Towards high energy density sodium ion batteries through electrolyte optimization

Abstract

International audienceA comprehensive study is reported entailing optimization of sodium ion electrolyte formulation and compatibility studies with positive and negative electrode materials. EC:PC:DMC and EC:PC:DME were found to exhibit optimum ionic conductivities and lower viscosities. Yet, hard carbon negative electrode materials tested in such electrolytes exhibit significant differences in performance, rooted in the different resistivity of the SEI, which results in too large polarization and concomitant loss of capacity at low potentials when DME is used as a co-solvent. EC0.45:PC0.45:DMC0.1 was found to be the optimum composition resulting in good rate capability and high capacity upon sustained cycling for hard carbon electrodes. Its compatibility with positive Na3V2(PO4)2F3 (NVPF) electrodes was also confirmed, which led to the assembly of full Na-ion cells displaying an operation voltage of 3.65 V, very low polarisation and excellent capacity retention upon cycling with ca. 97 mA h g−1 of NVPF after more than 120 cycles together with satisfactory coulombic efficiency (>98.5%) and very good power performance. Such values lead to energy densities comparable to those of the current state-of-the-art lithium-ion technology

Is single layer graphene a promising anode for sodium-ion batteries?

“…3, the cells start to show good electrochemical performance in terms of cycling stability as well as coulombic efficiency (≥ 90 %, ≥ 85 % for NaClO 4 in PC electrolyte) after 20 discharge-charge cycles. However, during the initial cycles (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20), these electrochemical parameters, particularly the capacity retention, were much lower.…”

“…To this end, a variety of electrode materials [1][2][3][4], cathode and anode, and electrolytes [1,2,5,6] for SIBs have been investigated, mainly, in the last two years. The results of the research in the field of cathode materials, several of them obtained by the simple replacement of lithium by sodium in the analogue compound, appear promising with a number of layered transition metal oxides, phosphates and fluorophosphates showing acceptable reversible capacity, stability and relatively high operating potentials [1,4].…”

“…Moreover, the sodium graphite intercalation compounds (NaC x with x = 36, 16,12,8,6) are unstable [9]. In fact, they do not exist under moderate conditions, which was reported to be a consequence of the clash between the graphite structure (graphite is stressed when some Na + ions intercalate into it) and the size of the Na + ion (its ionic radius is approximately 0.3 Å larger than that of Li + ion, this difference leading to changes in thermodynamic and kinetic properties) [9,10].…”

Solvation structure in dilute to highly concentrated electrolytes for lithium-ion and sodium-ion batteries

“…Lithium-ion batteries (LIBs) represent one of the most promising technologies, readily used already today, but recently also the prospect of sodium-ion batteries (SIBs) has re-emerged and grown into an active research topic. The cost of sodium is more than an order of magnitude lower than lithium and sodium is more than three orders of magnitude more abundant, while at the same time SIBs promise a similar level of performance as LIBs [3][4][5][6][7], rendering them future candidates for grid storage [8]. Moreover, the possibility to replace the Cu current collector in LIBs for Al current collectors at both sides in SIBs could push the energy densities further and again lower cost [6,9].…”

Optimization of Na-Ion Battery Systems Based on Polyanionic or Layered Positive Electrodes and Carbon Anodes

“…Negative electrodes based on alloying reactions, conversion reactions involving oxides, and also insertion reactions have been studied, with the best compromise in terms of performances and costs being hard carbons. Turning to the electrolytes, aside from the use of Na-salts (NaPF 6 , NaTFSI), the solvents are nearly identical, involving mixtures of cyclic carbonates (EC, PC) and non-cyclic carbonates (DMC) 3 with the use of fluoroethylene carbonate (FEC) 4 as additive like in Li-ion cells. The major difference encountered so far, and somewhat troublesome when studying Nahalf cells, lies in the physical/chemical nature of the solid electrolyte interface (SEI) layer formed and its stability upon cycling.…”