Borate Electrolytes for Lithium-Ion Battery Performance

Overview of Technical Issues:

The borate electrolyte in lithium-ion batteries currently provides insufficient ionic conductivity and insufficient electrochemical interface stabilization, resulting in limited battery power output, restricted operational voltage windows, and reduced cycling stability; the goal is to optimize borate electrolyte formulations to adequately transmit lithium ions while maintaining electrode-electrolyte interface integrity across the full charge-discharge range, thereby achieving competitive battery performance metrics including energy density, rate capability, and cycle life comparable to or exceeding conventional electrolyte systems.

Solution directions generated for this problem

Problem Direction 1 :

ImproveInterfacial layer stability
VS
ConstraintElectrolyte formulation complexity

Inspiration 1 : Cross-domain reference

Application Principle: #1 Segmentation
Cross-domain applicability Assess applicability
Battery system
Innovative Solution Refine solution

Single-salt microdomain borate electrolyte with built-in interface partitioning

Partition functions inside one salt
How to solve :
  • Use one LiDFOB-rich borate base and tune solvent pair so anion-rich microdomains form near electrodes without extra additives
  • Prepare 1.0-1.2 M LiDFOB in TMP/FEC 85:15 vol%, dry to H2O ≤20 ppm, mix 25-35°C, filter 0.2 μm, fill under dew point ≤-40°C
  • QC by Raman, EIS, XPS: free solvent peak ratio ±5%, conductivity 5.0-7.5 mS/cm, CEI/SEI B-F-O content 15-35 at%, interfacial rise <20% after 100 cycles
Expected Effect : 4.5 V class stability, 5-7 mS/cm, >85% retention at 500 cycles, interfacial impedance -30 to -45% vs carbonate+3 additives
Risk Control :
  • moisture-driven hydrolysis
  • phase drift from solvent ratio
  • excess film resistance from overconcentration

Problem Direction 2 :

ImproveCycling durability
VS
ConstraintElectrolyte formulation complexity

Inspiration 1 : Cross-domain reference

Application Principle: #1 Segmentation
Cross-domain applicability Assess applicability
Positive electrode active material, manufacturing method of positive electrode active material and secondary battery
Innovative Solution Refine solution

Modular three-additive borate electrolyte with independent functional segments

Modular electrolyte with independent protective segments
How to solve :
  • Divide borate electrolyte into three independent functional modules: anode-protective segment (2 wt% FEC for graphite SEI formation), cathode-protective segment (1 wt% TPPA for high-voltage stability at 4.5V), bulk-stabilizing segment (0.5 M LiBOB in baseline borate solvent for thermal stability)
  • each module optimized separately then combined at fixed mass ratios 2:1:97, eliminating combinatorial design complexity
  • Implement sequential module validation protocol: test each module independently in half-cell configuration (anode module targets SEI resistance <50 Ω·cm² after 50 cycles, cathode module maintains <5% capacity fade at 4.5V over 100 cycles, bulk module achieves ionic conductivity ≥5 mS/cm at 25°C), then combine validated modules without re-optimization
  • Establish modular quality control checkpoints: measure each module's key performance indicator before mixing (FEC purity ≥99.5% by GC-MS, TPPA oxidation onset ≥4.6V vs Li/Li⁺ by LSV, LiBOB moisture content <20 ppm by Karl Fischer titration), final electrolyte verified by single impedance test (interfacial resistance <80 Ω·cm² after 10 formation cycles) rather than full factorial screening
Expected Effect : Cycle life 500+ cycles with <20% fade; formulation variables reduced from 15+ to 3 fixed ratios; quality control time reduced 60%
Risk Control :
  • Module interaction effects at boundaries
  • FEC consumption rate variation
  • TPPA solubility in borate solvent

Problem Direction 3 :

ImproveInterfacial layer stability
VS
ConstraintMust not deteriorate

Inspiration 1 : Cross-domain reference

Application Principle: #10 Preliminary action
Cross-domain applicability Assess applicability
Lithium electrode and lithium secondary battery comprising the same
Innovative Solution Refine solution

Pre-formed dual-phase SEI architecture for borate electrolyte interfacial stabilization

Pre-form stable SEI before operation
How to solve :
  • Conduct controlled electrochemical pre-formation in first 3 cycles at C/20 rate between 0.01-1.5V with borate electrolyte containing 8 wt% reactive additives (VC 2%, FEC 3%, LiDFOB 3%) to build dense dual-phase SEI (inner inorganic Li₂O/LiF layer 15-25 nm, outer organic polymer layer 30-50 nm)
  • After pre-formation, replace with maintenance borate electrolyte containing only 1.5 wt% stabilizers (LiBOB 1%, TPPA 0.5%) that suppress further decomposition while maintaining 5-8 mS/cm conductivity at 25°C
  • Monitor interfacial impedance via electrochemical impedance spectroscopy after pre-formation: accept only if charge-transfer resistance Rct ≤35 Ω·cm² and SEI resistance RSEI ≤20 Ω·cm², ensuring pre-formed layer quality before switching electrolytes
Expected Effect : Interfacial resistance stable ±5% over 500 cycles; capacity retention ≥82% at 500 cycles; voltage window extended to 4.6V; ionic conductivity 6.2 mS/cm maintained
Risk Control :
  • Pre-formation protocol deviation causing incomplete SEI
  • electrolyte switching contamination risk
  • long-term SEI delamination under mechanical stress

Problem Direction 4 :

ImproveElectrolyte ionic conductivity
VS
ConstraintInterfacial side reaction rate

Inspiration 1 : Cross-domain reference

Application Principle: #17 Another dimension (Dimensionality change)
Cross-domain applicability Assess applicability
Positive electrode sheet and manufacturing method therefor, battery cell, battery, and electrical device
Innovative Solution Refine solution

Vertically-stratified dual-zone borate electrolyte with ion-selective gradient architecture

Stratified electrolyte with ion-selective gradient
How to solve :
  • Design a vertically-stratified electrolyte architecture with two distinct zones: bulk zone (high-conductivity borate formulation, 1.2-1.5 M LiBF4 in low-viscosity solvent blend) occupying 70-85% separator thickness for rapid ion transport
  • interface zone (reaction-suppressing borate layer, 0.8 M LiDFOB with fluorinated co-solvents) occupying 15-30% thickness adjacent to electrodes, blocking solvent molecules while conducting Li+ ions
  • Fabricate using sequential infiltration coating: pre-soak separator with interface-zone electrolyte (viscosity 8-12 mPa·s) at controlled rate 0.5 mm/min to achieve 15-30 μm penetration depth, verified by cross-sectional SEM
  • then fill bulk-zone electrolyte (viscosity 3-5 mPa·s) into remaining separator volume, creating stable concentration gradient maintained by viscosity differential and limited inter-diffusion (diffusion coefficient <10⁻⁷ cm²/s)
  • Implement quality control protocol: measure ionic conductivity of bulk zone ≥6 mS/cm at 25°C using AC impedance (tolerance ±0.3 mS/cm)
  • verify interface zone thickness 15-30 μm by optical profilometry (tolerance ±3 μm)
  • confirm side reaction suppression by cyclic voltammetry showing oxidation onset ≥4.6V and gas evolution <0.5 mL/Ah during formation cycles
Expected Effect : Ionic conductivity 6-8 mS/cm; side reaction rate reduced 60-70%; cycle life >450 cycles with <20% fade
Risk Control :
  • gradient layer inter-diffusion over time
  • separator wetting uniformity variation
  • viscosity-temperature sensitivity affecting stratification

Problem Direction 5 :

ImproveElectrochemical voltage window
VS
ConstraintInterfacial side reaction rate

Inspiration 1 : Cross-domain reference

Application Principle: #2 Taking out (Extraction)
Cross-domain applicability Assess applicability
Battery device, application method thereof and electric equipment
Innovative Solution Refine solution

Cathode-localized fluorinated borate electrolyte zone for high-voltage stability

Extract oxidation-vulnerable components from cathode region by creating a dual-zone electrolyte architecture with fluorinated borate near cathode (≥4.5V stable) and standard borate in bulk
How to solve :
  • Design cathode-adjacent electrolyte zone (0–50 μm from cathode surface) using lithium tetrafluoroborate (LiBF4) 1.2M in fluoroethylene carbonate/methyl (2,2,2-trifluoroethyl) carbonate (FEC/FEMC 1:1 v/v, oxidation threshold >5.2V) while bulk electrolyte uses standard lithium bis(oxalato)borate (LiBOB) 0.8M in EC/DMC for 5–8 mS/cm conductivity
  • Implement in-situ zone formation during first charge: inject fluorinated borate solution (5 wt% of total electrolyte volume) at 0.1C to C/20 rate, allowing preferential migration and concentration at cathode via electric field gradient, verified by EIS showing cathode interfacial resistance <50 Ω·cm² at 4.5V
  • Establish quality control protocol: fluorine content at cathode surface measured by XPS (F 1s peak intensity ≥15% atomic ratio, tolerance ±2%), zone thickness confirmed by cryo-TEM cross-section (target 30–50 μm, acceptance 25–60 μm), oxidation onset potential tested by linear sweep voltammetry (≥4.8V vs Li/Li+, minimum 4.6V)
Expected Effect : Voltage window expanded to 4.6V; side reaction rate reduced 60% vs uniform electrolyte; cathode capacity retention >85% at 500 cycles; energy density +18%
Risk Control :
  • Fluorinated zone thickness variation during cycling
  • bulk-zone intermixing over prolonged operation
  • cost increase from fluorinated solvents
Patsnap Eureka Solution