Thick Architected Silicon Composite Battery Electrodes Using Honeycomb Patterned Carbon Nanotube Forests

Developing thick electrodes is a promising strategy to increase the energy density of lithium-ion batteries (LIBs), but severe polarization and ion transport limitations hinder their electrochemical performance [1–3]. Laser structuring has recently emerged as an attractive method to create ion-conducting pathways within the electrode, thereby alleviating transport restrictions and enhancing performance [4–6]. In this study, we systematically investigate the influence of laser structuring on the electrochemical behavior of thick electrodes by combining experiments with a physics-based electrochemical model. Pouch-type mono-cells (50 × 50 mm²) composed of NMC622 cathodes and graphite anodes were fabricated with unstructured and laser-structured electrodes at pitches of 100, 200, and 300 μm. The model was validated against discharge experiments, achieving voltage RMSE values of 61–79 mV across all cases, confirming its predictive reliability. [5,6].The results show that for thin electrodes (~50 μm), laser structuring provides negligible improvement, whereas for electrodes thicker than 100 μm, the benefits become significant. At 100 μm thickness, the liquid-phase ohmic overpotential was reduced by ~62 mV at 1C, and the total overpotential decreased by ~220 mV at 3C compared to unstructured electrodes [4,7]. During 1C charging, structured electrodes achieved nearly twice the usable capacity while maintaining the anode overpotential above 0 V, thereby fully suppressing lithium plating [7]. For thicker electrodes (e.g., 300 μm), unstructured cells suffered from concentration depletion and failed even at 0.1C, whereas structured electrodes alleviated polarization and sustained stable operation. Furthermore, when electrolytes with higher ionic conductivity and diffusivity were employed, overall transport limitations in thick electrodes were substantially alleviated, and the beneficial effects of laser structuring were reinforced under demanding conditions [8,9].These findings demonstrate that laser structuring effectively mitigates transport limitations in thick electrodes, improving charging efficiency, reducing polarization, and suppressing lithium plating. Importantly, the results clarify the thickness and porosity ranges in which structuring is most effective and highlight its synergy with advanced electrolytes. Overall, this work provides design guidelines for next-generation LIBs that balance energy density and rate capability through application-specific electrode structuring strategies References [1] M. Singh, J. Kaiser, H. Hahn, Thick Electrodes for High Energy Lithium Ion Batteries, J. Electrochem. Soc., 162 (2015) A1196–A1201.[2] H. Gao, Q. Wu, Y.X. Hu, J.P. Zheng, K. Amine, Z.H. Chen, Revealing the Rate-Limiting Li-Ion Diffusion Pathway in Ultrathick Electrodes for Li-Ion Batteries, J. Phys. Chem. Lett., 9 (2018) 5100–5104.[3] H.H. Zheng, J. Li, X.Y. Song, G. Liu, V.S. Battaglia, A comprehensive understanding of electrode thickness effects on the electrochemical performances of Li-ion battery cathodes, Electrochim. Acta, 71 (2012) 258–265.[4] J. Kriegler, L. Hille, S. Stock, et al., Enhanced performance and lifetime of lithium-ion batteries by laser structuring of graphite anodes, Appl. Energy, 303 (2021) 117611.[5] J. Park, S. Hyeon, S. Jeong, H.J. Kim, Performance enhancement of Li-ion battery by laser structuring of thick electrode with low porosity, J. Ind. Eng. Chem., 70 (2019) 178–185.[6] V. Goel, K.H. Chen, N.P. Dasgupta, K. Thornton, Optimization of laser-patterned electrode architectures for fast charging of Li-ion batteries using simulations parameterized by machine learning, Energy Storage Mater., 57 (2023) 44–58.[7] J.B. Habedank, J. Kriegler, M.F. Zaeh, Enhanced Fast Charging and Reduced Lithium-Plating by Laser-Structured Anodes for Lithium-Ion Batteries, J. Electrochem. Soc., 166 (2019) A3940–A3949.[8] K.M. Diederichsen, E.J. McShane, B.D. McCloskey, Promising Routes to a High Li+ Transference Number Electrolyte for Lithium Ion Batteries, ACS Energy Lett., 2 (2017) 2563–2575.[9] P. Zhou, X.K. Zhang, Y. Xiang, K. Liu, Strategies to enhance Li+ transference number in liquid electrolyte for better lithium batteries, Nano Res., 16 (2023) 8055–8071.

Clarifying the limiting factor of material utilization in thick electrodes of lithium-ion batteries

One of the biggest obstacles to the widespread adoption of fully electrified vehicles is the limited volumetric/gravimetric energy density of lithium-ion batteries to achieve driving ranges comparable to vehicles with internal combustion engines. Electrode thicknesses are being increased to enhance the energy density of the battery cells. Furthermore, the space within the confinements of the cell housing is utilized as much as possible. Today’s state-of-the-art (SoA) electrode materials exhibit volume and Young’s modulus change during formation and cycling, e.g. a volume change up to ~10% for graphite [1] and a threefold increase of the Young’s modulus of the graphite active particles [2]. This leads to a pressure build up within the cells due to reversible and irreversible volume changes, especially of the anode materials, during cycling. The optimized packing for SoA electrodes and the volume changes of the electrodes result in increased electrochemical/mechanical interactions that leads to stress inside the cells.In this work, the interactions between mechanical bracing and aging are studied for large format prismatic 94 Ah lithium-ion battery cells [3]. The impact of external bracing is shown for lithium-ion cells cycled up to over 7000 cycles with 100% depth of discharge (Figure 1 (a)), where the braced cells show an enhanced performance in the region of 80% state of health (SOH). The braced cells reach this threshold around 900 cycles later compared to the unbraced cells. Furthermore, the unbraced cells have a thickness change of around 17.5% after more than 7000 cycles (Figure 1 (b)). After cycling, the cells are examined with post-mortem analysis, showing significantly increased aging phenomena (e.g. lithium plating) in the unbraced cell compared to the braced cell. Inductively coupled plasma optical emission spectrometry (ICP-OES) analyses confirm these assumptions (Figure 1 (c) + (d)). In contrary to the enhanced lithium plating on the anode of the unbraced cell, X-Ray diffraction (XRD) show that bracing leads to an increased structural cathode degradation compared to the unbraced cells. Those ex-situ post-mortem experiments were also confirmed by electrochemical tests in laboratory cells, showing only small capacity fading of the aged anodes of the braced cell compared to unaged reference anode cells. Nevertheless the main factor for capacity loss inside the prismatic 94 Ah cells is the loss of lithium inventory.External pressure on cells is beneficial to guarantee sufficient contact of the components within an electrode stack and hence decreased aging phenomena mainly on the anode. The downside of the increased pressure on the cells are the significantly increased morphological and structural degradation of the cathode, which, however, plays a minor role in the overall cell degradation. The external bracing results in a more ‘homogeneous’ aging over the entire cell with only little locally different degradation characteristics.

Electrochemical performance of lithium-ion batteries with two-layer gradient electrode architectures

For widespread adoption of electric vehicles, lithium-ion batteries need to achieve energy densities of around 350 Wh/kg, cost less than $100/Wh, and be able to charge quickly within 15 minutes. The production of most inactive materials within modern Li-ion cells (e.g. separator, current collector, packaging) have already undergone tremendous optimization but many opportunities remain for improving the performance of the electrodes and reducing the cost and time of wetting, formation and aging processes. By increasing the thickness of electrodes clear opportunities exist for enhancing the energy densities of conventional cell materials and reducing cost. For example, doubling the thickness of electrodes in full cells from 50 μm to 100 μm can increase the energy density of the cell by about 16% and reduce the cost of the cell by 50% (from $249/kWh to $172/kWh)1. These benefits arise from increasing the ratio of electrode active material to inactive material within cells; however, increased thickness is often accompanied by reduced rate performance and increasingly difficult electrolyte wetting and formation processes due to the challenge of infiltrating the electrode pore structure with electrolyte and displacing gases during formation2. One emerging electrode processing technology involves the laser-ablation of small micro pores or channels into Li-ion battery electrodes to enhance their electrolyte wetting and rate performance. Pulsed lasers are increasingly being used in advanced manufacturing processes due to their ability to weld, sinter, or remove materials quickly and with very high precision. When applied to high energy density thick electrodes, micro-structuring by laser patterning has been shown to improve the rate capabilities of cells while maintaining high capacity retention3. These laser ablated pores or channels provide low tortuosity paths for lithium ions to reach deeper regions in the thick electrodes more quickly than before, limiting concentration gradients and thus reducing unwanted lithium plating at elevated rates. Despite these benefits, the utilization of ultrafast lasing ablation systems as an in-line technique to selectively remove patterned regions of active material from lithium-ion battery electrodes during production has not yet been widely adopted by the industry. In this work, we identify and manufacture laser-ablated 3D electrode architectures for enhanced Li+ transport and electrochemical performance with the hope of inspiring confidence in the benefits, practicality and cost effectiveness of the laser patterning technique. Preliminary modelling work at NREL has explored the limitations of planar electrodes for fast charge performance and the importance of microscale features for improving ion-transport4-8. With the correct pore/channel geometry, the energy density of ablated electrodes can be significantly improved compared to traditional architectures. We have combined simulation models and experimental data to optimize the 3-D laser patterning of our electrodes. Modelling elucidated the electrodes baseline transport limitations and quickly identified the most promising electrode architectures for favorable cost, energy- and power-density. Next, we used our benchtop ultrafast femtosecond laser ablation system to pattern our thick (ca. 100 µm) electrodes. After processing, the electrodes were inspected using cross-section scanning electron microscopy (SEM) so that ablation parameters such as laser wavelength, power and repetition rate could be optimized and distributions of feature sizes could be identified giving insight into the limitations of the laser system. We observed that the anode and cathode materials responded significantly different to the laser ablation process and that this must be considered during electrode preparation. Next, scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) and x-ray diffraction (XRD) were used to probe for local chemical or structural changes in the electrodes’ with patterning to determine if the remaining active materials experienced permanent laser-induced damages. Once successful achievement of the target electrode architecture was confirmed, the benefits of the achieved 3-D patterning were investigated by cycling the electrodes in full cell coin cells and comparing their performance against standard cells with unmodified electrodes (benchmark). Cycling data clearly shows improved rate performance and capacity retention derived from the patterning of the thick graphite and NMC electrodes. Direct structuring of the electrodes has improved their ion transport and reduced lithium concentration gradients (cell polarization) resulting in high specific energy- and high power-density. While clear evidence of rapid lithium plating was observed in the standard benchmark cells at rates exceeding 1C, this has been largely mitigated in the laser ablated electrodes. Lastly, we probed the wetting of these electrodes with electrochemical impedance spectroscopy to map in real time the improved rate and extent of wetting achieved through the adoption of our 3-D laser patterns. Achieving shorter wetting times will correspond to reductions in cell manufacturing costs and is expected to present a significant market advantage. Figure 1

Introduction An internal resistance in an electrode for lithium ion batteries (LIB) is consisted of three resistances, which are an electric resistance, ionic resistance and charge-transfer resistance. Since a length of Li-ion conductive pathways decreases with decreasing electrode thickness, the internal resistance can be reduced by decreasing the electrode thickness [1]. Therefore, decreasing the electrode thickness is one of the effective methods to improve the power of LIB. On the other hand, making the thin electrodes by the same procedure as the thick electrodes probably causes a change in the electrode structure and increase of the internal resistance. However, it has not been clarified. In this study, the LIB electrodes with various thicknesses were examined to clarify the influence of decreasing the electrode thickness on its structure and the internal resistance. Half cell tests and scanning electron microscopy with focused ion beam (FIB-SEM) analyses were carried out to evaluate electrochemical and structural properties of the electrodes. Results and Discussion Fig. 1 shows the electrode thickness dependence on the three resistances: the ionic resistance (Rion), charge-transfer resistance (Rct), and total internal resistance (R).The resistances are normalized by the weight of active materials. At around 15 μm of the electrode thickness, R showed the minimum. At less than 15 μm of the electrode thickness, R increased due to the Rct increase. Fig. 2 shows 3D reconstructed images of active material phase, acetylene black (AB) and binder phase, and pore phase in the thin (9 μm) and thick (25 μm) electrodes . The porosity of the thin electrode was larger than that of the thick electrode. In addition, the ABs and binder in the thin electrode were dispersed less uniformly than those in the thick electrode. The large porosity and localization of the ABs and binder could produce a high contact resistance among active materials. As a result, the reduced reactive surface area increased the Rct in the electrode. In our presentation, we will discuss the influence of decreasing the electrode thickness on .the Rct more detail with other analysis results, and the method for improving Rct. Acknowledgment This work was supported by New Energy and Industrial Technology Development Organization (NEDO) of Japan. Reference [1] C. Fongy et al. , J. Electrochem. Soc , 157, A885 (2010). Figure 1

Lithium/sodium-selenium (Li/Na-Se) batteries are promising energy storage systems due to their relatively low cost and high volumetric energy density of Se cathode. Rechargeable lithium-ion batteries (LIBs) play a critical role in portable devices, electric vehicles and large-scale stationary energy storage, due to their relatively high energy density and low cost among available technologies [1]. Sodium-selenium (Na-Se) batteries have also drawn much attention, because of the large abundance and low cost of sodium and decent energy density of Se [2]. As a cathode material, Se provides a moderate gravimetric capacity of 678 mAh g−1, a high volumetric capacity of 3270 mAh cm−3, and possesses a high electronic conductivity of 1 ×10 −3 S m−1 [3, 4]. These advantages of Se have stimulated growing research in developing Li-Se and Na-Se batteries over the past years. However, the practical application of these batteries has been hindered by the polyselenides dissolution (or shuttle effect phenomena), which could cause low Coulombic efficiency and poor cycling lifetime. Microporous carbon (MPC) has been fabricated through a facile carbonization method from polyvinylidene fluoride (PVDF) and used without any further activation as selenium host to produce MPC/Se composite employed as cathode in rechargeable lithium/sodium-selenium (Li/Na-Se) batteries and the electrochemical properties of the prepared cell have been investigated in Li-Se batteries. (figures 1 and 4).Basically, in linear carbonate-containing electrolytes, the metal readily decomposes at the anode side, causing capacity drop over cycling. To address this problem, electrolyte design should accompany manifested cathode structure. Hence, fluoroethylene carbonate (FEC) has been used as an additive in the electrolyte solution for stabilizing the capacity in Na-Se batteries. Our investigation showed that exceptional cell stability could be reached by using the FEC in carbonate-based electrolyte. In lithium/sodium-selenium batteries, diethyl carbonate (DEC) electrolyte decomposes in contact with metal, producing some radicals and metal alkyl carbonates. These radicals start a chain reaction, causing the destruction of over cycles. By adding the FEC to the electrolyte solution, this side reaction will be prohibited. [5] FEC readily decomposes on the surface of the metal prior to any reduction of linear carbonates, making the protective and stable surface film on the metal. This layer makes the capacity much more stable for the cell contains FEC in the electrolyte. For the cell without FEC in the electrolyte, the capacity starts to fade from initial cycles and continue fading during the cycling. In sodium/selenium batteries, at the current rate of 0.1 C, the cell contains no FEC in the electrolyte, showed a capacity of 317 and 245 mAh g-1 after 100 and 200 cycles, respectively. However, the cell with an electrolyte solution containing 3% FEC, showing excellent cyclability by way of delivering 382 and 350 mAh g-1 capacity at those above-mentioned cycles, respectively (figures 2 and 5). Another important finding was that the use of FEC additive could prevent the corrosion of metal anode from soluble polyselenides, and preserve the structural integrity of metal anode, contributing to the enhanced cycling stability and specific capacity of Na-Se batteries.The utilization of nanoscale Al2O3 surface coating by atomic layer deposition (ALD) to protect a MPC/Se cathode and reduce polyselenide dissolution was also investigated in another stage. It was found that Al2O3 surface coating effectively suppressed the polyselenide dissolution from the MPC/Se cathode, thus reducing the loss of Se active material and improving the overall performance of Na-Se batteries. Compared to the pristine MPC/Se, Al2O3-coated MPC/Se cathode exhibited improved discharge capacity, cycling stability, and rate capability in Na-Se batteries (figures 3 and 6). Keywords: Fluoroethylene carbonate; lithium/sodium−selenium batteries; ALD coating; carbonate-based electrolyte; microporous carbon

<p>Carbon nanotubes (CNTs) are a group of pure carbon solid materials that possess one-dimensional structures with diameters down to less than one nanometre. They have interesting physical properties such as very high tensile strength, metallic and semiconducting conductivity, and great potential for applications. This work investigates the synthesis, alignment and purification of multi-walled carbon nanotubes, which were characterized by Electron Microscopy, measurement of electrical properties and Raman scattering. Synthesis of multi-walled carbon nanotubes (MWNTs) was carried out by Chemical Vapour Deposition, using three different precursors: Fe(NO3)3, ferrocene and iron phthalocyanine. Vertically aligned "forests" of large numbers of MWNTs were achieved using ferrocene and iron phthalocyanine as precursors. Products from iron phthalocyanine yield more graphitic CNT nanostructures, as determined by Scanning Electron Microscopy, Transmission Electron Microscopy, Thermogravity Analysis, Raman microscopy and Energy Dispersive X-ray spectroscopy. Patterned growth of vertical MWNTs arrays with a resolution of 2 microns was also obtained, using a predeposited substrate. A High Resolution Transmission Electron Microscope was employed to investigate the inner structures of individual MWNTs, giving well-resolved images of concentric nanostructures with inter-lattice spacings of 0.34 nm. Techniques for purification and manipulation of CNTs are required before CNTs' excellent properties can be exploited. In this thesis, dielectrophoresis (DEP) under high-frequency AC voltages using an array of micron-scale electrodes was adopted as the technique to align MWNTs between these, electrodes. This technique is effective for MWNTs since their long cylindrical structure and the high mobility of their charge carriers allow them to be electrically polarised. As a result, MWNTs experience large DEP forces in an AC electric field. In our experiments, inter-digitated electrodes were used to apply the electric field to CNT suspensions in various solvents. Alignment of CNTs along their axis was achieved within the gaps between adjacent electrodes at a frequency larger than 1.1 MHz, The AC admittance changes between the electrodes were monitored and were observed to be a clear reflection of the accumulation process of MWNTs. Also it was identified that distilled water was a better solvent than ethanol and isopropanol for DEP purpose on MWNTs. In addition, a prototype device was built to selectively purify MWNTs from as-grown samples by combining DEP and re-circulating fluid flow. It was found that this device is able to decrease the impurity content of MWNTs, which is collected on the electrode array, from the suspension of as-grown samples.</p>

During the last decades, most improvements in energy density of Li-ion batteries were done at both materials and electrode architecture levels. However, even today, the best batteries (eg laptop) have a small amount of active material (approximately 51% by weight for cells with high energy density), the rest divided between the current collectors 21%, packaging 13%, electrolyte 6.5%, binders and additives 8.5%. Attempts to increase the thickness of the electrodes and the electrode surface capacity (in mAh/cm2) while keeping architectures of conventional electrodes have encountered many difficulties mainly due to limitations in terms of electronic or ionic conduction or due to the limitations of charge transfer at the interfaces whose result is a strong limitation in terms of capacity even at very low rate of cycling.A very interesting solution to overcome these limitations was proposed 3 years ago by sintering the active material at high temperature providing the electronic contact while maintaining the initial preformed porosity. Indeed previous works have shown the possibility to prepare thick electrodes (LiCoO2 or LiFePO4) but the electrode processes are complicated to implement and the porosity is not necessarily controlled effectively [1-3].In this work, we propose to form thick composite sintered electrodes (active material, carbon, porosity) using a sintering technique of choice which is the Spark Plasma Sintering (SPS) which limits unwanted side chemical reactions thanks to the rapidity of the process. Our preliminary works carried out at LRCS have already shown the feasibility to manufacture by SPS thick porous composites electrodes. Indeed, by incorporating a salt (NaCl) in the electrodes, it is possible to dissolve it after sintering and therefore to generate porosity within the electrode. The porosity (pore size and volume) can be easily controlled by its percentage in volume and the particle size of NaCl. Our first electrochemical tests are very encouraging. On a thick electrode of LiFePO4, with 50% volume porosity, it was possible to obtain a capacity of 30 mAh/cm² for a theoretical capacity of 41 mAh/cm² at a rate of C/20, in liquid electrolyte, at room temperature and without additional carbon. Also, with Li4Ti5O12(the electrode having a porosity of 50% after sintering and dissolution of the salt), it was possible to obtain the theoretical capacity of 22 mAh/cm² in the first discharge.In this presentation, we will show the impact of the nature and the morphology of the porosity agent, the SPS conditions together with the addition of the conductor additives on the electrochemical performances of the individual electrodes (Capacity, Power rate studies) and in full cell configurations.[1] Wei Lai, Can K. Erdonmez, Thomas F. Marinis, Caroline K. Bjune, Nancy J. Dudney, Fan Xu, Ryan Wartena, and Yet-Ming Chiang, Adv. Mater. 2010, 22, E139–E144[2] Xue Qin, Xiaohui Wang, Jie Xieab and Lei Wen, J. Mater. Chem., 2011, 21, 12444[3] Chang-Jun Bae , Can K. Erdonmez , John W. Halloran , and Yet-Ming Chiang, Adv. Mater. 2013, 25, 1254–1258

High-energy electrode investigation for plug-in hybrid electric vehicles

A key aspect of any future battery technology development is safety. Although lithium-based batteries are ubiquitous, there are still challenges related to their energy density, cycle life, cost and safety. In regard to safety, compared with organic electrolyte, aqueous rechargeable batteries may provide a safer alternative for reliable, low-cost and large-scale energy storage systems. As seen from the penetration test in Fig. 1a-1b, the battery with organic electrolyte catches fire, yet the battery with aqueous electrolyte is relatively safe. Moreover, aqueous batteries have high ion conductivity and cost effectiveness. Generally, the cell voltage and energy density of aqueous batteries are lower than those of organic-based batteries (e.g. Li-ion) because of the relatively smaller electrochemical stability window of water. Among all the metals that are stable in water, zinc is the most active and has the lowest possible operating potential. This means using Zn anode can increase overall cell voltage of aqueous batteries. Moreover, zinc is globally available, inexpensive (3.19 USD kg-1), and has high capacity (820 Ah kg-1 and 5854 Ah L-1). Zinc-based aqueous batteries also possess the stability to be operated in ambient air. Accordingly, Zn aqueous rechargeable batteries are promising to become a safer energy storage system. Among zinc-based aqueous batteries, Zn-air batteries have high theoretical volumetric energy density, which is around three times that of conventional Li-ion batteries (LIB). Zn anodes have been investigated in neutral/mild acidic aqueous electrolytes. Yet in order to pair them with oxygen cathode to reach the highest energy density, alkaline aqueous electrolyte is ideal, in which the oxygen electrode has low polarization. In alkaline aqueous electrolyte, Zn anode undergoes a Zn (s) ↔ Zn(OH)4 2- (aq) ↔ ZnO (s) conversion. This solid-solute-solid transformation and insulating discharge product ZnO lead to three vital challenges: 1) ZnO passivates Zn surface and prevents further discharging, leading to low Zn utilization; 2) ZnO is insulating and can hardly be charged back to Zn; 3) diffusion of Zn(OH)4 2- causes the loss of active material and change of electrode morphology. Thus, anode modification and protection are needed to alleviate the passivation and dissolution. We firstly designed a Zn mesh@GO anode (Fig 1c). Graphene oxide (GO) layers on the Zn mesh surface deliver electrons across insulating ZnO and can slow down the Zn dissolution. However, the utilization of zinc is still low because passivation problem is not completely solved. Through SEM investigation, critical passivation size was found to be ~ 2 µm. Thus, we further designed a lasagna-inspired ZnO@GO anode (Fig 1d). ZnO nanoparticles are encapsulated by GO. ZnO lasagna structure has three features: 1) the size of ZnO nanoparticles is smaller than the critical size of passivation; 2) the fabrication of ZnO lasagna anode starts with commercially available ZnO nanoparticles (~100 nm), and is compatible with the roll-to-roll process, which is ideal for large-scale manufacturing; 3) GO allows permeation of OH- and water, and prevents loss of Zn active material through blocking bigger Zn(OH)4 2-. As a result, such lasagna anode achieves a high volumetric capacity of 2308 Ah/L and a remarkable capacity retention of 86% after 150 cycles. In contrast, the open-structured ZnO nanoparticle anode, without the protection of GO, completely died after 90 cycles. Figure 1

The demand for lithium-ion batteries, owing to their diverse applications such as in electric vehicles, aerospace, and electronic devices, has increased rapidly through the years. Since the first prototype of the Lithium-ion battery in 1985, new versions of the Li-ion battery have seen changes and modifications to the structure of the battery, particularly in the cathode and anode used. These, in turn, have increased efficiency and commercial viability in various ways, including by allowing for higher energy densities. This paper analyses trends in the volumetric and gravimetric energy densities of lithium-ion batteries from 2012 to 2022, ascertained using research papers which discuss lithium-ion batteries, and the implications of the evolution of these metrics.

Carbon nanotubes are very attractive for a wide range of potential applications. However, many applications require the growth of aligned/micropatterned carbon nanotubes with or without a modified nanotube surface. Simple pyrolytic methods for large scale production of aligned/micropatterned carbon nanotube arrays perpendicular to the substrate surface have been developed. These aligned carbon nanotube arrays can be transferred onto various substrates of particular interest in either a patterned or non-patterned fashion. The perpendicularly-aligned structure provides advantages for not only an efficient device construction but also surface functionalisation (both the inner and outer wall) while their alignment structure can be largely retained. These aligned carbon nanotubes with tunable surface characteristics are of great significance to various practical applications, ranging from plastic optoelectronics to bioceramics. Examples include biomolecule immobilised carbon nanotube biosensors, synthetic polymer supported aligned carbon nanotube chemical vapour sensors, metal nanoparticle decorated carbon nanotubes, and aligned coaxial nanowires of carbon nanotubes sheathed with titanium dioxide (TiO2) nanoparticles or thin films. These newly synthesised carbon nanotubes decorated with polymers, metal nanoparticles, and/or TiO2 coatings were demonstrated to show novel optoelectronic properties and should possess good bioactive behaviours with enhanced tissue attachment attractive for functional optoelectronic and bioceramic applications. This article reviews recent work carried out in the authors group on the preparation of nanocomposites based on aligned carbon nanotubes functionalised with polymers or metal (oxide) nanoparticles. Their potential applications as plastic optoelectronics and bioceramics will also be discussed.

Modeling the effect of electrode thickness on the performance of lithium-ion batteries with experimental validation

VO2/CNTs thick cathode electrode with multi-dimensional electron transport pathways enabled by rolling for high energy thermal batteries