During charging and discharging, Li+ inserts and de-inserts back and forth between the two electrodes: during charging, Li+ de-inserts from the positive electrode, passes through the electrolyte, and inserts into the negative electrode, which is in a lithium-rich state; the opposite occurs during discharging. On October 9, 2019, the Royal Swedish Academy of Sciences announced that the 2019 Nobel Prize in Chemistry would be awarded to Johann Goodenough, Stanley Whittingham, and Akira Yoshino in recognition of their contributions to the research and development of lithium-ion batteries. [1] From August 1, 2023, CCC certification management will be implemented for lithium-ion batteries and battery packs. From August 1, 2024, those that have not obtained CCC certification and are marked with certification marks shall not be manufactured, sold, imported, or used in other business activities.
Lithium-ion batteries
1. Basic Introduction
A lithium-ion battery is a battery whose electrochemical system contains lithium (including metallic lithium, lithium alloys, lithium ions, and lithium polymers). Lithium-ion batteries can be broadly classified into two categories: lithium metal batteries and lithium-ion batteries. Lithium-ion batteries do not contain metallic lithium and are rechargeable. The fifth generation of rechargeable batteries, the lithium metal battery, was developed in 1996. Its safety, specific capacity, self-discharge rate, and performance-price ratio are all superior to lithium-ion batteries. Due to its high technological requirements, only companies in a few countries currently produce lithium metal batteries.
2. Working principle
(1) Lithium metal batteries:
Lithium metal batteries typically use manganese dioxide as the positive electrode material, lithium metal or its alloy metals as the negative electrode material, and a non-aqueous electrolyte solution.
Discharge reaction: Li + MnO2 = LiMnO2
(2) Lithium-ion batteries:
Lithium-ion batteries typically use lithium alloy metal oxides as the positive electrode material, graphite as the negative electrode material, and a non-aqueous electrolyte.
The reaction that occurs at the positive terminal of the charger is
LiCoO2 == Li(1-x)CoO2 + XLi+ + Xe- (electrons)
The reaction that occurs at the negative terminal of the charger is
6C + XLi + Xe- = LixC6
Overall reaction of the rechargeable battery: LiCoO2 + 6C = Li(1-x)CoO2 + LixC6
How lithium-ion batteries work: A lithium-ion battery is a rechargeable battery that relies heavily on the movement of lithium ions between the positive and negative electrodes to function. During charging and discharging, Li+ ions repeatedly insert and extract between the two electrodes: during charging, Li+ ions extract from the positive electrode, pass through the electrolyte, and insert into the negative electrode, leaving the negative electrode in a lithium-rich state; the reverse occurs during discharging.
Lithium-ion batteries discharge through a chemical oxidation-reduction reaction. During discharge, which is when we use the battery and consume its power, lithium ions are inserted into the positive electrode and deposited into the negative electrode. Charging is the reverse process. This gain and loss of ions creates a voltage, resulting in a charge on the battery.
During each charge-discharge cycle, lithium ions (Li) act as carriers of electrical energy, repeatedly moving back and forth between the positive and negative electrodes. They react chemically with the positive and negative electrode materials, converting chemical energy into electrical energy and achieving charge transfer. This is the basic principle of a lithium-ion battery. Since the electrolyte and separator are electron insulators, there is no movement of electrons between the positive and negative electrodes during this cycle; they only participate in the chemical reactions at the electrodes.
Reasons for capacity decay in lithium-ion batteries: Lithium-ion batteries are the fastest-growing rechargeable batteries after nickel-cadmium and nickel-metal hydride batteries. The application of lithium-ion batteries largely depends on the stability of their charge-discharge cycles. Like other rechargeable batteries, capacity decay in lithium-ion batteries is unavoidable during cycling.
1. Structural changes in cathode materials
Cathode materials are a crucial component of lithium-ion batteries. When a lithium-ion battery is removed from the cathode, the metal elements must be oxidized to a high oxidation state to maintain the material's electrical neutrality, resulting in a compositional shift. This shift can easily lead to phase transfer and changes in bulk structure. Phase transitions in electrode materials can cause changes in lattice parameters and lattice mismatch. The resulting induced stress causes grain breakage and crack propagation, leading to mechanical damage to the material's structure and consequently, a decline in electrochemical performance.
2. Structure of negative electrode material
Commonly used negative electrode materials for lithium-ion batteries include carbon materials and lithium titanate. This article analyzes graphite as a typical negative electrode. The capacity decay of lithium-ion batteries first occurs during the formation stage, when an SEI (Sediment-Insulated Plate) forms on the negative electrode surface, consuming some lithium ions. As lithium-ion batteries are used, changes in the graphite structure also contribute to a decrease in battery capacity.
Although the morphology and structure of graphite are maintained, the half-width at half-maximum (WHM) of its (002) crystal plane increases, resulting in a smaller grain size in the c-axis direction. The change in crystal structure leads to cracks in the carbon material, which in turn damages the SEI film on the negative electrode surface and promotes the repair of the SEI film. The excessive growth of the SEI film consumes active lithium, thus causing irreversible capacity decay of the lithium-ion battery.
3. Oxidative decomposition and interfacial reactions of electrolyte
The properties of the electrolyte significantly affect the specific capacity, lifespan, rate charge/discharge performance, operating temperature range, and safety performance of lithium-ion batteries. The electrolyte mainly consists of three parts: solvent, electrolyte, and additives. The decomposition of both the solvent and the electrolyte leads to capacity loss in lithium-ion batteries. Electrolyte decomposition and side reactions are important factors in lithium-ion battery capacity decay. Regardless of the positive and negative electrode materials or manufacturing process used, with the cycling of lithium-ion batteries, electrolyte decomposition and interfacial reactions between the electrolyte and the positive and negative electrode materials will cause capacity decay.
4. Positive electrode overcharge reaction
When the ratio of positive electrode active material to negative electrode active material is too low, positive electrode overcharging is likely to occur. The capacity loss caused by positive electrode overcharging in lithium-ion batteries is mainly due to the presence of electrochemically inert materials (such as Co3O4, Mn2O3, etc.), which disrupts the capacity balance between electrodes, and the capacity loss is irreversible.
5. Electrode instability
During charging, the unstable positive electrode active material reacts with the electrolyte, causing a decrease in capacity. Factors affecting the instability of positive electrode materials include structural defects, carbon black content, and excessively high charging potential, among which structural defects are the most significant.
In this era of rapid technological advancement, lithium-ion batteries have become an indispensable part of our lives. From smartphones and laptops to electric vehicles, lithium-ion batteries provide convenient energy for our daily lives. So, what exactly is a lithium-ion battery? How does it work? This article will unveil the mysteries of lithium-ion batteries for you.
1. Lithium batteries have a long lifespan, are lightweight, and are small in size.
Lithium-ion battery electric bicycles currently come from a variety of brands, including Giant, Kaiqi, Jieaobi, and Tuer. The power performance of lithium-ion battery electric bicycles is similar to that of lead-acid battery (basic electric bicycles). Charging takes 6-8 hours, and depending on the battery capacity, they can travel 30-45 kilometers. They weigh only about 1/5 of lead-acid batteries. The biggest advantage of lithium-ion battery electric bicycles is their long lifespan. The high price of lithium-ion batteries globally is only superficially apparent; in reality, the cost is similar to that of lead-acid batteries. Currently, lithium-ion batteries generally have a 2-year warranty, while lead-acid batteries have a 1-year warranty.
2. Lithium batteries have activation-free characteristics.
It's important to note that lithium batteries enter a dormant state after being stored for a period of time, at which point their capacity is lower than normal, and their usage time is shortened. However, lithium batteries are easily activated; just 3-5 normal charge-discharge cycles are sufficient to activate the battery and restore its normal capacity. Due to the inherent characteristics of lithium batteries, they have virtually no memory effect. Therefore, users do not need special methods or equipment to activate new lithium batteries.
3. Lithium batteries have a memory effect.
Consumers have always worried about the memory effect when charging lead-acid and nickel batteries. However, with lithium batteries, everyone can breathe a sigh of relief, as they do not have a memory effect. If some consumers still don't know how to charge lithium batteries, they might want to read the following information.
1. The high price of lithium battery electric vehicles is mainly due to lithium batteries.
Currently, lithium battery electric bicycles are generally several hundred to a thousand yuan more expensive than lead-acid battery electric bicycles, making them difficult for consumers to accept in the market. Lithium batteries are lightweight, environmentally friendly, and do not cause pollution after disposal. Once the application technology matures and market sales increase, the price of lithium battery electric bicycles will decrease.
2. Overcharging lithium batteries can be counterproductive.
Lithium batteries and chargers automatically stop charging once the battery is fully charged; there is no "trickle" charging for 10+ hours as claimed by nickel-cadmium chargers. In other words, leaving your lithium battery on the charger after it's fully charged is pointless. Furthermore, no one can guarantee that the battery's charge/discharge protection circuitry will never change or that its quality will be flawless, so your battery will be constantly teetering on the edge of danger. This is another reason why we oppose prolonged charging.
Furthermore, in some electric vehicles, if the charger is not removed after a certain charging time, the system will not only not stop charging but will also begin a discharge-charge cycle. While the manufacturers may have their reasons for this practice, it is clearly detrimental to battery life. Therefore, when purchasing lithium batteries...
3. The power performance of lithium batteries needs to be improved.
Lithium batteries are much less resistant to fluctuations in charge and discharge than lead-acid batteries. This is one of the main reasons why lithium batteries cannot be effectively used in high-power vehicles, resulting in reduced durability.
After purchasing an electric vehicle, consult the manufacturer or dealer to ensure proper maintenance of the lithium battery.
