Lead-Acid Battery Applications Drive the Li-ion Market

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The consumer market for lithium-ion (Li-ion) batteries is huge—about $10 billion worth of battery packs—but it’s also relatively flat with only a modest 2% growth rate. Of course, there’s a news-grabbing growth market for electric vehicle batteries, with a forecasted compound annual growth rate (CAGR) of 10%, reaching $10 billion in 2025. Surprisingly, though, the biggest growth area for adoption of new batteries is “everything else,” from forklifts to ventilators. This battery market, which often falls into the “medium format” category, is maintaining a robust 11% CAGR and is also expected to reach $10 billion by 2025.

These “other” applications for Li-ion batteries generally have one thing in common—they’re devices that were typically powered by sealed lead acid (SLA). SLA batteries cornered the portable power market for the last nearly 200 years, but that’s finally changing thanks to Li-ion chemistry formulations with more diverse capabilities and more sophisticated electronics available. Because Li-ion batteries are directly replacing SLA in many cases, it’s worth comparing and contrasting Li-ion and SLA batteries, highlighting the commercial and technical applications for Li-ion in traditional lead-acid products.

历史和应用

Lead acid was the first rechargeable battery developed for commercial use in the 1850s. Although lead acid has been around for more than 150 years, it continues to be widely used. Not only is it still found in many of the same applications that it originally enabled, new uses for this old technology are being discovered to this day. Some common applications include backup power or uninterruptible power supply (UPS), and motive applications such as golf carts and forklifts. The lead-acid market is still growing at 4% for niche industries, and projects to be a $1.6B market by 2020 for these applications alone.

1970年代，即铅酸技术的首个，也许是唯一的，即铅酸技术的重大创新，即密封铅酸（或无维持的铅酸）。它包括在充电或快速放电过程中控制气体排气的阀。同样，湿润的分离器也没有将金属板浸入液体中，而是可以在任何方向上使用电池而不会泄漏。

SLA电池通常是由类型或分类的应用lication. Two types of SLA technology are common today: gel, also known as valve-regulated lead acid (VRLA), and absorbent glass mat (AGM). AGM batteries are used for small UPS, emergency lighting, and wheelchairs, while VRLA targets larger-format applications such as power backup for cellular repeater towers, internet hubs, and forklifts. Lead-acid batteries can also be categorized by use: automotive (starter or SLI—starting, lighting, ignition);motive power (traction or deep cycle); and stationary (UPS). The major drawback of SLA in all of these applications is cycle life—if the SLA batteries repeatedly drain, they’re heavily damaged.

1. Shown are examples of Li-ion cells incorporated into battery packs with electronics and either hard-plastic enclosures or shrink-wrapping.

Remarkably, the market dominance of lead-acid batteries remained relatively unchallenged for hundreds of years until the introduction of Li-ion batteries in the 1980s. A Li-ion battery is a rechargeable cell in which lithium ions move from the negative electrode to the positive electrode during discharge and back when charging. The nomenclature can be confusing, though. Li-ion batteries use an intercalated lithium compound, but don’t contain metallic lithium, which is used in lithium-based one-time-use cells.

The Li-ion battery was first invented in the 1970s. In the 1980s, a commercial version of the Li-ion battery, with a cobalt-oxide-based cathode, was introduced to the market. This battery featured a significantly better capacity by both weight and volume than nickel-based systems, which had primarily found use in hobby applications and limited adoption in early consumer portable electronics. The new Li-ion batteries enabled enormous growth in cell-phone and laptop computer markets. Initial safety concerns were abated by the introduction of safer variants that incorporated manganese and nickel-based additives into the cobalt-oxide cathode material, in addition to innovations in cell construction.

The first Li-ion cells introduced to the market were in hard aluminum or steel cans, and generally only a handful of cylindrical and prismatic (brick shaped) form-factors were available. However, as more applications adopted Li-ion technology, more variations on the cells emerged in terms of physical form, chemical performance, and price point.

For example, less expensive versions of the older technology lead to the adoption of laptops and cell phones all over the world. Modern, thin Li-polymer cells enabled smartphones, tablets, and wearable electronics. Now high- and medium-rate Li-ion batteries are used in power tools and e-bikes, respectively. Such variation foreshadows the replacement of SLA in more and more applications looking to improve weight and cycle life.

Chemistry Features

The fundamental working chemistry of the cells lends SLA and Li-ion batteries to certain features and different degrees of functionality. What follows are some of the benefits of SLA that have made it the solution of choice for many years and the deficiencies that now threaten it for replacement, as well as the attributes and challenges surrounding Li-ion batteries:

SLA

•SLA简单，可靠，健壮且价格便宜，可以在广泛的温度环境中使用。

• The batteries must be stored full state-of-charge (SOC), and they don’t lend themselves to fast charging.

• The flip side to the charge constraints is that SLA batteries can use simple float or trickle chargers.

• SLA batteries are very heavy; their gravimetric energy density is very low.

•循环寿命通常为200至300个周期，但即使是“深度循环” SLA也会因重复排放而损坏，从而导致循环寿命低至50个周期。

• The sloped discharge curve enables SOC measurement with simple voltage monitoring.

Li-ion

•常规的锂离子细胞旨在按大小和重量提供最高的能量密度。

•循环寿命通常为300至500个循环，但对于锂铁磷酸盐细胞的千分之一。

• The operating temperature is relatively narrow.

• A variety of cell sizes, shapes, and current capabilities are available.

• Maintenance cycling isn’t required and self-discharge is low.

•他们需要安全电路和复杂的充电算法。

• SOC measurement is complex because of the flat voltage discharge curve.

Electronics

区分电池和电池组很重要。该单元是包装的基本构建块；该包包括电子，连接器和外壳。Figure 1shows some examples of battery cells and packs. At a minimum, a Li-ion battery pack needs to have safety circuitry to protect and manage the cells, and the charger and fuel gauge must be more complex than those used with SLA technology.

2. U1 replacement batteries have features that contribute to a more efficient model, resulting in significant cost savings over the life of a medical device.

除了这些问题外,电子employed in a traditional SLA application will often have special requirements. Generally, these battery packs are “medium format,” i.e., larger than one- or two-cell packs common in consumer electronics and smaller than the enormous batteries used in electric vehicles. In addition, SLA applications are often motive, such as wheelchairs and forklifts, and the motor may introduce system noise and require electronics suited to high power.

在SLA应用中使用锂离子时，电子设备的某些差异包括：

•收费：Charging a lead-acid battery is simple when observing the correct voltage limits. Li-ion must generally use a more complex algorithm, with the exception of iron-phosphate-based packs (discussed further in the article). The standard method for charging Li-ion batteries is the constant current/constant voltage (CC/CV) method. It incorporates a two-step process of CC followed by a CV charge phase. In the first stage of the charging process, a constant current is applied. This stage continues until the battery-pack voltage approaches the preset threshold at the charger contacts. Once the charging voltage approaches the preset level, current begins to taper exponentially until a cutoff threshold is achieved.

另一种变化是虚拟电压终止（VVT）。通过消除电池组中电阻损耗的效果，VVT充电算法为电池电池堆栈充电，而不是外部电池端子。因此，充电算法不会偏离行业所接受的锂离子电池组方法。借助VVT，CC阶段在充电周期的大部分时间内延伸，直到微处理器感应标称细胞电压并启动过渡事件。

•Fuel gauging and communication:如前所述，通常通过简单的电压测量来监测SLA电池。锂离子电池需要一种库仑计数方法，该方法需要学习周期或循环的变化，或者需要库仑计数和阻抗查找表的组合，以避免学习周期。

I²C is the most common and cost-effective communications protocol used in Li-ion batteries, but it has limitations with respect to noise immunity, signal integrity over distance, and overall bandwidth. SMBus (System Management Bus), a derivative of I²C，在较小的电池中很常见，但目前缺乏对大功率包或较大包装的任何特别有效的支持。对于高噪声环境或需要长期运行的地方，例如在许多SLA应用程序中，CAN是很棒的，但这是有代价的。

Direct Replacements

令人惊讶的是，很少有标准SLA格式。其中之一是U1，这是医疗设备备份应用中使用的常见标准形式。锂铁磷酸化学已使这些电池的直接置换式替换能够开发。磷酸铁具有显着的循环寿命，高电流输送能力，安全性提高和阻抗低。液磷酸电池的电压也与SLA以12和24-V增量的增量非常匹配，并允许与常规的SLA充电器一起使用。包装包含智能功能，例如收费和周期计数沟通，大约是三分之一的重量。

与SLA电池在存储后几个月内经历了永久容量损失的SLA电池，液磷酸电池可保持100％的存储容量。Figure 2compares the two products and the types of gains achieved when switching from SLA to Li-ion.

Conclusion

很少有其他电池能像铅酸一样便宜地传递大量电力，这使电池成本效益用于更大的应用。锂离子技术的价格点下降了，化学和电子产品都可以使用新品种，这些品种使锂离子成为SLA的潜在替代品，并且在循环寿命和体重中有很大的上涨空间。Applications ripe to take advantage of this technology include material-handling equipment, battery backup units, lawn and garden equipment, industrial cleaners, aerial scissor lifts, industrial drones, golf carts, and other motive applications, which are fueling Li-ion’s growth in niche, medium-format markets.

Robin Schneider, Ph.D., is Technical Marketing Director atInventus Power.