P63mc Phase Positive Active Material for High Voltage Stability
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Solution Overview
Problem
Lithium-ion batteries face challenges in achieving high specific capacity, structural reversibility, and cycle stability at high voltages due to irreversible phase transitions and side reactions, leading to capacity fading and safety concerns with conventional LiCoO2 materials.
Innovation Solution
A positive active material with a P63mc space group, specifically LixNazCo1-yMyO2, is developed, which includes pores and cracks to manage stress and lithium vacancies, and introduces sodium to enhance structural stability, paired with a second active material like LiCo1-aRaO2 to create a double-layered structure that isolates the electrolyte and maintains interface stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If LiCoO2 is charged at higher voltage (>4.6 V) to achieve higher specific capacity, then more Li+ ions are deintercalated, but irreversible phase transitions occur (O3 to H1-3 to O1) deteriorating cycle performance and safety
Solution Approach 1:
The patent applies parameter changes by modifying the crystal structure phase from O3 to P63mc through compositional adjustment (LixNazCo1-yMyO2) and processing conditions. This phase change enables the material to operate at higher voltages (4.8V) without undergoing detrimental O3→H1-3→O1 transitions, thereby maintaining cycle performance while achieving higher specific capacity through increased Li+ deintercalation.
Solution Approach 2:
The patent employs composite materials by creating a dual-layer structure where the P63mc phase material (LixNazCo1-yMyO2) serves as the primary active material. This composite approach combines the high voltage stability of the P63mc phase with the electrochemical activity needed for high capacity, resolving the contradiction between capacity and cycle life.
2Quantity of substance
If LiCoO2 is charged at higher voltage to achieve higher specific capacity, then cobalt metal dissolves out severely and side reactions intensify at interface, but conventional electrolytic solution decomposes quickly leading to capacity fading
Solution Approach 1:
The patent uses the P63mc phase structure as an intermediary that mediates between the electrode and electrolyte at high voltages. This phase acts as a protective interface that reduces direct contact between conventional electrolyte and the electrode at 4.8V, minimizing electrolyte decomposition and cobalt dissolution while still allowing Li+ transport, thus enabling high capacity without severe side reactions.
Solution Approach 2:
By changing the phase parameter from O3 to P63mc, the patent modifies the electrochemical window and interface properties of the material. This parameter change allows the electrode to operate at higher voltages with reduced electrolyte decomposition, as the P63mc phase exhibits better interfacial stability and lower catalytic activity toward electrolyte breakdown compared to conventional LiCoO2.
3Use of energy by moving object
If conventional LiCoO2 material is used to achieve high energy density, then discharge voltage plateau is high, but structural reversibility and interface stability deteriorate at high voltage
Solution Approach 1:
The patent applies parameter changes by transforming the crystal structure from O3 phase to P63mc phase through compositional modification (LixNazCo1-yMyO2). This phase transformation maintains the high discharge voltage plateau (4.8V) needed for high energy density while simultaneously improving structural reversibility, as the P63mc phase undergoes reversible Li+ insertion/extraction without the irreversible O3→H1-3→O1 transitions that plague conventional LiCoO2.
Data Source
AI summary
A positive active material, containing a compound with a P63mc space group. In an XRD pattern of the positive active material, a (002) crystal plane of the compound with the P63mc space group is located between 17.5° and 19°, and a full width at half maximum of the (002) crystal plane falls between 0.05 and 0.1. The positive active material at a high voltage of 4.8 V exhibits a considerable discharge capacity and desirable structural reversibility and cycle stability.