Li-Ion Cathode-Electrolyte Design for High-Voltage Cycle Stability
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Solution Overview
Problem
Lithium-ion batteries using LiCoO2 as a positive active material face instability and capacity loss when operated at high voltages greater than 4.2 V due to lattice deformation, gas production, and corrosion, leading to poor performance and rapid degradation.
Innovation Solution
A lithium-ion battery design incorporating a metal ion-doped lithium cobalt oxide material (Lix1Coy1M1-y1O2-z1Qz1) with a polynitrile six-membered nitrogen-heterocyclic compound and an aliphatic dinitrile or polynitrile additive in the electrolyte to form a stable complex layer, reducing lattice deformation and surface oxidation, and an aliphatic dinitrile or polynitrile compound to repair the layer and prevent transition metal ion dissolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If LiCoO2 is used as positive active material and voltage is increased above 4.2V to extract more lithium ions, then capacity is improved, but structural stability deteriorates due to lattice deformation and Co4+ formation
Solution Approach 1:
The patent modifies the voltage operating parameters and compositional parameters of LiCoO2 by doping with metal ions (Al, Ti, Zr, Mg) to stabilize the lattice structure. This allows the battery to operate at higher voltages (>4.2V) for increased capacity while the doped structure prevents the detrimental formation of Co4+ and lattice collapse, thus resolving the contradiction between capacity extraction and structural stability
Solution Approach 2:
The patent creates a composite material system by doping LiCoO2 with multiple metal ions (Al3+, Ti4+, Zr4+, Mg2+) in specific ratios. This composite approach enhances the structural stability of the cathode material at high voltages while maintaining high lithium ion extraction capacity, effectively addressing the contradiction between capacity and stability
2Quantity of substance
If deep delithiation is performed to increase capacity, then more lithium ions are extracted, but harmful factors increase due to gas production from electrolyte oxidation
Solution Approach 1:
The patent changes the electrochemical parameters by limiting the voltage to 4.2V and modifying the compositional parameters through metal ion doping. This prevents the formation of unstable Co4+ that would otherwise oxidize the electrolyte and produce gas, while still achieving high capacity through the stabilized structure that allows efficient lithium ion extraction without deep delithiation
3Use of energy by moving object
If high voltage operation is used to increase capacity, then energy density is improved, but reliability deteriorates due to HF corrosion and transition metal dissolution
Solution Approach 1:
The patent optimizes the voltage parameter to 4.2V and modifies the compositional parameters by doping LiCoO2 with metal ions (Al, Ti, Zr, Mg). This combination reduces the corrosive effects of HF on the cathode surface and prevents transition metal dissolution, thereby maintaining high energy density while significantly improving reliability and cycle life
Solution Approach 2:
The patent uses small amounts of inexpensive metal ion dopants (Al3+, Ti4+, Zr4+, Mg2+) that can be easily incorporated into the LiCoO2 structure. These dopants provide long-term protection against corrosion and dissolution without requiring expensive materials or complex protective coatings, achieving reliable high-voltage operation through simple compositional modification
4Reliability
If metal ion doping is applied to stabilize structure, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent modifies the compositional parameters of LiCoO2 by doping with metal ions (Al, Ti, Zr, Mg) in controlled amounts. This relatively simple parameter change achieves significant improvements in structural stability and reliability at high voltages without requiring complex device architecture or manufacturing processes, thus improving reliability while minimizing increases in device complexity
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 enhances the cycle and storage performance of lithium-ion batteries under high-temperature and high-voltage conditions by stabilizing the structure, reducing gas production, and maintaining capacity retention, thereby extending the battery's lifespan.
Implementation Method 1
incorporating a metal ion-doped lithium cobalt oxide material (Lix1Coy1M1-y1O2-z1Qz1) with a polynitrile six-membered nitrogen-heterocyclic compound and an aliphatic dinitrile or polynitrile additive in the electrolyte to form a stable complex layer
Implementation Method 2
the additive A may be adsorbed on a surface of the positive active material during formation of the battery to form a loose porous protective film
Implementation Method 3
an aliphatic dinitrile or polynitrile compound with a relatively high oxidation potential, which can stably exist in the electrolyte for a long time, and can repair the damaged complex layer at any time during cycling or high-temperature storage
Implementation Method 4
can repair the damaged complex layer at any time during cycling or high-temperature storage, reduce dissolution of transition metal ions
Implementation Method 5
Co3+ is oxidized into quite unstable Co4+, which oxidizes an electrolyte together with surface oxygen that loses a large quantity of electrons. In this case, a large amount of gas is produced inside the batteries
Implementation Method 6
a positive active material of the positive electrode sheet includes Lix1Coy1M1-y1O2-z1Qz1, wherein M is a metal ion
Implementation Method 7
deep delithiation also causes lattice oxygen to lose a large quantity of electrons, resulting in sharp shrinkage of LiCoO2 unit cells along a c-axis direction, and leading to instability or even collapse of a local bulk structure
Data Source
AI summary
The present application provides a lithium-ion battery and an apparatus, the lithium-ion battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separation film. The positive active material in the positive electrode sheet includes Lix1Coy1M1-y1O2-z1Qz1, 0.5≤x1≤1.2, 0.8≤y1<1.0, 0≤z1≤0.1, and M is selected from one of Al, Ti, Zr, Y, and Mg, and Q is selected from one or more of F, Cl, and S. The electrolyte contains an additive A and an additive B, the additive A is a polynitrile six-membered nitrogen-heterocyclic compound with a relatively low oxidation potential, and the additive B is an aliphatic dinitrile or polynitrile compound with a relatively high oxidation potential. The lithium-ion battery of the present application has superb cycle performance and storage performance, especially under high-temperature and high-voltage conditions.