Improving cycling performance of the NaNiO_(2)cathode in sodium-ion batteries by titanium substitution

O3-type layered oxide cathodes,such as NaNi_(0.5)Mn_(0.5)O_(2),have garnered significant attention due to their high theoretical specific capacity while using abundant and low-cost sodium as intercalation species.Unlike the lithium analog(LiNiO_(2)),NaNiO_(2)(NNO)exhibits poor electrochemical performance resulting from structural instability and inferior Coulomb efficiency.To enhance its cyclability for practical application,NNO was modified by titanium substitution to yield the O3-type NaNi_(0.9)Ti_(0.1)O_(2)(NNTO),which was successfully synthesized for the first time via a solid-state reaction.The mechanism behind its superior performance in comparison to that of similar materials is examined in detail using a variety of characterization techniques.NNTO delivers a specific discharge capacity of∼190 mAh g^(−1)and exhibits good reversibility,even in the presence of multiple phase transitions during cycling in a potential window of 2.0−4.2 V vs.Na^(+)/Na.This behavior can be attributed to the substituent,which helps maintain a larger interslab distance in the Na-deficient phases and to mitigate Jahn–Teller activity by reducing the average oxidation state of nickel.However,volume collapse at high potentials and irreversible lattice oxygen loss are still detrimental to the NNTO.Nevertheless,the performance can be further enhanced through coating and doping strategies.This not only positions NNTO as a promising next-generation cathode material,but also serves as inspiration for future research directions in the field of high-energy-density Na-ion batteries.

Tailoring the LiNbO_(3)coating of Ni-rich cathode materials for stable and high-performance all-solid-state batteries

The research and development of advanced nanocoatings for high-capacity cathode materials is currently a hot topic in the field of solid-state batteries(SSBs).Protective surface coatings prevent direct contact between the cathode material and solid electrolyte,thereby inhibiting detrimental interfacial decomposition reactions.This is particularly important when using lithium thiophosphate superionic solid electrolytes,as these materials exhibit a narrow electrochemical stability window,and therefore,are prone to degradation during battery operation.Herein we show that the cycling performance of LiNbO_(3)-coated Ni-rich LiNi_(x)Co_(y)Mn_(z)O_(2)cathode materials is strongly dependent on the sample history and(coating)synthesis conditions.We demonstrate that post-treatment in a pure oxygen atmosphere at 350℃results in the formation of a surface layer with a unique microstructure,consisting of LiNbO_(3)nanoparticles distributed in a carbonate matrix.If tested at 45℃and C/5 rate in pellet-stack SSB full cells with Li_(4)Ti_(5)O_(12)and Li_(6)PS_(5)Cl as anode material and solid electrolyte,respectively,around 80%of the initial specific discharge capacity is retained after 200 cycles(~160 mAh·g^(−1),~1.7 mAh·cm^(−2)).Our results highlight the importance of tailoring the coating chemistry to the electrode material(s)for practical SSB applications.

The interplay between (electro)chemical and (chemo)mechanical effects in the cycling performance of thiophosphate-based solid-state batteries

Solid-state batteries(SSBs)are a promising next step in electrochemical energy storage but are plagued by a number of problems.In this study,we demonstrate the recurring issue of mechanical degradation because of volume changes in layered Ni-rich oxide cathode materials in thiophosphate-based SSBs.Specifically,we explore superionic solid electrolytes(SEs)of different crystallinity,namely glassy 1.5Li_(2)S-0.5P_(2)S_(5)-LiI and argyrodite Li_(6)PS_(5)Cl,with emphasis on how they affect the cyclability of slurry-cast cathodes with NCM622(60%Ni)or NCM851005(85%Ni).The application of a combination of ex situ and in situ analytical techniques helped to reveal the benefits of using a SE with a low Young’s modulus.Through a synergistic interplay of(electro)chemical and(chemo)mechanical effects,the glassy SE employed in this work was able to achieve robust and stable interfaces,enabling intimate contact with the cathode material while at the same time mitigating volume changes.Our results emphasize the importance of considering chemical,electrochemical,and mechanical properties to realize long-term cycling performance in high-loading SSBs.

On the role of surface carbonate species in determining the cycling performance of all-solid-state batteries

This short perspective summarizes recent findings on the role of residual lithium present on the surface of layered Ni-rich oxide cathode materials in liquid-and solid-electrolyte based batteries,with emphasis placed on the carbonate species.Challenges and future research opportunities in the development of carbonate-containing protective nanocoatings for inorganic solid-state battery applications are also discussed.