Novel sol-gel route for expanding the glass forming region of tin phosphate glass for secondary battery electrode applications.

In this paper, tin-phosphate amorphous glass and nano-crystallized ceramic materials were synthesized by sol-gel methods and heat treated at 400 °C with the composition of x SnO 2 − (100- x)P 2 O 5 (x SnP: ' x ' from 40 to 90 mol%). The electrical and thermal properties of tin-phosphate materials were investigated by electrical impedance spectroscopy (EIS) and thermogravimetry – differential thermal analysis – mass spectroscopy (TG–DTA–MS). Moreover, the local structure of x SnP was characterized by 119Sn-Mössbauer and magic angle spinning (MAS) 31P NMR spectroscopies. Homogeneous glasses were obtained for x SnP with ' x ' from 50 to 80, while Sn(HPO 4), SnO 2 , and Sn 3 (PO 4) 2 nanoparticles formed in 40SnP and 90SnP compositions, respectively. The nano-crystallized 40SnP and 90SnP samples showed large electrical conductivity (σ) of 2.02×10−5 and 1.04×10−4 S cm−1 due to the conductive crystalline phases of SnP 2 O 7 and defective SnO 2 , respectively. The lower σ of about 10−8 S cm−1 were recorded for x SnP with ' x ' from 50 to 80 owing to the decomposition of the 3D network built by phosphate tetrahedrons. 119Sn-Mössbauer spectra proved the growing number of SnIVO 6 units, which do not contribute to the rise of electrical conductivity. On the other hand, larger σ values of 1.79×10−4 and 6.4×10−3 S cm−1 were confirmed for 40SnP and 90SnP samples after heat treatment, resulting in partial reduction of SnIV to SnII and growing of the 3D network structure by PO 4 3−. It is concluded that highly electrically conductive x SnP samples can be synthesized by the sol-gel method followed by slow heat treatment. In addition, the battery evaluation was performed of x SnP samples as cathode and anode in a sodium-ion battery. The highest initial capacity recorded for 90SnP nano-crystallized ceramic at 37.97 mAh g−1 under a current rate of 20 mA g−1 with capacity retention (%) of 48.15% after 100 cycles as a cathode material. The anode test showed that the 40SnP nano-crystallized ceramic has the largest initial capacity of 375 mAh g−1 and after heat treatment 50SnP glass significantly increased to 425 mAh g−1 compared with 186 mAh g−1 before heat treatment. Also, the heat treatment effect on the initial capacity of 90SnP nano-crystallized ceramic with observation largest value of 470 mAh g−1. These results open the way to maybe applying these glass and nano-crystallized ceramic materials in all-solid-state batteries. • The x SnO 2 −(90− x)P 2 O 5 glass was successfully prepared with a wider chemical composition of SnO 2 concentration from 50 to 80 mol% by the sol-gel method. • The 40SnP and 90SnP samples exhibited notably high σ 's of 1.79×10−4 and 6.40×10−3 Scm−1 attributed to their elevated levels of proton conductivity. • 90SnP as cathode demonstrated the highest initial capacity, achieving 37.97 mAh g−1 and maintaining a capacity retention of 48.15% after 100 cycles. • 40SnP and 90SnP exhibited a large initial capacity of 375 mAh g−1 and 470 mAh g−1, as anode materials in SIBs. [ABSTRACT FROM AUTHOR]