Sodium Layered Oxide Cathode for High Cyclability
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Solution Overview
Problem
There is a need for composite metal oxides in sodium batteries that can deliver excellent and durable electrochemical properties, particularly high cyclability, which existing materials have not adequately addressed.
Innovation Solution
A mixed oxide composition of sodium, manganese, nickel, and cobalt with a P2 crystal structure is developed, synthesized using a co-precipitation method, which maintains structural stability and high ion diffusivity, preventing phase conversion and enhancing cyclability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing sodium layered oxide materials are used, then high capacity and ion diffusivity are achieved, but cyclability and structural stability deteriorate
Solution Approach 1:
The patent applies composite materials by combining three transition metals (Mn, Ni, Co) in a layered oxide structure with formula Na_x[MnNiCo]O2. This composite approach creates a material that leverages the complementary properties of each metal: Mn provides structural stability, Ni enhances capacity, and Co improves ion diffusivity. The resulting composite material achieves high cyclability (96% retention after 10 cycles) and maintains structural stability during charge-discharge cycles, resolving the contradiction between reliability and compositional stability.
Solution Approach 2:
The patent applies local quality by creating a non-uniform distribution of transition metals within the layered oxide structure. The formula Na_x[MnNiCo]O2 indicates a specific arrangement where different metals occupy different sites in the crystal lattice, with each metal contributing its unique properties to specific regions. This localized differentiation allows the material to simultaneously achieve high capacity (from Ni-rich regions), fast ion diffusivity (from Co-rich regions), and structural stability (from Mn-rich regions), thereby improving cyclability while maintaining overall structural integrity.
2Use of energy by moving object
If high voltage operation is implemented, then energy density is improved, but phase conversion and performance degradation occur
Solution Approach 1:
The patent applies beforehand cushioning by incorporating Mn and Co into the layered oxide structure prior to battery operation. These metals act as protective elements that preemptively stabilize the crystal structure against phase conversions that would normally occur at high voltages. The Mn4+ ions in particular provide structural reinforcement that prevents Jahn-Teller distortions and phase transitions, cushioning the material against degradation before it can occur during high-voltage charge-discharge cycles. This allows the battery to operate at high voltages (4.3V) with maintained phase stability and performance.
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 mixed oxide composition exhibits improved cyclability and structural stability, maintaining high performance even at high voltages, significantly increasing cycle retention and durability compared to materials with only one or two transition metals.
Implementation Method 1
synthesized using a co-precipitation method
Data Source
Figure 1
Figure 2
Figure 3a~3b
AI summary
The present invention relates to a mixed oxide of sodium and transition metals having the formula (1) : Nax[MnaNibCOc]02+y, wherein: 0.5≤ x ≤0.9, -0.1≤ y ≤0.1, a + b + c = 1, 4a + 2b + 3c = 4 - x + 2y, 0 < c ≤ 0.5 The present invention further relates to a process for producing such a mixed oxide, a positive electrode comprising such a mixed oxide and a sodium ion secondary battery comprising such a positive electrode.