The desirability to achieve low or reducing carbon emissions from energy conversion processes were agreed worldwide, suggested to the new global challenges towards positive impact on decreasing the climate change and environmental sustainability for the 21st century. While meeting the increasing energy demands, the energy system is to solve the complex problem of reducing carbon emissions.
The nanoengineering has proved to be one of the most effective strategies to enhance the lithium storage of conversion type anode materials (CTAMs) (Figure 1) [1]. The overall energy demand in a global world is expected to be in steady growth, although the increase rate is slower compared to the previous 40 years (see Figure 2a) [2]. Furthermore, the trend of global energy generation is shifting towards the renewables gaining share with chiefly lowering the portion of fossil fuels. Renewable energy is the fastest growing source of energy, and its share in the global energy sector is expected to increase around 30%, overtaking the coal within by 2040 as shown in Figure 2b. Accordingly, the importance of energy storage devices is being emphasized more, because the energy storage devices conserve the generated energy by converting it to electricity.
Recently, Prof. W.S. Yoon and his team from Sung Kyun Kwan University, Suwon, South Korea have reviewed a report on “Multiscale Factors in Designing Alkali-Ion (Li, Na, and K) Transition Metal Inorganic Compounds for Next-Generation Rechargeable Batteries”. Interesting reports are to understand better our future rechargeable batteries that are particularly based on alkali metal batteries.
Owing to the advantages of environment friendly, high energy density and efficiency, metal air batteries (MAB) has been considered as one of the most promising power sources [3]. Although, in such a case, screening and constructing low cost, high efficient and robust electrocatalysts with high oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity plays a crucial role in the rechargeable metal air batteries. Alkali-ion batteries have captured the largest portion (of around 70%) of whole technologies due to its high power and energy densities (Figure 2c) on compared to numerous electricity storage technologies [4]. Such alkali-ion rechargeable batteries are fruition for the researchers who have awarded the 2019 Nobel Prize in Chemistry and to provide an attractive solution for a range of energy and environmental problems. The electrochemical performance of the rechargeable batteries is determined by whole cell components (including cathode, anode, electrolyte and others) (Figure 2d).
In addition, the discovery of anionic redox chemistry has extended a great reach on electron resource species. A new paradigm for designing high energy cathode materials towards the next-generation rechargeable batteries were been re-evaluated by the alkali-ion insertion cathode materials for its potential in terms of impact [5,6]. Regarding, it is commonly a known fact that Na- and K-ion batteries were applied to a similar manufacturing process, which makes them promising candidates for next-generation rechargeable batteries.
Figure 2. Image credit to BP Energy Outlook 2019 & IRENA, Electr. Storage Renewables Costs Mark. to 2030.
Recently, Prof. J. Qiao and his research team have demonstrated a facile strategy to synthesize the cobalt phosphide anchored heteroatoms (N,P) co-doped porous carbon (CoP/NP-HPC) through one-step pyrolysis of bimetal-organic frameworks with a simple in-situ phosphorization process [5].
In alkaline solutions, the obtained CoP/NP-HPC catalyst exhibits high bifunctional catalytic activity towards ORR and OER, comparable to the commercial 20% Pt/C. This can be attributed to the synergistic effect between the CoP active sites, N,P codoped carbon and the porous framework as channel benefiting to the diffusion of reaction species. Remarkably, with CoP/NP-HPC as the air electrode catalyst, the rechargeable Zn–air battery delivers a good charge/discharge cyclic stability and a high power density of 186 mW cm-2, which can outperform to 20% Pt/C. The hybrid catalyst of CoP anchored with heteroatoms doped carbon provides a possibility to promote the development of low-cost and high efficiency bifunctional catalysts for ORR and OER for the metal air batteries applications.
New identification in the functional structure of secondary particles was continuously developed with enhanced battery performance. The battery property was enriched by changing the particle morphology, including Na, K and Li compounds. However, designing an appropriate structure of secondary particle considering with these categories remains a challenge because of the difficulties in synthesis (e.g. controlling the particle growth during the sintering process, agglomeration of nanoparticles etc.). Hence a considerable effort needs to be devoted to this research area.
Battery performance controlled variables and effects are summarized as follows:
(i) Exposed crystal planes of the primary particle: Ion diffusion is dependent on the crystal plane.
(ii) The surface area in the secondary particle: It has pros and cons. Large surface area leads to higher reaction rates, but can promote undesirable electrode/electrolyte reaction.
(iii) Grain boundary between primary particles: it is a resistance for transport parameters, and cause of cracking by volume change, so it needs to be reduced.
(iv) The density of secondary particle: Spatial distribution of the primary particles in a secondary particle is correlated with surface area in the secondary particle, and it affects the energy density of the electrode.
(v) The network system of transport parameters: The more ion and electron conducting species are efficiently combined, the more improved battery performance is obtained. It is applicable for all the battery systems.
Hence, controlling the particle morphology is a useful method to complement bad material characteristics or circumvent the undesirable environments (e.g. irreversible phase transition at the interface between particle and electrolyte) by modifying these five categories, and numerous reports have shown that the effective morphology design can get over the weakness or disadvantages of the materials.
Scientists, thanks to pioneers in the alkali-ion rechargeable batteries, energy consumption patterns that have undergone substantial changes, and the necessity for more energy and less carbon has led advances in energy-efficient and environment-saving technologies. The cathode is the main important part of the rechargeable batteries in consideration for the five requirements as energy, power, safety, life and cost. The progress in synthesis and analysis technologies enables a more complete understanding of what governs the properties and performance of the cathode materials. The fundamental understanding provided by diverse approaches from nano to micro level has already helped to bridge the gap between industrial and academic research fields for the improvement and commercialization of state-of-the-art cathode materials. Each level offers its challenges and attractions, but understanding how different levels of changes are linked to influence each other is needed with a holistic approach.
The multiscale approaches can access the key factors, overcoming the limits of cathode materials by combining different levels of parameters, bringing a new perspective to electrode material design (Figure 3). In addition, to the expectation of the rapid growth of renewable energy in the global energy system, enormous market potential of electric vehicles was encouraging the electricity storage technologies to advance a great deal together in the foreseeable future.
References
- Y. Lu et al., Chem. 4, 972 (2018).
- W. Lee et al., Energy Environ. Sci., (Accepted Manuscript) DOI: 10.1039/D0EE01277G.
- M. Wu et al., Energy Storage Mater., 21, 253 (2019).
- G. Assat and J.-M. Tarascon, Nat. Energy, 3, 373 (2018).
- M. Ben Yahia et al., Nat. Mater., DOI:10.1038/s41563-019-0318-3.
- Y. Wang et al., J. Mater. Chem. A, 2020, DOI: 10.1039/D0TA06435A.
Blog Written By
Dr. A. S. Ganeshraja
Assistant Professor
National College, Tiruchirappalli
Tamil Nadu, India
Editors
Dr. K. Rajkumar
Dr. S. Chandrasekar
Reviewers
Dr. Y. Sasikumar
Dr. K. Vaithinathan
Dr. S. Thirumurugan
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