Facts You Should Know About Lithium Battery

1. Introduction

A Lithium-ion battery or Li-ion battery is a new generation of green and high energy rechargeable battery with excellent performance, which has become one of cutting-edge technology.

Lithium-ion battery features:

--high voltage

--high capacity

--low consumption rate

--no memory effect

--no pollution

--small volume

--small internal resistance

--less self-discharge happenings

--good cycling performance

                                   cylindrical, hard-packed and soft-packed battery

2. Application of Lithium-ion battery materials

Lithium-ion batteries have been used in many civilian and military fields such as communication fields like for mobile phones, consumption fields like for laptop computers, video cameras and digital cameras as well as in commute fields like small-size e-vehicles.

3. Common materials for lithium-ion batteries

(1)Layer structure:

A.NCM, NCA (ternary battery material)

---Based on the percentage of nickel content, there are ternary materials 111, 422, 523 and 611, which are medium and low nickel ternary lithium materials as well as 622 and 811 high nickel ternary materials.

B. lithium cobalt oxides (LiCoO2)

---The calcining temperature of lithium cobalt oxides is higher than NCA. The initial charge-discharge efficiency of LiCoO2 is 90%.

C. Lithium Mangnese oxides (LiMnO2)

(2) Spinel structure

LiMn2O4

(3) Polyanion

lithium iron phosphate (LiFePO4)

4. Flip a coin or based on solid facts in choosing lithium carbonate and lithium hydrate as the source of lithium for the ternary cathode battery?

In reality, most factories in China choose lithium carbonate as raw materials to produce ternary cathode materials. The percentage of lithium in lithium carbonate is more stable than that of lithium hydrate. In addition, corrosion resistance of lithium carbonate is superior to lithium hydrate.

For ternary 111, 523 which contains a relatively low percentage of nickel, lithium carbonate is preferable while for ternary 6,811, which contains a relatively high percentage of nickel, lithium hydrate is a better choice. 

--The melting point of lithium carbonate is 720℃ and lithium hydrate is 471℃. 

During the calcining process, the melt lithium hydrate will blend with raw metallic materials more evenly and adequately so as to reduce remains of lithium at the surface and improve the specific capacity of ternary materials. Also, lithium hydrate with relatively low calcining temperature will lower the chance of cation mixing and improve cycling stability.

By contrast, the calcining temperature of lithium carbonate has to reach 900℃ before the composite get stabilized. Ternary lithium battery materials with high percentage of nickel can’t be fired at too high temperature, otherwise its charging and discharging rate will be negatively affected. The calcining temperature for NCM 811, for instance, should be controlled under 800℃, while that of NCM 90505 should be controlled under 740℃. 

--The melting and decomposition temperatures of lithium hydrate is lower than that of lithium carbonate.

--The price of lithium hydrate is higher and that’s why high nickel ternary cathode material cost is higher.

5. Manufacturing Process

Here lists the procedure for producing medium and low nickel ternary powder and high-nickel ternary powder.

Medium and low nickel ternary powder	feeds	High nickel ternary powder	feeds
	mixing the feeds and filling into the sagger		mixing the feeds and filling into the sagger
air atmosphere	First time calcining	oxygen atmosphere	First time calcining
	Rough and refined grinding		Rough and refined grinding
	screening		screening
coating agent	coating	This process is necessary because of the high PH level and free lithium ions. In the homogenization process, NCM 811 will solidify easily because of the high content of surface alkaline oxide which absorbs water. Alkaline oxide on the surface will influence electrochemical performance in the increase of irreversible capacity loss and deterioration of circulation performance. In addition, the decomposition of Li2CO3 at the surface under high pressure is one of the main causes of battery flatulence, thus bringing potential safety hazards.	cleansing
	filling into the sagger		dehydration
air atmosphere	second time calcining		desiccation
	screening	coating agent	coating
	deironing		filling into the sagger
	batch mixed packing	oxygen atmosphere	second time calcining
	finished product		screening
			deironing
			batch mixed packing
			finished product

6. The calcining process

--Some Know-hows

Inside the kiln, it varies in the rows and numbers of the saggers. Some will have 2, 4, or even 6 rows with 1, 2 or 3 layers. We suggested two rows with 2-3 layers depending on the size of your kiln. For each sagger, try not to fill up too much powder, about 3-5kg is appropriate.For each factory, the calcining temperature and endurance also vary, together with its calcining times. Some will only sinter one time, so will do 2 or even 3 times.

--What Kiln Furniture Shall You Choose?

(1)Size.

The usual sizes for saggers are: 320mm X 320 mm X 60 mm, 320mm X 320 mm X 65 mm, 320mm X 320 mm X 70 mm, 320mm X 320 mm X 75 mm, 320mm X 320 mm X 85 mm, 320mm X 320 mm X 100 mm.

(2)Shapes.

There are open saggers with gaps, closed saggers with footings and closed saggers. When we compare the three saggers, we find out that when piling up, the sagger with footings have the biggest gap, thus most efficient when stack up together while the closed sagger can’t be used for this occasion.

     

(3) Materials

When people calcine ternary cathode materials, fracture and chemical erosion are the two indications that saggers have to be changed. A sagger with a higher percentage of aluminum features more chemical inertness, and a lower percentage of scaling and slagging. Corundum mullite sagger and alumina sagger is alkali erosion resistant, but the higher the content of alumina, the more fragile the sagger is against thermal shock. Also, it will be more costly. 

(4) Cycling Stability You Should Know

On the production line, the factories usually use cordierite mullite sagger with the alumina content of 40-60%. Our company produce both primary and secondary kiln furniture and we have supplied both open saggers and saggers with footings of corundum mullite and cordierite mulllite for our customers and the cycling times can be up to 15 times, but when it is used after 4 times, it starts to scale slightly.

---Calcining Temperature

The calcining time won’t have too much influence on the capacity, SSA, tap density and PH value of the materials, but it will exert great effect on lithium remains at the surface as well as single crystal of the products.

Testing samples	Calcining time (h)	Capacity(mA•h•g-1)	TD(g•cm-3)	SSA(m2•g)	Lithium Carbonate at the surface(%)	pH
523-1	9	156.5	2.48	0.32	0.96	11.75
523-2	11	156.2	2.43	0.31	0.61	11.71
523-3	14	156.3	2.44	0.29	0.31	11.69

--Air Flow is Critical

As is indicated from the chart, we can conclude that, the exhaust after the reaction is more than the oxygen it needs, so people have to make sure of the timely venting of the exhaust while also ensuring enough oxygen supply. Otherwise, the reaction speed will slow down, stifle the formation and growth of grains, lead to inadequate chemical reaction, and eventually result in poor performance of the products.

The source of lithium	CO2(L)	Vapor (L)	O2(L)	Air exhaust (L)
Lithium carbonate	116.5	233	58	278
Lithium hydrate		582	58	278

                      The O2 and exhaust volume involved when calcining 1kg of NCM 523

--Conclusion

In ternary cathode materials production industry, there are two aspects worth mentioning considering the calcining process and equipment. One is that since there are so many variants affecting the calcining process, the quality and performance of the cathode materials vary for each batch of the products; Second is that due to the various size and designing of the kiln equipment and the calcining process, the performance of the cathode and anode material vary in SSA, granular size, as well as in the shapes and sizes of mono crystal and crystal texture. Therefore, you've got to choose the appropriate sagger in consideration with the kiln, the raw materials and take good control of the calcinig temperature.

High temperature solid phase calcining method is adopted for synthesizing high nickel ternary materials. The energy band of Ni3+ and Ni4+ overlaps with that of O, so when discharging lithium, O might discharge from lattice and Ni2+/ Li+ mixing results in unstable structure; the product is very sensitive to humidity and CO2, with high base level; it is more critical for in stability, safety performance, storage and processing, thus the calcining should be oxygen atmosphere.

Special note: All the information (content, pictures and charts) I hereby writes are what I've learned from  a Chinese scientist's livestreamming share, whose Douyin is 275511859. I'd like to thank him for his sharing.