Perspectives on NCM-Based Cathodes in Hybrid Battery-Supercapacitor Devices

The rapid development of energy storage technology and the explosive demand in the energy market have led to the emergence of new types of energy storage devices. Hybrid battery-supercapacitor devices (HBSDs), as a novel energy storage device, utilizes the complementary characteristics of batteries and supercapacitors [1], combines the advantages of batteries and supercapacitors, and is able to simultaneously meet high energy and high power demands for a wide range of complex application scenarios [2]. Current research on such hybrid systems focuses on combining mature lithium ion batteries (LIBs) and supercapacitors again to form HBSDs. As illustrated in Figure 1, HBSDs consist of a dual-functional material cathode where battery and capacitor materials coexist, and a battery material anode, where the cathode is typically a combination of lithium nickel cobalt manganese oxide (LiNi_xCoyMn₁−_x−_yO₂, NCM), or lithium iron phosphate (LFP) materials with activated carbon (AC) [3]. The composite cathode stores/releases energy through adsorption/desorption of anions by the bilayer formed on the surface of AC and a reversible Li+ embedding/de-embedding process in the NCM material. Compared with LIBs, the capacitor material added in the composite cathode of HBSDs can store/release energy rapidly through the physical adsorption/desorption process, and the supercapacitor shares high power loads, reduces the number of battery charging/discharging times and thermal stresses, and thus prolongs the battery life, which greatly improves the power performance and the cycling stability of the energy storage device [4]. Although the energy density decreases slightly with the addition of capacitor material to the cathode, the power density of the energy storage device can be significantly increased by, for example, adjusting the relative content of battery and capacitor material in the cathode. By combining the high energy storage capability of batteries with the high power output capability of supercapacitors, such hybrid devices are widely used in scenarios that require fast charging/discharging and high energy demand, such as electric vehicles, renewable energy systems, and pulsed power devices [5]. It is worth exploring that although HBSDs has made some progress, how to realize the efficient synergy between batteries and ultracapacitors and reduce the usage costs is still a significant technical difficulty due to the different energy storage mechanisms of the two components.

Figure 1:a) Schematic of HBSDs with NCM as cathode. b) The SEM image of NCM.

NCM, commonly referred to as ternary material, is an oxide compound that incorporates three transition metal elements: nickel (Ni), cobalt (Co), and manganese (Mn), conferring NCM with distinct performance advantages. The incorporation of Ni can enhance the specific capacity of the material, while the addition of Mn can reduce costs and improve the safety and stability of the material. Furthermore, the introduction of Co can decrease cation occupation, stabilize the layered structure, and enhance electrical conductivity and power performance. However, the introduction of excess elements can also produce side effects, such as excessive Ni will exacerbate the cation mixing and deteriorate the cyclic stability, excessive Mn will lead to the destruction of the lamellar structure of the material, and excessive Co will reduce the specific capacity and increase the cost, etc. Therefore, it is necessary to conduct precise proportioning of the content of the three elements in accordance with the application requirements, and to utilize the synergistic effect of Ni, Co and Mn to make NCM play the most advantageous role.

NCM has already made relatively mature progress in the energy storage applications of LIBs [6], and thus shows unusual potential in HBSDs. In conjunction with the technical advantages, NCM-based HBSDs has attracted the attention of many researchers, and the current investigations mainly focuses on the high energy density, multiplicative performance, and cycling performance. Chen et al. [7] combined NCM and AC proportionally as cathode, and utilized pre-lithiated hard carbon as anode to construct a lithium-ion hybrid capacitor, which demonstrated an energy density of up to 323.8Wh kg-1 [7]. In the hybrid system, the energy loss and heat loss are significantly reduced, which improves the overall energy efficiency, and the high power load is shared by the supercapacitor, which reduces the number of battery charge/discharge times and thermal stresses, thus prolonging the battery life. It is noteworthy that NCM-based HBSDs demonstrated significant potential in terms of rate performance and cycling performance; however, further improvements are necessary. The energy and power densities of HBSDs have not yet exceeded 300Wh kg-1 and 10kW kg-1, respectively. Consequently, the development of novel electrode materials and optimized device structures is essential in future research to enhance performance and reduce costs.

HBSDs based on NCM has obtained some satisfactory research results, and it is expected that it can be more widely used in electric vehicles, renewable energy systems, and portable electronic devices in the future because it combines the advantages of two excellent energy storage periods. In light of the current research status, further investigation can be conducted in the following areas:
1) Development of additional NCM-based cathode materials to modulate performance and meet the requirements of diverse applications.
2) Development of intelligent control systems to optimize energy distribution between batteries and supercapacitors through advanced control algorithms, thereby enhancing the efficiency of hybrid systems.
3) Exploration of integration with other energy technologies to develop more efficient energy storage systems.

In conclusion, HBSDs have demonstrated significant potential as an innovative energy storage solution. With advancements in material science and control technology, HBSDs is anticipated to assume a more prominent role in the future energy sector.

1. Xing F, Bi Z, Wu ZS, Su F, Liu F (2022) Unraveling the design principles of battery-supercapacitor hybrid devices: From fundamental mechanisms to microstructure engineering and challenging perspectives. Advanced Energy Mater 12: 2200594.
2. Ding J, Hu W, Paek E, Mitlin D (2018) Review of hybrid ion capacitors: From aqueous to lithium to sodium. Chemical Reviews 118(14): 6457-6498.
3. Guo Z, Liu Z, Ma Y, et al. (2023) Battery-type lithium-ion hybrid capacitors: Current status and future perspectives. Batteries 9(2): 74.
4. Qin J, Wang S, Zhou F, Das P, Wua Z, et al. (2019) 2D mesoporous MnO₂ nanosheets for high-energy asymmetric micro supercapacitors in water-in-salt gel electrolyte. Energy Storage Materials 18: 397-404.
5. Song T, Kendrick E (2021) Recent progress on strategies to improve the high voltage stability of layered-oxide cathode materials for sodium-ion batteries. Journal of Physics: Materials 4(3): 032004.
6. Li X, Zhao X, Wang MS, Zheng J, Huang Y, et al. (2017) Improved rate capability of a LiNi1/3Co1/3Mn1/3O2/CNT/graphene hybrid material for Li-ion batteries. RSC Advances 7: 24359-24367.
7. Chen X, Mu Y, Cao G, Qiu J, Ming H, et al. (2022) Structure-activity relationship of carbon additives in cathodes for advanced capacitor batteries. Electrochimica Acta 413: 140165.