Lithium Ion Technology

8/7/2019 Lithium Ion Technology

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Lithium-ion Batteries

An Introduction

May 2009


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CONTENTS

1. OVERVIEW OF CELLS AND BATTERIES......3

2. BRIEF GUIDE TO LITHIUM-ION CHEMISTRY...5

3. MARKETS AND APPLICATIONS......7

4. FUTURE TECHNOLOGIES....10

5. TERMINOLOGY.11


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1. OVERVIEW OF CELLS AND BATTERIES

o An electrochemical cell is a device which can supply electricityconveniently by direct conversion from chemical energy. Thevoltage of an individual cell is determined by its chemistry.

o A battery consists of an assembly of cells connected end to end(in series), or side by side (in parallel). If the cells are connectedin series, the battery voltage is the sum of the cell voltages. Ifthey are connected in parallel, then the battery has the samevoltage as a single cell, but longer discharge life. Batteries oftencontain cells in combinations of series and parallel asdetermined by the needs of the equipment they are powering.

o However, in common usage, a single cell supplied for usedirectly (usually labelled) is often referred to as a battery. Forexample, the Duracell Mn1500 or AA battery used in TV remotecontrol units, is technically a cell with a label.


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now. Recently, other nations such as China have begun todevelop their capability and the US Government is now offeringsubstantial funding to encourage domestic production.

o The mechanism of discharge in a lithium-ion cell can berepresented:

o In a charged cell, the graphite anode on the left contains lithiumions an ion is an atom with an electrical charge. During dischargethese ions travel through the liquid electrolyte to the cathode on theright. At the same time, electric current flows through the externalcircuit the radio, or motor or computer being powered by the cellor battery.

o When the cell is recharged, electric current is forced in the oppositedirection, and the lithium ions return from the cathode to the anode,

ready for the next discharge.

o The usefulness of a cell is due to the fact that the lithium onlytravels from one electrode to the other when the external electricalcircuit is completed by the user in other words, energy ondemand.

o Cells with lead-acid, NiCad or NiMH chemistry have electrolytesbased on water. However, the electrolyte through which the lithiumtravels in the Li-ion cell is based on organic solvents with very low


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freezing points. This means that the Li-ion cell can be effective attemperatures as low as -40oC

o Cell design can be optimised for long discharge life, or long cyclelife, or high power or wide temperature range. However, no one celltype can provide top performance in all these categories.

3. MARKETS AND APPLICATIONS

o The current total world battery market is estimated to be worth$85Bn, with the Li-ion share at some $9-10Bn. Of this, the non-consumer battery market is valued at $2.6Bn and is growing at therate of 15% to 20% per year

o Lithium-ion batteries are now used in a wide variety of markets andapplications. Examples include:

Consumer- Portable computers- Camcorders- Cell phones- I-Pods- Power tools

Medical- Portable monitoring equipment- Peristaltic pumps- Heart assist devices

Industrial- Portable meters- Oil & gas pipeline robots- Seismic survey sensors


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Automotive- Electric vehicles (EVs)- Hybrid electric vehicles (HEVs)

- Plug-in hybrid electric vehicles (PHEVs)

o Consumer and medical applications are well established andserved by batteries using cells from high volume manufacturerssuch as Panasonic, Sony, LG and E-Moli for example. These cells,known as 18650 cells, are optimised for long discharge life andlow cost.

o Industrial, military, aerospace and automotive applications usuallydemand specially designed cells and batteries. Although there hasbeen a recent trend to use consumer cells in batteries for theseapplications, that is increasingly regarded as inappropriate particularly with regard to safety liability by the consumer cellmanufacturers.

o For example, Panasonic, one of the biggest manufacturers of

consumer Li-ion cells, do not allow assemblers to use more than 1218650 cells (4 series, 3 parallel) in a battery as this compromisescell safety systems.

o Safety for high energy and power batteries is vital in mostapplications, and protective devices at both cell and battery levelare now mandatory in transport regulations and most performancespecifications.


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o For example, Li-ion cells with more than 20 watt hours, andbatteries with more than 100 watt hours of energy must comply withstringent UN transport regulations and remain safe during and afterthese tests:

- low pressure (high altitude)- thermal cycling (-40oC to +75oC)- mechanical vibration- mechanical shock- short circuit- mechanical impact- over charging- forced discharge

o Specific performance regulations for military or oil industry use, forexample, are even more stringent and also include safetyrequirements in the event of bullet penetration or fire.

o With the increasing interest in electric vehicles, recent Li-iondevelopments have focused on high rate that is cells andbatteries that can be charged and discharged rapidly. Thisapplication has further highlighted the need for safety in hazardousconditions.

4. FUTURE TECHNOLOGIES

o Although research continues on radically differentelectrochemistries, it is difficult to see these replacing Li-iontechnology in the foreseeable future. It is more likely that furtherdevelopment and improvement of Li-ion will continue for manyyears.

o For example, the increasing importance of EV technology hasled to development of new electrode materials for Li-ion cells

such as lithiated iron phosphate for the cathode and titaniumoxide for the anode.

o The new range of nano-structured electrode materials iscurrently being actively investigated and this will help in thequest for higher power cells and batteries for motorisedapplications where very large electric currents are required.


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o The combination of the internal combustion engine with Li-iontechnology will be important for HEVs current systemsutilising NiCad will be overtaken by lighter Li-ion systems.

o The continuing development of the fuel cell is seen in manycases as complementary to Li-ion rather than in competition toit. The ever increasing demand for longer life as well as higherpower will drive this hybrid system. This is already beingdeveloped for battlefield applications for Future Soldierequipment.

o Last but not least, an important area of development is theBattery Management System which can dramatically extendthe life and safety of a Li-ion battery by electronic monitoring

and control of charge and discharge.

5. TERMINOLOGY

o Anode The negative electrode of a cell - where chemicaloxidation takes place during discharge

o Battery An assembly of connected cells OR a single labelledcell for use by the consumer

o Battery Management System The electronics contained inmodern Li-ion batteries which maintains thebalance of cells and prevents overcharge,overdischarge and short circuit for example.

o Capacity The useful discharge life of a cell or battery often expressed as ampere-hours (Ah) orwatt-hours (Wh)

o Cathode The positive electrode of a cell - where chemicalreduction takes place during discharge

o Cell A device which converts chemical energy directlyinto electrical energy

o Charging (or Recharging) The process of regenerating a cellor battery by passing current through it from anexternal source

o Cycle Life The number of times a cell or battery can bedischarged/charged while retaining useful capacity


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o Current The rate of flow of electricity through a circuit- amperes (A)

o Discharge Life The length of time a cell or battery canoperate at a useful voltage without recharging

o Electron The individual negatively charged unit ofelectricity

o Electrolyte The medium usually liquid - through which ionstravel during charging and discharge

o Graphite A form of carbon used as the anode in a lithium-ion

cell it can accommodate a relatively large amountof lithium when fully charged

o IonA charged atom in a Lithium-ion cell, a positivelycharged lithium atom

o Lithiated Metal Oxide A powdered material used as thecathode in a lithium-ion cell usually cobalt, nickelor manganese oxides modified to contain lithium

o Lithium Element number 3 in the Periodic Table the

lightest metal

o Power The rate at which energy is delivered oftenexpressed as watts (W) (or voltage times current)

o Rate Alternative term for power in battery technology

o Separator A porous barrier to prevent electrodestouching(or shorting) usually a thin plastic membrane

o Shelf Life The length of time a cell or battery can be

stored without losing its charge

o State of Charge The percentage of the total capacity of acell or battery remaining at any particular moment

o Terminals The external points of contact positive andnegative - of a cell or battery

o Voltage The pressure or potential for flow of electricityin a circuit volts (V)

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