The relentless growth in global energy demand has led to a dramatic increase in fossil fuel consumption, exacerbating greenhouse gas emissions and precipitating a severe climate crisis. To address this challenge, the development of clean energy and efficient storage technologies has become a global strategic priority. Currently, advancing efficient electrochemical energy storage stands as a pivotal measure to resolve the intertwined energy and environmental crises. Among various technologies, the lithium-ion battery has emerged as the premier choice for renewable energy storage, owing to its superior energy density (>250 Wh/kg), long cycle life (>1000 cycles), low self-discharge rate (~5% per month), lightweight structure, and environmental friendliness. It has found widespread application in portable 3C electronics, new-energy electric vehicles, and large-scale grid storage systems.
As application scenarios diversify into more demanding fields such as polar research, deep-space exploration, and defense, there is an urgent need to develop high-energy-density lithium-ion batteries capable of operating reliably in extreme environments. However, most contemporary lithium-ion batteries are designed for a moderate ambient temperature range of approximately 15–35 °C. Their electrochemical performance deteriorates sharply under extreme conditions: at low temperatures ( 45 °C), they face accelerated interfacial side reactions, decomposition of the solid electrolyte interphase (SEI), and risks of thermal runaway. Concurrently, operation at high cutoff voltages (>4.5 V vs. Li+/Li) leads to continuous electrolyte decomposition, transition metal dissolution, and irreversible phase transitions in electrode materials. These issues severely constrain the application potential of lithium-ion batteries across wide temperature and voltage ranges.
Driven by the critical and growing demand for lithium-ion batteries that perform under wide-temperature and high-voltage conditions, and considering significant recent progress in multifunctional electrolyte design, a comprehensive review is timely. This article aims to dissect the fundamental challenges, systematically review cutting-edge electrolyte design strategies, and outline future directions. The central thesis is that the electrolyte, as the core medium for Li+ transport and interfacial reactions, is the key determinant for unlocking the performance of lithium-ion batteries in extreme environments. We will first analyze the intrinsic challenges and mechanisms from the perspectives of bulk transport, interfacial kinetics, and material stability. Subsequently, we will review state-of-the-art electrolyte design strategies from multiple dimensions. Finally, we will discuss future prospects and challenges, highlighting the potential role of artificial intelligence and advanced in-situ characterization.
Fundamental Challenges for Lithium-Ion Batteries Under Extreme Conditions
Challenges at Low Temperatures ( 20 °C)
The performance degradation of lithium-ion batteries at low temperatures is primarily attributed to hindered Li+ transport kinetics across the entire cell. The transport process involves: (1) diffusion of solvated Li+ through the bulk electrolyte, (2) desolvation at the electrode/electrolyte interface, (3) migration through the surface films (SEI on anode, CEI on cathode), and (4) solid-state diffusion within the electrode materials. Low temperatures adversely affect all these steps, with the interfacial processes often becoming rate-limiting.
1. Drastic Reduction in Bulk Ionic Conductivity: The ionic conductivity (σ) of the electrolyte, a key parameter governing bulk transport, decreases severely as temperature drops. Conductivity is governed by the concentration and mobility of charge carriers:
$$ \sigma = \sum_{i} n_i \mu_i Z_i e $$
where \(n_i\) is the number of free ions, \(\mu_i\) is the ionic mobility, \(Z_i\) is the charge number, and \(e\) is the elementary charge. The mobility \(\mu_i\) is inversely related to the electrolyte viscosity (η) and the effective ionic radius (\(r_i\)), as described by the Stokes-Einstein relation:
$$ \mu_i = \frac{1}{6\pi\eta r_i} $$
Conventional carbonate-based electrolytes, often containing ethylene carbonate (EC) for stable SEI formation, suffer from high viscosity at low temperatures. The temperature dependence of conductivity typically follows the Vogel-Tammann-Fulcher (VTF) equation:
$$ \sigma = A T^{-1/2} e^{-\frac{E_k}{R(T – T_0)}} $$
where \(A\) is a pre-exponential factor, \(E_k\) is the activation energy, \(R\) is the gas constant, and \(T_0\) is the ideal glass transition temperature. When σ falls below \(10^{-5}\) S/cm, bulk transport becomes a significant bottleneck for lithium-ion battery operation.
2. Increased Charge Transfer Resistance: Electrochemical impedance spectroscopy (EIS) reveals a dramatic, exponential increase in the medium-frequency semicircle (attributed to charge transfer resistance, \(R_{ct}\)) below -20°C. While traditionally associated with the electron transfer step of Li+ intercalation, compelling evidence now suggests that \(R_{ct}\) is predominantly governed by the Li+ desolvation process at the interface. The activation energy for this process (\(E_{a,ct}\)) is highly sensitive to electrolyte composition, particularly solvent coordination strength. Solvents with strong Li+ coordination (e.g., carbonates) create a high desolvation energy barrier, whereas weakly coordinating solvents (e.g., ethers) exhibit lower barriers, leading to better low-temperature kinetics. For a lithium-ion battery, overcoming this desolvation barrier is often the critical challenge for low-temperature operation.
3. Limited Ion Transport in Interfacial Phases: The properties of the Solid Electrolyte Interphase (SEI) and Cathode Electrolyte Interphase (CEI) crucially affect interfacial ion transport. A stable, ionically conductive interface is essential. The SEI is a complex, multicomponent layer. Recent “dual-layer dual-mechanism” models propose that Li+ transports via pore diffusion in a porous organic outer layer and via a “knock-off” mechanism in a dense inorganic inner layer. The ionic conductivity and Li+ diffusion activation energy within these interfacial films are critical. While anion-derived inorganic-rich SEIs (rich in LiF, Li2O) are generally valued for stability, some studies show that certain solvent-derived organic-rich SEIs can exhibit superior low-temperature ionic transport due to lower activation energy for Li+ diffusion, highlighting the importance of tailored interface design for the lithium-ion battery.
Challenges at High Temperatures (>45 °C)
Elevated temperatures accelerate parasitic chemical reactions within the lithium-ion battery, leading to irreversible degradation and safety hazards. The primary instigator is the thermal decomposition of the ubiquitous lithium salt, LiPF6:
$$ \text{LiPF}_6 \xrightarrow{T > 60^\circ\text{C}} \text{LiF} + \text{PF}_5 \uparrow $$
The generated PF5 is a strong Lewis acid that reacts vigorously with trace water, organic solvents, and components of the SEI/CEI:
$$
\begin{aligned}
\text{PF}_5 + \text{H}_2\text{O} &\rightarrow \text{POF}_3 + 2\text{HF} \\
\text{RCO}_2\text{Li} + \text{PF}_5 &\rightarrow \text{RCOF} + \text{LiF} + \text{POF}_3 \\
\text{Li}_2\text{CO}_3 + \text{PF}_5 &\rightarrow \text{POF}_3 + 2\text{LiF} + \text{CO}_2
\end{aligned}
$$
These reactions produce hydrofluoric acid (HF), which corrodes electrode materials and current collectors, and various gaseous products (CO2, POF3), leading to increased internal pressure, cell swelling, and electrolyte depletion. The continuous breakdown and reformation of the SEI/CEI increase impedance and consume active Li+. In extreme cases, these exothermic reactions can trigger thermal runaway in the lithium-ion battery. Therefore, enhancing the thermal stability of the electrolyte, particularly the lithium salt, is paramount.
Challenges at High Voltages (>4.5 V vs. Li+/Li)
Pushing the charge cutoff voltage is a direct route to increase the energy density of a lithium-ion battery, but it introduces severe stability issues.
1. Electrolyte Oxidation Decomposition: When the cathode potential exceeds the electrochemical stability window of the electrolyte (typically ~4.3 V for conventional carbonates), thermodynamic oxidation occurs. The driving force can be understood from the perspective of molecular orbital theory. Oxidation occurs when the cathode Fermi level (or electrochemical potential, \(\Phi_{\text{cathode}}\)) is higher than the highest occupied molecular orbital (HOMO) energy level of the electrolyte component (solvent or anion). The electrochemical window \(E_g\) is the gap between the HOMO and the lowest unoccupied molecular orbital (LUMO). For stable operation, the cell voltage \(V_{OC}\) must satisfy:
$$ eV_{OC} = \mu_A – \mu_C \leq E_g $$
where \(\mu_A\) and \(\mu_C\) are the anode and cathode chemical potentials, respectively. At high voltages, solvents and salts with insufficiently low HOMO levels undergo irreversible oxidative decomposition, generating resistive surface films and gas.
2. Transition Metal Ion Dissolution: High-voltage operation, especially coupled with elevated temperature and acidic species (like HF), accelerates the dissolution of transition metal ions (e.g., Mn2+, Co2+, Ni2+) from layered oxide cathodes (e.g., NCM, NCA). These dissolved ions migrate through the electrolyte and deposit on the anode surface, where they catalyze further decomposition of the SEI and electrolyte, leading to rapid capacity fade and impedance growth in the lithium-ion battery.
3. Structural Degradation of Cathode Materials: Deep delithiation at high voltages can induce irreversible phase transitions from a layered structure to spinel-like and finally rock-salt phases on the cathode particle surface. This rock-salt phase is electronically and ionically insulating, impeding charge transfer. Furthermore, anisotropic lattice expansion/contraction (“lattice breathing”) during cycling generates mechanical stress, leading to microcrack formation. Electrolyte penetrates these cracks, causing further parasitic reactions in the particle interior, accelerating the failure of the lithium-ion battery.
Recent Advances in Electrolyte Design for Wide-Temperature and High-Voltage Performance
The electrolyte, typically composed of lithium salt(s), organic solvent(s), and functional additives, is the central focus for overcoming these challenges. Advanced design strategies manipulate the composition to tailor bulk properties, solvation structure, and interfacial chemistry.
Strategies for Low-Temperature Electrolytes
The core objectives are to enhance bulk ionic conductivity, reduce the Li+ desolvation energy barrier, and form a low-impedance, ionically conductive SEI/CEI.
1. Solvent Engineering: Replacing high-viscosity, high-melting-point solvents (like EC) with low-viscosity co-solvents (e.g., linear carbonates like DMC, EMC, or esters like methyl acetate (MA), methyl propionate (MP)) is a fundamental approach. The use of MP as a main solvent has enabled lithium-ion batteries to operate from -80 °C to +80 °C.
2. Novel Electrolyte Architectures:
- Weakly Solvating Electrolytes (WSEs): These electrolytes use solvents with low donor number (DN) or low dielectric constant, resulting in a weak Li+-solvent interaction. This significantly lowers the desolvation activation energy (\(\Delta E_{dsv}\)), enabling fast charge transfer at low temperatures. Common designs employ fluorinated esters or ethers as the main solvent.
- Localized High-Concentration Electrolytes (LHCEs): By adding a non-coordinating diluent (e.g., bis(2,2,2-trifluoroethyl) ether) to a high-concentration electrolyte, LHCEs maintain the beneficial anion-rich solvation structure (promoting inorganic-rich SEI) while reducing viscosity and cost. The unique solvation structure facilitates rapid interfacial kinetics.
- High-Entropy Electrolytes (HEEs): Incorporating a multitude of different solvents and/or salts creates a highly disordered solvation shell with suppressed crystallization tendency. This can drastically lower the freezing point of the electrolyte (e.g., to -130 °C) and maintain relatively high ionic conductivity at ultra-low temperatures, significantly extending the operational range of the lithium-ion battery.
3. Functional Additives: Additives like fluoroethylene carbonate (FEC) and lithium bis(trimethylsilyl)phosphate (LiTMSP) are used to tailor the SEI/CEI composition, making it thinner and more ionically conductive at low temperatures.
| Strategy | Key Mechanism | Typical Components | Targeted Improvement |
|---|---|---|---|
| Solvent Blending | Reduces bulk viscosity | EC + MP/MA/DMC | Bulk conductivity |
| Weakly Solvating Electrolyte | Lowers desolvation barrier | Trifluoroethyl esters, TFEP | Interfacial charge transfer |
| Localized High-Concentration Electrolyte | Maintains anion-coordinated structure with low viscosity | LiFSI/DME + BTFE diluent | SEI quality & bulk transport |
| High-Entropy Electrolyte | Suppresses freezing point | Multi-solvent/multi-salt mixtures | Ultra-low T operation |
| SEI-modifying Additives | Forms low-impedance interface | FEC, LiTMSP, VC | Interfacial ion transport |
Strategies for High-Temperature Electrolytes
The focus is on improving the thermal stability of the lithium salt and mitigating its decomposition products.
1. Development of Thermally Stable Lithium Salts: Researchers have developed alternative salts with higher decomposition temperatures.
- LiFAP (LiPF3(CF2CF3)3): The bulky -CF2CF3 group increases steric hindrance, raising the decomposition temperature by ~40°C compared to LiPF6.
- LiBOB (Lithium bis(oxalato)borate): Features good thermal stability and HF-scavenging ability but suffers from low conductivity and poor Al current collector passivation at high voltage.
- LiBF2SO4: A modified salt showing promising high-temperature cycle stability in LiFePO4 cells.
2. Lithium Salt Stabilizers: These additives scavenge the harmful PF5 or shift the decomposition equilibrium of LiPF6.
- Lewis Base Additives: Compounds with lone-pair electrons (e.g., P=O group in tris(2,2,2-trifluoroethyl) phosphite (TTFP)) coordinate with PF5, preventing its reaction with solvents/water.
- LiF Scavengers/Stabilizers: According to Le Chatelier’s principle, adding excess LiF can suppress the decomposition of LiPF6.
| Approach | Example | Mechanism | Benefit |
|---|---|---|---|
| New Lithium Salts | LiFAP | Steric hindrance from perfluoroalkyl groups | Higher thermal decomposition onset |
| LiBOB | Stable boroxine ring structure, reacts with HF | Thermal stability, HF removal | |
| Stabilizer Additives | TTFP | Lewis base coordinates PF5 | Suppresses acid generation & gassing |
| Added LiF | Shifts LiPF6 ⇌ LiF + PF5 equilibrium | Reduces PF5 generation |
Strategies for High-Voltage Electrolytes
Design aims to widen the electrochemical stability window and construct robust cathode interfaces.
1. Fluorination Strategy: Substituting hydrogen atoms with fluorine in solvent molecules is highly effective. The strong C-F bond increases oxidation stability (lowers HOMO), reduces flammability, and promotes the formation of a LiF-rich, stable CEI. Examples include fluoroethylene carbonate (FEC), trifluoropropyl carbonate (TFPC), and highly fluorinated ethers. A fully fluorinated electrolyte system can enable stable cycling of NCM/graphite lithium-ion batteries up to 4.6 V.
2. High-Concentration Electrolyte (HCE) Strategy: Increasing salt concentration (e.g., > 3 mol/L) dramatically changes the solvation structure. Solvent molecules are fully coordinated to Li+, and anion participation increases, forming contact ion pairs (CIPs) and aggregates (AGGs). This leads to anion-dominated decomposition, forming a robust, inorganic-rich CEI/SEI. The reduced free solvent molecules also suppress solvent oxidation. While HCEs have high viscosity, the LHCE concept (mentioned for low-T) solves this issue while retaining high-voltage stability, making it a versatile strategy for high-performance lithium-ion batteries.
3. High-Voltage Additives: Specific additives like lithium difluoro(oxalato)borate (LiDFOB) or compounds containing nitrile groups (-CN) can polymerize or decompose preferentially at the cathode surface below the solvent oxidation potential, forming a protective CEI layer that shields the electrolyte from further oxidation.
Summary and Future Perspectives
In this review, we have systematically analyzed the challenges faced by lithium-ion batteries under extreme conditions of low temperature, high temperature, and high voltage. The electrolyte is identified as the critical component whose design dictates performance boundaries. For low temperatures, the key is to ensure fast bulk transport and facile interfacial desolvation through solvent selection, novel electrolyte structuring (WSE, LHCE, HEE), and interface engineering. For high temperatures, enhancing the thermal stability of the lithium salt system via new salts or stabilizers is paramount. For high voltages, expanding the anodic stability limit through fluorination and manipulating the solvation structure via high-concentration concepts are proven strategies.
The future development of electrolytes for wide-temperature, high-voltage lithium-ion batteries lies at the intersection of advanced characterization, computational design, and multifunctional formulation. Two promising directions are:
1. AI-Guided Electrolyte Discovery: Machine learning and high-throughput computational screening can rapidly predict the physicochemical properties (e.g., oxidation potential, melting point, viscosity, Li+ binding energy) of vast molecular libraries of solvents, salts, and additives. This data-driven approach can identify novel, high-performance electrolyte components and optimal formulations with tailored properties for specific extreme conditions, dramatically accelerating the development cycle for the next-generation lithium-ion battery.
2. In-situ/Operando Interface Characterization: Real-time monitoring of the dynamic evolution of the electrode-electrolyte interface during battery operation under extreme conditions is crucial. Techniques such as in-situ electrochemical atomic force microscopy (EC-AFM), electrochemical quartz crystal microbalance (EQCM), synchrotron-based X-ray spectroscopy, and cryo-electron microscopy (cryo-EM) can provide unprecedented insights into SEI/CEI formation, composition, morphology, and ionic transport properties as functions of temperature and voltage. This fundamental understanding will enable the rational design of electrolytes that construct ideal interfacial architectures “on-demand.”
Ultimately, the convergence of these approaches—combining intelligent material design with deep mechanistic understanding—will pave the way for the creation of robust, multi-functional electrolytes. This breakthrough is essential for unlocking the full potential of lithium-ion batteries, enabling their reliable deployment in the most demanding applications from electric vehicles in arctic climates to grid storage in deserts and power sources for aerospace and deep-sea exploration.