Ni-Based Sodium-Ion Cathode Composition for Higher Discharge Capacity
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Solution Overview
Problem
Ni-based positive electrode active materials for sodium ion secondary batteries face issues with low discharge capacity due to oxygen desorption during oxidation reactions and difficulty in forming a Na ion-conducting path in all-solid-state batteries.
Innovation Solution
A positive electrode active material with a specific composition of Nax(Ni1-aMa)yP2Oz, where M is a transition metal element, and pyrophosphoric or metaphosphoric acid forms the crystal structure, reducing oxygen desorption and enhancing discharge capacity by allowing reduction reactions and forming a Na ion-conducting path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If Ni-based positive electrode active materials are used to achieve high operating voltage (5V), then energy density is improved, but oxygen desorption occurs during oxidation reaction causing low discharge capacity
Solution Approach 1:
The patent changes the chemical composition parameters by introducing M metal elements (Fe, Cr, Mn, Co) to replace部分Ni, and adjusts the stoichiometric ratios (x, y, a, z parameters) to optimize the crystal structure. This composition optimization suppresses oxygen desorption while maintaining high operating voltage, resolving the contradiction between energy density and discharge capacity
Solution Approach 2:
The patent creates composite materials by combining Ni with M metals (Fe, Cr, Mn, Co) in specific ratios within the Nax(Ni1-aMa)yP2Oz structure. This composite approach leverages the high voltage characteristics of Ni while the M metals suppress oxygen desorption, achieving both high energy density and reliable discharge capacity
2Use of energy by moving object
If Ni-based positive electrode active materials are applied to all-solid-state batteries, then high voltage operation is achieved, but Na ion-conducting path formation is difficult causing low discharge capacity
Solution Approach 1:
The patent optimizes the compositional parameters (x, y, a, z) to control the crystal structure and surface properties of the material. By adjusting these parameters, the material develops enhanced Na ion conductivity at the solid electrolyte interface, enabling efficient ion transport while maintaining high operating voltage in all-solid-state configurations
Solution Approach 2:
The patent creates local structural modifications at the interface between the active material and solid electrolyte. The compositional optimization produces regions with enhanced Na ion conductivity specifically at the contact interfaces, facilitating ion transport without compromising the bulk material's high voltage characteristics
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 results in a Ni-based positive electrode active material with improved discharge capacity and energy density, suitable for sodium ion secondary batteries, especially in all-solid-state configurations.
Implementation Method 1
oxygen desorption from the active material is less likely to progress in the oxidation reaction of Ni2+→Ni3+ during the first charge
Implementation Method 2
the reduction reaction of Ni3+→Ni2+ is likely to occur during discharge
Implementation Method 3
a Na ion-conducting path is likely to be formed between the active material and the solid electrolyte
Data Source
AI summary
Provided is a Ni-based positive electrode active material for a sodium ion secondary battery having an excellent discharge capacity. A positive electrode active material for a sodium ion secondary battery, the positive electrode active material being composed of crystals represented by a general formula Nax (Ni1-aMa)yP2Oz (where M represents at least one transition metal element selected from the group consisting of Fe, Cr, Mn, and Co and the following are satisfied: 0.6≤x≤4, 0.3≤y≤2.7, 0≤a≤0.9, and 6≤z<7.5).