Dual-Functional Electrolyte Additives toward Long-Cycling Lithium-Ion Batteries: Ecofriendly Designed Carbonate Derivatives

Abstract

Long-term stability of the solid electrolyte interphase (SEI) and cathode–electrolyte interface (CEI) layers formed on anodes and cathodes is imperative to mitigate the interfacial degradation of electrodes and enhance the cycle life of lithium-ion batteries (LIBs). However, the SEI on the anode and CEI on the cathode are vulnerable to the reactive species of PF5 and HF produced by the decomposition and hydrolysis of the conventional LiPF6 electrolyte in a battery inevitably containing a trace amount of water. Here, we report a new class of cyclic carbonate-based electrolyte additives to preserve the integrity of SEI and CEI in LIBs. This new class of additives is designed and synthesized by an ecofriendly approach that involves fixing CO2 with functional epoxides bearing various reactive side chains. It was found that the cyclic carbonates of 3-(1-ethoxyethoxy)-1,2-propylene carbonate and 3-trimethoxysilylpropyloxy-1,2-propylene carbonate, possessing high capability for the stabilization of Lewis-acidic PF5, exhibit a capacity retention of 79.0% after 1000 cycles, which is superior to that of the pristine electrolyte of 54.7%. Moreover, TMSPC has HF-scavenging capability, which, along with PF5 stabilization, results in enhanced rate capability of commercial LiNi0.6Mn0.2Co0.2O2 (NCM622)/graphite full cells, posing a significant potential for high-energy-density LIBs with long cycle stability.

(3-Aminopropyl)triethoxysilane as an Electrolyte Additive for Enhancing the Thermal Stability of Silicon Anode in Lithium-Ion Batteries

“…Based on the results, we propose two possible pathways through which APTES stabilizes the carbonate-based electrolyte (Figure ). First, the nucleophilic nitrogen atom (III) with a lone pair of electrons in APTES may form a compound with PF 5 , suppressing the formation of POF 3 , HF, or that fluorophosphate, leading to the enhanced thermal stability of the electrolyte. , Second, APTES may act as a HF scavenger by breaking its Si–O bond, preventing further reaction between HF and the solvents. , …”

Multifunctional Electrolyte Additive for Bi-electrode Interphase Regulation and Electrolyte Stabilization in Li/LiNi0.8Co0.1Mn0.1O2 Batteries

“…Fortunately, all these abovementioned challenges from cathode, anode, and electrolyte aspects could be simultaneously conquered by developing multifunctional electrolyte additives to tailor bi-electrodes−electrolyte interphases and stabilize the electrolyte. 15 As reported, a series of additives such as borates, 18−20 sulfonates/sulfates, 21−23 phosphates/phosphites, 24−26 nitriles, 27,28 anhydrides, 29−31 and so forth can boost the electrochemical performances of lithium batteries, whereas most additives exhibit a single function so that regulation of the CEI/SEI films and stabilization of the electrolytes cannot be taken into account at the same time. 32 Toward the multifunctional roles for electrolyte additives, various functional groups are needed.…”

“…The principal reason is that the naturally formed cathode-/solid-electrolyte interphases (CEI/SEI) in carbonate-based electrolytes are too fragile to prohibit the following parasitic reactions on the surface of the cathode and anode upon cycling. − Additionally, LiPF 6 is sensitive to H 2 O to generate hydrogen fluoride (HF) and fluorophosphates, which will inevitably erode CEI/SEI films and electrode materials, directly leading to capacity loss. − Worse yet, corrosive HF accelerates the transition metal (TM) dissolution of NCM811 and the resulting TM deconstructs the SEI film when migrating to the anode side. Fortunately, all these abovementioned challenges from cathode, anode, and electrolyte aspects could be simultaneously conquered by developing multifunctional electrolyte additives to tailor bi-electrodes–electrolyte interphases and stabilize the electrolyte. − …”

Multifunctional Electrolyte Additive Stabilizes Electrode–Electrolyte Interface Layers for High-Voltage Lithium Metal Batteries

“…Moreover, the trace water in the electrolyte accelerates the decomposition of a lithium salt (LiPF 6 ) to produce hydrofluoric acid (HF), as shown in the eqs 1−4. 13,14 Highly corrosive HF can attack the electrode− electrolyte interface, leading to degradation of battery performance. Especially, the NMC811 cathode is vulnerable to damage by HF, resulting in increased side reaction, accelerated dissolution of transition metal ions and oxygen escape, and so forth.…”

“…With prolonged cycling, the decomposition of solvents and lithium salt makes the SEI layer thicker, resulting in a larger interfacial impedance and low transport rate of lithium ions among the SEI layer. Moreover, the trace water in the electrolyte accelerates the decomposition of a lithium salt (LiPF 6 ) to produce hydrofluoric acid (HF), as shown in the eqs –. , Highly corrosive HF can attack the electrode–electrolyte interface, leading to degradation of battery performance. Especially, the NMC811 cathode is vulnerable to damage by HF, resulting in increased side reaction, accelerated dissolution of transition metal ions and oxygen escape, and so forth. , Constructing a stable passivation layer [SEI/cathode electrolyte interface (CEI)] can alleviate the challenges faced by the lithium metal anode and Ni-rich high-voltage NMC811 cathode, and various strategies have been employed, with electrolyte additives being the most convenient and cost-effective method. …”