LiNiO2 Positive Electrode Material for Li-Ion Batteries
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Lithium ion secondary batteries face challenges in achieving high energy density and cyclability due to cation mixing and excessive lithium hydroxide residue on the positive electrode, leading to increased resistance and capacity loss.
Innovation Solution
A positive electrode active material with a layered structure, represented by the formula Li1+aM1O2+α, where Ni content exceeds 70 atom%, and site occupancy of transition metals is less than 2%, combined with a manufacturing method involving pulverizing, mixing, heat treatment, and firing at specific temperatures to minimize residual lithium hydroxide content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the proportion of Ni in the metal element or elements is increased to exceed 70 atom%, then the reversible capacity increases to exceed 180 Ah/kg and energy density is improved, but cation mixing occurs where Ni exchanges with Li sites, reducing capacity and increasing resistance
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the central part contains high Ni content (exceeding 70 atom%) for high capacity, while the peripheral part contains lower Ni content (70 atom% or less) to suppress cation mixing. This spatial differentiation of composition allows simultaneous achievement of high reversible capacity in the core and cycle stability in the shell region.
Solution Approach 2:
The patent changes the compositional parameter of Ni content across different regions of the particle. The central part has Ni content exceeding 70 atom% while the peripheral part has Ni content of 70 atom% or less. This parameter gradient enables optimization of both capacity and cycle stability by controlling cation mixing through compositional variation.
2Reliability
If a Li raw material is added in an excessive amount exceeding stoichiometric ratio to suppress cation mixing, then cation mixing is suppressed, but the excessive Li cannot sufficiently react in the firing step, resulting in increased residual Li compound on the surface
Solution Approach 1:
The patent extracts or removes the harmful residual Li compound from the system by controlling the firing process to reduce lithium hydroxide content to 1 mass% or less on the surface. This is achieved through optimized firing conditions that allow sufficient reaction of excessive Li while maintaining suppression of cation mixing, thereby eliminating the harmful effect of residual lithium hydroxide.
Solution Approach 2:
The patent changes the firing temperature parameter to optimize the reaction of excessive Li. By controlling the firing temperature within a specific range, the patent enables sufficient reaction of Li raw material to incorporate into the crystal structure while preventing formation of excessive residual Li compound, thus resolving the contradiction between suppressing cation mixing and reducing residual lithium hydroxide.
3Quantity of substance
If lithium hydroxide is used as Li raw material to achieve high capacity, then high capacity is obtained, but the proportion of lithium hydroxide left on the surface increases, causing water production and HF formation that increase resistance and reduce capacity
Solution Approach 1:
The patent converts the harmful effect of lithium hydroxide residue into a beneficial outcome by carefully controlling the firing process. The excessive Li from lithium hydroxide is transformed into incorporated Li in the crystal structure through optimized firing, while the harmful residual lithium hydroxide is reduced to 1 mass% or less. This converts the potential harm of water and HF production into the benefit of high capacity with suppressed side reactions.
Solution Approach 2:
The patent changes the firing temperature and time parameters to optimize the decomposition and reaction of lithium hydroxide. By controlling these parameters, the patent enables complete reaction of lithium hydroxide to incorporate Li into the crystal structure while minimizing residual lithium hydroxide, thus eliminating water and HF production while maintaining high capacity.
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 solution achieves a high energy density and cyclability by reducing cation mixing and residual lithium hydroxide, thereby suppressing resistance increase and capacity loss during charge-discharge cycles.
Implementation Method 1
a pulverizing and mixing step of pulverizing and mixing a raw material containing a metal element other than Li with a lithium raw material
Implementation Method 2
a heat treatment step of heat-treating, at 650° C. or lower, a pulverized and mixed powder obtained through the pulverizing and mixing step
Implementation Method 3
a firing step of firing, at 740° C. or higher and lower than 850° C., the heat-treated pulverized and mixed powder
Implementation Method 4
it has been considered that it is essential to use lithium hydroxide as a raw material in order to obtain a high capacity
Data Source
AI summary
A compound having a layered structure that is used for a positive electrode active material for a lithium ion secondary battery achieves both a high energy density and a high cyclability. The positive electrode active material for a lithium ion secondary battery contains a compound having a layered structure belonging to a space group R-3m, in which the compound having a layered structure is represented by a compositional formula: Li1+aM1O2+α wherein M1 represents a metal element or metal elements other than Li, and contains at least Ni, −0.03≤a≤0.10, and −0.1<α<0.1, a proportion of Ni in M1 is larger than 70 atom %, and a site occupancy of a transition metal or transition metals at a 3a site obtained by structural analysis by a Rietveld method is less than 2%, and a content of residual lithium hydroxide in the positive electrode active material is 1 mass % or less.