Mechanistic Basis of Enhanced Capacity Retention Found with Novel Sulfate-Based Additive in High-Voltage Li-Ion Batteries

Abstract

1,3-propanediolcyclic sulfate (PCS) was employed as a novel sulfate-based additive for high-voltage battery applications to reduce the capacity fading that occurs during cycling. Molecular energy calculations and cyclic voltammetry (CV) both proved the PCS was reduced earlier than the ethylene carbonate (EC), which suggests a better solid electrolyte interface (SEI) was formed. The electrochemical impedance spectra results confirmed the denser SEI formed by addition of PCS additive. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and scanning electron microscopy/energy dispersive X-ray (SEM/EDX) analysis reveal the addition of PCS is able to protectively modify the anodic SEI layer in a manner that suppresses anodic deposition of manganese oxide species resulting from the "cross-talk" effect.

Prescribing Functional Additives for Treating the Poor Performances of High‐Voltage (5 V‐class) LiNi0.5Mn1.5O4/MCMB Li‐Ion Batteries

“…2018, 8, 1701398 (Figure 7a, Top) demonstrate two peaks at ≈169.8 and ≈164.6 eV corresponding to Li 2 SO 4 /PCS-like species and alkyl sulfide species (such as C-S-S-C), respectively. [32,46,54,57] Their passivating properties can be ascribed to the good adhesion to electrode surface because of their inherent ionic structure and polarity. [68,69] Compared to the carbonate solvents, the calculated LUMO (−0.337 eV) and HOMO (−8.791 eV) energies of PCS are both lower (Figure 1; Figure S1, Supporting Information), indicating that, theoretically, the PCS is preferentially to be reduced and more difficult to be oxidized.…”

“…Specifically speaking, functional additives with a higher HOMO energy than carbonate solvents will be preferentially oxidized to modify the cathode SEI layer, while those with a lower LUMO energy than carbonate solvents will be preferentially reduced to modify the anode SEI layer. [31,32,[54][55][56][57][58][59] The most typical electrochemical reduction species of these organic sulfur-containing compounds are passivating ROSO 2 Li and Li 2 SO 3 , which can facilitate lithium ion diffusion through SEI layer and prevent the excessive reductive decomposition of carbonate solvents (such as propylene carbonate). [35,[48][49][50][51][52][53] With a higher HOMO energy relative to carbonate solvents, TMSP easily undergoes electrochemi cal oxidations and promotes the formation of a protective SEI layer on the surface of high-voltage cathode materials (such as LiNi 0.5 Mn 1.5 O 4 , LiNi 0.5 Co 0.2 Mn 0.3 O 2 , overlithiated layered oxide).…”

“…[2] Recently, tris(trimethylsilyl) phosphite (TMSP) has been intensively demonstrated to be an effective functional additive for performance enhancement of highvoltage LIBs. [32,46,54,57] With a lower LUMO energy than carbonate solvent, 1,3-propanediolcyclic sulfate (PCS) can be preferentially reduced to modify the anodic SEI layer by minimizing the deposition of Mn-species onto the negative electrode in LiNi 0.5 Mn 1.5 O 4 / MCMB (graphitic mesocarbon microbeads) battery system. Moreover, TMSP has the ability of stabilizing LiPF 6 salt and scavenging the erosive hydrofluoric acid (HF), thereby the metal dissolution behavior on cathode surface can be significantly alleviated.…”

“…[35,[48][49][50][51][52][53] With a higher HOMO energy relative to carbonate solvents, TMSP easily undergoes electrochemi cal oxidations and promotes the formation of a protective SEI layer on the surface of high-voltage cathode materials (such as LiNi 0.5 Mn 1.5 O 4 , LiNi 0.5 Co 0.2 Mn 0.3 O 2 , overlithiated layered oxide). [32] However, the capacity retention of full cell with single PCS is still unsatisfactory (90% after 30 cycles, at C/10 rate). As for LiNi 0.5 Mn 1.5 O 4 /graphite system, the addition of single TMSP additive can only obtain moderate capacity retention (81% after 100 cycles, at C/2 rate and 30 °C).…”

Electrolytes for electrochemical energy storage

“…The mechanism is that additives are preferably oxidised on the positrode surface to generate a stable interfacial layer, which inhibits the detrimental reaction of electrolytes at high positive potentials. Reported additives include (1) inorganic compounds such as lithium bis(oxalato)borate (LiBOB) [152][153][154][155][156][157][158] and lithium difluoro(oxalato)borate (LiDFOB) 159 , (2) phosphite-derivatives such as trimethyl phosphite (TMP) 160 , tris(hexafluoro-iso-propyl) phosphate (HFiP) 161,162 , tris(trimethylsilyl) phosphite (TMSP) [163][164][165][166] , (Ethoxy) pentafluorocyclotriphosphazene (PFPN), 167 and 1-propylphosphonic acid cyclic anhydride (PACA) 168 , (3) sulfonate esters such as 1,3-propane sultone (PS) 169 , 1,3-propanediol cyclic sulfate (PCS) 170 , and (4) some carboxyl anhydrides 169,171,172 . These additives, some of which are shown wither their molecular structures in Fig.…”