From Charge Storage Mechanism to Performance: A Roadmap toward High Specific Energy Sodium‐Ion Batteries through Carbon Anode Optimization

353

320

Hard carbons (HCs) are promising anodes of sodium‐ion batteries (SIBs) due to their high capacity, abundance, and low cost. However, the sodium storage mechanism of HCs remains unclear with no consensus in the literature. Here, based on the correlation between the microstructure and Na storage behavior of HCs synthesized over a wide pyrolysis temperature range of 600–2500 °C, an extended “adsorption–insertion” sodium storage mechanism is proposed. The microstructure of HCs can be divided into three types with different sodium storage mechanisms. The highly disordered carbon, with d002 (above 0.40 nm) large enough for sodium ions to freely transfer in, has a “pseudo‐adsorption” sodium storage mechanism, contributing to sloping capacity above 0.1 V, together with other conventional “defects” (pores, edges, heteroatoms, etc.). The pseudo‐graphitic carbon (d‐spacing in 0.36–0.40 nm) contributes to the low‐potential (<0.1 V) plateau capacity through “interlayer insertion” mechanism, with a theoretical capacity of 279 mAh g−1 for NaC8 formation. The graphite‐like carbon with d002 below 0.36 nm is inaccessible for sodium ion insertion. The extended “adsorption–insertion” model can accurately explain the dependence of the sodium storage behavior of HCs with different microstructures on the pyrolysis temperature and provides new insight into the design of HC anodes for SIBs.

Section: Resultsmentioning

confidence: 96%

Section: Resultsmentioning

confidence: 99%

Extended “Adsorption–Insertion” Model: A New Insight into the Sodium Storage Mechanism of Hard Carbons

Sun

Guan

Liu

et al. 2019

353

320

“…[5,9] It is known that the electrochemical reversibility and the rate and life performance of LIBs and SIBs are to a great extent dictated by the SEI formation and its chemical/electrochemical reactivity and stability. [10][11][12][13] Ether-based electrolyte has been extensively used in lithium-air and lithiumsulfur batteries. [10][11][12][13] Ether-based electrolyte has been extensively used in lithium-air and lithiumsulfur batteries.…”

mentioning

confidence: 99%

Lithium‐Pretreated Hard Carbon as High‐Performance Sodium‐Ion Battery Anodes

Xiao

Soto

et al. 2018

Self Cite

109

large size of sodium-ions, there are also uniqueness in the development of SIB materials and the tuning of electrodeelectrolyte interphases, etc. [3] One of the most representative examples is that the intercalation of sodium-ion in graphite is thermodynamically inhibited by the interlayer distance, whereas the lithium-ion intercalation is favorable. [1,3] Hard carbon (HC) with expanded interlayer distance was investigated as the-state-of-the-art anode that allows sodium-ion storage via pore absorption, defect binding, and intercalation into the turbostratic graphenic nanodomains. [4][5][6][7] HC structure and the unique ion storage mechanism inevitably induce more reduction decomposition of the electrolyte, solid electrolyte interphase (SEI) formation, ion trapping, and hence lead to worse Coulombic efficiency than graphite. [8] Delicate control of the HC defects and surface area is therefore particularly required. [5,9] It is known that the electrochemical reversibility and the rate and life performance of LIBs and SIBs are to a great extent dictated by the SEI formation and its chemical/electrochemical reactivity and stability. [5,10,11] Concerning this, attempts also have been made to tune the SEI coverage, thickness, stability, and ionic conductivity, etc., by developing novel electrolytes or electrolyte additives that decompose preferentially to form SEI or tailoring the surface area and physiochemical properties of the carbon materials. [10][11][12][13] Ether-based electrolyte has been extensively used in lithium-air and lithiumsulfur batteries. [14,15] The solvent-in-salt electrolyte design also has expanded the application of ether electrolyte to LIBs with graphite anodes and high-voltage cathodes. [16,17] In SIBs, ether Hard carbon (HC) is the state-of-the-art anode material for sodium-ion batteries (SIBs). However, its performance has been plagued by the limited initialCoulombic efficiency (ICE) and mediocre rate performance. Here, experimental and theoretical studies are combined to demonstrate the application of lithium-pretreated HC (LPHC) as high-performance anode materials for SIBs by manipulating the solid electrolyte interphase in tetraglyme (TEGDME)-based electrolyte. The LPHC in TEGDME can 1) deliver > 92% ICE and ≈220 mAh g −1 specific capacity, twice of the capacity (≈100 mAh g −1 ) in carbonate electrolyte; 2) achieve > 85% capacity retention over 1000 cycles at 1000 mA g −1 current density (4 C rate, 1 C = 250 mA g −1 ) with a specific capacity of ≈150 mAh g −1 , ≈15 times of the capacity (10 mAh g −1 ) in carbonate. The full cell of Na 3 V 2 (PO 4 ) 3 -LPHC in TEGDME demonstrated close to theoretical specific capacity of ≈98 mAh g −1 based on Na 3 V 2 (PO 4 ) 3 cathode, ≈2.5 times of the value (≈40 mAh g −1 ) with nontreated HC. This work provides new perception on the anode development for SIBs.

“…[119,120] The abundance of micropores in hard carbon materials and their evolution with heat treatment temperature is conceptually described by Dahn's "falling cards model," wherein micropores merge and enlarge as graphene layers stack, resulting in large, enclosed pores at elevated pyrolysis temperature. [119,120] The abundance of micropores in hard carbon materials and their evolution with heat treatment temperature is conceptually described by Dahn's "falling cards model," wherein micropores merge and enlarge as graphene layers stack, resulting in large, enclosed pores at elevated pyrolysis temperature.…”

Section: Disordered Carbonsmentioning

confidence: 99%

“…[169] Despite the rapid growth in research efforts over the past decade, carbon anodes still limit SIB commercialization, with high energy density at the full cell level requiring good capacity, low average oxidation voltage, and sufficient first cycle and long-term Coulombic efficiency. [120] [170] However, while hard carbon anodes offer the greatest feasibility and potential for first generation SIBs, they are limited by poor rate capability due to the low voltage plateau that can be cut off easily during high polarization.…”

Section: Wwwadvancedsciencenewscommentioning

confidence: 99%

Carbon Anodes for Nonaqueous Alkali Metal‐Ion Batteries and Their Thermal Safety Aspects

Adams

Varma

2019

140

electrolyte, but were limited by significant safety concerns, such as thermal runaway, arising from the lithium metal anode and its tendency for dendrite formation. These dendrites develop and grow due to uneven lithium deposition caused by irregularities in the solid electrolyte interphase (SEI) passivation layer, which forms via electrolyte decomposition on the highly reactive lithium anode surface. Eventually, repeated cycling can result in an internal short circuit via puncturing of the separator by dendrites for cell failure and possible thermal runaway. Extensive research was conducted to mitigate these concerns, primarily by electrolyte manipulation to improve SEI uniformity or implementation of a polymer based solid-state electrolyte. However, this issue has still not been fully overcome even to this day, resulting in the alternative strategy of replacing the lithium anode with an intercalation-based storage material.The development of these "rocking chair" batteries began in the 1980s, where charging transfers lithium from cathode to anode and discharging reverses this process, with the first practical demonstrations by Scrosati. [2] Substantial progress came with the discoveries of the standard electrode materials: LiCoO 2 cathode by Goodenough and co-workers in 1981, [3] and graphite anode by Yazami and Touzain in 1983. [4] The first cell comprising a carbon anode and LiCoO 2 cathode was tested by Yoshino in 1983, which exhibited superior safety features as compared to lithium metal anode. [5] Optimization of the electrolyte came from replacing propylene carbonate (PC), which underwent a decomposition reaction with graphite due to cointercalation and exfoliation, to ethylene carbonate (EC)/ diethyl carbonate (DEC) mixtures. A schematic of this mature LIB is shown in Figure 1a. Sony commercialized the lithiumion battery (LIB) in 1991, where the new electrochemistry demonstrated advantages of higher energy density, longer life time, and no memory effect, as compared to the conventional nickel-cadmium and nickel-metal hydride secondary cells. Further progress and improvement in electrolyte, electrode microstructure, and cell manufacturing has led to a doubling of energy density for LIBs since their inception, almost 30 years later, despite their analogous operation mechanism. [6] Additionally, from their initial application for handheld electronics, LIBs are now seeing rapid utilization in vehicle electrification, with the global LIB capacity projected to double to 278 GWh per year Since their commercialization by Sony in 1991, graphite anodes in combination with various cathodes have enabled the widespread success of lithium-ion batteries (LIBs), providing over 10 billion rechargeable batteries to the global population. Next-generation nonaqueous alkali metal-ion batteries, namely sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs), are projected to utilize intercalation-based carbon anodes as well, due to their favorable electrochemical properties. While traditionally graphite anodes have d...