 16C illustrates an example of an energy storage system 615. The energy storage system 615 includes a plurality of lithium-ion batteries 616 and is sometimes referred to as a battery pack. The positive electrodes of the lithium-ion batteries are in contact with and electrically connected to conductors 624 insulated by an insulator 625. The conductors 624 are electrically connected to a control circuit 620 via lines 623. The negative electrodes of the lithium-ion batteries are electrically connected to the control circuit 620 via a line 626. For example, a protection circuit for preventing overcharging or overdischarging can be used as the control circuit 620.

[0194] Fig. 16D illustrates an example of the energy storage system 615. The energy storage system 615 includes the plurality of lithium-ion batteries 616, and the plurality of lithium-ion batteries 616 are disposed between a conductive plate 628 and a conductive plate 614. The plurality of lithium-ion batteries 616 are electrically connected to the conductive plate 628 and the conductive plate 614 via a line 627. The plurality of lithium-ion batteries 616 may be connected in parallel or in series with each other, or may be connected in series after being connected in parallel with each other. With the energy storage system 615 including the plurality of lithium-ion batteries 616, a large electric current can be drawn.

[0195] The plurality of lithium-ion batteries 616 can be connected in series after being connected in parallel to each other.

[0196] A temperature control device may be provided between the plurality of lithium-ion batteries 616. If the lithium-ion batteries 616 become overheated, they can be cooled using the temperature control device, and if the lithium-ion batteries 616 become overcooled, they can be heated using the temperature control device. Thus, the performance of the energy storage system 615 is less likely to be affected by the outside air temperature.

[0197] In Fig. 16D, the energy storage system 615 is electrically connected to the control circuit 620 via a line 621 and a line 622. The line 621 is electrically connected to the positive electrodes of the plurality of lithium-ion batteries 616 via the conductive plate 628, and the line 622 is electrically connected to the negative electrodes of the plurality of lithium-ion batteries 616 via the conductive plate 614.

[0198] By including the positive electrode active material of one embodiment of the present invention, the cylindrical lithium ion battery 616 can be a secondary battery with high capacity, high discharge capacity, and excellent cycle performance. [Further structural examples of the lithium-ion battery]

[0199] Structural examples of lithium-ion batteries are shown using Fig. 17A to Fig. 17C and Fig. 18A to Fig. 18C described.

[0200] One in Fig. The lithium-ion battery 913 shown in Figure 17A includes a wound member 950 provided with a terminal 951 and a terminal 952 in a casing 930. The wound member 950 is immersed in an electrolyte solution within the casing 930. The terminal 952 is in contact with the casing 930. The terminal 951 is not in contact with the casing 930 using an insulator or the like. It should be noted that in Fig. 17A, the housing 930 is shown divided into two pieces for convenience; however, in the actual structure, the wound part 950 is covered with the housing 930, and the terminal 951 and the terminal 952 extend outside the housing 930. A metal material (e.g., aluminum) or a resin material can be used for the housing 930.

[0201] It should be noted that, as in Fig. 17B, ​​which is shown in Fig. 17A, the housing 930 can be formed using a variety of materials. Fig. For example, in the lithium-ion battery 913 shown in Fig. 17B, a casing 930a and a casing 930b are fixed to each other, and the wound part 950 is arranged in a region enclosed by the casing 930a and the casing 930b.

[0202] An insulating material such as an organic resin can be used for the housing 930a. Specifically, if a material such as an organic resin is used for the side where an antenna is formed, an electric field from the lithium-ion battery 913 can be prevented from being blocked. If an electric field is only slightly blocked by the housing 930a, an antenna can be arranged within the housing 930a. For example, a metal material can be used for the housing 930b.

[0203] Fig. 17C illustrates the structure of the wound part 950. The wound part 950 includes a negative electrode 931, a positive electrode 932, and electrolyte layers 933. The wound part 950 is obtained by winding a foil of a layered arrangement in which the negative electrode 931 and the positive electrode 932 overlap each other with the electrolyte layer 933 interposed therebetween. Note that further, a plurality of layered arrangements each including the negative electrode 931, the positive electrode 932, and the electrolyte layers 933 may be stacked.

[0204] As in Fig. 18A to Fig. 18C, the lithium-ion battery 913 may include a wound part 950a. Fig. The wound portion 950a shown in Figure 18A includes the negative electrode 931, the positive electrode 932, and the electrolyte layers 933. The negative electrode 931 includes a negative electrode active material layer 931a. The positive electrode 932 includes a positive electrode active material layer 932a.

[0205] The electrolyte layers 933 have a larger width than the negative electrode active material layer 931a and the positive electrode active material layer 932a, and are wound to overlap the negative electrode active material layer 931a and the positive electrode active material layer 932a. From a safety perspective, the width of the negative electrode active material layer 931a is preferably larger than that of the positive electrode active material layer 932a. The wound part 950a with such a shape is preferable due to its high degree of safety and high productivity.

[0206] As in Fig. As shown in Figure 18B, the negative electrode 931 is electrically connected to the terminal 951. The terminal 951 is electrically connected to a terminal 911a. The positive electrode 932 is electrically connected to the terminal 952. The terminal 952 is electrically connected to a terminal 911b.

[0207] As in Fig. As shown in Figure 18C, the wound part 950a is covered with the casing 930, thereby completing the lithium-ion battery 913. The casing 930 is preferably provided with a safety valve, an overcurrent protection element, and the like. A safety valve is a valve that is triggered by a predetermined internal pressure of the casing 930 to prevent the battery from exploding.

[0208] As in Fig. 18B, the lithium-ion battery 913 may include a plurality of wound parts 950a. The use of the plurality of wound parts 950a allows the lithium-ion battery 913 to have a higher charge / discharge capacity. For the other components of the Fig. 18A and Fig. 18B, the lithium-ion battery 913 can be referred to in the description of the Fig. 17A to Fig. 17C, reference may be made to the lithium-ion battery 913 shown.

[0209] By including the positive electrode active material of one embodiment of the present invention, the lithium ion battery 913 having the wound part can be a secondary battery with high capacity, high discharge capacity, and excellent cycle performance.

[0210] The contents of this embodiment may be appropriately combined with the contents of any of the other embodiments. (Embodiment 4)

[0211] In this embodiment, Fig. 19A to Fig. 19C describes an example of application to an electric vehicle (EV).

[0212] As in Fig. As shown in Figure 19A, the electric vehicle is provided with first batteries 1301a and 1301b as main lithium-ion batteries for operation, and a second battery 1311 that supplies electric power to an inverter 1312 for starting a motor 1304. By including the positive electrode active material of one embodiment of the present invention, the first batteries 1301a and 1301b can each be a secondary battery with high capacity, high discharge capacity, and excellent cycle performance.

[0213] The second battery 1311 is also called a booster battery (also called a starter battery). The second battery 1311 only needs a high output and does not necessarily need a high capacity, and the capacity of the second battery 1311 is lower than that of the first batteries 1301a and 1301b.

[0214] The internal structure of the first battery 1301a may be a wound structure or a multilayer structure. Alternatively, the first battery 1301a may be the secondary battery in the above embodiment. Using the secondary battery in the above embodiment as the first battery 1301a can achieve high capacity, improve safety, and reduce size and weight.

[0215] Although this embodiment describes an example in which the two first batteries 1301a and 1301b are connected in parallel, three or more batteries may be connected in parallel. If the first battery 1301a can store sufficient electric energy, the first battery 1301b may be omitted. By forming a battery pack including a plurality of lithium-ion batteries, a large amount of electric energy can be extracted. The plurality of lithium-ion batteries may be connected in parallel or in series, or connected in series after being connected in parallel. The plurality of lithium-ion batteries is also referred to as a composite battery.

[0216] To disconnect electrical energy from the plurality of lithium-ion batteries, the lithium-ion batteries in the vehicle include a service connector or circuit breaker that can disconnect high voltage without the use of a tool. The first battery 1301a is provided with such a service connector or circuit breaker.

[0217] The electrical energy from the first batteries 1301a and 1301b is mainly used to rotate the motor 1304 and is also supplied to 42V vehicle-mounted parts (such as an electric power steering 1307, a heater 1308, and a rear window defogger 1309) via a DC-DC circuit 1306. Even in the case where there is a rear motor 1317 for the rear wheels, the first battery 1301a is used to rotate the rear motor 1317.

[0218] The second battery 1311 supplies electrical energy to 14V vehicle-mounted parts (such as a stereo system 1313, a power window 1314, and lamps 1315) via a DC-DC circuit 1310.

[0219] The first battery 1301a is based on Fig. 19B.

[0220] Fig. 19B illustrates an example in which nine rectangular lithium-ion batteries 1300 constitute a battery pack 1415. The nine rectangular lithium-ion batteries 1300 are connected in series; one electrode of each battery is fixed by a fixing portion 1413 formed by an insulator, and the other electrode thereof is fixed by a fixing portion 1414 formed by an insulator. Although an example in which the lithium-ion batteries are fixed by the fixing portions 1413 and 1414 is described in this embodiment, they may be stored in a battery container box (also referred to as a casing). Since it is assumed that the vehicle is subjected to vibration or shock from the outside (e.g., a road surface), the plurality of, for example, lithium-ion batteries are preferably fixed by the fixing portions 1413 and 1414 and a battery container box.Furthermore, one electrode is electrically connected to a control circuit section 1320 via a line 1421. The other electrode is electrically connected to the control circuit section 1320 via a line 1422.

[0221] The control circuit section 1320 may include a memory circuit including a transistor using an oxide semiconductor. A charge control circuit or battery control system including a memory circuit including a transistor using an oxide semiconductor is sometimes referred to as a battery operating system or battery oxide semiconductor (BTOS).

[0222] A metal oxide serving as an oxide semiconductor is preferably used. As the oxide, for example, a metal oxide such as an In-M-Zn oxide (an element M is one or more selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, and magnesium) or the like is preferably used. Specifically, the In-M-Zn oxide that can be used as the oxide is preferably a c-axis aligned crystal oxide semiconductor (CAAC-OS) or a cloud-aligned composite oxide semiconductor (CAC-OS). An In-Ga oxide or an In-Zn oxide can alternatively be used as the oxide.CAAC-OS is an oxide semiconductor having a plurality of crystal regions, each of which has an alignment with respect to the c-axis in a specific direction. Note that the specific direction refers to the thickness direction of a CAAC-OS film, the normal direction of the formation surface of the CAAC-OS film, or the normal direction of the surface of the CAAC-OS film. The crystal region refers to a region having a periodic atom arrangement. Note that when an atom arrangement is regarded as a lattice arrangement, the crystal region also refers to a region having a uniform lattice arrangement. CAAC-OS includes a region in which a plurality of crystal regions are connected in the ab-plane direction, and the region has distortion in some cases.Note that a distortion refers to a portion where the direction of a lattice arrangement changes between a region with a uniform lattice arrangement and another region with a uniform lattice arrangement in a region where a plurality of crystal regions are connected. This means that the CAAC-OS is an oxide semiconductor that has a c-axis orientation and no significant ab-plane orientation.

[0223] The control circuit section 1320 preferably includes a transistor using an oxide semiconductor because the transistor can be used in a low-temperature environment. For process simplicity, the control circuit section 1320 can be formed using transistors of the same conductivity type. A transistor using an oxide semiconductor in its semiconductor layer has an ambient operating temperature range of -40°C to 150°C, which is wider than that of a single-crystal Si transistor, and therefore exhibits a smaller change in characteristics than the single-crystal Si transistor when the lithium-ion battery is heated. The off-state current of the transistor using an oxide semiconductor is lower than the lower measurement limit even at 150°C, regardless of the temperature.In contrast, the reverse current characteristics of the single-crystal Si transistor are highly dependent on temperature. For example, at 150°C, the reverse current of the single-crystal Si transistor increases, and a sufficiently high current on / off ratio cannot be achieved. The control circuit section 1320 can improve safety.

[0224] The control circuit section 1320, which includes a storage circuit including a transistor using an oxide semiconductor, can also serve as an automatic control device for the lithium-ion battery to eliminate ten instability factors such as a micro-short circuit. Examples of functions for eliminating the ten instability factors include overcharging prevention, overcurrent prevention, overheating control during charging, maintaining cell balance of an assembled battery, overdischarge prevention, a battery indicator, automatic control of the charging voltage and current amount according to temperature, control of the charging current amount according to the degree of deterioration, abnormal behavior detection for a micro-short circuit, and anomaly prediction regarding a micro-short circuit; the control circuit section 1320 has at least one of these functions.Furthermore, the automatic control device for the lithium-ion battery can be very miniaturized.

[0225] A microshort circuit refers to a tiny short circuit within a lithium-ion battery. One of the suspected causes of a microshort circuit is as follows: The uneven distribution of a positive electrode active material due to repeated charging and discharging causes a local current concentration in a portion of the positive electrode and a portion of the negative electrode. Another suspected factor is the generation of a byproduct from a side reaction.

[0226] It can be said that the control circuit section 1320 not only detects a micro-short circuit, but also detects a terminal voltage of the lithium-ion battery and controls the charge and discharge state of the lithium-ion battery. For example, to prevent overcharging, an output transistor of a charging circuit and a breaker switch can be turned off substantially simultaneously.

[0227] Fig. Figure 19C shows an example of a block diagram of the Fig. 19B shows the battery pack 1415.

[0228] The control circuit section 1320 includes a switch section 1324 that includes at least an overcharge prevention switch and an overdischarge prevention switch, a control circuit 1322 for controlling the switch section 1324, and a section for measuring the voltage of the first battery 1301a. The control circuit section 1320 is set to have the upper limit voltage and the lower limit voltage of the lithium-ion battery used, and to set the upper limit against current from the outside, the upper limit against output current to the outside, and the like. The range from the lower limit voltage to the upper limit voltage of the lithium-ion battery is within the recommended voltage range. When a voltage is outside the range, the switch section 1324 operates and serves as a protection circuit.The control circuit section 1320 can also be referred to as a protection circuit because it controls the switch section 1324 to prevent overdischarge and overcharge. For example, when the control circuit 1322 detects a voltage likely to cause overcharge, the power is interrupted by turning off the switch in the switch section 1324. Furthermore, a function for interrupting power according to a temperature rise can be provided by providing a PTC element in the charging and discharging path. The control circuit section 1320 includes an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0229] The switch section 1324 can be formed by combining an n-channel transistor and a p-channel transistor. The switch section 1324 is not limited to a switch with a Si transistor using single-crystal silicon; the switch section 1324 can be formed using, for example, a power transistor containing germanium (Ge), silicon germanium (SiGe), gallium arsenide (GaAs), gallium aluminum arsenide (GaAlAs), indium phosphide (InP), silicon carbide (SiC), zinc selenide (ZnSe), gallium nitride (GaN), gallium oxide (GaO x , where x is a real number greater than 0) or the like. A memory element using an OS transistor can be freely arranged, for example, by disposing it above a circuit using an Si transistor; therefore, integration can be easy. The control circuit section 1320 using an OS transistor can be arranged above the switch section 1324, so they can be integrated into one chip and their size can be reduced.

[0230] The first batteries 1301a and 1301b mainly supply electrical power to vehicle-mounted parts at 42V (for a high-voltage system), and the second battery 1311 supplies electrical power to vehicle-mounted parts at 14V (for a low-voltage system). Lead-acid storage batteries are typically used for the second battery 1311 due to their cost advantage. Using a lithium-ion battery has the advantage that the second battery 1311 is maintenance-free; however, if the battery is used for a long time, for example, three years or more, an abnormality may occur that cannot be determined during production.In particular, when the second battery 1311 for starting the inverter is inoperative, the engine cannot be started even if the first batteries 1301a and 1301b have remaining capacity; therefore, to prevent this, in the case where the second battery 1311 is a lead storage battery, the second battery is supplied with electric power from the first battery to constantly maintain a full charge state.

[0231] Although this embodiment describes an example in which lithium-ion batteries are used as both the first battery 1301a and the second battery 1311, a lead storage battery, an all-solid-state battery, or an electric double-layer capacitor may be used as the second battery 1311. By incorporating the positive electrode active material of one embodiment of the present invention, the lithium-ion batteries described above can each be a secondary battery with high capacity, high discharge capacity, and excellent cycle performance.

[0232] Renewable energy generated by the rotation of tires 1316 is transmitted to the motor 1304 via a transmission 1305 and stored in the second battery 1311 by a motor controller 1303 and a battery controller 1302 via a control circuit section 1321. Alternatively, the regenerative energy is stored in the first battery 1301a by the battery controller 1302 via the control circuit section 1320. Alternatively, the regenerative energy is stored in the first battery 1301b by the battery controller 1302 via the control circuit section 1320. For efficient charging with regenerative energy, the first batteries 1301a and 1301b are preferably suitable for rapid charging.

[0233] The battery controller 1302 can adjust the charging voltage, charging current, and the like of the first batteries 1301a and 1301b. The battery controller 1302 can adjust charging conditions according to the charging power of a lithium-ion battery in use, so that rapid charging can be performed.

[0234] Although not shown, in the case of connection to an external charger, a charger plug or a charger connection cable is electrically connected to the battery controller 1302. Electric energy supplied from the external charger is stored in the first batteries 1301a and 1301b via the battery controller 1302. Some chargers are provided with a control circuit, in which case the function of the battery controller 1302 is not used; to prevent overcharging, the first batteries 1301a and 1301b are preferably charged via the control circuit section 1320. In addition, a connection cable or the charger connection cable is provided with a control circuit in some cases. The control circuit section 1320 is also referred to as an electronic control unit (ECU).The ECU is connected to a Controller Area Network (CAN) provided in the electric vehicle. CAN is a type of serial communication standard used as a vehicle-mounted LAN. The ECU includes a microcomputer. The ECU also uses a CPU or GPU.

[0235] External chargers installed at charging stations and the like include, for example, a 100V outlet, a 200V outlet, and a three-phase 200V outlet (50 kW). Furthermore, charging can be performed with electrical energy supplied from an external charger using a contactless power supply method or the like.

[0236] Next, examples will be described in which the lithium-ion battery of one embodiment of the present invention is mounted on a vehicle, typically a transportation vehicle.

[0237] By installing lithium-ion batteries on vehicles, next-generation clean energy vehicles, such as hybrid vehicles (HV), electric vehicles (EV), and plug-in hybrid vehicles (PHV), can be realized. Lithium-ion batteries can also be installed on transportation vehicles such as agricultural machinery, motorized bicycles, including motor-assisted bicycles, motorcycles, electric wheelchairs, electric carts, boats and ships, submarines, aircraft (both fixed-wing and rotary-wing), rockets, artificial satellites, space probes, planetary probes, and spacecraft.

[0238] Fig. 20A to Fig. 20D illustrate examples of transport vehicles in which an embodiment of the present invention is used. An automobile 2001 shown in Fig. 20A is an electric vehicle that runs using an electric motor as an operating power source. Alternatively, the automobile 2001 is a hybrid vehicle that can appropriately select an electric motor or an internal combustion engine as an operating power source. In the case where the lithium-ion battery is mounted on the vehicle, an example of the lithium-ion battery described in the above embodiment is provided at one or more locations. By including the positive electrode active material of one embodiment of the present invention, the lithium-ion battery mounted on the vehicle can be a secondary battery with a high capacity, a high discharge capacity, and excellent cycle performance.

[0239] The 2001 automobile, which was Fig. 20A, includes a battery pack 2200, and the battery pack includes a battery module in which a plurality of lithium-ion batteries are interconnected. In addition, the battery pack 2200 preferably further includes a charge control device electrically connected to the battery module.

[0240] The automobile 2001 can be charged when the lithium-ion battery in the automobile 2001 is supplied with electric power from the external charger through a plug-in system, a contactless charging system, or the like. For charging, a given method such as CHAdeMO (registered trademark) or Combined Charging System can be used as a charging method, a connector standard, and the like, as needed. The lithium-ion battery can be a charging station in a commercial facility or a household power source. For example, using the plug-in technology, the energy storage device mounted on the automobile 2001 can be charged by supplying it with electric power from the outside. Charging can be performed by converting an alternating current (AC power) into a direct current (DC power) using a converter such as an AC-DC converter.

[0241] Although not shown, the vehicle may be provided with a power receiving device so that it can be charged by supplying it with electrical power from an above-ground power transmission device in a contactless manner. In the case of the contactless power supply system, charging can be performed not only while the vehicle is stopped but also while the vehicle is moving by installing a power transmission device in a road or an exterior wall. Furthermore, the contactless power supply system can be used to transmit and receive electrical power between two vehicles. In addition, a solar cell may be provided on the exterior of the vehicle to charge the lithium-ion battery while the vehicle is stopped or moving. For such a contactless power supply, an electromagnetic induction method or a magnetic resonance method can be used.

[0242] Fig. 20B illustrates a large van 2002 with an engine driven by electricity as an example of a transport vehicle. A battery module of the van 2002 includes, for example, a cell unit of four lithium-ion batteries with a nominal voltage higher than or equal to 3.0 V and lower than or equal to 5.0 V, and 48 cells connected in series to have a maximum voltage of 170 V. A battery pack 2201 has the same function as that in Fig. 19B, except for, for example, the number of lithium-ion batteries; therefore, the description is omitted. By including the positive electrode active material of one embodiment of the present invention, the lithium-ion batteries in the battery pack 2201 can each be a secondary battery with high capacity, high discharge capacity, and excellent cycle performance.

[0243] Fig. 20C illustrates, by way of example, a large transport vehicle 2003 with a motor driven by electricity. A battery module of the transport vehicle 2003 comprises, for example, 100 or more lithium-ion batteries with a nominal voltage greater than or equal to 3.0 V and less than or equal to 5.0 V, connected in series to have a maximum voltage of 600 V. A battery pack 2202 has the same function as that in Fig. 19B, except for, for example, the number of lithium-ion batteries constituting the battery module; therefore, the description is omitted. By incorporating the positive electrode active material of one embodiment of the present invention, the lithium-ion batteries of the battery module can each be a secondary battery with high capacity, high discharge capacity, and excellent cycle performance.

[0244] Fig. 20D is an example of an aircraft in 2004 with a combustion engine. Fig. The aircraft 2004 shown in Figure 20D can also be considered as a type of transport vehicle since it includes wheels for takeoff and landing, and includes a battery pack 2203 including a charge control device and a battery module formed by connecting a plurality of lithium-ion batteries.

[0245] For example, the battery module of the 2004 aircraft comprises eight 4 V lithium-ion batteries connected in series to provide a maximum voltage of 32 V. The 2203 battery pack has the same function as the one in Fig. 19B, except for, for example, the number of lithium-ion batteries constituting the secondary battery module; therefore, the description is omitted.

[0246] The contents of this embodiment may be appropriately combined with the contents of any of the other embodiments. (Embodiment 5)

[0247] In this embodiment, examples will be described in which a vehicle, such as a motorcycle or a bicycle, is provided with the lithium ion battery of one embodiment of the present invention.

[0248] Fig. Figure 21A illustrates an example of an electric bicycle using the lithium-ion battery of one embodiment of the present invention. The lithium-ion battery of one embodiment of the present invention can be used for a Fig. 21A. The lithium-ion battery of one embodiment of the present invention may include a protection circuit.

[0249] The electric bicycle 8700 includes an energy storage device 8702. The energy storage device 8702 can supply electrical energy to a motor that assists a rider. The energy storage device 8702 is portable and Fig. 21B illustrates the state in which the energy storage device 8702 is detached from the bicycle. A plurality of lithium-ion batteries 8701 of one embodiment of the present invention are installed in the energy storage device 8702, and the remaining battery capacity and the like can be displayed on a display section 8703. By incorporating the positive electrode active material of one embodiment of the present invention, the lithium-ion batteries 8701 can each be a secondary battery with high capacity, high discharge capacity, and excellent cycle performance.

[0250] The energy storage device 8702 includes a control circuit 8704 suitable for charge control and anomaly detection for the lithium-ion battery. The control circuit 8704 is electrically connected to a positive electrode and a negative electrode of the lithium-ion battery 8701. The control circuit 8704 can greatly contribute to the elimination of accidents caused by lithium-ion batteries, such as fires.

[0251] Fig. Figure 21C illustrates an example of a motorcycle incorporating the lithium-ion battery of an embodiment of the present invention. Fig. The scooter 8600 shown in Figure 21C includes an energy storage device 8602, side mirrors 8601, and turn signals 8603. The energy storage device 8602 can supply electrical power to the turn signals 8603. By incorporating the positive electrode active material of one embodiment of the present invention, the lithium-ion battery can be a secondary battery with high capacity, high discharge capacity, and excellent cycle performance.

[0252] In the Fig. In the scooter 8600 shown in Figure 21C, the energy storage device 8602 can be housed in a storage unit under the seat 8604. The energy storage device 8602 can be housed in the storage unit under the seat 8604 even if the storage unit under the seat 8604 is small.

[0253] The contents of this embodiment may be appropriately combined with the contents of any of the other embodiments. (Embodiment 6)

[0254] In this embodiment, examples of electronic devices each including the lithium-ion battery of one embodiment of the present invention will be described. Examples of electronic devices including the lithium-ion battery include a television set (also referred to as a television or television receiver), a monitor of a computer, and the like, a digital camera, a digital video camera, a digital photo frame, a mobile phone (also referred to as a cellular phone or mobile phone device), a portable game console, a portable information terminal, an audio playback device, and a large-scale gaming machine such as a pachinko machine. Examples of the portable information terminal include a laptop personal computer, a tablet computer, an e-book reader, and a mobile phone.

[0255] Fig. 22A illustrates an example of a mobile phone. A mobile phone 2100 includes a display section 2102 installed in a housing 2101, operation buttons 2103, an external connection terminal 2104, a speaker 2105, a microphone 2106, and the like. The mobile phone 2100 includes a lithium-ion battery 2107. By including the positive electrode active material of one embodiment of the present invention, the lithium-ion battery can be a secondary battery with high capacity, high discharge capacity, and excellent cycle performance.

[0256] The mobile phone 2100 can execute various applications, such as making mobile phone calls, sending and receiving emails, displaying and editing text, playing music, Internet communication, and running computer games.

[0257] The control buttons 2103 can perform various functions, such as setting the time, turning the power on / off, turning wireless communication on / off, activating and deactivating a sleep mode, and activating and deactivating a power-saving mode. For example, the functions of the control buttons 2103 can be freely configured by an operating system built into the mobile phone 2100.

[0258] The mobile phone 2100 can perform near-field communication that conforms to a communication standard. For example, mutual communication between the mobile phone 2100 and a headset capable of wireless communication enables hands-free phone calls.

[0259] The mobile phone 2100 includes the external connection port 2104 and can send and receive data to or directly from another information terminal via a connection. Furthermore, charging can be performed via the external connection port 2104. Note that charging can be performed without the external connection port 2104 by wireless power supply.

[0260] The mobile phone 2100 preferably includes a sensor. A sensor for the human body, such as a fingerprint sensor, a pulse sensor, a temperature sensor, a touch sensor, a pressure-sensitive sensor, or an acceleration sensor, is preferably mounted as the sensor.

[0261] Fig. 22B illustrates an unmanned aircraft 2300 with a plurality of rotors 2302. The unmanned aircraft 2300 is also referred to as a drone in some cases. The unmanned aircraft 2300 includes a lithium-ion battery 2301 of an embodiment of the present invention, a camera 2303, and an antenna (not shown). The unmanned aircraft 2300 can be remotely controlled using the antenna. By incorporating the positive electrode active material of an embodiment of the present invention, the lithium-ion battery can be a secondary battery with high capacity, high discharge capacity, and excellent cycle performance.

[0262] Fig. Figure 22C shows an example of a robot. A Fig. Robot 6400 shown in Fig. 22C includes a lithium-ion battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display section 6405, a lower camera 6406, an obstacle sensor 6407, a moving mechanism 6408, an arithmetic device, and the like.

[0263] The microphone 6402 has a function of detecting a user's speaking voice, ambient noise, and the like. The speaker 6404 has a function of outputting a sound. The robot 6400 can communicate with the user using the microphone 6402 and the speaker 6404.

[0264] The display section 6405 has a function for displaying various types of information. The robot 6400 can display information requested by the user on the display section 6405. The display section 6405 can be provided with a touchscreen. Furthermore, the display section 6405 can be a detachable information terminal, in which case, charging and data communication can be performed when the display section 6405 is set to the home position of the robot 6400.

[0265] The upper camera 6403 and the lower camera 6406 each have a function for capturing an image of the surroundings of the robot 6400. The obstacle sensor 6407 can detect the presence of an obstacle in the direction in which the robot 6400 moves forward with the movement mechanism 6408. The robot 6400 can move safely by detecting the surroundings with the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.

[0266] The robot 6400 further includes, within its interior, the lithium-ion battery 6409 of one embodiment of the present invention and a semiconductor device or an electronic component. By including the positive electrode active material of one embodiment of the present invention, the lithium-ion battery can be a secondary battery with high capacity, high discharge capacity, and excellent cycle performance.

[0267] Fig. 22D illustrates an example of a cleaning robot. A cleaning robot 6300 includes a display section 6302 disposed on a top surface of a housing 6301, a plurality of cameras 6303 disposed on a side surface of the housing 6301, a brush 6304, operation buttons 6305, a lithium-ion battery 6306, various sensors, and the like. Although not shown, the cleaning robot 6300 is provided with a tire, an intake port, and the like. The cleaning robot 6300 is self-propelled, collects dust 6310, and sucks the dust through the intake port provided on a bottom surface.

[0268] For example, the cleaning robot 6300 can determine whether an obstacle, such as a wall, a piece of furniture, or a step, is present by analyzing images captured by the cameras 6303. If the cleaning robot 6300 detects an object, such as a wire, that might be caught in the brush 6304 through image analysis, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 includes, in its interior, the lithium-ion battery 6306 of one embodiment of the present invention and a semiconductor device or an electronic component. By including the positive electrode active material of one embodiment of the present invention, the lithium-ion battery can be a secondary battery with high capacity, high discharge capacity, and excellent cycle performance.

[0269] This embodiment may be implemented in combination with any of the other embodiments. (Embodiment 7)

[0270] In this embodiment, examples of space equipment each including the lithium ion battery of one embodiment of the present invention will be described.

[0271] Fig. 23A illustrates an artificial satellite 6800 as an example of a space device. The artificial satellite 6800 includes a body 6801, a solar panel 6802, an antenna 6803, and a lithium-ion battery 6805. A solar panel is referred to as a solar cell module in some cases.

[0272] When the solar panel 6802 is irradiated with sunlight, electrical power required to operate the artificial satellite 6800 is generated. However, for example, in a situation where the solar panel is not irradiated with sunlight, or in a situation where the amount of sunlight irradiating the solar panel is small, the amount of generated electrical power is small. As a result, a sufficient amount of electrical power required to operate the artificial satellite 6800 may not be generated. In order to operate the artificial satellite 6800 even with a small amount of generated electrical power, the artificial satellite 6800 is preferably provided with the lithium-ion battery 6805.By containing the positive electrode active material of one embodiment of the present invention, the lithium ion battery can be a secondary battery with high capacity, high discharge capacity, and excellent cycle performance.

[0273] The artificial satellite 6800 can generate a signal. The signal is transmitted via the antenna 6803, and the signal can be received, for example, by a ground-based receiver or another artificial satellite. When the signal transmitted by the artificial satellite 6800 is received, the position of a receiver receiving the signal can be measured, for example. Therefore, the artificial satellite 6800 can form, for example, a satellite positioning system.

[0274] Alternatively, the artificial satellite 6800 may include a sensor. For example, with a structure including a visible light sensor, the artificial satellite 6800 may have a function of detecting sunlight reflected from a ground-based object. Alternatively, with a structure including a thermal infrared sensor, the artificial satellite 6800 may have a function of detecting thermal infrared rays emitted from the Earth's surface. Therefore, the artificial satellite 6800 may serve, for example, as an Earth observation satellite.

[0275] Fig. 23B illustrates a space probe 6900 with a solar sail as an example of a space device. The space probe 6900 includes a body 6901, a solar sail 6902, and a lithium-ion battery 6905. By incorporating the positive electrode active material of one embodiment of the present invention, the lithium-ion battery can be a secondary battery with high capacity, high discharge capacity, and excellent cycle performance. When photons emitted from the sun strike the surface of the solar sail 6902, the momentum is transferred to the solar sail 6902. Therefore, the surface of the solar sail 6902 preferably comprises a thin film with high reflectivity and more preferably faces the sun.

[0276] The solar sail 6902 can be designed in such a way that it is folded small before it exits the atmosphere and can be used outside the Earth’s atmosphere (in space) in a large sheet shape as in Fig. 23B is unfolded.

[0277] Fig. 23C illustrates a spacecraft 6910 as an example of a space facility. The spacecraft 6910 includes a body 6911, a solar panel 6912, and a lithium-ion battery 6913. By incorporating the positive electrode active material of one embodiment of the present invention, the lithium-ion battery can be a secondary battery with high capacity, high discharge capacity, and excellent cycle performance. The body 6911 may include, for example, a pressurized cabin and a non-pressurized cabin. The pressurized cabin may be configured so that the crew can enter the cabin. Electric power generated by irradiating the solar panel 6912 with sunlight can be stored in the lithium-ion battery 6913.

[0278] Fig. 23D illustrates a rover 6920 as an example of a space device. The rover 6920 includes a body 6921 and a lithium-ion battery 6923. By incorporating the positive electrode active material of one embodiment of the present invention, the lithium-ion battery can be a secondary battery with high capacity, high discharge capacity, and excellent cycle performance. The rover 6920 may include a solar panel 6922.

[0279] The rover 6920 can be designed so that the crew can board the rover 6920. Electrical energy generated by irradiating the solar panel 6912 with sunlight can be stored in the lithium-ion battery 6923, or electrical energy generated by another energy source, such as a fuel cell or a radioisotope thermoelectric generator, can be stored in the lithium-ion battery 6923.

[0280] The contents of this embodiment may be appropriately combined with the contents of any of the other embodiments. [Example 1]

[0281] In this example, the positive electrode active material of one embodiment of the present invention was prepared, its properties were analyzed, and its electrochemical properties were evaluated. <Herstellung des Positivelektrodenaktivmaterials>

[0282] The positive electrode active material of one embodiment of the present invention was prepared according to the flow chart in Fig. 2. As in Fig. As shown in Figure 2, commercially available LCO powder was doped with magnesium, nickel and aluminum.

[0283] MgF2 (purity: 99.9%), LiF (purity: 99%), Ni(OH)2 (purity: 99.9%), Al(OH)3 (purity: 99.99%), and LiCoO2 (purity: 99%; C-10N, manufactured by NIPPON CHEMICAL INDUSTRIAL CO., LTD.) were used for the synthesis. In addition, C-10N was used as the original reference LCO without any processing.

[0284] The muffle furnace was used for all heating processes, and the samples were placed in an alumina crucible.

[0285] First, the original LCO (D50 of 12.5 µm) was preheated at 850 °C for 2 hours without the addition of any additive elements in an oxygen atmosphere. In the first additive process, the preheated LCO, MgF2, and LiF were weighed and mixed in a molar ratio of 1:0.01:0.003. This mixture was heated at 900 °C for 20 hours in an oxygen atmosphere. In the second additive process, the LCO obtained in the first additive process was mixed with Ni(OH)2 and Al(OH)3 in a molar ratio of 1:0.005:0.005. The mixture was heated at 850 °C for 10 hours in an oxygen atmosphere.

[0286] For comparison, M-LCO, MF-LCO, FN-LCO, FA-LCO, FNA-LCO, F-LCO, NA-LCO, MFN-LCO, and MFA-LCO were synthesized using a similar process by adding only Mg(OH)2, MgF2-LiF, LiF-Ni(OH)2, LiF-Al(OH)3, LiF-Ni(OH)2-Al(OH)3, LiF, Ni(OH)2-Al(OH)3, MgF2-LiF-Ni(OH)2, and MgF2-LiF-Al(OH)3, respectively. A heated LCO without any additive elements was also prepared using the same first and second heating processes. The original LCO was not subjected to the heating process.

[0287] To synthesize M-LCO, the preheated LCO was mixed with Mg(OH)2 in a molar ratio of 1:0.01 and then subjected to heating as in the first addition process described previously. To synthesize MF-LCO, the preheated LCO, MgF2, and LiF were mixed in a molar ratio of 1:0.01:0.003 and then subjected to heating as in the first addition process. These products were finally subjected to heating without any additive elements as in the second addition process to obtain the final products.

[0288] For FN-LCO, FA-LCO, FNA-LCO, and F-LCO, the preheated LCO and LiF were mixed in a molar ratio of 1:0.023 and then subjected to heating as in the first addition process. The resulting LCO was mixed with Ni(OH)2 or Al(OH)3 in a molar ratio of 1:0.005, or with Ni(OH)2 and Al(OH)3 in a molar ratio of 1:0.005:0.005, and then subjected to the heating process as in the second addition process.

[0289] To synthesize NA-LCO, no additive element was added to the preheated LCO before the first heating. The LCO subjected to the first heating was mixed with Ni(OH)2 and Al(OH)3 in a molar ratio of 1:0.005:0.005 and then subjected to the second heating process. To synthesize MFN-LCO and MFA-LCO, the preheated LCO, MgF2, and LiF were mixed in a molar ratio of 1:0.01:0.003 and then subjected to the first heating process. The obtained LCO was mixed with Ni(OH)2 or Al(OH)3 in a molar ratio of 1:0.005 and then subjected to the second heating process. The heated LCO without additive elements was also prepared by the same first and second heating processes. <morphologische und strukturelle Analyse> < <xrd>>

[0290] Fig. 24A to Fig. 24C show powder XRD patterns of the positive electrode active material of one embodiment of the present invention and the original LCO, as well as a reference sample. The powder XRD patterns of the positive electrode active material of one embodiment of the present invention and the original LCO indicate the presence of an O3 phase and an R-3m space group; no other phases were observed.

[0291] Table 2 shows the results of Rietveld refinement of the powder XRD patterns of the samples. Rietveld refinement was performed using DIFFRAC TOPAS ver. 6 software on a single phase of LiCoO2 in the R-3m space group. The c-axis length of the positive electrode active material of one embodiment of the present invention was slightly elongated compared to that of the pristine LCO. A possible reason for the elongation could be the doping of nickel and aluminum. The change in the a-axis length is very small, indicating that a small amount of magnesium was substituted at the cobalt site. [Table 2] sample parameter a (Å) c (Å) V (Å -3 ) Lvol-IB (nm) R exp R wp GOF original LCO 2,816(3) 14,052(0) 96,522(8) 317(4) 6,92 11,09 1,6 Positive electrode active material of an embodiment of the present invention 2,816(1) 14,057(5) 96,552(8) 273(3) 7,26 8,06 1,11 M-LCO 2,816(7) 14,055(8) 96,578(6) 265(4) 9,08 9,91 1,09 MF-LCO 2,815(9) 14,051 (8) 96,493(7) 238(3) 8,47 9,07 1,07 FN-LCO 2,816(1) 14,053(1) 96,514(5) 260(3) 7,01 7,54 1,08 FA-LCO 2,815(8) 14,051(7) 96,485(5) 263(3) 7,25 8,38 1,16 FNA-LCO 2,816(0) 14,054(0) 96,516(6) 257(3) 6,91 7,7 1,12 < <sem>>

[0292] Fig. 25A and Fig. 25B shows scanning electron microscope (SEM) images of the original LCO. Fig. 25C and Fig. 25D show SEM images of the positive electrode active material of one embodiment of the present invention. The scale bars in Fig. 25A and Fig. 25C each represent 10 µm, and the scale bars in Fig. 25B and Fig. 25D each represent 2 µm. The SEM images were acquired using a Hitachi SU4800 or SU8030 field emission SEM (FE-SEM) with an accelerating voltage of 5 kV.

[0293] The SEM images revealed that the surface of the positive electrode active material of one embodiment of the present invention was smoother than that of the original LCO. This may be due to the partial melting of the surface of the LCO particle and the molten fluoride salt during the heating process. < <sem-edx>>

[0294] Fig. 26A to Fig. 26 years and Fig. 27A to Fig. 27F shows SEM-EDX mapping images of the positive electrode active material of one embodiment of the present invention in its synthesis steps. The SEM images were acquired using a Hitachi SU4800 or SU8030 field emission SEM (FE-SEM) with an acceleration voltage of 5 kV. SEM-EDX analysis was performed using an EMAX Evolution EX-370 (HORIBA Ltd.) with an acceleration voltage of 15 kV. Fig. 26A and Fig. 26B show SEM images of the original LCO, and Fig. 26C and Fig. 26D shows SEM images of the preheated LCO. Fig. 26E and Fig. 26F show SEM images of the mixture of preheated LCO, LiF and MgF2, and Fig. Figure 26G shows SEM-EDX mapping images of respective elements in the same area as Fig. 26F. Fig. 26H and Fig. 26I show SEM images of LCO added with magnesium and fluorine, and Fig. Figure 26J shows SEM-EDX mapping images of respective elements in the same area as Fig. 26I. Fig. 27A and Fig. 27B show SEM images of the mixture of LCO added with magnesium and fluorine, Ni(OH)2 and Al(OH)3, and Fig. Figure 27C shows SEM-EDX mapping images of respective elements in the same area as Fig. 27B. Fig. 27D and Fig. 27E show SEM images of the positive electrode active material of one embodiment of the present invention, and Fig. Figure 27F shows SEM-EDX mapping images of respective elements in the same area as Fig. 27E. The scale bars in Fig. 26A, Fig. 26C, Fig. 26E, Fig. 26H, Fig. 27A and Fig. 27D each represent 50 µm, and the scale bars in Fig. 26B, Fig. 26D, Fig. 26F, Fig. 26G, Fig. 26I, Fig. 26 years old, Fig. 27B, Fig. 27C, Fig. 27E and Fig. 27F each represent 5 µm.

[0295] As in Fig. 26E to Fig. 26J, SEM-EDX shows that the heating melted the added MgF2-LiF nanoparticles, which spread wet on the surface of the lithium cobalt oxide particle. As shown in Fig. 27D to Fig. As shown in Figure 27F, EDX element mapping analysis of the positive electrode active material particle of one embodiment of the present invention shows that magnesium, nickel, and aluminum are uniformly distributed. However, nanoparticles composed primarily of these additive elements were not observed. < <icp-ms>>

[0296] In the synthesis of the positive electrode active material of one embodiment of the present invention, the element ratio Co:Mg:F = 1:0.01:0.023. Table 3 shows the results of quantitative analysis of the additive elements using inductively coupled plasma mass spectrometry (ICP-MS). The ICP-MS analysis was performed using an Agilent 8900. As shown in Table 3, the element ratio of Co:Mg in the particles of the positive electrode active material of one embodiment of the present invention was confirmed to be 1:0.0093. [Table 3] sample Element ratio Li / Co Mg / Co Ni / Co Al / Co original LCO 1,06 0,0003 0,0004 0,0002 Positive electrode active material of an embodiment of the present invention 0,94 0,0093 0,0052 0,0055 < <epma>>

[0297] As shown in Table 4, an electron probe microanalyzer (EPMA) also revealed that Co:Mg = 1:0.009 in a cross-section of a particle of the positive electrode active material of one embodiment of the present invention. The EPMA analysis was performed using a JXA-iHP200F (JEOL Ltd.) with an accelerating voltage of 10 kV. To analyze the elements of the bulk, the measurement was performed around the center of the particle's cross-section. [Table 4] sample Element ratio F / Co Mg / Co Ni / Co Al / Co original LCO not recorded not recorded not recorded not recorded Positive electrode active material of an embodiment of the present invention not recorded 0,009 0,006 not recorded < <xps>>

[0298] However, X-ray photoelectron spectroscopy (XPS) showed that the ratios of magnesium and fluorine to cobalt in the positive electrode active material of one embodiment of the present invention were significantly higher than those of magnesium and fluorine added during synthesis to cobalt contained in the original LCO. This indicates that magnesium and fluorine were sufficiently distributed at the outermost surface of the particles of the positive electrode active material of one embodiment of the present invention. The element ratio obtained by XPS was Co:Mg:F = 1:0.93:0.53.

[0299] Table 5 shows the chemical compositions of the particle surfaces of the original LCO, the positive electrode active material of an embodiment of the present invention and the Fig. Two samples marked with asterisks were measured by XPS analysis. The XPS measurements were recorded using a spectrometer with an Al X-ray source (1486.6 eV) (Quantera-SXM, ULVAC-PHI, Inc.). All binding energies were calibrated using the C 1s peak at 284.8 eV. [Table 5] sample Element ratio Li / Co Mg / Co F / Co Ni / Co Al / Co original LCO 0,85 not recorded 0,08 not recorded not recorded preheated LCO 0,71 not recorded 0,12 not recorded not recorded Mixture of preheated LCO, LiF and MgF2 0,49 0,33 0,83 not recorded not recorded LCO with added Mg and F 0,74 0,8 0,57 not recorded not recorded Mixture of LCO to which Mg and F are added, Ni(OH)2 and Al(OH)3 0,75 0,67 0,42 2,02 0,6 Positive electrode active material of an embodiment of the present invention 0,95 0,93 0,53 0,1 0,06

[0300] Fig. 28 and Fig. 29A and Fig. 29B shows XPS characterization of the positive electrode active material of one embodiment of the present invention. Fig. 28 shows XPS wide-scan spectra of the original LCO and the positive electrode active material of one embodiment of the present invention. Fig. 29A shows XPS narrow-scan spectra of F 1s of the positive electrode active material of one embodiment of the present invention, LCO to which magnesium and fluorine are added, the mixture of the preheated LCO, LiF and MgF2, MgF2 (reference sample) and LiF (reference sample), and Fig. Figure 29B shows XPS narrow-scan spectra of Mg 1s.

[0301] As in Fig. As shown in Figure 29A, the F 1s binding energy of the positive electrode active material of one embodiment of the present invention differs from that of MgF2 used as a source of an additive element. Furthermore, as shown in Fig. As shown in Figure 29B, the Mg 1s binding energy of the positive electrode active material of one embodiment of the present invention indicates the presence of oxyfluoride. The Mg 1s peak (the maximum value within the range of 1300 eV to 1308 eV; 1303.6 eV) of the positive electrode active material of one embodiment of the present invention lies between the peak of MgO (1303.3 eV) and the peak of MgF 2 (1306.3 eV). <<HAADF-STEM, NBED> >

[0302] Fig. Figure 25E shows a high-angle annular dark field scanning transmission electron microscope (HAADF-STEM) image encompassing the particle surface portion of the original LCO. Fig. Figure 25F is an enlarged view of the area enclosed by the dotted rectangle in Fig. 25E is enclosed. Fig. Figure 25G shows nanobeam electron diffraction (NBED) patterns of the marked areas 1 and 2 in Fig. 25E. The cross-sectional HAADF-STEM observations and NBED measurements were performed using JEM-ARM200F, STEM with spherical aberration correction, manufactured by JEOL Ltd., at an accelerating voltage of 200 kV.

[0303] As in Fig. 25E and Fig. As shown in Figure 25F, a slight cation mixing occurs near the surface. Each of Regions 1 and 2 exhibits a pattern that exhibits a layered rock-salt crystal structure. This revealed a layered rock-salt structure in the surface portion of the original LCO particles, similar to their internal structure.

[0304] Fig. 25H shows a HAADF-STEM image including the particle surface of the positive electrode active material of one embodiment of the present invention, and Fig. Figure 25I shows an enlarged view of the area enclosed by the dotted rectangle in Fig. 25H is enclosed. Fig. Figure 25J shows NBED patterns of the marked areas 3 and 4 in Fig. 25H. Region 3 has a pattern showing a rock salt crystal structure, and region 4 has a pattern showing a layered rock salt crystal structure.

[0305] It should be noted that the scale bars in Fig. 25E to Fig. 25I each represent 3 nm. Both in Fig. 25G as well as Fig. 25J the incident direction of the electron beam is shown, and indices are added for some points. Fig. 25J includes points indicating a rock salt structure (dashed circles) and one point indicating a layered rock salt structure (a solid circle).

[0306] With the dashed line in Fig. 25I as a label indicates the coherent bond between the layered rock salt crystal structure (area I) and the rock salt crystal structure (area II). As shown in Fig. 25H and Fig. As shown in Figure 25I, the inner portion (also referred to as the bulk region) of the positive electrode active material of one embodiment of the present invention exhibits a layered rock-salt structure with a visible contrast between the Co and Li layers in the HAADF-STEM image. Cation mixing is also observed. In the outermost surface region, a 1 nm thick rock-salt structure is observed (as represented by the electron diffraction spots enclosed by the dashed circles), and a layered rock-salt structure is also observed (as represented by the electron diffraction spot enclosed by the solid circle).

[0307] It should be noted that, as in Fig. As shown in Figure 25I, the continuity of the alignment of atomic columns between Region I and Region II indicates that the rock-salt shell (Region II) is coherently bound to the layered rock-salt core (Region I). Since this rock-salt shell, as shown in the XPS results, contains similar amounts of lithium as cobalt and magnesium, lithium ions are expected to pass through the shell.

[0308] This means that lithium ions can pass through the shell via sites where lithium is present in the post-synthesis phase of the rock salt crystal structure. Here, it is assumed that when, for example, the cation occupancy rate of lithium, Li / (L+Co+Mg+Ni+Al), is greater than or equal to 20%, the cation occupancy rate of lithium exceeds the critical percolation probability of the face-centered cubic lattice, allowing the intercalation and deposition of Li ions. Since a cation vacancy can also serve as a Li diffusion pathway, it is assumed that Li ions can be intercalated and decalcified even when the above cation occupancy rate of lithium, considering a cation vacancy, (Li+cation vacancy) / (Li+Co+Mg+Ni+Al+cation vacancy), is greater than or equal to 20%. < <stem-edx>>

[0309] Fig. 30A to Fig. 30C and Fig. 31 shows an energy dispersive X-ray (EDX) elemental analysis of the positive electrode active material of one embodiment of the present invention.

[0310] Fig. Figure 30A shows a HAADF-STEM image and a corresponding STEM / EDX elemental mapping analysis of Co, F, Mg, Ni, and Al. The scale bars represent 5 nm each. Fig. Figure 30B shows a depth profile of an element distribution. Fig. 30C is an enlarged view of the Fig. 30B. Fig. Figure 31 shows a wide-area HAADF-STEM image of the surface of a particle of the positive electrode active material of one embodiment of the present invention and a corresponding wide-area STEM-EDX element mapping analysis of Co, F, Mg, Ni, and Al. The scale bars represent 50 nm each. Cross-sectional STEM-EDX analysis was performed using JED-2300T (JEOL Ltd.).

[0311] The above results revealed a uniform distribution of F, Mg, and Ni across the outermost surface, whereas their presence in the bulk was negligible in this measurement. Al is observed over a broad range from the particle surface. Distinct gradients of additive elements were visible near the surface of the positive electrode active material of one embodiment of the present invention. These observations indicate that a topotactic phase transition from the layered rock salt to the rock salt structure occurs during synthesis, which is due to the migration of additive elements into the LCO structure.

[0312] The distribution of additive elements in the particle surface portion of the positive electrode active material of one embodiment of the present invention could be explained as follows. First, the solubility of Mg 2+ in lithium cobalt oxide approximately 0.5%, while Al 3+ with lithium cobalt oxide can form a solid solution, which is replaced by LiAl x Co 1-x O2. Next, MgO, CoO, and NiO form solid solutions with a rock salt structure. Therefore, the Mg 2+ - and Ni 2+ -ions Co 2+ ions replace the CoO region in the surface portion of the lithium cobalt oxide particle, which was formed by reducing the surface area during high-temperature heating. Therefore, the rock salt layer in the surface portion of the lithium cobalt oxide contains large amounts of Mg and Ni. In contrast, the c-axis extension observed by XRD and EPMA analysis indicates that the majority of the added magnesium in the LCO particles forms a solid solution. The distribution of the additive elements is achieved using molten salts of LiF and MgF2 in combination with appropriate heating steps. < <morphologische und strukturelle Analyse in jedem Schritt bei der Synthese des Positivelektrodenaktivmaterials einer Ausführungsform der vorliegenden Erfindung> >

[0313] The detailed features of the positive electrode active material of one embodiment of the present invention in each step in the synthesis process will be described below.

[0314] To evaluate the structural properties, SEM-EDX, XPS, and XRD measurements were performed at each step of the synthesis process of the positive electrode active material of one embodiment of the present invention. The analyses were performed at the following stages shown in the flow chart of the synthesis of the positive electrode active material of one embodiment of the present invention. Fig. 2 are marked with an asterisk. -original LCO -preheated LCO -Mixture of preheated LCO, LiF and MgF2 -LCO, to which magnesium and fluorine are added -Mixture of LCO to which magnesium and fluorine are added, Ni(OH)2 and Al(OH)3 -the positive electrode active material of one embodiment of the present invention <sem-edx-analyse>

[0315] The results of SEM-EDX ( Fig. 26A to Fig. 26 years and Fig. 27A to Fig. 27F) show that the particle surface conditions in each step were as follows. The pristine LCO exhibited numerous scratches and adherent materials on the particle surface. The surface of the preheated LCO particles was smoother than that of the pristine LCO. The particles of the mixture of preheated LCO, LiF, and MgF2 were sparsely decorated with nanoparticles of MgF2 and LiF. After the first heating step, the LCO containing magnesium and fluorine exhibited a smooth surface, and SEM-EDX could no longer detect the nanoparticles containing Mg and F on the LCO particle surface, revealing that MgF2 and LiF had been melted on the LCO surface.

[0316] The particle surface of the mixture of LCO added with magnesium and fluorine, Ni(OH)2, and Al(OH)3 was coated with nanoparticles of Ni(OH)2 and Al(OH)3. The particle surface in the positive electrode active material of one embodiment of the present invention was smooth, unlike the mixture of LCO added with magnesium and fluorine, Ni(OH)2, and Al(OH)3, and a uniform coating of Mg, F, Ni, and Al was observed by SEM-EDX. <xps-analyse>

[0317] Fig. 28, Fig. 29A and Fig. Figure 29B and Table 5 show the XPS measurement results. From the XPS, as shown in SEM images, large amounts of magnesium and fluorine were detected in the mixture of preheated LCO, LiF, and MgF2 because the nanoparticles of MgF2 and LiF adhered to the LCO surface. The amount of magnesium detected after the first heating in the LCO with magnesium and fluorine added was larger than that before the first heating. This phenomenon was presumably caused by an increase in the amount of magnesium in the XPS sample area at a depth of approximately 5 nm from the surface. This increase resulted from the melting and dispersing of magnesium on the surface of the lithium cobalt oxide particle due to the action of the molten fluoride salt. The amount of fluorine detected was smaller than that in the previous step, possibly because some of the LiF volatilized when it was melted.Very large amounts of nickel and aluminum were detected from the mixture of LCO added with magnesium and fluorine, Ni(OH)2, and Al(OH)3. This result is believed to be caused by Ni(OH)2 and Al(OH)3 nanoparticles covering the particle surface, as shown in SEM images. In the positive electrode active material of one embodiment of the present invention, the detection amounts of nickel and aluminum were smaller than those in the mixture of LCO added with magnesium and fluorine, Ni(OH)2 and Al(OH)3. This indicates that nickel and aluminum form solid solutions in the surface portion of the lithium cobalt oxide particle. Furthermore, it is noted that since the detection amount of magnesium is greater than the detection amounts of nickel and aluminum, magnesium is located at the outermost surface of the LCO particle, and nickel and aluminum are located further inside than the outermost surface.

[0318] Fig. 29A and Fig. Figure 29B shows the binding energies of F and Mg. The binding energies of F 1s and Mg 1s in the mixture of preheated LCO, LiF, and MgF2 indicate the presence of MgF2. However, the LCO added with magnesium and fluorine exhibited different binding energies, indicating the presence of an O-Mg-F bond. The O-Mg-F bond is maintained in the positive electrode active material of one embodiment of the present invention after the addition of Ni(OH)2 and Al(OH)3. <xrd-analyse>

[0319] Table 6 shows the results of Rietveld refinement of the powder XRD patterns. The preheated LCO exhibits a smaller lattice parameter than the pristine LCO, which should be due to reduced cation mixing and improved crystallinity. The c-axis length of the LCO with magnesium and fluorine added was longer compared to that of the mixture of preheated LCO, LiF, and MgF. 2 A possible reason for the increase in the length of the c-axis could be that Mg 2+ , which has a larger ionic radius than Co 3+ has been substituted at the Co site. Another reason for this could be that Mg 2+ , which has an ionic radius similar to that of Li + similar to Li, was substituted at the Li site, thereby changing the valence of the adjacent cobalt from trivalent to divalent for electric charge compensation. The positive electrode active material of one embodiment of the present invention also retained an increased c-axis length. This indicates that, as disclosed in the XPS, not only was the surface of the positive electrode active material of one embodiment of the present invention coated with a large amount of magnesium, but also magnesium was doped into the bulk of the positive electrode active material of one embodiment of the present invention. [Table 6] sample parameter a (Å) c (Å) V (Å -3 ) Lvol-IB (nm) R exp R wp GOF original LCO 2,816(3) 14,052(0) 96,522(8) 317(4) 6,92 11,09 1,6 preheated LCO 2,816(1) 14,052(0) 96,510(1) 284(3) 6,83 7,64 1,12 Mixture of preheated LCO, LiF and MgF2 2,816(0) 14,051(3) 96,499(9) 230(3) 7,14 8,34 1,17 LCO with added Mg and F 2,816(3) 14,055(3) 96,547(3) 290(3) 7,02 8,18 1,17 Mixture of LCO to which Mg and F are added, Ni(OH)2 and Al(OH)3 2,816(3) 14,054(9) 96,546(9) 342(5) 6,79 11,2 1,65 Positive electrode active material of an embodiment of the present invention 2,816(1) 14,057(5) 96,552(8) 273(3) 7,26 8,06 1,11 <elektrochemische Eigenschaften> < <halbzelle>>

[0320] Fig. 32A and Fig. 32B show the cycle performance of a positive electrode containing the original LCO and a positive electrode containing the positive electrode active material of one embodiment of the present invention in half cells. Fig. 32A and Fig. 32B shows the cycle performance of the electrode containing the original LCO and the electrode containing the positive electrode active material of one embodiment of the present invention in the coin cell half-cells at 25°C. Fig. 32A and Fig. 32B show the charge / discharge cycle performance of the half-cells with the positive electrode containing the original LCO and the positive electrode containing the positive electrode active material of an embodiment of the present invention; the voltage range is 2.5 V to 4.6 V (versus Li + / Li) in Fig. 32A and 2.5 V to 4.7 V (versus Li + / Li) in Fig. 32B. Fig. 33A shows the charge / discharge curves of the original LCO and the positive electrode active material of an embodiment of the present invention at different cycles under the conditions shown in Fig. 32A shown condition. Fig. Figure 33B shows the rate performance of half-cells containing the original LCO and the positive electrode active material of one embodiment of the present invention. Fig. 32A and Fig. 32B, the white circles represent the Coulomb efficiency of the positive electrode active material of one embodiment of the present invention, and the black circles represent the discharge capacity of the positive electrode active material of one embodiment of the present invention. The white squares represent the Coulomb efficiency of the original LCO, and the black squares represent the discharge capacity of the original LCO. The same applies to Fig. 35A and Fig. 39A and Fig. 39B.

[0321] With the generally used electrolyte solution, the positive electrode active material of one embodiment of the present invention exhibited significantly higher capacity retention than the original LCO. Specifically, the capacity retention of the positive electrode active material of one embodiment of the present invention after 100 cycles was 96.4% (205.2 mAh / g) at 2.5 V to 4.6 V (versus Li + / Li) and 72.7% (160.9 mAh / g) at 2.5 V to 4.7 V (versus Li + / Li), which are much higher than those of the original LCO. The high Coulombic efficiency observed during cycling with the positive electrode active material of one embodiment of the present invention indicates that oxidative electrolyte decomposition was effectively suppressed by the surface coating layer.

[0322] The charge / discharge curves in Fig. 33A shows that the average discharge voltage of the positive electrode active material of one embodiment of the present invention remained high even after 100 cycles. In contrast, the average discharge voltage of the original LCO decreased with an increase in voltage polarization. Furthermore, the positive electrode active material of one embodiment of the present invention exhibited excellent rate performance at each discharge rate relative to that of the original LCO. As shown in Fig. As shown in Figure 34, the positive electrode active material of one embodiment of the present invention was found to be highly effective even at a high mass loading at a practical level (20 mg / cm 2 ) is subjected to a charge / discharge. In Fig. 33B, the white circles represent the discharge capacity of the positive electrode active material of one embodiment of the present invention, and the black squares represent the discharge capacity of the original LCO.

[0323] The first charge / discharge cycles of the positive electrode active material of one embodiment of the present invention showed a reduction in cell resistance and an increase in discharge capacity. This phenomenon is due to the formation of a solid electrolyte interphase (SEI) on the surface of lithium cobalt oxide and the diffusion of magnesium into the lithium cobalt oxide structure.

[0324] A modified fluorinated electrolyte solution was applied instead of a generally used electrolyte solution to prepare half-cells, considering possible decomposition of the generally used electrolyte solution at a high cut-off voltage of 4.7 V (versus Li + / Li) was taken into account. To mitigate the effect of electrolyte solution decomposition, cycling performance was evaluated using a high charge / discharge rate and a low mass loading electrode.

[0325] Fig. Figure 35A shows the cycle performance of the half-cells with the positive electrode containing the positive electrode active material of one embodiment of the present invention and the positive electrode containing the original LCO in the voltage range of 2.5 V to 4.7 V (versus Li + / Li); each half-cell contains the fluorinated electrolyte solution. Fig. 35B shows the charge / discharge curves of the original LCO and the positive electrode active material of an embodiment of the present invention at different cycles under the conditions shown in Fig. 35A. The electrolyte solution contains 1 M LiPF6 dissolved in FEC / MTFP (2:8 by volume) with 5 wt% PS. The cycling performance tests were performed by performing a CCCV charge at 200 mA / g with a final current of 40 mA / g and a CC discharge at 200 mA / g in the voltage range from 2.5 V to 4.7 V (versus Li + / Li). A rest period of 1 minute was provided after each charge and discharge step. Each measurement was performed at 25 °C.

[0326] This approach resulted in a high capacity retention of 88.5% (191.5 mAh / g) at 200 mA / g and a voltage range of 2.5 V to 4.7 V (versus Li + / Li) after 100 cycles, as in Fig. 35A and Fig. 35B shown.

[0327] The half-cells were prepared as follows. The LCO positive electrode was prepared by mixing 95 wt% active material, 3 wt% carbon black (DENKA BLACK (registered trademark), Denka Co., Ltd.) as a conductive additive, and 2 wt% polyvinylidene fluoride as a binder. The weighed powders were mixed in N-methyl-1,2-pyrrolidone (NMP, 99.9%, Tokyo Chemical Industry Co., Ltd.) to create a homogeneous slurry. The slurry was coated onto an aluminum foil current collector with a doctor blade. The NMP solvent was dried for 0.5 h at 80 °C in a forced convection drying oven. The mass loading of the active material was set to approximately 7 mg / cm 2 regulated, while the mass loading for Fig. 33A and Fig. 33B and Fig. 35A and Fig. 35B to approximately 20 mg / cm 2 or approximately 3 mg / cm 2 The button cell half-cells (CR2032) were assembled in an argon-filled glove box using the prepared positive electrode, lithium metal foil (thickness: 0.6 mm, purity: 99.9%, Honjo Metal Co., Ltd.) as the counter electrode, polypropylene (PP) as the separator, and an electrolyte solution.

[0328] Two types of electrolyte solutions were used for the half-cells: a commonly used electrolyte solution containing 1 M LiPF6 dissolved in ethylene carbonate / diethyl carbonate (EC / DEC = 3:7 by volume) with 2 wt% vinylene carbonate (VC) as an additive, and a fluorinated electrolyte solution containing 1 M LiPF6 dissolved in fluoroethylene carbonate / methyl 3,3,3-trifluoropropionate (FEC / MTFP, 2:8 by volume) with 5 wt% 1,3-propanesultone (PS) as an additive. The commonly used electrolyte solution was used unless otherwise stated.

[0329] The charging and discharging measurements were carried out using a TOSCAT-3100 (TOYO SYSTEM Co., Ltd.) battery testing system and a temperature-controlled chamber at 25°C. The cycling performance tests for the half-cells were carried out using constant current-constant voltage charging (CCCV charging) at 100 mA / g with a final current of 10 mA / g and constant current discharging (CC discharge) at 100 mA / g in the voltage range of 2.5 V to 4.6 V or 2.5 V to 4.7 V (versus Li + / Li). Capacity retention after 100 cycles was calculated using the maximum discharge capacity obtained during the cycle test.

[0330] The Fig. The discharge rate performance tests shown in Figure 33B were carried out using a constant current and constant voltage charge (a CCCV charge) at 100 mA / g with a final current of 10 mA / g, followed by a CC discharge in the voltage range of 2.5 V to 4.7 V (versus Li + / Li). The CC discharge current varied every five cycles as follows: 40 mA / g, 100 mA / g, 200 mA / g, 400 mA / g, 600 mA / g, 1000 mA / g, 2000 mA / g, and 100 mA / g. A rest period of 10 minutes was provided after each charge and discharge step.

[0331] For the Fig. 34, the discharge rate performance tests were carried out, whereby a constant current and constant voltage charge (a CCCV charge) was carried out at 40 mA / g with a final current of 4 mA / g, followed by a CC discharge in the voltage range of 2.5 V to 4.7 V (versus Li + / Li). The CC discharge current varied every five cycles as follows: 40 mA / g, 100 mA / g, 200 mA / g, 400 mA / g, 600 mA / g, 1000 mA / g, and 40 mA / g. A rest period of 10 minutes was provided after each charge and discharge step. < <vollzelle>>

[0332] To evaluate electrochemical properties under more practical conditions, pouch full cells having the same configuration as a commercial product were fabricated using a positive electrode containing the positive electrode active material of one embodiment of the present invention and a commercial graphite negative electrode.

[0333] The positive electrode was prepared in the same way as the half-cells. The negative electrode was formed using 96 wt% synthetic graphite (meso carbon micro beads (MCMB) Graphite G10, Linyi Gelon Lib Co., Ltd.) as the active material, 1 wt% vapor-deposited carbon nanofiber (VGCF (registered trademark)-H, Showa Denko Co., Ltd.) as the conductive additive, 1 wt% sodium carboxymethylcellulose (CMC, Kishida Chemical Co., Ltd.) as the thickener, and 2 wt% styrene-butadiene rubber (SBR, TRD2001, JSR Corporation) as the binder.

[0334] The weighted powders of the negative electrode active material, conductive additive, thickener, and binder were mixed with distilled water to form a slurry, which was then coated onto a copper foil current collector. The mass loadings of the positive electrode and the negative electrode were 10.6 mg / cm 2 or 7.6 mg / cm 2 , while their dimensions were 41 mm × 50 mm and 45 mm × 53 mm, respectively. The cell design was aimed at achieving a positive electrode to negative electrode capacity ratio of approximately 80% and a total cell capacity of 40 mAh, with the positive electrode and negative electrode capacities being 200 mAh / g and 300 mAh / g, respectively. The pouch full cells were assembled in an argon-filled glove box using a batch process. This process utilized single-sided coated negative electrode and positive electrode foils, a polypropylene (PP) separator, and an electrolyte solution containing 1 M LiPF6 in FEC / MTFP (2:8 by volume).

[0335] Cycle performance tests of the full cells prepared as described above were conducted with a CCCV charge (40 mA / g, final current of 4 mA / g) and a CC discharge (40 mA / g) in the voltage range of 3.0 V to 4.5 V or 3.0 V to 4.6 V (versus graphite). A rest period of 1 minute was provided after each charge and discharge step.

[0336] Fig. 36A and Fig. 36B show electrochemical performance of the pouch full cells at 25 °C. Fig. 36A and Fig. 36B show the cycle performance of the pouch full cells with the positive electrode containing the positive electrode active material of one embodiment of the present invention; the voltage range is 3.0 V to 4.5 V (versus graphite) in Fig. 36A and 3.0 V to 4.6 V (versus graphite) in Fig. 36B.

[0337] The energy density retention after 500 cycles of each full cell at 25 °C was 90.3% (656.8 Wh / kg) and 75.8% (593.4 Wh / kg) in the voltage range of 3.0 V to 4.5 V and 3.0 V to 4.6 V (versus graphite), respectively. The full cells using the positive electrode active material of one embodiment of the present invention exhibit significantly more stable cycling performance compared to previous studies (e.g., Non-Patent Documents 7, 12, and 17) on doping and coating for high-voltage LCO. <Analyse des Positivelektrodenaktivmaterials einer Ausführungsform der vorliegenden Erfindung und des ursprünglichen LCO nach Zyklustests>

[0338] Fig. 37A shows ex-situ XRD patterns of the positive electrodes in a discharge state after 100 cycles containing the original LCO and the positive electrode active material of one embodiment of the present invention. Fig. 37B shows an enlarged view in the 2θ range from 18° to 19.5°, and Fig. Figure 37C shows an enlarged view in the 2θ range from 44.5° to 45.5°.

[0339] For the measurements of the original LCO and the positive electrode active material of an embodiment of the present invention in Fig. 37A to Fig. 37C, the coin cell half-cells were used with generally used electrolyte solutions. For the ex-situ XRD of the positive electrodes with the original LCO and the positive electrode active material of an embodiment of the present invention in a discharge state after 100 cycles, the cells were tested using CCCV charging (40 mA / g, final current of 10 mA / g) and CC discharging (40 mA / g) in the voltage range from 2.5 V to 4.7 V (versus Li + / Li) subjected to the cycle.

[0340] XRD measurements were performed using a Bruker D8 ADVANCE diffractometer with Cu Kα (λ = 1.5406 Å). Powder samples were analyzed within the 15°–90° scan range (2θ) with a 0.005° step width and a scan speed of 0.1 s / step. Rietveld refinement was performed using DIFFRAC TOPAS V6 software (Bruker). The ex situ XRD measurements described below were also performed under similar conditions.

[0341] As in Fig. 37A to Fig. As shown in Figure 37C, the ex situ XRD patterns of the pristine LCO in a discharge state after 100 cycles exhibited broad XRD peaks, indicating low crystallinity.

[0342] The Fig. 37A to Fig. The XRD patterns shown in Figure 37C are samples from which the background and a peak originating from Cu Kα2 were removed using DIFFRAC.EVA. The background was obtained under conditions with a curvature of 25 and a threshold of 1e -5 removed.

[0343] It is known that 003 of lithium cobalt oxide has a peak at 2θ of approximately 19° (within the range of 18° to 19.5°). The half-width of the 003 peak of the original LCO (a half-width refers to a full width at half maximum, unless otherwise specified in this specification and the like) was 0.0325° before the charge / discharge cycle test, but it was significantly expanded to 0.1836° and shifted to the lower angle side after the 100-cycle charge / discharge cycle test. It is also known that 104 of lithium cobalt oxide has a peak at 2θ of approximately 45° (within the range of 44.5° to 45.5°). The half-width of the 104 peak of the original LCO was 0.0644° before the charge / discharge cycle test and was also extended to 0.1594° after a similar test.

[0344] In contrast, the positive electrode active material of one embodiment of the present invention exhibited sharp peaks, indicating that its high crystallinity was maintained after 100 cycles. The half-width of the 003 peak of the positive electrode active material of one embodiment of the present invention before the charge / discharge cycle test was 0.0333°, and it was less than or equal to 0.10°, or more specifically, 0.0515°, which means that the peak is sufficiently sharp even after the 100-cycle charge / discharge cycle test. The half-width of the 104 peak before the charge / discharge cycle test was 0.0636°, and it was less than or equal to 0.11°, or more specifically, 0.0646°, which means that the peak is sufficiently sharp even after a similar test.

[0345] Fig. 38A to Fig. 38H shows SEM images of the original LCO and the positive electrode active material of one embodiment of the present invention in a discharge state after cycling. Fig. 38A and Fig. 38B show the SEM images of the original LCO after 5 cycles, and Fig. 38C and Fig. 38D shows the SEM images of the original LCO after 50 cycles. Fig. 38E and Fig. 38F show the SEM images of the positive electrode active material of one embodiment of the present invention after 5 cycles, and Fig. 38G and Fig. 38H shows the SEM images of the positive electrode active material of one embodiment of the present invention after 50 cycles. Fig. Figure 39A shows the cycle performance of the original LCO and the positive electrode active material of an embodiment of the present invention in a voltage range of 2.5 V to 4.7 V (versus Li + / Li) at 25 °C for the SEM images after 5 cycles. Fig. Figure 39B shows the cycle performance of the original LCO and the positive electrode active material of an embodiment of the present invention in a voltage range of 2.5 V to 4.7 V (versus Li + / Li) at 25 °C for the SEM images after 50 cycles. The scale bars in Fig. 38A, Fig. 38C, Fig. 38E and Fig. 38G each represent 50 µm, and those in Fig. 38B, Fig. 38D, Fig. 38F and Fig. 38H each represent 5 µm. In Fig. 39A and Fig. 39B, the Coulomb efficiencies for measurement points with a discharge capacity of less than 10 mAh / g are not plotted.

[0346] As in Fig. 38A to Fig. As shown in Figure 38D, in the SEM observation of the original LCO in a discharge state after 5 cycles of the cycling test, the original LCO had a small number of cracks, which were clearly observed, particularly near the grain boundaries. In the original LCO in a discharge state after 50 cycles, cracks were multiplied and enlarged. In the positive electrode active material of one embodiment of the present invention, no crack was observed in the discharge state after 5 cycles, and very few cracks were observed in the discharge state after 50 cycles.

[0347] In addition, HAADF-STEM images and NBED patterns of the original LCO and the positive electrode active material of one embodiment of the present invention were obtained after 50 cycles in the voltage range of 2.5 V to 4.7 V. Fig. Figure 40A shows the HAADF-STEM image of the surface section of the original LCO particle, and Fig. Figure 40B shows the NBED patterns of the marked areas 1 to 3 in Fig. 40A. Region 1 represents a sample showing a rock salt crystal structure, region 2 represents a sample showing a spinel crystal structure, and region 3 represents a sample showing a layered rock salt crystal structure.

[0348] Fig. 40C shows the HAADF-STEM image of the surface portion of a particle of the positive electrode active material of one embodiment of the present invention, and Fig. Figure 40D shows the NBED patterns of the marked areas 4 and 5 in Fig. 40C. Area 4 represents a sample showing a rock salt crystal structure, and area 5 represents a sample showing a layered rock salt crystal structure. The scale bars in Fig. 40A and Fig. 40C each represent 3 nm.

[0349] Fig. Figure 40B shows the formation of an approximately 3 nm thick spinel and rock salt phase in the surface portion of the original LCO. Importantly, even after 50 cycles, the outermost surface of the positive electrode active material of one embodiment of the present invention, as shown in Fig. 40C and Fig. 40D, retained its approximately 1 nm thick rock salt structure.

[0350] The formation of spinel and then rock salt phases in the degraded surface portion of the original LCO is due to the release of oxygen from the LCO surface. However, due to the high concentrations of magnesium, nickel, and aluminum in the surface layer of the positive electrode active material of one embodiment of the present invention, the release of oxygen from the LCO surface was prevented under highly delithiated conditions; thus, the formation of the spinel region was prevented. <Analyse der Kristallstruktur des Positivelektrodenaktivmaterials einer Ausführungsform der vorliegenden Erfindung in dem in hohem Maße delithiierten Zustand>< <ex-situ-xrd>>

[0351] To reveal the mechanism of performance improvement, a structural analysis was performed during high voltage cycling.

[0352] It is known that typically LCO when charging up to 4.55 V (x < 0.3 in Li x CoO2) undergoes a phase transition from the O3 phase to the H1-3 phase. This structural change reduces the capacity retention of LCO at high voltages. Considering that the excellent electrochemical performances of the positive electrode active material of one embodiment of the present invention at high voltage might strongly correlate with the prevention of this phase transition, ex situ XRD measurements were performed on the charged positive electrodes taken from half-cells.

[0353] Fig. 41A to Fig. 41C and Fig. 42A to Fig. 42C show ex-situ XRD patterns of the positive electrodes at different cycles containing the original LCO and the positive electrode active material of one embodiment of the present invention. Fig. Figure 41A shows ex-situ XRD patterns of the original LCO in the first and fifth charge states up to 4.7 V, Fig. 41B shows an enlarged view within the 2θ range of 18° to 21°, and Fig. Figure 41C shows an enlarged view within the 2θ range from 42° to 48°. Fig. 42A shows ex-situ XRD patterns of the positive electrode active material of one embodiment of the present invention in the first, second, fifth and fiftieth charge states up to 4.7 V, Fig. 42B shows an enlarged view within the 2θ range of 18° to 21°, and Fig. Figure 42C shows a magnified view within the 2θ range from 42° to 48°. The XRD reference patterns of the Li 0,35 CoO2-O3 phase (Non-Patent Document 18 and ICSD Collection Code 172912), the Li 0,12 CoO2-H1-3 phase (Non-Patent Document 19) and the O3' phase described in this specification and the like. In Fig. 41A to Fig. 41C, Fig. 42A to Fig. 42C, Fig. 43A to Fig. 43C and Fig. 44A to Fig. 44C, rhombuses (◇) represent peaks originating from the conventional delithiated O3 phase, triangles (Δ) represent peaks originating from the H1-3 phase, and dots (•) represent peaks originating from the O3' phase.

[0354] To carry out ex-situ XRD measurements in Fig. 41A to Fig. 41C, Fig. 42A to Fig. 42C, Fig. 43A to Fig. 43C and Fig. 44A to Fig. 44C, the button cell half-cells were used, in which generally used electrolyte solutions were used. For the positive electrodes with the original LCO and the positive electrode active material of an embodiment of the present invention in Fig. 41A to Fig. 41C and Fig. 42A to Fig. 42C, the cells were charged with CC (10 mA / g) up to 4.7 V prior to ex-situ XRD measurements at the first, second, fifth, or fiftieth charge. Before the second, fifth, or fiftieth charge, the cells were charged 1, 4, or 49 times using a CCCV charge (100 mA / g, final current of 10 mA / g) and a CC discharge (100 mA / g) in the voltage range from 2.5 V to 4.7 V (versus Li + / Li) subjected to the cycle.

[0355] In an argon-filled glove box, the positive electrode foils of the charged or discharged cells were removed and prepared for ex situ XRD measurements. The positive electrode foils were washed with dimethyl carbonate to remove the electrolyte solution, dried, and then fixed to a flat glass substrate with double-sided tape. These samples were sealed in an airtight sample holder (part no.: A100B33) within the argon glove box. XRD measurements were performed in an argon atmosphere within the scanning range of 15° to 75° (2θ) with a step size of 0.01° and a scanning speed of 1.0 s / step.

[0356] As in Fig. 41A to Fig. 41C, when the first charge of the original LCO at 4.7 V resulted in a charge capacity of 239.4 mAh / g and a Li concentration (Li x CoO2) of x = 0.13, the H1-3 phase formation was confirmed by ex-situ XRD.

[0357] Fig. 43A to Fig. 43C show ex-situ XRD patterns of the positive electrodes with the original LCO in the charge states up to 4.6 V and 4.7 V. Fig. Figure 43A shows ex-situ XRD patterns of the positive electrodes with the original LCO at the first charge up to 4.6 V and 4.7 V at 10 mA / g. Fig. Figure 43B shows an enlarged view within the 2θ range of 18° to 21°. Fig. Figure 43C shows an enlarged view within the 2θ range from 42° to 48°.

[0358] As in Fig. 43A to Fig. 43C, even when the first charge was carried out up to 4.6 V and resulted in a lower charge capacity of 224.6 mAh / g (x = 0.18 in Li x CoO2), the H1-3 phase was formed.

[0359] As in Fig. 41A to Fig. As shown in Figure 41C, it was likely that after the fifth charge at 4.7 V, the surface portion of the original LCO was damaged by exposure to the high voltage, and the damaged surface hindered lithium diffusion, resulting in a charge capacity of 145.6 mAh / g (x = 0.47). Since the original LCO suffered from a severe deterioration in reversibility, the phase transitions from the O3 phase to the H1-3 phase at x < 0.3 in Li x CoO2 not observed.

[0360] Fig. 42A to Fig. 42C show ex-situ XRD patterns of the positive electrodes containing the positive electrode active material of one embodiment of the present invention. Fig. 42A shows ex-situ XRD patterns of the positive electrode active material of one embodiment of the present invention in the first, second, fifth and fiftieth charge states up to 4.7 V, Fig. 42B shows an enlarged view within the 2θ range of 18° to 21°, and Fig. Figure 42C shows an enlarged view within the 2θ range from 42° to 48°. Fig. 44A to Fig. 44C show ex-situ XRD patterns of the positive electrodes in the charge states up to 4.5V, 4.6V, and 4.7V containing the positive electrode active material of one embodiment of the present invention.

[0361] Fig. 42A to Fig. 42C show the ex-situ XRD patterns of the positive electrodes containing the positive electrode active material of one embodiment of the present invention during the first charge up to 4.7 V, which corresponds to a charge capacity of 220.1 mAh / g (x = 0.20 in Li x CoO2). Surprisingly, the ex situ XRD patterns of the positive electrode active material of one embodiment of the present invention charged to 4.7 V show a superposition of diffraction patterns of two O3 phases, while the diffraction pattern corresponding to the H1-3 phase is not observed.

[0362] The diffraction pattern of the first O3 phase exhibits peaks at 2θ = 19.0° and 45.3° on the lower angle side, while the diffraction pattern of the second O3 phase exhibits peaks at 2θ = 19.2° and 45.5° on the higher angle side. The first O3 phase corresponds to the conventional, delithiated O3 phase. This classification is based on the continuous shift of diffraction peaks in the charge state from 4.5 V to 4.7 V, as shown in Fig. 44A to Fig. 44C shown. Fig. 44A shows ex-situ XRD patterns of the positive electrodes containing the positive electrode active material of one embodiment of the present invention and charged at 10 mA / g up to 4.5V, 4.6V, and 4.7V. Fig. Figure 44B shows an enlarged view within the 2θ range of 18° to 21°. Fig. Figure 44C shows an enlarged view within the 2θ range from 42° to 48°.

[0363] The second O3 phase is considered a distinct phase with a smaller unit cell volume and the same symmetry as the O3 phase. In this description and the like, this phase is referred to as the "O3' phase."

[0364] The charging capacity of the second charge was 215.4 mAh / g (x = 0.21 in Li x CoO2), which was slightly smaller than that of the first charge. During the second charge, the area intensity ratio of the diffraction peaks associated with the O3' phase increased, and peak positions shifted toward the higher angle. The shift of peaks toward the higher angle indicates a decrease in the unit cell volume, which indicates a decrease in the lithium concentration in the lithium cobalt oxide. This contradicts the lithium concentrations during the first and second charges estimated from the electrochemically observed capacities (first: x = 0.20, second: x = 0.21). It should be noted that during the first charge, the electric charge can be consumed not only by lithium leaching but also by the decomposition of the electrolyte solution accompanied by the formation of SEI, which can be confirmed by the Coulombic efficiency.

[0365] Therefore, it is assumed that the actual lithium concentration during the first charge is higher than the lithium concentration estimated from the capacity (x = 0.20), and likely higher than the actual lithium concentration during the second charge. After the fifth charge with a capacity of 225.3 mAh / g (x = 0.18), the O3' phase emerged as a single phase, and the diffraction peaks shifted to higher angles as the charge capacity increased from that of the second charge.

[0366] The O3' phase remained after the fiftieth charge with a capacity of 214.5 mAh / g (x = 0.22), although weak diffraction peaks related to the H1-3 phase were detected. <<dQ / d V-Kurve> >

[0367] Fig. Figure 45 shows dQ / dV curves of the positive electrode active material of one embodiment of the present invention at the first, fifth, and fiftieth cycles. Half-cells were used to measure dQ / dV in a voltage range of 2.5 V to 4.7 V with a current of 10 mA / g at 25°C. Before the fifth or fiftieth dQ / dV measurement, the cells were cycled 4 or 49 times using a CCCV charge (100 mA / g, final current of 10 mA / g) or a CC discharge (at 100 mA / g) in the voltage range of 2.5 V to 4.7 V (versus Li + / Li) at 25°C. A rest period of 10 minutes was provided after each charge and discharge step. A large voltage polarization was observed in the first cycle, which is consistent with the low capacity of the first cycle in the cycle performance tests. The voltage polarization became smaller in the fifth cycle and also remained small in the fiftieth cycle. The dQ / dV curves of the positive electrode active material of one embodiment of the present invention show reversible peaks at voltages higher than 4.5 V during the fifth and fiftieth charge / discharge at 25°C.

[0368] As in Fig. As shown in Figure 45, the dQ / dV curves of the positive electrode active material of one embodiment of the present invention show reversible peaks at voltages higher than 4.5 V during charge / discharge, indicating that the phase transition from the O3 phase to the O3' phase is persistently reversible. < <rietveld-verfeinerung>>

[0369] The lattice parameters of the O3' phase were determined using Rietveld refinement of the XRD pattern from the first and fifth charging cycles, as detailed in Tables 7 and 8. Compared with the values ​​reported in the previous studies on highly delithiated O3 phases (Non-Patent Document 18 and the like), the c-lattice parameter of the positive electrode active material of one embodiment of the present invention is significantly smaller. [Table 7] Positive electrode active material of an embodiment of the present invention 4.7 V 1st charge Charging capacity 220.1 mAh / g Li x CoO2 (x = 0.20) 1st phase (O3) 58,6 % 2nd phase (O3') 41,4 % Space group R3̅m Space group R3̅m x y z Bel. (Occ.) x y z Bel.(Occ.) Li 3a 0 0 0 0,20 Li 3a 0 0 0 0,20 Co 3b 0 0 0,5 1 Co 3b 0 0 0,5 1 O 6c 0 0 0,223(6) 1 O 6c 0 0 0,210(8) 1 a-axis / A 2,813(9) a -axis / Å 2,814(7) c-axis / Å 13,994(7) c-axis / Å 13,791 (5) Volume / A 3 95,967(1) Volumen / A 3 94,627(1) R wp 1,44 R p 1,01 GOF 1,58 [Table 8] Positive electrode active material of an embodiment of the present invention 4.7 V 5. Charge Charging capacity 225.3 mAh / g Li x CoO2 (x = 0.18) Space group R3m x y Z Bel. (Occ.) Li 3a 0 0 0 0,18 Co 3b 0 0 0,5 1 O 6c 0 0 0,217(7) 1 a -axis / Å 2,818(6) c-axis / Ä 13,666(3) Volume / A 3 94,028(1) R wp 1,63 R p 1,08 GOF 1,86

[0370] The equivalent isotropic temperature factors (B eq ) used for the Rietveld refinement were constant values: Li = 1.105; Co = 0.371; and O = 0.552. The loading capacity before the ex-situ XRD measurement was used to calculate the site occupancy of Li ions. The site occupancy of O and Co ions was set to 1. <<Teilen der Bedingungen des additiven Elements> >

[0371] In this description and the like, it is assumed that the columnar effect of magnesium in the positive electrode active material of one embodiment of the present invention prevents the sliding of CoO2 plates. To verify this assumption, the cycling performance of the positive electrodes containing M-LCO, MF-LCO, FA-LCO, FN-LCO, FNA-LCO, and the positive electrode active material of one embodiment of the present invention was evaluated in combination with ex situ XRD measurements for highly charged states.

[0372] Fig. 46A to Fig. 46C and Fig. 47A and Fig. 47B show ex-situ XRD patterns and cycling performance of M-LCO, MF-LCO, and the positive electrode active material of one embodiment of the present invention. Fig. Figure 46A shows the ex situ XRD patterns of the positive electrodes containing M-LCO, MF-LCO, and the positive electrode active material of one embodiment of the present invention charged at 4 mA / g up to 4.6 V. Fig. 46B shows an enlarged view in the 2θ range from 18° to 21°, and Fig. Figure 46C shows an enlarged view in the 2θ range from 42° to 48°. Fig. 47A shows the cycle performance in a voltage range of 2.5 V to 4.6 V (versus Li + / Li) at 25 °C, and Fig. Figure 47B shows the cycle performance in a voltage range of 2.5 V to 4.7 V (versus Li + / Li) at 25 °C.

[0373] Fig. 48A to Fig. 48C and Fig. 49A and Fig. 49B shows ex-situ XRD patterns and cycling performance of FN-LCO, FA-LCO, FNA-LCO, and the positive electrode active material of one embodiment of the present invention. Fig. 48A shows the ex situ XRD patterns of the positive electrodes containing FN-LCO, FA-LCO, FNA-LCO, and the positive electrode active material of one embodiment of the present invention charged at 4 mA / g up to 4.6 V. Fig. 48B shows an enlarged view in the 2θ range from 18° to 21°, and Fig. Figure 48C shows an enlarged view in the 2θ range from 42° to 48°. Fig. 49A shows the cycle performance in the voltage range from 2.5 V to 4.6 V (versus Li + / Li) at 25°C, and Fig. Figure 49B shows the cycle performance in the voltage range from 2.5 V to 4.7 V (versus Li + / Li) at 25°C. In Fig. 47A and Fig. 47B, Fig. 49A and Fig. 49B, Fig. 50A and Fig. 50B, Fig. 51A and Fig. 51B and Fig. 52A and Fig. 52B, the filled markers represent the discharge capacity, and the outline markers represent the Coulomb efficiency. The Coulomb efficiencies for measurement points with a discharge capacity of less than 25 mAh / g are not plotted.

[0374] For the ex-situ XRD measurements of the positive electrodes containing M-LCO, MF-LCO, FN-LCO, FA-LCO, FNA-LCO and the positive electrode active material of an embodiment of the present invention, the cells were tested using a CCCV charge (40 mA / g, final current of 10 mA / g) and a CC discharge (40 mA / g) in the voltage range of 2.5 V to 4.5 V (versus Li + / Li) cycled. The cells were charged with CC (4 mA / g) up to 4.6 V prior to ex-situ XRD measurements.

[0375] Only MF-LCO and the positive electrode active material of one embodiment of the present invention showed high cycling performance and no H1-3 phase. The formation of the O3' phase therefore results from the introduction of magnesium through treatment with molten fluoride salts.

[0376] The cycling performances of preheated LCO, F-LCO, FNA-LCO and NA-LCO were measured to investigate the effect of LiF only.

[0377] Fig. 50A shows the cycle performance of the original LCO, preheated LCO and F-LCO in the voltage range from 2.5 V to 4.6 V (versus Li + / Li) at 25 °C, and Fig. Figure 50B shows the cycle performance of this in the voltage range of 2.5 V to 4.7 V (versus Li + / Li) at 25 °C.

[0378] Fig. Figure 51A shows the cycle performance of NA-LCO, FNA-LCO and the positive electrode active material of one embodiment of the present invention in the voltage range of 2.5 V to 4.6 V (versus Li + / Li) at 25 °C, and Fig. Figure 51B shows the cycle performance of this in the voltage range of 2.5 V to 4.7 V (versus Li + / Li) at 25 °C. Coulombic efficiencies for measurement points with a discharge capacity of less than 25 mAh / g are not plotted.

[0379] As in Fig. 50A and Fig. 50B and Fig. 51A and Fig. As shown in Figure 51B, the addition of LiF and no MgF2 did not produce a drastic improvement in the charge / discharge cycle performance.

[0380] As in Fig. As shown in Figure 6, in a highly delithiated state, the presence of magnesium substituted in the lithium layer provides structural support, preventing the sliding of the CoO2 plates and the phase transition from the O3 phase to the H1-3 phase. Furthermore, the sliding is likely to be initiated at the surface of LCO and could therefore be suppressed by the presence of the magnesium-rich rock salt structure region in the surface portion of the positive electrode active material of one embodiment of the present invention. Since the sliding was prevented, the surface portion of the positive electrode active material of one embodiment of the present invention was less likely to deteriorate after cycling, as shown in the SEM images ( Fig. 38E to Fig. 38H) and the STEM image ( Fig. 40C). Consequently, lithium diffusion was not prevented in the positive electrode active material of one embodiment of the present invention, enabling excellent rate and cycle performances to be demonstrated.

[0381] MFN-LCO and MFA-LCO were synthesized using a method similar to that of the positive electrode active material of one embodiment of the present invention by adding MgF2-LiF-Ni(OH)2 and MgF2-LiF-Al(OH)3, respectively.

[0382] Fig. Figure 52A shows the cycle performance of pristine LCO, MFN-LCO, MFA-LCO, and the positive electrode active material of one embodiment of the present invention in the voltage range of 2.5 V to 4.6 V (versus Li + / Li) at 25 °C, and Fig. Figure 52B shows the cycle performance of this in the voltage range of 2.5 V to 4.7 V (versus Li + / Li) at 25 °C.

[0383] As in Fig. 52A and Fig. As shown in Figure 52B, the sample containing both nickel and aluminum along with magnesium and fluorine exhibited the highest capacity retention. This is due to the fact that the positive electrode active material of one embodiment of the present invention has very high Coulombic efficiencies (e.g., 99.79%, 99.48%, and 99.34% for the positive electrode active material of one embodiment of the present invention, MFN-LCO, and MFA-LCO, respectively, when compared to the third cycle with a cut-off voltage of 4.7 V).

[0384] As described above, in this specification and the like, the diffusion and doping of magnesium from the surface of the LCO particles into the bulk were achieved using a molten fluoride salt as a reaction accelerator. Furthermore, the excess magnesium coated the surface portion of the positive electrode active material particles of one embodiment of the present invention. This innovative invention effectively prevented the damaging phase transition to the H1-3 phase, especially at a charging voltage of 4.7 V.

[0385] Furthermore, ex-situ XRD analysis of the positive electrode active material of one embodiment of the present invention at 4.7 V revealed the formation of another O3 phase (O3' phase). By preventing the phase transition to the H1-3 phase through this surface treatment and magnesium doping, deterioration in crystallinity and cracking after cycling were suppressed at a cut-off voltage of 4.7 V.

[0386] The Fig. The Ragone diagram shown in Figure 53 shows that among practical positive electrode materials, the positive electrode active material of one embodiment of the present invention has the highest energy density. Therefore, the positive electrode active material of one embodiment of the present invention has the potential to significantly impact the field of high-energy-density batteries, thereby contributing to the progress of mobile electronics.

[0387] This description and the like also provide valuable insight into the fundamental mechanism of phase transition through cation intercalation / exclusion. These discoveries could also be applied to other positive electrode materials whose degradation is caused by phase transition. [Example 2]

[0388] In this example, half-cells were prepared under conditions partially different from those in Example 1, using the positive electrode active material of one embodiment of the present invention prepared in a manner similar to that in Example 1. The half-cells were subjected to charge / discharge tests under conditions partially different from those in Example 1. The crystal structure was analyzed by ex-situ XRD. < <halbzelle>>

[0389] The LCO positive electrode was prepared by mixing 96 wt% active material, 2 wt% carbon black (DENKA BLACK (registered trademark), Denka Co., Ltd.) as a conductive additive, and 2 wt% polyvinylidene fluoride as a binder. At this time, pressing was performed using a roller press machine to increase the density of the positive electrode active material layer over the positive electrode current collector. The pressing conditions were as follows: the first pressing (linear pressure: 210 kN / m) was followed by the second pressing (linear pressure: 1467 kN / m). Note that the temperature of an upper roller and that of a lower roller of the roller press machine were both 120 °C. The mass load of the active material was approximately 14.5 mg / cm³. 2 . The electrode density was approximately 3.9 g / cm 3 .

[0390] An electrolyte solution containing 1 M LiPF6 dissolved in ethylene carbonate / diethyl carbonate (EC / DEC = 3:7 by volume) with 2 wt% vinylene carbonate (VC) was used.

[0391] Apart from the above conditions, the half-cells were prepared in a manner similar to that in Example 1. < <lade- entladetest>>

[0392] Charge / discharge tests were performed on the half-cells prepared as above. A discharge rate test and a charge / discharge cycle test were performed successively in this order.

[0393] The conditions for the discharge rate test are described. In the first charge / discharge cycle, constant current charging was performed at 0.2 C up to approximately 4.6 V, constant voltage charging was performed until the current value reached 0.05 C, and then constant current discharging was performed at 0.2 C up to 3.0 V. In the second charge / discharge cycle, constant current charging was performed at 0.5 C up to approximately 4.6 V, constant voltage charging was performed until the current value reached 0.05 C, and then constant current discharging was performed at 0.1 C up to 3.0 V. In the third charge / discharge cycle, constant current charging was performed at 0.5 C up to approximately 4.6 V, constant voltage charging was performed until the current value reached 0.05 C, and then constant current discharging was performed at 1.0 C up to 3.0 V.In the fourth charge / discharge cycle, constant current charging was performed at 0.5 C up to approximately 4.6 V, constant voltage charging was performed until the current value reached 0.05 C, and then constant current discharging was performed at 2.0 C up to 3.0 V. Note that 1 C was set to 200 mA / g. The ambient temperature of the measurement was 25 °C. A rest period after charging, which lasts from the completion of charging to the start of discharging, and a rest period after discharging, which lasts from the completion of discharging to the start of charging, were each 10 minutes.

[0394] The conditions for the charge / discharge cycle test are described. A constant current charge at 0.5 C was performed up to approximately 4.6 V, and then a constant voltage charge was performed until the current value reached 0.05 C. During discharge, a constant current discharge was performed at 1 C up to 3.0 V. Note that 1 C was set to 200 mA / g here. The ambient temperature of the measurement was 45 °C. A rest period after charge, which lasts from the completion of charge to the start of discharge, and a rest period after discharge, which lasts from the completion of discharge to the start of charge, were each 10 minutes. Note that the termination conditions of charge and discharge include a termination time of 20 hours in addition to the voltage and current values ​​described above. < <ex-situ-xrd>>

[0395] It was investigated whether, in the above-described charge / discharge cycles, the positive electrode active material of one embodiment of the present invention had the crystal structure of lithium cobalt oxide in a discharge state and whether the positive electrode active material had the O3' phase in a charge state.

[0396] For the analysis of the discharge states, a plurality of half-cells were prepared and subjected to the discharge rate test. Then, the following three post-discharge XRD measurements were performed: one XRD measurement on the half-cell degraded after one charge / discharge cycle under the conditions of the above charge / discharge cycle test; one XRD measurement on the half-cell degraded after five charge / discharge cycles under the conditions of the above charge / discharge cycle test; and one XRD measurement on the half-cell degraded after 30 charge / discharge cycles under the conditions of the above charge / discharge cycle test.

[0397] For the post-charge XRD measurements, a plurality of half-cells were prepared and subjected to the discharge rate test. Charging and discharging were performed in a manner similar to that of the above discharge rate test. Then, the following three post-charge XRD measurements were performed: one XRD measurement on the half-cell degraded after charging following one charge / discharge cycle under the conditions of the above charge / discharge cycle test; one XRD measurement on the half-cell degraded after charging following five charge / discharge cycles under the conditions of the above charge / discharge cycle test; and one XRD measurement on the half-cell degraded after charging following 30 charge / discharge cycles under the conditions of the above charge / discharge cycle test.

[0398] For each measurement, the half-cell was disassembled within one hour after the completion of charge or discharge. Specifically, the half-cells in the charged states were carefully disassembled; the positive electrodes were removed using an insulating tool, as they are in the high-voltage charged states, to prevent short circuits. For disassembly, an argon-filled glove box was used, in which the dew point and oxygen concentration were controlled. It should be noted that the dew point of the glove box is preferably less than or equal to -70°C, and the oxygen concentration is preferably less than or equal to 5 ppm. Since the crystal structure of the positive electrode active material may change due to self-discharge after a long period of time has elapsed since the above charging, disassembly and analysis are preferably performed as early as possible.

[0399] In the glove box, the positive electrode obtained by disassembling the half-cell was placed in a sealable sample holder for XRD measurement. The sample holder was placed on a table of the XRD device, keeping the positive electrode in an argon atmosphere during the XRD measurement.

[0400] XRD measurements were then started within 15 minutes. The XRD setup and conditions are as follows. XRD equipment: D8 ADVANCE, manufactured by Bruker AXS X-ray source: Cu Kα1 radiation Output: 40 kV, 40 mA Divergence angle: various. Slit, 0.5° Detector: LynxEye Sampling method: continuous 2θ / θ sampling Measuring range (2θ): from 15° to 75° Step size (2θ): 0.01° Counting time: 1 second / step Rotation of sample table: 15 rpm

[0401] Fig. Figure 54 shows XRD patterns of the positive electrodes after discharge. The patterns of lithium cobalt oxide, LiCoO2, which is the stoichiometric O3 phase, and Li 0,68 CoO2, which is a lithium-poor O3 phase, are also shown as references. Fig. 55A shows an enlarged diagram within the range of 18° to 21° in Fig. 54, and Fig. 55B shows an enlarged diagram within the range of 42° to 48° in Fig. 54. The results indicate that the positive electrode containing the positive electrode active material of one embodiment of the present invention has a sharp peak even after 30 cycles at 45°C and that the crystallinity is not reduced by discharge.

[0402] Fig. Figure 56 shows XRD patterns of the positive electrodes after charging. Patterns of the O3' phase, the H1-3 phase, and the O3 (Li 0,35 COO2-) phase are also shown as references. Fig. 57A shows an enlarged diagram within the range of 18° to 21° in Fig. 56, and Fig. Figure 57B shows an enlarged diagram within the range of 42° to 48° in Fig. 56. The patterns of the positive electrode containing the positive electrode active material of one embodiment of the present invention in the high-voltage charge states are substantially similar to the reference pattern of the O3' phase (O3'). That is, it is confirmed that the positive electrode active material of one embodiment of the present invention exhibits the O3' phase even after charging following one cycle, after charging following five cycles, and after charging following 30 cycles. Therefore, in a battery containing the positive electrode active material of one embodiment of the present invention, the O3' phase can be maintained even if charge / discharge cycles are repeated many times, which is presumably a factor in the battery's ability to exhibit high charge / discharge cycle performance.

[0403] This application is based on Japanese Patent Application Serial No. 2023-186796 filed with the Japan Patent Office on October 31, 2023, Japanese Patent Application Serial No. 2023-200455 filed with the Japan Patent Office on November 28, 2023, Japanese Patent Application Serial No. 2024-022686 filed with the Japan Patent Office on February 19, 2024, and Japanese Patent Application Serial No. 2024-063843 filed with the Japan Patent Office on April 11, 2024, the entire contents of which are hereby incorporated by reference. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Zitierte Patentliteratur

[0000] JP 2023-186796

[0403] JP 2023-200455

[0403] JP 2024-022686

[0403] JP 2024-063843

[0403] Zitierte Nicht-Patentliteratur

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[0005] Bae, J. G. et al. Structural evolution of Mg-doped single-crystal LiCoO2 cathodes: importance of morphology and Mg-doping sites. ACS Appl. Mater. Interfaces 15, 7939-7948 (2023

[0005] Mladenov, M., Stoyanova, R., Zhecheva, E. & Vassilev, S. Effect of Mg doping and MgO-surface modification on the cycling stability of LiCoO2 electrodes. Electrochem. Commun. 3, 410-416 (2001

[0005] Jang Y. I. et al. Synthesis and characterization of LiAl y Co 1-y O2 and LiAl y Ni 1-y O2. J. Power Sources 81-82, 589-593 (1999

[0005] Luo, W. & Dahn, J. R. Comparative study of Li[Co 1-z Al z ]O2 prepared by solid-state and co-precipitation methods. Electrochim. Acta 54, 4655-4661 (2009

[0005] Liu, A., Li, J., Shunmugasundaram, R. & Dahn, J. R. Synthesis of Mg and Mn doped LiCoO2 and effects on high voltage cycling. J. Electrochem. Soc. 164, A1655-A1664 (2017

[0005] Zhang, J. N. et al. Trace doping of multiple elements enables stable battery cycling of LiCoO2 at 4.6V. Nat. Energy 4, 594-603 (2019

[0005] Kong, W. et al. Unraveling the distinct roles of Mg occupation on Li or Co sites on high-voltage LiCoO2. J. Electrochem. Soc. 168, 030528 (2021

[0005] Shim, J-H., Lee, S. & Park, S. S. Effects of MgO coating on the structural and electrochemical characteristics of LiCoO2 as cathode materials for lithium ion battery. Chem. Mater. 26, 2537-2543 (2014

[0005] Cho, J., Kim, Y. J. & Park, B. Novel LiCoO2 cathode material with Al2O3 coating for a Li ion cell. Chem. Mater. 12, 3788-3791 (2000

[0005] Lee, J. G., Kim, B., Cho, J., Kim, Y. W. & Park, B. Effect of AlPO4-nanoparticle coating concentration on high-cutoff-voltage electrochemical performances in LiCoO2. J. Electrochem. Soc. 151, A801-A805 (2004

[0005] Qian, J. et al. Electrochemical surface passivation of LiCoO2 particles at ultrahigh voltage and its applications in lithium-based batteries. Nat. Commun. 9, 4918 (2018

[0005] Moon, S. H. et al. TiO2-coated LiCoO2 electrodes fabricated by a sputtering deposition method for lithium-ion batteries with enhanced electrochemical performance. RSC Adv. 9, 7903-7907 (2019

[0005] Taguchi, N., Akita, T., Tatsumi, K. & Sakaebe, H. Characterization of MgO-coated-LiCoO2 particles by analytical transmission electron microscopy. J. Power Sources 328, 161-166 (2016

[0005] He, Y. et al. A bi-functional strategy involving surface coating and subsurface gradient co-doping for enhanced cycle stability of LiCoO2 at 4.6 V. J. Energy Chem. 77, 553-560 (2023

[0005] Orikasa, Y. et al. Origin of surface coating effect for MgO on LiCoO2 to improve the interfacial reaction between electrode and electrolyte. Adv. Mater. Interfaces 1, 1400195 (2014

[0005] Yang, X. et al. Pushing lithium cobalt oxides to 4.7 V by latticematched interfacial engineering. Adv. Energy Mater. 12, 2200197 (2022

[0005] Takahashi, Y. et al. Structure and electron density analysis of electrochemically and chemically delithiated LiCoO2 single crystals. J. Solid State Chem. 180, 313-321 (2007

[0005] Chen, Z., Lu, Z. & Dahn, J. R. Staging phase transitions in Li x CoO2. J. Electrochem. Soc. 149, A1604-A1609 (2002

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[0005] Momma, K. & Izumi, F. VESTA3 for three-dimensional visualization of crystal, volumetric and morphology data. J. Appl. Crystallogr. 44, 1272-1276 (2011

[0005] JIS C 8711:2019

[0042] < / halbzelle> < / vollzelle> < / halbzelle> < / xps> < / epma> < / sem> < / xrd> < / negativelektrodenstromkollektor> < / negativelektrodenaktivmaterial> < / positivelektrodenstromkollektor> < / bindemittel> < / berechnung> < / dsc>

Claims

[1] Positive electrode active material comprising: a positive electrode active material particle comprising a surface portion and a bulk region, wherein the positive electrode active material particle comprises lithium cobalt oxide, magnesium, fluorine, nickel and aluminum, wherein the positive electrode active material in a discharge state has a layered rock salt crystal structure belonging to an R-3m space group, wherein the layered rock-salt crystal structure in the discharge state has a c-lattice parameter greater than 14.055 Å and GOF less than or equal to 1.4 when fitted as LiCoO2 with the R-3m space group and subjected to Rietveld refinement, wherein the surface portion comprises a magnesium-rich rock salt structural region, and where the magnesium-rich rock salt structural region is coherently bound to the bulk region. [2] The positive electrode active material according to claim 1, wherein the c-lattice parameter is less than 14.060 Å. [3] The positive electrode active material according to claim 1, wherein magnesium, fluorine, nickel and aluminum are present in the surface portion. [4] Positive electrode active material according to claim 1, wherein the volume energy density calculated using the true density of the positive electrode active material is greater than or equal to 4250 Wh / L, and wherein the gravimetric energy density calculated using the true density of the positive electrode active material is greater than or equal to 865 Wh / Kg. [5] Secondary battery comprising: the positive electrode active material according to claim 4; and an electrolyte solution, wherein the electrolyte solution comprises 1 M LiPF6 dissolved in FEC / MTFP in a volume ratio of 2:8 with 5 wt% PS. [6] The positive electrode active material according to claim 1, wherein when a cross section of the positive electrode active material particle is analyzed with an electron beam microanalyzer, an atomic ratio of Mg / Co is greater than or equal to 0.005 and less than or equal to 0.015, and an atomic ratio of Al / Co is less than or equal to 0.

005. [7] Positive electrode active material comprising: a positive electrode active material particle comprising lithium cobalt oxide, magnesium, fluorine, nickel and aluminum, wherein a narrow-scan spectrum of Mg 1s of the positive electrode active material obtained by X-ray photoelectron spectroscopy has a maximum intensity at a binding energy between a binding energy at which a narrow-scan spectrum of Mg 1s of magnesium oxide obtained by X-ray photoelectron spectroscopy has a maximum intensity and a binding energy at which a narrow-scan spectrum of Mg 1s of magnesium fluoride obtained by X-ray photoelectron spectroscopy has a maximum intensity. [8] The positive electrode active material according to claim 7, wherein the narrow-scan spectrum of Mg 1s of the positive electrode active material obtained by X-ray photoelectron spectroscopy has the maximum intensity at a binding energy of greater than 1303.3 eV and less than 1306.3 eV. [9] The positive electrode active material according to claim 8, wherein when a cross section of the positive electrode active material particle is analyzed with an electron beam microanalyzer, an atomic ratio of Mg / Co is greater than or equal to 0.005 and less than or equal to 0.015, and an atomic ratio of Al / Co is less than or equal to 0.

005. [10] Positive electrode active material according to claim 7, wherein the positive electrode active material comprises a surface portion and a bulk region, and where magnesium, fluorine, nickel and aluminum are present in the surface section. [11] Positive electrode active material according to claim 7, wherein the volume energy density calculated using the true density of the positive electrode active material is greater than or equal to 4250 Wh / L, and wherein the gravimetric energy density calculated using the true density of the positive electrode active material is greater than or equal to 865 Wh / Kg. [12] Secondary battery, which includes: the positive electrode active material according to claim 11; and an electrolyte solution, wherein the electrolyte solution comprises 1 M LiPF6 dissolved in FEC / MTFP in a volume ratio of 2:8 with 5 wt% PS. [13] Positive electrode active material comprising: a positive electrode active material particle comprising lithium cobalt oxide, magnesium, fluorine, nickel and aluminum, wherein the positive electrode active material in a discharge state has a layered rock salt crystal structure belonging to an R-3m space group, wherein when a positive electrode containing the positive electrode active material is analyzed in a discharge state by powder X-ray diffraction using Cu Kα1 radiation after a charge / discharge cycle test, a peak having a half-width of less than or equal to 0.08° is detected within a 2θ range of 18.7° to 19.0°, and a peak having a half-width of less than or equal to 0.12° is detected in a 2θ range of 45.0° to 45.3°, wherein the charge / discharge cycle test is conducted under an environment of 25°C on a cell comprising the positive electrode, lithium metal as a negative electrode, and a mixture of lithium hexafluorophosphate, ethylene carbonate, and diethyl carbonate with 2 wt% vinylene carbonate as an electrolyte solution, wherein in the charge / discharge cycle test, a charge / discharge cycle is repeated 100 times in which a constant current charge is carried out at a current value of 0.5 C up to a voltage of 4.7 V, a constant voltage charge is carried out until the current value reaches 0.05 C, a rest period of 10 minutes is provided, a constant current discharge is carried out at a current value of 0.5 C up to a voltage of 2.5 V and then a rest period of 10 minutes is provided, and where 1 C = 200 mA / g. [14] Positive electrode active material according to claim 13, wherein the positive electrode active material comprises a surface portion and a bulk region, and where magnesium, fluorine, nickel and aluminum are present in the surface section. [15] Positive electrode active material according to claim 13, wherein the volume energy density calculated using the true density of the positive electrode active material is greater than or equal to 4250 Wh / L, and wherein the gravimetric energy density calculated using the true density of the positive electrode active material is greater than or equal to 865 Wh / Kg. [16] Secondary battery comprising: the positive electrode active material according to claim 15; and an electrolyte solution, wherein the electrolyte solution comprises 1 M LiPF6 dissolved in FEC / MTFP in a volume ratio of 2:8 with 5 wt% PS.

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