There are two paths to improving the energy density of ternary layered oxides (NCM/NCA): increasing the nickel content and increasing the cutoff voltage. The former is constrained by cost and thermal stability; the latter requires the least modification to the material and is therefore the most popular. However, the oxidation resistance window of commercial carbonate electrolytes (with EC as the main film-forming component) is around 4.3–4.5 V. Once it enters 4.4–4.8 V, a series of failures occur:
01Solvent oxidation and decomposition produce organic acids and CO₂, which consume active lithium.
02As the CEI continues to thicken, the charge transfer impedance (Rct) increases with each revolution.
03Ni⁴⁺/Co³⁺ strong oxidation accelerates interfacial side reactions, causing transition metals to dissolve and "crosstalk" to the negative electrode;
04The HF released from the decomposition of LiPF₆ corrodes the cathode;
05Under high temperature/high pressure, side reactions produce gas, causing soft packaging to swell and even posing safety hazards.
Essentially, it all points to one thing: the electrode-electrolyte interface is unstable . Introducing a small amount (0.5%–5%) of functional additives that can "preemptively redox," allowing it to form a film before the solvent, is widely recognized in the industry as the king of cost-effectiveness. This article focuses on the four most representative types (Table 1).
Note: PST is often referred to as PES (the same substance) in the Dahn team's literature; in this article, it will be referred to as PST.abbreviation Chinese name / English name Chemical formula molecular weight Category features FEC PST/PES MMDS (MDO) DTD
The four types of additives have vastly different structures, but their core logic is the same: "preferential reaction, early film formation, and dual protection . "
① Preferential redox : The molecular LUMO/HOMO energy level matches the electrode potential, allowing it to be reduced before the solvent at the negative electrode (SEI) or oxidized before the solvent at the positive electrode (CEI); ② Dual interface protection : High-quality additives can form films on both the positive (CEI) and negative (SEI) sides, blocking direct contact between the solvent and the electrode; ③ Inhibition of HF and metal dissolution : Fluorine-containing (FEC) or sulfur-containing (PST/MMDS/DTD) decomposition products neutralize HF and capture dissolved metals, alleviating "crosstalk"; ④ Low impedance, thin and uniform : Thicker films are not necessarily better, but rather films that conduct ions, block electrons, and are thin and dense.
FluorineHigh voltage + silicon/lithiumIt can be used as an additive (1%–10%) or as a co-solvent (approximately 20 vol%). It performs exceptionally well in high-nickel ternary and silicon-based anode systems, representing a classic combination of "high voltage + high-activity anode".
NCM111, 3.0–4.6 V, 100 cycles: FEC/DMC (approx. 20 vol% FEC cosolvent) capacity retention 82.7% vs EC-containing conventional electrolyte 41.3% (Electrochim. Acta, 2016). NMC811‖Lithium metal, LHCE + 5.5 wt% FEC, 81.5% retention after 300 cycles (Jülich report, not peer-reviewed); NCM811, 4.3 V, 300 cycles: MNTB + FEC synergistic inorganic CEI-rich, maintaining 81.10% vs standard electrolyte 32.8% (ACS AMI, 2024).
Disadvantages : Some systems tend to produce gas at high temperatures, and in industrial applications, they are often used in conjunction with LiDFP; note that the dosage difference between "co-solvent grade" and "additive grade" is one order of magnitude.
sulfurSuppress gas productionContaining a C=C double bond, its reduction potential is higher than that of saturated PS, enabling it to ring-open/polymerize "earlier"; the sulfonyl group contributes to the inorganic (sulfur-containing) stable interface. Its most prominent advantages are the suppression of gas production and high-temperature stability (data from the Dahn team).
The cycling performance of 2% PST is comparable to that of 2% VC, while 4% and 6% are better, at the cost of slightly higher interface impedance (JES, 2014). Gas production at 60 °C is reduced by about 90% compared to the VC system ; 2% PST produces almost no gas at 4.2 V and 60 °C (JES, 2014). At 55 °C and 1000 cycles, the capacity decay of PST was <20% ; in contrast, the VC system showed >10% bulging and >20% decay (JPS, 2015).
Extremely high sulfur content (34%)Antioxidant up to 4.6–4.7VThe most "sulfur-rich" of the four types. DFT/MD simulations show that MMDS interacts strongly with PF₆⁻, promoting its preferential decomposition at the interface and widening the oxidation window (PCCP, 2019). It is preferentially oxidized at the cathode at about 3.8 V, forming an ultrathin CEI of only 3–5 nm (compared to 15–20 nm in conventional applications).
4.6 V NCM523‖Graphite Soft Pack: 87.99% Retention After 800 Cycles (Li Lin, Wenzhou University; Zeng Ronghua, South China Normal University Team, Angew. Chem., 2023); LiCoO₂/graphite (4.5 V): 0.5% MMDS increased the 150-cycle retention rate from 32.0% to 69.6%(J. Power Sources, 2012). LiMn₂O₄/graphite: 55 °C, 200 cycles 51.6% → 72.8% (JPS, 2014); 60 °C, 100 cycles 52.7% → 79.2%(Electrochim. Acta, 2014).
Disadvantages : Sensitive to water/acid, requiring low water and low acid electrolyte (≤10 ppm), and attention should be paid to synergistic effects with lithium salts when compounding.
minimum impedanceFast charging/low temperatureLUMO has the lowest energy level and is the most likely to be preemptively reduced at the negative electrode among the four types. It opens the ring at the graphite negative electrode at about 1.3–1.4 V (higher than 0.95 V of EC), forming a sulfur-rich, low-resistivity SEI of Li₂SO₃/ROSO₂Li, while stabilizing the high-voltage positive electrode CEI.
In collaboration with LiDFP, graphite/LFP cells achieve a 2C fast charging cycle life of over 2400 cycles ; Derivative bis-DTD: Ni65/graphite, stable cycling for 2500 cycles to end of life at 40 °C and 4.4 V (JES, 2024). Manufacturer data: Under a specific NCM811 formulation, 2% DTD reduces the 4.4 V SEI impedance by approximately 40% and maintains >90% after 500 cycles (highly affected by process, for engineering reference only).
Weakness : Poor bulk storage stability – approximately 50% DTD degradation occurs in room temperature premixed electrolyte after 15 weeks (bis-DTD has significantly improved this). Approximately 1% is commonly used in engineering.
Dimension FEC PST/PES MMDS DTD Priority response Typical dosage Core advantages Main shortcomings Representative data Typical Partner
A single additive is unlikely to simultaneously satisfy the requirements of "high pressure stability + low impedance + low gas production + wide temperature range," so compound formulations are the mainstream approach. Representative formulation:
PES-211D (2% PST + 1% DTD + 1% TTSPi) : Listed as one of the preferred blends for EC-based NCM/graphite (including high-pressure) by multiple studies and reviews. PST suppresses gas production, DTD increases negative electrode resistance, and TTSPi clears HF and dissolves metals, complementing each other.
FEC + LiDFP (2% FEC + 1% LiDFP) : Superior to PES for more easily oxidized systems such as lithium-rich manganese-based systems—FEC builds SEI, LiDFP builds robust CEI and suppresses "crosstalk". High voltage NCM442/cobalt-free NCM640 systems reach the end of life in about 200 cycles at 4.4 V and 40 °C (actual measurement verification is recommended for specific systems).
LiDFP is itself a powerful tool for constructing high-voltage cathodes : in the 4.8 V NCM811 system, LiDFP increases the capacity retention rate after 100 cycles from 73.3% to 91.8% (Electrochim. Acta, 2025).
VC + MMDS : Compared to using VC alone, 2% VC + 1% MMDS results in less coulombic efficiency loss, slower terminal capacity slippage, and lower interface impedance, making it suitable for long-life energy storage and high-end portable power supplies.
The underlying logic is the synergy of sulfur-containing and fluorine-containing components: sulfur-containing components (PST/MMDS/DTD) build sulfur-rich, low-resistance interfaces, while fluorine-containing components (FEC) and fluorinated lithium salts (LiDFP/LiFSI) improve oxidation window and thermal stability.
Dosage window : All four categories are prone to adverse effects with excessive dosage; the standard dosage is 0.5%–5% wt, requiring titration optimization based on the target system. High-temperature gas generation : PST is the benchmark; some FEC systems require caution regarding high-temperature gas generation, and it is advisable to combine with LiDFP or reduce the proportion. Storage and compatibility : DTD has poor bulk storage (preferably bis-DTD or freshly mixed and used); MMDS/sulfonyl lactones require low water and low acidity (≤10 ppm). Cost : DTD is approximately $200/kg (decreasing with domestic production); the cost of sulfonyl lactones and sulfur-containing disulfonates is gradually decreasing with the implementation of microchannel continuous flow processes.
High voltage, long lifespan (4.4–4.6 V) ternary lithium batteries → MMDS and PST batteries are preferred ; High-nickel + silicon/lithium metal anode → FEC preferred ; Fast charging/low temperature/low impedance → DTD (or bis-DTD) preferred . In actual mass production, compound formulations are almost always used, and the combination of "additives + positive electrode coating + dual salt/LHCE" synergistically pushes the window to 4.5–4.8 V.
The performance bottleneck of high-voltage ternary batteries has shifted from "material capacity" to "interface stability". FEC, PST, MMDS, and DTD approach the problem from four angles: fluorine-containing CEI/SEI, sulfur-containing gas production suppression, ultra-high sulfur content and ultra-thin CEI, and lowest impedance SEI. Each has solid data support, but there is no "universal single additive" - their advantages and disadvantages are complementary.
The future direction is highly clear: ① Sulfur-containing/fluorine-containing synergistic blends (PES-211D, FEC+LiDFP) will continue to be the mainstream; ② Derivative engineering (bis-DTD, fluorinated DTD, fluorine-nitrogen co-solvents) will compensate for the shortcomings of the parent compound in terms of storage/thermal stability; ③ Coupling with dual salts, LHCE, and cathode coating will push the operating window to 4.5–4.8 V. "High-performance additive design" will remain the key to success in the commercialization of high-voltage ternary lithium batteries for a long time to come.
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