1. What is a lithium-ion battery?
Lithium-ion batteries (LIBs) are also known as lithium batteries. There are two main types: liquid lithium-ion batteries (LIBs) and polymer lithium-ion batteries (PLBs). Liquid lithium-ion batteries are secondary batteries that use Li+ intercalation compounds as both the positive and negative electrodes. The positive electrode uses lithium compounds such as LiCoO2 or LiMn2O4, while the negative electrode uses a lithium-carbon intercalation compound.
Lithium-ion batteries are the best-performing secondary chemical power source among all commercially available batteries to date, which is a key factor in promoting their use in electric bicycles.
1.1 higher specific energy
Both in terms of volumetric energy density and gravimetric energy density, lithium batteries have more than three times the energy density of lead-acid batteries. This results in lithium batteries being smaller and lighter, making them more appealing to consumers.
1.2 Long cycle life
Lithium-ion batteries used in electric bicycles typically have a cycle life of over 800 cycles, while lithium-ion batteries using lithium iron phosphate cathode materials can reach around 2000 cycles, exceeding lead-acid batteries by 1.5 to 5 times. This significantly reduces the cost of using lithium-ion batteries and improves convenience for consumers.
1.3 It has a wide charging power range.
This is a unique advantage of lithium batteries. When needed, charging time can be controlled within 20-60 minutes, with a charging efficiency exceeding 85%. With further technological innovation, this characteristic can be even better utilized, potentially leading to significant commercial value.
1. Good discharge performance at 4x rate
Lithium-ion batteries can achieve a discharge rate of over 10 times, and with special manufacturing processes, up to 30 times. This characteristic is highly beneficial for the development of intelligent control riding technology in electric-assisted bicycles. However, this characteristic has not yet been well developed and utilized.
my country is the world's largest producer of lithium-ion batteries, accounting for more than one-third of global production. Over 100 lithium battery manufacturers have a strong demand for lithium-ion battery materials, and many plan to significantly increase production within the next two years. Currently, China's lithium battery manufacturing industry has formed two major giants: BYD leading the way in liquid lithium batteries, and TCL leading the way in polymer lithium batteries. TCL has completed the entire process of polymer lithium-ion cell development and mass production, and has rapidly reached the forefront of this technology. TCL's polymer lithium-ion cells have reached world-class levels in terms of electrochemical impedance, energy density, and high and low temperature discharge performance. While BYD is the leader in liquid lithium-ion batteries, TCL is the leader in next-generation polymer lithium-ion batteries, which have advantages over liquid lithium batteries.
2. Raw materials for lithium batteries
Lithium-ion batteries consist of positive and negative electrodes, an electrolyte, a polymer separator, and a protection circuit chip. The upstream components of a lithium battery include positive electrode materials, negative electrode materials, a separator, electrolyte, and lithium resources. The materials used are shown in Table 1.
2.1 Cathode Material
The history of battery development is essentially a history of advancements in materials science. Improvements in manufacturing processes have led to quantitative changes in battery technology, while the invention of new materials has resulted in qualitative leaps. It is foreseeable that using lithium-containing conductive materials (ionic compounds, polymers) as electrode materials will be the optimal choice for high-energy batteries.
Lithium batteries can be classified into three types based on their cathode materials: lithium cobalt phosphate, lithium manganese phosphate, and lithium iron phosphate.
Lithium cobalt phosphate was abandoned due to the high price of cobalt; lithium manganese phosphate is inferior to lithium iron phosphate in terms of safety and lifespan; in the foreseeable future, lithium iron phosphate will become the main cathode material for lithium batteries. Both GM's Volt and BYD's F3DM use lithium iron phosphate batteries. With the technological advancements of promising cathode materials such as lithium manganese oxide and lithium iron phosphate, their application in the power battery field has begun to expand.
BTR is a leading manufacturer of carbon anode materials and lithium iron phosphate cathode materials for lithium batteries. BTR holds over 40 patents in China for lithium battery cathode and anode materials. In 2008 , its sales reached 180 million yuan, with a net profit of 30 million yuan. It projected total sales of 400-500 million yuan in 2009 and 800-1 billion yuan in 2010, maintaining a historical growth rate of 100% year-on-year.
2.2 Anode Materials
Currently, there is relatively little research on anode materials in the industry. In fact, the anode and cathode are equally important for lithium-ion batteries. In the selection of anode and cathode materials, the cathode material must be a high-potential lithium intercalation compound, and the anode material must be a low-potential lithium intercalation compound.
Currently, the main lithium-ion battery anode materials developed and used include graphite, soft carbon, and hard carbon. Graphite includes natural graphite, artificial graphite, and graphite carbon fiber. Common soft carbon materials include petroleum coke, needle coke, carbon fibers, and mesocarbon microbends (MCMB). Hard carbon refers to the pyrolytic carbon of polymers. Common types include resin carbon, organic polymer pyrolytic carbon, and carbon black.
Currently, apart from graphite, other materials still face unresolved challenges and cannot be applied to LIB production. For example, disordered carbon, despite its large discharge capacity, also exhibits a large irreversible capacity and severe potential hysteresis; that is, the Li+ insertion potential is close to 0V while the Li+ extraction potential is close to 1V, similar to disordered carbon. BCN-based and C-Si-O-based compounds show a "slope" discharge curve, unlike graphite which has a potential plateau at low potentials. The main problems with transition metal oxides as LIB anode active materials are their large irreversible capacity and high charge/discharge potential plateaus. Lithium-transition metal nitrides are limited in practical application due to their sensitivity to air humidity. As for lithium alloy materials, the excessive volume expansion during alloying causes pulverization and disruption of the conductive network during repeated charge/discharge cycles, resulting in poor cycle performance. Further research is needed to address these issues and obtain newer and better anode materials.
2.3 Electrolyte
Electrolyte is one of the four key materials in lithium-ion batteries, often referred to as the "blood" of lithium-ion batteries, ensuring their high voltage and high specific energy. As an essential material for lithium-ion batteries, the development of lithium-ion battery electrolytes depends on the development of lithium-ion batteries themselves. Lithium-ion battery electrolytes are formulated from lithium hexafluorophosphate (LiFL6) and organic solvents. Lithium hexafluorophosphate is formed by the reaction of phosphorus pentachloride and lithium fluoride dissolved in anhydrous hydrogen fluoride. Its suppliers are mainly overseas, such as Merck in Germany and Stella in Japan, and its products are of relatively high quality. my country became the second country in the world, after Japan, to industrialize lithium hexafluorophosphate. Domestic companies such as Jinguang High-Tech Co., Ltd., Tianjin Chemical Engineering Design Institute, and Xingtai Chemical Plant in Feicheng City, Shandong Province, are capable of producing it.
In 2007, Jiangsu Guotai's lithium battery electrolyte production reached 2,490 tons, ranking second in the world. Currently, Huarong Chemical, Ube Industries of Japan, and Samsung of South Korea are the three largest lithium battery electrolyte producers globally. Jiangsu Guotai's lithium battery electrolyte business already accounts for 30% of its operating profit, becoming a new profit growth point for the company. After the company's new production capacity came online in 2009, Huarong Chemical's lithium battery electrolyte production capacity will reach 3,000 tons per year.
Juhua Group possesses complete production technology for lithium hexafluorophosphate and supplies anhydrous hydrogen fluoride, an upstream raw material for lithium hexafluorophosphate. Lithium hexafluorophosphate projects are listed on Juhua Group's website and in the investment projects it has coordinated in Quzhou, Zhejiang. The booming lithium-ion battery industry will drive the upstream fluorochemical industry chain of lithium hexafluorophosphate electrolyte, presenting Juhua Group with an opportunity.
It is estimated that each new type of electric vehicle requires approximately 30 kg of lithium carbonate . Assuming that 1% of new passenger vehicles worldwide use lithium batteries starting in 2009 , and this figure increases by 1% annually thereafter , and based on the global production and sales volume of approximately 50 million vehicles in 2007 , the annual increase in lithium carbonate demand would reach tens of thousands of tons. Currently, the global supply and demand for lithium carbonate is basically balanced . However, if there is a surge in demand due to new types of electric vehicles , this balance will be completely disrupted, and the rapid expansion of the market will bring revolutionary changes to existing lithium carbonate producers.
2.4 Separating membrane
Separator materials account for about one-third of the cost of lithium-ion batteries. Lithium-ion battery separators generally use single-layer microporous membranes of polypropylene (PP) and polyethylene (PE) , as well as multi-layer microporous membranes composed of PP and PE . Taking polypropylene as an example , its raw material cost is about 8,000 yuan/ton , while after being processed into separators , its value can reach 3 million yuan/ton , a significant increase of several hundred times.
2.5 Battery Protection IC
Overcharging, over-discharging, and overcurrent during lithium battery use can all affect battery life and performance, and in severe cases, can lead to lithium battery combustion and explosion. There have been cases of mobile phone lithium battery explosions causing injuries and deaths, and IT and mobile phone manufacturers frequently recall lithium battery products. Therefore, each lithium battery must be equipped with a safety protection board, consisting of a dedicated IC and several external components. This board effectively monitors and prevents damage to the battery through a protection loop, preventing dangers such as combustion and explosion caused by overcharging, over-discharging, and short circuits. Because each lithium-ion battery requires a battery protection IC, the lithium battery protection IC market is enormous, worth billions of dollars annually. Silan Microelectronics Group, a professional microelectronics manufacturer, is a leading enterprise in the production of "lithium battery protection circuit chips." The integrated circuits for lithium battery protection produced by the company are comparable to those of Ricoh in Japan, but at a much lower price, indicating significant market potential.
Due to the high energy density of lithium-ion batteries, ensuring battery safety is challenging. In an overcharged state, the battery temperature rises, resulting in excess energy. This leads to electrolyte decomposition and gas generation, increasing internal pressure and posing a risk of spontaneous combustion or rupture. Conversely, in an over-discharged state, electrolyte decomposition degrades battery characteristics and durability, reducing the number of rechargeable cycles. Lithium-ion battery protection circuits include overcharge protection, overcurrent/short circuit protection, and over-discharge protection. Overcharge protection requires high precision, low power consumption of the protection IC, high voltage withstand capability, and zero-volt rechargeability. Silan Microelectronics has developed the SA1412 dual-cell lithium battery protection circuit, the SA45141 3- or 4-cell lithium battery protection circuit, the SC8261G single-cell lithium battery protection circuit, the SC121 single-cell lithium battery protection circuit with built-in delay capacitor, the SC8201 single-cell lithium battery protection circuit, and the SC8821 single-cell lithium battery protection chip with built-in MOSFET. The SA1412 is an integrated circuit specifically designed for lithium battery protection. The SC8821 protects lithium batteries from over-discharge, overcharge, and overcurrent. It is a single-cell lithium battery protection chip with a built-in MOSFET, designed to prevent shortened battery life or damage caused by overcharging, over-discharge, or excessive current. The SC8821 features high-precision voltage detection and time delay functions.
Overcharge, over-discharge, overcurrent, and short-circuit protection for lithium batteries are very important. Otherwise, serious problems such as combustion and explosion can occur, causing injury or death. Therefore, protection circuits are usually designed into the battery pack to protect lithium batteries. Lithium battery protection circuit chips are the guardians of every lithium battery, and the market prospects are very broad.
3. Obstacles to the development of lithium batteries
Lithium-ion batteries also have many drawbacks: short cycle life, complex charging circuits, and high requirements for internal protection circuits. In particular, for lithium-ion batteries with fully sealed aluminum casings, there is a fatal flaw in their safety protection design.
3.1 Resource scarcity
Lithium constitutes approximately 0.0065 % of the Earth's crust, ranking 27th in abundance among all elements. The total lithium reserves in seawater reach 260 billion tons, but the concentration is too low, making extraction difficult. Global salt lake lithium resources are mainly distributed in Chile, Argentina, China, and the United States. Granite pegmatite lithium deposits are mainly distributed in Australia, Canada, Finland, China, Zimbabwe, South Africa, and the Democratic Republic of Congo. Pegmatite lithium deposits have also been discovered in India and France, but they lack commercial development value. Currently, only a few countries in the world possess economically exploitable lithium resources.
Tang Yougen, director of the Institute of Chemical Power Sources and Materials at Central South University, said that even if the cost and safety issues of lithium are completely resolved, lithium batteries will not be able to meet all the demand in the future, because it is equivalent to replacing one scarce resource with another scarce resource.
3.2 Smelting pollution
Lithium-ion batteries contain chemicals such as lithium hexafluorophosphate and polypropylene glycol, which cause organic pollution to the environment. Heavy metals, such as cobalt, also pose environmental hazards, especially cobalt, which is relatively abundant and considered a rare and valuable metal with high recycling value. Although the pollution from lithium batteries themselves is not severe, the environmental pollution caused by the extraction and smelting of lithium metal is comparable to that from gasoline. The main industrial production methods for lithium metal are molten salt electrolysis and vacuum thermal reduction. Molten salt electrolysis uses lithium chloride as a raw material, which decomposes into metallic lithium and chlorine gas during electrolysis in a molten electrolytic cell. Lithium is deposited at the cathode, and chlorine gas is deposited at the anode. During electrolysis, lithium chloride dissociates into lithium ions, which move towards the cathode and discharge. The resulting metallic lithium gradually rises to the surface of the electrolytic cell or to the lithium collection chamber through the molten salt. The chlorine gas deposited at the anode rises through the molten salt to the outlet for discharge or collection. The biggest drawback of this method is the severe chlorine pollution generated during electrolysis, the difficulty in controlling product quality, and the high production cost.
3.3 Security Issues
Experts believe that most high-capacity lithium batteries on the market, due to differences in chemical composition, are prone to explosions and injuries when quality problems occur. Nickel-metal hydride (NiMH) and nickel-cadmium (NiCd) batteries are relatively safer. Lithium is too reactive, making it unsafe to use; it often burns or explodes during charging. Later, improved lithium-ion batteries incorporated components that suppress the reactivity of lithium, thus improving the safety and efficiency of lithium batteries.
During the development of lithium batteries, safety incidents such as explosions and combustions have occurred due to differences in the positive and negative electrode materials and their formulations. The main issue is that the negative electrode uses metallic lithium, which, after cycling, produces dendrites, leading to short circuits and subsequent combustion and explosions. The positive electrode materials used are lithium cobalt oxide or lithium nickel cobalt oxide, which have higher chemical reactivity. Combined with a graphite negative electrode, they are prone to explosion and combustion under high temperatures. Although the actual probability of such incidents is only one in ten thousand or one in a million, the sheer number and widespread use of consumer electronics, primarily mobile phones and laptops, makes the absolute number of safety incidents seem significant. Because these consumer electronics are indispensable in people's daily lives, any safety issues they cause have a major impact, leading to widespread fear of lithium batteries. This perception of safety issues with lithium batteries used in electronic digital products has begun to affect lithium batteries used in electric bicycles.
The safety design of lithium-ion batteries relies excessively on their internal electronic safety protection chips, lacking necessary physical safety protection measures. If these chips malfunction during charging and use, the consequences can be disastrous. At best, gas buildup inside the battery can cause it to swell; at worst, internal short circuits or other abnormalities can lead to a tragic battery explosion.
3.4 Cost Issues
Compared to lead-acid batteries, lithium batteries are more expensive for use in electric bicycles, which is a key factor hindering the large-scale replacement of lead-acid batteries in electric bicycles.
The main materials for lithium batteries, such as positive electrode materials, negative electrode materials, current collectors, separators, and electrolytes, are much more expensive than those for lead-acid batteries. However, the cost of assembly auxiliary materials and external circuit systems is almost nonexistent for lead-acid batteries. Although the cost of raw materials per unit power is not as large as the apparent cost difference due to the significantly higher energy density of lithium batteries compared to lead-acid batteries, a substantial difference in material costs does exist, often by multiples. Due to manufacturing processes, lithium batteries have higher labor costs. Labor costs account for over 40% of the manufacturing cost for lithium batteries, while for lead-acid batteries it is typically 10%–20%. Most processes in lithium battery production are irreversible, while lead-acid batteries are reversibly repairable, resulting in a lower overall yield rate for lithium batteries. The recycling value of lead-acid batteries after use is over 40%, while the recycling value of lithium batteries is almost zero.
4. Market prospects of lithium batteries
Currently, power batteries mainly come in two forms: nickel-metal hydride (NiMH) batteries and lithium-ion batteries. Hybrid power batteries mostly use NiMH materials, but because some technical performance characteristics of NiMH batteries are approaching their theoretical limits, they are not considered the future direction of development. In contrast, lithium-ion batteries have gained widespread acceptance due to their high operating voltage, small size, light weight, high energy density, no memory effect, no pollution, low self-discharge, and long cycle life.
Since its commercialization, lithium-ion batteries have been rapidly expanding their market share, becoming widely used in portable electronic devices such as laptops, camcorders, and mobile communications. Lithium-ion battery electrolytes are currently mainly used in mobile phones, digital cameras, laptops, and mining lamps, accounting for approximately 90% of all lithium-ion battery usage. They have dominated the high-end market for mobile phones and laptops, becoming the primary power source for various electronic products. Demand for lithium batteries in electronic products and mining lamps is expected to maintain a stable annual growth rate of 10%.
High-capacity lithium-ion batteries currently under development are being tested in electric vehicles. Leitian Lithium-ion Power Battery is collaborating with automotive giant FAW Group to focus on developing three models: lithium-ion electric commercial minibuses, lithium-ion electric luxury buses, and lithium-ion electric city buses. Production has commenced at its Changchun and Wuxi production bases, with mass production planned for 2009. Buses equipped with Leitian lithium-ion power batteries can travel approximately 300km at a speed of 130km/h after a 20-minute charge, consuming only 18 kWh per 100km. Japanese and overseas automakers are increasingly adopting lithium-ion rechargeable batteries in passenger vehicles. In Japan, Toyota, Subaru Heavy Industries, and Mitsubishi Motors have already decided to adopt them, while Daimler in Europe and America has also indicated its intention to do so. Audi in Germany and General Motors in the United States are also preparing to adopt them in 2010.
Among the batteries currently used in hybrid electric vehicles (HEVs) and future electric vehicles (EVs), there is a debate between nickel-metal hydride (NiMH) batteries and lithium-ion batteries. Compared to lithium-ion batteries, NiMH batteries have drawbacks such as insufficient range and the inability to be externally charged. Market analysts believe that with advancements in lithium-ion battery technology and cost reductions due to large-scale manufacturing, it may eventually replace NiMH batteries as the mainstream power battery for HEVs. Lithium-ion batteries represent the future of HEV power batteries, but currently, from a cost and commercialization perspective, NiMH batteries are a more realistic choice. NiMH batteries are just entering maturity and are currently the only battery system used in HEVs that has been practically verified and commercialized on a large scale. All mass-produced HEVs worldwide use NiMH battery systems.
Currently, nickel-metal hydride (NiMH) batteries account for 99% of the hybrid vehicle battery market share, with Toyota's Prius being a prime example of commercialization. It is projected that by 2020, non-NiMH hybrid batteries will account for less than 20% of the market share, indicating a promising market outlook for NiMH hybrid batteries. In the next 8-10 years, NiMH batteries will remain the dominant product in the power battery system for new hybrid vehicles.
Experts had optimistically predicted that the total market value of lithium-ion batteries could reach $10 billion by 2016. It is expected to become one of the main power sources for electric vehicles in the 21st century and will also be applied in satellites, aerospace, and energy storage. Its future market prospects are very broad, and it is considered an ideal energy source for 21st-century development. As chairman of Berkshire Hathaway, world-renowned investor Warren Buffett has also set his sights on new energy power. In September 2008, Buffett's MidAmerican Energy announced the purchase of approximately 225 million shares of BYD for $ 232 million, demonstrating the allure of lithium batteries.
