NMC111 is considered the most commonly used commercial cathode with a theoretical capacity of 278 mAh g⁻¹ with an operating voltage of 4.3 V. Table 14 summarizes all the electrolyte and additive combinations for NMC111. Ohzuku et al. first reported the solid-state synthesis of this material and obtained 150 mAh gm⁻¹ of capacity with 1 M LiPF₆ in EC: DMC (3:7, v/v) within a voltage range of 2.5–4.2 V ^[1][120]. Moreover, 0.5 wt% of Tris(trimethylsilyl) phosphite (TMSPi) as an additive can push the upper cut-off voltage to 4.5 V ^[2][64]. Other linear carbonate electrolytes, such as DEC and EMC, are also used along with EC to reduce viscosity. For example, 1 M LiPF₆ in EC: EMC (3:7, w/w) (commonly known as LP57) is most commonly used by prominent research groups. Gasteiger et al. used LP57 to study the effect of upper cut-off voltage (UCV) on NMC111/graphite ^[3][14]. The highest specific capacity of 183.4 mAh g⁻¹ was achieved at 4.6 V but with poor capacity retention, whereas, at 4.4 V, the capacity was well maintained for 295 cycles at 1 C. Adding different electrolyte additives such as VC, PES, MMDS, DTD, TTSPi, and TTSP with a control electrolyte improves the cycling performance of an NMC/graphite pouch cell at various temperature ranges ^[4][5][6][65,72,121]. Ternary electrolyte solvent systems along with additives such as 3,3′-(ethylenedioxy)dipropiononitrile (EDPN), 3,3′-(sulfonyl)dipropionitrile (SDPN) and di(methylsulfonyl) methane (DMSM) at UCV of 4.6 V show higher cathode voltage performances ^[7][8][9][122,123,124]. Boron-based additive trimethyl boroxine (TMB) with 1 M LiPF₆ in EC, DEC, and DMC enhances the cycle stability from 40% to 99% after 300 cycles at a 1 C rate ^[10][125]. Apart from carbonate electrolytes, thermally stable cyano-ester solvents with 1 M LiTFSI salt and 3 wt% FEC perform well in the full cell ^[11][126].

^][80,142]. Zuo et al. exhibited lower impedance due to interfacial modification by adding only 1 wt% of LiBF₄ in the baseline electrolyte ^[35][143]. A novel electrolyte additive, N, O-bis(trimethylsilyl)-trifluoroacetamide (NOB), is a nitrogen and silicon-containing compound that acts as an HF scavenger sacrificial additive ^[36][144]. Dimethyl sulfite (DMS) is a sulfur-containing electrolyte additive that performs under low temperatures of −10 °C and outperforms commercially available additives ^[37][145]. Zuo et al. retained about 92.3% of initial capacity by adding 0.5 wt% of tris(trimethylsilyl)borate (TMSB) due to forming a thinner film on the surface ^[38][146]. Adding 1,10-sulfonyldiimidazole (SDM) can improve the electrochemical performance at high voltages ^[39][147]. The modified version of DTD, namely [4,4′-bi(1,3,2-dioxathiolane)] 2,2′-dioxide (BDTD), is also developed as a cathode additive, which improved the cycle retention up to 91.6% ^[40][148]. Shi and his co-workers used the synergistic effect of lithium sulfide (Li₂S) salt and acetonitrile (AN) solvent additive and developed a stable cathode–electrolyte interface (CEI) layer, which reduced the electrolyte decomposition ^[41][149].

. Lan et al. proposed a new additive, phenyl trans-styryl sulfone (PTSS), which builds a stable interfacial film on the surface during the charge–discharge process ^[67][171]. The multifunctional film-forming additive, 4-fluorobenzene sulfonate (PFBS), constructs a stable interface layer on both positive and negative electrodes and protects the electrolyte solvent from decomposition and structural degradation ^[68][172]. Adiponitrile (ADN) is a nitrile group that contains additives favorable for high-voltage performance and low flammability ^[69][173].

Ni-rich NMC cathodes (NMC442) are cheaper by reducing the compound’s cobalt amount, allowing for a charge potential of 4.7 V without any structural changes. The conventional electrolyte starts to degrade over the positive electrode above 4.3 V. All the electrolyte–additive combinations for NMC442 are tabulated in Table 25. Aiken et al. performed NMC442/graphite pouch cells at higher voltage (>4.2 V) in different temperature conditions and observed less gaseous product formation with 2 wt% PES additive in baseline electrolytes ^[22][23][134,135]. Nelson et al. studied the impedance growth of full cells after long-term cycling and reduced them with appropriate electrolyte additives ^[24][136]. The ternary mixture of additives such as PES211 is beneficial in mitigating impedance growth and retains its capacity up to 85% after 500 cycles at 4.4 V under 45 °C ^[5][25][72,137]. Petibon et al. tried to develop a new electrolyte combination free of EC that works better in all required electrochemical aspects ^[26][138]. Fluorinated electrolytes and 1 wt% PES showed better cycle stability of about 80% than binary and ternary additives-based EC: EMC (3:7, v/v) electrolytes ^[27][139]. As a high-voltage electrolyte, EC co-solvent can be replaced by sulfolane (SL), which has high anodic stability ^[28][140]. Rong and his co-workers have studied ternary electrolyte combinations and Tris (trimethylsilyl) phosphate (TMSP) as an additive for an NMC422 full cell, and it exhibited better rate performance ^[29][141].

Liu et al. applied one of the most popular additive VCs in an NMC532/graphite full cell and tested it at an elevated temperature. VC-containing electrolyte cells produce fewer decomposition products than free ones ^[30][60]. A fluorinated additive such as FEC was studied in a Li metal battery and performed excellently ^[31][61]. Table 36 summarizes all the electrolyte additive combinations with NMC532. Phosphorus-containing electrolyte additive tris(trimethylsilyl)phosphite (TMSPi) and triethyl phosphite (TEPi) produce a protective surface film on the cathode side ^[32][68]. Salt-type additives such as lithium difluoro phosphate (LiDFP) are quite popular in Ni-rich cathode-based full cells with graphite as an anode at various temperatures ^[33][34

NMC622 is a more recent material than other matured NMC cathodes, and commercialization needs further modification. The advantage of increased energy density with Ni content attracts commercialization and reduces battery pack costs. Electrolyte additives or solvents that are stable at the upper cut-off voltage need to be developed to utilize the full potential of NMC662. The electrolyte optimization in a combination of solvents and additives for NMC622 is detailed in Table 47. Gasteiger et al. performed testing of NMC622/graphite full cells with different upper cut-off potential and temperature conditions to observe oxygen release due to electrolyte decomposition ^[46][154]. Small amounts of 1,4-phenylene diisocyanate (PPDI) acted as HF and H₂O scavengers and film-forming additives over the NMC622 cathode surface in pouch cells and exhibited long-term cyclability at a 1 C rate ^[47][155]. Liao et al. introduced a new kind of additive, namely 1-(2-cyanoethyl) pyrrole (CEP), which suppresses HF formation from cycling at high voltages ^[48][156]. Hexamethylene diisocyanate (HDI) ^[49][157] and 4-propyl-^[50][51][52][1,3,2]dioxathiolane-2,2-dioxide (PDTD) ^[53][158] in 1 M LiPF₆ in EC: EMC (1:2, w/w) can reduce the interfacial impedance and increase cycling performance. Functional additives such as (3-(N, N-dimethylamino) diethoxypropyl) pentamethyldisiloxane (DSON) ^[54][159], p-toluenesulfonyl fluoride (pTSF) ^[55][160], triisopropyl borate (TIB) ^[56][161], diphenyldimethoxysilane (DPDMS) ^[57][162], 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetra- siloxane (ViD4) ^[58][163], 3-hexylthiophene (3HT) ^[59][164], and tris(hexafluoroisopropyl)phosphate (THFP) ^[60][165] are assigned with different roles, such as film-forming ability, HF scavenger, gas-suppressing agent, and thermal safety.

Another Ni-rich NMC, NMC811, is also quite popular in battery research labs due to its high specific capacity of 200 mAh gm⁻¹ at 4.3 V and low cost (less cobalt). However, its low cycling stability at high voltages and inferior safety issue makes it a poor choice for a commercial approach. An optimized combination of electrolytes with its additives enhances the performance of NMC811 with both graphite and lithium metal anodes. The battery metrics of NMC811 with various electrolyte–additive combinations are tabulated in Table 58. Gasteiger et al. studied oxygen release and cycle stability in NMC811/graphite full cells at different end-of-charge potentials ^[3][14]. A combination of VC and TMSPi additives in 1 M LiPF₆ in EC: DMC (1:1, v/v) enhances the capacity retention and achieves 91% after 200 cycles ^[65][67]. The addition of triphenylphosphine oxide (TPPO) to the baseline electrolyte improves the cell’s first coulombic efficiency and specific capacity ^[66][170]

3,3-diethylene di-sulfite (DES) forms a stable protection layer on the cathode surface and assists in the Li⁺ ion extraction/insertion process ^[70][174]. Cheng et al. proposed binary additives, which are comprised of lithium difluoro(oxalato)borate (LiDFOB) and tris(trimethylsilyl)phosphate (TMSP), and checked their capability in both half-cell and full-cell and even in the commercial pouch cell at different conditions. The synergistic effect of both additives produces B-, Si-, and F-rich interface layers, which protect electrolyte decomposition, gas formation, and the cathode from structural degradation ^[71][175]. Film-forming additives such as tris(trimethylsilyl)borate (TMSB) ^[72][176], triphenyl phosphate (TPPa) ^[73][177], phenyl vinyl sulfone (PVS) ^[74][178], and 2,4,6-triphenyl boroxine (TPBX) ^[75][179] are also reported in NMC811-cathode-based Li-metal batteries. Multifunctional organic electrolyte additives such as ethoxy(pentafluoro) cyclotriphosphazene (PFN) ^[76][180] and trimethylsilyl trifluoroacetate (TMSTFA) ^[77][181] act as both the HF/H₂O scavenger and the stable CEI layer-forming agent. Hu et al. reported a functional electrolyte additive, cyclopropane sulphonic amide (CPSA), combined with ether electrolyte to improve electrochemical properties ^[78][182].