In recent years, the solar cell photovoltaic power generation technology has been highly valued by countries around the world. From the European and American solar photovoltaic "roof plan" to China's western photovoltaic power generation projects and "bright project". Solar photovoltaic power generation has shown its strong development momentum. With the development of photovoltaic power generation technology and the industrialization of low-cost photovoltaic modules, solar lamps and lanterns, photovoltaic power plants and photovoltaic household power, are required to provide battery suppliers with all-weather operation of the battery, and the current photovoltaic system mostly uses valve-regulated sealed lead-acid battery (hereinafter referred to as lead-acid battery abbreviated as VRLAB) gel lead-acid battery and maintenance-free lead-acid battery (not VRLA battery ) as energy storage power. Weatherability refers to the characteristics of the battery to adapt to the natural environment. This article mainly discusses the impact of temperature on battery life and capacity in natural environment and the solution, as well as the selection of energy storage lead-acid battery.
First, the influence of temperature on the life of lead-acid battery
VRLA lead-acid battery is affected by temperature, according to the principle of Arinius, in more than 40 ℃, the temperature rises 10 degrees, life doubled, the main reasons for the termination of life are: (a) sulfuric acid electrolyte drying; (b) thermal runaway; (c) internal short circuit, etc.
(a) Sulfuric acid electrolyte drying up: one of the key problem factors. Acid drying will cause the battery capacity to reduce, or even failure. This factor causes the battery to dry up and fail is unique to lead-acid batteries. The reasons for acid drying: (1) low efficiency of gas recombination, hydrogen and oxygen precipitation, water evaporation; (2) water seepage from the inside of the battery shell; (3) improperly designed control valves; (4) mismatch between charging equipment and battery voltage, battery voltage is too high, heat, water loss, dryness and failure.
VRLA lead-acid battery is affected by the above (1) (2) (3) (4) four factors, of which (2) (3) (4) three factors caused by water loss speed up with the rise of ambient temperature, thus accelerating the failure of lead-acid battery by drying out. Acid drying is a fatal factor affecting the life of VRLA lead-acid battery, and VRLA battery is not suitable for use under high temperature conditions above 35℃.
(ii) Thermal runaway.
The battery generally generates heat in the charging and discharging process. When charging, the oxygen produced by the positive terminal reaches the negative terminal, and the reaction with the negative lead produces a lot of heat, which will make the battery temperature rise if it is not guided away in time. If the battery works in a high temperature environment, the accumulated heat inside the battery will be difficult to be dissipated, which may lead to overheating of the battery, increased water loss, increased internal resistance and more heat, resulting in a vicious cycle, gradually developing into thermal runaway and eventually leading to battery failure.
VRLA lead-acid battery adopts liquid-poor tight assembly design, the acid cannot enter the 10% pore space in the partition, so the thermal conductivity inside the battery is extremely poor and the thermal capacity is very small, the reason why VRLA lead-acid battery is easy to happen thermal runaway in high temperature environment is that the amount of gas discharged from the safety valve is too small to take away the accumulated heat inside the battery. The huge heat of thermal runaway will cause the battery shell to be seriously deformed, swelling and cracking, and the battery will completely fail.
(C) internal short circuit: due to the degradation of the diaphragm material aging perforation, the active material off the expansion of the two poles connected, or charging process to generate dendrites through the diaphragm caused by internal short circuit. After deep discharge of the battery, the adsorbed diaphragm is prone to lead velvet or diffuse precipitation, or the formation of dendrite, resulting in micro short circuit of positive and negative plates.
Due to the redundant design of the negative electrode of VRLA lead-acid batteries, the charging efficiency in the early and middle stages of charging is higher than that of the positive plate, so before the positive plate precipitates oxygen, the negative electrode already generates enough velvet lead for recombination of oxygen. The amount of active material in the negative electrode is used as a control factor to slow down the deterioration of battery performance in the process of making batteries.
In addition to this, additives are now commonly used in lead-acid batteries to improve battery performance, such as the addition of zinc, cadmium, lithium, cobalt, copper, magnesium and other metal salts or oxides. These additives are strong electrolytes and their ions migrate to the negative electrode during the discharge process. These metal ions play the role of chemical coordination, reducing the probability of forming lead sulfate, and even if lead sulfate is formed, it is relatively soft and easy to soften or reduce. In the use of the battery, the temperature should be kept constant as much as possible to avoid large fluctuations in temperature and reduce the chance of dendrite precipitation.
To sum up, high temperature plays an accelerating role on battery water loss and drying, thermal runaway, positive plate grid corrosion and deformation, low temperature will cause negative passivation failure, temperature fluctuation will accelerate the internal short circuit of lead-acid battery and so on. All these will affect the battery life.
Second, the impact of temperature on the capacity of lead-acid battery
(a) The first category of early capacity loss, abbreviated as PCL-Ⅰ.
The main reason for the sudden loss of capacity of lead-acid battery is the blocking layer. Due to the Pb-Ca-Sn-Al alloy regeneration defects and semiconductor effect, the positive active material and the plate grid between the formation of a single conductive barrier layer, the conductive layer consists of a more complex composition and has semiconductor properties of the crystal, extremely sensitive to temperature, through the study of corrosion layer, improved the battery alloy and lead paste additives and other semiconductor doping manufacturing process, the principle of semiconductor crystals are extremely sensitive to the purity This principle, a ppm of doping can increase the conductivity of 103, through a reasonable doping process, this failure mode is basically solved.
(ii) The second type of early capacity loss, abbreviated as PCL-II
The main reason for the slow loss of capacity of lead-acid battery is not the commonly seen plate and grid corrosion sulfation or softening off of the active material, but due to the expansion of porous active material caused by the particles isolated from each other, greatly affected by temperature, by PbO2 → PbSO4 expansion and contraction during the softening process, causing irreversible damage to the flabby and complexed structure of the positive active material, gradually softening off. Causes the positive electrode plate to lose capacity at a lower rate.
(C) The third category of early capacity loss, abbreviated as PCL-Ⅲ
The main reason why the lead-acid battery cannot be charged is due to the reduction or loss of activity of the negative additive, which makes charging difficult, poor charging acceptance and insufficient re-charging, thus leading to sulfation at the bottom 1/3 of the negative plate.
In room temperature 10h - 20h rate discharge battery capacity is limited to the positive electrode, in low temperature (-15 ℃ below) and high rate (1h rate above) discharge battery capacity is limited to the negative electrode, low temperature high current discharge or by high temperature negative electrode is prone to passivation, the reason is that there is a large number of ions to enter the acid in a very short time during the discharge process, and the formation of nuclei need some time, so that the surface of the electrode Present excessive saturation, compared with the normal discharge current density will be able to form a large number of nuclei with small size, making the electrode surface into a dense layer with small pores, hindering the continuation of the discharge reaction, similar to the partial discharge consumed on this lead sulfate salt layer.
The high temperature drives the decomposition of the negative additive or dissolves it in the electrolyte and loses it early, making the negative chamois lead passivated. In the low temperature state, the solubility decreases significantly, even though the discharge current is the same as at low temperature and low concentration, and the speed generated during discharge is unchanged, but the saturation is increased relative to the low equilibrium solubility. In the low temperature state, it also leads to an increase in the viscosity of the acid solution, resulting in a decrease in the acid diffusion rate, an increase in the internal resistance of the battery, and a deterioration in the high-speed mass transfer performance.
The thickness of the passivation layer is related to the crystalline size, porosity and pore structure of lead sulfate, i.e., to the solubility of lead sulfate and the solution saturation of the lead electrode surface. At low temperature and high current density and sulfuric acid concentration, the solution saturation of the negative electrode surface is too high and the passivation layer becomes thicker. Therefore, it is easy to cause the battery to fail due to the difficulty of discharge. The passivation of the negative plate is neither charged nor discharged.
The mechanism and degree of temperature influence on the above factors (i), (ii) and (iii) involves the theory of electrochemical thermodynamics, electrochemical kinetics, semiconductor physics, metal physics, etc., which is still under further study. But high temperature does make the additives in the battery oxidation failure, causing the active material to fall off, and the negative electrode passivation makes the early capacity decay of the battery faster. This early capacity decay will lead to shorten the life of the lead-acid battery, the reliability becomes worse.
(D) Corrosion of positive electrode plate
According to the principle of chemical thermodynamics, the higher the ambient temperature, the greater the discharge depth of lead-acid battery, the higher the density of electrolyte, the more intense the corrosion of plate grid; the longer the storage time, the thicker the corrosion layer. Along with the plate grid corrosion and plate grid deformation and stretching, the result of which makes the plate grid tensile strength become smaller. Active material off, when the corrosion products become very thick or the plate grid becomes quite thin, the plate grid resistance increases, so that the battery capacity decreases, capacity drop 20% battery even if the failure.
As mentioned before, because the battery is an electrochemical container, extremely sensitive to changes in ambient temperature, the ambient temperature affects both the life of the battery and the capacity of the battery, which are inseparable.
Third, colloidal lead-acid battery (valve-regulated lead-acid battery) development
In just a few years, lead-acid batteries have been widely used in solar lamps and lanterns. In view of the poor weather resistance (-20℃~40℃) of VRLA lead-acid battery working in natural environment, we successfully developed the colloidal battery with better weather resistance (-40℃~60℃) with independent intellectual property rights, the colloidal battery also belongs to the valve regulated lead-acid battery, the colloidal lead-acid battery adopts the liquid-rich design scheme, adding 20% more acid than VRLA lead-acid battery. It is filled with gel electrolyte around the pole group and between the troughs, which has larger thermal capacity and good heat dissipation.
The gel battery is less affected by temperature and can overcome the above three early capacity losses and has the following advantages.
(a) Adopt special non-liquid non-gel electrolyte, increase assembly pressure (pressure on the surface of positive plate), assembly pressure 25-60Kp, inhibit the softening off of positive plate active material. Reasonably designed control valve to increase oxygen compound, reduce water loss and improve battery life (can improve life more than two times in various environments).
(ii) Adopt special plate grid structure (positive and negative plate grid mass ratio 1:0.75), process means and material formulation, organic and inorganic additives. The formation of microporous structure of the plate grid increases the reaction interface between the electrode and electrolyte, reduces the contact resistance, reduces the polarization of the electrode, substantially increases the utilization rate of the active material of the electrode, improves the charging efficiency, increases the discharge and output power of the battery, effectively prolongs the battery life exponentially, and improves the overall battery performance.
(c) The positive electrode plate grid adopts Pb-Ca-Sn-Al-Sb-Zn-Cd, the negative electrode plate grid adopts lead-calcium-tin-aluminum high hydrogen overpotential material plate grid and paste-coated electrode plate, with high capacity and long life. Lead-tin multi alloy current collector, small internal resistance, corrosion resistance, can withstand long-term floating charge use, analysis of pure electrolyte, small self-discharge.
(D) the use of new technologies, improved plate and grid material formulations to improve creep resistance and corrosion resistance, appropriate to increase the Sn, Ag content in Pb-Ca alloy, can improve creep resistance.
(E) the use of low-resistance porous PE partition plate, the design of the pole plate to leave a liquid-rich space in the battery shell, the acid does not spill, do not pollute the environment, do not corrode the equipment and mechanical parts, can be smoothly gas cathodic absorption. Improve the pressure of the pole group, tight assembly, can extend the battery life
(vi) The battery case cover adopts labyrinth type specially designed permeability valve, and special additives to reduce the water dissipation.
(vii) Adopting proper additives is good for maintaining the normal charging state of negative electrode, avoiding negative electrode sulfide and reducing negative electrode self-discharge. Therefore, while maintaining the normal charging state of the negative electrode, it also reduces the polarization potential of the positive electrode, thus reducing the corrosion rate of the positive plate grid, which is conducive to extending the life.
