Lithium Phosphate Cathode Suppressing Transition Metal Elution
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Solution Overview
Problem
Lithium-ion secondary batteries face challenges in maintaining long-term cycle characteristics due to the degradation of cathode materials, leading to reduced performance and safety concerns.
Innovation Solution
A cathode material comprising lithium phosphate salt particles with an oxidation-reduction potential at 4.2 V or lower and inorganic phosphate salt particles, which suppress the elution of transition metal ions, enhancing long-term cycle stability by forming a composite with carbonaceous film-coated central particles, thereby improving charge and discharge capacity retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional cathode materials are used to achieve high capacity and voltage, then energy density is improved, but long-term cycle characteristics and stability deteriorate due to transition metal elution
Solution Approach 1:
An inorganic phosphate salt layer is introduced as an intermediary between the cathode active material particles and the electrolyte. This layer acts as a protective barrier that prevents direct contact between the transition metal-containing cathode material and the electrolyte, thereby suppressing transition metal elution while allowing lithium ion transport. The phosphate salt layer serves as a mediator that maintains both high capacity and excellent cycle stability.
Solution Approach 2:
The invention creates a composite structure consisting of cathode active material particles coated with inorganic phosphate salt. This composite material combines the high capacity properties of transition metal phosphates (such as LiFePO4, LiCoPO4, LiNi0.8Co0.1Mn0.1O2) with the protective and stabilizing properties of the phosphate salt coating, achieving both high energy density and excellent long-term cycle characteristics.
2Power
If cathode materials with high oxidation-reduction potential are used, then voltage and energy are improved, but transition metal elution increases leading to reduced reliability
Solution Approach 1:
The inorganic phosphate salt layer serves as an intermediary barrier that physically separates the high-potential cathode active material from the electrolyte, preventing transition metal elution while maintaining efficient lithium ion transport. This allows the use of high-voltage materials without suffering from the harmful elution effects.
Solution Approach 2:
A thin inorganic phosphate salt film is formed on the surface of the cathode active material particles. This film is thin enough to allow efficient lithium ion diffusion but thick enough to provide effective protection against transition metal elution, creating a flexible protective barrier that maintains electrical performance while preventing harmful reactions.
3Quantity of substance
If conventional cathode materials are used, then initial discharge capacity is achieved, but irreversible capacity loss accumulates over cycles reducing long-term performance
Solution Approach 1:
The phosphate salt layer acts as a mediator that reduces irreversible capacity loss by preventing direct parasitic reactions between the cathode material and electrolyte. It facilitates reversible lithium ion insertion/extraction while blocking pathways for irreversible side reactions, thereby minimizing capacity fade over cycling.
Solution Approach 2:
The inorganic phosphate salt coating acts as a sacrificial protective layer that can undergo minor decomposition or structural changes to protect the underlying cathode active material. This disposable-like protective layer absorbs the degradation stress, preserving the long-term performance of the expensive cathode material beneath.
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 cathode material achieves excellent long-term cycle characteristics with reduced irreversible capacity loss and improved safety, maintaining high discharge capacity over 500 cycles while minimizing transition metal elution, thus enhancing the reliability and stability of lithium-ion secondary batteries.
Implementation Method 1
inorganic phosphate salt particles elute from the cathode, react with transition metal ions, and suppresses the transition metal ions reaching the anode
Implementation Method 2
cathode active material particles made of a lithium phosphate salt having an oxidation-reduction potential at 4.2 V (Li/Li+) or lower and inorganic phosphate salt particles in formed
Implementation Method 3
cathode active materials include a lithium transition metallic oxide and an oxoacid salt, a peak detected in the TEM-EDX analysis of cross sections of cathode active materials
Data Source
AI summary
A cathode material for a lithium-ion secondary battery including cathode active material particles which have central particles made of LixAyMzPO4 (0≤x≤1.1, 0.8≤y≤1.1, and 0≤z≤0.2; here, A represents at least one element selected from the group consisting of Fe, Mn, Co, and Ni, and M represents at least one element selected from the group consisting of Mg, Ca, Co, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, and rare earth elements) and a carbonaceous film that coats surfaces of the central particles; and inorganic phosphate salt particles.