Lithium Positive Electrode Surface Treatment for Cycle Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Lithium secondary cells with lithium metal composite oxides having a layer crystal structure face issues with chemical reactions at high temperatures, leading to decreased capacity and cycle ability when used as positive electrode active materials, and surface coatings to mitigate these issues often worsen rate capability and output characteristics.
Innovation Solution
A positive electrode active material with a surface portion containing Al, Ti, or Zr on lithium metal composite oxide particles, where the concentration ratio of surface elements to constituent elements is between 0 and 0.8, and the surface lithium impurity is less than 0.40%, enhancing charge-discharge cycle ability and output characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the particle surface of lithium metal composite oxide is coated with metal or metal oxide to suppress chemical reaction with electrolyte solution at high temperature, then charge-discharge cycle ability is improved, but rate capability and output characteristics worsen
Solution Approach 1:
The invention applies surface treatment only to specific regions of the lithium metal composite oxide particles, creating a localized protective layer with Al, Ti, or Zr elements. This local quality approach protects the surface from chemical reactions with the electrolyte solution while preserving the bulk material's electrochemical performance, thereby improving cycle ability without significantly degrading rate capability and output characteristics.
Solution Approach 2:
The invention optimizes the concentration ratio parameter (CA/CM) of surface elements to constituent elements within a specific range (0.01 to 0.80). By controlling this parameter, the protective effect against chemical reactions is achieved while minimizing the impact on lithium ion diffusion and electrochemical activity, thus resolving the contradiction between cycle stability and rate performance.
2Reliability
If surface coating is applied to prevent chemical reaction with electrolyte solution, then capacity retention is improved, but surface lithium impurity increases
Solution Approach 1:
The invention introduces Al, Ti, or Zr elements as intermediary substances on the particle surface. These intermediary elements form a protective barrier between the lithium metal composite oxide and the electrolyte solution, preventing direct chemical reactions that would otherwise lead to capacity degradation and lithium impurity formation. The intermediary layer protects the underlying lithium-containing material from degradation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed active material effectively suppresses reactions with the electrolyte solution, improving charge-discharge cycle ability and maintaining or exceeding the rate capability and output characteristics of conventionally surface-treated materials, making it suitable for vehicular applications.
Implementation Method 1
the particle surface of a lithium metal composite oxide having a layer crystal structure is coated with a metal or a metal oxide
Implementation Method 2
the lithium metal composite oxide chemically reacts with an electrolyte solution and changes occur including adhesion of a reaction product of the reaction on a surface of the positive electrode active material
Implementation Method 3
lithium dissolves out as ions from a positive electrode and migrates to a negative electrode and is intercalated therein
Implementation Method 4
lithium dissolves out as ions from a positive electrode and migrates to a negative electrode and is intercalated therein
Implementation Method 5
lithium ions reversely return from the negative electrode to the positive electrode
Implementation Method 6
in the discharge time, lithium ions reversely return from the negative electrode to the positive electrode, and their high energy density is known to be due to potentials of their positive electrode materials
Implementation Method 7
subjecting the dispersion to a heat treatment at 600° C.
Data Source
AI summary
The present invention relates to a positive electrode active material including a lithium metal composite oxide having a layer crystal structure, and provides a novel positive electrode active material for a lithium secondary cell, which can suppress the reaction with an electrolyte solution and can raise the charge-discharge cycle ability of the cell, and can make good the output characteristics of the cell. There is proposed a positive electrode active material for a lithium secondary cell, including an active particle having a surface portion where one or a combination of two or more (these are referred to as “surface element A”) of the group consisting of Al, Ti and Zr is present, on a surface of a particle including a lithium metal composite oxide having a layer crystal structure and represented by the general formula: Li1+xM1−xO2 (wherein M is one or a combination of two or more (these are referred to as “constituent element M”) of the group consisting of Mn, Co, Ni, transition elements of from the third group elements to the 11th group elements of the periodic table, and typical elements up to the third period of the periodic table), wherein the ratio (CA/CM) of a concentration CA of the surface element A to a concentration CM of the constituent element M is higher than 0 and lower than 0.8, as measured by XPS; the amount of surface lithium impurity is smaller than 0.40% by weight; and in an X-ray diffraction pattern measured by XRD, the ratio (003)/(104) of an integral intensity of the peak originated from the (003) plane to an integral intensity of the peak originated from the (104) plane is higher than 1.15.