T 1419/11 (FILM-STATE NON-AQUEOUS SECONDARY BATTERY/SONY CORPORATION) 25-11-2014

1. Amendments

1.1 Claims 1 of the main request and the first, third, fourth, sixth and seventh auxiliary requests contravene Article 123(2) EPC, because the claim features relating to a "drying time period of 5 days to 1 week" and to a "range of gelling temperatures of 70 to 75°C" are not disclosed in combination in the application as originally filed.

1.2 The application as originally filed discloses on pages 22, 26 and 27 combinations of particular drying times (5 days, 1 week) and particular gelling temperatures (70°C, 75°C). These combinations are indeed recited in claims 1 of the second, fifth and eighth auxiliary request. In contrast, the respective claims 1 of the main request and auxiliary requests 1, 3, 4, 6 and 7 relate to a combination which is neither as specific as the embodiments described nor as general as the general teaching of the application ("intermediate generalisation").

1.3 The appellant argued in the appeal brief that the construction of ranges from distinct values of drying time and gelling temperature, respectively, was allowable because said parameters were not functionally related to each other. However, in the opinion of the board, this is no so, because the examples (Table 1) clearly suggest that the negative effect of a short drying time on the free acid content can - at least partly - be compensated for by a low gelling temperature, and vice versa.

The appellant argued that drying and gelling of the electrolyte were two distinct and separate steps of manufacturing the polymer electrolyte layer in accordance with the application under appeal. It referred in particular to page 26, lines 7 to 13, disclosing a process wherein "in fabrication of the electrolyte, after sufficiently drying the lithium salt, solvent and polymer material, the electrolyte is gelled at low temperature of about 70°C" (emphasis added by the board). Consequently, the drying time and gelling temperature could be chosen independently.

The board is not convinced by this argument.

Firstly, the passage relied upon by the appellant fails to indicate the temperature at which the drying step is to be carried out. As the drying process is strongly temperature-dependent, such an omission qualifies any indication of drying times.

Secondly, from several other passages of the description, no separation of drying and gelling steps can be derived. Reference is in particular made to Examples 1-1 to 1-31, as described on page 22, lines 3 to 8: "The mixture solution was stored in a drying chamber for one week or longer and heated to about 70°C so as to be gelled" and to Comparative Examples 1-1 to 1-29 (page 22, lines 18 to 21): "...storage time in the dying [sic] chamber was set to one day and the heating temperature was set to 80 to 90°C". The board considers that the skilled person when performing the invention disclosed in the patent under appeal would follow the combined process of drying/gelling, wherein the temperatures of the drying/gelling are the same.

1.4 For these reasons, claims 1 of the main request and first, third, fourth, sixth and seventh auxiliary requests violate Article 123(2) EPC and are therefore not allowable.

Second and fifth auxiliary request

2. Novelty

2.1 The Appellant argued that the feature of claim 1 relating to the concentration of a free acid of 60 ppm and less was neither explicitly nor implicitly disclosed in document D5.

2.2 Since the subject-matter of claim 1 of the fifth auxiliary request was held to lack an inventive step (see point 3 below), there was no need for the board to deal in detail with novelty.

2.3 For the benefit of the Appellant, it was therefore assumed that the subject-matter of claim 1 of the second and fifth auxiliary requests meets the requirements of Article 54 EPC.

3. Inventive step

3.1 The invention

The present application is concerned with a film-type (laminated) non-aqueous, polymer electrolyte secondary battery wherein acid corrosion in the battery and subsequent increase in internal resistance and expansion of the laminated battery are suppressed (see application as filed, page 18, lines 1 to 8, and page 6, second paragraph).

3.2 Closest prior art

D4 may be regarded as the closest prior art because this document deals with the problem of reducing free acid in a non-aqueous electrolyte secondary battery.

3.3 Problem

According to the application in suit, the problem was to provide a battery capable of suppressing shape change and suppressing deterioration in battery characteristics (application as filed, page 4, lines 17 to 19) or in other words, a film-type (laminated) non-aqueous, gel polymer electrolyte secondary battery having high initial discharge characteristics and showing no or little expansion.

3.4 Solution

As a solution to that problem, the application proposes a non-aqueous secondary battery according to claim 1 of the second auxiliary request, characterised in that the concentration in mass ratio of a free acid in the electrolyte layer is 60 ppm and less controlled by adjusting the drying time to 5 days and the gelling temperature to 70°C or the drying time to one week and the gelling temperature to 70°C or the drying time to 5 days and the gelling temperature to 75°C, and in that in fabrication of the electrolyte after drying the lithium salt, solvent and polymer material the electrolyte is gelled.

The solution according to auxiliary request 5 differs from the solution according to auxiliary request 2 in that the lithium salts have been specified.

3.5 Success of the solution

Table 1 (page 27 of the application) shows the following test results (data made up by the board with the figures of drying time and gelling temperature, taken from the description of the respective examples):

invention |free

acid°

(ppm) |initial

discharge

capacity

(mAh) |capacity

sustain

ratio

(%) |change

in

shape

|drying

time

(days) |gelling

temperature

(°C) |

example 2-1|25 |582 |95 |* |7 |70 |

example 2-2|50 |584 |95 |* |5 |70 |

example 2-3|60 |571 |93 |* |5 |75 |

comparison |free

acid

(ppm) |initial

discharge

capacity

(mAh) |capacity

sustain

ratio

(%) |change

in

shape

|drying

time

(days) |gelling

temperature

(°C) |

example 2-1|100 |511 |89 |** |1 |80 |

example 2-2|200 |494 |84 |** |0 |85-95 |

example 2-3|400 |481 |81 |** |0 |95-105 |

*hardly occurred

°free acid = the term "free acid" denotes an acid generated when the lithium salt in the electrolyte is decomposed due to the presence of moisture or when the electrolyte is heated (see page 17, lines 18 to 23).

**expansion

These data suggest that by observing the conditions of drying time and gelling temperature an electrolyte with a free acid content of 60 ppm or lower can be obtained and that film state batteries made therefrom exhibit high charge/discharge capacity and no change in shape (no swelling or leakage).

The comparative data prove that a change in shape occurred (an expansion) when the drying time and gelling temperatures were not respected. However, they are not representive for embodiments of the closest prior art.

Although no comparison with respect to the closest prior art is available, and although the Comparative Examples 2-1 to 2-3 are deficient in that more than one parameter have been altered with respect to Examples 2-1 to 2-3, the board accepts, to the benefit of the appellant, that the problem has effectively been solved.

3.6 Obviousness

3.6.1 It remains to be decided whether the claimed subject-matter is obvious having regard to the prior art or, in other words, whether there are hints in the prior art relating to a correlation between

(a) a low level of free acid content and

(b) good battery properties.

(1) Document D4

(a) free acid content

Document D4 discloses a lithium secondary battery comprising an electrolyte solution having an HF content of below 30 ppm. Such a low HF electrolyte may be obtained by thoroughly purifying the organic solvent(s) by crystallisation and/or rectification, followed by drying with molecular sieves and water absorbing agents (see page 7, lines 19 to 33, page 8, lines 6 to 14; example 1). The mixed EC/DMC/LiPF6 electrolyte of example 1 exhibits a residual HF content of only 9 ppm.

(b) battery properties

Coin-shaped lithium batteries made from said low HF electrolytes exhibit superior capacity, cycle characteristics and longer shelf life (see D4, page 20, lines 8 to 14and page 25, line 34 to page 36, line 6).

The subject-matter claimed in the instant application differs from D4 by the shape of the battery (film-type battery vs. coin-shaped) and in that the electrolyte is gelled. However, it must be observed that D4 is not limited to a particular structure of the battery (coin, cylindrical or prismatic battery) (see D4, page 14, lines 24 to 32). Film-shaped sealed batteries are known per se and the skilled person would immediately realise that essentially the same benefits as in D4 could be obtained with a film-shaped, gel-type lithium polymer electrolyte battery.

Claim features relating to the drying time and the gelling temperature are not considered to provide a distinction over D4 at the level of the claimed product. These process parameters are limiting the product claim only inasmuch as the claimed battery must possess the inevitable properties resulting from said process steps. In terms of residual free acid content, the non-aqueous electrolyte secondary batteries obtained in accordance with D4 clearly fall below the 60 ppm limit of claim 1 of the instant application.

(2) Document D5

As mentioned above, sealed film-type (laminated) non-aqueous secondary batteries containing a gel-type polymer electrolyte are known in the art and described for instance in document D5. In accordance with D5, a gelled electrolyte is obtained by thermal polymerisation at 80°C of the polyethylene glycol diacrylate prepolymer in the battery (examples 17 to 58, Figures 2 to 5).

(3) Further aspects

The lithium salts recited in claim 5, last paragraph, are conventional in the art (see D2, D4, D5).

3.6.2 Therefore, the subject-matter of claim 1 of the second and fifth auxiliary requests does not involve an inventive step (Article 56 EPC).

Eighth auxiliary request

3.7 Invention

As far as

(1) the invention,

(2) the closest prior art and

(3) the problem are concerned, it is referred to

the reasons 3.1, 3.2 and 3.3 which apply mutatis mutandis to the eighth auxiliary request.

3.8 Solution

As a solution to the problem as defined under 3.3, the application proposes a process for preparing a non-aqueous, polymer electrolyte secondary battery sealed in a film-state packaging member according to claim 1 of the eighth auxiliary request, characterised in that the concentration in mass ratio of a free acid in the electrolyte layer is 60 ppm and less controlled by adjusting the drying time to 5 days and the gelling temperature to 70°C or the drying time to one week and the gelling temperature to 70°C or the drying time to 5 days and the gelling temperature to 75°C, and in that in fabrication of the electrolyte after drying the lithium salt, solvent and polymer material the electrolyte is gelled.

3.9 Success of the solution

The board accepts that the problem has effectively been solved. See reasons 3.5.

3.10 Obviousness

It remains to be decided whether the claimed subject-matter is obvious having regard to the prior art or, in other words, whether there are hints in the prior art relating to a correlation between a low level of free acid content and good battery properties.

3.10.1 The board refers to the reasons 3.6 (1), (2) and (3) which apply mutatis mutandis to the eight auxiliary request; under 3.6.(2) the following remarks apply:

It is not apparent in which respect a gelling temperature of 70 or 75°C, as defined in claim 1 of the eighth auxiliary request, would be patentably distinct from the prior art, in particular as the claim does not specify the kind of polymer to be gelled.

Although said claim features relating to the drying time and the gelling temperature do provide a distinction over D4 at the level of the claimed process, they do not provide batteries having lower residual free acid content than the non-aqueous electrolytes secondary batteries obtained in accordance with D4.

A drying time of five days or one week is not considered to involve an inventive step, either. In the board's view, the indication of drying times without specifying other equally important conditions such as drying atmosphere and temperature, is not very meaningful from a technical point of view.

The appellant argued that the claimed narrow selection of drying times and gelling temperatures would per se be indicative of inventiveness.

The board disagrees, because the selected values, although narrow, are not purposefully selected. For instance, it is evident that a drying time of, say, six days instead of five days, or one week, under slightly modified conditions of atmosphere and temperature, would give essentially the same results. The same applies to the gelling temperatures.

3.10.2 It is furthermore self-evident that a long drying time is beneficial for a complete removal of water (which is known to be the cause for the generation of free acid; see D2, D5) from the electrolyte. The claimed drying times of 5 days or 1 week are the result of an obvious, non-purposive choice, because Examples 1-1 to 1-31 of the application demonstrate that even drying times longer than one week may be successfully employed (see page 22).

As regards the gelling temperatures, it is known from D2 (column 1, lines 26 to 30) that electrolyte salts such as LiPF6 thermally decompose under formation of HF. It would thus be obvious to carry out the gelling of the polymer electrolyte at temperatures which are high enough for the gelling reaction to proceed smoothly, but low enough for preventing decomposition. Finding the most suitable temperature would be a matter of routine investigation and the exact temperatures would inter alia depend on the chemistry of the polymer. For example, D5 reports a gelling temperature of 80°C for an acrylate polymer (see paragraph [0078]). It follows from the above considerations that the proposed gelling temperatures of 70°C and 75°C, for unspecified polymers, cannot be regarded as involving an inventive step.

3.10.3 Therefore, the subject-matter of claim 1 of the eighth auxiliary request does not involve an inventive step (Article 56 EPC).

4. Remittal

4.1 The appellant requested that the case be remitted to the examining division, if the appeal was dismissed on the basis of lack of inventive step in view of D2 and/or D4 as the closest prior art.

4.2 Under Article 111(1) EPC the board of appeal may either exercise any power within the competence of the department which was responsible for the decision appealed or remit the case to that department for further prosecution. It is therefore a matter of discretion whether or not the board remits a case.

4.3 In the instant case, the board considers it appropriate not to remit the case to the examining division, for the following reasons.

It is established case law that there is no absolute right for a party to have an issue decided upon by two instances (see Case Law of the EPO, 7th edition 2013, page 1028, IV.E.7.6.1, in particular the decisions cited therein).

Documents D2 and D4 had already been discussed during the examination proceedings and the relevance of these documents also for the appeal proceedings was brought to the appellant's attention in the communication of the board dated 7 August 2014. Therefore, the appellant must have been aware of these documents for a long time and had sufficient time for preparing its defense at the oral proceedings before the board.

The interest of procedural economy was a further criterion taken into consideration by the board. As the present application had been filed in the year 2001 claiming a priority date of 4 April 2000, a remittal would unduly lengthen the overall procedure.

In view of the above, the board decided to decide itself on the case in accordance with Article 111(1) EPC.