JP7209449B2 - Manufacturing method of active material powder with LPO - Google Patents

Description

In the present invention, an active material powder (pre-processed active material powder) in which positive electrode active material particles (pre-processed positive electrode active material particles) capable of intercalating and desorbing lithium ions are aggregated is converted into an LPO having an amorphous LPO part. The present invention relates to a method for producing an LPO-attached active material powder, in which positive electrode active material particles are aggregated to produce an LPO-attached active material powder.

Li (lithium), P (phosphorus) and O An LPO-containing active material powder is known in which LPO-containing positive electrode active material particles forming an amorphous LPO part containing (oxygen) are aggregated. A battery manufactured using such an active material powder with LPO 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 portion are aggregated.

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

JP 2019-153462 A

However, an LPO-attached active material powder that can further reduce the battery resistance has been desired.

The present invention has been made in view of such a situation, and provides a method for producing an LPO-containing active material powder that can produce an LPO-containing active material powder that reduces battery resistance.

One aspect of the present invention for solving the above problems is a pre-treatment particle body made of a positive electrode active material capable of intercalating and desorbing lithium ions, and a surface Li present on the particle surface of the pre-treatment particle body and containing Li. From the unprocessed active material powder in which the unprocessed positive electrode active material particles including the compound part are aggregated, the particle body made of the positive electrode active material, and the non-containing non-containing Li, P and O formed on the particle surface of the particle body A method for producing an LPO-attached active material powder in which LPO-attached positive electrode active material particles having a crystalline amorphous LPO portion are aggregated, wherein the active material powder before treatment includes: Li-increased active material powder in which Li-increased positive electrode active material particles having a surface Li compound portion containing a larger amount of Li than the untreated positive electrode active material particles are aggregated by mixing water or an aqueous LiOH solution and drying. and a P treatment liquid containing P is mixed with the Li-increased active material powder to form the amorphous LPO portion from the surface Li compound portion, and the LPO-attached active material powder and an LPO forming step for obtaining the LPO-attached active material powder.

In the method for producing the active material powder with LPO described above, in the Li increasing step, it is possible to obtain the Li-increased active material powder having a surface Li compound portion containing a larger amount of Li than the untreated active material powder. can. Then, by performing the LPO formation step using this Li-increased active material powder, the LPO containing a larger amount of amorphous LPO part than when the LPO formation step is performed without performing the Li-increase step. Active material powder can be produced. Therefore, if a battery is manufactured using this active material powder with LPO, the battery resistance can be further reduced compared to a battery using the active material powder with LPO obtained without performing the Li increasing step.

Examples of the "positive electrode active material" include lithium transition metal oxides. Examples of the lithium transition metal oxide include lithium-nickel composite oxide (eg LiNiO ₂ ), lithium-cobalt composite oxide (eg LiCoO ₂ ), lithium-manganese composite oxide (eg LiMn ₂ O ₄ ), lithium-nickel-cobalt-manganese composite oxide. 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 ).

Examples of the "amorphous LPO portion" include compositions such as lithium phosphate _{( Li3PO4} ), dilithium hydrogen phosphate _{( Li2HPO4} ), and lithium dihydrogen phosphate _{( LiH2PO4} ). Amorphous films containing Li, P and O represented by are mentioned.
Examples of the "P treatment liquid" include diphosphorus pentoxide ₍ P2O5) (tetraphosphorus _decaoxide ( _P4O10 )), orthophosphoric acid _{( H3PO4} ), pyrophosphoric _{acid ( H4P2O 7} ), triphosphoric acid _{( H5P3O10} ), polyphosphoric acid (HO _{( HPO3} ) _nH ), lithium phosphate _{( Li3PO4} ), lithium hydrogen phosphate _{( Li2HPO4} ), etc. Treatment liquids obtained by dissolving or dispersing compounds in solvents such as alcohols such as 2-propanol (isopropyl alcohol, IPA), N-methylpyrrolidone (NMP), water, and the like can be mentioned.

Further, in the method for producing the LPO-containing active material powder, the Li-increasing step includes mixing the LiOH aqueous solution with the untreated active material powder to obtain the Li-increased active material powder. A method for manufacturing a substance powder is preferable.

Since the LiOH aqueous solution contains LiOH, it is possible to obtain a Li-increasing active material powder having a surface Li-compound portion containing a larger amount of Li in the Li-increasing step. Therefore, in the subsequent LPO forming step, an LPO-attached active material powder containing a larger amount of amorphous LPO portions can be produced. Therefore, if a battery is manufactured using this active material powder with LPO, the battery resistance can be further reduced.

1 is a schematic cross-sectional view of LPO-attached positive electrode active material particles forming an LPO-attached active material powder according to an embodiment. FIG. FIG. 2 is a schematic cross-sectional view of untreated positive electrode active material particles forming untreated active material powder according to the embodiment. 1 is a schematic cross-sectional view of Li-enriched positive electrode active material particles forming Li-enriched active material powder according to an embodiment. FIG. 1 is a flow chart of a method for manufacturing an LPO-attached active material powder according to an embodiment. FIG. 4 is an explanatory diagram schematically showing a state in which an untreated active material powder is mixed with an aqueous LiOH solution (or water) in a Li increasing step according to the embodiment; FIG. 4 is an explanatory view schematically showing a state in which the Li-increasing active material powder is mixed with the P treatment liquid in the LPO formation step according to the embodiment. 4 is a graph showing the Li amount WL contained in the surface Li compound portion in the unprocessed active material powder before the Li increasing process and the Li-increased active material powder after the Li increasing process. 4 is a graph showing the amount ratio of the amount of P existing in the vicinity of the particle surface in active material powders with LPO according to Examples and Comparative Examples. 4 is a graph showing battery resistance ratios of batteries according to examples and comparative examples.

(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 the positive electrode active material particles 40 with LPO according to this embodiment. The LPO-containing active material powder 30 in which the LPO-containing 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 positive electrode active material particles 40 with LPO include a particle body 41 made of a positive electrode active material capable of intercalating and deintercalating lithium ions, and an amorphous LPO portion 43 formed on the particle surface 41m of the particle body 41 .

In this embodiment, the median diameter D50 of the positive electrode active material particles 40 with LPO is about 5 μm. The positive electrode active material forming the particle body 41 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 portion 43 is considered to be an amorphous LPO portion containing Li, P and O, specifically, an amorphous film mainly having a composition of Li ₃ PO ₄ . It is considered that a plurality of amorphous LPO portions 43 are formed in a sea-island pattern on the entire grain surface 41m of the grain main body 41 (both on the edge surface 41ma and the basal surface 41mb). The thickness of each amorphous LPO portion 43 is about 0.2 nm. Each amorphous LPO portion 43 is generated from a surface Li compound portion 23Z (see FIG. 3) of the Li-increased positive electrode active material particle 20Z, which will be described later. The amorphous LPO portion 43 has high lithium ion conductivity, and can reduce the battery resistance R of the battery using the active material powder 30 with LPO, as will be described later.

Next, a method for manufacturing the active material powder 30 with LPO will be described (see FIGS. 2 to 6). First, an untreated active material powder 10 in which untreated positive electrode active material particles 20 are aggregated is prepared (see FIG. 2). The untreated positive electrode active material particles 20 are particles having a median diameter D ₅₀ of about 5 μm, and the untreated particle bodies 21 made of the positive electrode active material described above (LiNi _0.2 Co _0.5 Mn _0.3 O ₂ in this embodiment), and a surface Li compound portion 23 present on the particle surface 21m of the untreated particle main body 21 . The surface Li compound portion 23 originates from excess Li contained in the positive electrode active material forming the untreated particle body 21, and is considered to be mainly composed of LiOH. It is considered that a plurality of surface Li compound portions 23 are present in a sea-island pattern on the edge surface 21ma of the particle surface 21m.

Next, in the “Li increasing step S1” (see FIG. 4), the above-described active material powder 10 before treatment is mixed with an aqueous LiOH solution 110 and dried to obtain a larger amount than the active material powder 10 before treatment. Li-enriched active material powder 10Z is obtained in which Li-enriched positive electrode active material particles 20Z having surface Li compound portions 23Z containing Li in the WL are aggregated (see FIG. 5). Note that water 100 may be used instead of the LiOH aqueous solution 110 .

In this embodiment, 45.0 g of 10 wt % LiOH aqueous solution 110 is placed in a beaker, 30.0 g of pre-treated active material powder 10 is added thereto, and stirred and mixed with a magnetic stirrer at 300 rpm for 5 minutes. . Subsequently, this mixed solution is suction-filtered to recover the untreated active material powder 10 . Subsequently, the collected untreated active material powder 10 is placed in a vacuum drying oven (not shown) and dried at 100° C. for 3 hours. As a result, the Li-enriched active material powder 10Z (see FIG. 3) having the surface Li compound portion 23Z is obtained.

In the Li increasing step S<b>1 , the surface Li compound portion 23 originally present on the particle surface 21 m (specifically, the edge surface 21 ma ) of the untreated positive electrode active material particle 20 dissolves in the LiOH aqueous solution 110 . However, in the subsequent drying stage, Li seeps out from inside the particle main body 21Z of the Li-increased positive electrode active material particle 20Z, and a surface Li compound portion 23Z made of LiOH is newly generated on the edge surface 21Zma of the particle surface 21Zm. In the mixing and filtering steps, LiOH contained in the LiOH aqueous solution 110 and Li dissolved in the LiOH aqueous solution 110 adhere to the entire particle surface 21Zm, that is, not only the edge surface 21Zma but also the basal surface 21Zmb. As a result, a surface Li compound portion 23Z made of LiOH is newly generated. As a result, it is considered that the amount WL of Li contained in the surface Li compound portion 23Z increases.

Here, the result of investigating the Li amount WL (wt %) contained in the surface Li compound portions 23 and 23Z before and after the Li increasing step S1 will be described (see FIG. 7). 100 ml of water was added to a beaker, and 10.0 g of the untreated active material powder 10 before performing the Li increasing step S1 or the Li increasing active material powder 10Z after performing the Li increasing step S1 was added. Then, the surface Li compound portions 23 and 23Z (mainly LiOH) contained in the pre-treated active material powder 10 or the Li-increased active material powder 10Z are dissolved in water. bottom.

After that, each of these mixed liquids was filtered, and neutralization titration using HCl (hydrochloric acid) was performed on the obtained filtrates. Specifically, while stirring the filtrate in a beaker with a magnetic stirrer and measuring the pH of the filtrate with a pH meter, 25 μl of 1.0 M HCl was added at intervals of 30 seconds. It is believed that the following reactions occur in this neutralization titration.
LiOH+HCl→LiCl+H ₂ O

As a result, the unprocessed active material powder 10 before the Li increasing step S1 required 1.0 M HCl in a dropping amount Tc of 0.114 ml before the neutralization was completed. Also, in the Li-increased active material powder 10Z after performing the Li-increasing step S1, a dropping amount Tc=0.342 ml of 1.0 M HCl was required.
The Li amount WL (wt %) contained in the surface Li compound portions 23 and 23Z of the untreated active material powder 10 and the Li-increased active material powder 10Z is calculated using the following calculation formula (1).
WL (wt%) = Tc x (Mc/1000) x Fc x Mrl x (1/m) x 100 (1)
Tc (ml): the dropwise amount of HCl required to complete neutralization;
Mc (M, mol/L): concentration of HCl (Mc = 1.0 M in this embodiment),
Fc: concentration factor (Fc=1.01 in this embodiment);
Mrl (g/mol): atomic weight of Li (Mrl = 6.94 g/mol).
m (g): amount of pre-treatment active material powder 10 or Li-increased active material powder 10Z used (m=10.0 g in this embodiment).

In the untreated active material powder 10 before the Li increasing step S1, the dropping amount Tc=0.114 ml, so the Li amount WL=0.114×(1.0/1000)×1.01×6.94× (1/10.0)×100=0.0080 wt %.
On the other hand, in the Li-increasing active material powder 10Z after the Li-increasing step S1, the dropping amount Tc=0.342 ml, so the Li amount WL=0.342×(1.0/1000)×1.01×6. 94 x (1/10.0) x 100 = 0.024 wt%.
Therefore, in the present embodiment, it is considered that the Li amount WL contained in the surface Li compound portion 23Z is increased by 0.024/0.0080=3.0 times by performing the Li increasing step S1.

Next, in the “LPO forming step S2” (see FIG. 4), the Li-increased active material powder 10Z obtained in the Li-increasing step S1 and the P treatment liquid 150 containing P are mixed to form a surface Li compound portion 23Z. Amorphous LPO portions 43 are formed from the powder to obtain active material powder 30 with LPO in which positive electrode active material particles 40 with LPO are aggregated (see FIG. 6). In the present embodiment, first, in the Li-increased active material powder 10Z to be treated in the LPO formation step S2, the minimum amount (necessary amount) required to convert the entire amount of the surface Li compound portion 23Z into the amorphous LPO portion 43 Find P.

As described above, the Li amount WL contained in the surface Li compound portion 23Z in the Li-increasing active material powder 10Z is WL=0.024 wt %. On the other hand, since the amorphous LPO portion 43 is a film mainly represented by the composition of Li ₃ PO ₄ , the required minimum amount of P WP (wt%) is calculated using the following formula (2). .
WP (wt%)=(WL/3)×(Mrp/Mrl) (2)
Mrp (g/mol): atomic weight of P (Mrp = 30.97 g/mol).
In this example, the P amount WP=(0.024/3)×(30.97/6.94)=0.036 wt %.

Therefore, in the present embodiment, the P treatment liquid 150 is obtained by dissolving P ₂ O ₅ in IPA so that the content becomes 0.036 wt % in P conversion. Then, for example, 100 g of the untreated active material powder 10 is added with the same amount of 100 g of the P treatment liquid 150, and this mixture is mixed for 3 minutes in a planetary mixer to obtain the surface Li compound portion 23Z and the P treatment liquid 150. The amorphous LPO portion 43 is formed from the surface Li compound portion 23Z by reacting with the phosphate ions in the treatment liquid 150 . Thereafter, this mixture is heated to 80° C. and dried to obtain active material powder 30 with LPO in which positive electrode active material particles 40 with LPO are aggregated. By doing so, theoretically, the entire amount of the surface Li compound portion 23Z becomes the amorphous LPO portion 43, and excessive P is not included in the active material powder 30 with LPO.

(Test results)
Next, test results for verifying the effects of the present invention will be described (see FIGS. 8 and 9). As an example, an active material powder 30 with LPO manufactured by the manufacturing method according to the embodiment was prepared. On the other hand, as a comparative example, an active material powder 30 with LPO was also prepared by performing only the LPO forming step S2 on the untreated active material powder 10 without performing the Li increasing step S1. Next, the amounts Ca of the amorphous LPO portions 43 contained in the LPO-attached active material powders 30 of Examples and Comparative Examples were investigated.

Specifically, first, for the active material powder 30 with LPO, the amount of each element of Ni, Co, Mn, and P present in the vicinity of the particle surface 41 m is measured by XRF (X-ray Fluorescence). The P content Cp (%) present in the steel was obtained by Cp = P content/(Ni content + Co content + Mn content + P content) x 100 (%). Furthermore, the amount ratio of the P amount Cp in the active material powder 30 with LPO of the example was calculated using the P amount Cp in the active material powder 30 with LPO of the comparative example as a reference (=1.0). The results are shown in FIG.

As is clear from the graph of FIG. 8, in the active material powder 30 with LPO of the example, the P amount Cp existing in the vicinity of the particle surface 41 m was 3.0% as compared with the active material powder 30 with LPO of the comparative example. It is 0 times. That is, it is considered that the amount Ca of the amorphous LPO part 43 contained in the LPO-attached active material powder 30 is 3.0 times larger in the example than in the comparative example. As can be seen from the test results of FIG. 7 described above, the Li-increased active material powder 10Z before the LPO formation step S2 of the example is superior to the untreated active material powder 10 before the LPO formation step S2 of the comparative example. , the amount WL of Li in the surface Li compound portion 23Z is increased by 3.0 times. Since the amorphous LPO portion 43 is formed from the surface Li compound portion 23Z, the active material powder 30 with LPO of the example is amorphous compared to the active material powder 30 with LPO of the comparative example. It is considered that the amount Ca of the LPO portion 43 has increased 3.0 times. When the amount Ca of the amorphous LPO portion 43 is increased in this manner, the battery resistance R can be lowered in the battery manufactured using this active material powder 30 with LPO, as will be described later.

Next, using the LPO-attached active material powders 30 of Examples and Comparative Examples, laminated cell type lithium ion batteries (not shown) were produced. That is, using the LPO-attached active material powder 30, a positive electrode plate is produced. Specifically, the active material powder 30 with LPO, 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, the SOC of the battery is adjusted to 56% (battery voltage of 3.70 V) at an environmental 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, as a reference (=1.00) for the battery resistance R of the battery according to the comparative example, the "battery resistance ratio" of the battery resistance R of the battery according to the example was calculated. The results are shown in FIG.

As is clear from the graph of FIG. 9, the battery of the example has a smaller battery resistance ratio (battery resistance R) than the battery of the comparative example. Since the amorphous LPO portion 43 has high lithium ion conductivity, the more the amorphous LPO portion 43 exists on the particle surface 41m, the more lithium ions in the electrolytic solution pass through the amorphous LPO portion 43 during discharge. It becomes easier to move to the surface 41m. As described above, in the example, the amount Ca of the amorphous LPO part 43 contained in the LPO-attached active material powder 30 is increased by 3.0 times compared to the comparative example. In contrast, it is considered that the battery resistance ratio (battery resistance R) became smaller in the batteries of the examples. In addition, in the case of charging, lithium ions tend to move from the particle surface 41m into the electrolytic solution.

As described above, in the method for producing the active material powder 30 with LPO, in the Li increasing step S1, the surface Li compound portion 23Z containing a larger amount WL of Li than the untreated active material powder 10 has a surface Li compound portion 23Z. Li-increased active material powder 10Z can be obtained. Then, by performing the LPO formation step S2 using this Li-increased active material powder 10Z, more amorphous LPO can be obtained than when the LPO formation step S2 is performed without performing the Li-increase step S1. The LPO-attached active material powder 30 including the portion 43 can be produced. Therefore, if a battery is manufactured using this active material powder 30 with LPO, the battery resistance R can be further improved as compared with a battery using the active material powder with LPO obtained without performing the Li increasing step S1. can be lowered.

Furthermore, in the embodiment, since the LiOH aqueous solution 110 is used in the Li increasing step S1, the Li increasing active material powder 10Z having the surface Li compound portion 23Z containing a larger amount WL of Li is obtained in the Li increasing step S1. be able to. Therefore, in the subsequent LPO forming step S2, the LPO-attached active material powder 30 containing more amorphous LPO portions 43 can be produced. Therefore, if a battery is manufactured using this active material powder 30 with LPO, 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 Untreated active material powder 20 Untreated positive electrode active material particle 21 Untreated particle main body 21m Particle surface 23 Surface Li compound portion 10Z Li-increased active material powder 20Z Li-increased positive electrode active material particle 21Z Particles Main body 21Zm Particle surface 23Z Surface Li compound portion WL (contained in surface Li compound portion) Li amount 30 LPO-containing active material powder 40 LPO-containing positive electrode active material particle 41 Particle main body 41m Particle surface 43 Non Crystalline LPO part 100 Water 110 LiOH aqueous solution 150 P treatment liquid S1 Li increasing step S2 LPO forming step

Claims (2)

An untreated positive electrode active material particle comprising an untreated particle body made of a positive electrode active material capable of intercalating and releasing lithium ions and a surface Li compound portion containing Li existing on the particle surface of the untreated particle body and containing Li. From the active material powder before treatment,
LPO-attached LPO-attached cathode active material particles having LPO-attached cathode active material particles, comprising a particle body made of the positive electrode active material, and an amorphous LPO part formed on the particle surface of the particle body and containing Li, P, and O A method for producing active material powder with LPO, comprising:
The active material powder before treatment is mixed with water or an aqueous LiOH solution and dried to obtain a Li-increased positive electrode active material particle having a surface Li compound portion containing a larger amount of Li than the positive electrode active material particle before treatment. a Li increasing step of obtaining an aggregated Li increasing active material powder;
an LPO forming step of mixing the Li-increased active material powder with a P treatment liquid containing P to form the amorphous LPO portion from the surface Li compound portion to obtain the LPO-attached active material powder; A method for producing an LPO-attached active material powder comprising: A method for producing the active material powder with LPO according to claim 1,
The Li increasing step is
A method for producing active material powder with LPO to obtain the Li-increased active material powder by mixing the untreated active material powder with the LiOH aqueous solution.

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