eMerging trenDs in bATTery TeChNoLoGyGlobal warming and increasing levels of pollution are the two key factors driving the march towards electric vehi-

cles (eVs). eventually, the market adoption of eVs will increase purely because of economics and convenience.

As of now, consumer fear of adoption and lack of charging infrastructure are the major factors for the slow

growth in eV sales. however, multiple efforts from the government as well as the private sector are helping im-

prove charging infrastructure, and as more people start using eVs, the adoption will go beyond the early users.

how technology will evolve to make eVs the only choice to customers will be seen over a period of time. in this

article, we look at how battery technology – the backbone of all eVs – is changing for good.

BATTERy TECHNoLoGy TRENDS

The battery is usually the critical factor that dictates a vehicle’s major parameters, such as range, speed & acceleration, cost and life. These vehicle parameters get translated into battery parameters includ-ing the following: :: Energy density – gravimetric and

volumetric: energy density will decide how much range you can integrate into the vehicle;

:: Degradation rate: degradation rate will decide how fast the battery capacity fades in various conditions, which is very critical. Based on the cell design, the degradation rate can vary quite massively at different oper-ating conditions;

:: Power performance: power perfor-mance will decide the top speed and acceleration of the vehicle as well as the charging speed;

:: Safety: safety is the biggest concern with Lithium-ion batteries as the elec-trolyte is highly flammable;

:: Cost. Over the past decade, we’ve seen battery technology evolve. A big jump came from cell technology change, moving from lead acid or nickel metal hydride batteries (Ni-MH) to lithium ion. Though lithium ion cells and batteries have been around for two decades, the technology has just reached the ramp in the S-curve of the lifecycle. This is evident in how fast the prices are dropping, 1. Battery technol-ogy itself depends on improvement in var-

AUThOrs

SWApNIL JAINis Chief Technology Officer

and Co-Founder at Ather energy in bangalore (india)

www.autotechreview.com52

teCHNoLoGy bATTeries

ious technologies, for example, cells, ther-mal management and battery production.

CELL TECHNoLoGy

Cell is the major cost of the battery and a major contributor amongst other battery parameters. Let us look at the trends within each parameter:

a) Energy densityEnergy density is the single major factor with the highest impact on the industry. It improves range, both directly and indi-rectly, and helps in power performance. Though degradation rate and safety gets adversely affected, there are ways to tackle that by additives and playing with composition of electrodes.

Energy density also has a direct impact on cost reduction. As the energy density goes up, with the same effort (read over-head costs), you can package more energy in a cell and hence decrease the overall cost of the product. The process though isn’t linear, as the cost of high energy den-sity material as well as the amount of material going in the cell increases. The improvement in energy, 2, happens because of three reasons:i. New Electrode Chemistries: New

cathode chemistries such as NCA (Nickel Cobalt Aluminium oxide) vari-eties have high charge capacity in excess of 180 Ah/kg (more than any commercial chemistry so far) at high average voltage of 3.65 V. NCA also has high density that allows more material in same volume. Also, in recent times we have seen silicon com-

posites partially substituting graphite as anode materials. These composites have over five to eight times the charge capacity of graphite and hence increased energy density of cells. In addition to these, highly conductive advanced carbons are reducing the need for additives; thus reducing occu-pied volume and allowing more active materials in the cells.

ii. Better Cell Design: Packaging more material can have adverse effect on safety and lifecycle of the cell. Improvement in cell design by means of electrolyte additives, treated elec-trodes allows designers to start packag-ing higher amount of active materials in the cell.

iii. Improvement in Cell Manufacturing: Process improvement in terms of elec-

trode coating and winding also ena-bled adding more material in the same size. The move from 18,650 form factor to 21,700 is a demonstra-tion of the industry now trying to heavily optimise the designs from a manufacturing perspective.

b) Degradation rate and power performanceThere are two approaches while tackling degradation rate::: High lifecycle with low energy density

and high power performance; and:: Low lifecycle with high energy density

and low power performance.Some cell manufacturers are moving towards making cells that have a very high lifecycle at higher charge discharge rates – > 3,000 cycles by compromising on energy density. The idea is to give smaller range but to last longer. This works well for public transport. Lithium titanate and lithium iron phosphate are examples of this type of chemistry.

The other trend is to work with high energy density but lower lifecycle cells at lower charge discharge rates – ~ 1,000. This helps remove range anxiety and hence works better for personal vehicles. Nickel cobalt aluminium (NCA) and nickel manganese cobalt (NMC) are examples of this type of chemistry. The overall trend is towards getting the maxi-mum energy throughput out of the cell before its capacity drops significantly by 70-80 %.

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1 Despite a huge historical spread in li-ion prices, they are begnining to converge and keep falling

2 improvement of performance and cost of li-ion by a factor of three in energy density and fac-tor of 10 in cost

Source: source: Lux Research, Inc.www.luxresearch.com

Data Source Joint Center for Energy Storage Research (JCESR)

53autotechreview Januar y 2017 Vo lume 6 | is sue 1

c) SafetyThere are continuous improvements hap-pening on the safety front. Cells today are very safe in terms of over voltage toler-ance, short circuit and extreme operating conditions. These are mainly attributed to improvement in electrode chemistries and additives, which bring higher stability in the cells. Today’s cells can take a lot of abuse without any catastrophic effect. For instance, cells are tested for stability at twice their operating voltage, crushing scenarios, and temperatures up to 60° C.

d) CostMajor cost of the cell comes from its active materials and significant part of it is cathode. Traditional cathode comprises of lithium, nickel, cobalt and manganese, and most of these are expensive materi-als. Given this, the industry is moving to chemistries like NCA, where the attempt is to replace expensive nickel and cobalt with inexpensive aluminium, 3.

THERmAL mANAGEmENT AND SAFETy

Thermal management is very critical for battery performance. All batteries work best at around 25° C and hence it is necessary to deploy a thermal manage-ment system of some sort to keep the temperatures down, especially in India. The thermal management system adds to cost, space and weight. People are borrowing technologies from various industries – phase change materials, liq-uid cooling, potting, etc. – and using it

in batteries, but a battery presents its unique challenges.

Customers and designers are paranoid about safety, and hence various preven-tive as well as reactive measures are taken in the battery design process. Many pre-ventive measures, such as cell current interrupt devices, cell fuses, module fuses, battery fuses and increasing cell spacing are used in addition to reactive measures such as the use of intumescent materials and venting systems. The major trend in thermal management and safety is to reduce their size and assembly complexi-ties because the whole EV world revolves around increasing energy density.

BATTERy pRoDUCTIoN

A typical battery made up of 18,650 cells has about hundreds or thousands of cells sitting together. Two major challenges that this throws are in terms of probability of failure and assembly tolerances. Each cell needs at least four joints – one on each terminal and corresponding ones on the bus bar. Because of the high number of joints, the joining process needs to be of extreme high quality. Joining processes too have evolved from soldering to resist-ance welding, and from wire bonding to laser welding. Laser welding and wire bonding are competing today, while resist-ance welding is well established. In case of assembly tolerances, cells usually have poor tolerance but at the same time need to be in good thermal contact with cool-ing system. It is also good to not have a lot of variance in thermal contact.

To achieve all of this and do that at a high speed, while maintaining automotive grade quality, is the biggest challenge. OEMs are focusing on either making their designs automation friendly or are work-ing on developing new processes to improve speed, quality and packing effi-ciency of battery packs. A new industry is coming around battery pack automation and that is likely to make battery manu-facturing easier and cheaper.

FUTURE TECHNoLoGIES IN LABS

Certain cell technologies currently in development are very interesting, but only time will tell if they are mature enough to go in products::: Metal Air Technology – Lithium air

and aluminium air are some good examples. These are high energy den-sity technologies, because air acts as cathode. It also potentially allows for refuelling as fast as gasoline and regen-eration of electrode.

:: Lithium Sulphur Technology – This is a high energy density technology as well, with about 1.5 time higher density than existing lithium ion technologies.

THE WAy FoRWARD

Automotive is a very competitive domain with a very long development cycle and hence the barrier is very high. Every technology has a tipping point, where it just suddenly starts becoming main-stream, and the battery has reached its tipping point. OEMs and cell manufactur-ers are setting up giga factories to pro-duce Li-ion cells in quantities that are several folds higher than what was there a decade ago, or even now. There is a symbiosis between energy storage and renewable energy industry with electric vehicles and this is making electric mobility case even stronger.

read this article on www.autotechreview.com

3 Major battles are happening within cathode choice, with NCA rising quickly, NMC poised to grow

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Source: source: Lux Research, Inc.www.luxresearch.com

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