Cathode Composition and Electrolyte Additives for High-Voltage Cycle Stability
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Solution Overview
Problem
The increase in voltage of electrochemical devices leads to issues such as oxygen release from the positive electrode, electrolyte decomposition, and a sharp decline in cycle performance, necessitating improvements in cycle performance and high-temperature storage performance.
Innovation Solution
The positive active material in the electrochemical device is formulated with specific molar fractions of Ni, Co, Mn, and optionally Na, K, or Mg, along with a dinitrile compound and sulfur-oxygen double-bonded compound in the electrolyte, enhancing structural stability and forming a stable interface layer to improve cycle and high-temperature storage performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the voltage of the electrochemical device is increased to improve energy density, then the energy density is improved, but oxygen release from the positive electrode, electrolyte decomposition, and sharp decline in cycle performance occur
Solution Approach 1:
The patent changes the chemical composition parameters of the positive active material by doping with M2 elements (Na, K, or Mg) at specific molar ratios (d/a = 0.04 to 0.06). This parameter modification stabilizes the crystal structure and suppresses oxygen release, enabling the device to maintain high voltage (≥4.1V) while improving cycle performance and high-temperature storage stability.
Solution Approach 2:
The patent creates a composite positive active material by combining M1 elements (Ni, Co, Mn) with doped M2 elements (Na, K, or Mg). This composite structure leverages the synergistic effects of different elements to enhance structural stability, suppress electrolyte decomposition, and maintain reliable cycle performance at high voltages.
2Stability of the object's composition
If the doping content of M2 element is increased to improve structural stability, then the structural stability is improved, but the reversible capacity deteriorates
Solution Approach 1:
The patent optimizes the doping content parameter by controlling the molar ratio of M2 element to total metal elements (d/a) within the range of 0.04 to 0.06. This precise parameter control achieves the optimal balance between structural stability and reversible capacity, avoiding both insufficient stabilization and excessive capacity loss.
3Reliability
If a dinitrile compound is added to the electrolyte solution to suppress polarization and form stable interface layer, then the cycle performance is improved, but the viscosity of electrolyte solution increases when mass percent exceeds 10%
Solution Approach 1:
The patent optimizes the concentration parameter of the dinitrile compound in the electrolyte solution, controlling the mass percent within 0.1% to 10% (preferably 1% to 6%). This parameter optimization ensures sufficient polarization suppression and interface layer formation while preventing excessive viscosity increase that would hinder ion transport.
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 stabilizes the positive active material's structure, reduces internal resistance, and enhances cycle and high-temperature storage performance by suppressing oxygen release and electrolyte decomposition.
Implementation Method 1
The positive active material includes an M2 element. The molar fraction of the M2 element in the positive active material is d. The M2 element includes at least one of Na, K, or Mg. The value of d/a is 0.04 to 0.06. Doping the positive active material with the M2 element throughout the bulk phase can further stabilize the crystal structure of the positive active material.
Implementation Method 2
The dinitrile compound can suppress the polarization phenomenon of the electrolyte solution. In addition, the dinitrile compound can act in unison with the M2 doping element in the positive active material to form a stable interface layer on the negative electrode
Implementation Method 3
With the development of electrochemical energy storage technology, higher requirements have been imposed on the cycle performance and safety performance of electrochemical devices (such as a lithium-ion battery).
Data Source
AI summary
An electrochemical device includes a positive electrode plate. The positive electrode plate includes a positive active material layer. The positive active material layer includes a positive active material. After the electrochemical device is discharged, a molar fraction of an M1 element in the positive active material included in the positive electrode plate in a fully discharged state is a. The M1 element includes Ni, Co, and Mn. A molar fraction of Ni in the positive active material is b. A molar fraction of Mn in the positive active material is c. A molar fraction of an M2 element in the positive active material is d. The M2 element includes at least one of Na, K, or Mg. The value of b/a is 0.4 to 0.6, the value of c/a is 0.4 to 0.6, and the value of d/a is 0.04 to 0.06.