The Heart of Electric Vehicles: A Deep Dive into Battery Technology

Introduction

With the progress of electric vehicle (EV) technology in the last decade, EVs have become much more common and affordable for the average consumer. This progress correlates directly with the progress of EV technologies, where the cost of parts has steadily declined and will continue to do so in the near future [1]. This technological evolution brings about opportunities for consumers that may not have existed prior. The dropping cost of EV technology, rising cost of gas prices, and break-down of old internal combustion engines (ICE) bring about the possibility and viability of EV conversions, where older ICE vehicles are given new life with the injection of new EV technologies, revitalizing a vehicle near the end of its life. 

For these conversions, the options for integrable parts are immense. Different types of technologies exist for different parts, which can cause confusion and uncertainty, a big one being the battery. Battery sizing can be a challenge on its own. We must know the range, vehicle dimensions, power requirements, and more for the conversion vehicle. But, even before that, we need to focus on the different types of battery technologies on the market. 

With different battery technologies come different advantages and disadvantages. These are important to consider when managing our needs against what is possible for the conversion vehicle. By carefully weighing these options, you can ensure that your EV conversion delivers the right balance of performance, longevity, and cost-effectiveness for your goals.

Legacy battery chemistries in the EV industry

As electric vehicles have evolved, so too have the battery technologies used to power them. While once considered cutting-edge, earlier technologies have been surpassed by modern advancements. However, their significance and lasting impact on EV development cannot be understated. Understanding these legacy battery chemistries provides insight into the technological hurdles and advancements that brought us to the current state of EV battery technology. Let’s explore some of the early battery technologies and their roles in the electric vehicle industry.

Lead-Acid 

Lead-acid batteries are among the earliest battery technologies, having been commercially available for over a century [3]. Their widespread adoption was due to their low cost and mature manufacturing process, allowing large-scale production [3]. However, their low energy density and heavyweight limit their application in modern battery electric vehicles (BEVs), as these characteristics reduce vehicle range and efficiency [3]. While lead-acid batteries remain reliable in certain low-power applications, their short lifespan and poor energy-to-weight ratio make them unsuitable for full-electric applications [3]. As a result, they are mostly used today in starter batteries for internal combustion engine vehicles and in some hybrid systems, but they are no longer considered viable for modern BEVs [3].

Nickel-Metal-Hydride (NiMH)

NiMH batteries became prominent in the 1990s as one of the first widely adopted battery technologies for vehicle electrification [4]. They played a crucial role in early hybrid electric vehicles (HEVs) because of their high power output, reliability, and ability to operate over a wide temperature range [4]. NiMH batteries were favoured for their robustness and lack of memory effect (a factor affecting the maximum load capacity of the battery), which made them suitable for vehicles like the GM EV-1 and the early Toyota RAV4 EV [5][4]. However, NiMH has been phased out of the BEV market due to its lower energy density and higher self-discharge rates than lithium-ion batteries [5]. NiMH is no longer considered ideal for EV conversions, as lithium-ion batteries offer better performance in terms of energy density, lifespan, and efficiency [5]. Nevertheless, NiMH batteries are used in HEVs due to their proven track record [4].

Lithium-ion (Li-Ion) batteries

Li-ion batteries dominate the EV market due to their high energy density, longer lifespan, and overall efficiency compared to older battery technologies [6]. These batteries are widely used in BEVs and plug-in hybrid electric vehicles (PHEVs) because they provide superior energy storage and power delivery, allowing for increased vehicle range and reduced weight [6]. Different Li-ion chemistries offer tailored benefits and limitations, many of which are important to consider when choosing the right battery for EV conversions. 

Lithium-Nickel-Manganese-Cobalt (NMC)

Lithium Nickel Manganese Cobalt Oxide (NMC) batteries are commonly used in EVs due to their balance of energy density, cycle life, and power output. NMC batteries typically have an energy density between 150-220 Wh/kg [8], offering a good range for EVs like the BMW iX3 and Volvo EX30. Their depth of discharge (DoD) can reach 80-90%, allowing for deeper cycling without significant wear. When operated under ideal conditions (-20°C and 55°C) [9], NMC batteries can achieve a cycle life of 1000-2000 cycles [1], depending on factors such as charging rates and thermal management. However, one significant disadvantage is their susceptibility to thermal runaway, which can occur at around 210°C, especially under high charge or discharge rates. This makes battery management systems essential to monitor and prevent overheating, ensuring safe operation [10].

Lithium-Nickel-Cobalt-Aluminum (NCA)

Lithium Nickel Cobalt Aluminum Oxide (NCA) batteries are widely used in high-performance EVs due to their excellent energy density and long cycle life. NCA batteries typically have an energy density of around 200-260 Wh/kg [1], making them suitable for EVs like the Tesla Model S and Tesla Model 3, which prioritize range and performance. Their recommended DoD is 80% [11], allowing for deeper cycling without significantly compromising lifespan [11]. When maintained under ideal discharging temperatures (-30°C to 55°C) [9], NCA batteries can achieve a cycle life of around 500-1000 cycles [1]. However, they are more prone to thermal runaway, which can occur at temperatures around 150°C, making thermal management crucial to ensure safe operation, particularly in high-power applications [10]. This vulnerability makes advanced battery management systems essential to avoid overheating and ensure reliable use in EVs [8].

Lithium-Iron-Phosphate (LFP)

Lithium Iron Phosphate (LFP) batteries are known for their superior safety, thermal stability, and long cycle life, making them a preferred choice in certain electric vehicle applications [1]. LFP batteries typically have an energy density of around 90-120 Wh/kg [1], which is lower than NMC or NCA batteries, but they offer enhanced safety and durability. These batteries can operate effectively across a wide range of discharging temperatures, from -20°C to 60°C, allowing for versatile applications in various climates [8]. LFP batteries can achieve a cycle life of more than 2000 under optimal conditions, making them ideal for vehicles prioritizing longevity and reliability [1]. Notably, they exhibit a low self-discharge rate of about 3% per month [8]. LFP batteries are used in vehicles such as the Tesla Model 3 (Standard Range) and BYD cars [14], reflecting their suitability for EVs prioritizing safety and cost efficiency [8]. One of the key advantages of LFP batteries is their high resistance to thermal runaway, which typically occurs at a much higher temperature of around 270°C, offering increased safety compared to other lithium-ion chemistries [8][10].

BlueForce uses LFP batteries for many vehicle conversion projects. A high safety rating, long cycle life, and reasonable energy density make them ideal for meeting users' needs. The excellent safety rating of LFP batteries encourages confidence in the conversion as they better protect against thermal runaway to ensure safety and provide a longer cycle life than most other battery technologies to deliver consistent performance over many years. 

Lithium-Cobalt-Oxide (LCO)

Lithium Cobalt Oxide (LCO) batteries are widely known for their high energy density, typically ranging from 150-200 Wh/kg [1], which makes them ideal for applications requiring significant energy storage in compact sizes, such as laptops and smartphones. However, in EVs, LCO batteries are less favoured due to the combination of their limited cycle life of around 500-1000 cycles under optimal conditions and high cost [10]. These batteries also suffer from higher self-discharge rates compared to other lithium-ion chemistries, contributing to a loss of capacity when idle [12]. Their recommended DoD is typically 80%, which balances performance and longevity [13]. LCO batteries are prone to thermal runaway, which can be triggered by overcharging or excessive heating, with a runaway temperature of around 150°C [1]. This makes them more vulnerable than other chemistries and necessitates advanced battery management systems. Despite their high energy density, the high cost of cobalt and safety concerns limit their usage in EVs [1][8][10]

Lithium-Manganese-Oxide (LMO)

Lithium Manganese Oxide (LMO) batteries are recognized for their superior thermal stability and safety, which makes them an attractive option for certain EV applications, especially in hybrid vehicles [1]. These batteries have an energy density of 100-150 Wh/kg [1], lower than other lithium-ion chemistries, but they offer excellent discharge rates, typically supporting 1C discharge, and can handle 3-10C under short bursts [10]. The DoD for LMO batteries is around 80%, ensuring a balance between performance and longevity. One of the significant advantages of LMO is its improved resistance to thermal runaway, which occurs at approximately 250°C, providing better safety margins than NMC or LCO batteries [8]. LMO batteries are commonly used in EV models like the Nissan Leaf and Chevrolet Volt, especially in hybrid configurations where stability is key. However, they have a shorter cycle life, generally between 300-700 cycles, and moderate self-discharge rates of about 2-3% per month [10]. Their moderate energy density and shorter lifespan make them better suited for hybrid and power tool applications rather than full EVs [1][8][10].

Lithium-Titanate (LTO)

Lithium Titanate (LTO) batteries are known for their exceptional safety, longevity, and fast charging capabilities, making them ideal for specialized EV applications. While their energy density is lower than other lithium-ion batteries, typically around 50-80 Wh/kg [1], LTO batteries offer outstanding cycle life, often exceeding 3000-7000 cycles under optimal conditions [1]. They also support rapid charging, with charge and discharge rates up to 10C, which makes them suitable for applications requiring quick power replenishment [1]. The DoD for LTO batteries can safely reach 100%, maximizing their usage without compromising lifespan [15]. LTO batteries are also highly resistant to thermal runaway, one of their biggest advantages, with safe operation even under extreme conditions. They typically operate across a wide temperature range from -30°C to 55°C [8], making them suitable for various climates. However, their low energy density and higher cost per kWh limit their use in mainstream EVs, though they are commonly found in buses and heavy-duty commercial vehicles [1] [8].

Conclusions

As battery technology continues to advance, the EV industry is set to benefit in both cost and performance. The shift away from legacy chemistries like lead-acid and nickel-metal-hydride in favor of more efficient lithium-ion options has opened up new possibilities for electric vehicles and EV conversions. With each lithium-ion chemistry offering its own strengths, such as higher energy density, longer cycle life, or increased safety, there is now a broader range of options to meet the varied needs of the market. As these technologies evolve, they will make EVs more accessible, reliable, and efficient, further driving their adoption and solidifying their role in the future of transportation. Continued advancements in battery technology will be essential in ensuring the ongoing growth and sustainability of electric vehicles.

Glossary

Energy density: The amount of stored energy within a unit of mass (Wh/kg in our case).

Memory effect: The loss of maximum storage capacity from recharging batteries before they are completely discharged.

Self discharge: The process where a battery loses energy over time when not connected to a load. 

Cycle life: The number of times a battery can be fully charged and discharged until the maximum capacity of the battery reaches 80% of its original capacity. 

Depth of discharge: Indicates the percentage of the battery that has been discharged relative to the overall capacity of the battery [18].

Deeper cycling: Discharging the battery to a lower state of charge before recharging to a high capacity. 

References

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