RU2585170C1 - Method for production of electrolyte for primary lithium cells - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to electrical engineering and can be used in production of primary lithium power cells. Method for production of electrolyte for primary lithium current sources is performed by mixing lithium perchlorate, dimethoxyethane and propylene carbonate. Preliminarily one prepares concentrated solution of lithium perchlorate in propylene carbonate with low water content in following ratio, wt%: lithium perchlorate is 17-21; propylene carbonate is 79-83, then one mixes concentrated solution dimethoxyethane and propylene carbonate under pressure of 20-60 kPa (0.2-0.6 kgf/cm²) for 2-5 minutes with following ratio, wt%: concentrated solution is 27-38; dimethoxyethane is 10-19; propylene carbonate is 52-54.

EFFECT: reduced growth of current source inner pressure, normalisation of solubility of lithium electrode and, consequently, longer service life of current source.

1 cl, 3 tbl

Description

The invention relates to the electrical industry and can be used in the production of primary lithium chemical current sources.

Known electrolyte for a chemical current source of the manganese dioxide-lithium system (patent for utility model RU 90263, IPC H01M 6/16), including tetrahydrofuran or dioxolane as a functional additive to increase the electrolyte conductivity during operation in the range of low temperatures from -10 to - 40 ° C. The method includes mixing the components in the following ratio, wt.%: Lithium perchlorate - 5 ÷ 8.5; dimethoxyethane - 18 ÷ 45; tetrahydrofuran or dioxolane - 15 ÷ 42; propylene carbonate - the rest.

However, the disadvantages of this method are, firstly, the addition of tetrahydrofuran helps to improve the operation of the current source only at low temperatures and vice versa reduces its electrical characteristics when operating under normal conditions, and secondly, the low content of inorganic salt will lead to unstable operation of the current source due to reducing the electrolyte conductivity, thirdly, the high content of dimethoxyethane in the electrolyte will increase the cost of current sources and batteries based on them because of its high value as well as a reduction of electrical characteristics of the current source due to lower solubility of the lithium electrode.

Known electrolyte for lithium manganese dioxide chemical current source (USSR patent for the invention No. 1667177, IPC-5 H01M 6/16) containing a solution of a lithium salt, for example lithium perchlorate, in an aprotic dipolar solvent, for example propylene carbonate, with residual water, while In order to increase the energy intensity of the current source, the electrolyte contains the indicated ingredients in the following amounts, wt.%: lithium perchlorate - 8.4-8.6; water - 0.02-0.08; propylene carbonate - the rest.

The disadvantages of this method are, firstly, in the prepared electrolyte there is a rather high water content, which entails a decrease in the utilization rate of the lithium electrode (% utilization of lithium from its actual laying in the electrode) and its passivation, and, as a result, the instability of the electrochemical system , a voltage drop during operation of a lithium current source, as well as a decrease in charge persistence over a long period of time, secondly, the absence of dimethoxyethane in the electrolyte leads to A rupture of exchange processes between the cathode and anode, which adversely affects the service life of lithium current sources.

Closest to the claimed solution is a method for producing a non-aqueous electrolyte for a chemical current source (copyright certificate for invention SU 1828344, IPC H01M 6/14, H01M 6/16), including mixing the components in the following ratio, wt.%: Lithium perchlorate - 5, 1-8.0; propylene carbonate - 43.0-48.0; condensed polycyclic aromatic hydrocarbon - 0.05-0.4; macrocyclic polyester - 0.02-0.6; dimethoxyethane - the rest.

The disadvantages of the prototype are, firstly, in the manufacture of the electrolyte, certain macrocyclic polyesters and condensed polycyclic aromatic hydrocarbons are used, which leads to dependence on a particular manufacturer and an increase in the cost of electrolyte, and secondly, a complex manufacturing technology, since the total number of components of the final electrolyte is more than three, which leads to an increase in labor costs and, accordingly, to an increase in the final cost of primary lithium sources in the current and batteries based on them, thirdly, the amount of dimethoxyethane should be determined, since with a high or low content of it in the electrolyte, the electrical characteristics or the life of the current sources decreases due to a decrease or increase in the solubility of the lithium electrode, respectively.

The objective of the present invention is to develop a cost-effective and safe method for producing electrolyte, which will subsequently be used for the manufacture of primary lithium current sources with low self-discharge.

The technical result is:

firstly, in the use, in the preparation of the electrolyte, of a concentrated solution of lithium perchloride in propylene carbonate with a reduced water content, which subsequently leads to the absence of an increase in internal pressure in current sources,

secondly, the introduction of the required amount of dimethoxyethane into the electrolyte, which allows to normalize the solubility of the lithium electrode and thereby increase the life of the current source to 25 years.

The electrolyte is one of the most important components of primary lithium current sources. The main requirement for organic electrolytes (or inorganic salt solutions in an organic solvent) is their chemical and electrochemical stability, which should exclude the interaction of electrolytes or impurities in them with electrode materials and the separation of the current source housing, as well as the decomposition of solutions during storage and operation. The presence of impurities in organic electrolytes can cause an increase in the solubility of the cathode masses, a decrease in the corrosion resistance of the lithium electrode, and a decrease in the range of potentials of electrochemical stability of electrolytes. The consequence of these processes is self-discharge, a decrease in discharge voltage, and instability of the discharge characteristics. Accumulation of gaseous and volatile decomposition products of electrolytes during storage and operation can cause depressurization of current sources. Currently, propylene carbonate electrolytes are most widely used for the manufacture of primary lithium current sources and, for this reason, are of great interest for study and modernization.

SUMMARY OF THE INVENTION

The specified technical result is achieved by the fact that in the method for producing an electrolyte for lithium chemical power sources, including mixing lithium perchlorate, dimethoxyethane and propylene carbonate, according to the claimed solution, a concentrated solution of lithium perchlorate in propylene carbonate with a reduced water content is preliminarily prepared in the following ratio, wt.%:

lithium perchlorate - 17-21

propylene carbonate - 79-83,

then a concentrated solution of dimethoxyethane and propylene carbonate are mixed under pressure of 20-60 kPa for 2-5 minutes in the following ratio, wt.%:

concentrated solution - 27-38

dimethoxyethane - 10-19

propylene carbonate - 52-54.

Method description

All electrolyte components are prepared for dosing and stored in storage tanks made of stainless steel 12X18H10T or titanium alloy VT 1-00. During storage in storage tanks, argon pressure of 20-60 kPa (0.2-0.6 kgf / cm ² ) is maintained with a permissible pressure measurement error of ± 0.07 kgf / cm ² .

First, a concentrated solution of lithium perchloride in propylene carbonate is prepared in the following ratio, wt.%:

lithium perchlorate - 17-21

propylene carbonate - 79-83.

The amount of impurities in the concentrate does not exceed 1 wt.%, Including water - not more than 0.025 wt.%.

After that, the preparation of a batch of electrolyte begins. A batch is an electrolyte prepared in one container. The electrolyte is prepared in a 12X18H10T stainless steel container. During the preparation of the electrolyte in the room it is not allowed to prepare the concentrate.

Calculate the mass of the concentrated solution necessary for the preparation of the electrolyte, based on the content of lithium perchlorate in the concentrated solution taken to prepare this batch of electrolyte. The calculated amount of concentrated solution is pushed with argon into the container (approximately 15-18 kg with a weighing error of ± 100 g), controlling its weight by the dial of the balance. Then dimethoxyethane (approximately 7-9 kg with a weighing accuracy of ± 100 g) is pushed into a container with a concentrated solution of argon, controlling its weight according to the dial of the balance. Then, the mass of propylene carbonate necessary for the preparation of the electrolyte is calculated, after which the calculated amount of propylene carbonate is pressed with argon into a container (approximately 25-28 kg with a weighing accuracy of ± 100 g), controlling its weight according to the dial of the balance.

The final mixture contains, wt.%:

concentrated solution - 27-38

dimethoxyethane - 10-19

propylene carbonate - 52-54.

Next, the container with the final mixture is filled with argon to a pressure of 20-60 kPa (0.2-0.6 kgf / cm ² ). Permissible error of pressure measurement ± 0.07 kgf / cm ² . Then, the electrolyte is mixed in the container using a stirrer or manually. The duration of the mixing process is 2-5 minutes.

According to the claimed method, specific electrolyte compositions were made. Optimal is an electrolyte corresponding to the following indicators:

appearance - a colorless or light yellow liquid that does not contain mechanical impurities;

mass fraction of water - not more than 0.02%;

mass fraction of lithium perchloride (PCL) - 6.0 ± 0.5%;

mass fraction of propylene carbonate (PC) - 78 ± 3%;

mass fraction of dimethoxyethane (DME) - 16 ± 3%;

mass fraction of the sum of methanol, propylene glycol and dipropylene glycol - not more than 0.15%;

mass fraction of the sum of other organic impurities - not more than 0.15%;

mass fraction of potassium - not more than 0.001%;

mass fraction of sodium - not more than 0.01%;

mass fraction of calcium - not more than 0.001%;

mass fraction of iron - not more than 0,0005%;

mass fraction of nickel - not more than 0,0005%.

Analysis of the electrolyte for the content of the main components is performed for each batch prepared.

Examples of the results of the implementation of the proposed method for the content of PCL 6.0 ± 0.5% are shown in table 1.

Table 1

Examples of the results of the implementation of the proposed method for the content of the PC 78 ± 3% are shown in table 2.

table 2

Examples of the results of the implementation of the proposed method for the content of DME 16 ± 3% are shown in table 3.

Table 3

When the mass fraction of lithium perchloride is less than 5.5%, there is insufficient electroconductivity of the electrolyte, which leads to unstable operation of the primary current source and a decrease in its electrical characteristics. When the mass fraction of lithium perchlorate is more than 6.5%, cost overruns and wasteful use of expensive materials occur and, as a result, the economic efficiency of the proposed method is reduced.

The mass fraction of propylene carbonate, equal to 75-81%, is optimal for the electrolyte preparation process and ensures the rational use of expensive materials in the preparation, and also reduces the risk of manufacturing primary current sources with unstable electrical characteristics.

When the mass fraction of dimethoxyethane is less than 13%, there is an increase in the exchange processes between the cathode and the anode, which negatively affects the life of lithium current sources, and when the mass fraction of dimethoxyethane is more than 19%, the cost of current sources and batteries based on them increase due to its high cost and, as a consequence, a further decrease in the electrical characteristics of the current source due to a decrease in the solubility of the lithium electrode.

The advantages of the method are to improve the quality of the prepared electrolyte, as well as the production of an electrolyte for lithium current sources with a low water content and the required amount of dimethoxyethane, which will increase the persistence of the current source up to 25 years in the absence of an increase in internal pressure.

The use of this invention in industry can improve the quality of the prepared electrolyte, which entails the manufacture of primary lithium current sources and batteries based on them with improved characteristics.

Claims (1)

A method of producing an electrolyte for lithium chemical power sources, comprising mixing lithium perchlorate, dimethoxyethane and propylene carbonate, characterized in that a concentrated solution of lithium perchlorate in propylene carbonate with a reduced water content is preliminarily prepared in the following ratio, wt.%:
lithium perchlorate - 17-21
propylene carbonate - 79-83,
then a concentrated solution of dimethoxyethane and propylene carbonate are mixed under a pressure of 20-60 kPa (0.2-0.6 kgf / cm ² ) for 2-5 minutes in the following ratio, wt.%:
concentrated solution - 27-38
dimethoxyethane - 10-19
propylene carbonate - 52-54.