The coating surface density product of lithium batteries is generally 1540.25 because the coating surface area of lithium batteries refers to the coating thickness of a lithium battery electrolyte layer and a layer of electrode material deposited on a unit surface when packaging the battery. process, and 1540.25 means that the average thickness of the product is 1540.25 μm. The coating area mainly determines the capacity and discharge performance of the battery, so 1540.25 is a very important parameter and a standard that must be strictly adhered to during the battery manufacturing process.
Lithium Battery Electrolyte
The Toyota hybrid uses relatively inexpensive traditional nickel-metal hydride batteries, while Honda's Accord hybrid uses more expensive lithium batteries , so many friends think Toyota is simple and. Honda is nicehe. In fact, it cannot be judged so simply. The reason why Toyota and Honda choose different types of batteries for hybrid models is mainly based on the characteristics of nickel-metal hydride batteries and lithium batteries. its own hybrid model. Let me share with you:
There is a structural difference between lithium-ion batteries and nickel-hydrogen batteries.
Structurally speaking, the cathode of nickel-hydrogen batteries is Ni(OH). The negative electrode is a metal hydride and the electrolyte is a 6 mol/L potassium hydroxide solution.
Lithium-ion batteries integrate lithium ions into petroleum coke and graphite to form a negative electrode. Commonly used cathode materials are LixCoO2, LixNiO2 or LixMnO4. The composition of the electrolyte is relatively complex, LiPF6 + diethylene. carbonate+dimethyl Carbonatebase is mixed according to the proportion.
Advantages and disadvantages of nickel-hydrogen batteries
Advantages:
From the previous description of the structure, we can understand that liquid hydrogen battery has a simple structure and rich materials, so the price is relatively cheap. In addition, the number of charge and discharge cycles of nickel-metal hydride batteries is relatively long, generally up to 1,000 to 2,000 times.
NiMH batteries do not have overly strict charging requirements. They can be overloaded, are durable and have relatively stable quality.
Nickel-metal hydride batteries have a relatively large discharge current, so they are widely used in various fields.
The safety of nickel-metal hydride batteries is very high. The flash point of nickel-metal hydride batteries can reach 400°C, and the thermal capacity sspecific and the heat of evaporation of the electrolyte are relatively high. if extreme abnormalities such as short circuit and puncture occur, even if the battery is damaged, the ascent is too likely to cause violent burns.
Disadvantages:
Nickel-metal hydride batteries self-discharge, which means that the power of the nickel-metal hydride battery will decrease if it is not used for a certain period of time. time. after it is fully charged.
Ni-MH batteries have a relatively low memory effect if charged directly without being fully discharged, they will not be fully charged, thus shortening the life of the battery. This is why this phenomenon is also called battery memory effect.
In addition, compared with lithium-ion batteries, the energy density ratio of nickel-metal hydride batteries is verylow and the volume is relatively large for the same quantity of electricity.
The advantages and disadvantages of lithium-ion batteries
Relatively speaking, lithium-ion batteriesSub-batteries were developed to overcome the shortcomings of nickel-chromium and nickel- metal hydride.
Advantages:
Lighter and higher energy density ratio.
The self-discharge phenomenon is weak. In other words, although lithium-ion batteries have self-discharge, they are much lighter than nickel-metal hydride batteries.
An important advantage of lithium-ion batteries is that they do not have a memory effect, that is, regardless of the amount of energy remaining in the battery, it can be charged directly by plugging it into the charger. and it will be fully charged.
Disadvantages:
The cost of lithium-ion batteries is higher, the discharge current is relativelyatively low and the number of complete charge and discharge cycles is relatively low after several charges and. discharges, lithium-ion batteries The charging and discharging capacity will be reduced to a certain extent. According to the latest ternary lithium battery standards, after 1,000 full charges and discharges, the capacity of the lithium battery will be about 80%.
The price is higher. Since the structure of lithium-ion batteries is more complex and the cost of anode materials is higher, the overall cost of lithium-ion batteries is higher.
Lithium-ion batteries can catch fire in a collision. After the collision, the battery core may discharge with a large current and burn the diaphragm, resulting in a short circuit in a larger area, resulting in high current. Vaporization of the electrolyte temperature, when the pressure on the battery shellis exceeded, it will cause violent combustion and explosion.
Accord's I-MMD hybrid principle determines that it can only use lithium-ion batteries.
In most working conditions, the hybrid model's engine Accord i-MMD is not directly pushed. the car moves forward, the engine in hybrid mode only drives the generator to produce electricity. Most of the power drives the electric motor to drive the car. The remaining power charges the lithium battery. The engine is only used to drive the car directly while cruising. high speed and when the lithium battery is insufficient. This hybrid principle requires its battery to have higher charging and discharging efficiency and larger discharge capacity. Therefore, only lithium-ion batteries with high energy density ratio and high charging and discharging efficiency can be used.used.
The electrolyte in lithium batteries is an important component of the battery and has a significant impact on battery performance. In traditional batteries, the electrolytic system uses water as a solvent. However, since the theoretical voltage of water decomposition is only 1.23 V, even taking into account the overpotential of hydrogen or oxygen, the maximum voltage of a battery with an electrolytic system using water as a solvent is only about 2V (like a lead acid battery). acid battery). The voltage of lithium batteries reaches 3~4V. The traditional aqueous solution system is obviously no longer suitable for the needs of batteries, and a non-aqueous electrolyte system must be used as the electrolyte of lithium ion batteries. Lithium battery electrolytes mainly use organic solvents and electrolytes that can withstand high voltages without decompositionto set down.
The electrolyte used in lithium-ion batteries is an ionic conductor with electrolytic lithium salt dissolved in an organic solvent. Generally, as an organic electrolyte for practical lithium-ion batteries, it should have the following properties:
(1) High ionic conductivity, generally reaching 10-3~2*10-3S/cm lithium ion; the migration number should be close to 1;
(2) Electrochemically stable potentialWide range; should have an electrochemical stability window of 0~5V;
(3) Good thermal stability, wide operating temperature range;
(4) Stable chemical performance, in line with battery There is no chemical reaction between the current collector and soft substances;
(5) It is safe and low-toxic, and it is best to be biodegradable.
Suitable solvents should have a high dielectric constant and low viscosity. SolventsCommonly used include alkyl carbonates such as PC and EC, which are highly polar and have a high dielectric constant, but have high viscosity and intermolecular forces. , lithium ions move slowly there. Linear esters, such as DMC (dimethyl carbonate) and DEC (diethyl carbonate), have a low viscosity but also a low dielectric constant. Therefore, in order to obtain a solution with high ionic conductivity, they are generally used PC+DEC, EC+DMC. and other mixed solvents. These organic solvents have some odor, but generally speaking, they can meet EU RoHS and REACH requirements. They are very toxic, environmentally friendly and environmentally friendly materials.
The currently developed inorganic anion conductive salts mainly include three categories: LiBF4, LiPF6 and LiAsF6. Their electrical conductivity, theirthermal stability and their resistance to oxidation are in the order:
Conductivity: LiAsF6≥LiPF6. >LiClO4>LiBF4
Thermal stability: LiAsF6>LiBF4>LiPF6
Oxidation resistance: LiAsF6≥LiPF6≥LiBF4>LiClO4
LiAsF6 has conductivity and very high stability and charge and discharge rates of batteries, but its application is limited due to arsenic toxicity. Currently, LiPF6 is most commonly used.
All materials of currently commonly used lithium batteries, including electrolytes, comply with EU RoHS and REACH requirements and are environmentally friendly energy storage products.