The working principle of a lead-acid battery is to transform between electrical energy and chemical energy through an electrochemical reaction. The electrode is mainly made of lead and its oxide, and the electrolyte is a kind of storage battery with sulfuric acid solution.
In the discharge state, the important component of the positive electrode is lead dioxide, and the important component of the negative electrode is lead.
In the charged state, the important components of the positive and negative electrodes are lead sulfate.
There are many types of lead-acid batteries, and they are used in photovoltaic energy storage systems. There are three more types: flooded lead-acid batteries, valve-regulated sealed lead-acid batteries, lead-carbon batteries, and so on.
1. Flooded lead-acid battery
The sulfuric acid in the electrolyte of lead-acid batteries directly participates in the battery charging and discharging reaction process. In traditional lead-acid batteries, the remaining space in the battery tank except for the plates, separators and other solid assembly parts is completely filled with sulfuric acid electrolyte, and the electrolyte is surplus. Excessive state is called flooded battery. The battery plates are completely immersed in sulfuric acid electrolyte. It is characterized by low price and long lifespan, but the disadvantage is that it needs frequent maintenance.
2. Valve-regulated sealed lead-acid battery
Valve-regulated sealed lead-acid batteries, also known as maintenance-free batteries, are divided into AGM sealed batteries and GEL gel sealed batteries.
Compared with today's gel-sealed batteries, AGM sealed batteries have a smaller discharge capacity. Compared with the flooded battery of the same specification, the price is higher, and it has the following advantages:
(1) The cyclic charging capacity is 3 times higher than that of lead-calcium batteries and has a longer service life.
(2) Have higher capacitance stability throughout the life cycle.
(3) Low temperature performance is more reliable.
(4) Reduce the risk of accidents and reduce the risk of environmental pollution (because the acid is 100% sealed).
(5) Maintenance is very simple, reducing deep discharge.
Gel-sealed batteries (ie GEL type batteries), colloidal lead-acid batteries are an improvement of ordinary lead-acid batteries with liquid electrolytes. The sulfuric acid electrolyte is replaced with colloidal electrolyte, which is in terms of safety, storage capacity, discharge performance and service life. Compared with ordinary batteries, it has improved. The electrolyte is made up of silica sol and sulfuric acid. The concentration of the sulfuric acid solution is lower than that of the AGM battery, and the amount of electrolyte is more than that of the AGM battery, which is equivalent to the flooded battery. This electrolyte exists in a colloidal state and is filled in the separator and between the positive and negative electrodes. The sulfuric acid electrolyte is surrounded by gel and will not flow out of the battery.
The advantages of colloidal sealed batteries are as follows:
(1) The probability of acid leakage is small. The GEL type gel battery has no free electrolyte after the electrolyte gel, so the probability of acid leakage is much smaller than that of the AGM type battery.
(2) Less water loss. Because its pouring volume is more than that of dilute sulfuric acid and has less water loss, the gel battery will not fail due to water loss.
(3) Effectively extend battery life. The infusion of the colloid increases the strength of the separator, protects the electrode plate, and compensates for the defect of the separator shrinking when exposed to acid, so that the assembly pressure is not significantly reduced, which is one of the reasons for its prolonged battery life.
(4) The colloidal lead-acid battery has strong resistance to overcharge.
(5) Strong recovery ability under severe discharge conditions. The colloid fills the gap between the separator and the electrode plate, reduces the internal resistance of the battery, and improves the charge acceptance ability.
Therefore, the over-discharge, recovery ability and low-temperature charge-discharge performance of gel batteries are superior to those of AGM batteries.
(6) The self-discharge performance of the lead-acid battery is good. Under the same sulfuric acid purity and water quality, the storage time of the battery can be extended by more than 2 times.
(7) The anti-vulcanization performance of the colloidal lead-acid battery is very obvious in the case of severe power shortage.
(8) The colloidal lead-acid battery has good post-discharge performance.
3. Lead-carbon battery
Lead-carbon battery is a capacitive lead-acid battery, which is a technology evolved from the traditional lead-acid battery. It adds activated carbon to the negative electrode of the lead-acid battery, which can significantly increase the life of the lead-acid battery.
Lead-carbon battery is a new type of super battery that combines the advantages of both lead-acid batteries and super capacitors:
(1) It not only takes advantage of the instant large-capacity charging of supercapacitors, but also takes advantage of the specific energy advantages of lead-acid batteries, and has very good charge and discharge performance.
(2) The battery life is extended. Due to the addition of carbon (graphene), the phenomenon of sulfation of the negative electrode is prevented, a factor of battery failure in the past is improved, and the battery life is prolonged.
(3) The cost of electricity per kilowatt-hour has fallen. The cost per kilowatt-hour of lead-carbon batteries can be as low as 0.5 yuan/kWh. On the basis of large-scale production, lead-carbon batteries are even expected to reduce the cost per kilowatt-hour to less than 0.4 yuan.
Lead-carbon batteries are the most advanced technology in the field of lead-acid batteries, and they are also the development focus of the international new energy energy storage industry, and have very broad application prospects. It is widely used in energy storage fields such as photovoltaic power station energy storage, wind power energy storage and grid peak shaving.
Important anode materials for lithium-ion batteries include tin-based materials, lithium-based materials, lithium titanate, carbon nanomaterials, graphene materials, and so on. The energy density of the negative electrode material of lithium ion battery is one of the important factors that affect the energy density of lithium ion battery. The positive electrode material, negative electrode material, electrolyte, and separator of lithium ion battery are called the four core materials of lithium ion battery. Below we briefly introduce the performance indicators, advantages and disadvantages and possible improvement directions of various anode materials.
Carbon nanotubes
Carbon nanotube is a kind of carbon material with graphitized structure. It has excellent electrical conductivity. At the same time, because of its small depth and short stroke when releasing lithium, it is less useful as a negative electrode material for polarization during high-rate charging and discharging, which can improve The battery's high rate charge and discharge performance.
However, when carbon nanotubes are directly used as anode materials for lithium-ion batteries, there are problems such as high irreversible capacity, voltage lag, and unobvious discharge platform. For example, Ng and others have prepared single-walled carbon nanotubes by simple filtration and used them directly as negative electrode materials. The first discharge capacity is 1700mAh/g, and the reversible capacity is only 400mAh/g.
Figure 1 Carbon nanotube anode material
Another application of carbon nanotubes in the negative electrode is to composite with other negative electrode materials (graphite, lithium titanate, tin-based, silicon-based, etc.), using its unique hollow structure, high conductivity and large specific surface area as a carrier Improve the electrical properties of other negative electrode materials. For example, Guo et al. used the chemical vapor deposition method to grow carbon nanotubes in situ in the pores of expanded graphite, and synthesized expanded graphite/carbon nanotube composites. The first reversible capacity was 443mAh/g. After 50 cycles of charging and discharging at a rate of 1C, Guo et al. , The reversible capacity can still reach 259mAh/g. The hollow structure of carbon nanotubes and the pores of expanded graphite provide a large amount of lithium active sites, and this structure can buffer the volume effect of the material during the charge and discharge process.
