annual update on lithium-ion battery technology...lithium-ion attery technology introduction...

Annual Update on Lithium-ion

Battery Technology

White Paper

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Annual Update onLithium-ion Battery Technology

Table of ContentsIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Market Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4

System Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Technology Trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6

Materials Update . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-8

Safety Trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-9

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

About Inventus Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

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Introduction

There’s very good news across the rechargeable-battery landscape as we continue to look into 2019 and beyond. The existing markets for these batteries – primarily based on lithium-ion (Li-ion) chemistries – continue to grow rapidly. These energy sources are finding new applications in markets replacing Lead-Acid and/or the electrification of products that previously used internal combustion engines (ICE). This conversion to rechargeable Li-ion batteries is being driven by environmental concerns, or to improve performance, and extend their functionality. The consensus is that the compound annual growth rate (CAGR) as measured in megawatt-hours (Mh) has been in the range of 24%, a very impressive number by any standard.

This growth is driving the “virtuous cycle” which often characterizes many dynamic, growing markets: more demand leads to further improvements and advances, which in turn leads to more demand and adoptions, leading again to more advances, all in an ongoing cycle. Growth has been especially notable in the medium-to-large format area with larger systems becoming more prevalent. Rechargeable batteries are now extending far beyond providing the power for small, portable devices and are extending their adoption to larger mobile and stationary uses.

The market fundamentals of the raw materials used for rechargeable lithium-ion cells, and the sourcing of these materials continue to be issues. Increasing demand along with shifting prices for lithium, cobalt, and other materials has created volatility in the cost of the overall battery. Safety concerns associated with lithium-ion chemistry, although much better understood and largely contained, still require attention, especially as battery sizes and energy densities increase.

This white paper will look briefly at market trends, technology advancements, materials and safety updates.

Markets Show Growth in Size and Breadth

As the market for rechargeable batteries grows, transportation applications spanning smaller uses such as scooters to larger ones such as full-size autos are among the major drivers, Figure 1. Industrial applications are also playing a significant growth role as battery-based designs are replacing small internal combustion engines for lawn mowers and yard equipment in both commercial and consumer products. Enabling electrification brings benefits such as elimination of polluting emissions, reduced noise, and lower maintenance needs. Also, self-contained backup power systems for residential and commercial sites are benefiting from battery-based designs which eliminate the issues associated with on-site hydrocarbon-based fuel storage.

Rechargeable batteries are now extending far beyond providing the power for small, portable devices and are extending their adoption to larger mobile and stationary uses.

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Growth is not limited solely to new designs; it is also coming from the use of rechargeable batteries as replacements of already existing battery technologies particularly lead acid.

Figure 1: Applications driving growth of Li-ion

For these markets, growth is not limited solely to new designs; it is also coming from the use of rechargeable batteries as replacements of already existing battery technologies particularly lead acid. Implementing this is a not a simple “drop-in” situation, as use of lithium-based batteries requires attention to new issues such as charge/discharge profiles, battery pack management, and various safety issues, even if the resultant form factor is unchanged.

System Issues Go Beyond Batteries Alone

Increasingly, batteries are being viewed and managed as vital tangible assets rather than merely “consumables” or “expendables,” due to higher initial cost and longer life expectation from the ‘energy storage’ system. As a consequence, users want to know more about this asset with a viable life of five-to-ten years, rather than as a “two years and done” mindset.

Many markets are expecting more data with improved granularity being available throughout the battery life. There is a major effort ongoing to develop more sophisticated battery management algorithms to more accurately determine the true State of Health (SOH) of the battery, communicate data out of the battery to the host, as well as storing more detailed parameters on how the battery was used for warranty purposes (e.g. how long did it spend above 45degC).

Users are also looking to manage these assets and fleets of energy storage to maximize life. In situ real time monitoring of the energy storage asset allows users to modify charge or discharge profiles to further extend the life of the battery. This is leading to wider adoption of Internet of Things (IoT) sensing and connectivity with the use of wireless telemetry to get needed data from the battery and to central hubs or monitoring stations directly without having to physically connect to the battery pack in use.

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Widely used 18650 cylindrical cells are being supplemented in the market by 21700 cells which provide both higher capacity and power in a (larger) cylindrical form factor.

Technology Advances Also Drive Growth

There are three areas where lithium-based rechargeable-batteries are seeing technical changes and advances: the increase in cells designed for a specific purpose, with new form factors and higher performance; the use of enhanced chemistries and materials, and availability of battery management systems which provide greater detail and insight into the battery pack and its cell.

Form Factors: First, newer form factors are being introduced thanks to electric vehicles (e.g. Tesla), electric-bikes (a.k.a pedelecs), and larger power tools particularly for lawn and garden . The widely used 18650 cylindrical cells (18mm diameter × 65mm long) are being supplemented in the market by 21700 cells (21mm diameter × 70mm long) which provide both higher capacity (5.0Ah) and power (35-40 Amp) in a (larger) cylindrical form factor, Figure 2. These new form factors are enabling battery pack manufacturers to optimally match cells to user priorities with respect to voltage, discharge power, operating temperature range, in order to better meet the increasing longer service life requirements.

Figure 2: Cylindrical Li-ion Roadmap

21700 Region

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High-rate cells, which were originally designed specifically for power tools, are now being used in lawn and garden/outdoor power equipment as well as UPS and server applications

Another change taking place in the market relates to rate capability of cells and their adoption into new applications. C-rate is a rating of the rate capability as a function of cell capacity. Generally, there is a direct trade-off between rate capability and capacity. High capacity and lower (1C) rate capable 18650 cells traditionally used in consumer electronics products are generally being phased out. Mid-rate cells can deliver capacity with higher rate capability. Mid-rate cells were introduced initially for e-bikes but are making their way into applications such as material handling, telecom, and light electric vehicle. High-rate cells, which were originally designed specifically for power tools, are now being used in lawn and garden/outdoor power equipment as well as UPS and server applications requiring high discharge rates.

Chemistries and Materials: The performance of a lithium-ion cell is determined by an almost miraculous balance of competing trade-offs that depend largely on its major components: the cathode, anode, electrolyte, and internal cell design. While we have seen a significant change in materials used, this has resulted in mostly incremental improvement in overall performance. However, the changes have been meaningful in that they have been largely targeted improvements to address specific applications (EV, ESS, etc).

Battery Management System: Battery management has evolved over time with significant technological advances providing new and enhanced critical information about the electrochemistry and its interactions with the system surrounding it. Whether through improved sensors, more accurate and robust algorithms or complex architectures, the increased data points have led to higher power delivery, longer life cycles, improved diagnostics and overall better preventative care. The result is a more sophisticated and autonomous battery pack that adapts to changing environments and application specific demands. A typical BMS architecture is shown in Figure 3.

Figure 3: Typical Battery Management System (BMS) architecture

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A divide has occurred in recent years with LCO still being dominant cathode in polymer/pouch cells used in consumer electronics and NMC/NCA now being the cathode of choice for cylindrical (18650/217000) and larger format EV cells.

The Great Cathode Divide

The chart below gives an overview of the common cathode materials used today. LCO cathodes have been used from the beginning of Li-ion introduction with NCA, NMC, and LFP being relatively newer by comparison.

Figure 4: Features of common cathode materials

A divide has occurred in recent years with LCO still being dominant cathode in polymer/pouch cells used in consumer electronics and NMC/NCA now being the cathode of choice for cylindrical (18650/21700) and larger format EV cells. This is due to the different performance priorities and the trade-offs those respective markets are willing to make. Generally, consumer electronics are focused on squeezing as much energy into the smallest volume possible with faster charge rates, and with cycle/calendar life being important but still a lower priority. This focus on higher energy density has led the consumer electronics to push the charge voltages up to 4.5V today largely using only LCO cathodes. This is a significant increase form the traditionally 4.2V charging for Li-ion. Largely due to the higher charge voltages, LCO cathodes still dominant this market.

By contrast the cylindrical 18650/21700 and larger format cells have moved to NMC and NCA cathodes while keeping the charge voltage at 4.2V (or sometimes even lower). At the lower voltages these materials provide good energy density with improved cycle and calendar life which is the higher priority for the long-life applications like electrical vehicles and energy storage where these cells are used.

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Experienced designers know how critical it is to design battery packs to meet or exceed the requirements for an application to help ensure safe operation.

The NMC/NCA materials have also evolved particularly in the attempt to reduce further the Cobalt used going to higher and higher concentrations of Nickel. NMC for example has gone from an even ratio of Ni, Co, Mn (each in equal 1/3 proportions) to the so-called high Nickel content cathodes which are as high as 80% Ni with remaining roughly 10% each of Mn and Co (a.k.a. 811 NMC).

Lastly markets using Lithium Iron Phosphate (LFP) Cathodes continue to grow steadily after somewhat of a lull in the adoption. The stability of the LFP cathode provides very long cycle and calendar life with improved safety making it attractive for certain markets. LFP has been the dominant cell chemistry in the rapidly growing China electric bus and fleet vehicle market and is also gaining traction replacing Lead Acid in UPS, Material Handling, Medical, and Industrial markets where LFP is a good match helping to ease the transition from the legacy Lead Acid infrastructure.

Anode and Electrolyte Development

By comparison to the cathode materials, the changes in anode and electrolyte have perhaps been less noticeable but still noteworthy. Lithium-ion anodes have traditionally been Carbon (graphite) based but, in the last few years, Silicon has been added in relatively small increments to the graphite, (i.e. less than 10% of the anode by weight). The attraction of Silicon is a ~10X improvement in energy density at the raw material level translating to a potential ~3X improvement in capacity at the cell level. However, Si is very difficult to manage in the cell as it expands significantly with cycling. The market has shown growing pains implementing Silicon into the anode even in small amounts with cycle life and reliability being negatively impacted. Meanwhile there is significant development on even higher concentration Si anodes and even 100% Silicon anodes at various startups and major manufacturers.

Safety: An Ongoing Concern

No discussion of lithium-based rechargeable batteries would be complete without giving some attention to the issue of safety. Existing markets continue to push for higher energy density and new markets continue to adopt Lithium-ion; many without the experience to properly design a rechargeable battery system to meet the device requirements. This combination has created many opportunities for issues to occur, i.e. hoverboards, e-cigarettes.

Experienced designers know how critical it is to design battery packs to meet or exceed the requirements for an application to help ensure safe operation. Historically, the industry has focused on prevention with redundant mechanical and electrical solutions employed across the entire rechargeable system (i.e. charger, battery, host device) to prevent issues with all foreseeable misuse and abuse conditions.

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While prevention is still foundational to safe rechargeable system design, current best practice thinking is taking this one step further. The next step is to consider the ‘what-if’ scenario of a cell going into thermal runaway and preventing this from propagating into neighboring cells creating an even larger issue at the battery pack level. This single cell fault is most often caused by an internal short in the cell, that while very unlikely to occur (failure rates are often quoted in terms of 1 cell per 10 million or 100 million depending on supplier), is still nevertheless a possibility.

Mechanically, new battery geometries and enclosure designs in addition to new non-flammable or intumescent material are being employed to prevent propagation and fire escaping especially in larger systems. While electrically, new in-situ charge/discharge life cycle management techniques based on State of Health (SOH) of the battery are also being employed to try to prevent or detect cell failures before they happen.

Conclusion

The current rechargeable Li-ion battery market is vibrant, growing, innovating and expanding in both depth and breadth of application and uses. This growth demand is leading to further improvements and advancements in materials, system design, technology and safety. The inherent benefits of Lithium-ion (high energy density, high capacity, long cycle life, reliable charge performance and low maintenance) make it the preferred choice for applications spanning from portable consumer devices to stationary energy storage and backup systems to motive equipment and vehicles. Continued focus on safety at the cell, pack and system level will continue to drive safety enhancements and increased adoption.

Mechanically, new battery geometries and enclosure designs in addition to new non-flammable or intumescent material are being employed to prevent propagation and fire escaping especially in larger systems.

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About Inventus Power

Inventus Power, founded in 1960, is the leading provider of advanced battery systems for global OEMs. We specialize in the design and manufacture of Li-ion battery packs, smart chargers, and efficient power supplies across a broad range of portable, motive & stationary applications.

With nearly 60 years of experience, we understand that different applications have different needs. From advanced concept development, cell characterization & prototyping to complete power system design and BMS customization, our global engineering staff of 300+ degreed mechanical, electrical, software, qualification and compliance engineers have the knowledge and resources needed to design and develop power solutions that operate safely and correctly within their intended environment.

Plus, with global manufacturing facilities and vertically integrated design, tooling and testing capabilities, we are able to manage complex programs from concept to production providing a turnkey solution for our customers.

For more information about our products, experience and capabilities, visit inventuspower.com and follow @inventuspower.

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annual update on lithium-ion battery technology...lithium-ion attery technology introduction...

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