CN109708990B - Method for measuring content of trace moisture in electrode material for lithium ion battery - Google Patents
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Abstract
The invention discloses a method for measuring the content of trace moisture in an electrode material for a lithium ion battery, which comprises the following steps: selecting a proper sample container according to a Claperon equation and a relation between air pressure and water boiling point, and putting the electrode material to be measured into the sample container according to a relation between the specific volume of the sample container and the sample weighing amount; heating the sample container with the sample at a reasonable temperature to evaporate water in the sample and condense the water on the wall of the sample container; then methanol solvent which is pre-titrated by Karl Fischer and has extremely low moisture content is adopted to dissolve moisture in the sample container so as to reduce the measurement background interference as much as possible. And finally, calculating the moisture content in the sample by adopting a Karl Fischer micro-moisture tester after eliminating the interference of unsaturated gas in the sample container on water vapor absorption and the interference of a background value. The determination method provided by the invention is simple in implementation mode and easy to operate; the method has good repeatability and high accuracy of the measured result; the method is suitable for most anode and cathode materials and is widely applied.
Description
Technical Field
The invention relates to the technical field of determination of trace moisture content, in particular to a method for determining trace moisture content in an electrode material for a lithium ion battery.
Background
Lithium ion batteries have been widely used in the fields of portable electronic information devices, new energy vehicles, small electric vehicles, power storage, and the like because of their excellent performance. At present, lithium ion batteries are developing towards high safety, high energy density, high power density, and long cycle life. This goal is achieved without any optimization of the raw materials themselves. The raw materials for forming the lithium ion battery mainly comprise: the electrolyte comprises a positive electrode material, a negative electrode material, an electrolyte and a diaphragm, wherein the positive electrode material and the negative electrode material are together called an electrode material. Depending on the production process, transport, storage etc., a certain amount of moisture is present in the electrode material to a greater or lesser extent. After the moisture is incorporated into the battery along with the electrode material, the moisture reacts with the lithium salt in the electrolyte to form hydrogen fluoride, which increases the pressure inside the battery, thereby causing the danger of swelling and leakage of the battery. In addition, hydrogen fluoride generated by the reaction of the water and the electrolyte can also react with a Solid Electrolyte Interface (SEI) film of the negative electrode to generate lithium fluoride precipitates, so that lithium ions can generate irreversible chemical reaction on the negative electrode plate of the battery while the SEI film is damaged, active lithium ions are consumed, and the capacity of the battery is further reduced. Therefore, the moisture is strictly controlled in the production process of the electrode material, and the detection of the moisture content is enhanced in the purchasing and selling links of the electrode material.
The residual moisture in the electrode material is typically several hundred ppm, relatively low, and is typically measured by dry weight loss or karl fischer, using reference standards including: GB/T6284-. Wherein GB/T6284-. However, for the electrode material with high content of volatile organic compounds, after being heated at 105 ℃, the reduction of the volatile organic compounds leads to larger moisture measurement results. Therefore, when measuring the trace moisture in the chemical products, the industry generally tends to select the Karl Fischer method with high specificity, and GB/T6283-. However, the criterion of this method is that the sample is soluble in organic solvents (methanol, chloroform, glacial acetic acid, etc.) in the Karl Fischer titration cup. However, the lithium ion battery electrode material cannot be dissolved in an organic solvent, so a karl fischer determination method for trace moisture needs to be specially designed for the lithium ion battery electrode material.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide the method for measuring the content of trace moisture in the electrode material for the lithium ion battery, which has the advantages of convenient operation, higher accuracy and better repeatability and can meet the detection requirement of the lithium ion battery industry.
In order to achieve the purpose, the invention provides the following technical scheme: a method for measuring the content of trace moisture in an electrode material for a lithium ion battery comprises the following steps:
(1) taking 3 identical fully dried and fully cooled open sample containers, respectively recording as 0#、1#、2#A sample container, weighing a powdery electrode material sample to be measured at room temperature, and putting the electrode material sample into the container 1#The sample container is vibrated to the state that the surface of the sample is flat, and then the electrode material sample to be measured with double weight is weighed and put into the container 2#In a sample container and tapping until the sample surface is flat, 0#The sample container is used as a blank for holding no sample and is sealed 0#、1#、2#The opening of the sample container; the relationship between the volume of the sample container and the mass of the sample to be weighed is determined as follows: the sample is weighed to ensure that in the subsequent step (2), the 2 is heated at a temperature of T1#When a sample container is used, 2#The heated temperature T3 of all samples in the sample container is greater than the boiling point T2 of water at a pressure P1 in the sample container, wherein P1 is 2 at T1#After all the water in the sample container is changed into steam, and the internal temperature is increased to the pressure in the container after dynamic balance;
(2) heating the sealed 0 of step (1) at a temperature T1#Sample container and sealed container 1 containing sample#、2#The sample container is 2 to 4 hours till 1#、2#Fully evaporating the water in the electrode material sample to be detected in the sample container; naturally cooling for more than 30min to fully condense the water vapor evaporated from the sample on the wall of the container;
(3) starting a Karl Fischer micro-moisture tester, taking absolute methanol as a solvent, and carrying out moisture pre-titration according to an instrument instruction until the drift value is less than 10 mu L/min to obtain a methanol solvent with pre-titrated moisture;
(4) taking a fully dried and fully cooled suction device, and a suction stepThe methanol solvent obtained in the step (3) is added into the cooled 0 in the step (2) in equal amount#、1#、2#In the sample container, still sealing the sample container, and fully shaking each sample container to fully dissolve the condensed water attached to the wall of the sample container in the methanol solvent; wherein the relation between the absorption volume of the methanol solvent and the volume of the sample container is 1: 4-1: 2;
(5) for 0 in step (4)#Methanol solvent in sample container and 1#、2#Respectively measuring the moisture values of the methanol-sample mixed solution obtained in the sample container by using a Karl Fischer micro moisture tester, and correspondingly marking as A, B and C; if B is greater than A, description 1#The water vapor in the gas in the sample container is in a saturated state, and the moisture content of the sample can be calculated according to the step (6). If B is equal to A, description 1#And (3) returning to the step (1) when the water vapor in the gas in the sample container is in an unsaturated state or the moisture content of the sample is lower than the detection limit of the instrument, and re-measuring after increasing the sample amount.
(6) Calculating the mass percentage content W of water in the electrode material sample to be detected according to the following formula (I):
in formula (I):
b-step (1) 1#The water content value of the electrode material sample to be detected in the sample container is g;
c-step (1) 2#The water content value of the electrode material sample to be detected in the sample container is g;
m1-step (1) 1#The weight of the electrode material sample to be detected in the sample container is g;
m2-in step (1) 2#The weight of the electrode material sample to be detected in the sample container is g;
w1-1 determined in step (5)#The mass percentage of the water content of the electrode material sample to be detected in the sample container is percent;
w2-2 determined in step (5)#The mass percentage of water content of the electrode material sample to be detected in the sample container is percent.
Preferably, the sample container is a glass container, and the sealed sample container in step (1) can withstand at least 2 or more standard atmospheric pressures, i.e., at least 1 or more additional standard atmospheric pressures, during the heating in step (2).
More preferably, the step (1) adopts a sealing cover which is covered on the opening of the sample container to realize the sealing of the sample container; the sealing cover comprises a metal cover body, a through hole is formed in the center of the metal cover body, a sealing gasket is arranged at the position, corresponding to the through hole, of the metal cover body, and the sealing gasket has the same size as the opening of the sample container; the sealing gasket is made of a composite material of silicon rubber and polytetrafluoroethylene.
Preferably, in the step (2), judgment 1 is made#、2#The way that the moisture in the electrode material sample to be measured in the sample container is fully evaporated is as follows: firstly, weighing a proper amount of sample, drying the sample according to GB/T6284-; then, calculating the amount n of the substance containing moisture in the sample container, substituting the temperature T1 of the heating source into the Clapper's Ke-Long equation PV (in the formula, P is the air pressure in the closed space; V is the volume occupied by the gas in the closed space; n is the amount of the substance in the gas in the closed space; R is the gas constant; T is the temperature of the gas in the closed space) together with the temperature T1 of the heating source when the sample is heated in the step (2), and calculating the pressure P1 in the sample container after all the moisture in the amount n in the sample container is changed into steam; then obtaining the boiling point T2 of water under the pressure P1 according to the water boiling point comparison table under different air pressures; if the heated temperature T3 of the sample is higher than the boiling point T2 when the sample container is heated at the temperature T1 in the step (2), referring to the heating time specified in GB/T6284-;if the heated temperature T3 of the sample is equal to or lower than the boiling point T2 when the sample container is heated at the temperature T1 of step (2), the temperature T1 is increased until the heated temperature T3 of the sample is higher than the boiling point T2. In addition, the way of judging whether the heated temperature T3 of the sample is higher than the boiling point T2 is: putting the weighed sample into an open container and compacting, and selecting a solid indicator with a melting point slightly larger than T2 to be put above the sample in the open container and compacting; after sealing the open container, placing it on a heating source to heat at the temperature of T1 as described in step (2); if the solid indicator above the sample melts, it indicates that the temperature T1 of the heating source can make the temperature T3 of the whole area of the sample be greater than the boiling point T2 of water. Under the influence of heat conduction and heat radiation, the temperature in the container is far lower than the temperature T1 of the heating source when the sample container is heated, and the Clapperwire equation is calculated according to the temperature T1 of the heating source, so that the weighing capacity, the volume of the sample container and the heating temperature can be fully matched.
Preferably, the karl fischer trace moisture tester is stored in an inert gas glove box with less than 0.1ppm of water and oxygen before use.
Preferably, in step (3), the methanol is HPLC grade, and the mass fraction of the contained water is less than 0.02%.
Preferably, in the step (4), the aspirator is a medical syringe.
More preferably, in the step (4), in the process of adding the methanol solvent into the three sample containers, another medical syringe which is fully dried and fully cooled is taken, the needle head is pulled off, the needle head is inserted into the sample container from the position of the sealing gasket which is exposed from the sealing cover, and the sample container is kept communicated with the atmosphere.
Preferably, the D50 particle size of the electrode material sample to be tested is 0.5-30 microns; the electrode material to be detected is lithium cobaltate, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium manganate, graphite, lithium titanate or silicon carbon negative electrode material, soft carbon negative electrode material, hard carbon negative electrode material and the like.
The determination method provided by the invention is simple in implementation mode and easy to operate; the method has good repeatability and high accuracy of the measured result; the method is suitable for most anode and cathode materials and is widely applied.
Detailed Description
In the following examples and experiments, the sample container was an open cylindrical glass bottle having a diameter of 15mm and a volume of 20mL and a height of about 11cm, and the opening was sealed with a sealing cap. The sealing cover comprises an aluminum cover body, a sealing gasket is arranged at the position of the center of the cover body corresponding to the through hole, the sealing gasket is made of a composite material of silicon rubber and polytetrafluoroethylene and has the shape and the size matched with the opening of the sample container. The suction device adopts a medical injector.
Example 1
1) Taking 4 cylindrical glass bottles as sample containers, putting the sample containers into a forced air drying oven, and drying the sample containers for 4 hours at the temperature of 103-110 ℃.
2) And (3) putting 4 sealing covers and 2 medical syringes 20mL into a vacuum drying oven together, heating to 50 ℃ after the pressure in the vacuum drying oven is less than 1000Pa, and drying the sealing covers and the medical syringes for 4 hours.
3) And (3) putting the sample container, the sealing cover and the medical injector dried in the steps 1) and 2) into a dryer for cooling for 20 min.
4) At about 20 ℃ and room temperature, 1 sample container and a sealing cover are taken out of the dryer, 2g of a lithium cobaltate sample (the particle size of D50 is 19 microns) is weighed by an electronic balance and placed into the sample container and vibrated until the surface of the sample is smooth, and 0.2g of diphenyl carbodihydrazide (the melting point is about 170 ℃) is placed above the sample and vibrated. After a sealed cover is used for sealing a sample container, the sample container is placed on a flat-plate type induction cooker and heated at 290 ℃ for a plurality of minutes, diphenylcarbodihydrazide is melted, and the boiling point of water in the sample is smaller than the melting point of diphenylcarbodihydrazide, so that the heating of the sample container with the specification at 290 ℃ can ensure that the whole area of a lithium cobaltate sample below 2g in the sample container is larger than the boiling point of water.
5) At about 20 deg.C, the remaining sample container and sealing cap were removed from the desiccator, and 1g of lithium cobaltate sample (D50 particle size 19 μm) was weighed into 1 by an electronic balance#The sample is placed in a sample container and vibrated until the surface of the sample is flat, and 2g of the same lithium cobaltate is weighedSample introduction 2#The sample container is vibrated to the flat surface of the sample, and the container without the sample is marked as 0#The sealing cap was tightly closed over the 3 sample containers.
6) Vertically placing 3 sample containers above a flat-plate type induction cooker, adjusting the temperature to 290 ℃, and continuously heating the samples for 2 h. And taking the sample container off the induction cooker, and naturally cooling for 30 min.
7) Starting a Karl Fischer micro-moisture tester, taking absolute methanol (HPLC grade, the mass fraction of moisture is less than 0.02%) as a solvent, and carrying out moisture pre-titration according to the instruction of the tester until the drift value is less than 10 mu L/min.
8) Selecting one medical injector dried in the step (2), pulling out the needle head, and inserting the needle head into the position of the exposed sealing gasket at the through hole of the sealing cover to be 0#In the sample container, another medical syringe dried in the step (2) is used for sucking 16mL of methanol solvent in a Karl Fischer titration cup to 0#Injecting 5mL of methanol into the sample container, pulling off the needle head and inserting 1 in sequence#And 2#In a sample container, and to 1#And 2#5mL of methanol was injected into each sample container, and then the needle was pulled out. Each sample container was shaken well to dissolve the water on the container wall well in methanol.
9) Rapidly opening bottle caps of 3 sample containers in sequence to obtain a total of 0#Methanol solvent in sample container and 1#、2#The methanol-sample mixed solutions obtained in the sample containers were each poured into a karl fischer micro moisture tester to measure the moisture value. Experiments show that 1#The value of water content B in the sample container is greater than 0#The value of moisture in the sample vessel is A, so the sample moisture content (mass fraction) is calculated according to formula (I).
The above steps 1) to 9) were repeated three times except that the steps (1) and (2) were performed with only 3 sample containers and 3 sample caps, respectively, and the step (4) was omitted, and the measurement results are shown in Table 1. Because the number of samples is less than 8, the standard deviation is calculated by adopting a pole difference method and then divided by the measurement average value to obtain the relative standard deviation. And the standard deviation S is equal to R/C, wherein R is range, and C is range coefficient. The pole difference coefficient was 1.69 when the number of samples was 3.
TABLE 1
As can be seen from Table 1, 1 was measured#The average value of the water content of the samples in the sample container is 0.36mg, 2#The average moisture content of the samples in the sample containers was 0.56mg with a relative standard deviation of 0.0%.
10) The moisture content (mass fraction) W in the lithium cobaltate sample was calculated according to formula (i) to be 0.02%.
Example 2
The measurement was carried out by the method of example 1, except that in the step (4), a 1.0g sample of lithium iron phosphate (D50 particle size of 0.5 μm) was weighed into a sample container. In the step (5), 0.5g of lithium iron phosphate sample (D50 with the granularity of 0.5 micron) is weighed and put into 1#A sample container, weighing 1.0g of lithium iron phosphate sample and placing 2#A sample container.
The results of the measurement in step (9) are shown in Table 2.
TABLE 2
As can be seen from Table 2, 1 was measured#The average value of the water content of the sample in the sample container is 1.73mg, the average value of the water content of the sample in the No. 2 sample container is 3.16mg, and the relative standard deviation is less than 6.7%;
and 10), calculating according to a formula (I) to obtain that the water content (mass fraction) W in the lithium iron phosphate sample is 0.285%.
Example 3
The measurement was carried out by the method of example 1 except that 1.0g of a graphite sample (D50 particle size 13 μm) was weighed in the sample container in the step (4). In the step (5), 0.5g of a graphite sample (D50 having a particle size of 13 μm) was weighed into 1#Sample container, 1.0g graphite sample is weighed and put into 2#A sample container.
The results of the measurement in step (9) are shown in Table 3.
TABLE 3
As can be seen from Table 3, 1 was measured#The average water content of the sample in the sample container was 0.11mg, 2#The average value of the water content of the sample in the sample container is 0.2mg, and the relative standard deviation is less than 12.5%;
and 10), calculating according to a formula (I) to obtain that the water content (mass fraction) W in the graphite sample is 0.019%.
Accuracy verification test
In order to show the accuracy of the measurement result of the method, the method adopts the standard recovery rate for verification.
1) Taking 2 cylindrical glass bottles as sample containers, putting the sample containers into a forced air drying oven, and drying the sample containers for 4 hours at the temperature of 103-110 ℃.
2) And (3) putting 2 sealing covers and 2 medical syringes 20mL into a vacuum drying oven together, heating to 50 ℃ after the pressure in the vacuum drying oven is less than 1000Pa, and drying the sealing covers and the medical syringes for 4 hours.
3) And (3) putting the sample container, the sealing cover and the medical injector dried in the steps 1) and 2) into a dryer for cooling for 20 min.
4) Weighing 1.0g of lithium cobaltate sample, placing into the sample container in the step (3) and sealing with a sealing cover, and marking as 1#. Weighing the same weight of sample, placing into the sample container in step (3), transferring about 10.0 μ L of pure water with Agilent microsyringe (measuring range 10 μ L, precision 0.2 μ L), dropping about 5.0 μ L into the sample, sealing with sealing cap, and marking as 2#. Accurately calculating the dropping rate by a one-ten-thousandth precision balance through a decrement method#Mass of pure water in the sample container.
5) It was calculated that 5.0. mu.L of pure water changed to water vapor and the volume of the sample container became about 6.2mL, and the gas pressure in the sample container became about 1.31 standard atmospheres (since the moisture content in each sample was less than 0.3mg, the influence of the moisture in the sample changed to vapor on the gas pressure in the sample container was ignored). Assuming that the temperature of the sample bottle at the equilibrium is 290 ℃ of the heating temperature of the induction cooker, the gas pressure in the sample container under the condition is calculated to be about 2.7 standard atmospheric pressures, the boiling point of water in the sample container is less than 133 ℃ (the boiling point of water at 3 standard atmospheric pressures), and the heating temperature of each sample is more than 170 ℃ (the temperature is more than the melting point of diphenylcarbonyldihydrazide). The sample container is heated for 2 to 4 hours at 290 ℃, and the water in the sample in the container can be fully evaporated.
6) And (3) compacting the samples in the sample container No. 1 and the sample container No. 2, vertically placing the samples above a flat plate type induction cooker, adjusting the temperature to 290 ℃, and continuously heating the samples for 2 h. And taking the sample container off the induction cooker, and naturally cooling for 30 min.
7) Starting a Karl Fischer micro-moisture tester, taking absolute methanol (HPLC grade, the mass fraction of moisture is less than 0.02%) as a solvent, and carrying out moisture pre-titration according to the instruction of the tester until the drift value is less than 10 mu L/min.
8) Selecting one medical injector dried in the step (2), pulling out the needle head, and inserting the needle head into the position of the exposed sealing gasket of the sealing cover 1#In the sample container, another medical syringe dried in the step (2) is used for sucking 12mL of methanol solvent in a Karl Fischer titration cup, and the methanol solvent is firstly added into the sample container 1#5mL of methanol was injected into the sample container, and the needle was removed and inserted 2#In a sample container, and 2#The sample container was injected with 5mL of methanol, followed by pulling off the needle. Each sample container was shaken well to dissolve the water on the container wall well in methanol.
9) Sequentially and rapidly opened 1#、2#And (4) a sample container bottle cap, pouring the methanol-sample mixed solution in each sample container into a Karl Fischer micro moisture tester respectively, and measuring the moisture value. The water content of the sample is calculated according to the formula (I).
10) Then 1.0g of graphite and 0.1g of lithium iron phosphate were weighed, and the steps 1) to 9) were repeated to obtain table 4.
TABLE 4 results of the recovery test with addition of standard
As can be seen from Table 4, the recovery rate of the spiked sample of the method of the present invention is between 90% and 100%, and the method has high accuracy.
The present embodiment is only for explaining the present invention, and it is not limited to the present invention, and those skilled in the art can make modifications of the present embodiment without inventive contribution as needed after reading the present specification, but all of them are protected by patent law within the scope of the claims of the present invention.
Claims (10)
1. A method for measuring the content of trace moisture in an electrode material for a lithium ion battery is characterized by comprising the following steps of:
(1) taking 3 identical fully dried and fully cooled open sample containers, respectively recording as 0#、1#、2#A sample container; at room temperature, weighing a powdery electrode material sample to be measured and putting the electrode material sample into the container 1#The sample container is vibrated to the state that the surface of the sample is flat, and then the electrode material sample to be measured with double weight is weighed and put into the container 2#In a sample container and tapping until the sample surface is flat, 0#The sample container is used as a blank for holding no sample and is sealed 0#、1#、2#The opening of the sample container; wherein, put in 2#Weighing and 2 of electrode material sample to be measured in sample container#The volume relation of the sample container is as follows: the sample is weighed to ensure that in the subsequent step (2), the 2 is heated at a temperature of T1#When a sample container is used, 2#The heating temperature T3 of all samples in the sample container is more than 2#The boiling point of water at a pressure of P1 in the sample container is T2, wherein P1 is 2 at T1#After all the water in the sample container is changed into steam, and the internal temperature is increased to the pressure in the container after dynamic balance;
(2) heating the 3 sealed 0 s in step (1) at a temperature T1#、1#、2#The sample container is 2 to 4 hours till 1#、2#Fully evaporating the moisture in the electrode material sample to be measured in the sample container, and naturally cooling to room temperature;
(3) starting a Karl Fischer micro-moisture tester, taking absolute methanol as a solvent, and carrying out moisture pre-titration according to an instrument instruction until the drift value is less than 10 mu L/min to obtain a methanol solvent with pre-titrated moisture;
(4) taking a fully dried and fully cooled extractor, absorbing the methanol solvent obtained in the step (3) and adding the methanol solvent into the cooled 0 in the step (2) in equal quantity#、1#、2#In the sample container, still sealing the sample container, and fully shaking each sample container to fully dissolve the condensed water attached to the wall of the sample container in the methanol solvent; wherein the relation between the absorption volume of the methanol solvent and the volume of the sample container is 1: 4-1: 2;
(5) for 0 in step (4)#Methanol solvent in sample container and 1#、2#Respectively measuring the moisture values of the methanol-sample mixed solution obtained in the sample container by using a Karl Fischer micro moisture tester, and correspondingly marking as A, B and C; if B is greater than A, description 1#The water vapor in the gas in the sample container is in a saturated state, and the moisture content of the sample can be calculated according to the step (6); if B is equal to A, description 1#Returning to the step (1) when the water vapor in the gas in the sample container is in an unsaturated state or the moisture content of the sample is lower than the detection limit of the instrument, and re-measuring after increasing the sample amount;
(6) calculating the mass percentage content W of water in the electrode material sample to be detected according to the following formula (I):
in formula (I):
b-step (1) 1#The water content value of the electrode material sample to be detected in the sample container is g;
c-step (1) 2#The water content value of the electrode material sample to be detected in the sample container is g;
m1-step (1) 1#The weight of the electrode material sample to be detected in the sample container is g;
m2-in step (1) 2#The weight of the electrode material sample to be detected in the sample container is g;
w1-1 determined in step (5)#The mass percentage of the water content of the electrode material sample to be detected in the sample container is percent;
w2-2 determined in step (5)#The mass percentage of water content of the electrode material sample to be detected in the sample container is percent.
2. The assay method of claim 1, wherein the sample vessel is a glass vessel, and the sealed sample vessel of step (1) can withstand a pressure of at least 2 standard atmospheres during the heating of step (2).
3. The assay method according to claim 2, wherein the sealing of the sample vessel in step (1) is effected by a sealing cap covering the opening of the sample vessel; the sealing cover comprises a metal cover body, a through hole is formed in the center of the metal cover body, a sealing gasket is arranged at the position, corresponding to the through hole, of the metal cover body, and the sealing gasket has the same size as the opening of the sample container; the sealing gasket is made of a composite material of silicon rubber and polytetrafluoroethylene.
4. The method according to claim 1, wherein in the step (2), the moisture in the sample of the electrode material to be measured in the sample container # 1 or # 2 is judged to be sufficiently evaporated in such a manner that: firstly, weighing a proper amount of sample, drying the sample according to GB/T6284-; subsequently, the amount n of the substance containing moisture in the sample container is calculated, and the krabbe long equation PV ═ nRT is substituted together with the temperature T1 of the heating source when the sample is heated in step (2), and after all of the moisture in the sample container in which the amount n of the substance in the sample container is calculated to be vapor, the pressure P1 in the sample container is calculated, wherein: p is the air pressure in the closed space; v is the volume occupied by the gas in the closed space; n is the amount of the gaseous substance in the enclosed space; r is a gas constant; t is the temperature of the gas in the closed space; obtaining the boiling point T2 of water under the pressure of P1 according to a boiling point comparison table of water under different air pressures, and if the heated temperature T3 of the sample is higher than the boiling point T2 when the sample container is heated at the temperature T1 in the step (2), referring to the heating time specified in GB/T6284-; if the heated temperature T3 of the sample is equal to or lower than the boiling point T2 when the sample container is heated at the temperature T1 of step (2), the temperature T1 is increased until the heated temperature T3 of the sample is higher than the boiling point T2.
5. The method according to claim 4, wherein the sample is judged to have a heat receiving temperature T3 higher than the boiling point T2 in the following manner: putting the weighed sample into an open container and compacting, selecting a solid indicator with a melting point slightly larger than the boiling point T2 of water, putting the solid indicator above the sample and compacting; after the open container is sealed, it is heated by placing it on a heating source at the temperature T1 in step (2), and if the solid indicator above the sample melts, the heating temperature T1 indicates that the temperature T3 of all samples is greater than the boiling point T2 of water.
6. The method according to claim 1, wherein in the step (3), the Karl Fischer micro moisture tester is stored in an inert gas glove box containing water and oxygen in an amount of less than 0.1ppm before use.
7. The method according to claim 1, wherein in the step (3), the methanol is HPLC grade and contains water at a mass fraction of less than 0.02%.
8. The method according to claim 1, wherein in the step (4), the aspirator is a medical syringe.
9. The assay of claim 8 wherein in step (4) the sample container is maintained in communication with the atmosphere by removing the needle from a substantially dry, substantially cooled medical syringe and inserting the needle into the sample container from the position of the exposed sealing gasket of the sealing cap.
10. The assay method of claim 1, wherein the sample of electrode material to be tested has a D50 particle size of 0.5-30 microns; the electrode material to be detected is lithium cobaltate, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganate, lithium nickel cobalt aluminate, lithium titanate, graphite, a silicon carbon negative electrode material, a soft carbon negative electrode material or a hard carbon negative electrode material.
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