JP2022120609A - MEASURING METHOD FOR Li AMOUNT ON ACTIVE MATERIAL POWDER SURFACE AND MANUFACTURING METHOD FOR ACTIVE MATERIAL POWDER CONTAINING FILM - Google Patents

Abstract

To provide a measuring method, etc., for measuring the amount of Li on the surface of particles of an active material powder that can appropriately measure the amount of Li included in a surface Li compound layer concerning the active material powder in which positive electrode active material particles are assembled.SOLUTION: A measuring method for the amount of Li on a surface 21m of a particle of an active material powder 10 in which positive active material particles 20 are assembled is for measuring an amount WL of Li contained in a surface Li compound layer 23 in the active material powder 10 per unit weight. The measuring method for the amount of Li on the surface 21m of a particle of the active material powder 10 includes an immersion step S11 for immersing into water 100 a sample powder 10S, which is a portion of the active material powder 10 to solve the surface Li compound layer 23 into the water 100, a filtration step S12 for filtrating a mixed solution 110 obtained in the immersion step S11, and a measuring step S13 for measuring the amount WL of Li contained in a filtrate 120 obtained in the filtration step S12.SELECTED DRAWING: Figure 3

Description

The present invention provides a Li amount measuring method for measuring the amount of Li contained in a surface Li compound layer present on the surface of an active material powder in which positive electrode active material particles are aggregated, and an active material powder in which positive electrode active material particles are aggregated. and relates to a method for producing a film-containing active material powder in which film-containing positive electrode active material particles are aggregated.

Li (lithium), P (phosphorus) and O A coating-containing active material powder is known in which coated positive electrode active material particles forming an amorphous LPO coating containing (oxygen) are aggregated. A battery manufactured using such a coating-containing active material powder can have a lower battery resistance than a battery using an active material powder in which positive electrode active material particles without an amorphous LPO coating are aggregated.

This coating-containing active material powder is produced, for example, by the following method. That is, an active material powder is prepared in which positive electrode active material particles having a surface Li compound layer containing LiOH (lithium hydroxide) and Li ₂ CO ₃ (lithium carbonate) on the particle surface of the particle body made of the positive electrode active material are aggregated. do. Separately, a P-containing treatment liquid is prepared by dissolving a phosphorus compound such as H ₃ PO ₄ (orthophosphoric acid) in water. Then, these active material powders and a treatment liquid containing P are mixed to form an amorphous LPO coating from the surface Li compound layer, and coated positive electrode active material particles having the amorphous LPO coating on the particle surface are obtained. Aggregated film-containing active material powder is obtained. Incidentally, Patent Document 1 can be cited as a conventional technique related to this technique.

JP 2019-153462 A

As a result of investigation by the present inventors, the magnitude of the battery resistance differs depending on the amount of P added to the active material powder when producing the coating-containing active material powder from the active material powder. Specifically, when the amount of P to be added is set to an appropriate value, the battery resistance is the lowest, and the battery resistance increases regardless of whether the amount of P is less than or greater than this value. Specifically, the battery resistance is lowest when the Li contained in the surface Li compound layer of the active material powder and the P contained in the treatment liquid react just enough to form an amorphous LPO film. . Since the amorphous LPO coating is mainly represented by the composition of Li ₃ PO ₄ , the molar ratio of Li contained in the surface Li compound layer of the active material powder and P contained in the treatment liquid is 3:1. It has been found that the battery resistance becomes the lowest when .

Furthermore, as a result of investigation by the present inventors, the amount of Li contained in the surface Li compound layer of the active material powder varies depending on the lot of the active material powder. For this reason, in the method of forming an amorphous LPO film by mixing a treatment liquid containing a predetermined amount of P uniformly into the active material powder, the amount of P may be too small or too large depending on the lot of the active material powder. or Therefore, when a battery is manufactured using the film-containing active material powder produced from this active material powder, the battery resistance may not be appropriately reduced.

Therefore, the present inventor previously measured the amount of Li contained in the surface Li compound layer of the active material powder, for example, for each lot of the active material powder, and based on the measured amount of Li, the amount of P was mixed with the active material powder to form an amorphous LPO coating from the surface Li compound layer. Specifically, the active material powder is immersed in water to dissolve the surface Li compound layer in water. Subsequently, an attempt was made to measure the amount of Li contained in this mixed solution, for example, by neutralization titration using HCl (hydrochloric acid). However, when the active material powder is immersed in water for a long period of time, Li seeping from the inside of the particle body to the particle surface dissolves in water, so the measured Li amount is contained in the surface Li compound layer. It becomes more than the amount of Li.

The present invention has been made in view of this situation, and the particle surface of the active material powder that can appropriately measure the amount of Li contained in the surface Li compound layer for the active material powder in which the positive electrode active material particles are aggregated. and a film-containing active material powder that can produce a film-containing active material powder with low battery resistance by appropriately measuring the Li amount contained in the surface Li compound layer of the active material powder. A manufacturing method is provided.

One aspect of the present invention for solving the above problems is a particle body made of a positive electrode active material capable of absorbing and desorbing lithium ions, and a surface containing LiOH and Li ₂ CO ₃ present on the particle surface of the particle body. The amount of Li contained in the surface Li compound layer in the active material powder per unit weight is measured for an active material powder in which positive electrode active material particles having a Li compound layer are aggregated. A method for measuring the amount of Li on the surface of a particle, comprising: an immersion step of immersing part of the sample powder of the active material powder in water, and dissolving the surface Li compound layer in the water; A method for measuring the amount of Li on the surface of particles of active material powder, comprising: a filtering step of filtering a mixed liquid; and a measuring step of measuring the amount of Li contained in the filtrate obtained in the filtering step.

In the above-described method for measuring the amount of Li on the surface of the active material powder, first, a sample powder of a part of the active material powder is immersed in water, and after dissolving the surface Li compound layer in water (immersion step), The mixed solution is filtered (filtration step). Filtration in this way can prevent Li from oozing out from the inside of the particle body to the particle surface and dissolving in water. Therefore, by measuring the amount of Li contained in this filtrate, the amount of Li contained in the surface Li compound layer in the active material powder per unit weight can be appropriately measured.

In the "measurement step", as a specific method for measuring the amount of Li contained in the filtrate, for example, a method of measuring the amount of Li by neutralization titration using an acid such as HCl, A technique of measuring the amount of Li by ICP is exemplified.
Examples of the "positive electrode active material" include lithium transition metal oxides. Examples of lithium transition metal oxides include lithium-nickel composite oxides (eg, LiNiO ₂ ), lithium-cobalt composite oxides (eg, LiCoO ₂ ), lithium-manganese composite oxides (eg, LiMn ₂ O ₄ ), and lithium-nickel-cobalt-manganese composite oxides. ternary lithium transition metal oxides such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ . Furthermore, examples of lithium transition metal oxides include phosphates containing lithium and transition metal elements, such as lithium manganese phosphate (eg, LiMnPO ₄ ) and lithium iron phosphate (eg, LiFePO ₄ ).

In another aspect, a particle body made of a positive electrode active material capable of absorbing and desorbing lithium ions, and an amorphous amorphous LPO coating formed on the particle surface of the particle body and containing Li, P, and O A method for producing a film-containing active material powder in which the film-coated positive electrode active material particles are aggregated, wherein the above-mentioned active material powder per unit weight is measured by the Li amount measurement method on the particle surface of the active material powder a Li amount measuring step of measuring the amount of Li contained in the surface Li compound layer in the body; and a coating forming step of forming the amorphous LPO coating from the surface Li compound layer. , the minimum amount of P required to convert the total amount of the surface Li compound layer into the amorphous LPO coating in the active material powder treated in the coating forming step, based on the measured Li amount. A method for producing a coating-containing active material powder, comprising mixing a treatment liquid with the active material powder to form the amorphous LPO coating.

In the method for producing the coating-containing active material powder described above, the Li amount contained in the surface Li compound layer in the active material powder per unit weight is measured by the Li amount measurement method described above (Li amount measurement step), and then , forming an amorphous LPO film from the surface Li compound layer based on the measured Li amount (film forming step). Specifically, the active material powder is mixed with a treatment liquid containing the minimum amount (necessary amount) of P required to convert the entire amount of the surface Li compound layer into an amorphous LPO coating, to form an amorphous LPO coating. Form an LPO coating. As a result, it is possible to obtain a film-containing active material powder in which almost no surface Li compound layer remains and little excess P is contained. If a battery is manufactured using this film-containing active material powder, the battery resistance can be further reduced.

Examples of the "amorphous LPO coating" include compositions such as lithium phosphate _{( Li3PO4} ), dilithium hydrogen phosphate _{( Li2HPO4} ), and lithium dihydrogen phosphate _{( LiH2PO4} ). Amorphous coatings containing Li, P and O represented by are exemplified.
Examples of the "treatment liquid containing P" include diphosphorus pentoxide ₍ P2O5) (tetraphosphorus _decaoxide ( _P4O10 )), orthophosphoric acid _{( H3PO4} ), pyrophosphoric acid _{( H4P 2} O ₇ ), triphosphoric acid (H ₅ P ₃ O ₁₀ ), polyphosphoric acid (HO(HPO ₃ ) _n H), lithium phosphate (Li ₃ PO ₄ ), lithium hydrogen phosphate (Li ₂ HPO ₄ ), etc. is dissolved or dispersed in a solvent such as alcohol such as 2-propanol (isopropyl alcohol, IPA), N-methylpyrrolidone (NMP), or water.

1 is a schematic cross-sectional view of a positive electrode active material particle with a film forming a film-containing active material powder according to an embodiment; FIG. 1 is a schematic cross-sectional view of positive electrode active material particles forming active material powder according to an embodiment. FIG. 1 is a flow chart of a method for producing a coating-containing active material powder including a method for measuring the amount of Li on the surface of a particle of the active material powder, according to an embodiment. FIG. 4 is an explanatory diagram schematically showing an immersion process according to the embodiment; FIG. 4 is an explanatory diagram schematically showing a film forming process according to the embodiment; It is a neutralization titration curve which shows typically the relationship between the dripping amount of HCl, and pH of a filtrate. Fig. 2 is a neutralization titration curve showing the relationship between the amount of HCl added dropwise and the pH of a filtrate (mixed liquid in the comparative example) in Examples and Comparative Examples. 4 is a graph showing the relationship between the amount WP of P added in the film forming step and the battery resistance ratio.

(embodiment)
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 schematically shows a cross-sectional view of a coated cathode active material particle 40 according to this embodiment. The film-containing active material powder 30 in which the film-coated positive electrode active material particles 40 are aggregated is used for the positive electrode active material layer of the positive electrode plate constituting the lithium ion secondary battery. The coated positive electrode active material particles 40 include a particle body 21 made of a positive electrode active material capable of absorbing and releasing lithium ions, and an amorphous LPO coating 43 formed on the particle surface 21m of the particle body 21 .

In this embodiment, the median diameter _D50 of the coated positive electrode active material particles 40 is about 5 μm. The positive electrode active material forming the particle body 21 is a lithium transition metal oxide, specifically a lithium-nickel-cobalt-manganese composite oxide (more specifically, LiNi _0.2 Co _0.5 Mn _0.3 O ₂ ). On the other hand, the amorphous LPO coating 43 is considered to be an amorphous LPO coating containing Li, P and O, specifically, an amorphous coating whose composition is mainly Li ₃ PO ₄ . A plurality of amorphous LPO coatings 43 are formed in a sea-island pattern on a portion of the grain surface 21m of the grain body 21, more specifically, on a portion of the edge surface 21ma of the grain surface 21m. Each amorphous LPO coating 43 is a coating formed from the surface Li compound layer 23 (see FIG. 2) of the positive electrode active material particle 20, which will be described later. The thickness of each amorphous LPO coating 43 is about 0.2 nm.

Next, a method for manufacturing the film-containing active material powder 30 will be described (see FIGS. 2 to 7). First, an active material powder 10 in which positive electrode active material particles 20 are aggregated is prepared (see FIG. 2). The positive electrode active material particles ₂₀ are particles having a _{median diameter D 50} of about 5 μm. and a surface Li compound layer 23 present on the particle surface 21m of the This surface Li compound layer 23 originates from excess Li contained in the positive electrode active material forming the particle body 21, and is mainly composed of LiOH, and is considered to contain a small amount of Li ₂ CO ₃ (calculated as Li LiOH is 90% or more and Li ₂ CO ₃ is less than 10%). A plurality of surface Li compound layers 23 are present in a sea-island pattern on the edge surface 21ma of the particle surface 21m.

Next, in the “Li amount measurement step S1” (see FIG. 3), the Li amount WL (wt %) contained in the surface Li compound layer 23 in the active material powder 10 per unit weight is measured. In the Li amount measurement step S1, the "immersion step S11", the "filtration step S12" and the "measurement step S13" are performed in this order.
First, in the immersion step S11, a part of the sample powder 10S of the active material powder 10 is immersed in water 100 to dissolve the surface Li compound layer 23 in the water 100 (see FIG. 4). In this embodiment, 100 ml of water 100 is placed in a beaker, 10.0 g of sample powder 10S is added thereto, and stirred and mixed for 1 minute using a magnetic stirrer. This stirring and mixing may be performed using a device other than the magnetic stirrer (such as a glass rod) or a stirring device. As a result, the surface Li compound layer 23 (LiOH and Li ₂ CO ₃ ) contained in the sample powder 10S is dissolved in the water 100 to form an aqueous solution that becomes the filtrate 120 in the next step. Note that the amount of the sample powder 10S to be immersed in the water 100 is not limited to 10.0 g, and can be changed as appropriate.

Subsequently, in the filtration step S12, the mixture 110 obtained in the above-described immersion step S11 is filtered using a filter paper (not shown), and the sample powder 10S (the particle bodies 21 without the surface Li compound layer 23 are aggregated active material powder) and a filtrate 120 (a solution of LiOH and Li ₂ CO ₃ dissolved in water 100).

Next, in the measurement step S13, the filtrate 120 obtained in the filtration step S12 described above is subjected to neutralization titration using HCl (hydrochloric acid) to measure the Li amount WL contained in the filtrate 120 (Fig. 6 and Figure 7). In addition, the neutralization titration curve of FIG. 6 is shown schematically in an easy-to-understand manner for explaining the neutralization titration according to the present embodiment, and the neutralization titration curve of the example of FIG. It is based on the results of performing neutralization titration on the liquid 120 .

In the present embodiment, neutralization titration is performed in two steps of neutralization of LiOH and HCl and neutralization of Li ₂ CO ₃ and HCl, and the Li amount WL contained in the filtrate 120 is determined by LiOH-derived The amount of Li WLa and the amount of Li derived from Li ₂ CO ₃ WLb were separately measured (WL=WLa+WLb). Specifically, when Li ₂ CO ₃ contained in the surface Li compound layer 23 is dissolved in 100 water, it becomes Li ₂ CO ₃ →2Li ⁺ +CO ₃ ^2- , but CO ₃ ^2- (carbonate ion) When the pH of the filtrate 120 is about pH=8 or higher, CO ₃ ^2- +H ⁺ →HCO ₃ ^- , and when pH=about 4 to about 8, HCO ₃ ^- +H ⁺ →H ₂ O+CO ₂ ↑. . Since CO ₃ ²⁻ consumes H ⁺ in the filtrate 120 in this way, the pH of the filtrate 120 fluctuates accordingly. Therefore, in the method of simply adding HCl dropwise to the filtrate 120 _, the neutralization of LiOH and HCl and the neutralization of Li ₂ CO ₃ and HCl occur in parallel _. and HCl cannot be separated into two stages.

Therefore, in this embodiment, 2 ml of a 10% BaCl ₂ aqueous solution is added to the filtrate 120 prior to neutralization titration. This masks CO ₃ ^2- . That is _, Li ₂ CO ₃ becomes Li ₂ CO ₃ + ^BaCl ₂ →2LiCl+BaCO ₃ ↓ and becomes a precipitate of BaCO ₃ (barium carbonate). By doing so, in the subsequent neutralization titration, LiOH and HCl are neutralized (LiOH+HCl→LiCl+H ₂ O) up to the neutralization point A, as shown in FIG. Subsequently, from neutralization point A to neutralization point B, neutralization of Li ₂ CO ₃ and HCl (Li ₂ CO ₃ +2HCl→2Li ⁺ +H ₂ O+CO ₂ ↑) occurs (neutralization occurs in two stages). separate). Specifically, up to the neutralization point A, Li ₂ CO ₃ is Li ₂ CO ₃ +BaCl ₂ →2LiCl+BaCO ₃ as described above. This BaCO ₃ reacts with further dropwise HCl from neutralization point A to neutralization point B, resulting in BaCO ₃ +2HCl→BaCl ₂ +H ₂ O+CO ₂ ↑.

In the neutralization titration, in this embodiment, the filtrate 120 placed in a beaker is stirred with a magnetic stirrer, and while measuring the pH of the filtrate 120 with a pH meter, 25 μl of 1.0 M HCl is added at intervals of 30 seconds. added. An example of the results of this neutralization titration is shown in FIG. 7 (Example). As described above, the Li amount WL contained in the surface Li compound layer 23 of the active material powder 10 differs depending on the lot of the active material powder 10 .
In the example shown in FIG. 7, a dropping amount of Ta=0.325 ml of 1.0 M HCl was required until the neutralization point A at which the neutralization of LiOH and HCl was completed. Further, from the neutralization point A to the neutralization point B at which the neutralization of Li ₂ CO ₃ and HCl is completed, a further dropping amount Tb = 0.025 ml of 1.0 M HCl was required (dripping up to the neutralization point B The total volume is 0.325 + 0.025 = 0.350 ml). The reason why the neutralization titration curve in FIG. 7 is not clearly divided into two stages like the neutralization titration curve in FIG. 6 is that the amount of Li ₂ CO ₃ contained in the filtrate 120 is small. be. Therefore, the drop amount Tb from the neutralization point A to the neutralization point B was set to the drop amount for one neutralization titration (Tb=25 μl=0.025 ml).

Next, based on the results of the neutralization titration described above, the LiOH amount Wa (wt%) and the Li ₂ CO ₃ amount Wb (wt %) are calculated using the following calculation formulas (1) and (2), respectively.
Wa (wt%) = Ta x (Mc/1000) x Fc x Mra x (1/m) x 100 (1)
Wb (wt%) = (Tb/2) x (Mc/1000) x Fc x Mrb x (1/m) x 100 (2)
Ta (ml): the dropwise amount of HCl required to reach the neutralization point A;
Tb (ml): the amount of HCl dropped from neutralization point A to neutralization point B;
Mc (M, mol/L): concentration of HCl (Mc = 1.0 M in this embodiment),
Fc: concentration factor (Fc=1.01 in this embodiment);
Mra (g/mol): molecular weight of LiOH (Mra = 23.95 g/mol),
Mrb (g/mol): molecular weight of _{Li2CO3 (} Mrb=73.89 g/mol);
m (g): amount of sample powder 10S used (m=10.0 g in this embodiment).

In the example shown in FIG. 7, as described above, the amount Ta of HCl dropped up to the neutralization point A is Ta=0.325 ml. The amount of LiOH Wa is Wa = 0.325 x (1.0/1000) x 1.01 x 23.95 x (1/10.0) x 100 = 0.079 wt% with respect to the active material powder 10. be. Further, since the amount Tb of HCl dripping required from the neutralization point A to the neutralization point B is Tb=0.025 ml, the amount Wb of Li ₂ CO ₃ contained in the surface Li compound layer 23 of the active material powder 10 is , with respect to the active material powder 10, Wb = (0.025/2) x (1.0/1000) x 1.01 x 73.89 x (1/10.0) x 100 = 0.0093 wt% be.

Also, the Li amount WL (wt %) contained in the surface Li compound layer 23 of the active material powder 10 (sample powder 10S) is calculated using the following calculation formula (3).
WL (wt%)=WLa+WLb=Wa×(Mrl/Mra)+Wb×(2×Mrl/Mrb) (3)
WLa (wt%): amount of Li derived from LiOH WLb (wt%): amount of Li derived from _{Li2CO3 Mrl} (g/mol): atomic weight of Li (Mrl = 6.94 g/mol).

In the example shown in FIG. 7, the Li amount WL contained in the surface Li compound layer 23 of the active material powder 10 is WL=0.079×(6.94/23.95 ) + 0.0093 x (2 x 6.94/73.89) = 0.023 + 0.0017 = 0.025 wt%.
Therefore, in the example of FIG. 7, the Li amount WL contained in the surface Li compound layer 23 on the particle surface 21m is 0.025 g per 100 g of the active material powder 10, for example.
As can be seen from the above calculation, the Li amount WLa derived from LiOH is WLa=0.023 wt %, and the Li amount WLb derived from Li ₂ CO ₃ is WLb=0.0017 wt %. Among them, the ratio of LiOH is WLa/WL×100=approximately 93%, and the ratio of Li ₂ CO ₃ is WLb/WL×100=approximately 7% in terms of Li.

In this embodiment, as described above, the aqueous solution of BaCl ₂ is added to the filtrate 120 to separate the neutralization of LiOH and the neutralization of Li ₂ CO ₃ . A neutralization titration may be performed. That is, neutralization titration is performed on the filtrate 120 without adding the BaCl ₂ aqueous solution to the filtrate 120 after the filtration step S12. In this case, the active material powder 10 used in the example of FIG. 7 requires 1.0 M HCl of a dropping amount Tc=0.350 ml (=Ta+Tb=0.325+0.025) until the completion of neutralization. In this case, the Li amount WL (wt %) contained in the surface Li compound layer 23 of the active material powder 10 is calculated using the following calculation formula (4).
WL (wt%) = Tc x (Mc/1000) x Fc x Mrl x (1/m) x 100 (4)
In this example, Li amount WL = 0.350 × (1.0/1000) × 1.01 × 6.94 × (1/10.0) × 100 = 0.025 wt%, neutralization in two stages You get the same value as if you split it.

Here, as a comparative example, a case where the measurement step S13 is performed following the immersion step S11 without performing the filtering step S12 will be described (see the comparative example in FIG. 7). In this comparative example, the drop amount Ta of HCl required to neutralize point A was Ta=0.600 ml, and the drop amount Tb of HCl required from neutral point A to neutral point B was Tb=0.125 ml. (Total amount of drops up to neutral point B is 0.600+0.125=0.725 ml).
Therefore, the amount of LiOH Wa is Wa=0.600×(1.0/1000)×1.01×23.95×(1/10.0)×100=0.600×(1.0/1000)×1.01×23.95×(1/10.0)×100=0. 15 wt %.
Further, the Li ₂ CO ₃ amount Wb is Wb=(0.125/2)×(1.0/1000)×1.01×73.89×(1/10. 0)×100=0.047 wt %.
Furthermore, the Li amount WL contained in the surface Li compound layer 23 of the active material powder 10 (sample powder 10S) is WL=0.15×(6.94/23.95) from the above-described calculation formula (3). ) + 0.047 x (2 x 6.94/73.89) = 0.043 + 0.0088 = 0.052 wt%.

The reason why the Li amount WL measured using the active material powder 10 of the same lot was WL=0.025 wt% in the example and increased to WL=0.052 wt% in the comparative example is that In the example, since the measurement step S13 is performed following the immersion step S11 without performing the filtration step S12, Li is eluted from the particle body 21 into the mixed liquid 110 during the measurement step S13 (during neutralization titration). . For this reason, not only Li contained in the surface Li compound layer 23 but also Li eluted from the inside of the particle body 21 into the mixed liquid 110 is consumed in neutralization titration. From this result, it can be seen that only Li contained in the surface Li compound layer 23 can be appropriately measured by performing the filtering step S12 as in the example.

Next, in the “coating step S2” (see FIG. 3), the active material powder 10 and the treatment liquid 150 containing P are mixed to form the active material powder 10, and the Li compound on the surface of the positive electrode active material particles 20 is formed. An amorphous LPO coating 43 is formed from the layer 23 to obtain the coating-containing active material powder 30 in which the coated cathode active material particles 40 are aggregated (see FIG. 5).

First, the minimum amount of P required to convert the entire surface Li compound layer 23 into the amorphous LPO coating 43 in the active material powder 10 to be treated in the coating forming step S2 is determined. In the active material powder 10 used in FIG. 7, as described above, the Li amount WL contained in the surface Li compound layer 23 is WL=0.025 wt %. On the other hand, since the amorphous LPO coating 43 is mainly represented by the composition of Li ₃ PO ₄ , the required minimum amount of P WP (wt%) is calculated using the following formula (5). .
WP (wt%)=(WL/3)×(Mrp/Mrl) (5)
Mrp (g/mol): atomic weight of P (Mrp = 30.97 g/mol).
In this example, the P amount WP=(0.025/3)×(30.97/6.94)=0.037 wt %.

Therefore, in the present embodiment, P ₂ O ₅ is dissolved in IPA so that the P content becomes 0.037 wt % in terms of P, thereby obtaining a treatment liquid 150 containing P. Then, for example, 100 g of the active material powder 10 is added with the same amount of 100 g of the treatment liquid 150 as the active material powder 10, and this mixture is mixed for 3 minutes in a planetary mixer to obtain the surface Li compound layer 23 and the treatment liquid 150. phosphate ions to form an amorphous LPO film 43 from the surface Li compound layer 23 . Thereafter, this mixture is heated to 80° C. and dried to obtain coating-containing active material powder 30 in which coating-coated positive electrode active material particles 40 are aggregated. By doing so, theoretically, the entire amount of the surface Li compound layer 23 becomes the amorphous LPO film 43 , and excessive P is not included in the film-containing active material powder 30 .

(Test results)
Next, the results of tests conducted to verify the effects of the present invention will be described (see FIG. 8). Using the active material powder 10 shown in FIG. 7, the P amount WP added to the active material powder 10 in the film forming step S2 was 0 wt% (no P added), 0.009 wt%, and 0.015 wt%. , 0.018 wt %, 0.027 wt %, 0.044 wt %, or 0.073 wt %, and the coating-containing active material powders 30 were produced in the same manner as in the embodiment.

Next, each of these film-containing active material powders 30 was used to fabricate a laminate cell type lithium ion battery (not shown). That is, using the film-containing active material powder 30, a positive electrode plate is produced. Specifically, the film-containing active material powder 30, conductive particles (acetylene black particles), a binder (polyvinylidene fluoride), and a dispersion medium (NMP) are mixed to prepare a positive electrode active material paste. do. Then, this positive electrode active material paste is applied onto a positive current collecting foil made of aluminum foil and dried by heating to form a positive electrode active material layer on the positive current collecting foil. Thereafter, this was pressed to increase the density of the positive electrode active material layer to form a positive electrode plate.

Separately, a negative electrode plate is produced. Specifically, negative electrode active material particles (graphite particles), a binder (styrene-butadiene rubber), a thickener (carboxymethyl cellulose), and a dispersion medium (water) are mixed to form a negative electrode active material paste. make. Then, this negative electrode active material paste is applied onto a negative electrode collector foil made of copper foil and dried by heating to form a negative electrode active material layer on the negative electrode collector foil. Thereafter, this was pressed to increase the density of the negative electrode active material layer, thereby forming a negative electrode plate.
Next, each positive electrode plate and each negative electrode plate were opposed to each other with a separator interposed therebetween, and housed together with an electrolytic solution in an outer package made of a laminate film to fabricate a battery.

Next, the battery resistance R was measured for each battery. Specifically, each battery is adjusted to have an SOC of 56% (battery voltage of 3.70 V) at an ambient temperature of -10°C. Thereafter, the battery is discharged at a constant current I of 1 C for 2 seconds, the battery voltage V before and after the discharge is measured, and the amount of change ΔV in the battery voltage V is obtained. Also, the battery resistance (IV resistance) R of each battery is obtained by R=ΔV/I. Then, the "battery resistance ratio" of the battery resistance R was calculated for each battery other than the reference (=1) of the battery resistance R when P was not added at all (0 wt%). FIG. 8 summarizes the relationship between the added P amount WP (wt %) and the battery resistance ratio.

As is clear from the graph of FIG. 8, when the P amount WP added to the active material powder 10 shown in FIG. It can be seen that the battery resistance ratio (battery resistance R) increases regardless of whether the amount of P to be added is less than or greater than 0.037 wt%.
As described above, in the active material powder 10 shown in FIG. 7, the amount of Li contained in the surface Li compound layer 23 is WL=0.025 wt %. The minimum P amount WP required to convert the total amount of to the amorphous LPO coating 43 is WP = 0.037 wt%.

Therefore, when the added P amount WP is set to WP=0.037 wt%, the entire amount of the surface Li compound layer 23 in the active material powder 10 is changed to the amorphous LPO coating 43, and the coating-containing active material powder 30 no longer contains the excess P. Since the amorphous LPO coating 43 has a high lithium ion conductivity, the more amorphous LPO coating 43 is present on the particle surface 21m, the more lithium ions in the electrolyte flow through the amorphous LPO coating 43 during discharge. Makes it easier to move to surface 21m. Therefore, the battery resistance ratio (battery resistance R) is reduced. In addition, in the case of charging, lithium ions tend to move from the particle surface 21m into the electrolytic solution.

On the other hand, as the P amount WP to be added is less than 0.037 wt %, a large amount of the surface Li compound layer 23 remains and the amount of the amorphous LPO film 43 formed decreases. Therefore, as the P amount WP to be added is less than 0.037 wt %, the effect of lowering the battery resistance R decreases, and the battery resistance ratio (battery resistance R) increases.
On the other hand, as the P amount WP to be added is increased from 0.037 wt %, the surplus P contained in the film-containing active material powder 30 increases. Excess P reacts with moisture contained in the process of manufacturing the positive electrode plate and materials such as the electrolyte and changes into an acid such as H ₃ PO ₄ , which damages the coated positive electrode active material particles 40 . It is believed that this is the reason why the battery resistance ratio (battery resistance R) increased as the P amount WP to be added was increased from 0.037 wt%.

As described above, in the method for measuring the amount of Li on the particle surface 21m of the active material powder 10, first, a part of the sample powder 10S of the active material powder 10 is immersed in water 100, and the surface Li compound layer 23 is is dissolved in water 100 (immersion step S11), the mixed solution 110 is filtered (filtration step S12). Filtration in this way can prevent Li from seeping out from the inside of the particle body 21 to the particle surface 21 m and dissolving in the water 100 . Therefore, by measuring the Li amount WL contained in the filtrate 120, the Li amount WL contained in the surface Li compound layer 23 in the active material powder 10 per unit weight can be appropriately measured.

Further, in the method for producing the film-containing active material powder 30, the Li amount WL contained in the surface Li compound layer 23 in the active material powder 10 per unit weight is measured by the above-described Li amount measurement method (Li amount measurement Step S1), after that, an amorphous LPO film 43 is formed from the surface Li compound layer 23 based on the measured Li amount WL (film formation step S2). Specifically, the active material powder 10 is mixed with the treatment liquid 150 containing the minimum amount (necessary amount) of P required to convert the entire amount of the surface Li compound layer 23 into the amorphous LPO coating 43. , forming an amorphous LPO coating 43 . As a result, it is possible to obtain the film-containing active material powder 30 in which the surface Li compound layer 23 is hardly left and in which excessive P is hardly contained. If a battery is manufactured using this film-containing active material powder 30, the battery resistance R can be further reduced.

Although the present invention has been described above with reference to the embodiments, it goes without saying that the present invention is not limited to the embodiments, and can be appropriately modified and applied without departing from the scope of the invention.

10 Active material powder 10S Sample powder 20 Positive electrode active material particles 21 Particle main body 21 m Particle surface 23 Surface Li compound layer 30 Coated active material powder 40 Coated positive electrode active material particles 43 Amorphous LPO coating 100 Water 110 Mixed liquid 120 Filtrate 150 Treatment liquid (including P) S1 Li amount measurement step S11 Immersion step WL Li amount S12 Filtration step S13 Measurement step S2 Film formation step

Claims (2)

a particle body made of a positive electrode active material capable of intercalating and deintercalating lithium ions;
For the active material powder in which the positive electrode active material particles are aggregated and which is present on the particle surface of the particle body and includes a surface Li compound layer containing LiOH and Li ₂ CO ₃ , the active material powder per unit weight: measuring the amount of Li contained in the surface Li compound layer;
A method for measuring the amount of Li on the surface of particles of active material powder,
an immersion step of immersing part of the sample powder of the active material powder in water to dissolve the surface Li compound layer in the water;
A filtration step of filtering the mixed liquid obtained in the immersion step;
and a measurement step of measuring the amount of Li contained in the filtrate obtained in the filtering step. a particle body made of a positive electrode active material capable of intercalating and deintercalating lithium ions;
A method for producing a coating-containing active material powder in which coated positive electrode active material particles are aggregated and provided with an amorphous amorphous LPO coating containing Li, P, and O formed on the particle surface of the particle body. hand,
A Li amount measuring step of measuring the Li amount contained in the surface Li compound layer in the active material powder per unit weight by the method for measuring the Li amount on the surface of the active material powder according to claim 1;
a coating forming step of forming the amorphous LPO coating from the surface Li compound layer;
The film forming step is
Based on the measured amount of Li, a treatment containing the minimum amount of P required to convert the entire amount of the surface Li compound layer into the amorphous LPO coating in the active material powder treated in the coating forming step. A method for producing a coating-containing active material powder, comprising mixing a liquid with the active material powder to form the amorphous LPO coating.

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