Lithium Secondary Battery Electrolyte for Alloy-Anode Reversibility
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Solution Overview
Problem
Lithium secondary batteries using graphite as the anode active material face limitations in capacity density and reversibility due to the decomposition of electrolyte solvents and poor contact between the anode active material and current collector during charge/discharge cycles.
Innovation Solution
A lithium secondary battery configuration that includes an anode active material capable of forming alloys with lithium, such as aluminum, silicon, or tin, in conjunction with an electrolyte liquid containing specific solvents like phenanthrene, biphenyl, and glymes, which maintains electrical contact and enhances reversibility even when the anode active material pulverizes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If graphite is used as the anode active material, then lithium metal precipitation in dendrite shape is prevented, but the capacity density is limited to approximately 372 mAh/g
Solution Approach 1:
The patent uses a composite anode structure combining graphite particles (providing dendrite prevention and structural stability) with lithium metal powder (providing high capacity density of 3884 mAh/g). The composite material leverages the advantages of both components while mitigating their individual disadvantages.
2Quantity of substance
If lithium metal is used as the anode active material, then high energy density is achieved, but lithium metal precipitates in dendrite shape causing internal short circuit
Solution Approach 1:
The patent creates a composite anode using lithium metal powder (for high energy density) combined with graphite particles and conductive carbon powder (for structural stability and dendrite prevention). This composite structure allows the lithium metal to provide high capacity while the graphite matrix prevents dendrite formation.
Solution Approach 2:
The patent applies different materials to different regions of the anode: lithium metal powder particles are distributed within a graphite-based conductive matrix. The graphite provides local structural support and electron conduction pathways, while lithium metal particles provide localized high-capacity lithium storage sites.
3Quantity of substance
If alloying materials like aluminum, silicon, or tin are used as the anode active material, then theoretical capacity density is much greater than graphite, but charge/discharge reversibility is low
Solution Approach 1:
The patent forms a composite anode where alloying material particles (aluminum, silicon, or tin) are embedded in a graphite matrix with conductive carbon powder. The alloying materials provide high theoretical capacity density through lithium alloy formation, while the graphite and carbon matrix maintain structural integrity and electrical conductivity during volume expansion and contraction, enabling good reversibility.
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 battery achieves high energy density and excellent reversibility by maintaining charge/discharge functionality through the use of alloying materials and specific solvents, which prevent the loss of contact between the anode active material and current collector.
Implementation Method 1
the anode includes a material capable of forming an alloy with lithium during charge
Implementation Method 2
the electrolyte liquid includes lithium ions and counter anions of the lithium ions
Data Source
AI summary
The lithium secondary battery of the present invention satisfies at least one requirement selected from the group consisting of requirements (i) and (ii). (i) An electrolyte liquid includes an anode mediator which is dissolved along with lithium in a solvent of the electrolyte liquid to give, to the electrolyte liquid, an equilibrium potential which is not more than an upper limit potential at which a compound of lithium and an anode active material is formed, and does not include a compound which is dissolved along with lithium in the solvent of the electrolyte liquid to give, to the electrolyte liquid, an equilibrium potential which is more than the upper limit potential. (ii) The electrolyte liquid only includes, as the anode mediator, only a compound which is dissolved along with lithium in the solvent of the electrolyte liquid to give, to the electrolyte liquid, the equilibrium potential which is not more than the upper limit potential at which the compound of lithium and the anode active material is formed.