JP2007227310A - Lithium secondary battery and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reliable lithium ion secondary battery suppressed in risk of smoke generation or the like resulted from thermal runaway (excessive rise of temperature), and a method for manufacturing the same. <P>SOLUTION: This lithium ion secondary battery comprises a first bound water 161 located within a case and desorbing at a temperature higher than the highest temperature of a general using temperature range of the lithium ion secondary battery and lower than the decomposition temperature of a positive electrode active material 153, which generates first derived gas derived from the first bound water 161. The content of the first bound water 161 is set to an amount such that the internal pressure of the case reaches a valve opening pressure P by the first bound water 161 and another gas within the case before the temperature of the lithium ion secondary battery exceeds the highest temperature of the general using temperature range and reaches the decomposition temperature of the positive electrode active material 153. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a lithium ion secondary battery and a method for manufacturing the same.

  Lithium ion secondary batteries are attracting attention as power sources for portable devices and portable devices, and as power sources for electric vehicles and hybrid vehicles. However, in a lithium ion secondary battery, if the battery temperature rises excessively due to some abnormality, there is a risk that the battery temperature rapidly rises and a thermal runaway that reaches an excessively high temperature (for example, 200 ° C. or higher) occurs, resulting in smoke generation. . In addition, when the battery voltage rises too much due to overcharging, there is a risk of smoking due to thermal runaway. In recent years, various lithium ion secondary batteries and manufacturing methods thereof have been proposed to solve such problems (see, for example, Patent Document 1).

JP-A-9-306510

  Patent Document 1 proposes a lithium ion secondary battery in which a pressure-sensitive current interrupting mechanism that operates in response to an increase in internal pressure is provided and carbonate is disposed inside a battery can (case). The pressure-sensitive current interruption mechanism is constituted by the pressure-sensitive plate 20, and when charging, when the battery internal pressure rises due to overcharging, the pressure-sensitive plate 20 is deformed by the internal pressure, thereby interrupting the conduction path to the inside of the battery, This is a mechanism for preventing subsequent charging. In Patent Document 1, since the carbonate is further arranged inside the battery can (case), when the battery voltage rises due to overcharge, the carbonate is decomposed, so that the inside of the battery can (case). Gas can be generated. It is described that the internal pressure of the battery can be quickly raised by this gas, the pressure sensitive plate 20 can be quickly deformed, and the conduction path to the inside of the battery can be interrupted. Thus, it is described that smoke generation of the lithium ion secondary battery can be prevented.

  However, in the case of a lithium ion secondary battery, there is a risk of causing smoke or the like due to thermal runaway if the battery temperature rises abnormally for any reason, not only during charging. On the other hand, the lithium ion secondary battery proposed in Patent Document 1 is a gas generated by decomposition of carbonate during overcharge, and increases the internal pressure of the battery. For this reason, when the battery temperature rises abnormally due to a cause other than overcharge, the decomposition reaction of carbonate does not proceed sufficiently, and the internal pressure of the battery cannot be increased rapidly. Therefore, the technique of disposing carbonate in the battery can (case) has not been able to sufficiently prevent smoke and the like due to thermal runaway.

  The present invention has been made in view of the present situation, and provides a highly reliable lithium ion secondary battery in which the risk of fuming due to thermal runaway (overheating) is suppressed, and a method for manufacturing the same. The purpose is to provide.

  The solution includes a positive electrode plate including a positive electrode mixture containing a positive electrode active material, a negative electrode plate, and an electrode body having a separator, a case for housing the electrode body, and a safety valve for sealing the case, A lithium ion secondary battery comprising: a safety valve that opens a seal of the case and discharges gas in the case when a differential pressure between the internal pressure and the external pressure of the case reaches a predetermined valve opening pressure. The first bound water desorbed in a temperature range higher than the maximum temperature of the normal use temperature range of the lithium ion secondary battery and lower than the decomposition temperature of the positive electrode active material, Including the first combined water that generates the first derived gas derived from the first combined water, and the content of the first combined water is determined so that the temperature of the lithium ion secondary battery is the highest in the normal use temperature range. After the temperature is exceeded and Before reaching the decomposition temperature of the positive electrode active material, the lithium ion secondary gas is formed such that the differential pressure between the internal pressure and the external pressure of the case reaches the valve opening pressure by the first derived gas and the other gas in the case. Next battery.

  In a lithium ion secondary battery, when the temperature rises to the decomposition temperature of the positive electrode active material, the battery temperature rapidly rises due to the decomposition reaction of the positive electrode active material, resulting in thermal runaway that leads to overheating (eg, 200 ° C. or higher). There is a risk of smoke generation.

  In contrast, the lithium ion secondary battery of the present invention is located in the case and is desorbed at a temperature lower than the decomposition temperature of the positive electrode active material. The 1st combined water which generate | occur | produces the 1st origin gas originating from is included. Then, the content of the first bound water is determined so that the first derived gas in the case before the temperature of the lithium ion secondary battery exceeds the maximum temperature in the normal use temperature range and reaches the decomposition temperature of the positive electrode active material. In addition, the internal pressure of the case is increased by other gas, and the differential pressure between the internal pressure of the case and the external air pressure (the differential pressure obtained by subtracting the external air pressure from the internal pressure of the case) reaches the valve opening pressure.

  Therefore, even if the temperature of the lithium ion secondary battery rises beyond the normal operating temperature range, the differential pressure between the internal pressure of the case and the external pressure is opened before it rises to the decomposition temperature of the positive electrode active material. The pressure can be increased until the pressure is reached, and the sealing of the case by the safety valve can be opened. Thereby, thermal runaway can be prevented and the battery temperature can be quickly lowered. Therefore, the lithium ion secondary battery of the present invention is a highly reliable lithium ion secondary battery in which the risk of smoke generation due to thermal runaway (overheating) is suppressed.

The decomposition temperature of the positive electrode active material varies depending on the type of the positive electrode active material, but for example, it is about 170 ° C. for a LiNiO ₂ -based positive electrode active material. Here, examples of the LiNiO ₂ positive electrode active material include LiNiO ₂ , LiNi _0.81 Co _0.16 Al _0.03 O _{2 in} which a part of Ni is substituted with Co and Al, and the like. In addition, a material in which a part of Ni is substituted with at least one metal element selected from Mg, Ti, Cr, Mn, Fe, Cu, Zn, Ga, and Nb can be exemplified.

Further, the decomposition temperature of the LiCoO ₂ positive electrode active material is about 200 ° C. Here, as the LiCoO ₂ -based positive electrode active material, in addition to LiCoO ₂ , a material having a composition in which the molar ratio of Li to Co (number of moles of Li / number of moles of Co) is greater than 1 may be exemplified. it can. Moreover, in the LiMn ₂ O ₄ positive electrode active material, the decomposition temperature is about 280 ° C.

By the way, in a lithium ion secondary battery, a transition metal oxide containing Li is used as a positive electrode active material, a material (carbon or the like) capable of inserting / extracting lithium ions is used as a negative electrode active material, and LiPF ₆ or the like is used as an electrolyte. A lithium salt is used, and an organic solvent such as ethylene carbonate is used as a solvent. All of these materials are highly reactive with water, so when water is present in the battery, for example, in the negative electrode, lithium is consumed by the reaction of lithium and water, and the battery such as battery capacity is consumed. There is a possibility that the characteristics are significantly deteriorated.

  On the other hand, in the lithium ion secondary battery of the present invention, the desorption temperature of the first bound water is higher than the highest temperature in the normal use temperature range of the battery. For this reason, normally, 1st combined water does not detach | desorb in the environment where a lithium ion secondary battery is used. Therefore, normally, while using the lithium ion secondary battery, there is no possibility that the battery characteristics are remarkably deteriorated due to the reaction between the positive electrode active material and the first combined water.

In addition, the maximum temperature of the normal use temperature range concerning a lithium ion secondary battery changes with kinds and uses of a battery. For example, in a lithium ion secondary battery having a LiNiO ₂ -based positive electrode active material, the temperature usually rises to about 80 ° C., but the battery temperature rise varies depending on the use environment and the like. For this reason, in the lithium ion secondary battery having a LiNiO ₂ -based positive electrode active material, the desorption temperature of the first bound water is preferably set to 100 ° C. or higher.

Moreover, the 1st combined water may be couple | bonded with any members, such as a positive electrode plate (positive electrode active material etc.), if it is in a case.
Examples of the “first derived gas” derived from the first combined water include, for example, water vapor that is vaporized by the first combined water itself, CO ₂ that is generated by the reaction between the electrolytic solution and the first combined water, and the like. be able to.

Another solution is a positive electrode plate including a positive electrode mixture containing a positive electrode active material, an electrode body having a negative electrode plate and a separator, a case housing the electrode body, and a safety valve for sealing the case, When the differential pressure between the internal pressure and the external air pressure of the case reaches a predetermined valve opening pressure, the lithium ion secondary battery includes a safety valve that opens the case and discharges the gas in the case. The case includes first bound water that desorbs in a temperature range higher than a maximum temperature in a normal use temperature range of the lithium ion secondary battery and lower than a decomposition temperature of the positive electrode active material. W> 7.93 × 10 ⁻³ × where V (cm ³ ) is the volume of the inner space, P (MPa) is the valve opening pressure, and W (g) is the content of the first bound water. It is a lithium ion secondary battery that satisfies the relationship of V × P.

In the lithium ion secondary battery of the present invention, the case contains first bound water that desorbs in a temperature range higher than the maximum temperature in the normal use temperature range of the battery and lower than the decomposition temperature of the positive electrode active material. . Moreover, the content W (g) of the first bound water satisfies the relationship of W> 7.93 × 10 ⁻³ × V (volume of the void in the case) × P (valve opening pressure). Yes. By including such an amount of the first combined water in the case, even if the battery temperature rises beyond the normal use temperature range, the first derived gas is not yet increased to the decomposition temperature of the positive electrode active material. Thus, by increasing the internal pressure of the case until the differential pressure from the external air pressure reaches the valve opening pressure P, the case sealing by the safety valve can be opened. Thereby, the battery temperature can be lowered soon without causing thermal runaway. Therefore, the lithium ion secondary battery of the present invention is a highly reliable lithium ion secondary battery in which the risk of smoke generation due to thermal runaway (overheating) is suppressed.

The relational expression of W> 7.93 × 10 ⁻³ × V × P can be derived as follows. The molecular weight of water is 18, and the volume occupied by 1 mol of gas molecules at 1 atm is 22.4 × 10 ³ (cm ³ ). Therefore, when the content of the first bound water is W (g), the volume (cm ³ ) of the gas (for example, water vapor) derived from the desorbed first bound water is 1 atm (0.1013 MPa). , (W / 18) × 22.4 × 10 ³ . Therefore, if the volume of the void in the case is V (cm ³ ) and the partial pressure of the gas (water vapor) derived from the first combined water in the case is P1 (MPa), P1 × V = 0.1013 × (W / 18) × 22.4 × 10 ³ . When this equation is modified, P1 = (W / 18) × 22.4 × 10 ³ × 0.1013 / V. However, if P1 exceeds the valve opening pressure P (MPa), that is, if the relationship of (W / 18) × 22.4 × 10 ³ × 0.1013 / V> P (equation 1) is satisfied, it is sure. In addition, the sealing of the case by the safety valve can be opened. By transforming (Equation 1), a relational expression of W> 7.93 × 10 ⁻³ × V × P can be derived.

  Furthermore, any one of the above lithium ion secondary batteries may be a lithium ion secondary battery including the first binding water bonded to the positive electrode mixture.

  In the lithium ion secondary battery of the present invention, first binding water is bound to a positive electrode mixture (such as a positive electrode active material). Thereby, the 1st combined water couple | bonded with the positive electrode compound material can be appropriately desorbed in the above-mentioned predetermined temperature range, and a 1st origin gas can be generated.

  Another solution is a positive electrode plate including a positive electrode mixture containing a positive electrode active material, an electrode body having a negative electrode plate and a separator, a case housing the electrode body, and a safety valve for sealing the case, When the differential pressure between the internal pressure and the external air pressure of the case reaches a predetermined valve opening pressure, the lithium ion secondary battery includes a safety valve that opens the case and discharges the gas in the case. First binding water that desorbs in a temperature range higher than the maximum temperature in the normal use temperature range of the lithium ion secondary battery and lower than the decomposition temperature of the positive electrode active material is bonded to the positive electrode mixture. In addition, the content of the first combined water in the positive electrode composite material is a lithium ion secondary battery having a weight conversion of 1500 ppm or more.

  In the lithium ion secondary battery of the present invention, the first bound water that binds to the positive electrode mixture and desorbs in a temperature range higher than the maximum temperature in the normal use temperature range of the battery and lower than the decomposition temperature of the positive electrode active material. Contains. Furthermore, the content of the first combined water in the positive electrode mixture is set to 1500 ppm or more in terms of weight. By including the first bound water at such a ratio, even if the battery temperature rises beyond the normal use temperature range, the internal pressure of the case is changed to the external atmospheric pressure before rising to the decomposition temperature of the positive electrode active material. Is increased until the pressure difference reaches the valve opening pressure, and the case sealing by the safety valve can be opened.

  Specifically, before the temperature of the lithium ion secondary battery exceeds the maximum temperature of the normal use temperature range and before reaching the decomposition temperature of the positive electrode active material, the gas derived from the first combined water and other in the case Due to the gas, the differential pressure between the internal pressure and the external air pressure of the case reaches the valve opening pressure, and the case sealing by the safety valve can be opened. Thereby, thermal runaway can be prevented and the battery temperature can be quickly lowered. Therefore, the lithium ion secondary battery of the present invention is a highly reliable lithium ion secondary battery in which the risk of smoke generation due to thermal runaway (overheating) is suppressed.

  Moreover, in the lithium ion secondary battery of the present invention, the desorption temperature of the first bound water is higher than the highest temperature in the normal use temperature range of the battery. For this reason, normally, 1st combined water does not detach | desorb in the environment where a lithium ion secondary battery is used. Therefore, normally, while using the lithium ion secondary battery, there is no possibility that the battery characteristics are remarkably deteriorated due to the reaction between the positive electrode active material and the first combined water.

  Furthermore, the lithium ion secondary battery according to any one of the above, wherein the second binding water desorbed at a temperature within the normal use temperature range is bound to the positive electrode mixture, The content of the second bound water is preferably a lithium ion secondary battery having a weight conversion of less than 2200 ppm.

  In the lithium ion secondary battery of the present invention, the content of the second bound water desorbed at a temperature within the normal use temperature range is suppressed to less than 2200 ppm in terms of weight in the positive electrode mixture. Thereby, normally, while using a lithium ion secondary battery, reaction with a positive electrode active material and water can be suppressed, and the fall of a battery characteristic (increase in the IV resistance value of a battery) can be suppressed.

Furthermore, in any of the above lithium ion secondary batteries, the positive electrode active material is a LiNiO ₂ positive electrode active material, and the first bound water is in a temperature range higher than 100 ° C. and lower than 170 ° C. A lithium ion secondary battery that is water to be detached is preferable.

The lithium ion secondary battery of the present invention has a LiNiO ₂ -based positive electrode active material as the positive electrode active material. Since the decomposition temperature of the LiNiO ₂ -based positive electrode active material is about 170 ° C., when the battery temperature rises to 170 ° C., the battery temperature rapidly rises due to the decomposition reaction of the positive electrode active material and overheats (for example, about 350 ° C. There is a risk of fumes, etc.

  In contrast, in the lithium ion secondary battery of the present invention, the first bound water is desorbed at a temperature lower than 170 ° C. As a result, the first bound water is desorbed at a temperature of less than 170 ° C. in the case, and a gas derived from the desorbed first bound water is generated, so that the temperature of the lithium ion secondary battery becomes the positive electrode active material. Before the temperature rises to the decomposition temperature (about 170 ° C.), the internal pressure of the case can be increased until the differential pressure from the external air pressure reaches the valve opening pressure, thereby opening the case sealed by the safety valve.

  In this way, before the battery temperature rises to the decomposition temperature of the positive electrode active material (about 170 ° C), the case is sealed with a safety valve to prevent thermal runaway and quickly lower the battery temperature. Can be made. Therefore, the lithium ion secondary battery of the present invention is a highly reliable lithium ion secondary battery in which the risk of smoke generation due to thermal runaway (overheating) is suppressed.

  Moreover, in the lithium ion secondary battery of the present invention, the first bound water is desorbed at a temperature higher than 100 ° C. (the boiling point of the first bound water). As a result, since the first bound water does not normally desorb in an environment where the lithium ion secondary battery is used (100 ° C. or lower), the positive electrode active can be performed while the lithium ion secondary battery is being used. There is no possibility that the battery characteristics are remarkably deteriorated due to the reaction between the substance and the first bound water.

  Furthermore, the lithium ion secondary battery according to any one of the above, comprising an electrolytic solution having one or more kinds of organic solvents, the content of the first bound water, the temperature of the lithium ion secondary battery being the above Before rising to the boiling point of at least one of the one or more kinds of organic solvents, the internal pressure and external pressure of the case are reduced by the first derived gas and the other gas derived from the first combined water in the case. A lithium ion secondary battery may be used as an amount by which the differential pressure reaches the valve opening pressure.

  In the lithium ion secondary battery, a flammable organic solvent such as ethylene carbonate is used as a solvent for the electrolytic solution. For this reason, when the battery temperature exceeds the boiling point of the organic solvent, the case is filled with a combustible gas, and it is easy to emit smoke.

  On the other hand, in the lithium ion secondary battery of the present invention, the content of the first bound water is set so that the battery temperature reaches the boiling point of the organic solvent (or at least one of the organic solvents when plural kinds of organic solvents are included). Before rising, the differential pressure between the internal pressure and the external pressure of the case reaches the valve opening pressure by the first derived gas and other gases in the case. As a result, before the temperature of the lithium ion secondary battery rises to the boiling point of the organic solvent (or at least one of the organic solvents if multiple types of organic solvents are included), the internal pressure of the case is changed from the external pressure. The pressure can be increased until the valve opening pressure is reached, and the sealing of the case by the safety valve can be opened. For this reason, the risk of smoke generation can be extremely reduced.

  For example, in a lithium ion secondary battery using an electrolytic solution containing three types of organic solvents, ethylene carbonate (boiling point 238 ° C.), dimethyl carbonate (boiling point 90 ° C.), and ethyl methyl carbonate (boiling point 108 ° C.), at least the battery temperature It is advisable to contain a predetermined amount of first bound water so that the safety valve can be opened before reaching the boiling point of ethylene carbonate (238 ° C.). Since at least the ethylene carbonate gas can be prevented from being filled in the case, the risk of smoke generation can be reduced.

Furthermore, it is more preferable to open the safety valve before the battery temperature reaches the boiling point (108 ° C.) of ethyl methyl carbonate. Since it is possible to prevent the ethylene carbonate and ethyl methyl carbonate gases from being filled in the case, the risk of smoke generation can be further reduced.
Furthermore, it is more preferable to open the safety valve before the battery temperature reaches the boiling point (90 ° C.) of dimethyl carbonate. Since it is possible to prevent the ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate gas from being filled in the case, the risk of smoke generation can be further reduced.

  Furthermore, in any of the above lithium ion secondary batteries, the positive electrode mixture is preferably a lithium ion secondary battery whose surface is coated with carbonate.

  In the lithium ion secondary battery of the present invention, the surface of the positive electrode mixture is coated with carbonate. Thus, by covering the surface of the positive electrode mixture (positive electrode active material, conductive carbon, etc.) with carbonate (lithium carbonate, etc.), the contact between the positive electrode mixture and the electrolyte solution is suppressed, and the electrolyte solution is decomposed. The reaction can be suppressed. As a result, it is possible to suppress the formation of a film of the compound produced by the decomposition reaction of the electrolytic solution on the surface of the positive electrode plate, thereby suppressing an increase in the IV resistance value (internal resistance) of the battery and the output characteristics of the battery. Can be suppressed.

In addition, the carbonate covering the surface of the positive electrode mixture is decomposed during overcharge to generate CO ₂ gas. For this reason, when the battery temperature rises due to overcharging, the internal pressure of the case can be quickly raised to open the case sealed by the safety valve at a lower temperature. Therefore, the lithium ion secondary battery of the present invention is a highly reliable lithium ion secondary battery.

  Furthermore, in the above lithium ion secondary battery, the positive electrode plate has a weight of carbonate ions contained in the carbonate of 0.6 wt% to 2.5 wt% based on the weight of the positive electrode mixture. A lithium ion secondary battery containing a certain amount of carbonate is preferable.

  In the lithium ion secondary battery of the present invention, on the basis of the weight of the positive electrode mixture, the surface of the positive electrode mixture is coated with an amount of carbonate in which the weight of carbonate ions contained in the carbonate is 0.6 wt% or more. ing. Thereby, a contact with a positive electrode compound material and electrolyte solution can be suppressed appropriately, and decomposition reaction of electrolyte solution can be controlled.

By the way, as the carbonate covering the positive electrode mixture is increased, the decomposition reaction of the electrolytic solution can be suppressed. However, when the amount of the carbonate covering the positive electrode mixture is excessively increased, the IV resistance value (internal resistance) is increased by the carbonate. There is a possibility that the output characteristics will be greatly increased and the output characteristics will be deteriorated. On the other hand, in the lithium ion secondary battery of the present invention, the amount of carbonate covering the positive electrode mixture is suppressed to an amount such that the carbonate ion is 2.5 wt% or less of the weight of the positive electrode mixture. Thereby, the raise of IV resistance value (internal resistance) by carbonate can be suppressed.
As described above, the lithium ion secondary battery of the present invention is a lithium ion secondary battery with high output and high reliability.

  Another solution is a method for manufacturing a lithium ion secondary battery, which is a method for manufacturing a lithium ion secondary battery including a step of bringing at least a positive electrode active material into contact with water (liquid).

  In the production method of the present invention, the positive electrode active material is brought into contact with water (liquid). Thereby, the 1st combined water desorbed at the temperature higher than the maximum temperature of the normal use temperature range concerning a lithium ion secondary battery and lower than the decomposition temperature of a positive electrode active material can be combined with a positive electrode active material. In the lithium ion secondary battery manufactured using such a positive electrode active material, the first bound water is desorbed at a temperature lower than the decomposition temperature of the positive electrode active material in the case, and is derived from the desorbed first bound water. Gas can be generated.

  For this reason, even if the temperature of the lithium ion secondary battery rises beyond the normal operating temperature range, the pressure difference between the internal pressure of the case and the external air pressure is the valve opening pressure before it rises to the decomposition temperature of the positive electrode active material. It is possible to open the case so that the case is sealed. As a result, thermal runaway can be prevented and the battery temperature can be quickly reduced. Therefore, according to the manufacturing method of the present invention, it is possible to manufacture a highly reliable lithium ion secondary battery in which the risk of fuming due to thermal runaway (overheating) is suppressed.

  The step of bringing at least the positive electrode active material into contact with water (liquid) includes, for example, a step of preparing a first positive electrode paste by mixing at least the positive electrode active material, an aqueous binder resin, and water (liquid). it can. Moreover, the process of immersing a positive electrode active material etc. in water can also be illustrated.

Examples of the positive electrode active material include a LiNiO ₂ -based positive electrode active material and a LiCoO ₂ -based positive electrode active material. Examples of the LiNiO ₂ positive electrode active material include LiNiO ₂ and LiNi _0.81 Co _0.16 Al _0.03 O _{2 in} which a part of Ni is substituted with Co and Al. In addition, a material in which a part of Ni is substituted with at least one metal element selected from Mg, Ti, Cr, Mn, Fe, Cu, Zn, Ga, and Nb can be exemplified. Examples of the LiCoO ₂ positive electrode active material include LiCoO ₂ and materials having a composition in which the molar ratio of Li to Co (the number of moles of Li / the number of moles of Co) is greater than 1. . Also, as the positive electrode active material, it is also possible to use a material based on LiMnO ₂ (positive electrode active material LiMnO ₂ system).

  Further, in the method of manufacturing the lithium ion secondary battery, the lithium ion secondary battery includes a positive electrode paste preparation step of preparing a first positive electrode paste by mixing at least a positive electrode active material, an aqueous binder resin, and water (liquid). A secondary battery manufacturing method is preferable.

In the manufacturing method of the present invention, in the positive electrode paste manufacturing step, at least a positive electrode active material, an aqueous binder resin, and water (liquid) are mixed to prepare a first positive electrode paste. Thus, by mixing the positive electrode active material or the like with water, the first bound water that desorbs at a temperature higher than the maximum temperature in the normal use temperature range of the lithium ion secondary battery and lower than the decomposition temperature of the positive electrode active material. Can be bonded to a positive electrode active material or the like.
In the positive electrode paste manufacturing step, conductive carbon or the like may be mixed in addition to the positive electrode active material, the water-based binder resin, and water.

  Furthermore, in the method of manufacturing the lithium ion secondary battery, an application step of applying the first positive electrode paste to the surface of the positive electrode substrate, and drying the first positive electrode paste applied to the surface of the positive electrode substrate From the time when at least the positive electrode active material is brought into contact with water (liquid) in the positive electrode paste preparation step to the start of drying of the first positive electrode paste in the positive electrode paste drying step. A method for manufacturing a lithium ion secondary battery in which the time is within 8 hours is preferable.

When the positive electrode active material or the like is brought into contact with water (liquid) for a long time, the reaction between the positive electrode active material and water proceeds, and Li desorption proceeds from the positive electrode active material. If a battery is manufactured using such a positive electrode active material, the battery characteristics may be significantly deteriorated.
On the other hand, in the manufacturing method of the present invention, the time from when at least the positive electrode active material is brought into contact with water (liquid) until the drying of the first positive electrode paste is started is within 8 hours. Thereby, reaction with a positive electrode active material and water can be suppressed, and detachment | desorption of Li can be suppressed from a positive electrode active material.

  Furthermore, in the method of manufacturing a lithium ion secondary battery, the first positive electrode paste is dried in the positive electrode paste drying step from the time when at least the positive electrode active material is brought into contact with water in the positive electrode paste preparation step. It is preferable to use a method for manufacturing a lithium ion secondary battery in which the time until the start is 2 hours or longer.

  In the production method of the present invention, the time from when at least the positive electrode active material is brought into contact with water (liquid) until the drying of the first positive electrode paste is started is set to 2 hours or more. In this way, by bringing the positive electrode active material and the like into contact with water (liquid) for 2 hours or more, a necessary and sufficient amount of the first bound water can be bonded to the positive electrode active material and the like.

Furthermore, in any one of the above-described methods for producing a lithium ion secondary battery, after the coating step, the first positive electrode paste is exposed to a gas atmosphere containing CO ₂ , whereby the surface of the first positive electrode paste is applied. After the first positive electrode paste is dried and cured after the positive electrode paste drying step, the first hardened material is exposed to a gas atmosphere containing CO ₂ to form a surface of the first hardened material. It is good to set it as the manufacturing method of a lithium ion secondary battery provided with the carbonate production | generation process which produces | generates carbonate.

In the positive electrode paste manufacturing step, when a positive electrode active material or the like is brought into contact with water, an alkali compound such as a metal hydroxide (LiOH or the like) is generated by a reaction between the positive electrode active material and water. For this reason, an alkali compound (LiOH etc.) will be contained in the 1st positive electrode paste. Accordingly, the first positive electrode paste, by exposure to a gas atmosphere containing CO _2, the alkali compound contained in the first positive electrode paste was reacted (LiOH, etc.) and the CO _2, the carbonate on the surface of the first positive electrode paste Can be generated. The first cured product obtained by drying and curing the first positive electrode paste also contains an alkali compound (LiOH or the like). Therefore, by exposing the first cured product to a gas atmosphere containing CO ₂ , the first cured product is reacted with an alkali compound (such as LiOH) contained in the first cured product and CO _2, and carbonate is formed on the surface of the first cured product. Can be generated.

Moreover, since the first positive electrode paste is a mixture of the positive electrode active material and the like and water, the alkali compound (LiOH and the like) exists over the entire surface of the positive electrode active material and the like. By exposing the first positive electrode paste or the first cured product obtained by drying and curing the first positive electrode paste to a gas atmosphere containing CO ₂ , the surface of the first positive electrode paste or the first cured product (surface of the positive electrode active material or the like) Can be entirely coated with carbonate.

  Therefore, in the lithium ion secondary battery manufactured by the manufacturing method of the present invention, the contact between the positive electrode active material and the electrolyte solution can be suppressed, and the decomposition reaction of the electrolyte solution can be suppressed. As a result, it is possible to suppress the formation of a film of the compound produced by the decomposition reaction of the electrolytic solution on the surface of the positive electrode plate, thereby suppressing an increase in the IV resistance value (internal resistance) of the battery and the output characteristics of the battery. Can be suppressed.

In addition, carbonates decompose during overcharge and produce CO ₂ gas. For this reason, when the battery temperature rises due to overcharging, the internal pressure of the case can be quickly raised to open the case sealed by the safety valve at a lower temperature. Therefore, according to the manufacturing method of the present invention, a lithium ion secondary battery with high output and high reliability can be manufactured.

In the carbonate generation step, when the first cured product is exposed to a gas atmosphere containing CO ₂ , for example, the positive electrode substrate including the first cured product is exposed to a gas atmosphere containing CO ₂ alone. Cases can be mentioned. In addition, the first cured product on the positive electrode base material is exposed to a gas atmosphere containing CO ₂ in a state where the electrode body is formed together with the negative electrode plate and the separator, and further in a state where the electrode body is accommodated in the case. Also good.

  Further, in the method for producing the lithium ion secondary battery, the immersion step of immersing the positive electrode active material in water, mixing at least the positive electrode active material immersed in the water, a solvent-based binder resin, and a solvent, And a positive electrode paste manufacturing step of manufacturing a second positive electrode paste.

In the production method of the present invention, in the positive electrode paste manufacturing step, a solvent-based binder resin (for example, PVDF) is used as the binder resin, and a solvent is used instead of water as the solvent. However, prior to the positive electrode paste preparation step, the positive electrode active material used for the second positive electrode paste is immersed in water in the dipping step. Thereby, since the 1st combined water can be combined with the surface of a positive electrode active material, the 1st combined water can be contained also in the 2nd positive electrode paste using solvent system binder resin.
In the dipping step, conductive carbon or the like may be dipped in water in addition to the positive electrode active material.

  Furthermore, in the method for producing a lithium ion secondary battery described above, a positive electrode active material drying step for drying the positive electrode active material immersed in the water after the immersion step and before the positive electrode paste preparation step is provided. A method for producing a lithium ion secondary battery, wherein a time from when the positive electrode active material is immersed in water in the immersion step to when the positive electrode active material is dried in the positive electrode active material drying step is within 8 hours; Good.

When the positive electrode active material and water are brought into contact with each other for a long time, the reaction between the positive electrode active material and water proceeds, and Li desorption proceeds from the positive electrode active material. If a battery is manufactured using such a positive electrode active material, the battery characteristics may be significantly deteriorated.
On the other hand, in the production method of the present invention, the time from when the positive electrode active material is immersed in water until the start of drying of the positive electrode active material is within 8 hours. Thereby, reaction with a positive electrode active material and water can be suppressed, and detachment | desorption of Li can be suppressed from a positive electrode active material.

  Furthermore, in the method for manufacturing the lithium ion secondary battery, a time from when the positive electrode active material is immersed in water in the immersion step to when the positive electrode active material starts drying in the positive electrode active material drying step Is preferably a method for manufacturing a lithium ion secondary battery having a duration of 2 hours or longer.

  In the production method of the present invention, the time from when the positive electrode active material is immersed in water to the start of drying of the positive electrode active material is 2 hours or more. In this way, by bringing the positive electrode active material and water into contact with each other for 2 hours or more, a necessary and sufficient amount of the first binding water can be bonded to the positive electrode active material.

Further, in any one of the above-described methods for producing a lithium ion secondary battery, after the positive electrode active material drying step, the positive electrode active material is exposed to a gas atmosphere containing CO ₂ to obtain a surface of the positive electrode active material. To generate carbonate on the surface of the substance constituting the second positive electrode paste, or to expose the second positive electrode paste to a gas atmosphere containing CO ₂ , or to form the second positive electrode paste. A method for producing a lithium ion secondary battery comprising a carbonate production step of producing a carbonate on the surface of the second cured product by exposing the second cured product obtained by drying and curing the product to a gas atmosphere containing CO ₂ ; Good.

When the positive electrode active material is immersed in water in the dipping step, an alkali compound, for example, a metal hydroxide (such as LiOH) is generated on the surface of the positive electrode active material by a reaction between the positive electrode active material and water. For this reason, this positive electrode active material, the second positive electrode paste containing it, or the second cured product obtained by drying and curing it also contains an alkali compound (LiOH or the like). Accordingly, by exposing the positive electrode active material, the second positive electrode paste, or the second cured product to a gas atmosphere containing CO ₂ , the alkali compound (LiOH or the like) and CO ₂ are reacted with each other to form a surface of the positive electrode active material. The carbonate can be generated on the surface of the substance constituting the second positive electrode paste or on the surface of the second cured product. Here, the substance constituting the second positive electrode paste refers to a positive electrode active material, a binder resin, or the like.

  Therefore, in the lithium ion secondary battery manufactured by the manufacturing method of the present invention, the contact between the positive electrode active material and the electrolyte solution can be suppressed, and the decomposition reaction of the electrolyte solution can be suppressed. As a result, it is possible to suppress the formation of a film of the compound produced by the decomposition reaction of the electrolytic solution on the surface of the positive electrode plate, thereby suppressing an increase in the IV resistance value (internal resistance) of the battery and the output characteristics of the battery. Can be suppressed.

In addition, carbonates decompose during overcharge and produce CO ₂ gas. For this reason, when the battery temperature rises due to overcharging, the internal pressure of the case can be quickly raised to open the case sealed by the safety valve at a lower temperature. Therefore, according to the manufacturing method of the present invention, a lithium ion secondary battery with high output and high reliability can be manufactured.

Next, embodiments of the present invention will be described with reference to the drawings.
Example 1
First, the lithium ion secondary battery 100 according to the first embodiment will be described. As shown in FIG. 1, the lithium ion secondary battery 100 is a rectangular sealed battery including a rectangular parallelepiped case 110, a safety valve 140, a positive electrode terminal 120, a negative electrode terminal 130, and an electrode body 150.

The case 110 is made of metal, and includes a rectangular housing portion 111 that forms a rectangular parallelepiped housing space, and a metal lid portion 112. An electrode body 150, a positive electrode current collecting member 122, a negative electrode current collecting member 132, an electrolyte solution (not shown), and the like are accommodated in the case 110 (rectangular accommodating portion 111). The positive electrode current collecting member 122 and the negative electrode current collecting member 132 are elongated plate-shaped metal members, and are connected to the positive electrode terminal 120 and the negative electrode terminal 130, respectively. In the lithium ion secondary battery 100 of Example 1, the volume V of the gap G in the case 110 is 22 (cm ³ ).

A through hole 112 b is formed in the lid portion 112. The through hole 112b is sealed from the outside of the case 110 by a disc-shaped metal safety valve 140. Specifically, the safety valve 140 is welded onto the outer surface 112f of the lid portion 112 so as to seal the through hole 112b. In such a lithium ion secondary battery 100, when the pressure difference ΔP (internal pressure−external air pressure) between the internal pressure and the external air pressure of the case 110 exceeds the valve opening pressure P, the safety valve 140 is cleaved so that the case 110 is sealed. Is opened, and the gas in the case 110 can be discharged to the outside.
In the battery 100 of the first embodiment, the valve opening pressure P is set to about 0.4 (MPa).

  The electrode body 150 is an oblong cross section, and is a flat wound body formed by winding a belt-like positive electrode plate 155, a negative electrode plate 156, and a separator 157. The electrode body 150 is positioned at one end portion (right end portion in FIG. 1) in the axial direction (left and right direction in FIG. 1), and a positive electrode winding portion 155b in which only a part of the positive electrode plate 155 overlaps in a spiral shape, It is located at the other end (left end in FIG. 1) and has a negative electrode winding part 156b in which only a part of the negative electrode plate 156 overlaps spirally. A positive electrode mixture containing a positive electrode active material is coated on the positive electrode plate 155 at a portion other than the positive electrode winding portion 155b. Similarly, the negative electrode plate 156 is coated with a negative electrode mixture containing a negative electrode active material at a portion other than the negative electrode winding portion 156b.

Here, the positive electrode plate 155 will be described in detail with reference to FIG. As shown in FIG. 2, the positive electrode plate 155 includes a positive electrode base material 151 made of an aluminum foil, and a positive electrode mixture 152 applied to the surface of the positive electrode base material 151. The positive electrode mixture 152 contains a positive electrode active material 153 (in this embodiment, LiNi _0.81 Co _0.16 Al _0.03 O ₂ ). The surface of the positive electrode active material 153 is covered with a carbonate 158 (Li ₂ CO ₃ or the like). Note that the decomposition temperature of the positive electrode active material 153 is about 170 ° C.

Further, the positive electrode mixture 152 includes a conductive material 159 (carbon in the first embodiment) and a binder resin (not shown) (CMC, PTFE in the first embodiment). These surfaces are also coated with carbonate 158 (such as Li ₂ CO ₃ ).
Further, the positive electrode mixture 152 (the positive electrode active material 153, the conductive material 159, etc.) is desorbed at a temperature of 100 ° C. or less, and first bonded water 161 desorbed in a temperature range higher than 100 ° C. and lower than 170 ° C. The 2nd bond water 162 to separate is couple | bonded. The contents (g) of the first combined water 161 and the second combined water 162 included in the positive electrode mixture 152 will be described in detail later.

In Example 1, as the solvent of the electrolytic solution, three types of organic solvents of ethylene carbonate (boiling point 238 ° C.), dimethyl carbonate (boiling point 90 ° C.), and ethyl methyl carbonate (boiling point 108 ° C.) were used at 30:30: A solvent mixed at a weight ratio of 40 is used. Further, lithium hexafluorophosphate (LiPF ₆ ) is used as a solute.

  By the way, although the temperature of the lithium ion secondary battery 100 usually rises to about 80 ° C., the temperature rise of the battery varies depending on the use environment and the like. For this reason, in the present Example 1 (the same applies to Examples 2 to 10 described later), as described above, the desorption temperature of the first combined water 161 is set higher than 100 ° C. As a result, normally, in an environment where the lithium ion secondary battery 100 is used (100 ° C. or less), the first combined water 161 is not desorbed, and when desorbed, it is desorbed (evaporated) as water vapor. It is considered that the gas is once extracted into the electrolytic solution and reacted with the electrolytic solution or electrolyzed to generate gas. Therefore, normally, while using the lithium ion secondary battery 100, there is no possibility that the battery characteristics are significantly deteriorated due to the reaction between the positive electrode active material 153 and the first combined water 161.

Next, a method for manufacturing the lithium ion secondary battery 100 of the first embodiment will be described with reference to the drawings.
First, in the positive electrode paste manufacturing step, as shown in FIG. 4, a positive electrode active material 153 (LiNi _0.81 Co _0.16 Al _0.03 O ₂ ), a conductive material 159 (carbon), and a binder resin (CMC, PTFE) are purified. The first positive electrode paste 152c is produced by putting them into water W and mixing them. Next, the process proceeds to the application step, and as shown in FIG. 5, the first positive electrode paste 152c is applied to the surface of the positive electrode base material 151 (aluminum foil).

By the way, the first positive electrode paste 152c contains an alkali compound (LiOH or the like) generated by a reaction between the positive electrode active material 153 (LiNi _0.81 Co _0.16 Al _0.03 O ₂ ) and water. In particular, since the first positive electrode paste 152c is a mixture of the positive electrode active material 153 and the like and pure water, the alkali compound (LiOH and the like) is present over the entire surface of the positive electrode active material 153 and the like. In particular, in Example 1, a LiNiO ₂ positive electrode active material (specifically, LiNi _0.81 Co _0.16 Al _0.03 O ₂ ) is used as the positive electrode active material 153. Since the LiNiO ₂ positive electrode active material easily generates LiOH by reaction with water, a sufficient amount of LiOH can be attached to the surface of the positive electrode active material 153 and the like.

Subsequently, it progressed to the positive electrode paste drying process, and as shown in FIG. 6, the 1st positive electrode paste 152c apply | coated to the surface of the positive electrode base material 151 was hot-air dried. Thereafter, press forming was performed by pressing to obtain a positive electrode sheet. In Example 1, hot air drying was performed for 40 seconds using a dryer 10 having three hot air zones in which the temperature of the hot air to be blown was different from 40 ° C., 120 ° C., and 150 ° C. Specifically, the positive electrode base material 151 to which the first positive electrode paste 152c was applied was passed through three hot air zones over 40 seconds.
In Example 1, the elapsed time T from the time when the positive electrode active material 153 or the like was immersed in water in the positive electrode paste preparation process until the start of the drying of the first positive electrode paste 152c in the positive electrode paste drying process, 2 hours.

  Separately, a negative electrode paste in which a negative electrode active material (carbon powder) and a binder resin (CMC, SBR) were mixed was prepared. This negative electrode paste was applied to the surface of a negative electrode substrate (copper foil), dried with hot air in the same manner as the positive electrode sheet, and subjected to press working to obtain a negative electrode sheet.

  Next, proceeding to an assembling step, a positive electrode sheet (positive electrode plate 155), a negative electrode sheet (negative electrode plate 156), and a separator 157 were laminated, and this was wound to form an electrode body 150 having an oval cross section. Next, the electrode body 150 was connected to external terminals (the positive electrode terminal 120 and the negative electrode terminal 130) and accommodated in the rectangular accommodating portion 111. Thereafter, as shown in FIG. 1, the case 110 was formed by welding the square housing part 111 and the lid part 112. Subsequently, it progressed to the vacuum drying process and the electrode body 150 accommodated in the case 110 was vacuum-dried at 80 degreeC for 12 hours.

Next, proceeding to the carbonate generation step, as shown in FIG. 7, the case 110 containing the electrode body 150 was left in the chamber 20 filled with CO ₂ gas. In the first embodiment, after the inside of the chamber 20 a vacuum state, by filling the CO ₂ gas into the chamber 20, to enhance the purity of the CO ₂ gas in the chamber 20. This makes it possible to the surface of the first cured 152b drying curing the first positive electrode paste 152c (including the positive active material 153), to generate a carbonate 158 (such as Li ₂ CO ₃₎ (see FIG. 2) . Specifically, by reacting an alkali compound (LiOH or the like) existing over the entire surface of the first cured product 152b (positive electrode active material 153 or the like) obtained by drying and curing the first positive electrode paste 152c with CO ₂ , As shown in FIG. 2, a positive electrode mixture 152 in which the entire surface of the positive electrode active material 153 and the like are covered with a carbonate 158 can be formed.

In the first embodiment, the case 110 in which the case 110 containing the electrode body 150 is left in the chamber 20 filled with CO ₂ gas has three different times of 0 hour, 1 hour, and 12 hours. Various types of lithium ion secondary batteries (samples 1 to 3) were produced. Here, the lithium ion secondary battery left in the chamber 20 for 0 hours (not left in the chamber) was sample 1 and the lithium ion secondary battery left in the chamber for 1 hour was left in sample 2 for 12 hours in the chamber. Sample 3 is a lithium ion secondary battery.

Separately, lithium hexafluorophosphate (LiPF ₆ ) is dissolved in a mixed solvent in which three organic solvents of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed at a weight ratio of 30:30:40. An electrolytic solution was prepared. Next, an electrolytic solution was injected into the case 110 through the through hole 112b of the lid portion 112, and then the safety valve 140 was welded onto the outer surface 112f of the lid portion 112 to temporarily seal the through hole 112b. After 5 hours had passed since the electrolyte was injected, predetermined initial charge / discharge was performed. Thereafter, the temporary sealing of the through hole 112b was released, and the gas generated inside the case 110 was discharged to the outside.

  By the way, the gas generated with the initial charge / discharge is mainly hydrogen gas. This hydrogen gas is considered to be generated by the reduction reaction of the second bonded water 162 (water having a weak binding force that desorbs at a temperature of less than 100 ° C.) that was bonded to the positive electrode plate 155 and the negative electrode plate 156. Therefore, after the initial charging / discharging, the second sealing water 162 in the case 110 can be reduced by opening the temporary sealing of the through hole 112b and discharging the gas generated inside the case 110 to the outside. . Thereby, the internal pressure rise of case 110 at the time of normal use can be suppressed. Thereafter, the through hole 112b is resealed by the safety valve 140, and the lithium ion secondary battery 100 of Example 1 is completed (see FIG. 1). The electrolyte injection, the temporary sealing, opening, and resealing of the through-hole 112b were performed in a low moisture environment with a dew point of about −40 ° C.

  Next, the moisture content (contents of the first combined water 161 and the second combined water 162) contained in the positive electrode plate 155 of Example 1 was measured by the Karl Fischer method. Specifically, first, two measurement samples having diameters of 30 mm (measurement samples A and B) were punched from the positive electrode plate 155 that had been subjected to the vacuum drying process. Next, of the measurement samples A and B, the measurement sample A is heated at 100 ° C. for 30 minutes, and during this time, the second bound water 162 desorbed from the measurement sample A together with the carrier gas (nitrogen) is the Karl Fischer solution. Led inside. Thereby, about positive electrode plate 155 (positive electrode compound material 152), content of the 2nd binding water 162 desorbed at 100 degrees C or less can be measured.

Further, the measurement sample B was heated at 170 ° C. for 30 minutes, and during this time, water desorbed from the measurement sample B was introduced into the Karl Fischer solution together with the carrier gas (nitrogen). Thereby, about positive electrode plate 155 (positive electrode compound material 152), content of the water desorbed at less than 170 ° C. can be measured.
In Example 1, a Karl Fischer MKC-510N manufactured by Kyoto Electronics Industry and a moisture vaporizer ADP-511 are used as measurement devices.

  Next, by deducting the content of the second combined water 162 desorbed at 100 ° C. or less from the content of water desorbed at less than 170 ° C., desorption is performed in a temperature range higher than 100 ° C. and lower than 170 ° C. The content of the first combined water 161 can be obtained. In Example 1, the content of the first combined water 161 and the second combined water 162 is calculated as the content (ppm) contained in the positive electrode mixture 152 in terms of weight. The result is shown in FIG. As shown in FIG. 8, in Example 1, the content of the first combined water 161 contained in the positive electrode mixture 152 was 2850 ppm, and the content of the second combined water 162 was 1150 ppm.

  Further, for the negative electrode plate 156 that had been subjected to the vacuum drying step, the content of the second bound water 162 that was desorbed at 100 ° C. or lower was measured in the same manner as the positive electrode plate 155. When the content of the second combined water 162 was calculated as the content (ppm) contained in the negative electrode composite material in terms of weight, it was 190 ppm.

Next, regarding the positive electrode plates 155 of Samples 1 to 3 according to Example 1, the ratio of carbonate ions (CO ₃ ²⁻ ) in the carbonate 158 contained in the positive electrode mixture 152 was detected. Specifically, 0.1 g of the positive electrode mixture 152 was scraped from the positive electrode plate 155 of the sample 1, and this was dissolved in 0.1 liter of pure water. Next, this aqueous solution was filtered through a membrane filter having a pore diameter of 0.22 μm, 100 μL of the filtrate was injected into an ion chromatography apparatus, and the carbonate ion (CO ₃ ²⁻ ) concentration (mg / L) was measured.

Further, based on the measured carbonate ion concentration (mg / L), the weight ratio of carbonate ions (CO ₃ ²⁻ ) based on the weight of the positive electrode mixture 152 is calculated, and this is calculated as the carbonate ion amount x of the sample 1 x (Wt%). For the positive plates 155 of Samples 2 and 3, the carbonate ion amount x (wt%) was calculated in the same manner as Sample 1 described above. The result is shown in FIG.
As shown in FIG. 8, in Example 1, the sample 1 (not left in the CO ₂ gas chamber) had a carbonate ion amount x of 0.7 wt%. In Sample 2 (left in a CO ₂ gas chamber for 1 hour), the carbonate ion amount x was 2.2 wt%. In sample 3 (left in a CO ₂ gas chamber for 12 hours), the carbonate ion amount x was 2.7 wt%.

  In Example 1, DX-320 manufactured by Dionex Corporation was used as the ion chromatography apparatus. The column used was a weakly acidic column and the detector used was an electrical conductivity detector. Moreover, 0.3 mmol / liter octanesulfonic acid was used as a solution. As a regenerating solution, a mixed solution of 0.5 mmol / liter tetrabutylammonium hydroxide and 50 mmol / liter boric acid was used.

(Example 2)
In Sample 1 of Example 1, the elapsed time T from the time when the positive electrode active material 153 or the like was immersed in water in the positive electrode paste preparation step to the start of the drying of the first positive electrode paste 152c in the positive electrode paste drying step, 2 hours. On the other hand, in the present Example 2, the elapsed time T was changed to 8 hours, and the other conditions were the same as in the sample 1, and the lithium ion secondary battery 100 (referred to as the sample 4) was manufactured.

For Sample 4 of Example 2, the content of the first combined water 161 and the content of the second combined water 162 were measured in the same manner as Example 1. Further, in the same manner as in Example 1, the amount of carbonate ions x (wt%) contained in the positive electrode mixture 152 was measured. These results are shown in FIG.
As shown in FIG. 8, in Sample 4 of Example 2, the content of the first combined water 161 contained in the positive electrode mixture 152 was 2700 ppm, and the content of the second combined water 162 was 1200 ppm. Further, the content of the second combined water 162 contained in the negative electrode composite material was 190 ppm. Further, the carbonate ion amount x was 0.7 wt%.

(Example 3)
In Sample 1 of Example 1, the elapsed time T from the time when the positive electrode active material 153 or the like was immersed in water in the positive electrode paste preparation step to the start of the drying of the first positive electrode paste 152c in the positive electrode paste drying step, 2 hours. On the other hand, in Example 3, the elapsed time T was changed to 12 hours, and the other conditions were the same as in Sample 1, and a lithium ion secondary battery 100 (referred to as Sample 5) was manufactured.

For the sample 5 of Example 3, the content of the first combined water 161 and the content of the second combined water 162 were measured in the same manner as in Example 1. Further, in the same manner as in Example 1, the amount of carbonate ions x (wt%) contained in the positive electrode mixture 152 was measured. These results are shown in FIG.
As shown in FIG. 8, in Sample 5 of Example 3, the content of the first combined water 161 contained in the positive electrode mixture 152 was 2750 ppm, and the content of the second combined water 162 was 1200 ppm. Further, the content of the second combined water 162 contained in the negative electrode composite material was 190 ppm. Further, the carbonate ion amount x was 0.8 wt%.

Example 4
In Sample 1 of Example 1, in the positive electrode paste drying step, the drying time of the first positive electrode paste 152c applied to the surface of the positive electrode substrate 151 was set to 40 seconds. On the other hand, in this Example 4, the drying time was changed to 120 seconds, and the other conditions were the same as in Sample 1, and a lithium ion secondary battery 100 (referred to as Sample 6) was manufactured.

For the sample 6 of Example 4, the content of the first combined water 161 and the content of the second combined water 162 were measured in the same manner as in Example 1. Further, in the same manner as in Example 1, the amount of carbonate ions x (wt%) contained in the positive electrode mixture 152 was measured. These results are shown in FIG.
As shown in FIG. 8, in Sample 6 of Example 4, the content of the first combined water 161 contained in the positive electrode mixture 152 was 2700 ppm, and the content of the second combined water 162 was 1100 ppm. Further, the content of the second combined water 162 contained in the negative electrode composite material was 190 ppm. Further, the carbonate ion amount x was 0.6 wt%.

(Example 5)
In Sample 1 of Example 1, in the positive electrode paste drying step, the drying time of the first positive electrode paste 152c applied to the surface of the positive electrode substrate 151 was set to 40 seconds. On the other hand, in this Example 5, the drying time was changed to 20 seconds, and the other conditions were the same as in Sample 1, and a lithium ion secondary battery 100 (referred to as Sample 7) was manufactured.

For Sample 7 of Example 5, the content of the first combined water 161 and the content of the second combined water 162 were measured in the same manner as Example 1. Further, in the same manner as in Example 1, the amount of carbonate ions x (wt%) contained in the positive electrode mixture 152 was measured. These results are shown in FIG.
As shown in FIG. 8, in Sample 7 of Example 5, the content of the first combined water 161 contained in the positive electrode mixture 152 was 2600 ppm, and the content of the second combined water 162 was 1900 ppm. Further, the content of the second combined water 162 contained in the negative electrode mixture was 190 ppm. Further, the carbonate ion amount x was 1.5 wt%.

(Example 6)
In Sample 1 of Example 1, in the positive electrode paste drying step, the drying time of the first positive electrode paste 152c applied to the surface of the positive electrode substrate 151 was set to 40 seconds. On the other hand, in this Example 6, the drying time was changed to 10 seconds, and the other conditions were the same as in Sample 1, and a lithium ion secondary battery 100 (referred to as Sample 8) was manufactured.

For Sample 8 of Example 6, the content of the first combined water 161 and the content of the second combined water 162 were measured in the same manner as Example 1. Further, in the same manner as in Example 1, the amount of carbonate ions x (wt%) contained in the positive electrode mixture 152 was measured. These results are shown in FIG.
As shown in FIG. 8, in Sample 8 of Example 6, the content of the first combined water 161 contained in the positive electrode mixture 152 was 2800 ppm, and the content of the second combined water 162 was 2200 ppm. Further, the content of the second combined water 162 contained in the negative electrode mixture was 190 ppm. Further, the carbonate ion amount x was 1.5 wt%.

(Example 7)
In Example 1, the drying temperature in the vacuum drying process was set to 80 ° C. On the other hand, in this Example 7, the drying temperature was changed to 60 ° C., and the other conditions were the same as in Example 1, and the lithium ion secondary battery 100 was manufactured. In Example 7, as in Example 1, in the carbonate production step, the time for leaving the case 110 containing the electrode body 150 in the chamber 20 filled with CO ₂ gas is 0 hour, 1 Three types of lithium ion secondary batteries (referred to as samples 9 to 11) were produced by varying the time and time for three types. Here, the lithium ion secondary battery left in the chamber for 0 hours (not left in the chamber) was sample 9, the lithium ion secondary battery left in the chamber for 1 hour was sample 10, and the lithium left in the chamber for 12 hours An ion secondary battery is designated as Sample 11.

For Samples 9 to 11 of Example 7, the content of the first combined water 161 and the content of the second combined water 162 were measured in the same manner as Example 1. Further, in the same manner as in Example 1, the amount of carbonate ions x (wt%) contained in the positive electrode mixture 152 was measured. These results are shown in FIG.
As shown in FIG. 8, in Samples 9 to 11 of Example 7, the content of the first combined water 161 contained in the positive electrode mixture 152 was 2800 ppm, and the content of the second combined water 162 was 1300 ppm. Further, the content of the second combined water 162 contained in the negative electrode mixture was 200 ppm. Further, the carbonate ion amount x was 0.7 wt% in sample 9, 2.3 wt% in sample 10, and 2.8 wt% in sample 11.

(Example 8)
In Example 1, as shown in FIG. 3, the vacuum drying process was performed after the assembly process. On the other hand, in the present Example 8, as shown in FIG. 9, the vacuum drying process was performed after the positive electrode paste drying process and before the assembly process. Furthermore, the drying temperature in the vacuum drying step was changed to 100 ° C., and the other conditions were the same as in Example 1, and the lithium ion secondary battery 100 was manufactured.

In Example 8, as in Example 1, in the carbonate production step, the time for leaving the case 110 containing the electrode body 150 in the chamber 20 filled with CO ₂ gas is 0 hour, 1 Three types of lithium ion secondary batteries (referred to as Samples 12 to 14) were manufactured by varying the time and time of 3 types. Here, the lithium ion secondary battery left in the chamber for 0 hour (not left in the chamber) is sample 12, the lithium ion secondary battery left in the chamber for 1 hour is sample 13, and the lithium left in the chamber for 12 hours An ion secondary battery is referred to as Sample 14.

For Samples 12 to 14 of Example 8, as in Example 1, the content of the first combined water 161 and the content of the second combined water 162 were measured. Further, in the same manner as in Example 1, the amount of carbonate ions x (wt%) contained in the positive electrode mixture 152 was measured. These results are shown in FIG.
As shown in FIG. 8, in Samples 12 to 14 of Example 8, the content of the first combined water 161 contained in the positive electrode mixture 152 was 2650 ppm, and the content of the second combined water 162 was 1050 ppm. Moreover, content of the 2nd combined water 162 contained in a negative electrode compound material was 180 ppm. Further, the carbonate ion amount x was 0.6 wt% in the sample 12, 2.0 wt% in the sample 13, and 2.5 wt% in the sample 14.

Example 9
In Example 1, as shown in FIG. 3, the vacuum drying process was performed after the assembly process. On the other hand, in this Example 9, as shown in FIG. 9, the vacuum drying process was performed after the positive electrode paste drying process and before the assembly process. Further, the drying temperature in the vacuum drying step was changed to 120 ° C., and the other conditions were the same as in Example 1, and the lithium ion secondary battery 100 was manufactured.

In Example 9, as in Example 1, in the carbonate production step, the time for leaving the case 110 containing the electrode body 150 in the chamber filled with CO ₂ gas was 0 hour, 1 hour. , 12 types of lithium ion secondary batteries (samples 15 to 17) were produced. Here, the lithium ion secondary battery left in the chamber for 0 hours (not left in the chamber) is sample 15; the lithium ion secondary battery left in the chamber for 1 hour is sample 16; lithium left in the chamber for 12 hours An ion secondary battery is designated as Sample 17.

For Samples 15 to 17 of Example 9, the content of the first combined water 161 and the content of the second combined water 162 were measured in the same manner as in Example 1. Further, in the same manner as in Example 1, the amount of carbonate ions x (wt%) contained in the positive electrode mixture 152 was measured. These results are shown in FIG.
As shown in FIG. 8, in Samples 15 to 17 of Example 9, the content of the first combined water 161 contained in the positive electrode mixture 152 was 2400 ppm, and the content of the second combined water 162 was 800 ppm. Further, the content of the second combined water 162 contained in the negative electrode mixture was 160 ppm. Further, the carbonate ion amount x was 0.6 wt% in sample 15, 1.5 wt% in sample 16, and 1.8 wt% in sample 17.

(Example 10)
As shown in FIG. 1, the lithium ion secondary battery 200 of Example 10 differs from the lithium ion secondary battery 100 of Example 1 in the positive electrode plate (specifically, positive electrode mixture), The same applies to the site. Below, the manufacturing method of the lithium ion secondary battery 200 of the present Example 10 is demonstrated, referring drawings.

In Example 10, the method for producing the positive electrode paste was different from that in Example 1, and the others were substantially the same, and the lithium ion secondary battery 200 was manufactured.
Specifically, in Example 1, in the positive electrode paste manufacturing step (see FIG. 3), as shown in FIG. 4, a positive electrode active material 153 (LiNi _0.81 Co _0.16 Al _0.03 O ₂ ) and a conductive material 159 (carbon ) And a binder resin (CMC, PTFE) were added into pure water, and these were mixed to produce a first positive electrode paste 152c.

On the other hand, in Example 10, as shown in FIG. 10, first, in the dipping process, only the positive electrode active material 153 (LiNi _0.81 Co _0.16 Al _0.03 O ₂ ) was dipped in pure water for 2 hours, and thereafter The aqueous solution was filtered. Subsequently, it progressed to the positive electrode active material drying process, and the positive electrode active material 153 after filtration was vacuum-dried at 120 degreeC for 24 hours. Next, the process proceeds to a positive electrode paste preparation step, the positive electrode active material 153 vacuum-dried, the same conductive material 159 (carbon) as in Example 1, a binder resin (PVDF) different from that in Example 1, and a solvent (N-methyl 2 Pyrrolidone) was mixed to prepare a second positive electrode paste 252c.

  Next, the process proceeded to an application step, and as shown in FIG. 5, the second positive electrode paste 252c was applied to the surface of the positive electrode substrate 151 (aluminum foil). Subsequently, it progressed to the positive electrode paste drying process, and as shown in FIG. 6, the 1st positive electrode paste 152c apply | coated to the surface of the positive electrode base material 151 was hot-air dried with the dryer 10. As shown in FIG. Then, it progressed in order of the vacuum drying process, the assembly | attachment process, and the carbonate production | generation process, and the lithium ion secondary battery 200 was manufactured.

In the carbonate production step, as shown in FIG. 7, the case 110 containing the electrode body 250 was left in the chamber 20 filled with CO ₂ gas. Thus, it is possible to react the alkali compound present throughout the surface of the first cured product for drying and curing the second positive electrode paste 252c 252b (such as a positive active material 153) (such as LiOH) and CO _2. Thereby, as shown in FIG. 2, a positive electrode mixture 252 in which the entire surface of the positive electrode active material 153 or the like is covered with the carbonate 158 can be formed.

  In Example 10, unlike Example 1, hot air drying was performed for 120 seconds in the positive electrode paste drying step. Moreover, unlike Example 1, the vacuum drying process is performed after the positive electrode paste drying process and before the assembly process. Furthermore, the drying temperature in the vacuum drying process is changed to 120 ° C.

Similarly to the first embodiment, in the carbonate production process, the time for leaving the case 110 containing the electrode body 150 in the chamber 20 filled with CO ₂ gas is 3 hours of 0 hours, 1 hour, and 12 hours. Three kinds of lithium ion secondary batteries (referred to as samples 18 to 20) were produced in different types. Here, the lithium ion secondary battery left in the chamber 20 for 0 hours (not left in the chamber) was sample 18, and the lithium ion secondary battery left in the chamber for 1 hour was left in sample 19 for 12 hours in the chamber. A lithium ion secondary battery is designated as Sample 20.

For Samples 18 to 20 of Example 10, the content of the first combined water 161 and the content of the second combined water 162 were measured in the same manner as Example 1. Further, in the same manner as in Example 1, the amount of carbonate ions x (wt%) contained in the positive electrode mixture 152 was measured. These results are shown in FIG.
As shown in FIG. 8, in Samples 18 to 20 of Example 10, the content of the first combined water 161 contained in the positive electrode mixture 152 was 1500 ppm, and the content of the second combined water 162 was 1500 ppm. Moreover, content of the 2nd combined water 162 contained in a negative electrode compound material was 140 ppm. Further, the carbonate ion amount x was 0.6 wt% for sample 18, 1.3 wt% for sample 19, and 1.6 wt% for sample 20.

(Comparative Example 1)
In Comparative Example 1, the method for producing the positive electrode paste was different from that in Example 1, and the other processes were similarly performed to manufacture a lithium ion secondary battery.
Specifically, in the positive electrode paste manufacturing step, a positive electrode active material (LiNi _0.81 Co _0.16 Al _0.03 O ₂ ), a conductive material (carbon), a binder resin (PVDF), and a solvent (N methyl 2-pyrrolidone) are added. A second positive electrode paste was prepared by mixing. Thereafter, in the same manner as in Example 1, the coating process, the positive electrode paste drying process, the assembling process, the vacuum drying process, and the carbonate generating process were performed in this order to manufacture a lithium ion secondary battery.

In Comparative Example 1, as in Example 10, in the carbonate production step, the time for leaving the case containing the electrode body in the chamber filled with CO ₂ gas was set to 0 hour, 1 hour, 12 Three types of lithium ion secondary batteries (referred to as samples 21 to 23) were produced by varying the time for three types. Here, the lithium ion secondary battery left in the chamber for 0 hours (not left in the chamber) was sample 21, the lithium ion secondary battery left in the chamber for 1 hour was sample 22, and the lithium left in the chamber for 12 hours The ion secondary battery is referred to as Sample 23.

For Samples 21 to 23 of Comparative Example 1, the content of the first combined water and the content of the second combined water were measured in the same manner as in Example 1. Further, in the same manner as in Example 1, the amount of carbonate ions x (wt%) contained in the positive electrode mixture was measured. These results are shown in FIG.
As shown in FIG. 8, in Samples 21 to 23 of Comparative Example 1, the content of the first combined water contained in the positive electrode mixture was 700 ppm, and the content of the second combined water was 400 ppm. Moreover, content of the 2nd combined water contained in a negative electrode compound material was 170 ppm. Further, the carbonate ion amount x was 0.6 wt% in sample 21, 1.1 wt% in sample 22, and 1.3 wt% in sample 23.

(Comparative Example 2)
Also in Comparative Example 2, a method for producing the positive electrode paste was different from that of the sample of Example 1, and the others were similarly manufactured to produce a lithium ion secondary battery. Specifically, a second positive electrode paste was produced in the same manner as in Comparative Example 1, and thereafter, a lithium ion secondary battery (referred to as Sample 24) was produced in the same manner as in Example 1. In this comparative example 2, unlike the example 1, the vacuum drying process is performed after the positive electrode paste drying process and before the assembly process. Furthermore, the drying temperature in the vacuum drying process is changed to 100 ° C.

For the sample 24 of Comparative Example 2, the content of the first combined water and the content of the second combined water were measured in the same manner as in Example 1. Further, in the same manner as in Example 1, the amount of carbonate ions x (wt%) contained in the positive electrode mixture was measured. These results are shown in FIG.
As shown in FIG. 8, in the sample 24 of this comparative example 2, the content of the first combined water contained in the positive electrode mixture was 550 ppm, and the content of the second combined water was 350 ppm. Moreover, content of the 2nd combined water contained in a negative electrode compound material was 140 ppm. Further, the carbonate ion amount x was 0.5 wt%.

(Comparative Example 3)
Also in Comparative Example 3, the method for producing the positive electrode paste was different from that of Sample 1 of Example 1, and the others were similarly manufactured to produce a lithium ion secondary battery. Specifically, a second positive electrode paste was produced in the same manner as in Comparative Example 1, and thereafter, a lithium ion secondary battery (referred to as Sample 25) was produced in the same manner as Sample 1 in Example 1. In this comparative example 3, unlike the example 1, the vacuum drying process is performed after the positive electrode paste drying process and before the assembly process. Furthermore, the drying temperature in the vacuum drying process is changed to 120 ° C.

For the sample 25 of Comparative Example 3, the content of the first combined water and the content of the second combined water were measured in the same manner as in Example 1. Further, in the same manner as in Example 1, the amount of carbonate ions x (wt%) contained in the positive electrode mixture was measured. These results are shown in FIG.
As shown in FIG. 8, in Sample 25 of Comparative Example 3, the content of the first combined water contained in the positive electrode mixture was 580 ppm, and the content of the second combined water was 200 ppm. Moreover, content of the 2nd combined water contained in a negative electrode compound material was 130 ppm. Further, the carbonate ion amount x was 0.5 wt%.

(Comparative Example 4)
Also in Comparative Example 3, compared with Sample 1 of Example 1, a positive electrode paste preparation method and a humidification step were added, and the others were similarly manufactured to produce a lithium ion secondary battery. Specifically, after preparing the second positive electrode paste in the same manner as in Comparative Example 1, the process proceeds to the coating process, the positive electrode paste drying process, and the assembly process in the same manner as in Example 1, and the electrode body is accommodated in the case. did. Next, unlike Example 1, the process proceeded to a humidification step, and the electrode body housed in the case was left in a thermostat having a humidity of 70% for 72 hours. Thereafter, in the same manner as Sample 1 of Example 1, a lithium ion secondary battery (referred to as Sample 26) was produced.

For the sample 26 of Comparative Example 4, the content of the first combined water and the content of the second combined water were measured in the same manner as in Example 1. Further, in the same manner as in Example 1, the amount of carbonate ions x (wt%) contained in the positive electrode mixture was measured. These results are shown in FIG.
As shown in FIG. 8, in the sample 26 of this comparative example 4, the content of the first combined water contained in the positive electrode mixture was 1600 ppm, and the content of the second combined water was 1600 ppm. Moreover, content of the 2nd combined water contained in a negative electrode compound material was 170 ppm. Further, the carbonate ion amount x was 2.5 wt%.

(Battery evaluation)
Next, IV resistance values after normal use were measured for samples 1 to 26, respectively.
Specifically, after each sample produced as described above was allowed to stand at 25 ° C. for 10 days, it was charged at a constant current-constant voltage for 1.5 hours until the battery voltage reached 4.1V. Thereafter, discharging was performed at a current value of 1 C until the battery voltage reached 3V. When the discharge capacity at this time was defined as the battery capacity, all the samples were about 7 Ah.

  Next, each sample was charged with a constant current-constant voltage of 1 C for 1.5 hours until the battery voltage reached 3.72 V, and SOC (State Of Charge) was adjusted. Thereafter, charging and discharging were performed at a maximum current value of 12 C, and the amount of voltage drop after 10 seconds was measured. The relationship between the current value (X axis) and the voltage (Y axis) at this time is represented as an IV diagram, and the IV resistance value (internal resistance) of each sample was calculated based on this IV diagram.

  Then, for each IV resistance value of Samples 2 to 26, the ratio of the IV resistance value of Sample 1 to the IV resistance value of Sample 1 was calculated as the IV resistance ratio. The IV resistance ratio concerning Samples 2 to 26 was as shown in FIG. In addition, the above-mentioned series of processes are performed in a 25 degreeC thermostat.

Here, the result of the IV resistance ratio is examined.
First, Sample 1 (Example 1), Sample 4 (Example 2), and Sample 5 (Example 3) are compared. As shown in FIG. 8, these samples have elapsed time T (from the time when the positive electrode active material 153 and the like are immersed in water in the positive electrode paste manufacturing step, the drying of the first positive electrode paste 152c is started in the positive electrode paste drying step. The only difference is that the elapsed time is different), and the others are manufactured in the same manner.

Comparing these IV resistance ratios, sample 4 with elapsed time T of 2 hours compared to sample 1 with elapsed time T of 2 hours, the IV resistance ratio was 1.04, and the IV resistance value (internal Although the resistance was increased, good output characteristics could be obtained. On the other hand, in the sample 5, the IV resistance ratio was 1.23, and the IV resistance value (internal resistance) was greatly increased as compared with the sample 1, and the output characteristics were greatly deteriorated. This is presumably because the positive electrode active material 153 and water were brought into contact with each other for a long time of 12 hours, so that the reaction between the positive electrode active material 153 and water progressed, and Li desorption proceeded from the positive electrode active material 153. .
From the above results, the elapsed time T (the elapsed time from the time when the positive electrode active material 153 and the like are immersed in water in the positive electrode paste preparation process to the start of drying of the first positive electrode paste 152c in the positive electrode paste drying process) is It can be said that it is preferably within 8 hours.

  Next, Sample 1 (Example 1) and Samples 6 to 8 (Examples 4 to 6) are compared. As shown in FIG. 8, these samples have the same elapsed time T of 2 hours, but different drying times thereafter. Specifically, the drying times are different from 10 seconds (sample 8), 20 seconds (sample 7), 40 seconds (sample 1), and 120 seconds (sample 6) in order from the sample with the shortest drying time. For this reason, the content of the second combined water 162 in the positive electrode becomes 2200 ppm, 1900 ppm, 1150 ppm, and 1100 ppm in order from the sample with the shortest drying time, and the content of the second combined water increases as the sample has a shorter drying time. .

  Comparing these IV resistance ratios, compared with sample 1, in samples 6 and 7 (Examples 4 and 5), the IV resistance ratio was 0.98 and 1.01, and good output characteristics could be obtained. . On the other hand, in the sample 8 (Example 6), the IV resistance ratio was 1.25, and the output characteristics were greatly deteriorated compared to the sample 1. This is probably because the content of the second bonded water 162 is as high as 2200 ppm, and the reaction between the desorbed second bonded water 162 and the positive electrode active material 153 has progressed during normal use. From this result, it can be said that the content of the second combined water 162 is preferably less than 2200 ppm in terms of weight in the positive electrode mixture 152.

Moreover, it compares about the samples 1-3 of Example 1. FIG. As shown in FIG. 8, these samples are different only in that the time for leaving them in the chamber 20 filled with CO ₂ gas in the carbonate production step (referred to as CO ₂ treatment time) is different. The relationship is similar. That is, only the carbonate ion amount x is different.
In sample 2 (carbonate ion amount x = 2.2 wt%), the IV resistance ratio is 0.99, and the IV resistance value (internal resistance) is smaller than sample 1 (carbonate ion amount x = 0.7 wt%). It was. This is because by covering the surface of the positive electrode mixture 152 with more carbonate 158, it was possible to suppress the contact between the positive electrode mixture 152 and the electrolytic solution, and to suppress the decomposition reaction of the electrolytic solution. Conceivable. This suppresses the formation of a film of a compound produced by the decomposition reaction of the electrolytic solution on the surface of the positive electrode plate 155, suppresses an increase in IV resistance value (internal resistance), and suppresses a decrease in output characteristics. It is thought that it was made.

  On the other hand, in the sample 3 (carbonate ion amount x = 2.7 wt%), the IV resistance ratio is 1.06, and compared with the sample 1 (carbonate ion amount x = 0.7 wt%), the IV resistance value (internal resistance). ) Has grown. This is presumably because the IV resistance value (internal resistance) was greatly increased by the carbonate 158 and the output characteristics were lowered because the amount of the carbonate 158 covering the surface of the positive electrode mixture 152 was excessively increased.

  Moreover, also about the samples 9-11 of Example 7, as shown in FIG. 8, it was the same result as the above-mentioned samples 1-3. Specifically, in the sample 10 (carbonate ion amount x = 2.3 wt%) in which the carbonate ion amount x is increased compared to the sample 9 (carbonate ion amount x = 0.7 wt%), the IV resistance value (internal resistance) ) Has become smaller. However, in the sample 11 (carbonate ion amount x = 2.8 wt%), the carbonate ion amount x was increased too much, so that the IV resistance value (internal resistance) was larger than that in the sample 9.

Moreover, also about the samples 12-14 of Example 8, as shown in FIG. 8, it was the same result as the above-mentioned samples 1-3. Specifically, compared to sample 12 (carbonate ion amount x = 0.6 wt%), sample 13 (carbonate ion amount x = 2.0 wt%) in which carbonate ion amount x is increased has an IV resistance value (internal resistance). ) Has become smaller. However, Sample 14 in which the carbonate ion amount x was further increased (carbonate ion amount x = 2.5 wt%) had an IV resistance value (internal resistance) equivalent to that of Sample 9.
From the above results, it can be said that the carbonate ion amount x is preferably 2.5 wt% or less in order to reduce the IV resistance value and improve the output characteristics.

  In Sample 26 (Comparative Example 4), the content of the second combined water 162 in the positive electrode is less than 2200 ppm (specifically 1600 ppm), and the carbonate ion amount x is 2.5 wt% or less (specifically 2.5 wt%). %), The IV resistance ratio was as extremely high as 1.5. This is considered because the 1st combined water 161 and the 2nd combined water 162 were combined by performing a humidification process (the positive electrode compound material 152 grade | etc., Is contacted with water vapor | steam). From this result, in order to reduce the IV resistance value and improve the output characteristics, the first combined water 161 and the like are combined by a method of bringing the positive electrode mixture 152 and the like into contact with water (liquid). It can be said that it is preferable.

(Heating test)
Next, the heating test was implemented about the samples 1-25, respectively. Specifically, each sample manufactured as described above was charged with constant current-constant voltage for 1.5 hours until the battery voltage reached 4.1 V, and the SOC was 100%. Then, each sample was arrange | positioned in a thermostat, and the inside of the thermostat was heated with the temperature increase rate of 2 degree-C / min until the sealing by the safety valve 140 was open | released about each sample. At this time, for each sample, the battery temperature (referred to as the valve opening temperature) when the sealing by the safety valve 140 was opened (opened) was measured. The result is shown in FIG.

  In Samples 21 to 25 (Comparative Examples 1 to 3), the valve opening temperature was 190 ° C. or higher. Specifically, the safety valve was opened after the battery temperature rose to 190 ° C. or higher, and thermal runaway occurred in which the battery temperature rose rapidly even after the valve was opened. This is presumably because in each sample, the battery temperature rose above the decomposition temperature (170 ° C.) of the positive electrode active material 153 (increased to 190 ° C. or more) before the case was sealed with the safety valve. As a result, it is considered that the decomposition reaction of the positive electrode active material 153 progressed and thermal runaway occurred.

  On the other hand, in samples 1 to 20 (Examples 1 to 10), the valve opening temperature was 110 ° C or 120 ° C. Specifically, the safety valve 140 was opened after the battery temperature reached 110 ° C. or 120 ° C., and the battery temperature rose for a while after the opening, but the battery temperature dropped soon without thermal runaway. This is presumably because the sealing of the case 110 by the safety valve 140 could be opened before the battery temperature reached the decomposition temperature (170 ° C.) of the positive electrode active material 153 in each sample. Thereby, it is considered that the decomposition reaction of the positive electrode active material 153 was suppressed and thermal runaway was prevented.

  Here, the lithium ion secondary batteries 100 and 200 according to the example and the lithium ion secondary battery according to the comparative example will be compared in detail with respect to the results of the heating test. Here, on behalf of the lithium ion secondary batteries 100 and 200 according to the example, the internal pressure change and the battery temperature change due to the heating test of Sample 3 are shown by solid lines in FIG. Furthermore, as a representative of the lithium ion secondary battery according to the comparative example, the internal pressure change and the battery temperature change due to the heating test of the sample 22 are shown by broken lines in FIG. In FIG. 11, the differential pressure ΔP is a differential pressure obtained by subtracting the external atmospheric pressure (atmospheric pressure in this embodiment) from the internal pressure of the case 110.

  As shown by a broken line in FIG. 11, in the sample 22 of the comparative example, the differential pressure ΔP gradually increases even after the battery temperature exceeds 100 ° C. (that is, the internal pressure of the battery gradually increases). ). After that, when the battery temperature began to rise rapidly, the battery internal pressure suddenly increased, so that the differential pressure ΔP suddenly increased and the valve opened when the battery temperature rose to 190 ° C. Even after the valve was opened, the battery temperature continued to rise rapidly, and the battery temperature rose to about 350 ° C.

  On the other hand, in the sample 3 of the example, as shown by a solid line in FIG. 11, after the battery temperature exceeds 100 ° C., the internal pressure of the battery suddenly rises so that the differential pressure ΔP suddenly rises. The sealing of the case 110 by 140 is opened. At this time, the battery temperature was 110 ° C., which was lower than the decomposition temperature (170 ° C.) of the positive electrode active material 153, and thus thermal runaway could be prevented. Specifically, the battery temperature rose for a while after the valve opening, and the battery temperature rose to about 150 ° C., but then the battery temperature dropped.

  Thus, in the battery of the example, compared with the battery of the comparative example, after the battery temperature exceeds 100 ° C., the battery internal pressure is reached early, and the differential pressure ΔP reaches the valve opening pressure P (0.4 MPa). The safety valve 140 could be opened early. This is because, as shown in FIG. 8, the battery of the example (samples 1 to 20) has an extremely large content of the first combined water 161 compared to the battery of the comparative example (samples 21 to 25). it is conceivable that. Specifically, in the battery of the comparative example (samples 21 to 25), the content of the first combined water in the positive electrode mixture 152 is 700 ppm or less, whereas in the battery of the example (samples 1 to 20). In addition, the content of the first combined water in the positive electrode mixture 152 is set to 1500 ppm or more.

As described above, when the first combined water 161 desorbed in a temperature range higher than 100 ° C. and lower than 170 ° C. is included in the positive electrode mixture 152 by 1500 ppm or more, the case 110 has a battery temperature exceeding 100 ° C. A large amount of gas derived from the first combined water 161 (water vapor or CO ₂ produced by the reaction between the electrolytic solution and the first combined water 161) is generated in the inside. As a result, the internal pressure of the case 110 rapidly increases. Therefore, before the battery temperature rises to the decomposition temperature (170 ° C.) of the positive electrode active material 153, the internal pressure of the case 110 and the differential pressure ΔP become the valve opening pressure P (0. 4 MPa), the case 110 can be opened by the safety valve 140.

By the way, the molecular weight of water is 18, and the volume occupied by 1 mol of gas molecules at 1 atm is 22.4 × 10 ³ (cm ³ ). Accordingly, when the content of the first bound water is W (g), the volume (cm ³ ) of the gas (water vapor) derived from the desorbed first bound water is (W) at 1 atm (0.1013 MPa). /18)×22.4×10 ³ Therefore, if the volume of the void in the case is V (cm ³ ) and the partial pressure of the gas (water vapor) derived from the first combined water in the case is P1 (MPa), P1 × V = 0.1013 × (W / 18) × 22.4 × 10 ³ . When this equation is modified, P1 = (W / 18) × 22.4 × 10 ³ × 0.1013 / V. However, if P1 exceeds the valve opening pressure P (MPa), that is, if the relationship of (W / 18) × 22.4 × 10 ³ × 0.1013 / V> P (equation 1) is satisfied, it is sure. Furthermore, it is considered that the case sealing by the safety valve can be opened. By transforming (Equation 1), a relational expression of W> 7.93 × 10 ⁻³ × V × P can be derived.

In the lithium ion secondary batteries 100 and 200 of Examples 1 to 10, the volume V of the gap G in the case 110 is 22 (cm ³ ), and the valve opening pressure P is 0.4 MPa. Substituting these values into the relational expression of W> 7.93 × 10 ⁻³ × V × P results in W> 0.07 (g). That is, in the lithium ion secondary batteries 100 and 200 of Examples 1 to 10, if the case 110 contains more than 0.1 g of the first combined water 161, the battery temperature is the decomposition temperature of the positive electrode active material 153 ( 170 ° C), the internal pressure of the case 110 can be increased until the differential pressure ΔP reaches the valve opening pressure P (0.4 MPa), and the sealing of the case 110 by the safety valve 140 can be opened. it is conceivable that.

In the lithium ion secondary batteries 100 and 200 of Examples 1 to 10, the positive electrode plate 152 includes about 47 g of the positive electrode mixture 152. And in the lithium ion secondary batteries 100 and 200 (Samples 1 to 20) of Examples 1 to 10, as shown in FIG. 8, the content of the first combined water 161 is calculated in terms of weight in the positive electrode mixture 152. 1500 ppm or more. Therefore, the lithium ion secondary batteries 100 and 200 of Examples 1 to 10 contained the first combined water 161 at least 47 × 1500 × 10 ⁻⁶ = 0.071 (g). Thus, in the lithium ion secondary batteries 100 and 200 of Examples 1 to 10, since the first bound water 161 was contained in the case 110 in an amount of more than 0.07 g, the battery temperature was the decomposition temperature of the positive electrode active material 153. Before the pressure rises to (170 ° C.), the internal pressure of the case 110 is increased until the differential pressure ΔP reaches the valve opening pressure P (0.4 MPa), and the sealing of the case 110 by the safety valve 140 is released. It can be said that it was made.

  Moreover, in the lithium ion secondary batteries 100 and 200 of Examples 1 to 10, the desorption temperature of the first combined water 161 is higher than the maximum temperature (100 ° C.) in the normal use temperature range of the battery. For this reason, normally, the 1st combined water 161 does not detach | desorb in the environment where the lithium ion secondary battery 100,200 is used. Therefore, normally, while using the lithium ion secondary batteries 100 and 200, there is no possibility that the battery characteristics are remarkably deteriorated due to the reaction between the positive electrode active material 153 and the first combined water 161.

  In addition, in the lithium ion secondary batteries 100 and 200 of Examples 1 to 10, as shown in FIG. 8, the content of the second binding water 162 desorbed at a temperature of 100 ° C. or less is set in the positive electrode mixture 152. It is suppressed to less than 2200 ppm in terms of weight. That is, the content of the second bound water 162 that is desorbed at a temperature within the normal use temperature range of the lithium ion secondary batteries 100 and 200 (100 ° C. or less) is suppressed to less than 2200 ppm in terms of weight in the positive electrode mixture 152. is doing. Thereby, normally, while using the lithium ion secondary batteries 100 and 200, reaction between the positive electrode active material 153 and water can be suppressed, and deterioration of battery characteristics (increase in IV resistance value) can be suppressed. It was. Specifically, as shown in FIG. 4, in Examples 1 to 10, the IV resistance ratio was only slightly increased as compared with Comparative Examples 1 to 4 having a relatively small amount of water.

  By the way, in the lithium ion secondary batteries 100 and 200 of Examples 1 to 10, 3 of ethylene carbonate (boiling point 238 ° C.), dimethyl carbonate (boiling point 90 ° C.), and ethyl methyl carbonate (boiling point 108 ° C.) are used as the solvent of the electrolytic solution. A solvent in which various organic solvents are mixed at a weight ratio of 30:30:40 is used. Since the carbonate-based organic solvent is flammable, if the battery temperature exceeds the boiling point of the organic solvent, the case 110 is filled with a flammable gas and is likely to emit smoke.

  On the other hand, in the lithium ion secondary batteries 100 and 200 of Examples 1 to 10, the valve opening temperature is set to 110 ° C. or 120 ° C. as described above. For this reason, before the battery temperature reaches the boiling point of ethylene carbonate (238 ° C.), the safety valve 140 can be opened and the gas in the case 110 can be discharged to the outside. Thereby, it is possible to prevent at least the ethylene carbonate gas from filling the case 110 out of the organic solvent contained in the electrolytic solution, thereby reducing the risk of smoking.

(Overcharge test)
Next, an overcharge test was performed on each of samples 1 to 25. Specifically, each sample manufactured as described above was charged with constant current-constant voltage for 1.5 hours until the battery voltage reached 4.1 V, and the SOC was 100%. Thereafter, each sample was further charged with a constant current of 20A. At this time, the battery voltage (referred to as the valve opening voltage) at the time when the sealing by the safety valve 140 was opened (opened) was measured for each sample. The result is shown in FIG.

  As shown in FIG. 8, in samples 21 to 25 (lithium ion secondary batteries of Comparative Examples 1 to 3), the sealing by the safety valve 140 is not opened (opened) until the battery voltage becomes 5.1 V or higher. It was. Furthermore, when the safety valve 140 is opened, the battery temperature has already risen above the decomposition temperature (170 ° C.) of the positive electrode active material 153, so that the battery temperature continues to rise rapidly after the valve is opened, resulting in thermal runaway. Oops.

  On the other hand, in samples 1 to 20 (lithium ion secondary batteries 100 and 200 of Examples 1 to 10), as shown in FIG. 8, both are sealed with a safety valve 140 at a battery voltage of 5.0 V or less. Was opened (opened). Thereby, also in the overcharge test, thermal runaway did not occur in Samples 1 to 20 (the lithium ion secondary batteries 100 and 200 of Examples 1 to 10). This is similar to the heating test described above, in the samples 1 to 20 (the lithium ion secondary batteries 100 and 200 of Examples 1 to 10), before the battery temperature reaches the decomposition temperature (170 ° C.) of the positive electrode active material 153. This is because the sealing by the safety valve 140 could be opened (opened).

  Here, when the valve opening voltages of Samples 1 to 3 according to Example 1 are compared, in Sample 1, the valve opening voltage was 4.8 V, whereas in Samples 2 and 3, the valve opening voltage was 4. The voltage was 7 V, which was 0.1 V lower than that of Sample 1. As shown in FIG. 8, this is considered to be due to the difference in the carbonate ion amount x.

Specifically, unlike Sample 1, Samples 2 and 3 are subjected to CO ₂ treatment in the carbonate production step, so the surface of positive electrode mixture 152 is covered with a larger amount of carbonate 158 than Sample 1. Has been. The carbonate 158 covering the surface of the positive electrode mixture 152 is decomposed during overcharge to generate CO ₂ gas. Therefore, in Samples 2 and 3, when the battery temperature rises due to overcharge, in addition to the gas derived from the first combined water 161, CO ₂ gas is also generated due to decomposition of the carbonate 158. Can be greatly increased. For this reason, it is considered that in the samples 2 and 3, the case 110 was sealed by the safety valve 140 at a lower voltage than the sample 1, that is, at a lower temperature.

Furthermore, each sample of Example 7 (Samples 9 to 11), Example 8 (Samples 12 to 14), Example 9 (Samples 15 to 17), and Example 10 (Samples 18 to 20) When the valve opening voltages were compared, the same result as in Example 1 was obtained. That is, in either embodiment, the sample (sample of CO ₂ treatment time 1 hour or 12 hours) subjected to CO ₂ treatment in carbonate production step, a sample not subjected to CO ₂ treatment (CO ₂ processing time Compared to the 0 hour sample), the sealing of the case 110 by the safety valve 140 could be opened at a lower voltage, that is, at a lower temperature.

In the above, the present invention has been described with reference to the first to tenth embodiments. However, the present invention is not limited to the above-described embodiments and the like, and it can be applied as appropriate without departing from the gist thereof. Not too long.
For example, in Examples 1 to 10, CO ₂ may be dissolved in the electrolytic solution. As a result, when the battery temperature rises beyond the normal operating temperature range, CO ₂ gas is released from the electrolytic solution, so that the internal pressure of the case 110 is increased early (at a lower temperature), and early ( The safety valve 140 can be opened (at a lower temperature). Therefore, a lithium ion secondary battery with higher reliability is obtained.

It is sectional drawing of the lithium ion secondary battery 100 concerning Examples 1-9 and the lithium ion secondary battery 200 concerning Example 10. FIG. It is an expanded sectional view of the positive electrode plate 155 (255) of the lithium ion secondary battery 100 (200). It is a block diagram which shows the flow of the manufacturing process concerning Examples 1-7. It is explanatory drawing explaining a positive electrode paste preparation process. It is explanatory drawing explaining an application | coating process. It is explanatory drawing explaining a positive electrode paste drying process. It is explanatory drawing explaining a carbonate production | generation process. It is a table | surface which shows the result of an evaluation test about the lithium ion secondary battery 100,200 concerning Examples 1-10 and the lithium ion secondary battery concerning Comparative Examples 1-4. It is a block diagram which shows the flow of the manufacturing process concerning Examples 8 and 9. FIG. It is a block diagram which shows the flow of the manufacturing process concerning Example 10. FIG. It is a graph which shows the battery temperature change and differential pressure | voltage change in a heating test about the lithium ion secondary battery of an Example, and the lithium ion secondary battery of a comparative example.

Explanation of symbols

100 Lithium ion secondary battery 110 Case 140 Safety valve 150 Electrode body 250 Electrode body 151 Positive electrode base material 152 Positive electrode mixture 152b First cured product 152c First positive electrode paste 252b Second cured product 252c Second positive electrode paste 153 Positive electrode active material 155 Positive electrode Plate 156 Negative electrode plate 158 Carbonate 161 First combined water 162 Second combined water G Gap in case P Valve opening pressure ΔP Differential pressure (differential pressure between internal pressure and external pressure in case)

Claims (18)

A positive electrode plate including a positive electrode mixture containing a positive electrode active material, a negative electrode plate, and an electrode body having a separator;
A case for housing the electrode body;
A safety valve for sealing the case, wherein when the differential pressure between the internal pressure and the external pressure of the case reaches a predetermined valve opening pressure, the case is opened and the gas in the case is discharged A lithium ion secondary battery comprising:
In the case, there is first bound water that desorbs in a temperature range that is higher than a maximum temperature in a normal use temperature range of the lithium ion secondary battery and lower than a decomposition temperature of the positive electrode active material, Including first bound water that generates a first derived gas derived from the first bound water;
The content of the first bound water is
After the temperature of the lithium ion secondary battery exceeds the maximum temperature in the normal use temperature range and before reaching the decomposition temperature of the positive electrode active material, the first derived gas and other gases in the case A lithium ion secondary battery in which the differential pressure is an amount that reaches the valve opening pressure. A positive electrode plate including a positive electrode mixture containing a positive electrode active material, a negative electrode plate, and an electrode body having a separator;
A case for housing the electrode body;
A safety valve for sealing the case, wherein when the differential pressure between the internal pressure and the external pressure of the case reaches a predetermined valve opening pressure, the case is opened and the gas in the case is discharged A lithium ion secondary battery comprising:
The case includes first bound water that desorbs in a temperature range that is higher than a maximum temperature of a normal use temperature range of the lithium ion secondary battery and lower than a decomposition temperature of the positive electrode active material,
The volume of the gap in the case is V (cm ³ ),
The valve opening pressure is P (MPa),
When the content of the first bound water is W (g),
A lithium ion secondary battery satisfying a relationship of W> 7.93 × 10 ⁻³ × V × P. The lithium ion secondary battery according to claim 1 or 2,
A lithium ion secondary battery comprising the first bound water bound to the positive electrode mixture. A positive electrode plate including a positive electrode mixture containing a positive electrode active material, a negative electrode plate, and an electrode body having a separator;
A case for housing the electrode body;
A safety valve for sealing the case, wherein when the differential pressure between the internal pressure and the external pressure of the case reaches a predetermined valve opening pressure, the case is opened and the gas in the case is discharged A lithium ion secondary battery comprising:
The first binding water desorbed in a temperature range higher than the maximum temperature of the normal use temperature range of the lithium ion secondary battery and lower than the decomposition temperature of the positive electrode active material, and bonded to the positive electrode mixture,
Content of the said 1st combined water in the said positive electrode compound material is a lithium ion secondary battery which is 1500 ppm or more in conversion of a weight. The lithium ion secondary battery according to claim 3 or 4,
Second bound water that desorbs at a temperature within the normal use temperature range, bound to the positive electrode mixture,
The lithium ion secondary battery in which the content of the second combined water in the positive electrode mixture is less than 2200 ppm in terms of weight. The lithium ion secondary battery according to any one of claims 1 to 5,
The positive electrode active material is a LiNiO ₂ -based positive electrode active material,
The lithium ion secondary battery, wherein the first bound water is water desorbed in a temperature range higher than 100 ° C and lower than 170 ° C. It is a lithium ion secondary battery as described in any one of Claims 1-6,
Including an electrolytic solution having one or more kinds of organic solvents,
The content of the first bound water is
Before the temperature of the lithium ion secondary battery rises to the boiling point of at least one of the one or more organic solvents, the first derived gas derived from the first combined water in the case and other A lithium ion secondary battery in which an amount of pressure difference between the internal pressure and external pressure of the case reaches the valve opening pressure by gas. The lithium ion secondary battery according to any one of claims 1 to 7,
The positive electrode composite material is a lithium ion secondary battery having a surface coated with carbonate. The lithium ion secondary battery according to claim 8,
The positive electrode plate is
A lithium ion secondary battery comprising carbonate in an amount such that the weight of carbonate ions contained in the carbonate is 0.6 wt% or more and 2.5 wt% or less based on the weight of the positive electrode mixture. A method for producing a lithium ion secondary battery, comprising:
A method for producing a lithium ion secondary battery comprising a step of bringing at least a positive electrode active material into contact with water. It is a manufacturing method of the lithium ion secondary battery according to claim 10,
A method for manufacturing a lithium ion secondary battery comprising a positive electrode paste preparation step of preparing a first positive electrode paste by mixing at least a positive electrode active material, an aqueous binder resin, and water. It is a manufacturing method of the lithium ion secondary battery according to claim 11,
An application step of applying the first positive electrode paste to the surface of the positive electrode substrate;
A positive electrode paste drying step of drying the first positive electrode paste applied to the surface of the positive electrode substrate;
In the positive electrode paste preparation step, at least the positive electrode active material is brought into contact with water, and in the positive electrode paste drying step, the time from the start of drying of the first positive electrode paste is within 8 hours. A method for manufacturing a secondary battery. It is a manufacturing method of the lithium ion secondary battery according to claim 12,
In the positive electrode paste preparation step, at least a positive electrode active material is brought into contact with water, and in the positive electrode paste drying step, the time from the start of drying of the first positive electrode paste is 2 hours or more. A method for manufacturing a secondary battery. A method of manufacturing a lithium ion secondary battery according to claim 12 or claim 13,
After the coating step, the first positive electrode paste is exposed to a gas atmosphere containing CO ₂ to generate carbonate on the surface of the first positive electrode paste, or after the positive electrode paste drying step, Production of a lithium ion secondary battery comprising a carbonate generation step of generating carbonate on the surface of the first cured product by exposing the first cured product obtained by drying and curing the positive electrode paste to a gas atmosphere containing CO ₂ Method. It is a manufacturing method of the lithium ion secondary battery according to claim 10,
An immersion step of immersing the positive electrode active material in water;
A method of manufacturing a lithium ion secondary battery comprising: a positive electrode paste preparation step of preparing a second positive electrode paste by mixing at least a positive electrode active material immersed in water, a solvent-based binder resin, and a solvent. A method of manufacturing a lithium ion secondary battery according to claim 15,
After the immersion step, before the positive electrode paste preparation step, a positive electrode active material drying step for drying the positive electrode active material immersed in the water,
The manufacturing method of the lithium ion secondary battery which makes the time from the time of immersing a positive electrode active material in water in the said immersion process to the start of drying of the said positive electrode active material in the said positive electrode active material drying process within 8 hours. A method of manufacturing a lithium ion secondary battery according to claim 16,
A method for producing a lithium ion secondary battery, wherein the time from when the positive electrode active material is immersed in water in the immersion step to when the positive electrode active material is dried in the positive electrode active material drying step is 2 hours or longer. A method for producing a lithium ion secondary battery according to any one of claims 15 to 17,
After the positive electrode active material drying step, the positive electrode active material is exposed to a gas atmosphere containing CO ₂ to generate carbonate on the surface of the positive electrode active material, or the second positive electrode paste is changed to CO ₂ By exposing to a gas atmosphere containing carbon dioxide on the surface of the material constituting the second positive electrode paste, or by drying and curing the second positive electrode paste, the second cured product is converted into a gas atmosphere containing CO _2. A manufacturing method of a lithium ion secondary battery provided with a carbonate production process which produces carbonate on the surface of the 2nd above-mentioned hardened material by exposing.

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