JP-7855674-B2 - Method for manufacturing lithium metal phosphate, lithium metal phosphate, positive electrode material for lithium-ion secondary battery, positive electrode of lithium-ion secondary battery, and lithium-ion secondary battery

Inventors

• 伊藤 猛

Assignees

• 株式会社オキサイド

Dates

Publication Date

20260508

Application Date

20220222

Claims (7)

1. A mixing step to obtain a mixture of a solute raw material containing a compound containing the element Li; a compound containing the metal element M (where M represents at least one selected from the group consisting of Fe, Co, Ni, and Mn); at least one of a compound containing the element B and a compound containing the element Si; and a compound containing the element P containing a pyrophosphate ion, and a flux, A melting step to obtain a molten product of the mixture, A cooling step in which the molten material is cooled to obtain precipitates, A method for producing lithium metal phosphate having an olivine-type crystal structure.
2. A mixing step to obtain a mixture of a solute raw material containing a compound containing the element Li; a compound containing the metal element M (where M represents at least one selected from the group consisting of Fe, Co, Ni, and Mn); a compound containing the element B containing a tetraborate ion; and a compound containing the element P containing a phosphate ion, and a flux, A melting step to obtain a molten product of the mixture, A cooling step in which the molten material is cooled to obtain precipitates, A method for producing lithium metal phosphate having an olivine-type crystal structure.
3. The manufacturing method according to claim 1, wherein the compound containing element B contains a tetraborate ion.
4. The manufacturing method according to claim 2, wherein the solute raw material further comprises a compound containing the element Si.
5. The manufacturing method according to any one of claims 1 to 4, wherein the melting temperature in the melting step is 600°C or higher.
6. The manufacturing method according to any one of claims 1 to 5, wherein the ratio of element B to element P in the mixture is 1/99 to 99/1.
7. The manufacturing method according to claim 1 or 4, wherein the ratio of Si element to P element in the mixture is 1/99 to 99/1.

Description

The present invention relates to a method for producing lithium metal phosphate, lithium metal phosphate, a positive electrode material for a lithium-ion secondary battery, a positive electrode for a lithium-ion secondary battery, and a lithium-ion secondary battery. LiCoO₂ (LCO) is known as a positive electrode material for lithium-ion secondary batteries. LCO has a high energy density (electromotive force × capacitance), but it has problems with stability and lifespan. As a more stable alternative to LCO, olivine-type lithium metal phosphate, represented by the general formula LiFePO₄, has been put into practical use. On the other hand, Li₂FeSiO₄ , which is similar to lithium metal phosphate, is expected to have twice the capacitance because it has two Li atoms in its molecule, but it cannot be used as a positive electrode material because it is an insulator. Incidentally, Fe, Co, Ni, and Mn are known as transition metal elements (hereinafter referred to as "M" or "M element") that have a valence of +2 in stoichiometric composition and whose valence can change to +3 in order to maintain charge neutrality upon the elimination of Li (for example, Patent Document 1). However, as described in Patent Document 1, the electrical conductivity of olivine-type lithium metal phosphates is generally low. For this reason, olivine-type lithium metal phosphates other than LiFePO4 (for example, LiCoPO4 and LiMnPO4 ) are not widely used (Patent Document 2). Therefore, attempts have been made to improve the conductivity of this material by substituting some of the pentavalent element P with trivalent elements such as B and Al, and compensating for the charge by adding Li or creating oxygen vacancies. However, increasing the ratio of B to P creates different phases such as spinel ( M3O4 ), phonsenite ( M3BO5 ), metal borate salt { M3 ( BO3 ) 2 }, lithium metal borate salt, and lithicone Li3-2αMα (P,B) O4 ( a Li3PO4 structure in which some of the Li is substituted with a divalent metal element) , which degrades electrical conductivity. Furthermore, in the powder calcination of Li1 +xFe (P1 -x , Bx ) O4 , different phases are mixed into the olivine phase, degrading electrical conductivity (Patent Document 3). This phenomenon also occurs in the powder calcination of Li 1 + x M(P 1 - x , B x )O 4 , and the amount of B substitution is severely limited (Patent Document 4). In the above compositional formula, M represents a transition metal. The following are some undesirable side reactions that reduce crystal purity when producing olivine-type lithium metal phosphates, in order to increase electrical conductivity and capacitance. In each composition formula, M represents a transition metal. 3Li₂O + 3MCl₂ + O → M₃O₄ + 6LiCl₂ (Formation of spinel) 3/ 2Li2O +3MCl2+ Li3BO3 + 1 / 2(O)→ M3BO5 + 6LiCl (Formation of phonsenite) Li 3 PO 4 +xMCl 2 →Li 3-2x MxPO 4+2x LiCl (generation of LISICON) Li₃BO₃ + MCl₂ → LiMBO₃ + 2LiCl₂ ( Formation of lithium metal borate salt ) 2Li₃BO₃ + 3MCl₂ → M₃ ( BO₃ ) ₂ + 6LiCl₂ (Formation of metal borate salt) Japanese Patent Publication No. 2008-184346Japanese Patent Publication No. 2008-130525Japanese Patent Publication No. 2004-178835Japanese Patent Publication No. 2010-123339 Uehara: Manufacturing and evaluation of raw material powders for electrodes of secondary batteries, "Crushing" No. 56 (2013) pp. 18-24 This is the powder X-ray diffraction chart for Example 1.This is the powder X-ray diffraction chart for Example 2.This is the powder X-ray diffraction chart for Example 3.This is the powder X-ray diffraction chart for Example 4.This is the powder X-ray diffraction chart for Example 5.This is the powder X-ray diffraction chart for Example 6.This is the powder X-ray diffraction chart for Example 7.This is the powder X-ray diffraction chart for Example 8.This is the powder X-ray diffraction chart for Comparative Example 1.This is the powder X-ray diffraction chart for Comparative Example 2.This graph shows the results of the electrical conductivity evaluation of lithium metal phosphate in Example 1.This graph shows the results of the electrical conductivity evaluation of lithium metal phosphate salts in Example 2.This graph shows the results of the electrical conductivity evaluation of lithium metal phosphate in Example 3.This graph shows the results of the electrical conductivity evaluation of lithium metal phosphate in Example 4.This graph shows the results of the electrical conductivity evaluation of lithium metal phosphate in Example 5.This graph shows the results of the electrical conductivity evaluation of lithium metal phosphate in Example 6.This graph shows the results of the electrical conductivity evaluation of lithium metal phosphate in Example 7.This graph shows the results of the electrical conductivity evaluation of lithium metal phosphate in Example 8.This graph shows the results of the electrical conductivity evaluation of lithium metal phosphate in Comparative Example 1. Several embodimen