Interfacing Si‐Based Electrodes: Impact of Liquid Electrolyte and Its Components

Abstract

As the demand for mobile energy storage devices has steadily increased during the past decades due to the rising popularity of portable electronics as well as the continued implementation of electromobility, energy density has become a crucial metric in the development of modern batteries. It was realized early on that the successful utilization of silicon as negative electrode material in lithium‐ion batteries would be a quantum leap in improving achievable energy densities due to the roughly ten‐fold increase in specific capacity compared to the state‐of‐the‐art graphite material. However, being an alloying type material rather than an intercalation/insertion type, silicon poses numerous obstacles that need to be overcome for its successful implementation as a negative electrode material with the most prominent one being its extreme volume changes on (de‐)lithiation. While, as of today, a plethora of different types of Si‐based electrodes have been reported, a universally common feature is the interface between Si‐based electrode and electrolyte. This review focuses on the knowledge gained thus far on the impact of different liquid electrolyte components/formulations on the interfaces and interphases encountered at Si‐based electrodes.

Electron and Ion Transport in Lithium and Lithium-Ion Battery Negative and Positive Composite Electrodes

“…Batteries are complex systems including electrochemically active materials typically as part of a composite containing a conductive additive and binder system . Further, electrolytes are present that allow transport of ions internally, allowing current flow external to the battery. − Internal membranes play a critical role in allowing charge transport within the cell yet preventing electrical contact . The following introductory paragraphs provide the reader references for information on the battery components beyond the scope of this review.…”

“…It is noted that the liquid electrolyte is a critical component of Li-based battery systems as it facilitates the effective shuttling of electroactive ions between the negative and the positive electrodes. − The electrolytes must satisfy a myriad of criteria to be effectively utilized in a battery system including sufficient ionic conductivity, stability over the relevant voltage range, appropriate viscosity, and formation of an interphase on the surface of the battery electrodes with sufficient ion transport to sustain the needed electrochemistry. − ,− In addition, from a safety perspective, nonflammability is preferred as flammable electrolytes can pose a significant danger in the event of a thermal runaway or other battery failure especially as larger form factor Li-ion batteries proliferate in technologies such as electric vehicles. ,− , This important topic is beyond the scope of this review, and the reader is referred to the recent references and reviews cited for further insight on the topic.…”

Si-Cr alloy anodes for Lithium-ion batteries Synthesized by a High-energy Ball-milling method: Microstructure, Carbon Coating, and Electrochemistry

“…First, Si's huge volume change in the lithiation-delithiation processes (± 280%) would lead to Si particle fractures with poor electrical contact and mechanical failure [6,9,10]. Secondly, the fractures would expose the new surface of Si bulk to electrolyte causing the repeated growth of solid electrolyte interface (SEI) film irreversibly consuming Li + [11]. Besides, the low electrical conductivity (∼10 -5 S• cm -1 ) of intrinsic Si semiconductors will bring about the slow reaction kinetics with Li + and negatively affects the electrochemical performance [12].…”

Practical Implementation of Magnetite-Based Conversion-Type Negative Electrodes via Electrochemical Prelithiation

“…The practical capacity of the state-of-the-art (SOTA) intercalation-type negative electrodes such as graphite and Li 4 Ti 5 O 12 (LTO) are limited due to the limited amount of Li + ions that can be hosted in their crystal structures. Thereby, they cannot satisfy the mentioned increasing demands even combined with a high energy density positive electrode. ,, So-called “alloying-type” electrode materials such as silicon (Si) can deliver a practical specific capacity above 3500 mAh g –1 at room temperature. − However, commercial application of alloying-type negative electrodes is hindered by extreme volume changes upon cycling, causing low Coulombic efficiency and continuous loss of active Li + as a result of solid electrolyte interphase (SEI) formation throughout cycling . Additionally, alloying-type negative electrode materials, such as Si, cannot be used in their natural form (SiO 2 ); thus, the processing cost of the natural ores increases the total cost of the battery …”

“…7−9 However, commercial application of alloying-type negative electrodes is hindered by extreme volume changes upon cycling, causing low Coulombic efficiency and continuous loss of active Li + as a result of solid electrolyte interphase (SEI) formation throughout cycling. 10 Additionally, alloying-type negative electrode materials, such as Si, cannot be used in their natural form (SiO 2 ); thus, the processing cost of the natural ores increases the total cost of the battery. 11 Transition-metal oxides (TMOs) based on a conversiontype storage mechanism have attracted much attention as negative electrode active materials.…”