JP2015118806A - Solvent amount deriving method, solvent amount deriving apparatus, electrode slurry producing method, and electrode slurry producing system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solvent amount deriving technique by which when kneading a powder mixture including active material powder and a conductive assistant, a proper amount of solvent to supply to the powder mixture can be derived efficiently; and an electrode slurry-producing technique which enables the production of an electrode slurry with an active material and a conductive assistant uniformly distributed in solvent by such a solvent amount deriving technique.SOLUTION: A solvent amount deriving method comprises: a compacting step for compacting powder to be measured which is identical in composition with a powder mixture; a cavity volume calculation step of calculating a pore volume of the compacted powder to be measured; and a solvent amount decision step of deciding an amount of solvent based on the pore volume.

Description

  The present invention relates to a solvent amount deriving technique for obtaining an appropriate amount of a solvent to be supplied to a mixed powder when kneading a mixed powder containing a powdered active material and a conductive additive, and electrode slurry preparation using the solvent amount deriving technique It is about technology.

  Lithium secondary batteries are used not only for portable devices such as mobile phones and laptop computers, but also for hybrid vehicles and electric vehicles in recent years as a high-capacity and high-output power source. In the technical field of this type of battery, various techniques have been proposed in order to further improve the performance of the battery (for example, Patent Document 1).

JP 2012-74203 A

  In the invention described in Patent Document 1, the structure of the active material layer is devised to reduce the size and increase the output of the secondary battery, but in order to increase the capacity, the unit volume of the electrode in the secondary battery Attempts have been proposed to increase the amount of active material present at the moment. That is, a battery electrode is formed by dispersing a mixed powder containing a powdered active material and a conductive additive in an appropriate solvent to prepare an electrode slurry, which is applied to a current collector. This electrode slurry is prepared through a kneading step in which a solvent is added to the mixed powder and kneaded, and a dilution step in which the kneaded product obtained by the kneading step is diluted with a solvent. The solvent added to the mixed powder in the kneading step By optimizing the amount, it is possible to prevent the particles from being present in a daisy chain or agglomerated state in the electrode slurry and to disperse the particles uniformly. And the number of active materials per unit volume of an electrode increases by manufacturing an electrode using such an electrode slurry.

  However, the appropriate amount of the solvent to be added during the kneading process largely depends on experience, and has been derived through repeated trial and error. In addition, the appropriate amount often varies depending on the specifications of the active material used and the conductive additive (variety, blending ratio, lot, etc.), and trial and error must be repeated each time the specification is changed, which is wasteful. There were many.

  The present invention has been made in view of the above problems, and can efficiently derive an appropriate amount of a solvent to be supplied to a mixed powder when a mixed powder containing a powdered active material and a conductive additive is kneaded. It is an object of the present invention to provide a solvent amount deriving technique and an electrode slurry producing technique capable of producing an electrode slurry in which an active material and a conductive additive are uniformly dispersed in a solvent using the solvent amount deriving technique.

  A first aspect of the present invention is a method for deriving an amount of solvent for obtaining an amount of a solvent to be supplied to a mixed powder when kneading the mixed powder containing a powdered active material and a conductive additive, and has the same composition as the mixed powder A compression step of compressing the measurement target powder, a void volume calculation step for obtaining a void volume of the compressed measurement target powder, and a solvent amount determination step for determining the amount of the solvent based on the void volume Yes.

  A second aspect of the present invention is an electrode slurry preparation method, wherein an amount of the solvent derived by the solvent amount deriving method is supplied to a mixed powder containing a powdered active material and a conductive additive. A kneading step for kneading and a diluting step for diluting a kneaded product obtained by the kneading step with a solvent to prepare an electrode slurry are characterized.

  According to a third aspect of the present invention, there is provided a solvent amount deriving device for obtaining an amount of a solvent to be supplied to the mixed powder when kneading the mixed powder containing the powdered active material and the conductive auxiliary agent. A container for storing the powder to be measured having the same composition, a compression unit for compressing the powder to be measured contained in the container, a void volume of the powder to be measured compressed by the compression unit, and the amount of the solvent based on the void volume And a solvent amount calculation unit for calculating the value.

  Furthermore, in the fourth aspect of the present invention, a mixed powder containing a powdered active material and a conductive additive and a solvent are kneaded to prepare a kneaded product, and the kneaded product is diluted with a solvent to prepare an electrode slurry. An electrode slurry production system comprising the above-described solvent amount deriving device, wherein an amount of a solvent used when producing a kneaded product is adjusted to an amount derived by the solvent amount deriving device.

  As described above, there is an appropriate value for the amount of the solvent to be added during the kneading process, but no detailed discussion has been made on the reason. Therefore, as will be described in detail later, the present inventor considered the existence state of the solvent between the particles when the solvent was added to the mixed powder, and the particles were observed when the capillary state developed during the kneading process. It was found that the particles can be separated from each other and the particles can be dispersed uniformly. That is, it has been found that the amount of solvent is preferably set so that the voids between the particles are filled with the solvent, and this amount of solvent is an optimum value. The present invention is based on the above findings, and is a state similar to the above-mentioned capillary state (hereinafter referred to as “pseudocapillary”) except that no solvent is present by compressing a powder to be measured having the same composition as the mixed powder. State)). Then, a void volume between particles of the measurement target powder in a pseudo capillary state is obtained, and an appropriate value of the solvent is derived based on the void volume.

  As described above, according to the present invention, the measurement target powder having the same composition as the mixed powder is compressed to form a pseudo capillary state, and the kneading process is performed based on the void volume between the particles of the measurement target powder at that time. The amount of solvent supplied to the mixed powder is derived. For this reason, compared with the case where the amount of solvents is derived by experience and trial and error as in the prior art, the appropriate amount of solvent can be efficiently derived. Further, by using this solvent amount deriving technique, an electrode slurry in which the active material and the conductive additive are uniformly dispersed in the solvent can be produced.

It is a figure showing an electrode slurry preparation system equipped with one embodiment of a solvent amount derivation device concerning the present invention. It is a flowchart which shows operation | movement of the electrode slurry preparation system shown in FIG. It is a figure which shows the relationship between the amount of solvent added to mixed powder, and a volume density.

A. The flow state of particles when a solvent is added to the powder The powder is an aggregate of fine solid particles, and exists in an agglomerated state or a chain of states due to intermolecular forces. When a solvent is added to the powder, the fluidity of the particles varies depending on the amount added. More specifically, when the amount of the solvent to be added is small, the state becomes a pendular state or a funicular state, and friction between particles is relatively large, and fluidity cannot be obtained. Then, as the amount of the solvent to be added increases, the state approaches the capillary state and the flow starts. When the amount of the solvent further increases, the solvent enters all the voids between the particles and reaches the capillary state. In this way, the bonds between the particles can be broken most efficiently from the beginning of the flow. However, when the amount of the solvent to be added is further increased, a slurry state is obtained, friction between particles is reduced, and it becomes difficult to break the bond. And it will flow in the agglomerated state or the daisy chain state.

  Therefore, by adding a solvent in an amount that can realize a capillary state or a state close to it, kneading is performed to separate the particles that existed in a daisy chain or agglomerated state from each other, and to uniformly disperse the particles. It is considered possible. That is, the knowledge that the amount of the solvent is an appropriate amount of the solvent added to the mixed powder during the kneading process was obtained.

  Therefore, the inventor of the present application creates a state in which particles in the mixed powder are densely packed to form a pseudo state close to the capillary state, that is, a state similar to the capillary state except that no solvent is present. It was concluded that the void volume in the state corresponds to the amount of solvent necessary to realize the capillary state in the kneading process. That is, the void volume in a state where the particles are densely packed is obtained, and from this, it has been found that an amount of solvent that can realize a capillary state or a state close thereto can be derived. And based on the said knowledge, when knead | mixing the mixed powder containing a powdery active material material and a conductive support agent, the technique which derives | leads-out efficiently the amount of the solvent supplied to mixed powder was created. Hereinafter, a solvent amount deriving technique based on the above knowledge and a technique for producing an electrode slurry using the technique will be described with reference to the drawings.

B. Embodiment FIG. 1 is a diagram showing an electrode slurry preparation system equipped with an embodiment of a solvent amount deriving device according to the present invention. This electrode slurry preparation system 1 adds a solvent to, for example, a coating solution used when manufacturing an active material layer of a lithium ion secondary battery, that is, a mixed powder obtained by mixing a plurality of types of powders at a desired weight ratio. This is a system for producing a suspension for electrode formation (hereinafter referred to as “electrode slurry”).

The electrode slurry production system 1 is provided with a mixed powder supply device 2 that prepares and supplies mixed powder. The mixed powder supply apparatus 2 has a storage unit 21 that stores a plurality of types of powders in advance in order to produce electrode slurry with various specifications. In the storage unit 21, different powder A, powder B, powder C,... Are stored independently in different powder storage tanks 211, respectively. More specifically, for forming the positive electrode, as the positive electrode active material, for example, a powdered active material mainly composed of LiCoO ₂ (LCO) is stored in the powder storage tank 211. For forming the negative electrode, as the negative electrode active material, for example, a powdered active material mainly composed of Li ₄ Ti ₅ O ₁₂ (LTO) is stored in the powder storage tank 211. Further, powdered acetylene black (AB) and ketjen black as conductive assistants are stored in different powder storage tanks 211, respectively. Further, powder storage tanks 211 in which powdery polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA) and polytetrafluoroethylene (PTFE) are different as binders. Stored in In the present embodiment, the storage unit 21 is preliminarily equipped with the powder storage tank 211 storing the above-described powder. However, the type of the powder is not limited to the above-described one, and is manufactured. It can prepare suitably according to the kind of electrode slurry which should be carried out.

  The mixed powder supply apparatus 2 includes a powder mixing and stirring unit 22 and a control unit 23 in addition to the storage unit 21 described above. The powder mixing and stirring unit 22 has a storage space for temporarily storing powder. Then, the control unit 23 controls a separate charging mechanism (not shown) according to the specification of the electrode slurry instructed by an operator, a host computer, etc., and selects a plurality of types of powders necessary for producing the electrode slurry. In addition, the powder is mixed into the storage space of the powder mixing and stirring unit 22 at a weight ratio that matches the specifications. An agitation mechanism (not shown) is disposed in the accommodation space of the powder mixing and agitation unit 22, and a plurality of types of powders that are input by operating the agitation mechanism in response to an agitation command from the control unit 23. Are uniformly mixed to prepare a mixed powder. The mixed powder thus prepared is supplied to the kneading unit 31 of the kneading device 3 and subjected to the kneading process at the normal time, that is, at the time of preparing the electrode slurry, and the amount of the solvent suitable for the kneading process is derived as described later. When it does, it is supplied to the container 41 of the solvent amount deriving device 4.

  The kneading apparatus 3 includes a solvent storage and supply unit 32 and a control unit 33 in addition to the kneading unit 31 described above. The kneading unit 31 performs a kneading process by adding the solvent supplied from the solvent storage and supply unit 32 to the mixed powder prepared by the powder mixing and stirring unit 22. In the present embodiment, the solvent storage supply unit 32 stores N-methyl-2-pyrrolidone (NMP) as a solvent in advance in a solvent storage tank (not shown), and responds to a supply command given from the control unit 33. The amount is taken out from the solvent storage tank and supplied to the kneading unit 31. Thus, the amount of solvent used for the kneading process can be adjusted by the supply command. This supply command is determined by the control unit 33 based on the solvent amount data derived by the solvent amount deriving device 4, and details thereof will be described later together with the description of the configuration of the solvent amount deriving device 4. Describe.

  When a desired kneaded product (= mixed powder + solvent) is produced by the kneading process by the kneading device 3, the kneaded product is supplied to the diluting device 5. The diluting device 5 dilutes the kneaded material with a solvent to produce an electrode slurry having a desired solid content concentration (55% by weight in the examples later). And the said electrode slurry is apply | coated on a collector as a coating liquid, and an active material layer is formed. In the present embodiment, the kneading device 3 and the diluting device 5 are provided as separate devices, but the kneading process and the diluting process may be executed in this order by one apparatus. That is, instead of providing the kneading device 3 and the diluting device 5, a kneading / diluting device may be provided, and the solvent amount data derived by the solvent amount deriving device 4 when the kneading process is performed by the kneading / diluting device. Based on this, the addition amount of the solvent to the mixed powder may be adjusted.

Next, the configuration of the solvent amount deriving device 4 will be described. The solvent amount deriving device 4 includes a container 41 that accommodates the mixed powder prepared by the powder mixing and stirring unit 22. In the present embodiment, the internal volume of the container 41, that is, the “bulk” is 10.40 [cm ³ ], but is not limited to this value, and an arbitrary size can be adopted.

  In addition to the container 41 described above, the solvent amount deriving device 4 includes a press unit 42 that presses the mixed powder charged in the container 41, a weight measuring unit 43 that measures the weight of the mixed powder stored in the container 41, and a weight. A solvent amount calculation unit 44 that calculates an appropriate value of the solvent during the kneading process based on the measurement result of the measurement unit 43 is provided. In the solvent amount deriving device 4, the pressing unit 42 presses the mixed powder stored in the container 41 after the mixed powder is supplied to the container 41, so that the particles in the mixed powder are in the internal space of the container 41. A state close to the capillary state is formed except that the solvent is not present by creating a densely packed state (hereinafter, this state is referred to as a “pseudo-capillary state”). In the present specification, an object formed by compressing the mixed powder is referred to as a “compressed body”.

  The weight measuring unit 43 measures the weight of the container 41 in an empty state, and measures the weight of the container 41 in a pseudo capillary state, that is, the total weight of the container 41 and the compressed body (mixed powder), thereby calculating the amount of solvent. Part 44 is given. And the solvent amount calculating part 44 calculates | requires the weight of a compression body (mixed powder in the container 41) by subtracting the weight of the container 41 in an empty state from the weight of the container 41 in a filling state.

Although not shown, the solvent amount calculation unit 44 has a memory. The memory stores the true densities ρ _A , ρ _B , ρ _C ,... For each of the powders A, B, C,..., And the powder that composes the electrode slurry for each specification of the electrode slurry. The weight ratio is stored in advance. For example, in order to produce an electrode slurry used to form a positive electrode, the true density of a powdered active material mainly composed of LiCoO ₂ (LCO) is 5.1 [g / cm ³ ], and acetylene is used as a conductive auxiliary agent. 2.0 [g / ^cm 3] as the true density of the black, as the true density of polyvinylidene fluoride (PVDF) [1.78g / cm ^3] it is previously stored in the memory as a binder. In addition, 8: 1.2: 0.8 is stored in the memory as the weight ratio of LiCoO ₂ , acetylene black, and polyvinylidene fluoride.

  The solvent amount calculation unit 44 calculates the volume of the compressed body in a pseudo capillary state based on the weight of the compressed body, the true density of the powder composing the compressed body, and the weight ratio. Further, the void volume is calculated by subtracting the volume of the compressed body from the internal volume of the container 41. Further, the solvent amount calculation unit 44 derives an appropriate amount of the solvent from the void volume, and gives this to the control unit 33 of the kneading apparatus 3 as solvent amount data.

  Next, operation | movement of the electrode slurry preparation system 1 comprised as mentioned above is demonstrated, referring FIG. FIG. 2 is a flowchart showing the operation of the electrode slurry production system shown in FIG. If the specifications of the electrode slurry, that is, the active material used, the type of conductive assistant or binder, the blending ratio, the lot, and the like are different, the amount of solvent suitable for the kneading process often differs. Therefore, in this embodiment, a host computer (not shown) that controls the entire electrode slurry production system 1 determines whether or not the specification of the electrode slurry is changed (step S1). If a specification change occurs ("NO" in step S1), the host computer controls the mixed powder supply device 2 and the solvent amount deriving device 4 as follows to execute the solvent amount deriving process to perform the kneading process. A suitable amount of solvent is derived (step S2).

  In this solvent amount derivation process, the mixed powder supply device 2 prepares a mixed powder according to the changed specifications of the electrode slurry (step S21). In addition, since the mixed powder prepared in this way receives a compression process and a weight measurement process in order to obtain | require the appropriate value of a solvent so that it may demonstrate below, it differs from the mixed powder used in order to produce an electrode slurry. Therefore, the mixed powder used in the solvent amount derivation process is referred to as “measurement target powder”, and is distinguished from the mixed powder used for preparing the electrode slurry. However, it goes without saying that the powder to be measured may be used for electrode slurry preparation after determining the appropriate value of the solvent.

  When the preparation of the measurement target powder is completed, the mixed powder supply device 2 supplies the measurement target powder to the container 41 of the solvent amount deriving device 4 (step S22). In this measurement target powder, the particles exist in an aggregated state or a daisy chain state, and there are many voids. Here, in order to improve the capacity density of the battery, it is important to efficiently destroy the binding and aggregation of particles in the mixed powder by a kneading process, and it is necessary to obtain an appropriate amount of solvent. . Therefore, in the present embodiment, a pseudo capillary state is formed based on the above knowledge. More specifically, the measurement object powder supplied to the container 41 is pressed by the press unit 42 to form a compressed body (step S23). The inside of the compression body thus formed is in a pseudo capillary state.

  Then, the solvent amount calculation unit 44 subtracts the weight of the empty container 41 from the weight of the container 41 in the state in which the compressed body is accommodated (= total weight of the container 41 and the compressed body). The weight X [g] of the powder to be measured) is determined. The mixed powder supply device 2 may measure the amount of the powder to be measured supplied to the container 41, and obtain the weight X [g] based on the measured amount.

により計測対象粉末を構成する粉体Ａ、粉体Ｂ、…、粉体Ｎの体積Ｖｎ（ｎ＝Ａ、Ｂ、…、Ｎ）を求める。 The solvent amount calculation unit 44 obtains the volume V of the measurement target powder from the weight X [g], the true density of each powder stored in the memory, and the weight ratio of the powder composing the electrode slurry. Here, the measurement object powder powder A, powder B, ..., a total of N types of powders in a weight ratio X _A powder _N: X _{B: ...:} If is a mixture with X _N, the following a formula

To obtain the volume Vn (n = A, B,..., N) of the powder A, powder B,.

を実行する。 Further, the volume V of the measurement target powder is obtained by adding these volumes Vn (step S24). That is, the solvent amount calculation unit 44

Execute.

に基づいて擬似キャピラリー状態での粒子間の空隙体積Ｖｐ［ｃｍ^３］を算出する（ステップＳ２５）。 The solvent amount calculation unit 44 subtracts the volume V of the measurement target powder from the internal volume V0 of the container 41, that is, the following formula:

Based on the above, the void volume Vp [cm ³ ] between the particles in the pseudo capillary state is calculated (step S25).

に基づいて得られる溶媒の重量ｍｓを溶媒量データとして制御部３３のメモリ（図示省略）に書き込む（ステップＳ２６）。 By adding a solvent sufficient to fill the voids during the kneading process, a capillary state can be obtained, and particles existing in a daisy chain or agglomerated state can be separated from each other to uniformly disperse the particles. Therefore, the solvent amount calculation unit 44 obtains the solvent weight ms [g] by multiplying the void volume Vp by the solvent density ρs. In other words,

The solvent weight ms obtained based on the above is written in the memory (not shown) of the control unit 33 as solvent amount data (step S26).

  In this way, when the solvent amount data indicating the proper value of the solvent is obtained or when the specification has not changed (“YES” in step S1), the host computer sets the mixed powder supply device 2, the kneading device 3 and the dilution device 5 as follows. The electrode slurry is prepared under the control as described above. That is, the mixed powder supply device 2 prepares a mixed powder according to the specifications of the electrode slurry and supplies it to the kneading part 31 of the kneading device 3 (step S3). And in the kneading apparatus 3, the control part 33 reads the solvent amount data calculated | required by the solvent amount derivation | leading-out process (step S2) from memory (step S4). Then, the control unit 33 gives a supply command to the solvent storage and supply unit 32 to supply an amount of solvent suitable for the kneading process based on the solvent amount data. In response to this supply command, the solvent storage and supply unit 32 supplies the solvent to the kneading unit 31 based on the supply command, and the kneading process in the kneading unit 31 is executed (step S5). For example, when the electrode slurry is prepared with the same amount of mixed powder as the mixed powder in the solvent amount deriving process, the same amount of solvent as that derived in the solvent amount deriving process is transferred from the solvent storage and supply unit 32 to the kneading unit 31. To be supplied. In addition, when the electrode slurry is produced with a mixed powder of an amount different from the mixed powder in the solvent amount derivation process, the amount of solvent supplied from the solvent storage supply unit 32 to the kneading unit 31 is adjusted in consideration of the difference amount. The When the kneading process is completed, the kneading device 3 supplies the kneaded material to the diluting device 5, and dilutes the kneaded material with a solvent to produce an electrode slurry (step S6).

  As described above, according to the present embodiment, the measurement target powder having the same composition as the mixed powder for producing the electrode slurry is prepared, and the measurement target powder is compressed to create a pseudo capillary state. Then, the amount of the solvent supplied to the mixed powder in the kneading process is derived based on the void volume between the particles of the measurement target powder in the pseudo capillary state. For this reason, compared with the case where the amount of solvents is derived by experience and trial and error as in the prior art, the appropriate amount of solvent can be efficiently derived. Further, by using this solvent amount deriving technique, an electrode slurry in which the active material and the conductive additive are uniformly dispersed in the solvent can be produced.

  In the above embodiment, the measurement target powder is compressed to form a compressed body in a pseudo capillary state, and the volume Vp of the measurement target powder is subtracted from the volume V0 of the compression body to obtain the void volume Vp. It is possible to accurately determine the volume Vp. Here, since the measurement target powder is prepared by mixing a plurality of types of powders, in this embodiment, the volume of the measurement target powder is calculated from the weight and true density of each powder contained in the measurement target powder. Yes. Thereby, the volume of the measurement object powder V can be calculated | required correctly. In addition, in order to perform the above calculation process, it is necessary to obtain the weight Xn for each powder, and these may be calculated based on the weight X of the compressed body and the weight ratio of the powder constituting the compressed body. Well, it is possible to accurately determine the weight of each powder.

  Further, regarding the volume of the compressed body, the compressed body may be imaged after compression of the measurement target powder, or the volume may be derived based on the sensed result, that is, the volume derivation process may be executed. When the powder is compressed and the container 41 is filled with the compressed body, the inner volume V0 of the container 41 can be set as the volume of the compressed body, and the above-described volume derivation process becomes unnecessary, which is efficient and accurate. Measurement is possible.

Thus, in this embodiment, the press part 42 is equivalent to an example of the “compression part” of the present invention, and the measurement object powder supplied to the container 41 by the press part 42 is pressed to form a compressed body. The process (step S23) corresponds to an example of the “compression process” of the present invention. Further, the step of calculating the void volume Vp [cm ³ ] (step S25) corresponds to an example of the “void volume calculating step” of the present invention. The step of determining the solvent weight ms as the solvent amount data based on the equation (4) (step S26) corresponds to an example of the “solvent amount determining step” of the present invention.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the above embodiment, the measurement target powder is prepared by the mixed powder supply device 2 that prepares the mixed powder for producing the electrode slurry and is supplied to the solvent amount deriving device 4, but the operator manually measures the measurement target. You may comprise so that powder may be prepared.

  Moreover, in the said embodiment, although the mixed powder supply apparatus 2, the kneading apparatus 3, and the solvent amount deriving device 4 cooperate, the electrode slurry preparation system 1 is comprised so that a solvent amount deriving process and a kneading process may be performed. Alternatively, the solvent amount deriving device 4 may be provided in a form independent and independent from the electrode slurry production system 1 having the mixed powder supply device 2, the kneading device 3, and the dilution device 5. That is, the solvent amount deriving device 4 alone may execute the solvent amount deriving process to derive the solvent amount data, and the operator may input and set the data via the host computer of the electrode slurry preparation system 1. .

  Next, examples of the present invention will be described. However, the present invention is not limited by the following examples. Accordingly, it is of course possible to carry out the present invention with appropriate modifications within a range that can be adapted to the gist of the preceding and following descriptions, all of which are included in the technical scope of the present invention.

Below,
Active material: Lithium cobaltate powder (hereinafter referred to as “powder LCO”)
Conductive aid: Acetylene black powder (hereinafter referred to as “powder AB”)
Binder: Polyvinylidene fluoride powder (hereinafter referred to as “powder PVdF”)
Are stored in the powder storage tank 211, and the weight ratio of each powder is (powder LCO) :( powder AB) :( powder PVdF) = 8: 1.2: 0.8
The mixed powder 20 [g] mixed in the above is prepared, and this is used as the measurement target powder. In this case, the weights of the powder LCO, the powder AB, and the powder PVdF are 16 [g], 2.4 [g], and 1.6 [g], respectively. The true densities of the powder LCO, the powder AB, and the powder PVdF are 5.1 [g / cm ³ ], 2.0 [g / cm ³ ], and 1.78 [g / cm ³ ], respectively. .

The 20 [g] powder to be measured was filled into a container having a bulk (internal volume) of 10.40 [cm ³ ] and pressed to form a compressed body. Here, the volume of the compression body is the same as the inner volume of the container, and is 10.40 [cm ³ ]. On the other hand, the volume of the powder LCO in the measurement target powder is 16 [g] /5.1 [g / cm ³ ] = 3.14 [cm ³ ].
The volume of the powder AB is 2.4 [g] ÷ 2.0 [g / cm ³ ] = 1.2 [cm ³ ]
The volume of the powder PVdF is 1.6 [g] ÷ 1.78 [g / cm ³ ] = 0.9 [cm ³ ].
The volume of the powder to be measured is 5.24 (= 3.14 + 1.2 + 0.9) [cm ³ ]. Therefore, the void volume existing in the compressed body is 10.40-5.24 = 5.16 [cm ³ ].
It can be seen that it is.

When N-methyl-2-pyrrolidone (NMP) having a density satisfying the void volume is an appropriate value and density ρs = 1.03 [g / cm ³ ] is used as a solvent, the weight of the solvent ms is 5.16 [cm ³ ] × 1.03 [g / cm ³ ] = 5.31 [g]
It becomes.

An amount of the solvent (NMP) thus obtained is added to the mixed powder 20 [g] having the above composition and kneaded to prepare a kneaded product. The solid content concentration in the kneaded product corresponds to 79 [wt%]. Furthermore, the kneaded product was diluted with 11.05 [g] of a solvent (NMP) to reduce the solid content concentration from 79 to 55 [wt%] to prepare an electrode slurry. And the said electrode slurry was apply | coated on the electrical power collector with the predetermined amount of an amount, and after drying, it pressed at 30 [MPa] and formed the active material layer, and formed the positive electrode. The weight per unit area is the weight of the electrode paste per unit area, and is a weight per unit area that provides a capacity of 1.5 [mAh / cm ² ]. And the electrode of (phi) 14 [mm] was punched out from the said positive electrode, the weight and the film thickness were measured, and capacity density [mAh / cm < ³ >] was computed from them. As a result, capacity density = 288 [mAh / cm ³ ] was obtained.

  As described above, when the active material layer is formed using the electrode slurry kneaded with the solvent amount obtained by using the solvent amount deriving technique according to the present invention, the active material layer has an excellent capacity density. High capacity is possible.

  In the above examples, the kneading process is performed by adding a solvent corresponding to the void volume of the mixed powder. However, the kneading process is performed by changing only the addition amount of the solvent, and the volume density is obtained in the same manner as described above. The result shown in FIG. 3 was obtained. (1)-(7) in the same figure has shown the Example of a different amount of solvent, respectively.

  Example (4) in the figure is the result of the above example (solvent amount = 5.31 [g]). Examples (1) to (3) and (5) to (7) in the figure are the same. Kneaded by adding 2.22 [g], 3.53 [g], 5 [g], 6.67 [g], 10.77 [g] and 16.36 [g] respectively to the solvent (NMP). The result of processing is shown. The sum of the solvents added in the kneading process and the dilution process is unified to 16.36 [g], and in any of the examples, the dilution process is performed so that the final solid content concentration is 55 [wt%]. The amount of solvent to be added was adjusted. This is for the following reason. That is, if it is smaller than 55 [wt%], the viscosity of the electrode slurry (coating liquid) becomes small, the coated film after coating spreads along the surface of the flat electrode, and an active material layer with a desired film thickness cannot be obtained. On the other hand, when it is larger than 55 [wt%], the viscosity increases, and the surface of the coating film has an uneven shape. Therefore, in order not to cause these problems, the solid content concentration of the electrode slurry is adjusted to 55 [wt%].

As is clear from FIG. 3, an active material layer having an excellent capacity density can be obtained by adding an amount of solvent that completely fills the void volume of the mixed powder and performing kneading, and the amount of solvent added during kneading Even if fluctuates slightly, an active material layer having a high capacity density can be obtained. However, from the viewpoint of increasing the capacity of the secondary battery, a capacity density of 270 [mAh / cm ³ ] or more is often required at present, and the implementation in FIG. 3 is performed from the viewpoint of satisfying this technical requirement. Examples (3) to (6) are preferred, and the amount of solvent is set so that the solid content concentration in the kneaded product obtained by kneading treatment is 65 [wt%] to 80 [wt%]. desirable.

  The present invention relates to a solvent amount deriving technique for obtaining an appropriate amount of a solvent to be supplied to a mixed powder when kneading a mixed powder containing a powdered active material and a conductive additive, and electrode slurry preparation using the solvent amount deriving technique It can be suitably applied to technology.

DESCRIPTION OF SYMBOLS 1 ... Electrode slurry preparation system 3 ... Kneading apparatus 4 ... Solvent amount deriving apparatus 5 ... Dilution apparatus 41 ... Container 42 ... Press part (compression part)
44 ... Amount of solvent calculation unit

Claims (10)

A solvent amount derivation method for obtaining an amount of a solvent to be supplied to the mixed powder when kneading the mixed powder containing the powdered active material and the conductive auxiliary agent,
A compression step of compressing the powder to be measured having the same composition as the mixed powder;
A void volume calculating step for obtaining a void volume of the compressed powder to be measured;
And a solvent amount determining step for determining the amount of the solvent based on the void volume. The solvent amount derivation method according to claim 1,
In the compression step, the measurement object powder is compressed to form a compressed body,
In the void volume calculation step, a solvent amount derivation method for obtaining the void volume by subtracting the volume of the powder to be measured from the volume of the compressed body. The solvent amount derivation method according to claim 2,
In the void volume calculation step, a solvent amount derivation method for calculating the volume of the measurement target powder from the weight and true density of each powder contained in the measurement target powder. The solvent amount derivation method according to claim 3,
In the void volume calculation step, a solvent amount derivation method of calculating a weight for each powder based on a weight of the compressed body and a weight ratio of the powder in the powder to be measured. A solvent amount deriving method according to any one of claims 1 to 4,
In the compression step, the measurement object powder is compressed in a container to fill the container with the compressed body,
In the void volume calculation step, a solvent amount derivation method of calculating the void volume using the internal volume of the container as the volume of the compressed body. A kneading step of supplying and kneading the amount of solvent derived by the solvent amount deriving method according to any one of claims 1 to 5 to a mixed powder containing a powdered active material and a conductive aid;
And a dilution step of preparing an electrode slurry by diluting the kneaded product obtained in the kneading step with the solvent. It is an electrode slurry preparation method of Claim 6, Comprising:
The method of preparing an electrode slurry, wherein the mixed powder is a mixture of a lithium cobaltate powder as the active material, an acetylene black powder as the conductive additive, and a polyvinylidene fluoride powder as a binder. The electrode slurry preparation method according to claim 7,
In the kneading step, an electrode slurry preparation method in which the concentration of the powder in the kneaded product is adjusted to 65 [wt%] to 80 [wt%]. A solvent amount deriving device for obtaining an amount of a solvent to be supplied to the mixed powder when kneading the mixed powder containing the powdered active material and the conductive auxiliary agent,
A container for storing a powder to be measured having the same composition as the mixed powder;
A compressing unit that compresses the powder to be measured contained in the container;
A solvent amount deriving device comprising: a solvent amount calculation unit that obtains a void volume of the measurement target powder compressed by the compression unit and calculates the amount of the solvent based on the void volume. An electrode slurry preparation system for preparing an electrode slurry by kneading a mixed powder containing a powdered active material and a conductive additive and a solvent to prepare a kneaded product, and diluting the kneaded product with the solvent,
A solvent amount deriving device according to claim 9,
An electrode slurry preparation system, wherein the amount of the solvent used when preparing the kneaded product is adjusted to the amount derived by the solvent amount deriving device.

Images