JP6248639B2 - Positive electrode active material for lithium ion secondary battery, positive electrode for lithium ion secondary battery and lithium ion secondary battery using the same, and method for producing positive electrode active material for lithium ion secondary battery - Google Patents

Description

  The present invention relates to a positive electrode active material for lithium ion secondary batteries, a positive electrode for lithium ion secondary batteries and a lithium ion secondary battery using the same, and a method for producing a positive electrode active material for lithium ion secondary batteries.

  Lithium ion secondary batteries have a feature of high energy density and low memory effect compared to other secondary batteries such as nickel / hydrogen storage batteries and nickel / cadmium storage batteries. Therefore, from small power sources such as portable electronic devices and household electric appliances to stationary power sources such as power storage devices, uninterruptible power supply devices, power leveling devices, and driving power sources for ships, railways, hybrid vehicles, electric vehicles, etc. Applications have expanded to large power supplies, and further improvements in battery performance are required. In particular, lithium ion secondary batteries deployed as medium and large power supplies are required to have a high energy density that can achieve a high capacity with a low volume.

In response to such a request, development of a solid solution positive electrode active material represented by Li ₂ MnO ₃ —LiM ₁ O ₂ (M 1 represents an element such as Co, Ni, Mn, etc.) has been intensively advanced. The solid solution positive electrode active material is expected as a positive electrode active material having a lithium-excess elemental composition and capable of realizing a high capacity. On the other hand, the solid solution positive electrode active material is not necessarily excellent in charge / discharge cycle characteristics, and when charged to a high potential, it causes elution of transition metals and decomposition of the electrolytic solution, resulting in deterioration of battery performance. There is.

Therefore, a technique for improving the charge / discharge cycle characteristics of the solid solution positive electrode active material by coating the surface of the positive electrode active material has been proposed. For example, Patent Document 1 includes xLi ₂ MnO ₃ — (1-x) LiMn _a Co _b Ni _c O ₂ (where 0.2 ≦ x ≦ 0.5, 0.3 ≦ a ≦ 0.5, At least part of the surface of the solid solution represented by 0.1 ≦ b ≦ 0.3, 0.3 ≦ c ≦ 0.5, and a + b + c = 1), where Me is Mn, Co And a transition metal other than Ni.) A positive electrode coated with MoO ₃ , Li ₂ MoO ₄ , Li ₂ CrO ₄ or Li ₂ WO ₄ as a positive electrode active material coated with an oxide or a lithium salt of oxide Examples of active materials are disclosed.

JP 2012-129166 A

  As disclosed in Patent Document 1, by covering the surface of the positive electrode active material with an oxide or the like, the positive electrode active material and the electrolyte constituting the battery are isolated, so that charging / discharging of the lithium ion secondary battery It is thought that cycle characteristics can be improved. However, when the positive electrode active material is simply coated with an oxide or the like in order to improve the charge / discharge cycle characteristics, the coating film becomes a resistance component, so that the discharge rate characteristics are likely to deteriorate. For this reason, it is difficult to achieve both charge / discharge cycle characteristics and discharge rate characteristics in a solid solution positive electrode active material.

  Accordingly, an object of the present invention is to provide a positive electrode active material for a lithium ion secondary battery excellent in charge / discharge cycle characteristics and discharge rate characteristics, a positive electrode for lithium ion secondary batteries and a lithium ion secondary battery using the same, and lithium ion It is providing the manufacturing method of the positive electrode active material for secondary batteries.

In order to solve the above problems, a positive electrode active material for a lithium ion secondary battery according to the present invention has the following composition formula (1),
xLi ₂ MnO _3- (1-x) LiM _y O _{{(2-3x) / (1-x)}} (1)
[Wherein x is a number satisfying 0 <x ≦ 0.6, y is a number satisfying 0.7 ≦ y ≦ 1.0, and M is Ni, Co, Mn, Ti, Zr , At least one element selected from the group consisting of Al, Mg and V. ] And a lithium ion conductive glass covering at least a part of the surface of the solid solution particle, wherein the lithium ion conductive glass is Li ₂ O—B ₂ O ₃ , Li _2. From the group consisting of O—Al ₂ O ₃ , Li ₂ O—SiO ₄ , Li ₂ O—P ₂ O ₅ , Li ₂ O—V ₂ O ₅ , LiF—BF ₃ , LiF—AlF ₃ , LiF—VF _3. At least one selected, the lithium ion conductivity of the lithium ion conductive glass is 1 × 10 ⁻¹⁰ S / cm or more at room temperature , and the solid solution particles have a lithium concentration in the surface layer , It is characterized by being 80% by mass or less of the lithium concentration in the inner layer.

  Moreover, the positive electrode for lithium ion secondary batteries which concerns on this invention is characterized by including the said positive electrode active material for lithium ion secondary batteries.

  In addition, a lithium ion secondary battery according to the present invention includes the positive electrode for a lithium ion secondary battery.

Further, the method for producing a positive electrode active material for a lithium ion secondary battery according to the present invention includes immersing the solid solution particles represented by the composition formula (1) in a solvent having a pH of 7 or more and 9 or less to remove lithium on the surface layer of the solid solution particles. released was Rutotomoni, the surface of the solid-solution particles, B, Al, Si, depositing a precursor of the lithium ion conductive glass having a composition comprising at least one element selected from the group consisting of P and V When the subjecting the solid solution particles 20 hours following heating for 1 hour or more at 200 ° C. or higher 600 ° C. or less, the solid solution _{particles, Li 2 O-B 2 O} 3, Li 2 O-Al 2 O 3, Li It is at least one selected from the group consisting of ₂ O—SiO ₄ , Li ₂ O—P ₂ O ₅ , Li ₂ O—V ₂ O ₅ , LiF—BF ₃ , LiF—AlF ₃ , LiF—VF _3. Re Characterized in that it comprises a step of coating with Ion conductive glass, a.

  According to the present invention, a positive electrode active material for a lithium ion secondary battery excellent in charge / discharge cycle characteristics and discharge rate characteristics, a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery using the same, and a lithium ion secondary battery A method for producing a positive electrode active material for a battery can be provided.

It is a cross-sectional schematic diagram which shows an example of the lithium ion secondary battery which concerns on this embodiment. It is a figure which shows the relationship between the rate capacity | capacitance maintenance rate and cycle capacity maintenance factor of the lithium ion secondary battery which concerns on an Example and a comparative example.

  Hereinafter, a positive electrode active material for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, a lithium ion secondary battery, and a production method thereof according to an embodiment of the present invention will be described in detail.

  The positive electrode active material for a lithium ion secondary battery according to the present embodiment is mainly composed of solid solution particles responsible for an electrochemical reaction as the positive electrode active material and lithium ion conductive glass covering the surface of the solid solution particles. That is, the positive electrode active material particles responsible for the positive electrode reaction of the lithium ion secondary battery are configured to be covered with a glassy coating having lithium ion conductivity that is responsible for electrical conduction between the positive and negative electrodes. .

The solid solution particles constituting the positive electrode active material for a lithium ion secondary battery according to the present embodiment,
The following composition formula (1),
xLi ₂ MnO _3- (1-x) LiM _y O _{{(2-3x) / (1-x)}} (1)
[Wherein x is a number satisfying 0 <x ≦ 0.6, y is a number satisfying 0.7 ≦ y ≦ 1.0, and M is Ni, Co, Mn, Ti, Zr , At least one element selected from the group consisting of Al, Mg and V. ] The primary particle of the solid solution system positive electrode active material which has an elemental composition represented by this. The atomic ratio (molar ratio) between lithium (Li) and metal elements (Mn and M) contained in the positive electrode active material of the above formula (1) is 1 <(Li / (Mn + M)) ≦ 1.8.

This solid solution positive electrode active material is electrochemically inactive but exhibits high theoretical capacity, Li ₂ MnO ₃ having a layered rock salt structure as a basic structure, and electrochemically active, layered rock salt type layered oxide having the structure as a basic structure (represented as LiM1O _2, M1 is, Co, Ni, showing the elements such as Mn.) and has a solid solution, a lithium-containing metal having a layered crystal structure as the main structure It is a complex oxide. Since it has a layered crystal structure, it is possible to repeat reversible insertion and desorption of lithium ions with charge and discharge, and not only Li arranged between layers of the layered structure but also Li arranged in a metal layer Since it can be detached, it is a positive electrode active material expected to have a high capacity.

The solid solution positive electrode active material represented by the composition formula (1) has a feature that charge / discharge cycle characteristics are not necessarily excellent while high capacity is expected. When a lithium ion secondary battery using this solid solution positive electrode active material is charged to a high voltage, the battery performance is greatly deteriorated. Therefore, the end-of-charge voltage is usually kept low, and a high theoretical capacity is sufficient. There is a current situation that cannot be utilized. As a factor for reducing the charge / discharge cycle characteristics of the solid solution positive electrode active material, there is an irreversible change in the battery configuration due to electrochemically inactive Li ₂ MnO ₃ . Li ₂ MnO ₃ is considered to cause an irreversible reaction represented by the following formula (I) as a lithium ion desorption reaction at the time of the initial charge when the end-of-charge voltage exceeds 4.4 V (vs. Li ⁺ / Li). It has been.
Li ₂ MnO ₃ → MnO ₂ + 1 / 2O ₂ + 2Li ⁺ + 2e ⁻ (I)

As shown in the formula (I), in Li ₂ MnO ₃ , it is considered that charge compensation when Li ionized at the time of charging is desorbed is not oxygen but a transition metal. For this reason, the release of oxygen along with the desorption of Li changes the crystal structure of the solid solution positive electrode active material irreversibly, and further promotes the elution of transition metals and the oxidative decomposition of the electrolyte, thereby improving battery performance. It is thought to cause deterioration.

  Therefore, in the positive electrode active material for a lithium ion secondary battery according to the present embodiment, the surface of the solid solution particles is used to suppress the elution of transition metals and the progress of oxidative decomposition of the electrolyte without hindering the conduction of lithium ions. At least a part of this is coated with lithium ion conductive glass to improve charge / discharge cycle characteristics and discharge rate characteristics. Moreover, in order to suppress the irreversible reaction shown to Formula (I), the surface layer of a solid solution particle shall be comprised with a lithium deficiency layer. This lithium-deficient layer not only suppresses irreversible reaction, but also contributes to the realization of appropriate coating with lithium ion conductive glass, resulting in improved charge / discharge cycle characteristics and discharge rate characteristics.

In the composition formula (1), x represents the ratio of Li ₂ MnO ₃ in the solid solution positive electrode active material. The higher the ratio of Li ₂ MnO _3, the higher the capacity because the solid solution positive electrode active material becomes lithium-excess. On the other hand, the higher the ratio of Li ₂ MnO _3, the higher the resistance because the electrochemical activity of the solid solution positive electrode active material decreases. Therefore, x is in the range of more than 0 and not more than 0.6, preferably not less than 0.1 and not more than 0.3. If x is a composition of 0.1 or more, lithium can be enriched to a certain extent to increase the capacity. Moreover, since it can avoid that resistance becomes excessive by setting it as a composition whose x is 0.3 or less, a discharge rate characteristic can be improved.

  In the composition formula (1), M is composed of at least one element selected from the group consisting of Ni, Co, Mn, Ti, Zr, Al, Mg, and V, and the composition ratio y of these elements Is in the range of 0.7 to 1.0. In composition formula (1), the electrochemical activity in the solid solution positive electrode active material can be ensured by containing at least Mn as a metal element. Further, by substituting these transition metal sites with at least one element selected from the group consisting of Co, Ti, Zr, Al, Mg and V as the elements of M, mainly Ni and Mn, It is possible to improve the structural stability and the electrochemical properties (cycle characteristics, etc.) of the solid solution positive electrode active material. The content of at least one element selected from the group consisting of Ti, Zr, Al, Mg, and V is preferably 10% by mass or less with respect to 100% by mass of the total mass of M elements.

As described above, the element of M preferably contains Mn, and more preferably contains Ni and Mn. Specifically, the solid solution particles preferably have a composition represented by the following composition formula (2).
xLi ₂ MnO ₃ — (1-x) LiNi _y1 Mn _y2 M ′ _y3 O _{{(2-3x) / (1-x)}} (2)
[Wherein x is a number satisfying 0 <x ≦ 0.6, y1 is a number satisfying 0 ≦ y1 ≦ 1.0, and y2 is a number satisfying 0 ≦ y2 ≦ 1.0. Y3 is a number satisfying 0 ≦ y3 <1.0, 0.7 ≦ y1 + y2 + y3 ≦ 1.0, and M ′ is selected from the group consisting of Co, Ti, Zr, Al, Mg and V At least one element. ]

  In particular, by setting the solid solution positive electrode active material to a composition represented by the composition formula (2), it is possible to suppress raw material costs while ensuring a good discharge capacity.

The atomic concentration of Ni and Mn in the whole M element is preferably 75 at% or more by adding Ni and Mn. Therefore, in the composition formula (2), it is preferable that (y1 + y2) / (y1 + y2 + y3) × 100 ≧ 75 is satisfied. If the solid solution positive electrode active material has such a composition, it is possible to appropriately achieve solid solution of Li ₂ MnO ₃ and the layered oxide.

  The composition of the positive electrode active material for a lithium ion secondary battery according to the present embodiment is not limited to strictly following the stoichiometric ratio, and the composition may be an indefinite ratio without departing from the gist of the present invention. There may be substitution or defect between sites on the crystal structure.

  The lithium ion conductive glass according to the present embodiment is made of an oxide, fluoride, or sulfide that has lithium ion conductivity and is stable as an amorphous solid in the vicinity of a normal temperature range. As the lithium ion conductive glass, glass that vitrifies at a temperature at which the solid solution particles are thermally stable, preferably 200 ° C. or higher and 600 ° C. or lower is preferable.

_The glass composition components constituting the lithium ion conductive _{glass, Li 2 O, SiO 2,} Al 2 O 3, Fe 2 O 3, TiO 2, CaO, MgO, Na 2 O, K 2 O, SO 3, As _{2 O 3, B 2 O 3} , V 2 O 5, P 2 O 5, ZrO 2, MoO 3, PbO, GeO 2, Nb 2 O 5, Ga 2 O 3, Sb 2 O 3, Bi 2 O 3 , etc. Oxides of LiF, AlF ₃ , CeF ₃ , BaF ₂ , CaF ₂ , MgF ₂ , BeF ₂ , InF ₃ , ZrF ₄ , GdF ₃ , LaF ₃ , NaF, HfF ₄ , CdF ₂ , PbF ₂ , GaF ₃ , Fluorides such as ZnF ₃ , and sulfides such as Li ₂ S, SiS ₂ , B ₂ S ₃ , P ₂ S ₅ , GeS ₂ . In the molecular structure formed by these glass composition components, vitrification is performed by increasing the content ratio of Li ₂ O in oxide glass, LiF in fluoride glass, and Li ₂ S in sulfide glass. By performing, lithium ion conductive glass with improved lithium ion conductivity can be obtained.

As a glass composition component that increases the content ratio of lithium, Li ₂ SO ₄ , Li ₂ MoO ₄ , Li ₄ SiO ₄ , Li ₃ PO ₄ , Li ₄ GeO ₄ , Li ₄ ZrO ₄ , Li ₂ CO ₃ , LiW ₂ O ₇ , one or more modifiers such as LiNbO ₃ , Li ₃ VO ₄ , LiCl, LiBr, LiI, Li ₂ Se may be added.

The lithium ion conductive glass according to this embodiment preferably has a composition containing at least one element selected from the group consisting of B, Al, Si, P, and V. Among these compositions, Li ₂ O—B ₂ O ₃ , Li ₂ O—Al ₂ O ₃ , Li ₂ O—SiO ₄ , Li ₂ O—P ₂ O ₅ , Li ₂ O—V ₂ O _{5, LiF-BF 3, LiF} -AlF 3, having at least one glass composition ingredients are selected from the group consisting of LiF-VF ₃ are preferred. If the lithium ion conductive glass has such a composition, it is relatively easy to adjust the lithium ion conductivity by adjusting the heating temperature in vitrification. Therefore, the lithium ion conductive glass having high lithium ion conductivity. Can be obtained.

The lithium ion conductive glass according to the present embodiment preferably has a lithium ion conductivity of 1 × 10 ⁻¹⁰ S / cm or more. In the solid solution particles, the diffusion rate of lithium is smaller than in the case of the layered compound particles, but if the lithium ion conductivity in the lithium ion conductive glass is 1 × 10 ⁻¹⁰ S / cm or more, the lithium ion conductivity Since the glass coating does not significantly interfere with lithium ion conduction between the positive electrode active material and the non-aqueous electrolyte, good rate characteristics can be ensured even when solid solution particles are coated. .

  The lithium ion conductivity in the lithium ion conductive glass is calculated based on the electric resistance of the lithium ion conductive glass at a room temperature with a predetermined cross-sectional area and a predetermined interelectrode distance. Specifically, lithium ion conductive glass is applied on an aluminum foil so as to have a thickness of 300 μm, and is punched into a disk shape having a diameter of 15 mm to form a working electrode, and metallic lithium is used as a counter electrode. The measured resistance value in the coin-type battery is obtained by measuring using the AC impedance method. The measurement frequency in this alternating current impedance method shall be 100 Hz-20 MHz.

  The lithium ion conductive glass according to the present embodiment is not limited to a glass that is substantially amorphous in the vicinity of a normal temperature range (about 5 ° C. to 40 ° C.), and is a crystallized glass containing a crystalline phase together with an amorphous phase It may be. Even when the proportion of the crystal phase is high, the lithium ion conductivity is high, and when a high-temperature stable phase that can be maintained at room temperature is formed, the lithium ion conductivity is ensured. It is possible to ensure rate characteristics. However, in general, the ionic conductivity of an amorphous material tends to be higher than that of a crystal having few voids. Therefore, by making the lithium ion conductive glass according to the present embodiment a glass that is substantially amorphous, the diffusion of lithium ions is improved and the influence due to the grain boundary resistance is also reduced, so that favorable rate characteristics are obtained. Can be obtained. Further, even if the crystal structure of the solid solution particles changes during the charge / discharge process and the volume expands or contracts, the glass can follow the volume variation if the glass has a high ratio of amorphous material having fluidity. The coating of the particles can be maintained stably.

  It is preferable that content of the lithium ion conductive glass which concerns on this embodiment is 0.5 to 5.0 mass% with respect to 100 mass% of the whole positive electrode active material. In the positive electrode active material for a lithium ion secondary battery according to the present embodiment, the solid solution particles are coated with lithium ion conductive glass at least a part of the surface, preferably 50% or more and 100% or less of the surface of the solid solution particles. If it is done, the elution of the transition metal and the suppression of the oxidative decomposition of the electrolytic solution are achieved accordingly. Therefore, if the content of the lithium ion conductive glass is 0.5% by mass or more, it is possible to cover at least a part of the solid solution particles with a film thickness of a certain level or more, thereby improving the charge / discharge cycle characteristics. Can be made. In addition, by setting the content of the lithium ion conductive glass to 5.0% by mass or less, the energy density in the positive electrode for the lithium ion secondary battery is greatly reduced by the lithium ion conductive glass contained in the positive electrode. Can be avoided.

  The solid solution particles of the positive electrode active material for a lithium ion secondary battery according to the present embodiment have a composition in which the lithium concentration in the surface layer is lower than the lithium concentration in the inner layer. That is, in the vicinity of the outermost surface of the solid solution particles, a lithium deficient layer showing a relatively low lithium concentration even during non-charging in a range from the outermost surface of the solid solution particles coated with lithium ion conductive glass to a certain depth. Is formed. The lithium-deficient layer is a region having a composition in which the composition ratio of lithium is smaller than the average composition of the entire solid solution particle represented by the composition formula (1). As described above, when the irreversible reaction shown in the formula (I) occurs during charging, battery performance deteriorates due to elution of transition metals and oxidative decomposition of the electrolytic solution, so it is difficult to obtain good charge / discharge cycle characteristics. . Therefore, in the positive electrode active material for a lithium ion secondary battery according to this embodiment, the surface layer of the solid solution particles is made a composition with a small composition ratio of lithium by previously extracting lithium from the surface layer of the solid solution particles, so that the positive electrode active material at the time of initial charge is reduced. Reduces irreversible changes in materials.

  The solid solution particle whose surface layer is a lithium-deficient layer has a concentration gradient indicating a decrease in lithium concentration from the inner layer side to the outermost surface side of the solid solution particle. Accordingly, the outermost surface of the solid solution particles having a lower lithium concentration is more stable against lithium insertion and detachment accompanying charge / discharge, and it is possible to appropriately moderate irreversible changes in the positive electrode active material. . On the other hand, on the inner layer side of the lithium-deficient layer, the lithium concentration is relatively high and lithium that can participate in the interelectrode reaction remains, so that the discharge capacity is secured.

  The lithium concentration in the surface layer is preferably 80% by mass or less of the lithium concentration in the inner layer. Moreover, it is preferable that it is 8 mass% or less with respect to the whole solid solution particle. In addition, it is preferable that the lithium concentration in an inner layer is 9 to 11 mass% with respect to the whole solid solution particle. When the lithium concentration in the inner layer is 9% by mass or more and 11% by mass or less, a good discharge capacity can be obtained. At this time, if the lithium concentration in the surface layer is 8% by mass or less, the irreversible reaction can be suppressed while securing the discharge capacity, and the charge / discharge cycle characteristics can be improved.

  Here, the surface layer of the solid solution particle is a region in the vicinity of the surface having a depth of 0 nm or more and 30 nm or less from the outermost surface of the solid solution particle, and the inner layer of the solid solution particle is a region on the particle center side exceeding the depth of 30 nm from the outermost surface of the solid solution particle. Defined. Further, the lithium concentration in each region means the average atomic concentration of lithium per region. The particle diameter of the solid solution particles according to the present embodiment is usually about 100 nm to 500 nm, but when the particle diameter of the solid solution particles is less than 100 nm, the depth from the outermost surface of the solid solution particles is the particle diameter. The region on the outermost surface side of 15% or less may be a composition having a smaller lithium composition ratio than the inner layer of the solid solution particles.

  The element distribution in the solid solution particles and the lithium ion conductive glass according to the present embodiment includes time-of-flight secondary ion mass spectrometry (TOF-SIMS), Auger Electron Spectroscopy; AES), X-ray photoelectron spectroscopy (XPS), transmission electron microscope-electron energy loss spectroscopy (TEM-EELS), and the like.

  The method for manufacturing a positive electrode active material for a lithium ion secondary battery according to the present embodiment is mainly an adhesion in which lithium on the surface layer of solid solution particles is desorbed and a precursor of lithium ion conductive glass is attached to the surface of the solid solution particles. The process and the heating process which heat-processes a solid solution particle. The solid solution particles subjected to the process can be produced in accordance with a general production method of a positive electrode active material. Examples of such production methods include a solid phase method, a coprecipitation method, a sol-gel method, a hydrothermal method. Law.

  In the production of solid solution particles using the solid phase method, raw material Li-containing compounds, Mn-containing compounds, and the like are weighed at a ratio of a predetermined elemental composition, pulverized and mixed to prepare raw material powders. As the Li-containing compound, for example, lithium acetate, lithium nitrate, lithium carbonate, lithium hydroxide, lithium chloride, lithium sulfate and the like can be used, and lithium carbonate and lithium hydroxide are preferable. In addition, as the Mn-containing compound, for example, manganese acetate, manganese nitrate, manganese carbonate, manganese sulfate, manganese oxide, manganese hydroxide and the like can be used, but manganese carbonate and manganese oxide are preferable. In addition, when M element is contained, acetate, nitrate, carbonate, sulfate, hydroxide, oxide and the like can be used.

  For the pulverization and mixing for preparing the raw material powder, any of dry pulverization and wet pulverization methods can be used. As the pulverizing means, for example, a pulverizer such as a ball mill, a bead mill, a planetary ball mill, an attritor, or a jet mill can be used.

  The prepared raw material powder is fired to form solid solution particles. The raw material powder is preferably fired by pre-baking to thermally decompose the raw material compound, appropriately pulverizing and classifying, and then sintering by firing. The heating temperature in the preliminary baking is, for example, about 300 ° C. to 600 ° C., and the heating temperature in the main baking is, for example, 400 ° C. to 1100 ° C., preferably 500 ° C. to 1000 ° C. Within such a temperature range, the crystallinity can be improved while avoiding decomposition of solid solution particles and volatilization of components. The firing time in the main firing is 4 hours to 48 hours, preferably 10 hours to 24 hours. The firing may be repeated a plurality of times.

  The firing atmosphere may be either an inert gas atmosphere or an oxidizing gas atmosphere, but is preferably an oxidizing gas atmosphere such as oxygen or air. By performing firing in an oxidizing gas atmosphere, it is possible to avoid contamination by impurities due to incomplete thermal decomposition of the raw material compound and to improve crystallinity. The fired solid solution particles may be air-cooled, gradually cooled in an inert gas atmosphere, or rapidly cooled using liquid nitrogen or the like.

  The average primary particle diameter of the solid solution particles thus fired is preferably about 50 nm to 500 nm. By setting the average primary particle diameter of the solid solution particles to about 500 nm or less, the filling property in the positive electrode is improved and a good energy density can be achieved. The solid solution particles may be formed into secondary particles by granulating the produced primary particles by dry granulation or wet granulation. As the granulating means, for example, a granulator such as a spray dryer can be used.

  In the attaching step, first, the manufactured solid solution particles are immersed in a solvent such as water adjusted to a predetermined pH to desorb some lithium from the surface layer of the solid solution particles, and the surface layer has a small lithium composition ratio. The composition. That is, by placing the solid solution particles in a low pH environment simulating a charging reaction, the lithium desorption reaction (elution) is promoted to remove lithium existing on the surface layer side of the solid solution particles to form a lithium deficient layer. . The pH of the solvent in which the solid solution particles are immersed is preferably 7 or more and 9 or less. If the pH of the solvent is 7 or more, lithium is not excessively desorbed from the solid solution particles, so that the crystal structure of the solid solution particles can be stably maintained, and the deterioration of cycle characteristics is suppressed. Also, if the pH of the solvent is 9 or less, the elimination reaction of lithium proceeds moderately, so lithium is removed from the surface layer side, and the surface layer of the solid solution particles has a composition with a moderately small composition ratio of lithium. Can do. As the pH adjuster for adjusting the pH of the solvent in which the solid solution particles are immersed, lithium hydroxide is preferable.

  Subsequently, the precursor of lithium ion conductive glass is made to adhere to the surface by making the precursor of lithium ion conductive glass contact the surface of the solid solution particle which removed lithium of the surface layer. As a method for attaching the glass precursor, any of a gas phase method, a liquid phase method, and a solid phase method can be used, but it is based on a gas phase method or a liquid phase method capable of performing coating with excellent uniformity. preferable.

  As a glass precursor to be attached to the surface of the solid solution particles, depending on the attachment method, for example, lithium carbonate, lithium hydroxide, lithium sulfide, lithium fluoride, and other glass compositions constituting the lithium ion conductive glass An acetate, nitrate, carbonate, sulfate, ammonium salt, fluoride, hydroxide, oxide or the like containing the element of the component can be used. As the compound containing an element of another glass composition component, a compound having a composition containing at least one element selected from the group consisting of B, Al, Si, P and V is preferable.

In the case of attaching the glass precursor by the liquid phase method, a predetermined amount of the glass precursor is weighed, dissolved in an aqueous solvent or an organic solvent, and solid solution particles produced in the solvent are immersed. And about a solvent, the solid solution particle | grains to which the glass precursor adhered were dried by heat drying, spray drying, etc., and removed. In this process, the lithium ion conductive glass precursor penetrates into the surface layer of the solid solution particles by adhering the glass precursor to the surface of the solid solution particles having a composition with a small composition ratio of lithium. It becomes possible to form a lithium-deficient layer mixed with solid solution on the surface layer of solid solution particles. In the Li ₂ MnO ₃ phase of the solid solution particles in the lithium-deficient layer, the irreversible reaction shown in the formula (I) is suppressed by the elimination of lithium, so that the lithium ion conductivity can be obtained even when charging and discharging are repeated. The effect of stabilizing the coating with glass is obtained.

  In addition, when performing an adhesion process by a liquid phase method, it is good also as an integrated process combined with the said immersion process, and solid solution particle | grains are immersed in the solvent of pH 7-9 below which melt | dissolved the precursor of lithium ion conductive glass. By doing so, lithium in the surface layer of the solid solution particles can be desorbed, and the solid solution particles can be covered with lithium ion conductive glass. At this time, by using a lithium-containing compound such as lithium hydroxide as a pH adjuster, even when a lithium-free compound is used as a precursor of lithium ion conductive glass, lithium having good lithium conductivity It becomes possible to form ion conductive glass.

  In the heating step, the solid solution particles to which the lithium ion conductive glass precursor is attached are heat-treated to form a film of lithium ion conductive glass on the surface of the solid solution particles. The temperature of the heat treatment is preferably a glass transition temperature or higher and lower than a crystallization temperature, 200 ° C. or higher and 600 ° C. or lower, preferably 300 ° C. or higher and 500 ° C. or lower. The heat treatment time is 1 hour to 20 hours, preferably 3 hours to 8 hours. The atmosphere of the heat treatment may be either an inert gas atmosphere or an oxidizing gas atmosphere. For example, when coating with fluoride glass, the heat treatment may be performed in a fluorine gas atmosphere. As the fluorine-based gas, nitrogen trifluoride gas that is relatively stable at room temperature is preferable.

  In this step, the solid solution particles to which the glass precursor is adhered are heat-treated, whereby the lithium ion conductive glass precursor undergoes glass transition, and the surface of the solid solution particles is coated with the lithium ion conductive glass. Moreover, since the glass precursor reacts with lithium remaining in the surface layer of the solid solution particles by heat-treating the glass precursor, a concentration gradient of lithium concentration is formed in the depth direction on the surface layer of the solid solution particles. . In the immersion step, it is necessary to stably maintain the structure of the solid solution particles, so that it is difficult to sufficiently desorb lithium. However, in the dipping process, the lithium ion conductive glass precursor penetrates the surface layer of the solid solution particles so as to form a lithium-deficient layer in which glass and solid solution are mixed. It is possible to react efficiently.

  The positive electrode active material for a lithium ion secondary battery produced as described above is used as a material for a positive electrode for a lithium ion secondary battery.

  The positive electrode for a lithium ion secondary battery according to the present embodiment is mainly coated with a positive electrode mixture layer comprising a positive electrode active material for a lithium ion secondary battery, a conductive material and a binder, and a positive electrode mixture layer. A positive electrode current collector.

  As the conductive material, a conductive material used in a general lithium ion secondary battery can be used. Specific examples include carbon particles such as graphite powder, acetylene black, furnace black, thermal black, and channel black, carbon fibers, and the like. What is necessary is just to use the quantity used as a electrically conductive material from about 3 mass% or more and about 10 mass% or less with respect to the mass of the whole positive electrode compound material, for example.

  As the binder, a binder used in a general lithium ion secondary battery can be used. Specific examples include polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyhexafluoropropylene, styrene-butadiene rubber, and carboxymethyl cellulose. What is necessary is just to use the quantity used as a binder about 2 mass% or more and 10 mass% or less with respect to the mass of the whole positive electrode compound material, for example.

  As the positive electrode current collector, foil made of aluminum or aluminum alloy, expanded metal, punching metal, or the like can be used. The foil may have a thickness of about 10 μm to 30 μm, for example.

  The positive electrode for a lithium ion secondary battery according to this embodiment can be manufactured according to a general positive electrode manufacturing method using the positive electrode active material for a lithium ion secondary battery. An example of a method for producing a positive electrode for a lithium ion secondary battery includes a positive electrode mixture preparation step, a positive electrode mixture coating step, and a molding step.

  In the positive electrode mixture preparation step, a positive electrode active material, a conductive material, and a binder are mixed in a solvent to prepare a slurry-like positive electrode mixture. Depending on the type of binder, N-methylpyrrolidone, water, N, N-dimethylformamide, N, N-dimethylacetamide, methanol, ethanol, propanol, isopropanol, ethylene glycol, diethylene glycol, glycerin, dimethyl It can be selected from sulfoxide, tetrahydrofuran and the like. Examples of the stirring means for mixing the materials include a planetary mixer, a disper mixer, and a rotation / revolution mixer.

  In the positive electrode mixture coating step, the prepared slurry-like positive electrode mixture is applied onto the positive electrode current collector, and then the solvent is dried by heat treatment to form the positive electrode mixture layer. Examples of the coating means for applying the positive electrode mixture include a bar coater, a doctor blade, and a roll transfer machine.

  In the molding step, the dried positive electrode mixture layer is subjected to pressure molding using a roll press or the like, and is cut together with a positive electrode current collector as necessary to obtain a positive electrode for a lithium ion secondary battery having a desired shape. . The thickness of the positive electrode mixture layer formed on the positive electrode current collector may be, for example, about 50 μm to 300 μm.

  The positive electrode for a lithium ion secondary battery manufactured as described above is used as a material for a lithium ion secondary battery. The lithium ion secondary battery according to the present embodiment mainly includes a positive electrode for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, a separator, and a non-aqueous electrolyte, which are cylindrical, rectangular, It is set as the structure accommodated in exterior bodies of shapes, such as a button type | mold and a laminate sheet type | mold.

  FIG. 1 is a schematic cross-sectional view showing an example of a lithium ion secondary battery according to the present embodiment. FIG. 1 illustrates a cylindrical lithium ion secondary battery. The lithium ion secondary battery 1 includes a positive electrode 2 in which a positive electrode mixture is coated on both surfaces of a positive electrode current collector, and a negative electrode current collector. The electrode group which consists of the negative electrode 3 by which the negative electrode compound material was coated on both surfaces of this, and the separator 4 interposed between the positive electrode 2 and the negative electrode 3 is provided. The positive electrode 2 and the negative electrode 3 are wound through a separator 4 and accommodated in a cylindrical battery can 5. The positive electrode 2 is electrically connected to the sealing lid 8 via the positive electrode lead piece 6, and the negative electrode 3 is electrically connected to the battery can 5 via the negative electrode lead piece 7, and the positive electrode lead piece 6 and the negative electrode 3. Between the negative electrode lead piece 7 and the positive electrode 2, an insulating plate 10 made of an epoxy resin or the like is disposed to be electrically insulated. Each lead piece is a current drawing member made of the same material as each current collector, and is joined to each current collector by spot welding or ultrasonic welding. The battery can 5 has a structure in which a non-aqueous electrolyte is injected into the battery can 5 and then sealed with a sealing material 9 such as rubber and the top is sealed with a sealing lid 8.

  As the negative electrode for a lithium ion secondary battery, a negative electrode active material and a negative electrode current collector used in a general lithium ion secondary battery can be used.

  As the negative electrode active material, for example, one or more of a carbon material, a metal material, a metal oxide material, and the like can be used. Examples of the carbon material include graphites such as natural graphite and artificial graphite, carbides such as coke and pitch, amorphous carbon, and carbon fibers. Examples of the metal material include lithium, silicon, tin, aluminum, indium, gallium, magnesium, and alloys thereof, and examples of the metal oxide material include metal oxides including tin, silicon, and the like.

  As the negative electrode for the lithium ion secondary battery, a material selected from the same group as the binder and conductive material used in the positive electrode for the lithium ion secondary battery may be used as necessary. What is necessary is just to use the quantity used as a binder about 5 mass% with respect to the mass of the whole negative electrode compound material, for example.

  As the negative electrode current collector, copper or nickel foil, expanded metal, punching metal, or the like can be used. The foil may have a thickness of about 5 μm to 20 μm, for example.

  A negative electrode for a lithium ion secondary battery is coated with a negative electrode mixture obtained by mixing a negative electrode active material and a binder on a negative electrode current collector, and pressure-molded, as with a positive electrode for a lithium ion secondary battery. It is manufactured by cutting according to. The thickness of the negative electrode mixture layer formed on the negative electrode current collector may be, for example, about 20 μm to 150 μm.

  As the separator, a polyolefin resin such as polyethylene, polypropylene, and a polyethylene-polypropylene copolymer, a microporous film such as a polyamide resin and an aramid resin, a nonwoven fabric, and the like can be used.

Non-aqueous electrolytes include LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) _2. A solution in which a lithium salt such as LiN (CF ₃ SO ₂ ) ₂ or LiC (CF ₃ SO ₂ ) ₃ is dissolved in a non-aqueous solvent can be used. The concentration of the lithium salt in the non-aqueous electrolyte is preferably 0.7M or more and 1.5M or less.

  As the non-aqueous solvent, diethyl carbonate, dimethyl carbonate, ethylene carbonate, propylene carbonate, vinylene carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl acetate, dimethoxyethane and the like can be used. In addition, various additives should be added to the non-aqueous electrolyte for the purpose of suppressing oxidative decomposition and reductive decomposition of the electrolytic solution, preventing precipitation of metal elements, improving ion conductivity, and improving flame retardancy. Can do. Examples of such additives include 1,3-propane sultone and 1,4-butane sultone that suppress decomposition of the electrolytic solution, insoluble polyadipic anhydride that improves the storage stability of the electrolytic solution, and hexahydrophthalic anhydride. Examples include acids and the like, and fluorine-substituted alkylborons that improve flame retardancy.

  The lithium ion secondary battery according to the present embodiment having the above-described configuration is, for example, a small power source such as a portable electronic device or a household electric device, a power storage device, an uninterruptible power supply device, a stationary power source such as a power leveling device. It can also be used as a drive power source for ships, railways, hybrid cars, electric cars and the like.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated concretely, the technical scope of this invention is not limited to this.

  A solid solution particle provided with a lithium-deficient layer is coated with a different lithium ion conductive glass to produce a positive electrode active material for a lithium ion secondary battery, and a lithium ion secondary battery including a positive electrode containing the positive electrode active material The charge / discharge cycle characteristics and discharge rate characteristics were evaluated.

[Example 1]
The positive electrode active material for a lithium ion secondary battery according to Example 1 was manufactured according to the following procedure. First, raw material lithium carbonate, nickel carbonate, and manganese carbonate are weighed so that Li: Ni: Mn is in a molar concentration ratio of 1.25: 0.20: 0.60, and these are wet-ground and mixed. Thus, raw material powder was prepared. After drying the obtained raw material powder, it was put into a high-purity alumina container and pre-baked at 500 ° C. for 12 hours in the air. Then, the obtained calcined body was air-cooled, crushed, and then charged again into a high-purity alumina container, followed by main firing at 1000 ° C. for 12 hours in the atmosphere. The obtained fired body was air-cooled, crushed and classified to obtain solid solution particles.

Upon elemental analysis of the obtained solid solution particles, Li: Ni: Mn was 1.20: 0.20: 0.60. Thus, elemental composition _is estimated to be _{0.2Li 2 MnO 3 -0.8LiNi 0.25 Mn 0.50} O 1.75.

  Next, in the following procedure, lithium was desorbed from the surface layer of the obtained solid solution particles, and lithium ion conductive glass was attached to the surface of the solid solution particles to produce a positive electrode active material for a lithium ion secondary battery. First, 100 g of solid solution particles were dispersed in 500 mL of ion exchange water to obtain a dispersion. Moreover, after dissolving 7.4 g of aluminum nitrate in 500 mL of ion exchange water, 0.5 g of lithium hydroxide was added to adjust the pH to 8.0 to obtain a glass precursor solution. And these dispersion liquids and a glass precursor solution were mixed, and the glass precursor was made to adhere to the solid solution particle | grain surface by stirring at normal temperature for 1 hour. Subsequently, after this solution was spray-dried, the obtained particles were put into a high-purity alumina container, and the solid solution particles were coated with lithium ion conductive glass by heat treatment in the atmosphere at 350 ° C. for 5 hours. A positive electrode active material for a lithium ion secondary battery according to Example 1 was obtained.

  Next, elemental analysis and crystallinity analysis of the film covering the surface of the positive electrode active material were performed. A sample of the produced positive electrode active material was sliced by argon ion etching using a polishing machine (type 600 manufactured by Gatan), and then subjected to elemental analysis and electron diffraction. Elemental analysis such as concentration distribution of atoms in the film and crystallinity analysis are performed using a field emission transmission electron microscope equipped with an X-ray analyzer (hereinafter abbreviated as EDS) (manufactured by Thermo Fisher Scientific; NORAN System 300). (Hereinafter abbreviated as TEM) (manufactured by Hitachi, Ltd .; HF-2000) was measured and confirmed at an acceleration voltage of 200 kV. In addition to this, the element distribution is confirmed by TEM-EELS, which combines TEM and electron energy loss spectroscopy (EELS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), Auger electron spectroscopy (AES), etc. Is possible.

As a result of elemental analysis, it was confirmed that Li, Al, and O exist in the region from the surface of the positive electrode active material to a depth of about 30 nm, and the lithium concentration is lower toward the surface side of the positive electrode active material. It was. As a result of measuring the lithium concentration using EDS, the lithium concentration in the surface layer was 5.0% by mass, the lithium concentration in the inner layer was 10% by mass, and the lithium concentration in the surface layer was about 50% of the lithium concentration in the inner layer. Moreover, as a result of confirming the electron beam diffraction image, it was confirmed that the film had an amorphous structure. Therefore, it was confirmed that the coating film in the positive electrode active material for a lithium ion secondary battery according to Example 1 is Li ₂ O—Al ₂ O ₃ glass.

  Next, the lithium ion secondary battery provided with the positive electrode containing the obtained positive electrode active material for lithium ion secondary batteries was manufactured. The shape of the lithium ion secondary battery was a cylindrical 18650 type battery having a diameter of 18 mm and a height of 650 mm.

First, 90 parts by mass of the obtained positive electrode active material, 6 parts by mass of a conductive material, and 4 parts by mass of a binder are mixed in a solvent and stirred for 3 hours using a planetary mixer. Was prepared. The conductive material was carbon particle powder, the binder was polyvinylidene fluoride, and the solvent was N-methylpyrrolidone. Then, after apply | coating the obtained positive electrode compound material on both surfaces of the positive electrode electrical power collector which is 20-micrometer-thick aluminum foil using a roll transcription | transfer machine, compound material density is 2. Pressure was applied to 60 g / cm ³ and cutting was performed to obtain a positive electrode for a lithium ion secondary battery.

  In addition, 95 parts by mass of a negative electrode active material and 5 parts by mass of a binder were mixed in a solvent, and stirred for 30 minutes using a slurry mixer to prepare a negative electrode mixture. Note that graphite was used as the negative electrode active material, polyvinylidene fluoride was used as the binder, and N-methylpyrrolidone was used as the solvent. Subsequently, the obtained negative electrode mixture was applied to both surfaces of a negative electrode current collector, which is a copper foil having a thickness of 10 μm, using a roll transfer machine, and then pressed and cut using a roll press, and lithium lithium A negative electrode for an ion secondary battery was obtained.

  The obtained positive and negative electrodes were each joined by ultrasonic welding, and then wound into a cylindrical shape with a porous polyethylene film sandwiched between the electrodes, and each lead piece was sealed in a battery can After each connection with the lid, the battery can and the sealing lid were joined and sealed by laser welding. Thereafter, a non-aqueous electrolyte was injected into the battery can from the injection port to obtain a lithium ion secondary battery according to Example 1.

  Next, the manufactured lithium ion secondary battery was subjected to a charge / discharge test to evaluate discharge rate characteristics and charge / discharge cycle characteristics. The charge / discharge test was performed at an environmental temperature of 25 ° C.

  The discharge rate characteristics were obtained by the following procedure. The charging and discharging conditions are a constant current and low voltage charge up to an upper limit voltage of 4.6 V at a current corresponding to 0.1 C for charging, and a constant current corresponding to 0.1 C after discharging for 30 minutes after charging. The discharge was set to a lower limit voltage of 2.0V. After repeating this charge / discharge cycle for a total of 5 cycles, the battery is charged at a constant current and low voltage up to an upper limit voltage of 4.5 V with a current equivalent to 0.1 C, and after a 30-minute pause, the lower limit voltage of 2 at a constant current equivalent to 1.0 C Discharged to 0V. The fraction of the 1.0C discharge capacity at the 6th cycle with respect to the 0.1C discharge capacity at the 5th cycle was calculated as the rate capacity retention rate, and the discharge rate characteristics were evaluated.

  The charge / discharge cycle characteristics were determined by the following procedure. After calculating the rate capacity maintenance rate, charge at a constant current and low voltage up to an upper limit voltage of 4.5 V with a current corresponding to 0.1 C, and after a pause of 30 minutes, to a lower limit voltage of 2.0 V with a constant current equivalent to 1.0 C Discharged. Subsequently, the battery was charged at a constant current and low voltage up to an upper limit voltage of 4.5 V with a current corresponding to 1.0 C. After a pause of 10 minutes, the battery was discharged to a lower limit voltage of 2.0 V at a constant current equivalent to 1.0 C. This charge / discharge cycle was repeated for a total of 198 cycles, and then charged at a constant current and low voltage up to an upper limit voltage of 4.5 V with a current corresponding to 0.1 C. After resting for 30 minutes, a lower limit voltage of 2 with a constant current equivalent to 0.1 C. Discharged to 0V. Then, after calculating the rate capacity maintenance rate, the fraction of the 0.1C discharge capacity at the 200th cycle with respect to the 0.1C discharge capacity (initial discharge capacity) at the first cycle is calculated as the cycle capacity maintenance rate. The discharge cycle characteristics were evaluated.

  As a result, the initial discharge capacity of the lithium ion secondary battery according to Example 1 was 264 Ah / kg, the rate capacity maintenance rate was 83%, and the cycle capacity maintenance rate was 92%.

[Example 2]
A positive electrode active material for a lithium ion secondary battery according to Example 2 was produced by the following procedure. First, solid solution particles having an elemental composition of 0.2Li ₂ MnO ₃ —0.8LiNi _0.25 Mn _0.50 O _1.75 were produced in the same procedure as in Example 1.

Next, the obtained solid solution particles were subjected to heat treatment in a nitrogen trifluoride gas atmosphere in the same procedure as in Example 1, except for removing lithium from the surface layer and coating with lithium ion conductive glass. The positive electrode active material for a lithium ion secondary battery according to Example 2 was manufactured. When elemental analysis and crystallinity analysis of the film covering the surface of the obtained positive electrode active material were performed, the film in the positive electrode active material for a lithium ion secondary battery according to Example 2 was LiF-AlF ₃ glass. It was confirmed.

  Next, in the same procedure as in Example 1, a lithium ion secondary battery according to Example 2 including the positive electrode containing the obtained positive electrode active material was produced, and the discharge rate characteristics and the charge / discharge cycle characteristics were evaluated. As a result, the initial discharge capacity of the lithium ion secondary battery according to Example 2 was 261 Ah / kg, the rate capacity maintenance rate was 85%, and the cycle capacity maintenance rate was 95%.

[Example 3]
A positive electrode active material for a lithium ion secondary battery according to Example 3 was produced by the following procedure. First, solid solution particles having an elemental composition of 0.2Li ₂ MnO ₃ —0.8LiNi _0.25 Mn _0.50 O _1.75 were produced in the same procedure as in Example 1.

  Next, with respect to the obtained solid solution particles, lithium in the surface layer was removed in the same procedure as in Example 1 except that boric acid was used instead of aluminum nitrate. As a result of measuring the lithium concentration using EDS, the lithium concentration in the surface layer was 7.5% by mass, the lithium concentration in the inner layer was 10% by mass, and the lithium concentration in the surface layer was about 75% of the lithium concentration in the inner layer.

Furthermore, it covered with lithium ion conductive glass, and manufactured the positive electrode active material for lithium ion secondary batteries which concerns on Example 3. Was subjected to elemental analysis and crystallinity analysis of coating covering the surface of the obtained positive electrode active material, the coating on the positive active material for a lithium ion secondary battery according to Example _{3, Li 2 O-B 2} O 3 It was confirmed to be a glass based.

  Next, in the same procedure as in Example 1, a lithium ion secondary battery according to Example 3 including the positive electrode containing the obtained positive electrode active material was manufactured, and discharge rate characteristics and charge / discharge cycle characteristics were evaluated. As a result, the initial discharge capacity of the lithium ion secondary battery according to Example 3 was 268 Ah / kg, the rate capacity maintenance rate was 86%, and the cycle capacity maintenance rate was 87%.

[Example 4]
A positive electrode active material for a lithium ion secondary battery according to Example 4 was produced by the following procedure. First, solid solution particles having an elemental composition of 0.2Li ₂ MnO ₃ —0.8LiNi _0.25 Mn _0.50 O _1.75 were produced in the same procedure as in Example 1.

Next, with respect to the obtained solid solution particles, the removal of lithium on the surface layer and lithium ions were performed in the same procedure as in Example 1, except that fine silicon dioxide and ammonium dihydrogen phosphate were used instead of aluminum nitrate. Conductive glass coating was performed to produce a positive electrode active material for a lithium ion secondary battery according to Example 4. Was subjected to elemental analysis and crystallinity analysis of coating covering the surface of the obtained positive electrode active material, the coating on the positive active material for a lithium ion secondary battery according to Example _{4, Li 2 O-SiO 2} -P It was confirmed to be ₂ O ₅ glass.

  Next, in the same procedure as in Example 1, a lithium ion secondary battery according to Example 4 provided with a positive electrode containing the obtained positive electrode active material was produced, and discharge rate characteristics and charge / discharge cycle characteristics were evaluated. As a result, the initial discharge capacity of the lithium ion secondary battery according to Example 4 was 260 Ah / kg, the rate capacity maintenance rate was 88%, and the cycle capacity maintenance rate was 92%.

[Example 5]
A positive electrode active material for a lithium ion secondary battery according to Example 5 was produced by the following procedure. First, solid solution particles having an elemental composition of 0.2Li ₂ MnO ₃ —0.8LiNi _0.25 Mn _0.50 O _1.75 were produced in the same procedure as in Example 1.

Next, with respect to the obtained solid solution particles, the removal of lithium on the surface layer and the covering with lithium ion conductive glass were carried out in the same procedure as in Example 1 except that ammonium vanadate was used instead of aluminum nitrate. The positive electrode active material for a lithium ion secondary battery according to Example 5 was manufactured. Was subjected to elemental analysis and crystallinity analysis of coating covering the surface of the obtained positive electrode active material, the coating on the positive active material for a lithium ion secondary battery according to Example _{5, Li 2 O-V 2} O 5 It was confirmed to be a glass based.

  Next, in the same procedure as in Example 1, a lithium ion secondary battery according to Example 5 provided with a positive electrode containing the obtained positive electrode active material was manufactured, and discharge rate characteristics and charge / discharge cycle characteristics were evaluated. As a result, the initial discharge capacity of the lithium ion secondary battery according to Example 5 was 263 Ah / kg, the rate capacity maintenance rate was 82%, and the cycle capacity maintenance rate was 93%.

[Example 6]
A positive electrode active material for a lithium ion secondary battery according to Example 6 was produced by the following procedure. First, the raw material lithium carbonate, nickel carbonate, manganese carbonate, and cobalt carbonate are mixed so that the molar ratio of Li: Ni: Mn: Co is 1.25: 0.13: 0.53: 0.13. Solid solution particles were produced in the same procedure as in Example 1 except for the points used. When elemental analysis of the obtained solid solution particles was performed, Li: Ni: Mn: Co was 1.20: 0.13: 0.50: 0.13. Thus, elemental _composition, it was confirmed that the _{0.2Li 2 MnO 3 -0.8LiNi 0.16 Mn 0.38} Co 0.16 O 1.75.

Next, the obtained solid solution particles were subjected to removal of surface layer lithium and coating with lithium ion conductive glass in the same procedure as in Example 1 using ammonium fluoride in addition to aluminum nitrate. The positive electrode active material for lithium ion secondary batteries which concerns on 6 was manufactured. When elemental analysis and crystallinity analysis of the film covering the surface of the obtained positive electrode active material were performed, the film in the positive electrode active material for a lithium ion secondary battery according to Example 6 is LiF-AlF ₃ glass. It was confirmed.

  Next, in the same procedure as in Example 1, a lithium ion secondary battery according to Example 6 including a positive electrode containing the obtained positive electrode active material was manufactured, and discharge rate characteristics and charge / discharge cycle characteristics were evaluated. As a result, the initial discharge capacity of the lithium ion secondary battery according to Example 6 was 282 Ah / kg, the rate capacity maintenance rate was 85%, and the cycle capacity maintenance rate was 88%.

[Example 7]
A positive electrode active material for a lithium ion secondary battery according to Example 7 was produced by the following procedure. First, the raw material lithium carbonate, nickel carbonate, manganese carbonate, and titanium oxide are mixed so that Li: Ni: Mn: Ti has a molar concentration ratio of 1.25: 0.19: 0.60: 0.01. Solid solution particles were produced in the same procedure as in Example 1 except for the points used. Upon elemental analysis of the obtained solid solution particles, Li: Ni: Mn: Ti was 1.20: 0.19: 0.60: 0.01. Therefore, it was confirmed that the elemental composition was 0.2Li ₂ MnO ₃ —0.8LiNi _0.24 Mn _0.50 Ti _0.01 O _1.75 .

Next, with respect to the obtained solid solution particles, removal of lithium on the surface layer and covering with lithium ion conductive glass were performed in the same procedure as in Example 1 except that boric acid was used instead of aluminum nitrate. A positive electrode active material for a lithium ion secondary battery according to Example 7 was produced. Was subjected to elemental analysis and crystallinity analysis of coating covering the surface of the obtained positive electrode active material, the coating on the positive active material for a lithium ion secondary battery according to Example _{7, Li 2 O-B 2} O 3 It was confirmed to be a glass based.

  Next, in the same procedure as in Example 1, a lithium ion secondary battery according to Example 7 including a positive electrode containing the obtained positive electrode active material was manufactured, and discharge rate characteristics and charge / discharge cycle characteristics were evaluated. As a result, the initial discharge capacity of the lithium ion secondary battery according to Example 7 was 264 Ah / kg, the rate capacity maintenance rate was 86%, and the cycle capacity maintenance rate was 90%.

[Example 8]
A positive electrode active material for a lithium ion secondary battery according to Example 8 was produced by the following procedure. First, the raw material lithium carbonate, nickel carbonate, manganese carbonate, and zirconium oxide are mixed so that Li: Ni: Mn: Zr has a molar concentration ratio of 1.25: 0.19: 0.60: 0.01. Solid solution particles were produced in the same procedure as in Example 1 except for the points used. Upon elemental analysis of the obtained solid solution particles, Li: Ni: Mn: Zr was 1.20: 0.19: 0.60: 0.01. Thus, elemental _composition, it was confirmed that the _{0.2Li 2 MnO 3 -0.8LiNi 0.24 Mn 0.50} Zr 0.01 O 1.75.

Next, with respect to the obtained solid solution particles, removal of lithium on the surface layer and covering with lithium ion conductive glass were performed in the same procedure as in Example 1 except that boric acid was used instead of aluminum nitrate. A positive electrode active material for a lithium ion secondary battery according to Example 8 was produced. Was subjected to elemental analysis and crystallinity analysis of coating covering the surface of the obtained positive electrode active material, the coating on the positive active material for a lithium ion secondary battery according to Example _{8, Li 2 O-B 2} O 3 It was confirmed to be a glass based.

  Next, in the same procedure as in Example 1, a lithium ion secondary battery according to Example 8 provided with a positive electrode containing the obtained positive electrode active material was produced, and discharge rate characteristics and charge / discharge cycle characteristics were evaluated. As a result, the initial discharge capacity of the lithium ion secondary battery according to Example 8 was 260 Ah / kg, the rate capacity retention rate was 87%, and the cycle capacity retention rate was 92%.

[Example 9]
A positive electrode active material for a lithium ion secondary battery according to Example 9 was produced by the following procedure. First, the raw material lithium carbonate, nickel carbonate, manganese carbonate, and aluminum oxide are mixed so that Li: Ni: Mn: Al has a molar concentration ratio of 1.25: 0.19: 0.60: 0.01. Solid solution particles were produced in the same procedure as in Example 1 except for the points used. Upon elemental analysis of the obtained solid solution particles, Li: Ni: Mn: Al was 1.20: 0.19: 0.60: 0.01. Therefore, it was confirmed that the elemental composition was 0.2Li ₂ MnO ₃ —0.8LiNi _0.24 Mn _0.50 Al _0.01 O _1.75 .

Next, with respect to the obtained solid solution particles, removal of lithium on the surface layer and covering with lithium ion conductive glass were performed in the same procedure as in Example 1 except that boric acid was used instead of aluminum nitrate. A positive electrode active material for a lithium ion secondary battery according to Example 9 was produced. Was subjected to elemental analysis and crystallinity analysis of coating covering the surface of the obtained positive electrode active material, the coating on the positive active material for a lithium ion secondary battery according to Example _{9, Li 2 O-B 2} O 3 It was confirmed to be a glass based.

  Next, in the same procedure as in Example 1, a lithium ion secondary battery according to Example 9 including a positive electrode containing the obtained positive electrode active material was manufactured, and discharge rate characteristics and charge / discharge cycle characteristics were evaluated. As a result, the initial discharge capacity of the lithium ion secondary battery according to Example 9 was 264 Ah / kg, the rate capacity retention rate was 84%, and the cycle capacity retention rate was 89%.

[Example 10]
A positive electrode active material for a lithium ion secondary battery according to Example 10 was produced by the following procedure. First, the raw material lithium carbonate, nickel carbonate, manganese carbonate, and magnesium oxide are mixed so that Li: Ni: Mn: Mg has a molar concentration ratio of 1.25: 0.19: 0.60: 0.01. Solid solution particles were produced in the same procedure as in Example 1 except for the points used. Upon elemental analysis of the obtained solid solution particles, Li: Ni: Mn: Mg was 1.20: 0.19: 0.60: 0.01. Accordingly, it was confirmed that the elemental composition was 0.2Li ₂ MnO ₃ —0.8LiNi _0.24 Mn _0.50 Mg _0.01 O _1.75 .

Next, with respect to the obtained solid solution particles, removal of lithium on the surface layer and covering with lithium ion conductive glass were performed in the same procedure as in Example 1 except that boric acid was used instead of aluminum nitrate. A positive electrode active material for a lithium ion secondary battery according to Example 10 was produced. Was subjected to elemental analysis and crystallinity analysis of coating covering the surface of the obtained positive electrode active material, the coating on the positive active material for a lithium ion secondary battery according to Example _{10, Li 2 O-B 2} O 3 It was confirmed to be a glass based.

  Next, in the same procedure as in Example 1, a lithium ion secondary battery according to Example 10 including a positive electrode containing the obtained positive electrode active material was manufactured, and discharge rate characteristics and charge / discharge cycle characteristics were evaluated. As a result, the initial discharge capacity of the lithium ion secondary battery according to Example 10 was 258 Ah / kg, the rate capacity retention rate was 84%, and the cycle capacity retention rate was 92%.

[Example 11]
A positive electrode active material for a lithium ion secondary battery according to Example 11 was produced by the following procedure. First, the raw material lithium carbonate, nickel carbonate, manganese carbonate, and vanadium oxide are mixed so that Li: Ni: Mn: V is in a molar concentration ratio of 1.25: 0.19: 0.60: 0.01. Solid solution particles were produced in the same procedure as in Example 1 except for the points used. Upon elemental analysis of the obtained solid solution particles, Li: Ni: Mn: V was 1.20: 0.19: 0.60: 0.01. Thus, elemental _composition, it was confirmed that the _{0.2Li 2 MnO 3 -0.8LiNi 0.24 Mn 0.50} V 0.01 O 1.75.

Next, with respect to the obtained solid solution particles, removal of lithium on the surface layer and covering with lithium ion conductive glass were performed in the same procedure as in Example 1 except that boric acid was used instead of aluminum nitrate. And the positive electrode active material for lithium ion secondary batteries which concerns on Example 11 was manufactured. Was subjected to elemental analysis and crystallinity analysis of coating covering the surface of the obtained positive electrode active material, the coating on the positive active material for a lithium ion secondary battery according to Example _{11, Li 2 O-B 2} O 3 It was confirmed to be a glass based.

  Next, in the same procedure as in Example 1, a lithium ion secondary battery according to Example 11 including a positive electrode containing the obtained positive electrode active material was manufactured, and discharge rate characteristics and charge / discharge cycle characteristics were evaluated. As a result, the initial discharge capacity of the lithium ion secondary battery according to Example 11 was 266 Ah / kg, the rate capacity maintenance rate was 88%, and the cycle capacity maintenance rate was 93%.

[Comparative Example 1]
A positive electrode active material for a lithium ion secondary battery according to Comparative Example 1 was produced by the following procedure. In addition, the positive electrode active material for a lithium ion secondary battery according to Comparative Example 1 has solid solution particles that do not have a crystal structure in which lithium is deficient in the surface layer and are not covered with lithium ion conductive glass.

First, solid solution particles having an elemental composition of 0.2Li ₂ MnO ₃ —0.8LiNi _0.25 Mn _0.50 O _1.75 were produced in the same procedure as in Example 1. In addition, it was set as the positive electrode active material for lithium ion secondary batteries which concerns on the comparative example 1 about the obtained solid solution particle | grains, without performing the removal of lithium of surface layer, and coating | cover of lithium ion conductive glass.

  Next, in the same procedure as in Example 1, a lithium ion secondary battery according to Comparative Example 1 including a positive electrode containing the obtained positive electrode active material was manufactured, and discharge rate characteristics and charge / discharge cycle characteristics were evaluated. As a result, the initial discharge capacity of the lithium ion secondary battery according to Comparative Example 1 was 265 Ah / kg, the rate capacity maintenance rate was 78%, and the cycle capacity maintenance rate was 80%.

[Comparative Example 2]
A positive electrode active material for a lithium ion secondary battery according to Comparative Example 2 was produced by the following procedure. In addition, the positive electrode active material for lithium ion secondary batteries which concerns on the comparative example 2 consists of solid solution particle | grains coat | covered with the insulating film which does not have lithium ion conductivity.

First, solid solution particles having an elemental composition of 0.2Li ₂ MnO ₃ —0.8LiNi _0.25 Mn _0.50 O _1.75 were produced in the same procedure as in Example 1.

Next, the obtained solid solution particles and Al ₂ O ₃ were dry pulverized and mixed to adhere Al ₂ O ₃ to the surface of the solid solution particles, and the positive electrode active material for a lithium ion secondary battery according to Comparative Example 2 was obtained. Manufactured. When elemental analysis and crystallinity analysis of the film covering the surface of the obtained positive electrode active material were performed, the film in the positive electrode active material for a lithium ion secondary battery according to Comparative Example 2 was crystalline Al ₂ O ₃ . It was confirmed that there was.

  Next, in the same procedure as in Example 1, a lithium ion secondary battery according to Comparative Example 2 including a positive electrode containing the obtained positive electrode active material was manufactured, and discharge rate characteristics and charge / discharge cycle characteristics were evaluated. As a result, the initial discharge capacity of the lithium ion secondary battery according to Comparative Example 2 was 257 Ah / kg, the rate capacity maintenance rate was 70%, and the cycle capacity maintenance rate was 89%.

[Comparative Example 3]
A positive electrode active material for a lithium ion secondary battery according to Comparative Example 3 was produced by the following procedure. The positive electrode active material for a lithium ion secondary battery according to Comparative Example 3 is composed of solid solution particles coated with a crystalline film having lithium ion conductivity.

First, solid solution particles having an elemental composition of 0.2Li ₂ MnO ₃ —0.8LiNi _0.25 Mn _0.50 O _1.75 were produced in the same procedure as in Example 1.

Next, with respect to the obtained solid solution particles, except that the heat treatment was performed at 800 ° C., the surface lithium was removed and the lithium ion conductive glass was coated in the same procedure as in Example 1. A positive electrode active material for a lithium ion secondary battery according to Comparative Example 3 was produced. When elemental analysis and crystallinity analysis of the coating film covering the surface of the obtained positive electrode active material were performed, the coating film in the positive electrode active material for the lithium ion secondary battery according to Comparative Example 3 was crystalline Li ₂ O—Al It was confirmed to be ₂ O ₃ .

  Next, in the same procedure as in Example 1, a lithium ion secondary battery according to Comparative Example 3 including a positive electrode containing the obtained positive electrode active material was manufactured, and discharge rate characteristics and charge / discharge cycle characteristics were evaluated. As a result, the initial discharge capacity of the lithium ion secondary battery according to Comparative Example 3 was 262 Ah / kg, the rate capacity maintenance rate was 84%, and the cycle capacity maintenance rate was 83%.

Table 1 shows the initial discharge capacity (Ah / kg), rate capacity maintenance rate (%), cycle capacity maintenance rate (%) in the lithium ion secondary batteries according to Examples 1 to 11 and Comparative Examples 1 to 3 described above. Is shown together with the solid solution composition and the coating composition. In Table 1, the solid solution is represented by 0.2Li ₂ MnO ₃ —0.8LiNi _y1 Mn _y2 M ′ _y3 O _1.75 , and each element ratio is shown. M ′ represents any one of Ti, Zr, Al, Mg, and V, and “−” represents that they are not contained.

In addition, the ionic conductivity of the lithium ion conductive glass at room temperature is as follows: Li ₂ O—Al ₂ O ₃ system (Example 1): 5 × 10 ⁻⁹ S / cm, LiF—AlF ₃ system (Examples 2 and 6) ): 6 × 10 ⁻⁸ S / cm, Li ₂ O—B ₂ O ₃ system (Example _3, 7-11): 7 × 10 ⁻⁶ S / cm, Li ₂ O—SiO ₂ —P ₂ O ₅ System (Example 4): 2 × 10 ⁻⁵ S / cm, Li ₂ O—V ₂ O ₅ system (Example 5): 1 × 10 ⁻⁷ S / cm, Al ₂ O ₃ crystal (Comparative Example 1) : <1 × 10 ⁻¹⁰ S / cm, Li ₂ O—Al ₂ O ₃ crystal (Comparative Example 2): <1 × 10 ⁻¹⁰ S / cm.

  FIG. 2 is a diagram showing the relationship between the rate capacity maintenance rate and the cycle capacity maintenance rate of the lithium ion secondary batteries according to the example and the comparative example. As shown in FIG. 2, the lithium ion secondary batteries according to Examples 1 to 11 have high rate capacity maintenance rate and cycle capacity maintenance rate, and are excellent in charge / discharge cycle characteristics and discharge rate characteristics. have. On the other hand, in the lithium ion secondary batteries according to Comparative Examples 1 to 3, at least one of the rate capacity maintenance rate and the cycle capacity maintenance rate does not reach the example, and good charge / discharge cycle characteristics and discharge rate characteristics are obtained. It is not compatible.

  In particular, Comparative Example 1 having no coating showed a relatively high initial discharge capacity as shown in Table 1, but the rate capacity maintenance rate was 78% and the cycle capacity maintenance rate was as low as 80%. On the other hand, in Examples 1-5 which have the same solid solution composition as this comparative example 1, both the rate capacity retention ratio and the cycle capacity retention ratio were improved by the coating with lithium ion conductive glass. In addition, also about Examples 2-11 which have a film, the rate capacity | capacitance maintenance factor and the cycle capacity | capacitance maintenance factor showed the improvement tendency.

Further, Comparative Example 2 having a film made of crystalline Al ₂ O ₃ showed a relatively high cycle capacity maintenance rate, but the initial discharge capacity was 257 Ah / kg and the rate capacity maintenance rate was 70%, which were low. . It is considered that the initial discharge capacity and the rate capacity retention ratio of Comparative Example 2 were lowered by increasing the overvoltage (voltage drop) because the film made of crystalline Al ₂ O ₃ became a resistance component. On the other hand, in Example 1 having a solid solution composition similar to that of Comparative Example 1 and having a film made of amorphous Al ₂ O ₃ , both the initial discharge capacity and the rate capacity retention rate were improved. . Furthermore, also about Examples 2-11 which have an amorphous film similarly, the initial stage discharge capacity and the rate capacity | capacitance maintenance factor showed the improvement tendency. Therefore, the coating with amorphous lithium ion conductive glass is effective in improving the conductivity of lithium ions while maintaining the charge / discharge cycle characteristics by the coating of solid solution particles, and the discharge capacity, discharge rate characteristics and It was confirmed that it contributed to the improvement of charge / discharge cycle characteristics.

As shown in Table 1, Comparative Example 3 having a film made of crystalline Li ₂ O—Al ₂ O ₃ showed a relatively high initial discharge capacity and rate capacity maintenance ratio, but the cycle capacity maintenance ratio was 83. % Was low. Although the lithium ion conductivity has been improved by the coating with lithium ion conductive glass, crystallization occurs when volume expansion or contraction occurs due to a change in the crystal structure of the solid solution particles during the charge / discharge process. This is considered to be because the film made of Li ₂ O—Al ₂ O ₃ was unable to follow the volume variation, and damage such as cracking occurred in the film. Therefore, in order to effectively improve the charge / discharge cycle characteristics, it was confirmed that it is effective that the amorphous phase is present in a higher ratio than the crystalline phase in the coating made of lithium ion conductive glass. . Moreover, it was confirmed that the ion conductivity of the lithium ion conductive glass is preferably 1 × 10 ⁻¹⁰ S / cm or more. Thus, when the lithium ion conductivity is higher than that of the solid solution particles, it is possible to suppress a decrease in output even if the particles are covered with glass.

DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 2 Positive electrode for lithium ion secondary batteries 3 Negative electrode for lithium ion secondary batteries 4 Separator 5 Battery can 6 Positive electrode lead piece 7 Negative electrode lead piece 8 Sealing lid 9 Sealing material 10 Insulating plate

Claims (7)

The following composition formula (1),
xLi ₂ MnO _3- (1-x) LiM _y O _{{(2-3x) / (1-x)}} (1)
[Wherein x is a number satisfying 0 <x ≦ 0.6, y is a number satisfying 0.7 ≦ y ≦ 1.0, and M is Ni, Co, Mn, Ti, Zr , At least one element selected from the group consisting of Al, Mg and V. ]
Solid solution particles represented by
Lithium ion conductive glass covering at least a part of the surface of the solid solution particles,
The lithium ion conductive glass is Li ₂ O—B ₂ O ₃ , Li ₂ O—Al ₂ O ₃ , Li ₂ O—SiO ₄ , Li ₂ O—P ₂ O ₅ , Li ₂ O—V ₂ O _5. , LiF—BF ₃ , LiF—AlF ₃ , LiF—VF ₃ , and the lithium ion conductivity of the lithium ion conductive glass is 1 × 10 ⁻¹⁰ S at room temperature. / Cm or more, and
The positive electrode active material for a lithium ion secondary battery, wherein the solid solution particles have a lithium concentration in a surface layer of 80% by mass or less of a lithium concentration in an inner layer. 2. The lithium ion secondary according to claim 1 , wherein a content of the lithium ion conductive glass is 0.5% by mass or more and 5.0% by mass or less with respect to a total mass of the positive electrode active material. Positive electrode active material for batteries. The lithium concentration in the surface layer of the solid solution particle is 8% by mass or less with respect to the whole solid solution particle, and the lithium concentration in the inner layer of the solid solution particle is 9% by mass or more and 11% by mass with respect to the whole solid solution particle. Is
The positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, characterized in that: The solid solution particles have a surface layer mixed with the lithium ion conductive glass.
The positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 3, wherein A positive electrode for a lithium ion secondary battery comprising the positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 4 . A lithium ion secondary battery comprising the positive electrode for a lithium ion secondary battery according to claim 5 . The following composition formula (1),
xLi ₂ MnO _3- (1-x) LiM _y O _{{(2-3x) / (1-x)}} (1)
[Wherein x is a number satisfying 0 <x ≦ 0.6, y is a number satisfying 0.7 ≦ y ≦ 1.0, and M is Ni, Co, Mn, Ti, Zr , At least one element selected from the group consisting of Al, Mg and V. ]
In represented by Rutotomoni the solid solution particles is immersed in a pH7 to 9 of solvent desorbed lithium surface layer of the solid solution particles, the surface of the solid-solution particles, B, Al, Si, from the group consisting of P and V a step of depositing a precursor of the lithium ion conductive glass having a composition comprising at least one element selected,
The solid solution particles at 200 ° C. or higher 600 ° C. or less and subjected to 20 hours or less heat for 1 hour or more, the solid solution _{particles, Li 2 O-B 2 O} 3, Li 2 O-Al 2 O 3, Li 2 O _{-SiO 4, Li 2 O-P} 2 O 5, Li 2 O-V 2 O 5, LiF-BF 3, LiF-AlF 3, lithium ion is at least one selected from the group consisting of LiF-VF ₃ a step of coating a conductive glass,
The manufacturing method of the positive electrode active material for lithium ion secondary batteries characterized by including this.

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