Dissecting lithium battery technology

By Cameron Perks

Rechargeable batteries are an essential part of every modern day person's life, and are used by most people in the developed world on a daily basis. The most common rechargeable batteries are known as lead acid, NiCd, NiMH and lithium-ion or Li-ion.

Lead acid, with its heavy physical weight, environmental toxicity, low specific energy and limited cycle count, still holds a solid position for starter and standby batteries, as no other system can currently beat its cheap price and ruggedness.

Rechargeable battery family tree

The Li-ion family receives the most attention and is slowly replacing its nickel-based predecessors which dominated the battery world until the 1990s. And while the lead acid family may still be the cheapest on the market up-front, the cost of ownership for a Li-ion battery versus a lead acid one could tip the scales in lithium's favor.

Shipping, set-up, engineering, maintenance, installation and disposal cost benefits may outweigh the lead-acid argument in many cases, as well as its improved safety, reliability, and reduced environmental impact.

Variability between Li-ion batteries

Li-ion batteries have a vast array of chemistries with end use depending on weight, lifespan, safety performance, specific energy and power, cost and the overall power supply performance. Development of these batteries is driven by end uses, as well as the cost of raw materials.

The Li-ion system was conceived as far back as the 1970s, but, like all cutting-edge technology, did not gain traction right away. By the 1990s, Li-ion was being taken up rapidly.

The term 'lithium-ion' refers to a family of batteries in which ions move from the negative electrode (anode) to the positive electrode (cathode) during discharge and back again when being charged.

Lithium battery performance (Source: Sealed Performance Batteries)

Li-ion batteries are broken down into two sub-types; lithium iron phosphate (LFP) and metal oxides -nickel manganese cobalt (NMC), nickel cobalt aluminum (NCA), cobalt (LCO), manganese (LMO) - and lithium titanite (LTO). With the exception of lithium titanite (LTO), it is usually the material composition of the cathode which gives its name to the Li-ion type, with the anode most commonly made of graphite.

A speaker at this year's IDC Technologies Lithium Battery Conference, Ryan Hammond, an electrical engineer by trade and now director of Sealed Performance Batteries, stressed that Li-ion batteries are a "family of batteries".

In his talk, which focused on how the world is to replace lead-acid battery systems with Li-ion, Hammond said that "the important thing to note is that the best battery technology depends on the application".

Nickel manganese cobalt

The NMC has become one of the most widely used lithium technologies in the world. The battery is gaining popularity in home energy storage systems, such as the 7kWh Tesla Powerwall, the LG Chem equivalent and the Leclance Apollion Cube.

Importantly, this battery is relatively safe with a 210°C thermal runaway threshold, as well having a good charge time and low cost of production.

The NMC battery additionally has a relatively high number of charge cycles, defined as the number of times the battery can be discharged and charged again before the maximum capacity of the battery is reduced to 80-85% of its initial capacity. In NMCs this can be anywhere between 3,000 and 8,000 cycles.

Another advantage of NMC batteries is that their composition can be modified to produce high specific power while maintaining low specific energy. This characteristic has already given rise to NMC use in electric vehicles (EVs) such as the BMW i3 and the Nissan Leaf.

Specific energy refers to the battery's gravimetric energy density and defines battery capacity in terms of weight (Wh/kg). Similarly, energy density (as opposed to gravimetric energy density, or specific energy), reflects volume in litres.

Specific power, a separate term, can be defined as gravimetric power density and is indicative of loading capability. To make these terms simpler, the relationship can be represented by water flowing from a water bottle into a glass, seen below.

Specific energy in Li-ion batteries (Source: Battery University)

The water in the bottle represents specific energy (capacity); the spout pouring the water governs specific power (loading). Here, the bottle of water has high energy density (or specific energy) and lower specific power.

A battery can have high specific energy but poor specific power as is the case with the alkaline battery, or low specific energy but high specific power as with the  supercapacitor.

Nickel cobalt aluminum

Moving on to NCAs, which are closely related to NMC batteries in terms of characteristics but differ in that they are slightly less safe with a thermal runaway point of 150°C, in addition to being more expensive.

Thermal runaway occurs when a battery is overheated and results in heat spreading from the inside to the outside of the battery, occasionally resulting in explosions and fires. This has already become a major concern for airlines carrying Li-ion batteries.

On the plus side, NCAs have a higher energy density than NMCs, while still maintaining a higher specific power. This is important, because it means that like NMCs, NCAs are well suited to EVs, and are now known for their use in Tesla cars. NCA battery packs are the most expensive part of a Tesla, and provide power with a 435km range.

Lithium iron phosphate

Lithium iron phosphate, or LiFePO₄, is a well-known lithium technology due to its wide use and suitability for a range of applications. The battery is recognised for its moderate specific energy, excellent safety characteristics, good number of cycles (5,000-8,000), great charge/discharge capabilities, as well as its moderate price point.

These characteristics make the LiFePO₄ battery a strong option for residential storage as per their use in the Alpha ESS battery and the Enphase battery system.

The cell voltage of 3.2V/cell also makes it the lithium technology of choice for sealed lead acid replacement in a number of key applications.

There are a number of reasons why LiFePO₄ is the most suitable lithium technology for replacement of sealed lead acid batteries (SLA). These include its similar voltage, similar charge voltage and its all-round good performance for multiple applications.

LiFePO₄ batteries are also one of the safest forms of the lithium technologies when considering temperature and abuse such as overcharge and discharge, short circuit and penetration, as they have the highest thermal runaway point of any of the lithium batteries mentioned, have a long shelf life (they experience a slow rate of capacity loss, meaning that they can sit on a shelf for up to 12 months without requiring a refresh charge) and have a high cycle life, making them very cost affective.

LiFePO₄ batteries are also environmentally friendly due to their chemistry components. When considering this against the environmental risk posed by lead acid chemistry against the direction in which companies are heading in terms of environmental care and sustainability, LiFePO₄ makes a compelling case.

^{Source: Ryan Hammond, Sealed Performance Batteries}

However, although LiFePO₄ batteries are becoming a very viable option for SLA replacement, they still have a long way to go, as demonstrated by a 2015 Avicenne Energy study demonstrating SLA's current 90% market share.

­And while LiFePO₄ shows exemplary safety characteristics, talks at this year's IDC Technologies Lithium Battery Conference were quick to point out that a battery monitoring system (or BMS) is still necessary in every case.

Li-ion batteries require a BMS for safety and to protect the cells from damage in scenarios such as over-temperature, over-charge, cell imbalance and short circuit.

In addition to home energy storage, LiFePO₄ batteries are suited to mobility vehicles, recreational vehicles, caravans and campers for their high cycle applications, medical devices, RC devices for their quick-charge capability, as well as boats and gold carts for their weight.

Atlas Copco announced this year the first 100% battery driven underground loader, something that the company says offers potential for greater production, reduced costs and zero emissions. The system also allows for lower heat emission, reducing cost of mine ventilation or refrigeration.

The Scooptram ST7 Battery will first be introduced in Canada and the US and will be gradually rolled out across the globe.

Battery-driven underground loader (Source: Atlas Copco)

LTO as a battery cell is distinguished by the fact it is not the material located in the cathode, rather it replaces the graphite in the anode of a typical Li-ion battery. The cathode is made of graphite and resembles the architecture of a typical lithium-metal battery.

LTO batteries have a nominal cell voltage of 2.40V, can be fast-charged and deliver a high discharge current of 10 times the rated capacity. The cycle count is said to be higher than that of a regular Li-ion of 15,000 cycles or more, depending on the depth of discharge, operation temperature and charge/discharge rates. Li-titanate is safe, has excellent low-temperature discharge characteristics and obtains a capacity of 80 percent at -30°C. 

LTO batteries can operate in conditions of up to around 60°C, thus a thermal runaway event is significantly less likely to occur. LTO cells can also be re-operated after an event of an over-discharge, unlike conventional graphite-based Li-Ion cells. This feature enables the user to operate the battery cells under extreme environmental and operational conditions.

The two characteristics which work against LTO are the low energy density at approximately 63Wh/kg and its relative high cost compared to the other options, however these are offset by the very high specific power and extremely high cycle life.

Despite its benefits LTO technology is relatively unknown. The cell's characteristics make it an ideal solution for applications that require the battery to be cycled highly or where there is a short amount of power required in a short time, such as grid applications and electric buses. It can also to be charged at a rapid rate, again an advantage for heavy EVs.

Applications such as grid stabilisation, frequency shifting and peak saving, as well as industrial type EVs (those which can handle the heavy weight) such as buses, ferries and trucks are ideally suited to LTO. The Leclanche Ti-Box is an example of an energy storage system that currently used LTO technology.

Lithium sulphur

Like LTO, lithium sulphur batteries use a lithium anode, this time with a carbon/sulphur cathode. The battery is known for its extremely high energy density, doubling that of NCA energy density. Sony, which also commercialised the first Li-ion battery, plans to introduce lithium sulfur batteries to the market in 2020.

Alternative Li-ion battery chemistries

Two more popular Li-ion battery chemistries exist, including manganese oxide (LMO), and lithium cobalt oxide (LCO) chemistries. LMOs have a specific energy between that of a LFP and NMC cell, and the LCO has a specific energy equal to the NMC.

LCO cells are the more commonly known cell type, having a high capacity that is used in handheld devices such as cell phones, laptops and cameras, while LMOs have a lower capacity, but a higher specific power and long life.

Battery market share (Avicenne Energy)

Like the LFP and NMC, LMO cells may be used in batteries which are in medical devices, hobby equipment, e-bikes and even find use in EVs.

Another battery is the lithium-air (Li-air) cell; a metal-air battery that uses lithium oxidation at the anode and reduction of oxygen at the cathode to induce a current flow. The reason behind the drive from EV manufacturers for Li-air battery technology is that pairing lithium and oxygen (from air) can theoretically lead to electrochemical cells with the highest specific energy possible. 

The energy density of gasoline is approximately 13 kWh/kg, which corresponds to 1.7 kWh/kg of energy provided to the wheels after losses. Theoretically Li-air can achieve 12 kWh/kg excluding the oxygen mass and deliver the same 1.7 kWh/kg to the wheels, after losses from over-potentials, other cell components and battery pack auxiliaries.

Avicenne Energy expects Li-air issues to be overcome and commercialised by 2030.

Lithium battery composition and supply

The six Li-ion battery chemistries - LTO, LFP, LMO, NMC, LCO and NCA - use varying amounts of lithium in their cathode and electrolyte formulations.

According to John Petersen, a global thought leader on energy and sustainability issues, a Li-ion battery with perfect electrochemical efficiency would need 80 grams of lithium per kWh of capacity, but "perfection doesn't exist in the real world, the industry average is closer to 160 g/kWh".

Peterson goes on to say "while LTO cells don't use carbon-based anodes, the five remaining chemistries use about 1kg of processed carbon per kWh of battery capacity".

Material	Global Supply 2015 (metric tonnes)	Demand 2015 (metric tonnes)	2020 (metric tonnes)	2025 (metric tonnes)
Flake graphite	380,000	133,000	164,000	290,000
Lithium metal	32,500	9,760	12,160	21,520
Cobalt	92,000	35,000	40,110	64,842

^{Global battery mineral supply and demand. Source: John Peterson, Investorintel - based off Avicenne Energy studies}

When Avicenne Energy forecast cathode active materials in 2012, the study concluded that while NMC and LCO chemistries would still dominate the market, LFP would become a new significant player in the cathode space.

Cathode active materials, worldwide battery market 2012-2025 (Avicenne Energy)

Cathode materials are heavily dependent on the cost of the chemistry's active materials, with UBS revealing that 70% of the price of a lithium battery is accounted for by the raw material.

Cobalt supply difficulties could be a major blockage when it comes to cheap Li-ion technology, with no primary cobalt mine in existence and very little transparency. Li-S batteries are already significantly outperforming Li-ion batteries incorporating cobalt alloy cathodes and could be a replacement as a cathode material as cobalt prices rise.

Adrian Griffin, Managing Director of Lithium Australia, told IDC Technologies Lithium Battery Conference delegates that "the Li-S configuration, as well as being a prime contender in resolving cobalt supply issues, may even come to dominate the portable energy storage space in due course".

Adding that "while commercialisation of Li-S cells is in its infancy, the potential to substitute a cathode material costing US$200/tonne (sulphur) for one costing US$24,000/tonne (cobalt) while achieving a fivefold increase in efficiency is beguiling".

Supplying those materials today are a vast array of companies, summarised by Avicenne in the below graphs. In addition to those companies dominating the space, recent new entrants in the field include 3M LG Chem, Du Pont, BASF, Mitsubishi and Dow.

^{Battery material suppliers (Source: Avicenne)}