Batteries have long played a significant role in the construction of portable tools, computers, and mobile phones, as well as uninterruptible power supplies and satellites. Scientists have been attempting to increase the energy density of batteries for years (the amount of energy in a given size and weight). As the number of portable devices, ranging from industrial measurement equipment to mobile phones, expanded, so did the demand for larger energy densities. Battery weight became a problem as the number of telecommunications satellites expanded. Every advancement in technology has tended to place a premium on battery power. While scientists strove to enhance battery technology, electronics continued to advance at a dizzying speed, requiring ever-increasing quantities of energy and power. But it wasn't until the arrival of electric cars (EVs) that manufacturers started to take notice. Consider the value of batteries in providing a better range, greater reliability, and cheaper costs. Size and weight are just as important as cycle life in the EV market. Primary (single-use) and secondary (rechargeable) batteries, which are divided into primary (single-use) and secondary (rechargeable) categories, have experienced one advancement after another in their quest to give more energy density than ever before.

THE CURRENT STATE OF BATTERIES

Lithium-ion batteries have been the favored choice in a wide range of applications in recent years. It's simple to understand why. They meet all eight of the ideal battery's requirements: high specific energy, high specific power, affordability, long life, safety, wide working range, low toxicity, and quick charging.

Furthermore, lithium-ion batteries are extremely adaptable, have a high energy density, a low self-discharge rate (less than half that of nickel-based batteries), and require less maintenance. They also meet the most important need of any battery: the ability to offer instant start-up when required.

However, they have their limitations as well: transportation concerns have been well-documented, and lithium-ion batteries age even when not in use, necessitating the inclusion of a protective circuit to keep voltage and current within safe limits.

Li-ion battery technology has progressed significantly over the last 30 years, but the best Li-ion batteries are nearing their performance limits due to material limitations. They also have significant safety concerns—such as catching on fire if overheated—leading to increased costs because safety features must be designed into the battery system.

Fig.1. Li ion battery

recent advancements in battery technology

Solid-State Batteries

Despite the fact that the present market is dominated by lithium-ion batteries, there is a movement toward solid-state battery architecture. Moving from a liquid electrolyte battery to a solid-state battery may appear to be unconventional, but it's all about outpacing current energy density capabilities. In a liquid battery system, metallic lithium generates dendrites, reducing cycle life and endangering the batteries' safety. The energy density of the battery is increased without compromising safety by replacing the highly reactive liquid electrolyte with a solid-state electrolyte, which is naturally safer and structurally more robust. For a      variety of reasons, the industry is currently migrating to solid-state batteries. The first is that, even when fine-tuning the design to gain more density, standard lithium batteries with a liquid electrolyte have reached the theoretical limits of the electrode combinations being used. 

Small cells are now the only solid-state batteries that can compete in the market. Thin-film batteries were the first commercially accessible solid-state batteries. The electrodes and electrolytes of these nano-sized batteries are made up of layered materials. Thin-film solid-state batteries are similar to traditional rechargeable batteries in construction, but they are much thinner and more flexible. Thin-film batteries, in addition to being lighter and smaller, provide a better energy density for tiny electronic devices like pacemakers, wireless sensors, smart cards, and RFID tags.

 

Fig.2.Solid State Battery Photo: Solid Power

Solid-state batteries have technological obstacles in addition to addressing concerns of price and scalability. Solid-state batteries are more safer, although dendrites, the root-like build-up on lithium metal in the anodes that occurs when the battery charges and discharges, still exist. The quantity of solid electrolyte capacity and hence the stored charge is reduced when dendrites form. The largest issue for developers is finding the correct separator material that permits lithium ions to pass between the electrodes while inhibiting dendrites. Researchers employed materials such as a polymer, which is extensively used in liquid electrolyte batteries, or a hard ceramic, according to the new publication Interface Stability in Solid-State Batteries. The polymer does not prevent dendrite formation, and the majority of the ceramics utilised are brittle and can not withstand several charging cycles. Solid-state batteries are projected to give customers several appealing performance improvements once the dendrite problem is solved:faster charging, higher energy density, longer life cycle, and greater safety.

Tabless battery tesla

Tesla has a design for a table electrode battery that has been patented. A "Cell With A Tabless Electrode" was described in the Tesla patent. The cathode, anode, and separators are all wrapped together in a jelly-roll configuration in traditional tab batteries. The cathode is the positive end of a terminal that allows electrons to flow out of a device, whereas the anode is the negative end of a terminal that allows electrons to enter. The anode is a source of electrons for an external circuit, whereas the cathode is a sink of electrons.         Separators are seals that keep the cathode and the anode from colliding.              Although no electrons flow if contact is made because there is no potential difference, a short circuit can cause harm if direct contact is established between the two electrodes when the circuit is closed.The electrolyte, which is a             chemical component (e.g. soluble salt) that helps transfer Lithium ions during a discharge (when the battery is in use) and the opposite process when recharging the battery, is located between the two electrodes. 

This produces free electrons, which go through a circuit to power a device          during discharge and charge the battery during recharging.

 

Fig.3.Sample illustration of new tabless electrode battery (Source Tesla Patent)

Prior to the invention, the Tesla battery was made out of a cylindrical cell with electrode tabs. The cells are then put together into a battery module and placed in the car's trunk (e.g. Model S, Model X, Model 3). Normally, tabs supply current to the circuit that powers a device, such as the EV in this example (Electric Vehicle). During the production process, the tabs must be linked to the circuits they are powering using specialised welding. According to Tesla, this will "...raise costs and create manufacturing issues." Tabs also provide greater resistance, which can generate more heat, resulting in worse energy transfer efficiency. This was the impetus for developing a better battery architecture.

The use of a table electrode would speed up the fabrication of batteries. It will also improve the battery's efficiency and reliability. By removing the tabs, the connection can be made with taps or spikes that connect directly to non-welded components. To transfer energy more efficiently, the design increases conductivity by using a connection with lower ohmic resistance. This could be useful for Tesla vehicles that need to be supercharged or charged quickly.

According to the patent:

“The maximum distance current will travel is therefore the height of the electrode as opposed to its length. Depending on the cell form factor, the height of an electrode is typically 5% to 20% of its length. Therefore, the ohmic resistance in the negative electrode during electrochemical cycling can be reduced by 5 to 20 times via embodiments of the present disclosure.”

This could lead Tesla to abandon its portable battery pack development in favour of an integrated battery module. That would need switching to a less flexible and non-removable kind, comparable to Apple's computer design. Because the manufacture of tabless electrodes eliminates the need for complex welding, battery modules may be smaller and take up less space.

 

Catl's sodium ion batteries

CATL's first generation of sodium-ion batteries, which are based on a series of chemical system breakthroughs, have high energy density, quick charging capabilities, exceptional thermal stability, remarkable low-temperature performance, and high integration efficiency, among other features.

CATL's sodium-ion battery cell has an energy density of up to 160Wh/kg and can charge to 80 percent SOC in 15 minutes at room temperature.

Furthermore, the sodium-ion battery has a capacity retention rate of more than 90% in a low-temperature environment of -20°C, and its system integration efficiency may reach more than 80%.

Fig.4.Catl's sodium ion batteries

The thermal stability of sodium-ion batteries exceeds the national safety criteria for traction batteries. The first generation of sodium-ion batteries may be employed in a variety of transportation electrification situations, particularly in areas with extremely low temperatures, where their great benefits become apparent. It may also be easily customised to meet the demands of any situation in the energy storage industry.

The energy density of the next generation of sodium-ion batteries is expected to approach 200Wh/kg.

Dr. Qisen Huang, deputy dean of the CATL Research Institute, stated at the event that sodium-ion battery manufacturing equipment and processes are perfectly compatible with lithium-ion battery manufacturing equipment and processes, and that production lines can be quickly switched to achieve high-production capacity.

CATL has begun commercial deployment of sodium-ion batteries and expects to complete a basic industrial chain by 2023. CATL encourages upstream suppliers, downstream customers, and research institutes to collaborate on sodium-ion battery promotion and development.

 CATL sodium-ion battery (SIB) specification

·       Energy-density: 160 Wh/kg

·       Fast charging: 80 % in 15 minutes

·       Capacity retention at low temperatures: above 90 % at -20º C

Fig.5

Graphene battery

The graphene batteries do have graphene electrodes for both cathode and anode. Graphene has a highest intrinsic mechanical strength (1060 Gpa) and thermal conductivity (3000Wm-1k-1) . The graphene battery operates based on fast surface reaction occurring in both electrodes, thus delivering a high-power density, which is better than that of conventional lithium ion battery. The properties like porous morphology and high electrical conductivity helps to increase the power density. Among various high performance energy-storage devices such as lithium-ion battery (LIBs), superconductors, and lithium ion capacitors (LICs), the LIBs are promising candidates because of their high energy density. However, the power density of available LIBs is not suitable for large-scale applications, and the cost is too high . These issues of low power density and high cost – are closely related to the fundamental electrode reaction characteristic of LIBs. Moreover, it retains high energy density, attributable to the wide potential difference between the anode and cathode. From the literature, it is observed that the electrochemical property, i.e., specific capacity of graphene battery evaluated at a current density of 0.05 A g-1 in the voltage window between 0.01 and 4.3 V is approximately 170 mAh g-1 based on the weight of the cathode, which corresponds to 100% utilization of the graphene cathode, whereas the graphene anode delivers a capacity of 430 mAh g-1, which corresponds to 80% utilization. The charge/discharge profiles of the graphene batteries are not significantly altered upon repeated charging and discharging cycle, thereby ensuring that the electrochemical reaction is highly reversible in graphene batteries, and showing better performance as compared to LIBs and superconductors.

Fig.6.Graphene battery

Aluminum-air battery

Amongst all metal-air batteries, the aluminum-air battery is attractive candidate as a power source for electric vehicles (EVs) because of its high theoretical voltage (2.7 V) and high energy density (8100 Wh kg-1), which is significantly greater than that of the state-of-the-art lithiumion batteries (LIBs), apart from high capacity, and lower cost (depending on the metal anode). Al-air batteries reveal high energy densities ranging between 2~10 folds higher than that of LIBs. The lowest cost coupled with high specific capacity of 2.98 Ah g-1, makes is more suitable for large- scale applications. The specific capacity of Al-air batteries is much higher than those of manganese (2.20 Ah g-1) and zinc (0.82 Ah g-1). Al-air battery has the potential to be used to produce power to operate cars and other vehicles . The Al-air battery has proven to be very attractive as an efficient and sustainable technology for energy storage and conversion with the capability

Fig.7.Aluminum-air battery

 Sinanode battery

A set of technologies for fusing silicon nanowires directly onto commercial graphite particles used in the anodes of electric vehicle batteries. The quantity of energy stored, charging speed, and power provided are all "supercharged" by these technologies.

Silicon is being used in a few electric vehicle models because it can store ten times more energy than graphite alone. However, due to technological difficulties, it is restricted to a tiny quantity and only minor increases in battery performance. Adding more silicon to EVs in a more efficient manner is now seen as the critical breakthrough required to produce competitive EVs that meet market demand for high performance across entire EV product lines. Other alternatives are unable to satisfy the technological and economic hurdles in the short future, but SINANODE silicon nanowire technology can.

Electrical wires made of silicon nanowires are hundreds of times smaller than human hair. The SINANODE technique binds silicon nanowires directly to the graphite using just silane (a gas made from metallurgical grade silicon and accessible from numerous manufacturers), nitrogen, and small quantities of power, similar to putting an electrical cord into an outlet. Silicon nanowires stay pliable and do not break when charged. The silicon triples the energy density of the anode by having hundreds of thousands of wires on each graphite particle.

SINANODE redefines the battery's performance and cost while using every component of the present value chain, including large-scale graphite powder production and existing manufacturing investments. In reality, the SINANODE process is unconcerned with the type of graphite employed or the particle size of the graphite particles. The SINANODE method ensures uniform silicon dispersion independent of particle size.

Silane delivers excellent yields and lowers anode cost (in dollars per kWh) by using existing production equipment. More crucially, the resultant silicon-graphite composite anode material can be employed right away with current industrial scale electrode coating equipment and is compatible with the other materials, cell design specs, and procedures used in today's EV cell manufacturers.

A 300 tonne (300,000 kg) SINANODE prototype production capacity of 20 percent silicon and 80 percent graphite anode material delivers a 1 GWh energy storage capacity in lithium batteries. The silicon nanowire / graphite composite material delivers higher first cycle efficiency and better cycling at a cheaper cost than even the greatest energy density EV cells on the market today when blended with pure graphite. Leading EV firms confirmed their exceptional success in 2019 and 2020, opening the road for large-scale manufacturing ambitions.

Fig.8. Sinanode 

SELECTION OF ADVANCED BATTERY TECHNOLOGIES

As discussed in the previous section, it is realized that there is a need to develop a tool or method for selecting the best advanced battery technology to help EV OEMs. Based on the literature, and interaction with the some of the OEMsof EV batteries and battery management systems, an MCDM (Multi-Criteria Decision Making) method is proposed to select the advanced battery technology that is based on WPM (Weighted Product Method) . In this method, the performance factors of various battery technologies are selected, compared, appropriately weighted based on the importance, and combined to obtain A performance score, which is then used to rank the battery technologies. Table 1 presents comparison of performance factors of four different battery technologies, which have been reviewed in the previous section. The following performance factors are identified and considered for the selection of advanced battery technology;

1. Cost effectiveness (C): 

The cost of batteries is one of the major stumbling blocks standing in the way of widespread use of electric vehicles. Hence, the price of the battery must be as low as possible.

2. Performability (Pr): 

This represents the ability of battery to perform under combined effect of C-rate, E-rate, nominal capacity and energy of the battery. A C-rate is defined as the measure of the rate of discharge that is relative to its maximum capacity, whereas, E-rate represents the discharge power. The nominal capacity and energy are reduced with an increase in C- and E- rates. After a few thousand of charging cycles, the performability of a typical EV battery pack does not stay up to the task of powering the vehicle. Hence, the batteries with reduced C- and E- rates are preferred for electric vehicles.

3. Safety (S): 

Though the battery related safety issues are being addressed by the battery developers, yet the failures are bound to happen during application. The battery technology should ensure the maximum safety for EV applications.

4. Life (L): 

In general, batteries degrade with time regardless whether they are in use or not. Moreover, High temperature and charging and discharging cycles accelerates the failures. It is, therefore, crucial to consider the aging characteristics of the battery before installing onto EVs.

5. Weightlessness (W):

In order to reduce the gross vehicle weight of the EV, it is important to use light weight batteries.

6. Recyclability (R): 

The stringent environmental regulations have forced EV OEMs to have closed loop recycling of batteries. Although the OEMs have the contingency plans to recycle their batteries to a great extent, yet the battery developer/ manufacturers must ensure that the batteries are fully recyclable.

7. Maintainability (Mn): 

The batteries lose their efficiency due to frequent charging / discharging cycles, and eventually become week to retain the charge. This lessens driving range gradually. Moreover, a cooling system is required to be integrated with the battery to maintain safe operating temperatures. This may require regular inspection and periodic maintenance. The complete battery management system should need less maintenance and/ or should be less complex to be easily maintainable.

8. Manufacturability (Mf): 

The design and manufacturing of complex battery management system that contains various subsystems like control, and cooling subsystems remain a crucial task for the battery manufacturers / developers. The battery elements should be good enough to reduce or eliminate the requirements of the complex battery management system. This will help to lessen the manufacturing difficulty of the battery system.

9. Fast Charging (F): 

Fast charging of EV batteries is in huge demand. The battery must be developed to accept the fast charge, without affecting the life of the battery.

 

CONCLUSION

The race has begun. With EV sales surging, the need for high-density, long-life, and low-cost batteries is heating up, resulting in a congested battery market. This is fantastic news for battery research and development, as this is what is required to get batteries to market rapidly. Several materials and designs are currently being investigated and are making substantial development.Soon, EV fast charging stations will have batteries to serve as buffers and keep the electrical grid more stable, SIBs seem perfect for the job. 

REFERENCES

https://eepower.com/technical-articles/examining-current-advances-in-battery-technologies/

https://www.asme.org/topics-resources/content/advancing-battery-technology-for-modern-innovations

https://medium.com/0xmachina/the-tesla-tabless-electrode-battery-breakthrough-8f032fb67b81

https://onedsinanode.com/sinanode/

https://pushevs.com/2021/07/29/catl-reveals-its-first-generation-sodium-ion-battery/