锂电池制造论文

Lithium ion battery production

Antti Väyrynen,Justin Salminen ⇑

European Batteries Oy, Karapellontie 11, 02610Espoo, Finland

a r t i c l e i n f o a b s t r a c t

Recently, new materials and chemistry for lithium ion batteries have been developed. There is a great emphasis on electrificationin the transport sector replacing part of motor powered engines with battery powered applications. There are plans both to increase energy efficiencyand to reduce the overall need for consumption of non-renewable liquid fuels. Even more significantapplications are dependent on energy storage. Materials needed for battery applications require specially made high quality products. Diminishing amounts of easily minable metal ores increase the consumption of separation and purifi-cation energy and chemicals. The metals are likely to be increasingly difficultto process. Iron, manganese, lead, zinc, lithium, aluminium, and nickel are still relatively abundant but many metals like cobalt and rare earths are becoming limited resources more rapidly.

The global capacity of industrial-scale production of larger lithium ion battery cells may become a lim-iting factor in the near future if plans for even partial electrificationof vehicles or energy storage visions are realized. The energy capacity needed is huge and one has to be reminded that in terms of cars for example production of 100MWh equals the need of 3000full-electric cars. Consequently annual produc-tion capacity of 106cars requires 100factories each with a 300MWh capacity. Present day lithium ion batteries have limitations but significantimprovements have been achieved recently [1–8]. The main challenges of lithium ion batteries are related to material deterioration, operating temperatures, energy and power output, and lifetime. Increased lifetime combined with a higher recycling rate of battery mate-rials is essential for a sustainable battery industry.

Ó2011Elsevier Ltd. All rights reserved.

Article history:

Available online 22September 2011Keywords:Lithium Ion Battery Production Properties

Battery management Energy Lifetime Recycling

1. Introduction

Metals and metal products play important role in our industrial development. Sustainable use of the earth’sresources in metal products production, end use, and recycling of metals has to be ta-ken into account. Lithium ion batteries have developed rapidly and different types of chemistry have successfully been introduced. Common applications are power sources for cell phones, laptops, and other portable devices. Development is currently going on in larger applications such as energy storage, partly or fully powered electric vehicles, industrial vehicles, lifts, cranes, harbour ma-chines, mining vehicles, boats, and submarines. Production of cells and battery management system electronics scaling from the indi-vidual cell to large modular solutions are ramping up globally. These new applications demand huge amounts of specially made products (copperand aluminium metal foils, electrolyte, lithium metal oxide, separator polymers, binders, graphite, conductive additives, cover bags, tabs, and production hardware). Over the long term, diminishing amounts of easily minable metal ores sites influencematerial availability. Iron, manganese, lithium, and nick-Corresponding author. Tel.:+[1**********]5.

E-mail addresses:[email protected](A.Väyrynen),Justin. [email protected](J.Salminen).

0021-9614/$-see front matter Ó2011Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2011.09.005

el are still relatively abundant but metals like cobalt, and rare earths are becoming limited resources in coming decades.

The driving force behind this growing interest in Li-ion batteries is both the desire to increase energy efficiencyand to reduce con-sumption of hydrocarbon-based fuels. The deployment of battery systems and the battery industry are expected to grow rapidly over the next 2to 3years.

The main challenges of Li-ion battery technology are related to chemistry, material deterioration, lifetime, operating temperatures, energy and power output, and, scaling up, long term material supply for some, and overall costs. Cost targets for Li-ion batteries are ambi-tious, only a couple of hundred dollars per kWh, while currently the price is closer to $1000per kWh. In the near future, the price is ex-pected to decrease only modestly due to more challenging chemis-try and safety requirements of the electric vehicle (EV)industry. Batteries are specificin their uses and one type does not fitall purposes. Challenges appear, for example, when individual cells are combined into in larger battery systems. In larger combina-tions, cooling is required to avoid hot spots and deterioration of lifetime due to overheating. Thermal control is also necessary for safety reasons.

Advanced Li-ion battery systems include electronic control known as the battery management systems (BMS)which is crucial when operating electric vehicles (EV),and hybrid electric vehicles

A. Väyrynen,J. Salminen /J. Chem. Thermodynamics 46(2012)80–8581

Abbreviations LFP Lithium iron phosphate

NCA Lithium nickel cobalt aluminium oxide LCO

Lithium cobalt oxide

(HEV).BMS also prevents battery overcharging and deep discharg-ing of the battery.

2. Lithium ion batteries

Batteries are devices that convert stored chemical energy into electricity within a closed system. Electrochemical conversion oc-curs at two electrodes, viz., cathode and anode. The nature of the reaction is dependent on the chemistry of the electrodes. The power of the battery is more determined directly by the area of the electrodes in contact with the electrode while the energy content is depends more on mass and volume of the active material. In a rechargeable battery (secondarybattery), if the external load is replaced with power supply the direction of electrons (andlithium ions) are reversed, and the battery is charged. Lithium ions (Li+) move from anode to cathode during discharge and from cathode to anode in charging. Electrons move in the external circuit into the same direction as Li-ions. The anode (negativeelectrode) is usually graphite or lithium titanate. The cathode (positiveelectrode) is typically lithium metal oxide [1–6].

Lead acid, nickel-metal hydride, and lithium ion batteries are the most common rechargeable batteries. Lead acid battery technology is well proven and is more than a century old. However the lead acid battery shows low gravimetric and volumetric energy density. Nickel-metal hydride batteries provide reliable cyclability and are commonly used in hybrid vehicles. Their downside is a rela-tively low energy density and low cycle life and relatively high self-discharge rate up to 10%per month. That makes lithium ion

NCM Lithium nickel cobalt manganese oxide LMO Lithium manganese oxide SOC

State of charge

Battery electrodes provide electron conductivity outside, they store chemical energy, and generate electrical energy by releasing of stored energy.

All these functions should be completed isothermally, and with as little mechanical or chemical strain as possible. New novel lithium cathode materials are continuously developed in universi-ties and company research laboratories to improve battery perfor-

82A. Väyrynen,J. Salminen /J. Chem. Thermodynamics 46(2012)80–85

(LFP)electrode coating line. LFP is coated on special made thin aluminum foil keeping coating thickness and weight per surface area uniform. Separate lines for both cathode and anode are needed. The coated electrode is tried in the long oven shown in the figure.The electrode is rolled at the end of the coating line and goes through many process steps including calentering, slit-ting, notching, and drying. After that the electrode is ready for bat-tery assembly in the dry room where cathode, anode, separator, cover bag, and electrolyte are put together.

Lithium cobalt oxide cells benefitfrom well established powder and cell production processes. Hundreds of million cells are pro-duced annually. Cobalt based cathodes are easier to produce than LFP-based cells. Currently there exist tens of manufacturers for dif-ferent battery applications, variations, sizes and shapes. The move from small cell sizes to large-format cells has caused new safety is-sues to cell manufacturers. Novel new materials like LFP have been introduced to increase the safety in large-format cells. Table 1shows some common lithium ion battery chemistries, their uses, characteristics, relative cycle lifes, and nominal voltages.

The most recent lithium-ion cathode material:discovered 1995and development to commercial products started in 1997. The LiFePO 4(LFP)is considered the most promising lithium-ion tech-nology for large-format batteries due its long cycle life and safety. The LFP material is still in the pilot phase and powder production is ramping up from pilot-scale to mass production. The production of high quality LFP-powder is difficult.

The advantages of LiFePO 4(LFP)are summarized as follows. LFP shows reasonable good cell voltage 3.2V depending on the active materials and it also shows extremely good safety features. LiFePO 4powder is non-toxic, shows no thermal runaway, and is chemically stable. It shows long cycle (+4000cycles) and calendar life (+5years), and reasonably large energy density, (110to 150) Wh Ákg À1, 1/4weight and 1/3size of lead acid batteries. The charging time is short, viz., 1h and even half an hour. The self-discharge rate of a LFP battery is extremely small and it can be stored fully charged or par-tially charged, unlike a lead acid battery. Figure 4shows the typical flatdischarge curve for LiFePO 4chemistry. From the figure,one can see that the voltage remains almost stable and independent of

discharge over a wide capacity%(SOC)range. Overcharging the cell does not cause major problems below 4.5V.

Also hard short-nail penetration may cause minor smoking but no propagation, see figure7. In the case of overheating, LFP does not react prior to pressure/electrolyterelease in a pouch cell which minimizes the thermal runaway that is more likely with energetic oxide materials like LiCoO 2.

Figure 4shows discharge curves of 42Ah capacity battery based on LFP chemistry. The lithium iron-phosphate (LFP)cell has a very stable discharge voltage. The only drawback of stable voltage behaviour, as in figure4, is estimation of the state of charge (SOC).Due to a nearly constant voltage from 5%to 80%state of charge, estimation of SOC is usually based on coulomb counting (integrationof current).

The temperature range of operation for special purpose batter-ies or vehicle applications is from À40°C to above 100°C. In prac-tice, current lithium-ion batteries operate within the temperature range À20°C to 60°C. Development is underway to improve the low temperature and high temperature performance, and lifetime at higher temperatures.

Low temperature performance is limited by temperature depen-dencies of electrochemical reactions, transport properties and phase changes of the electrolyte. Good ionic transport properties corre-spond to high conductivity, low viscosity, and sufficientlyhigh diffu-sion coefficientof Li +while charging and discharging the battery. At lower temperatures the capacity (inAh) of the cell falls and the voltage drops. This behaviour is shown in figures5and 6. The C -rate corresponds to the current at which useful capacity of the battery is consumed with time t in hours. It is also the charge or discharge rate. A 1C discharge or charge occurs a 1h; 0.5C dis-charge or charge occurs in 2h, etc .

4. Abuse tolerance

Lithium iron phosphate has increased safety compared to other lithium chemistries. Also Lithium titanate is considered as safe as LFP. Figure 7shows EB’scell after putting six zinc plated iron nails through the cell. No smoke or firewas observed and the cell voltage

TABLE 1

Properties of different lithium ion cathode materials. Cycle life depends how the testing has been carried out [1,7,8]. Cathode LCO NCM NCA LFP LMO

Formula

LiCoO 2

LiCo 1/3Ni 1/3Mn 1/3O 2LiNi 0.8Co 0.15Al 0.05O 2LiFePO 4LiMn 2O 4

Type

Energy/powerEnergy

Energy/powerEnergy

Energy/power

Energy density/(WhÁkg À1) 170to 185155to 185145to 165100to 14090to 120

Energy density/(WhÁdm À3) [**************]

to to to to to [**************]

Relative cycle life 133>41

Voltage/V3.653.73.653.23.8

thermal tests, altitude test, vibration, external shorting, overcharg-ing, and forced discharge. The United Nations tests refer to recommendations on transport of dangerous goods which lithium ion batteries have to pass in order to be eligible for transportation.

5. From a cell into a system

There is often confusion in the terms used to describe the vari-ous components of a battery system because the word ‘‘battery’’is used when referring to both a single cell and for example a 12V car battery comprising six cells. In this paper, we use the following terms (seefigure1):

Cell :The most basic element of a battery (nominalvoltage 3.2V for a LFP cell).

Module :A collection of cells connected in series/parallelprovid-ing a higher voltage and capacity than a single cell. A module includes a measurement unit (slaveunit) of the BMS.

Pack :A collection of modules connected in series and located in a single enclosure.

System :One or multiple packs connected in series/parallelincluding the cooling system, the BMS master unit and the remained above 3V overnight. That was an example of a safe soft

84A. Väyrynen,J. Salminen /J. Chem. Thermodynamics 46(2012)80–85

Thermal management is one of the biggest challenges in the development of a battery pack. Although the efficiencyof a lithium ion battery is significantlyhigher than of conventional batteries (e.g. lead acid), the dissipation may limit the performance of the battery system under hot conditions. Operating the battery in a high temper-ature environment may result in premature ageing, irreversible ef-fects and even safety problems. Similarly, the battery pack must be heated in cold conditions. Due to IP requirements of the pack, ambient air cannot usually be used as a coolant. Therefore, a liquid circulation through the pack or a heat exchanger is required. Figure 8shows water cooling elements that are designed for EBattery30modules.

Prevent the voltage of any cell from dropping below a limit by reducing discharging current, asking it to be reduced.

Prevent the voltage of any cell from exceeding a limit by reduc-ing charging current, stopping the charging or asking it to be stopped.

Prevent the temperature of the battery system from exceeding a limit by reducing battery current or asking for cooling.

Prevent charging/dischargingcurrent from exceeding a limit that depends of battery temperature, SOC and various other parameters.

Provide relevant status information (e.g. SOC, SOH) about the battery pack to the host system and the user via a data link. 5.2. Topology and communication of the BMS

The BMSs are often categorized based on how they are installed; directly on each cell or centralized in a single device, or in some intermediate form. The various topologies are as follows [8]: Centralized :BMS in located in a single assembly that is con-nected to cells with a cable harness.

Modular :BMS comprises multiple identical cards one of which is designated as a master, and the cards communicate with a data link (e.g . CAN bus).

Master –slave :The system comprises multiple identical cards (theslaves), each measuring the voltage of a group of cells, and a separate master unit that handles computation and communications.

Distributed :The voltage (andtemperature) of each cell is mea-sured by a card connected directly to the cell. The cells are con-nected via data link to a controller that handles computation and communications.

A simple BMS often uses digital signals to report to an external device or system the state of the battery pack. These on/offsignals indicate the status of a fault/alarmand if a certain operation is en-abled (charging,discharging).

In a more advanced application, the BMS master unit uses a data link to communicate with the host system. The data link can be pro-prietary or use a standard protocol, but even in the latter case, the coding of the data is usually proprietary. The most common stan-dards are RS232, RS485, CAN bus, Ethernet and USB. Figure 9shows block diagram of EBatterymanagement system [8,9]

.

5.1. Battery management system (BMS)

A lithium-ion battery stack comprising several cells cannot be operated as if it were a single power source. Lithium-ion cells are very susceptible to damage outside the allowed voltage range that is typically within (2.5to 3.65) V for most LFP cells. Exceeding this voltage range results in premature ageing of the cells and, further-more, results in safety risks due to the reactive components in the cells. This is why a proper battery management system monitoring individual cell voltages and temperatures is necessary.

The variation of the electrical characteristics (capacity,internal resistance) caused by manufacturing differences, ageing and un-equal temperature distribution can result in deviations in the state of charge (SOC)inside a battery stack. If the SOC is not periodically balanced some cells may be eventually overcharged or over dis-charged, leading to irreversible damage, and eventually complete battery stack failure. This process is inherently divergent, and re-duces the available capacity even if the damage can be avoided by careful voltage control [11].

A conventional passive balancing method is to connect a load resistor parallel to each cell to discharge individually selected cells. This method is only suitable in the charge mode to suppress a volt-age rise in the strongest cells, and can be used for a periodical equalizing of the battery stack. Active balancing means a method that transfers energy between battery cells instead of dissipating. A bi-directional balancing module can both charge and discharge an individual cell. The balancing can be based on real-time cell voltages or estimated capacity distribution of the stack definedby an adaptive algorithm during previous load cycles.

The core functions of a BMS systems are as follows [10]:

A. Väyrynen,J. Salminen /J. Chem. Thermodynamics 46(2012)80–8585

The CAN bus is the standard in vehicles and most industrial appli-cations. Industry groups have attempted to definethe application layer with a set of standard messages, such as SAE J1939and CAN-open. None of them is focused on the functions of BMS, and therefore each OEM and BMS designer definesCAN messages differently [8]. However, standard device profilesfor CANopen have been definedfor a battery and a charger (CiA418/9).6. Conclusions

Lithium ion battery technology has developed hugely in recent years. This is due to new lithium electrode materials which have improved the battery performance towards needed targets. The lifetime can be extended by using clever algorithms in a battery system and keeping the system temperature sufficientlylow. The battery management system (BMS)is crucial for larger battery sys-tems. Lithium-ion cells are very susceptible to damage outside the allowed voltage range that is typically within (2.5to 3.65) V for most LFP cells. Exceeding this voltage range results in premature ageing of the cells and, furthermore, results in safety risks due to the reactive components in the cells. This is why a proper battery management system monitoring individual cell voltages and tem-peratures is necessary. The chemistry, cell and system construction are under intensive development resulting in improvements of temperature tolerances and lifetime. The future development is towards increasing efficiencyin materials and energy usage in pro-duction. Also the trend is to use less toxic materials and solvents in

production. The recycling of materials is taken seriously and is also increasingly mandated by legislation. Acknowledgements

Comments and support from cell development team and Mika Räsänenare gratefully acknowledged. References

[1]D. Linden, T.B. Reddy (Eds.),Handbook of Batteries, third ed., McGraw-Hill,

New York, 2002.

[2]D.A. Scherson, A. Palencrar, Interface (Spring)(2006)17–22.[3]B. Ellis, Chem. Mater. 22(2010)691–714.

[4]B. Scrosati, J. Garche, J. Power Sources 195(2010)2419–2430.[5]M. Winter, R.J. Brodd, Chem. Rev. 104(2004)4245–4269.[6]J.M. Tarascon, M. Armand, Nature 414(2001)359–367.

[7]J. Salminen, D. Steingart, T. Kallio, Fuel cells and batteries, in:T. Letcher et al.

(Eds.),Future Energy –Improved Sustainable and Clean Options for Our Planet, Elsevier-IUPAC, 2008, pp. 259–276.

[8]A. Väyrynen,J. Salminen, Modular li-ion battery systems for electric and hybrid

powertrains, in:ICPC 2011, 6th AVL International Commercial Powertrain Conference, Graz, Austria, 25–26May 2011. [9].

[10]D. Andrea, Battery Management Systems for Large Lithium-Ion Battery Packs,

Artech House, Norwood, USA, 2010.

[11]A. Väyrynen,Control Criteria of an Electric Vehicle Battery Equalizing System,

Licenciate’sThesis, Helsinki University of Technology, Espoo, Finland, 2008.

JCT 11-394