With the rapid development of the lithium-ion battery industry, there is growing concern that shortages of lithium-ion raw materials such as cobalt, nickel and lithium will limit the production of existing ion batteries, leaving the growing demand unmet. Whether it is trolling motor battery or fish finder battery, the most popular is lithium battery at present.
This has prompted researchers to look for alternatives to lithium-based electrochemical energy storage systems. Among potential sodium, potassium, magnesium, zinc, calcium ion batteries, calcium ion batteries have shown great potential.
1.Challenges in developing calcium ion batteries
On the one hand, calcium ions are the fifth most abundant element in the Earth's crust, and the global resource is evenly distributed. More importantly, calcium ion batteries can provide higher power densities than other polyvalent metal ion-based battery systems.
However, the research and development of calcium ion batteries faces multiple challenges, mainly reflected in the following aspects:
- Lack of effective electrolytes and viable cathode materials for reversible calcium ion intercalation;
- In addition, the strong reducing ability of calcium ions can induce electrolyte decomposition to form an ionic insulating layer on the metal anode;
- True full-cell testing of potential cathodes has not yet been achieved; Meanwhile, the use of conventional half-cell setups may lead to underestimated electrode performance due to the severe passivation of the electrodes by calcium ion metal in the electrolyte. Therefore, further research to understand the interfacial chemistry and design a suitable anode-electrolyte interface is crucial for realizing viable calcium ion-based batteries.
2.Potential of calcium ion batteries
Researchers at the Helmholtz Institute in Ulm, Germany, demonstrate the suitability of calcium-tin (Ca-Sn) alloys as anodes for calcium ion batteries and elucidate their electrochemical performance. The calcium ion battery demonstrated in this paper (consisting of a Ca-Sn alloy anode, a quinone-based polymer cathode, and a high-efficiency borate Ca[B(hfip)4]2 electrolyte) exhibits excellent performance and can output a voltage of 1.8 V, And it can run at least 5000 cycles at a specific current of 260 mA g-1. The discovery of novel Ca-Sn alloy anodes opens a promising avenue for high-performance calcium ion batteries.
- Using X-ray diffraction (XRD) microscopy and scanning electron microscopy (SEM) techniques, the electrochemical calcification and decalcification of Ca-Sn alloys were characterized, and it was found that Sn formed during the initial electrochemical treatment of calcium-rich alloys was The subsequent alloying process converts to CaSn3, and this new phase is capable of reversible calcification/decalcification. Therefore, Ca-Sn alloys are proposed as potential anodes for calcium ion batteries, and their feasibility is demonstrated by a calcium ion full cell prototype.
- Constructing a full cell with a kinetically favorable organic cathode (1,4-polyanthraquinone) and a Ca-Sn alloy anode to circumvent the barrier of metal anode passivation originating from calcium ions and enable the anode and cathode to The redox reactions are carried out simultaneously.
3.Schematic diagram of calcium ion battery research
【Fig.1】a XRD pattern of the as-prepared Ca-Sn alloy, b Schematic diagram and working principle of the quasi-full-cell configuration with Ca-Sn alloy anode and 14PAQ cathode.
【Fig. 2】Constant current charge-discharge curves of Caǀǀ14PAQ and bCaxSnǀǀ14PAQ batteries using Ca[B(hfip)4]2/DME electrolyte at 260 mA g-1. c CV curves of 14PAQ electrodes using CaxSn as counter and reference electrodes with a scan rate of 0.1 mV s-1. Cycling performance of dCaxSnǀǀ14PAQ cells at 130 mA g-1 (0.5 C) and 260 mA g-1 (1 C), respectively.
Figure 2a shows that the Caǀǀ14PAQ cell exhibits a discharge voltage of ~2.05 V and a capacity of 253 mAhg-1 in the first cycle. However, rapid capacity fading and voltage drop were observed within 6 cycles, most likely caused by passivation on the Ca metal anode.
【Fig. 3】 In situ XRD of the anode of the CaxSnǀǀ14PAQ battery during the first, second, and 201st to 203rd charge-discharge cycles.
【Fig. 4】 The CaxSn anode material is in the original state of a, b after the 20th discharge to 0.5 V, and c after the 20th charge to 2.5 V, d SEM image and elemental distribution after the 3000th charge to 2.5 V. e XRD patterns of the CaxSn alloy at various discharge and charge states. Schematic diagram of the phase evolution of fCaxSn anode during electrochemical processes.
【Fig. 5】 The refined XRD pattern of aCaSn3. Constant current charge-discharge curves of bCaSn3ǀǀǀ14PAQ battery and CaxSnǀǀǀ14PAQ battery. The CaSn3 single phase was prepared by heating a mixture of Ca and Sn at a molar ratio of 1.1:3. The XRD pattern shows that the as-prepared CaSn3 material is a pure single phase with high crystallinity (Fig. 5a). The CaSn3ǀǀ14PAQ cell provides about 200 mAhg-1 capacity at 260 mA g-1 (1 C), and the average cell voltage is lower compared to the CaxSnǀǀ14PAQ cell (Fig. 5b), which is due to the higher decalcification potential of CaSn3.
【Fig. 6】The charge-discharge curves of the aCaSn3ǀǀ14PAQ battery during the first cycle and the ex-situ XRD patterns of the CaSn3 anode under different electrochemical states. b Original, c20 cycles of discharging to 0.5 V, d20 cycles of charging to 2.5 V, and e200 cycles of charging to 2.5 V SEM and EDX mapping images of the CaSn3 alloy.
【Fig. 7】 Rate performance and b-cycling performance of aCaSn3ǀǀǀ14PAQ and CaxSnǀǀ14PAQ cells. Figure 7a shows that the CaxSnǀǀ14PAQ cells exhibited higher capacities at different current densities, while the CaSn3ǀǀ14PAQ cells exhibited relatively fast capacity decay during the initial 100 cycles at 260 mA g-1.
In conclusion, a calcium full battery composed of a quinone-based polymer cathode and a Ca-Sn alloy anode combined with a high-efficiency borate Ca[B(hfip)4]2 electrolyte was developed. This complete battery prototype exhibits a battery voltage of about 1.8V and can operate at least 5000 times at a specified current of 260mA g-1. Electron microscopy and crystallographic investigations of the compositional and microstructural features of alloy electrodes during electrochemical processes revealed that micron-sized bulk Ca-Sn electrode materials can be converted to active Sn by initial electrochemical treatment, a unique in situ formation. The interconnected porous structure is beneficial for cycling stability.
This study shows that the design of alloy anode reversibility for calcium ion batteries should consider not only alloy composition but also microstructure. In addition, micron-sized Ca-Sn alloy powders can be directly synthesized with potential for large-scale applications. Using a full-cell configuration rather than the traditional half-cell setup could provide a viable option for the discovery of new electrode materials for calcium ion batteries. Future work in tailoring alloy compositions and exploring high-voltage cathodes may lead to more energetic full cells.
If you want to know more about new battery technology, you can take a look at 4680 battery.