A P2‐Type Layered Superionic Conductor Ga‐Doped Na₂Zn₂TeO₆ for All‐Solid‐State Sodium‐Ion Batteries

Abstract

Here, a P2-type layered Na Zn TeO (NZTO) is reported with a high Na ion conductivity ≈0.6×10 S cm at room temperature (RT), which is comparable to the currently best Na Zr Si P O NASICON structure. As small amounts of Ga substitutes for Zn , more Na vacancies are introduced in the interlayer gaps, which greatly reduces strong Na -Na coulomb interactions. Ga-substituted NZTO exhibits a superionic conductivity of ≈1.1×10 S cm at RT, and excellent phase and electrochemical stability. All solid-state batteries have been successfully assembled with a capacity of ≈70 mAh g over 10 cycles with a rate of 0.2 C at 80 °C. Na nuclear magnetic resonance (NMR) studies on powder samples show intra-grain (bulk) diffusion coefficients D on the order of 12.35×10 m s at 65 °C that corresponds to a conductivity σ of 8.16×10 S cm , assuming the Nernst-Einstein equation, which thus suggests a new perspective of fast Na ion conductor for advanced sodium ion batteries.

Na1.5La1.5TeO6: Na+ conduction in a novel Na-rich double perovskite

“…26,27 In the case of the P2-type Na 2 M 2 TeO 6 tellurates oxides materials, the original work reported conductivities of 10 À6 S cm À1 which have been now optimized to reach the mS cm À1 range. 5,12 It is reasonable to expect therefore that similar improvements are possible for the Na 1.5 La 1.5 TeO 6 double perovskite presented here through, for example, aliovalent doping or morphological control.…”

“…40 The m + SR measurements indicate that the activation energy required for local Na + diffusion is 0.163(9) eV. This low activation energy is similar to related oxide materials, such as the Ga-doped Na 2 Zn 2 TeO 6 with an activation energy of 0.12 eV as observed from NMR measurements, 12 or b 0 -alumina single crystals with activations energies in the 0.12-0.16 eV range. 41 The higher activation energy values obtained from the macroscopic EIS measurements which probes long range Na + conduction through multiple intra-grain crystalline sites and grain boundaries, compared to microscopic m + SR measurements which are more sensitive to individual Na + hops within the crystalline grain, could have its origin in the contribution to the resistance from grain boundaries to ionic conduction which is virtually invisible to m + SR. Lower conductivity values and higher energy barriers to diffusion could also result from the presence of La 3+ ions in the A-sites, which could hinder longrange Na + conductivity.…”

“…Here, we present a new sodium-rich solid-state electrolyte Na 1.5 La 1.5 TeO 6 , where the robust perovskite framework and redox stability of the Te 6+ ions [8][9][10][11][12] could enable its use in combination with high voltage electrodes.…”

An idealised approach of geometry and topology to the diffusion of cations in honeycomb layered oxide frameworks

“…However, K + has a vastly larger ionic radius with a correspondingly larger inter-layer distance and hence forms weaker inter-layer bonds. Generally, A + cations with larger ionic radii such as K + and Na + form weaker inter-layer bonds in the aforementioned compositions resulting in layered oxides with prismatic or octahedral coordination of alkali metal and oxygen (technically referred to as P-type or O-type layered structures, respectively) 1, [3][4][5][6][7][8][9][10][11][12][13][14][15][16]19,20,27,[34][35][36] . The weaker inter-layer bonds in prismatic layered (P-type) structures create more open voids within the transition metal layers allowing for facile two-dimensional diffusion of alkali atoms within the slabs 41 .…”

Advanced Characterization Techniques for Interface in All‐Solid‐State Batteries

“…For ASSBs interface, SEM technique is usually used for observation of morphology of interface between grain of SEs in ASSBs, examining the morphology and determining element composition (combine with EDX) of interface on SEs or electrode. [ 109 ] For example, Li et al [ 110 ] used SEM to observe the particles of Na 2‐ x Zn 2‐ x Ga x TeO 6 ( x = 0, 0.05, 0.1, 0.15) and found that the morphology and density are not influenced by Ga doping; Luo et al [ 111 ] used SEM and EDX to prove the existence of Ge layer on Li 6.85 La 2.9 Ca 0.1 Zr 1.75 Nb 0.25 O 12 ; Fu et al [ 112 ] used SEM and EDX to characterize morphology of the interface between Li 7 La 2.75 Ca 0.25 Zr 1.75 Nb 0.25 O 12 and metallic Li anode.…”