Occlusion and release of lithium ion are likely to one-dimensionally occur in the b-axis direction of a crystal in a lithium-containing composite oxide having an olivine structure. Thus, a positive electrode in which the b-axes of lithium-containing composite oxide single crystals are oriented vertically to a surface of a positive electrode current collector is provided. The lithium-containing composite oxide particles are mixed with graphene oxide and then pressure is applied thereto, whereby the rectangular parallelepiped or substantially rectangular parallelepiped particles are likely to slip. In addition, in the case where the rectangular parallelepiped or substantially rectangular parallelepiped particles whose length in the b-axis direction is shorter than those in the a-axis direction and the c-axis direction are used, when pressure is applied in one direction, the b-axes can be oriented in the one direction.

Occlusion and release of lithium ion are likely to one-dimensionally occur in the b-axis direction of a crystal in a lithium-containing composite oxide having an olivine structure. Thus, a positive electrode in which the b-axes of lithium-containing composite oxide single crystals are oriented vertically to a surface of a positive electrode current collector is provided. The lithium-containing composite oxide particles are mixed with graphene oxide and then pressure is applied thereto, whereby the rectangular parallelepiped or substantially rectangular parallelepiped particles are likely to slip. In addition, in the case where the rectangular parallelepiped or substantially rectangular parallelepiped particles whose length in the b-axis direction is shorter than those in the a-axis direction and the c-axis direction are used, when pressure is applied in one direction, the b-axes can be oriented in the one direction.

Electrophoresis of an ethanol dispersion of an octacalcium phosphate (OCP) crystal is performed to form a multilayer deposited film of the OCP crystal on a cathode (gold sensor) that is an electrode made of a conductive material such as gold. The multilayer deposited film is subjected to ultrasonic cleaning to form a single-layer deposited film of the OCP crystal on the cathode. The OCP crystalline film formed on the gold sensor surface is a stable crystalline film having a layered structure in which a hydrated layer and an apatite layer are regularly repeated, where a specific crystal plane is oriented in a specific direction with the hydrated layer being an uppermost layer.

Electrophoresis of an ethanol dispersion of an octacalcium phosphate (OCP) crystal is performed to form a multilayer deposited film of the OCP crystal on a cathode (gold sensor) that is an electrode made of a conductive material such as gold. The multilayer deposited film is subjected to ultrasonic cleaning to form a single-layer deposited film of the OCP crystal on the cathode. The OCP crystalline film formed on the gold sensor surface is a stable crystalline film having a layered structure in which a hydrated layer and an apatite layer are regularly repeated, where a specific crystal plane is oriented in a specific direction with the hydrated layer being an uppermost layer.

Electrophoresis of an ethanol dispersion of an octacalcium phosphate (OCP) crystal is performed to form a multilayer deposited film of the OCP crystal on a cathode (gold sensor) that is an electrode made of a conductive material such as gold. The multilayer deposited film is subjected to ultrasonic cleaning to form a single-layer deposited film of the OCP crystal on the cathode. The OCP crystalline film formed on the gold sensor surface is a stable crystalline film having a layered structure in which a hydrated layer and an apatite layer are regularly repeated, where a specific crystal plane is oriented in a specific direction with the hydrated layer being an uppermost layer.

Electrophoresis of an ethanol dispersion of an octacalcium phosphate (OCP) crystal is performed to form a multilayer deposited film of the OCP crystal on a cathode (gold sensor) that is an electrode made of a conductive material such as gold. The multilayer deposited film is subjected to ultrasonic cleaning to form a single-layer deposited film of the OCP crystal on the cathode. The OCP crystalline film formed on the gold sensor surface is a stable crystalline film having a layered structure in which a hydrated layer and an apatite layer are regularly repeated, where a specific crystal plane is oriented in a specific direction with the hydrated layer being an uppermost layer.

A cathode electrode includes a cathode current collector and a cathode active material layer arranged on at least one side of the cathode current collector. The cathode active material layer includes cathode active material comprising a plurality of cores each including a single crystal particle and a high entropy layer encapsulating each of the single crystal particles of the plurality of cores. The high entropy layer includes at least 5 different transition metal elements.

A cathode electrode includes a cathode current collector and a cathode active material layer arranged on at least one side of the cathode current collector. The cathode active material layer includes cathode active material comprising a plurality of cores each including a single crystal particle and a high entropy layer encapsulating each of the single crystal particles of the plurality of cores. The high entropy layer includes at least 5 different transition metal elements.

A crystal is of a non-centrosymmetric structure and belongs to the 43 m point group of the cubic crystal system. M denotes an alkaline earth metal, which can be Ba, Ca, or Sr, and RE denotes a rare earth element, which can be Y, La, Gd, or Yb. The growth method of the M.sub.3RE(PO.sub.4).sub.3 crystal comprises steps as follows: (1) polycrystalline material synthesis: MCO.sub.3, RE.sub.2O.sub.3, and phosphorous compound are used as raw materials and blended according to the stoichiometric proportions; then, the phosphorous compound is further added to be excessive; the raw materials are sintered twice to obtain the M.sub.3RE(PO.sub.4).sub.3 polycrystalline material; (2) polycrystalline material melting; (3) Czochralski crystal growth. The M.sub.3RE(PO.sub.4).sub.3 crystal prepared by the invention is a high-quality single crystal.

A crystal is of a non-centrosymmetric structure and belongs to the 43 m point group of the cubic crystal system. M denotes an alkaline earth metal, which can be Ba, Ca, or Sr, and RE denotes a rare earth element, which can be Y, La, Gd, or Yb. The growth method of the M.sub.3RE(PO.sub.4).sub.3 crystal comprises steps as follows: (1) polycrystalline material synthesis: MCO.sub.3, RE.sub.2O.sub.3, and phosphorous compound are used as raw materials and blended according to the stoichiometric proportions; then, the phosphorous compound is further added to be excessive; the raw materials are sintered twice to obtain the M.sub.3RE(PO.sub.4).sub.3 polycrystalline material; (2) polycrystalline material melting; (3) Czochralski crystal growth. The M.sub.3RE(PO.sub.4).sub.3 crystal prepared by the invention is a high-quality single crystal.